WO2020049444A1

WO2020049444A1 - A device and a lateral flow assay method for differential identification of plasmodium species

Info

Publication number: WO2020049444A1
Application number: PCT/IB2019/057397
Authority: WO
Inventors: Sachin DUBEY; Usman Khan; Rahul CHAUDHARI; Maya KV
Original assignee: Module Innovations Private Limited
Priority date: 2018-09-03
Filing date: 2019-09-03
Publication date: 2020-03-12

Abstract

The present invention provides an immunochromatographic test strip, immunoassay device, kit and a rapid lateral flow assay method for detection and differential identification of Plasmodium species in a sample. The immunochromatographic test strip comprises a plurality of test lines, each of said test lines carrying capture antibodies that exhibits specificity towards one of the antigenic sequences selected from a group comprising SEQ ID NO: 1 to SEQ ID NO: 8 present within subtilisin-like protease-2 (SUB2) protein of Plasmodium species. The test strip is highly sensitive, precludes false positives, enables detection of mixed infections in a liquid sample and differential identification of one or more Plasmodium species present in a sample.

Description

A DEVICE AND A LATERAL FLOW ASSAY METHOD FOR

DIFFERENTIAL IDENTIFICATION OF PLASMODIUM SPECIES

FIELD OF THE INVENTION

[0001] The present invention generally relates to devices and methods for assaying biological samples. In particular, the present invention relates to devices and a lateral flow assay method for detection and differential identification of Plasmodium species in a sample.

BACKGROUND OF THE INVENTION

[0002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.

[0003] Malaria remains a major health burden in tropical and sub-tropical regions of the world, including Asia, Sub-Saharan Africa and Latin America, with 216 million cases worldwide resulting in 731000 deaths. Malaria in humans is known to be caused by five Plasmodial species, namely, Plasmodium falciparum, P. vivax, P. ovalae, P. malariae and P. knowle i.

[0004] Diagnostic confirmation of the Plasmodial species is important, prior to the treatment. For example, patients with P. falciparum malaria are treated with artemisinin combination therapy while patients with P. vivax malaria are treated with chloroquine and primaquine (Douglas et ak, 2010, Lancet Infectious Diseases; Guidelines for diagnosis and treatment of Malaria in India, NIMR Report, 2009). Therefore, correct diagnosis is absolutely crucial for disease management and surveillance. Misdiagnosis can have profound consequences and presumptive treatment in the absence of correct diagnosis results in overuse of anti-malarial drugs and contribute to drug resistance. An excellent example of this is chloroquine, a golden drug used to treat all cases of malaria. However, emergence of chloroquine resistant P. falciparum malaria has been reported throughout the world and persistent use of chloroquine in such cases due to lack of correct diagnosis caused higher proportion of P. falciparum malaria compared to P. vivax malaria. Now, reports are emerging that higher frequency of misdiagnosis is contributing to the spread of chloroquine resistant P. vivax. Thus correct diagnosis of malarial Plasmodium species can help reduce the spread of drug resistance thereby reserving anti-malarial drugs for people who actually have the disease. [0005] Correct diagnosis of Plasmodium species is often difficult due to the similar morphology of P. malariae and P. knowlesi. There also exists difficulty in differentiating P. falciparum , P. malariae and P. knowlesi (Lee et al., 2009, Malaria Journal; Ong et al., 2009, The American Journal of Tropical Medicine and Hygiene). The absence of accurate diagnostic tests, clinical diagnosis and presumptive treatment pose a major challenge for achieving global malaria control. Microscopy of the thin blood smears has been in use for more than 100 years and is often considered a gold standard for identification of pathogenic species. However, its reliability is questionable at low parasitemia levels and its failure to detect mixed infections (Mouatcho et al., 2013, Journal of Medical Microbiology). Currently available methods for identification of the infectious Plasmodium species include strategies like immunochromatography based rapid diagnostic tests. These tests are based on detection of certain antigens like Histidine-rich protein 2 (HRP2) and plasmodial lactate dehydrogenase (pLDH) (Mouatcho et al., 2013, Journal of Medical Microbiology). Malaria rapid diagnostic tests (RDTs) detecting a combination of HRP2 and pLDH can detect mixed infections. However, these tests have significant drawbacks like false positives due to persistence of antigens in the blood circulation post-treatment (HRP2), low sensitivity/specificity for one of the antigens during mixed infection and gene deletions (HRP2) (Mouatcho et al., 2013, Journal of Medical Microbiology; Global Malaria Programme, WHO, 2016). pLDH based RDTs also pose significant problems like decreased sensitivity at low parasitemias, expression of LDH by gametocytes thereby giving false positive results at high gametocytaemia, and decreased sensitivity at high temperature (Mueller et al., 2007, Journal of Clinical Microbiology; Chiodini et al., 2007, Transaction of Royal Society: Tropical Medicine and Hygiene). Using antibodies against pan-LDH can detect all species; however, it cannot differentiate amongst them. Therefore currently available techniques do not provide a complete picture, fail to correctly diagnose the infecting parasite species and thus, contribute profoundly to anti-malarial resistance.

[0006] Thus, there is an urgent need in the art for reliable tools and techniques for detection of mixed infection, identification and differentiation amongst various malarial Plasmodium species for rendering an effective control of malarial diseases.

OBJECTS OF THE INVENTION

[0007] An object of the present invention is to provide reliable, point-of-care diagnostic tools and rapid method for detection of mixed infection and identification of Plasmodium at species level in a sample, which can overcome the deficiencies associated with the present art.

[0008] An object of the present invention is to provide an immunochromatographic test strip that enables reliable, rapid, easy-to-use, detection of one or more Plasmodium sp. and differential identification of Plasmodium species in a sample.

[0009] An object of the present invention is to provide an immunoassay device that enables reliable, rapid, easy-to-use detection of one or more Plasmodium sp. and differential identification of Plasmodium species in a sample.

[0010] Another object of the present invention is to provide a one- step assay method for reliable, rapid detection of one or more Plasmodium sp. and differential identification of Plasmodium species in a sample.

[0011] Still another object of the present invention is to provide a kit that enables reliable, rapid, easy-to-use, detection of one or more Plasmodium sp. and differential identification of Plasmodium species in a sample.

SUMMARY OF THE INVENTION

[0012] This summary is provided to introduce a selection of concepts in a simplified form that are further described below in Detailed Description section. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

[0013] The present disclosure relates to immunochromatographic test strip, immunoassay device, kit, and lateral flow assay method for the reliable, rapid detection of mixed infection and differential identification of Plasmodium species in a sample.

[0014] One aspect of the present disclosure provides an immunochromatographic test strip for the detection of Plasmodium genus present in a sample and also enables identification of one or more Plasmodium to the species level. The immunochromatographic test strip detects and identifies one or more unique antigenic sequences present within subtilisin-like protease 2 (SUB2) protein of Plasmodium species having amino acid sequences selected from a group comprising SEQ ID NO: 1, SEQ ID NO: 2, SEQ ID NO: 3, SEQ ID NO: 4, SEQ ID NO: 5, SEQ ID NO: 6, SEQ ID NO: 7 and SEQ ID NO: 8.

[0015] In an aspect of the present disclosure, the immunochromatographic test strip for the detection and differential identification of one or more Plasmodium species in a sample comprises a planar substrate having (i) a sample receiving zone; (ii) a conjugate zone comprising labeled conjugates; (iii) a transport zone comprising immobili ed antibodies; and (iv) an absorbent zone; characterized in that the transport zone comprises: a) a control line; b) a PAN test line; and c) one or more SUB2 test lines, wherein the PAN test line comprises antibodies capable of specifically binding to Plasmodium lactate dehydrogenase (panLDH) of Plasmodium sp. other than P. falciparum·, and wherein each SUB2 test line comprises antibodies capable of binding to any one of the species-specific antigenic sequences present within SUB2 protein of Plasmodium species selected from a group comprising SEQ ID NO: 1, SEQ ID NO: 2, SEQ ID NO: 3, SEQ ID NO: 4, SEQ ID NO: 5, SEQ ID NO: 6, SEQ ID NO: 7 and SEQ ID NO: 8.

[0016] In another aspect of the present disclosure, the immunochromatographic test strip enables detection and differential identification of one or more Plasmodium species selected from P. falciparum, P. vivax, P. knowlesi and P. malariae.

[0017] In another aspect of the present disclosure, the immunochromatographic test strip comprises labeled conjugates that are gold-labeled antibodies. The antibodies comprise heavy chain and light chain constant regions (CH and CL) and heavy chain and light chain variable regions (VH and VL) , wherein each of the antibody heavy chain variable region (VH) and the antibody light chain variable region (VL) comprises a region capable of binding to the species-specific antigenic sequences of Plasmodium sp. as set forth in SEQ ID NO: 1, SEQ ID NO: 2, SEQ ID NO: 3, SEQ ID NO: 4, SEQ ID NO: 5, SEQ ID NO: 6, SEQ ID NO: 7 and SEQ ID NO: 8. Preferably, the gold labeling is by conjugating gold nanoparticles to said antibodies.

[0018] In yet another aspect of the present disclosure, the immunochromatographic test strip comprises gold-labeled antibodies wherein only the heavy chain constant region (CH) of the antibody specifically bind with the gold nanoparticles and the heavy and light chain variable regions (HL and VL) of the antibody are capable of binding to the species-specific antigenic sequences of Plasmodium having SEQ ID NO: 1, SEQ ID NO: 2, SEQ ID NO: 3, SEQ ID NO: 4, SEQ ID NO: 5, SEQ ID NO: 6, SEQ ID NO: 7 and SEQ ID NO: 8.

[0019] Another aspect of the present disclosure provides an immunoassay device for the detection and differential identification of one or more Plasmodium species, comprising one or more immunochromatographic test strips encased in a housing, wherein the housing comprises a) a base and a top cover; b) a sample well for receiving the sample directly on the sample zone on the test strip, and c) a viewing pane for visibly determining the presence or absence of the colored control line, PAN test line and SUB2 test lines, wherein the PAN test line on the test strip comprises antibodies capable of specifically binding to panLDH of Plasmodium sp. other than P. falciparum·, and wherein each SUB2 test line on the test strip comprises antibodies capable of binding to any one of the antigenic sequence present within SUB2 protein of Plasmodium species selected from a group comprising SEQ ID NO: 1, SEQ ID NO: 2, SEQ ID NO: 3, SEQ ID NO: 4, SEQ ID NO: 5, SEQ ID NO: 6, SEQ ID NO: 7 and SEQ ID NO: 8.

[0020] Yet another aspect of the present disclosure provides an immunoassay device for the detection and differential identification of one or more Plasmodium species, comprising a) two immunochromatographic test strips encased in a housing having a base and a top cover; b) common sample well; and c) viewing pane; wherein the SUB2 test lines on the first strip comprises antibodies capable of binding to the antigenic sequence present within SUB2 protein of any two of the Plasmodium species selected from a group of P. falciparum, P. vivax, P. knowlesi and P. malariae and the SUB2 test lines on the second test strip comprises antibodies capable of binding to the antigenic sequence present within SUB2 protein of the remaining two Plasmodium species present in the said group, and wherein the antigenic sequence present within SUB2 protein for the Plasmodium sp. is selected from a group comprising SEQ ID NO: 1, SEQ ID NO: 2, SEQ ID NO: 3, SEQ ID NO: 4, SEQ ID NO: 5, SEQ ID NO: 6, SEQ ID NO: 7 and SEQ ID NO: 8.

[0021] Another aspect of the present invention provides a kit for detection and differential identification of one or more Plasmodium species present in a sample comprising (a) one or more immunochromatographic test strip or immunoassay device disclosed herein b) a buffer component having pH in the range of 7.4 to 9.0, c) one or more capillary tubes for transfer of sample, d) and reading material comprising directions for use and comprehending the results for detection and identification of the Plasmodium species in the sample.

[0022] Another aspect of the present invention provides a lateral flow assay method for detection and differential identification of one or more Plasmodium species present in a sample comprising: a) contacting sample at the sample zone of the immunochromatographic test strip or the immunoassay device of the present disclosure; b) adding buffer having pH in the range of 7.4 to 9.0 c) allowing the buffered sample to flow through the length of the test strip or device including the transport zone comprising the control, PAN test line and SUB2 test lines; and d) determining the presence of analyte in the sample by visual inspection of the accumulation of colored particles in the transport zone; wherein (i) presence of visible colour in the PAN test line indicates presence of mixed Plasmodium infection; and (ii) presence of visible colour in the species-specific SUB2 test lines indicates and identifies the causal Plasmodium species of the Plasmodium infection. [0023] In a further aspect of the present disclosure, there is provided a lateral flow assay method using the immunoassay device having two immunochromatographic test strips comprising: a) contacting sample at the common sample well; b) adding buffer having pH in the range of 7.4 to 9.0 c) allowing the buffered sample to flow through the entire length of both the test strips including the transport zone comprising the control line, PAN test line and SUB2 test lines; and d) determining the presence of analyte in the sample by visual inspection of the accumulation of colored particles in the transport zone in both the test strips; wherein (i) presence of visible colour in the PAN test line indicates presence of Plasmodium infection other than P. falciparum, and (ii) presence of visible colour in the species specific SUB2 test lines indicates and identifies the causal Plasmodium species of the Plasmodium infection.

[0024] In an aspect of the present disclosure, the specific antigenic sequences of the Plasmodium in a sample are reliably and rapidly detected and identified within a short duration of time, preferably in less than 30 minutes using the diagnostic tools and methods of the present disclosure. The diagnostic tools of the present disclosure can be used at point-of- care testing, as a single test and requiring one-time sample.

[0025] Various objects, features, aspects and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing and figures in which numerals represent components.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings are included to provide a further understanding of the present disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure.

[0027] FIGURE 1 illustrates the position of the unique antigenic sequences (SEQ ID

NO: 1 to SEQ ID NO: 8) within SUB2 protein of Plasmodium falciparum, P. vivax, P. knowlesi and P. malariae.

[0028] FIGURE 2 is a schematic illustration of a top view of an immunochromatographic test strip according to an embodiment of the present invention.

[0029] FIGURE 3 is a schematic illustration of a lateral view of an immunochromatographic test strip according to an embodiment of the present invention. [0030] FIGURE 4 is a schematic illustration of a top view of an immunoassay device according to an embodiment of the present invention.

[0031] FIGURE 5 is a schematic illustration of a lateral view of an immunoassay device according to an embodiment of the present invention.

DETAILED DESCRIPTION

[0032] The following is a detailed description of embodiments of the disclosure depicted in the accompanying drawings. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.

[0033] Various terms as used herein are shown below. To the extent a term used in a claim is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in printed publications and issued patents at the time of filing. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.

[0034] As used in the description herein and throughout the claims that follow, the meaning of“a,”“an,” and“the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of“in” includes“in” and “on” unless the context clearly dictates otherwise.

[0035] As used herein, the term‘analyte' is intended to refer to any component of a sample such as molecule, compound, antigenic portions, protein fragments, or aggregate thereof to be detected and optionally quantitatively determined by the diagnostic tools. Examples of analytes include proteins expressed by or caused to be expressed by Plasmodium infection. Preferably, the proteins are subtilisin-like protease 2, lactate dehydrogenase, and fragments and variants thereof.

[0036] As used herein, the term‘mixed infection’ is intended to refer to a Plasmodium infection wherein more than one Plasmodium sp. is the present or acts as a causal organism.

[0037] As used herein, the terms‘capable of binding’ capable of binding specifically’ ‘capable of specifically binding’ and‘binding specificity’ is used interchangeably and is intended to refer to the specificity of the binding of the antibodies to the antigenic sequences.

[0038] As used herein, the term 'sample receiving zone”, and“sample zone” are used interchangeably and refer to the portion of the assay tool that is the first point of direct contact with the sample. For example, the zone receives the sample to be tested for the analyte in question.

[0039] As used herein, the term‘about’ used in the context of pFI or other measurement or parameter described herein refers to the intrinsic variability due to reagents, apparatus, and human error in any measurement or apparatus or human interpretation of a parameter or result.

[0040] As used herein, the abbreviation‘LDFF denotes lactate dehydrogenase.

[0041] As used herein, the abbreviation ‘panLDFF denotes Plasmodium lactate dehydrogenase.

[0042] As used herein, the abbreviation‘SUB2’ denotes subtili sin-like protease 2 of

Plasmodium sp.

[0043] As used herein the term ‘diagnostic tools’ and ‘diagnostic devices’ is used interchangeably and is intended to include all product inventions disclosed herein, such as immunochromatographic test strip and all its embodiments, immunoassay device and all its embodiments, and kit.

[0044] The present invention provides diagnostic devices and methods for the rapid, reliable, detection and differentiation identification of Plasmodium at species level in a sample. The present inventors have for the first time identified unique antigenic amino acid sequences specific for different Plasmodium species present in the SUB2 protein of the parasitic microorganism that can cause malaria. The diagnostic tools and method of the present invention for the first time provides a sensitive and reliable detection and identification of unique antigenic sequences in the SUB2 protein of different Plasmodium species in a single test and single sample.

[0045] The SUB2 is a serine protease that plays an important step in maturation of merozoite surface protein 1 (MSP1) in the Plasmodium sp. The SUB2 protein is essential for the Plasmodium parasite and failure of expression of SUB2 leads to parasite death. Therefore, identification of these particular protein sequences signifies the presence of the parasite in the sample. Expression of LDH by gametocytes results in false positive results during the stage of high gametocytaemia of the causal microorganism. As SUB2 protein is expressed exclusively during schizogony and in merozoites, identification of sequences of SUB2 excludes the false positives due to the gametocytic stage. Further, the SUB2 protein does not persist in the bloodstream once the infection cycle is over, thereby eliminating the false positives as observed in the case of HRP2 used in existing methods. It is the inventors’ ingenuity in providing diagnostic tools and methods for achieving the objects of the invention by employing the unique SUB2 antigenic determinants as set forth in SEQ ID NO: 1, SEQ ID NO: 2, SEQ ID NO: 3, SEQ ID NO: 4, SEQ ID NO: 5, SEQ ID NO: 6, SEQ ID NO: 7 and SEQ ID NO: 8, which provide a key advantage of differentiating among 4 different Plasmodium species and correct identification of the infecting Plasmodium microorganism in a single, rapid assay. The objects of the present invention can be achieved by diagnostic tools of the present invention that employ lateral flow assay arrangement and by lateral flow assay method.

[0046] The specific antigenic sequences present in the SUB2 protein that act as target sequences have been identified and predicted using tools such as EpiC, Antibody Epitope Prediction Tool and SVMTriP. The unique, species-specific antigenic sequences present in SUB2 are presented below in Table 1 with their amino acid sequences and sequence identifiers. The position of the unique antigenic sequences of SEQ ID NO: 1, SEQ ID NO: 2, SEQ ID NO: 3, SEQ ID NO: 4, SEQ ID NO: 5, SEQ ID NO: 6, SEQ ID NO: 7 and SEQ ID NO: 8 within SUB2 protein from each Plasmodium species are provided in Figure 1. In the Figure 1, the PvSUB2 refers to Plasmodium vivax subtilisin-like protease 2, PkSUB2 to Plasmodium knowlesi subtili in-like protease 2, PmSUB2 to Plasmodium malariae subtilisin- like protease 2, and PfSUB2 to Plasmodium falciparum subtilisin-like protease 2. The sequences for SUB2 protein for the Plasmodium species are available on the public domain freely (Plasmodb.org), and can be accessed with Accession numbers PF3D7_l 136900 for P. falciparum SUB2 protein, PVP0l_0937800 for P. vivax SUB2 protein, PKNH_0935l00 for P. knowlesi SUB2 protein, and PmUG0l_09046200 for P. malariae SUB2 protein.

Table 1: Antigenic sequences present within SUB2 protein of Plasmodium species

[0047] In an aspect, the present invention relates to an immunochromatographic test strip for the detection and differential identification of one or more Plasmodium species in a sample comprising a planar substrate (1) having (i) a sample receiving zone (2); (ii) a conjugate zone (3); (iii) a transport zone (4); and (iv) an absorbent zone (5). Figure 2 provides a schematic illustration of a top view of an immunochromatographic test strip according to an embodiment of the present invention. The immunochromatographic test strip comprises permeable material on a single plane which enables fluid communication from the sample zone to the absorbent zone through the conjugate zone and the transport zone. The arrow in Figure 2 indicates the direction of flow of the liquid sample. The immunochromatographic strip is a membrane -based, immunoassay strip which falls under lateral flow assay category. In an embodiment of the present invention, the immunochromatographic test strip employs the sandwich ELISA performed on the nitrocellulose membrane. In an embodiment of the present invention, a length of a test strip is preferably in the range of 50 mm to 70 mm and the width in a range of 2 mm to 4 mm.

[0048] In an embodiment of the present invention, all the zones of the immunochromatographic test strip are fixed or mounted over the planar substrate, as shown in Figure 3. The planar substrate allows for all the zones to be in the same plane so as to permit capillary flow communication with each other. Each of these zones has the capacity to transport fluid samples instantly. The planar substrate serves as a support and it makes easy to handle the strip. Materials for the planar substrate are highly flexible as they provide a platform for proper assembling of all the zones. In an embodiment of the present invention, the planar substrate of the immunochromatographic test strip is selected from a group including but not limited to cellulose fiber, glass fiber, paper, micro structured polymer, sintered polymer and combinations thereof.

[0049] In an embodiment of the present invention, the sample zone of an immunochromatographic test strip is the zone for receiving the sample. The function of the sample zone is to transport the sample in a smooth, continuous and homogenous manner to the conjugate zone. Preferably, the sample zone is made of material including but not limited to cellulose fibers, glass fibers or combinations thereof. In an aspect, the immunochromatographic test strip is triggered to function when sample is added to the sample zone.

[0050] The term‘sample’ as used herein refers to any sample that could contain an analyte for detection. Preferably the sample is in liquid form or can be changed into a liquid form. The sample is selected from a group including but not limited to blood, serum, urine, saliva, nasal discharge, sweat, plasma, semen, cerebrospinal fluid, tears, pus, amniotic fluid, lung aspirate, gastrointestinal contents, vaginal discharge, urethral discharge, chorionic villi specimens, epithelials, hair, and sputum. Preferably, the sample is blood. Samples may be buffered or may have their pH altered prior to being applied to the devices or being subjected to the methods of the invention. Preferably, the blood sample may be buffered with a buffer such as lysis buffer, Tris buffer, acid, or base, to a pH in the range of about 7.4 to about 9.0, and preferably in the range of about 7.5 to about 8.5.

[0051] In an embodiment of the present invention, the sample volumes can range from between about 0.05 mL to about 0.5 mL, and about 0.1 mL to about 0.2 mL applied to the test strip. Alternately, enough sample should be applied to ensure proper sample flow through the test strip and to ensure proper flow of analyte (if present) through the test strip. Preferably, the amount of sample may depend on the absorbency of the sample zone, the length of the transport zone, width of the test strip, temperature at the time of use and whether or not a reagent is added to the sample prior to the application of the sample to the sample zone.

[0052] In an embodiment of the present invention, the conjugate zone is made up of materials including but not limited to glass fiber, cellulose, polyesters and combinations thereof. Preferably, the conjugate zone of an immunochromatographic test strip comprises labeled conjugates, also referred to as ‘labeled conjugate particles’, which are movably supported within the conjugate pad. These labeled conjugate particles are immediately released upon contact with moving liquid sample. Preferably, the conjugates are bio recognition molecules including but not limited to antibodies, nano colloid particles, sol particles and the like. The conjugates are labeled using but not limited to fluorescence tags, dye labels, enzyme reporters, biotin, epitope tags, gold particles, metal nanopartciles, carbon, coloured latex nanoparticles, magnetic beads, fluorescence beads, and coloured polystyrene beads.

[0053] The present inventors have prepared antibodies and antibody conjugate particles that exhibit binding specifically to the antigenic sequences present within SUB2 protein of Plasmodium species having amino acid sequences as set forth in SEQ ID NO: 1, SEQ ID NO: 2, SEQ ID NO: 3, SEQ ID NO: 4, SEQ ID NO: 5, SEQ ID NO: 6, SEQ ID NO: 7 and SEQ ID NO: 8.

[0054] In one embodiment of the present invention, the antibody comprises heavy chain and light chain constant regions (CH and CL) and heavy chain and light chain variable region (CH and VH), wherein each of the antibody heavy chain variable region (VH) and the antibody light chain variable region (VL) comprises a region that can specifically bind to the species-specific antigenic sequences of Plasmodium having SEQ ID NO: 1, SEQ ID NO: 2, SEQ ID NO: 3, SEQ ID NO: 4, SEQ ID NO: 5, SEQ ID NO: 6, SEQ ID NO: 7 and SEQ ID NO: 8.

[0055] In an embodiment of the present invention, there is provided a labeled antibody as a conjugate particle which is bound to gold. In another embodiment of the present invention, the gold labeling is done by using gold nanoparticles. Preferably, the immunochromatographic test strip comprises gold-labeled antibodies as conjugate particles in the conjugate zone. Preferably, gold nanoparticles labeled with antibodies are temporarily adsorbed on the conjugate zone and released upon contact with the liquid sample. The labeled-conjugates can be flushed away by flow of liquid buffer solution. During assay in the immunochromatographic test strip, the accumulation and immobilization of the gold particles at a test line or control line results in appearance of the red colored line.

[0056] In one embodiment of the present invention, the gold labeled antibody is a tetramer having two heavy chain variable regions (VH) and two light chain variable regions (VL), wherein the variable regions comprises a region that can specifically bind to gold.

[0057] In another embodiment of the present invention, only the heavy chain constant regions can specifically bind with the gold nanoparticles. In such an embodiment, the antigen binding variable regions are freely available to bind with the antigenic sequences present in the sample.

[0058] In a further embodiment of the present invention, the gold nanoparticles employed for gold labeling the antibodies specific to the antigenic sequences of SEQ ID NO: 1, SEQ ID NO: 2, SEQ ID NO: 3, SEQ ID NO: 4, SEQ ID NO: 5, SEQ ID NO: 6, SEQ ID NO: 7 and SEQ ID NO: 8 exhibit more surface area. Such an embodiment of the invention provides enhanced antibody binding and retention. The novel gold nanoparticles improve the Limit of Detection (LOD), stability and shelf life of the immunochromatographic test strip. The gold-labeled antibodies of the present invention are stable over entire life span of the lateral flow strip and provide high sensitivity of the assay carried out using the immunochromatographic test strip.

[0059] In an embodiment of the present invention, the transport zone of an immunochromatographic test strip is made up of nitrocellulose membrane. This zone is highly critical in determining the sensitivity of the test strip. The membrane provides support, is porous, and has good binding capacity to capture labeled conjugate particles present in the sample that has traveled from the conjugate zone. In an embodiment of the present invention, the transport zone exhibits very low non-specific adsorption in the regions of test and control lines and thus provides excellent sensitivity of the assay.

[0060] In an embodiment of the present invention, the transport zone of an immunochromatographic test strip comprises: a) a control line (6); b) a PAN test line (7); and c) one or more SUB2 test lines (8). Figure 3 provides a lateral view of an immunochromatographic test strip according to an embodiment of the present invention. The control line captures any particle and thereby shows that reaction conditions and technology worked fine. Excess labeled antibody is captured at the control zone by secondary antibody. The test lines contain specific capture molecule and only captures those particles onto which an analyte molecule has been bound. The PAN test line comprises panLDH antibodies that bind to the lactate dehydrogenase enzyme protein of Plasmodium species and exhibit specificity to Plasmodium species other than P. falciparum. The PAN test line detects infections which are caused by Plasmodium species other than P. falciparum. In a further embodiment of the present invention, the immunochromatographic test strip enables differential identification of one or a combination of Plasmodium species present in a sample. In an embodiment of the present invention, the immunochromatography test strip comprises a plurality of SUB2 test lines. Each SUB2 test line comprises antibodies that exhibit specificity towards any one of the antigenic sequence present within SUB2 protein of Plasmodium species selected from a group comprising of SEQ ID NO: 1, SEQ ID NO: 2, SEQ ID NO: 3, SEQ ID NO: 4, SEQ ID NO: 5, SEQ ID NO: 6, SEQ ID NO: 7 and SEQ ID NO: 8. The PAN test line detects the presence of infection with multiple Plasmodium species and the species specific SETB2 test lines identify the causal Plasmodium species in the infection.

[0061] In an embodiment of the present invention, the control line may be used to perform a variety of control functions such as to ensure that the test strip is in good working order, to determine whether the sample has wicked through the membranes properly, to indicate when the assay may be read, signal the end of the reaction, and as internal standards.

[0062] In an embodiment of the present invention, the immobilized antibodies in the transport zone capture the analyte bound to the labeled conjugate and provide a discrete visible signal from which to view the results of the test. Preferably, the control lines and test lines comprising immobilized antibodies also referred to as‘capture antibodies’ are applied on the membrane by means of an antibody printer. The printer applies the antibodies on the nitrocellulose membrane in the form of lines of the specified dimensions.

[0063] In an embodiment of the present invention, the immunochromatography test strip enables detection, differential identification and quantification of Plasmodium species selected from P. falciparum, P. vivax, P. knowlesi and P. malariae. In an embodiment of the present invention, the immunochromatographic test strip comprises 8 SUB2 test lines along with a PAN test line and a control line. Each SUB2 test lines comprises immobilized antibodies specific for one of the antigenic sequences selected from a group comprising SEQ ID NO: 1, SEQ ID NO: 2, SEQ ID NO: 3, SEQ ID NO: 4, SEQ ID NO: 5, SEQ ID NO: 6, SEQ ID NO: 7 and SEQ ID NO: 8. In another embodiment, the immunochromatographic test strip comprises at least 4 SUB2 test lines along with a PAN test line and a control line wherein at least one of the SUB2 test line comprises immobilized antibodies specific for SUB2 antigenic sequences of Plasmodium falciparum, Plasmodium vivax, Plasmodium knowlesi and Plasmodium malariae selected from a group comprising SEQ ID NO: 1, SEQ ID NO: 2, SEQ ID NO: 3, SEQ ID NO: 4, SEQ ID NO: 5, SEQ ID NO: 6, SEQ ID NO: 7 and SEQ ID NO: 8.

[0064] In an embodiment of the present invention, the absorbent zone of an immunochromatographic test strip at the end of the strip acts as a wicking pad to pull in liquid from the transport zone. The absorbent zone is made up of wicking material and helps in maintaining flow rate of the liquid over the membrane and stops back flow of the sample. Preferably, the wicking material is selected from a group including but not limited to silica gel, cellulose fiber matrix and combinations thereof. [0065] In an embodiment, the immunochromatographic test strip is suitable for sandwich type lateral flow assays performed for analytes such as SUB2 proteins, LDH proteins, fragments and variants thereof. In another embodiment, the immunochromatographic test strip is suitable for competition type lateral flow assays, for example, carried out with analytes such as SUB2 proteins, LDH proteins, fragments and variants thereof. In an embodiment of the present invention, the immunochromatographic test strip can be incorporated further for use as a device in the form of a dipstick or encased in a cassette for the detection and differential identification of Plasmodium species in a sample.

[0066] In another aspect of the present invention, there is provided an immunoassay device for the detection and differential identification of one or more Plasmodium species comprising one or more immunochromatographic test strip encased in a housing or a cover as shown in Figure 4. The housing comprises a) a well for receiving the sample directly on the sample zone on the test strip, and b) a viewing pane for determining the results of the assay. In an embodiment, the immunoassay device comprises a test strip comprising a planar substrate having (i) a sample receiving zone for receiving the liquid sample; (ii) a conjugate zone comprising labeled conjugates; (iii) a transport zone comprising immobilized capture antibodies; and (iv) an absorbent zone comprising a wicking material wherein the transport zone comprises: a) a control line; b) a PAN test line; and c) a plurality of SUB2 test lines.

[0067] In an embodiment of the present invention, the immunoassay device comprises an immunochromatographic test strip wherein each SUB2 test line comprises immobilized antibodies that exhibit binding specificity towards any one of the antigenic sequence present within SUB2 protein of Plasmodium species selected from a group comprising SEQ ID NO: 1, SEQ ID NO: 2, SEQ ID NO: 3, SEQ ID NO: 4, SEQ ID NO: 5, SEQ ID NO: 6, SEQ ID NO: 7 and SEQ ID NO: 8. Each SUB2 test line is species specific and is preferably labeled on the top cover of the housing or provided in an instruction material as a reading material or schematic illustration. The PAN test line comprises antibodies that exhibit specificity to panLDH of Plasmodium sp. other than P. falciparum.

[0068] In a preferred embodiment of the present invention, there is provided an immunoassay device as shown in Figure 5, comprising a) two immunochromatographic test strips (6, 7) encased in a housing having a base (1) and a top cover (8). The test strips are connected to a sample zone (5) that is common to both the strips. The top cover has a sample well (4) for receiving the sample and is preferably positioned over the common sample zone (5). There is also a viewing pane (9) on the top cover of the housing to view the results of an assay carried out using this device. The housing base comprises blocks to fix the immunochromatographic test strips (2) and a lock (3) to lock-in the base and the top cover of the housing. In an embodiment of the invention, the immunoassay device comprising two immunochromatographic test strips comprises on the first strip the control line, PAN test line and SUB2 test lines comprising immobilized antibodies that that exhibit binding specificity towards the antigenic sequence present within SUB2 protein of any two of the Plasmodium species selected from a group of P. falciparum, P. vivax, P. knowlesi and P. malariae and on the second strip the control line, PAN test line and the SUB2 test lines that comprise immobilized antibodies that exhibit binding specificity towards the antigenic sequence present within SUB2 protein of the remaining two Plasmodium species present in the group. The Plasmodium species-specific antigenic sequence present within SUB2 protein is selected from a group comprising SEQ ID NO: 1, SEQ ID NO: 2, SEQ ID NO: 3, SEQ ID NO: 4, SEQ ID NO: 5, SEQ ID NO: 6, SEQ ID NO: 7 and SEQ ID NO: 8 and as shown in Table 1 of this description.

[0069] In an embodiment of the present invention, the immunoassay device comprising two individual strips is connected to a common sample zone and when sample is applied on the zone, it bifurcates equally among both the strips and runs along in the direction as shown in Figure 5. After the complete run, results can be read as the presence or absence of the colored lines depending on the presence or absence of the corresponding Plasmodium species in the sample. The results are interpreted as a presence or absence of a red colored line in the transport zone which can be viewed through the viewing pane of the device. Each test line is species specific and is preferably labeled on the top cover of the housing or provided in an instruction material. The immunoassay device comprising two individual strips avoids the requirement for lengthy strips to accommodate a large number of test lines required for differential identification of causal Plasmodium sp. in a mixed infection. The device is also easy-to-use, does not require any prior training, requires a one time sample at one spot, and is rapid with high sensitivity.

[0070] Another aspect of the present invention provides a kit for a reliable, rapid detection and differential identification of Plasmodium species present in a sample. The diagnostic tools according to the present invention as disclosed herein, immunochromatographic test strips and immunoassay devices, can be provided as kits suitable for transport, point-of-care testing, home use and the like. Kits comprising diagnostic tools according to the invention may be packaged and sold together with instructions for use. The instructions may contain information on testing procedures, interpretation procedures, performance characteristics, information on the test device, storage and handling of the devices. In an embodiment of the present invention, a kit may include, for example: (i) one or more immunoassay devices; (ii) one or more immunochromatographic test strips; (iii) transfer pipettes; (iv) capillary tubes with 1 capillary bulb; (v) diluent which contains buffer; and (vi) directional insert.

[0071] In an embodiment of the present invention, the kit comprises a) one or more immunochromatographic test strip as disclosed herein, immunoassay devices as disclosed herein or combinations thereof b) buffer having pH range of 7.4 to 9.0, c) one or more capillary tubes for transfer of sample, and d) reading material comprising directions for use and comprehending the results for detection and differential identification of the Plasmodium species in the sample. In an embodiment, the kit comprises at least one immunochromatographic test strip comprising a control line, a PAN test line and a plurality of SUB2 test lines, wherein each SUB2 test line carries immobilized antibodies that exhibits specificity towards one of the antigenic sequences present within SUB2 protein of Plasmodium species as set forth in SEQ ID NO: 1 to SEQ ID NO: 8; and the PAN test lines carries anti-panLDH antibodies. The anti-panLDH antibodies enable differential identification of presence of one or a combination of Plasmodium species other than P. falciparum in the sample. Preferably, the Plasmodium species is P. falciparum, P. vivax, P. knowlesi and P. malariae. The utilization of antibodies labeled with gold nanoparticles, in accordance with embodiments of the present disclosure, improves Limit of Detection (LOD), stability and shelf life of the kit.

[0072] In a further aspect of the present invention, there is provided a lateral flow assay method for the reliable, rapid detection and differential identification of one or more Plasmodium species present in a sample using an immunochromatographic test strip of the present invention. The sample zone receives the liquid sample and the fluid migrates to the conjugate zone in which the gold-labeled antibodies specific for unique antigenic sequences within SUB2 protein from each Plasmodium species as shown in Table 1, is present in a dried format as conjugate particles. Preferably the labeled conjugate particles are present in a matrix that contains reagents for an optimized chemical reaction between the antigen SUB2 protein of Plasmodium sp. and the labeled antibody to the SUB2. The gold-labeled antibodies bind to the parasite antigens present in buffered blood sample. While the sample fluid dissolves the matrix, it also releases the gold-labeled antibodies and the sample and gold- labeled antibodies mix while flowing through the porous structure of the conjugate zone. In the transport zone, the gold-labeled antibody-antigen complexes are captured on the SUB2 test lines specific for each antigenic sequence by the immobilized antigen- specific antibodies, depending on the presence or absence of the antigen in the sample. The PAN test line confirms infection by Plasmodium species other than P. falciparum. As more fluid passes the lines, the gold-labeled particles accumulate and the lines change colour from neutral/invisible to a very visible red colour easily detected by the unaided eye. The buffer or excess solution is absorbed in the absorbent zone.

[0073] In an embodiment of the present invention, the lateral flow assay method comprises the steps of: a) contacting a liquid sample at the sample zone of the immunochromatographic test strip as disclosed herein or the immunoassay device as disclosed herein; b) addition of buffer having pH in the range of 7.4 to 9.0; c) allowing the buffered sample to flow through the length of the test strip or device including the transport zone comprising the control, PAN test line and SUB2 test lines; and d) determining the presence of analyte in the sample by visual inspection of the control, PAN test line and SUB2 test lines. The presence of visible colour in the PAN test line indicates presence of mixed Plasmodium infection; and presence of visible colour in the species specific SUB2 test lines indicates and identifies the causal Plasmodium species of the Plasmodium infection.

[0074] In another embodiment of the invention, the lateral flow assay method for the detection and differential identification of one or more Plasmodium species present in a sample comprises a) contacting a liquid sample at the common sample well of the immunoassay device comprising two immunochromatographic test strips as disclosed herein; b) addition of buffer having pH in the range of 7.4 to 9.0; c) allowing the buffered sample to flow through the entire length of both the test strips including the transport zone comprising the control line, PAN test line and SUB2 test lines; and d) determining the presence of analyte in the sample by visual inspection of the control, PAN test line and SUB2 test lines in both the test strips. The presence of visible colour in the PAN test line indicates presence of Plasmodium infection other than P. falciparum·, and the presence of visible colour in the species specific SUB2 test lines indicates and identifies the causal Plasmodium species of the Plasmodium infection.

[0075] In another aspect of the present invention, there is provided a method of diagnosing mixed infection and identification of one or more Plasmodium sp. comprising: a) contacting a liquid sample at the sample zone of the immunochromatographic test strip as disclosed herein or an immunoassay device as disclosed herein; b) addition of buffer having pH in the range of 7.4 to 9.0; c) allowing the buffered sample to flow through the length of the test strip or device including the transport zone comprising the control, PAN test line and SUB2 test lines; and d) determining the presence of analyte in the sample by visual inspection of the control, PAN test line and SUB2 test lines. The presence of visible colour in the PAN test line indicates presence of mixed Plasmodium infection; and presence of visible colour in the species specific SUB2 test lines indicates and identifies the causal Plasmodium species of the Plasmodium infection.

[0076] In an embodiment of the present invention, the step of determining formation of the complex comprises measurement of amount of gold accumulated at said any or a combination of test lines. Unlike fluorescence or magnetic labeled particles that require an additional reader to asses the test results, the results in the present test strip can be viewed by unaided eye as the test lines and control lines appear red in colour. After the complete run, results are interpreted visually as the presence or absence of the colored lines. Intensity of color at test line corresponds to the amount of target analyte and is measured with an optical strip reader or visually inspected. For interpretation, the intensities of the test bands will determine the amount of gold nanoparticles accumulated on the test lines. The intensities of the test bands will differ depending on the amount of antigens present and can be co -related to the amount of parasites present in the circulating blood. The complex is detected by visual observation of color development at the test line which is species specific. The presence of visible red coloured line at the PAN line indicates the presence of mixed infection. The presence of visible red coloured line at the SUB2 line indicates the causal Plasmodium sp.

[0077] In an embodiment, the assay enables quantification of said one or a combination of Plasmodium species present in the sample using a readily available lateral flow reader or a customized lateral flow reader designed for the test strip of the present invention. Color development at the test site may be compared with the color of one or more standards or internal controls to determine whether the development of color is a true indication of the presence or absence of the ligand, or an artifact caused by nonspecific sorption.

[0078] The present invention provides reliable diagnostic tools and method for the detection and differential identification of one or more Plasmodium species present in a sample without false positives and in a highly rapid duration. Preferably, the tools and lateral flow assay method of the present invention enables rapid differential identification of one or more Plasmodium species present in a sample in less than about 30 minutes. In an embodiment of the present invention, the results from the diagnostic tools and method can be integrated with onboard electronics, reader systems, and information systems.

[0079] While the foregoing describes various embodiments of the invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. The scope of the invention is determined by the claims that follow. The invention is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.

Example 1

[0080] An immunochromatographic test strip embodying the invention as shown in

Figure 3 was used for the lateral flow assay method. Around 3-4 drops of blood of approximately 50pl from a patient suspected of malarial infection was obtained by finger pricking. The blood drops were added to the sample well on the immunoassay device. To this, 150m1 (~ 9-12 drops) of lysis buffer comprising 0.1-1% Triton X-100, 1% NaCl, 1% BSA, 0.1-1% Tween-20 in 50 mM Borate buffer/50mM Phosphate Buffer/50mM PBS/50mM Tris Buffer/ 50mM HEPES Buffer, and having pH range of 7.4 to 9.0 was added in the sample well. The addition of the liquid sample triggers the assay and the sample is allowed to run. The end of a successful run is detected by an unaided eye by detection of a visible red line forming in the control test line of the immunoassay device. The time taken for a sample to run the entire strip is around 15 minutes.

[0081] Table 2: The parameters and results of a run using the immunochromatographic test strip according to the present invention.

Example 2

[0082] A total of 80 tests were conducted by spiking the blood samples with each

Plasmodium parasite. The Limits of Detection (LOD) of the test was determined at 100 parasitcs/mΐ of whole blood which is equivalent to 0.002% parasitemia and in line with the WHO standards.

[0083] Table 3: Results of the comparative tests conducted on 80 samples

[0084] The results provided in the Table above show that of the 80 samples, 20 blood samples were tested‘as is’ and therefore, considered disease negative. 60 samples were actually spiked with relevant Plasmodium specie as given in the Table above and could be considered disease positive. The sensitivity was found to be 96.6 % and the specificity was found to be 100 %. The diagnostic tools of the present invention enable detection, and species-specific identification of all 4 Plasmodium species that cause malaria.

ADVANTAGES OF THE INVENTION

[0085] The present invention provides an immunochromatographic test strip that enables detection of mixed infection and differential identification of Plasmodium species in a sample.

[0086] The present invention provides an immunochromatographic test strip that enables diagnosis of malarial mixed infections in an easy-to-use manner, requires a one time sample input at one point only and obliterates the need of adding samples at multiple points for detection and identification of Plasmodium species in a sample.

[0087] The present invention provides an immunoassay device that enables detection and differential identification of Plasmodium species in a sample in an easy-to-use manner and enables diagnoses of malarial mixed infections in a rapid, and safe manner.

[0088] The present invention provides a kit that enables detection and differential identification of Plasmodium species in a sample and enables diagnoses of malarial mixed infections in an easy-to-use manner.

[0089] The present invention provides a rapid assay method for detection and differential identification of Plasmodium species in a sample in less than 30 minutes.

[0090] The present invention provides a rapid and robust assay method and diagnostic tools for detection and differential identification of Plasmodium species in a single test which can detect mixed infections, precludes false positive results, has excellent sensitivity and can differentiate among four different causal Plasmodium species, unlike currently available Rapid Diagnostics Tests currently available in the market.

[0091] The present invention is a reliable tool and method for identifying the causal Plasmodium species and help medical practitioners in prescribing the correct course of anti- malarial drugs for treatment, thus tackling the rampant misuse of anti-malarials and the problem of anti-malarial drug resistance.

Claims

We Claim:

1. An immunochromatographic test strip for the detection and differential identification of one or more Plasmodium species in a sample comprising a planar substrate having

(i) a sample receiving zone;

(ii) a conjugate zone comprising labeled conjugates;

(iii) a transport zone comprising immobilized antibodies; and

(iv) an absorbent zone;

characterized in that, the transport zone comprises:

a) a control line;

b) a PAN test line; and

c) one or more SUB2 test lines,

wherein

the PAN test line comprises antibodies capable of specifically binding to Plasmodium lactate dehydrogenase (panLDH) of Plasmodium sp. other than P. falciparum; and

wherein

each SUB2 test line comprises antibodies capable of binding specifically to any one of the species-specific antigenic sequences present within subtilisin-like protease-2 (SUB2) protein of Plasmodium species selected from a group comprising SEQ ID NO: 1, SEQ ID NO: 2, SEQ ID NO: 3, SEQ ID NO: 4, SEQ ID NO: 5, SEQ ID NO: 6, SEQ ID NO: 7 and SEQ ID NO: 8.

2. The immunochromatographic test strip as claimed in claim 1, wherein the Plasmodium species are P. falciparum, P. vivax, P. knowlesi and P. malariae.

3. The immunochromatographic test strip as claimed in claim 1, wherein the planar substrate is selected from a group comprising cellulose fiber, glass fiber, paper, microstructured polymer, sintered polymer and combinations thereof.

4. The immunochromatographic test strip as claimed in claim 1, wherein the sample zone is selected from a group comprising cellulose fibers, glass fibers and combinations thereof.

5. The immunochromatographic test strip as claimed in claim 1, wherein the conjugate zone is selected from a group comprising glass fiber, cellulose, polyesters and combinations thereof.

6. The immunochromatographic test strip as claimed in claim 1, wherein the labeled conjugates are labeled antibodies comprising heavy chain and light chain constant regions (CH and CL) and heavy chain and light chain variable region (VH and VL), wherein each of the antibody heavy chain variable region (VH) and the antibody light chain variable region (VL) comprises a region capable of binding to the species-specific antigenic sequences of Plasmodium sp. as set forth in SEQ ID NO: 1, SEQ ID NO: 2, SEQ ID NO: 3, SEQ ID NO: 4, SEQ ID NO: 5, SEQ ID NO: 6, SEQ ID NO: 7 and SEQ ID NO: 8.

7. The immunochromatographic test strip as claimed in claim 6, wherein the labeled antibodies are antibodies conjugated with gold nanoparticles.

8. The immunochromatographic test strip as claimed in claim 7, wherein only the heavy chain constant region (CH) specifically bind with the gold nanoparticles and the heavy and light chain variable regions (VH and VL) are capable of binding to the species-specific antigenic sequences of Plasmodium having SEQ ID NO: 1, SEQ ID NO: 2, SEQ ID NO: 3, SEQ ID NO: 4, SEQ ID NO: 5, SEQ ID NO: 6, SEQ ID NO: 7 and SEQ ID NO: 8.

9. The immunochromatographic test strip as claimed in claim 1, wherein the transport zone is a nitrocellulose membrane.

10. The immunochromatographic test strip as claimed in claim 1, wherein the absorbent zone is a wicking material selected from a group comprising silica gel, cellulose fiber matrix and combinations thereof.

11. An immunoassay device for the detection and differential identification of one or more Plasmodium species comprising one or more immunochromatographic test strip as claimed in claim 1 encased in a housing comprising:

a) a base and a top cover;

a) a sample well; and

b) a viewing pane;

wherein

the PAN test line on the test strip comprises antibodies capable of specifically binding to panLDH of Plasmodium sp. other than P. falciparum·, and

wherein

each SUB2 test line on the test strip comprises antibodies capable of binding specifically to any one of the antigenic sequence present within SUB2 protein of Plasmodium species selected from a group comprising SEQ ID NO: 1, SEQ ID NO: 2, SEQ ID NO: 3, SEQ ID NO: 4, SEQ ID NO: 5, SEQ ID NO: 6, SEQ ID NO: 7 and SEQ ID NO: 8.

12. An immunoassay device as claimed in claim 11 comprising

a) two immunochromatographic test strips encased in a housing having a base and a top cover; b) a common sample well; and

c) a viewing pane;

wherein

the SUB2 test lines on the first strip comprises antibodies capable of specifically binding to the antigenic sequence present within SUB2 protein of any two of the Plasmodium species selected from a group of P. falciparum, P. vivax, P. knowlesi and P. malariae and the SUB2 test lines on the second test strip comprises antibodies capable of specifically binding to the antigenic sequence present within SUB2 protein of the remaining two Plasmodium species present in the said group, and

wherein

the antigenic sequence present within SUB2 protein for the Plasmodium sp. is selected from a group comprising SEQ ID NO: 1, SEQ ID NO: 2, SEQ ID NO: 3, SEQ ID NO: 4, SEQ ID NO: 5, SEQ ID NO: 6, SEQ ID NO: 7 and SEQ ID NO: 8.

13. A kit for the detection and differential identification of one or more Plasmodium species, comprising:

a) one or more immunochromatographic test strip as claimed in claim 1 or immunoassay device as claimed in claim 11;

b) buffer having pH range of 7.4 to 9.0,

c) one or more capillary tubes for transfer of sample, and

d) reading material comprising directions for use and comprehending the results for detection and identification of Plasmodium species in the sample.

14. A lateral flow assay method for the detection and differential identification of one or more Plasmodium species present in a sample comprising:

a) contacting a liquid sample at the sample zone of the immunochromatographic test strip as claimed in claim 1 or the immunoassay device as claimed in claim 10;

b) adding buffer having pH in the range of 7.4 to 9.0;

c) allowing the buffered sample to flow through the length of the test strip or device including the transport zone comprising the control, PAN test line and SUB2 test lines; and

d) determining the presence of analyte in the sample by visual inspection of the control, PAN test line and SUB2 test lines;

wherein

(i) presence of visible colour in the PAN test line indicates presence of mixed Plasmodium infection; and (ii) presence of visible colour in the species specific SUB2 test lines indicates and identifies the causal Plasmodium species of the Plasmodium infection.

15. A lateral flow assay method for the detection and differential identification of one or more Plasmodium species present in a sample comprising:

a) contacting a liquid sample at the common sample well of the immunoassay device as claimed in claim 11 ;

b) addition of buffer having pH in the range of 7.4 to 9.0;

c) allowing the buffered sample to flow through the entire length of both the test strips including the transport zone comprising the control line, PAN test line and SUB2 test lines; and

d) determining the presence of analyte in the sample by visual inspection of the control, PAN test line and SUB2 test lines in both the test strips;

wherein

(i) presence of visible colour in the PAN test line indicates presence of Plasmodium infection other than P. falciparum, and

(ii) presence of visible colour in the species specific SUB2 test lines indicates and identifies the causal Plasmodium species of the Plasmodium infection.

16. A method of diagnosing mixed infection and identification of one or more Plasmodium sp. comprising:

a) contacting a liquid sample at the sample zone of the immunochromatographic test strip as claimed in claim 1 or an immunoassay device as claimed in claim 10;

b) addition of buffer having pH in the range of 7.4 to 9.0;

wherein

(i) presence of visible colour in the PAN test line indicates presence of mixed Plasmodium infection; and

17. The method as claimed in claims 14 to 16, wherein the sample is selected from a group comprising blood, serum, urine, saliva, nasal discharge, sweat, plasma, semen, cerebrospinal fluid, tears, pus, amniotic fluid, lung aspirate, gastrointestinal contents, vaginal discharge, urethral discharge, chorionic villi specimens, epithelials, hair, and sputum.