FR2499411A1 - Live vaccine against contagious ecthyma of sheep - prepd. from virus attenuated by passaging on foetal skin cells - Google Patents

Abstract

Live viral vaccine against contagious ecthyma of sheep comprises the attenuated viral strain 'L-1' (deposition number 8). This is isolated from the infected areas of the skin of a lamb and adapted by repeated passages on a primary culture of sheep foetal skin cells. Esp. 10-20 passages on cells from a 3-3.5 month old foetus are carried out at 36-37 deg.C. The attenuated strain is grown on cells of 3-month old sheep foetal skin at 36 deg.C. pref. using medium N199 contg. 2% bovineserum for maintenance. Particularly the virus contg. material is first harvested when 50-70% of the cells are infected and the second harvest is taken 24-36 hrs. later. This vaccine is highly immunogenic, safe and free from contaminating viruses. The attenuated strain can be grown on readily available substrates and provides immunity (which lasts for at least 9 months) against a wide range of epizootic viral strains.

Description

 The present invention relates to the field of veterinary medicine and, more specifically, a live viral vaccine cultivated against contagious ecthyma of sheep breeds and its preparation process.

 Contagious ecthyma (contagious pustular stomatitis, pustular dermatitis, fake smallpox, etc.) is an infectious disease of viral etiology with acute course. Under natural conditions, sheep, goats and rarely humans suffer from ecthyma.

Under experimental conditions, we manage to infect rabbits and puppies.

 The disease is characterized by a pustular vesicular lesion of the superficial layers of the skin with subsequent formation of a thick crust and with the appearance of ulcers and erosions on the mucosa of the oral cavity.

 On permanently defective farms, young lambs have contagious ecthyma and clinically suffer from ecthyma at the age of 4 to 5 days. Annual enzootic relapses are observed and the peak of morbidity corresponds to the spring-winter lambing period, when young animals are infected with ecthyma in certain flocks of sheep at 80 - 100%.

 There have also been relapses of the disease in the fall due to sheep driving on winter pastures.

 The disease is observed in countries dealing with sheep farming in Europe, Asia, Africa, America and Australia.

 The contagious ecthyma causes enormous economic damage to sheep farms. Animals affected by ecthyma see their fattening and their weight decrease, they are retarded in growth and development: their meat and woolen productivity as well as their breed value decrease.

 Vaccine prophylaxis is the effective means in the fight against the contagious ecthyma of sheep and goats. In veterinary practice, a viral vaccine against contagious ecthyma is widely used, prepared from epizootic "street" strains of the contagious ecthyma virus.

 For the first time, Aynaud M. prepared in 1921 and used a so-called crusty vaccine. "To prepare such a vaccine, the author picked up scabs on the affected areas of the skin of the lips of sheep affected by l 'ecthyma contagious, 15 - 20 days after the onset of the disease; he dried them over concentrated sulfuric acid in an exciccator, very finely ground in a mortar, kept in chloroform selling for 24 hours, dried again in the air and kept in the ampoules until use. Directly before use, the powder containing the viral material is ground in the mortar and suspended in physiological saline containing 50% glycerin (Aynaud M.

Acad. Scien., 1921, 173, pp. 950-952; Aynaud
M., Ann. Inst. Pasteur, 1923, 37, pp. 498-527).

 In later years, several authors in various countries used the method of vaccine preparation proposed by Aynaud and used it widely (Altara J., Nuova veterinaria, 1925, 3, pp. 4-9, Barrat E .

Rev. Med. Vet., 1933, 111, pp. 10-12).

 Some authors have perfected and insignificantly modified the preparation of the vaccine by the Aynaud method.

 Thus, for several decades, the live vaccine, prepared from the epizootic virus, was the sole means of specific prophylaxis of the contagious ecthyma of sheep, particularly in foreign countries. The live vaccine against the contagious ecthyma being prepared from the "street" etizootic virus. All non-immune animals were infected with the preparation obtained, to cause disease simultaneously in all receptive animals with the formation of immunity in them. During the use of the live vaccine prepared from the epizootic virus under the conditions of use, care should be taken during vaccination. The inoculated animals were isolated from the uninoculated animals for 3 weeks, the measures of Sanitation and veterinary disinfection were carried out regularly, since the scabs, detaching themselves from the infected foci of vaccinated animals, present the same danger as natural disease.

The live scab vaccine, collected from infected areas of the skin of sick sheep, contains the bacterial flora and treatment with antibiotics does not ensure the sterility of the preparation (Alboiu M. di Simon M., Birnaure CH,
Lucrarileetiintifice ale institutului de seruri ai vaccinuri Pasteur, Bucuresti, 1960, 4, 237).

 The use of the contagious sheep ecthyma vaccine prepared from accidental, little studied, highly virulent strains of the epizootic virus makes this vaccine dangerous for widespread use. The vaccine prepared from the epizootic virus has a high reactogenicity and the post-vaccination reaction in inoculated animals evolves seriously, like natural disease, with all the consequences.

 The live vaccine against the contagious ecthyma of sheep, prepared from epizootic strains of the virus, does not meet the requirements imposed on modern antiviral preparations, because of its high virulence, bacterial impurity and the epizootic danger, since vaccination of animals creates new foci of infection.

 The use of the killed Formalin inactivated vaccine with aluminum hydroxide as well as the vaccine prepared by culture of the epizootic strain of contagious ecthyma virus in chicken embryos has not produced positive results (Pegreffi G., Atti. 5 Congr.

naz. Microbiology, 1936, pp. 358-362; Olah P. et al.,
Acta vet. Hung. 1953, p. 237).

 The present invention proposes to create a vaccine against the contagious ecthyma of sheep breeds, which would have a high immunogenicity, safety and would not contain foreign viruses.

 According to the aim indicated, the invention aims to develop a method for preparing the vaccine using a weakened strain of the contagious ecthyma virus, capable of being cultured on an easily accessible substrate, characterized by high immunogenicity , safety and absence of foreign viruses.

According to the invention, a live viral vaccine cultivated against contagious ecthyma of sheep breeds is proposed, characterized in that it contains an attenuated strain "La1" of the contagious ecthyma virus, deposited under the
N 8, obtained from the "street" virus, isolated in affected areas of the skin of the lamb affected by contagious echyma, by adaptation of this strain to the primary culture of fetal skin cells sheep during several passes.

 A vaccine is proposed which is characterized in that it contains an attenuated strain "La%" of the contagious ecthyma, deposited under number 8 and suitable for the primary culture of skin cells of the fetus of sheep aged 3- 3.5 months, at a temperature of 36 to 370C for 4 - 5 days.

 The indicated attenuated strain of the virus, used to erenate the vaccine against contagious ecthyma of sheep breeds, is designated here by convention the "L-1" strain of contagious ecthyma virus.

The above-mentioned strain is a newly obtained vaccine strain deposited under No. 8 in
Vsesojuznom Gosudar-stvennom nauchno-controlnom institute veterinarnych oreparatov inisterstva vieskogo khozjastva
SSSR, April 25, 1980.

In accordance with the invention, the strain "L1" of the contagious ecthyma virus, deposited under the N 8, is isolated in lambs affected by the contagious ecthyma and adapted to the primary monolayer culture of skin cells of the sheep fetus, at a temperature of 36 + 10C for 10-20 passages and has a cytopathic activity with a titer reaching 10 'DCTSO / mî
The vaccine strain "L-1" N 8 has the following properties
MorPholoaic characters.

 In the primary culture of skin cells from the fetus of sheep and the kidney epithelium of sheep, the virus forms circular, regularly-bordered negative colonies under the agar layer.

Culture characters.

 The strain 'La1 "multiplies regularly with cytopathic effect in the primary culture of kidney epithelium cells of calves, sheep and the skin of the fetus of sheep.

In the cell systems, characteristic cytopathic changes and accumulations of the virus in the titer up to 106'5 DCTSO / ml are recorded after 5 days of incubation.
Virulent properties.

 Infection with the "L-1" strain of lambs-infants by application to the scarified surface of the skin of the upper lip at a dose of 0.2-0.3 ml causes the formation of 8 to 15 nodules not painful, can be kept for 5-6 days which, without passing into papules, are absorbed without leaving a trace. The nodules are generally observed 3-4 days after application. Animals do not respond to the introduction of the virus strain by other routes of infection. Rabbits and white mice are not susceptible to the "L-1" strain regardless of the route of infection.

Immunological characters.

 Stable spontaneous immunity is formed in 12-15 days and the duration of immunity is at least 9 months.

Antigenic properties.

 The "La1" strain has an immunological affinity with various enizootic strains of the original virus.

 Animals inoculated with the vaccine virus acquire stable immunity against epizootic strains, isolated in various geographic areas.

 The above-mentioned immunogenic properties of the virus "L-1" vaccine strain allow it to be used to prepare a harmless viral vaccine against contagious ecthyma of sheep, sheep and goat breeds, by multiplication in primary cell culture from the skin of the sheep's fetus and from inoculating lambs from the first day of birth, the inoculated animals are then not subject to any restrictions.

 The invention also relates to a process for the preparation of a live vaccine cultivated against contagious ecthyma of sheep breeds, which, according to the invention, consists in cultivating in the culture of skin cells of the fetus of sheep the attenuated strain "L-1" N 8 of a contagious ecthyma virus obtained from the "street" virus, isolated in affected areas of the skin of the lamb affected by the contagious ecthyma.

 It is recommended to cultivate the strain indicated in the culture of skin cells of the fetus of sheep aged 3 or 3.5 months, at a temperature of 36 to 370C in a maintenance medium N 199, containing 2% serum large cattle.

 According to the invention, the first harvest of the material containing the viruses is carried out after the infection of 50 to 70% of cells of the culture at the expiration of 3-4 days, and the second harvest of the material containing the viruses is carried out 24-26 hours after the first harvest.

 The process for the preparation of the live viral vaccine cultivated against contagious ecthyma of sheep breeds is based on the system of the seeding virus, which provides for the preparation of the vaccine virus in sufficient quantity, and meeting all the requirements of the attenuated strain. , as well as frozen storage and use when necessary to prepare the vaccine.

 To prepare the vaccine against the contagious ecthyma of sheep breeds, use the attenuated strain "L-1" deposited under N 8.

 The indicated strain was obtained from the epizootic "street" virus of contagious ecthyma, isolated in the affected areas of the skin of lambs with contagious ecthyma. The epizootic strain of the virus is attenuated by repeated passages in the primary culture of skin cells from the fetus of sheep. After 10 consecutive passages in the primary culture of skin cells of the fetus of the sheep at a temperature of 36 to 370C, the strain acquires a clearly manifested cytopathic activity, which makes it possible to control the whole process of preparation of the vaccine, to carry out the virus harvests in optimal time, to determine the specificity of the virus in tissue culture and to note the titer of accumulation.

The "Ll" strain of the virus obtained is characterized by the following indices
1. Safety for laboratory animals: mice, rabbits and also lambs
2. Cytopathic activity in the culture of skin cells of the fetus of sheep, epithelium of kidney of sheep and large bovids
3. Immunogenic activity on naturally receptive animals: sheep and goats
4. Absence of viruses - contaminants
5. Bacterial sterility and absence of mycoplasmas;
6. Stability and high resistance to storage
7. Lack of contagiousness.

 The seed virus is prepared from the strain "t-1" of the virus having all the above-mentioned indices in the culture of sheep fetal water cells.

The seed virus must have all the qualitative characteristics specific to the attenuated strain.

 The seeding virus is stored in the frozen state at a temperature of 10 to 200C and used when necessary.

 To prepare the vaccine, a trypsinized culture of the skin cells of the fetus of the sheep is used.

For this, the fetus of the sheep aged 3-3.5 months is extracted under sterile conditions from the uterus, the skin is removed, it is ground and trypsinized by the generally accepted method. The cells obtained are suspended in a nutritive medium. The suspension obtained at a concentration of 600,000-800,000 cells / ml is inoculated into culture flasks of 1000 ml capacity with 200 ml in each flask and incubated in a thermostat at a temperature of 36 + 1 ° C. until formation of the entire monolayer. As a nutritive medium, it is possible to use media generally employed for cultivating cells and viruses, for example, medium N 199, containing lo% of serum of large bovines, of pH equal to 7, 2 - 7.4, or a balanced Hanks saline solution, with the addition of 0.5 z of lactalbumin hydrolyzate and 10% serum of bovine breeds at pH 7.2 - 7.4.

 After the formation of the cell monolayer, in the absence of spontaneous degeneration, the culture obtained from the tissue is infected by the introduction into each flask of 5.0 ml of seed virus. For this, the culture medium is purged, 5.0 ml of seeding material containing the viruses is introduced, it is kept at room temperature (20-220C) for one hour and then 200 ml of medium are poured into each flask. maintenance, that is to say the same nutrient medium but containing 2.0 S of serum from cattle breeds. The culture of infected tissue was made to ineuberate at a temperature of 360 ° C. + 1 0 and after the appearance of the cytopathic action of the virus in 50-70% of cells (generally 3 - 4 days after the infection), the first harvest of the virus-containing liquid and the same amount of fresh maintenance medium is added and the incubation is continued for another 24-36 hours during which the cells in the culture are infected at 10%. We remove all flasks with infected tissue culture from the thermostat, cool to room temperature for 3-5 hours and freeze at -10-200C for 20-24 hours, for complete detachment of cells from glass.

 The frozen matras with the tissue culture are weakly thawed and in the presence of pieces of ice are carefully shaken and poured into a bottle.

The two crops of virus-containing material are brought together, mixed carefully and a series of vaccines is obtained in this way, which is poured into vials for storage (liquid vaccine) or for freeze-drying (dry vaccine).

 The desiccated preparation has a residual humidity up to 3.0 X and a cytopathic activity of 106.0 106 DCT50 / ml. The period of validity of the lyophilized preparation is more than one year at a temperature of 1 - 200C in a dark place. Before use, to dilute the dried vaccine, physiological solution, tap water or Hanks solution is used.

 The liquid vaccine has a cytopathic activity 60 65 that of 10 10 DCT50 / ml. The period of validity of the liquid vaccine is at least 4 months when stored under the conditions of (-) lo-200C. Before use, the vaccine preparation is thawed slowly and shaken slightly.

 The vaccine preparation obtained is subjected to the control of sterility, safety, immunogenic activity, cytopathic activity, and the dry preparation to control the residual humidity. After that, the vaccine can be used for prophylactic immunization of lambs and kids. An average dose for the vaccination of lambs contains at least 100,000 DCT50 / cytopathic dose. Increasing the virus content to 5,000,000 DCT50 does not cause adverse reactions in animals. Immunization of lambs and kids is carried out by applying 0.1-0.3 ml of vaccine to the freshly scarified skin of the upper lip.

 The proposed vaccine has passed a large production trial in several republics and sheep farming regions, and has been successfully used on farms where infection has been recorded. On farms with stationary infection, after vaccination of the lambs, no relapses of the contagious ecthyma were observed.

 The results obtained with wide use testify to the property of the vaccine prepared from the strain "La1" N 8 of the contagious ecthyma virus of sheep, to prevent the relapse of the disease on farms with stationary infection. The vaccine from strain "L-1" N 8 is effective and can be used to clear the focus of infection.

 A great advantage of the cell substrate, used for the preparation of the contagious ecthyma vaccine, is that the primary culture of the skin cells of the sheep fetus is free of foreign viruses and is not infected with mycoplasma.

 Another important advantage of cell culture of the skin of the fetus of sheep is that it has a high multiplication activity and the monolayer is formed 2 - 3 days after seeding the cells.

 Yet another advantage of the invention is a double harvest of the material containing the viruses in the infected culture, which considerably increases the yield of vaccine material.

 An essential advantage of the vaccine proposed against the contagious ecthyma of the sheep races is the fact that it is absolutely harmless, sterile and one can vaccinate the infants lambs from the age of one day.

 Other advantages and characteristics of the invention will be better understood on reading the description which follows of examples of its execution, among which example 1 shows the preparation of the strain "L-1" of the virus. 'contagious ecthyma, deposited under N 8, e temple 2 illustrates the method of preparation of the cultivated live vaccine, examples 3 - 6 the use of the vaccine for the vaccination of animals.

EXAMPLE 1.

Preparation of an attenuated "L-1" strain of the contagious echyma virus, deposited under the N 8, from the "street" epizootic virus.

 In 10 vials of 50 ml capacity, containing a monolayer culture of skin cells from the fetus of sheep, 1.0 ml of bacterial sterile virus suspension are introduced into each vial.

After one hour of contact at room temperature, the cultures are washed with a nutritive medium three times, and 10 ml of maintenance medium are introduced into each bottle.
N 199 fresh, containing 2% blood serum from cattle breeds and the cultures are incubated at a temperature of 36.00C + 10 until complete degeneration of the cells in the infected culture. Generally, 120 hours after the contagion, the virus-containing liquid is taken from the vials and used to infect a new portion of cell culture from the skin of the fetus in sheep.

 For this, in each of the 10 vials, containing the new primary culture of skin cells of the fetus of the sheep, are introduced 1 ml of virus culture liquid obtained and 10 ml of maintenance medium, with the addition of 2% of bovine breed serum, and the cultures of the infected cells are incubated at a temperature of 360C + 1.00.

 By a similar infection method, 10 consecutive passages are carried out, which is sufficient to attenuate and adapt the virus to the culture of the tissue. After the 50 step wise, the virus regularly causes cytopathic destruction of the cells that are observed 3-4 days after infection.

The attenuated "t-1" virus obtained and adapted to the culture of skin cells of the sheep fetus undergoes the following checks:
1. Specificity / identification / according to structural morphological characters in an electron microscope
2. Safety, on laboratory animals / white mice, rabbits and lambs /
3. Cytopathic activity in the culture of sheep kidney epithelium cells or the skin of the fetus of sheep
4. Immunogenic activity
5. Bacterial sterility and absence of mycoplasmas;
6. Stability and resistance of the preparation to storage
7. Absence of contagiousness.

EXAMPLE 2.

Preparation of seed virus and vaccine.

a) Preparation of the seeding virus.

 The seed virus is prepared from the "L1" strain obtained according to Example 1. The skin of sheep fetuses aged 3-3.5 months, supplied by a butcher's shop after the slaughter of the sheep, is then used. artificially fertilized. The ground pieces of the skin are trypsinized because the generally known method and a suspension of cells at a concentration of 600,000-800,000 is obtained in 1 ml of nutritive medium, compared with 10% of serum from large bovines and antibiotics per 100 units ( penicillin and streptomycin). The cell suspension is poured into culture flasks of 1 liter capacity at a rate of 200 ml in each and incubated under stationary conditions, at a temperature of 360c + 1.00 until the formation of the complete monolayer . 3 to 4 days after the formation of the entire monolayer, the nutrient medium is eliminated and 5.0 ml of seed virus are introduced, contact is made for one hour at room temperature and 200 ml of medium are introduced. interview containing 2% serum from large bovines, and incubated at a temperature of 360C + 1.00. 4 days after infection, in the event of damage to 50 - 70% of cells in the culture, the virus culture liquid is poured (first harvest) and 200 ml of fresh maintenance medium are introduced into the flasks. each flask containing 2% serum from large bovines and incubated in a thermostat for 24-36 hours. 24 to 36 hours after the first harvest of the virus, the matras are removed with the infected culture from the thermostat, cooled to room temperature and frozen at a temperature of (-) 10 to -200C.

Thaw the frozen tissue culture and in the presence of small pieces of ice, shake the flasks to completely detach the cells from the glass and pour
(second harvest). The liquid containing the first harvest viruses is mixed with the culture suspension of the second harvest viruses in a common bottle. The seed virus obtained in this way is subject to the control of specificity, safety, cytopathic activity, immunogenicity, sterility, absence of contaminating viruses and contagiousness. The seed virus, meeting the indicated requirements, is stored frozen at a temperature of (-) 10 to -200c.

b) Preparation of the vaccine.

 For this, the skin of 3-3.5 month old sheep fetuses, supplied by the butcher's shop, is used. The skin pieces are trypsinized by the generally accepted method after careful mechanical grinding and a suspension is obtained at a concentration of 600,000 to 800,000 cells / ml, in the nutrient medium, containing 10% serum of large bovines and per 100 units of penicillin and streptomycin in one milliliter. The cell suspension is distributed in the flasks of 1 liter capacity per 200 ml in each flask and is incubated under stationary conditions at a temperature of 360C + 1.00 until the formation of a complete monolayer of the cells. After the formation of the cell monolayer, the tissue culture is infected by introducing 5.0 ml of seeding virus into each my trams. For this, the culture medium is poured in, 5.0 ml of material containing the viruses is introduced, it is brought into contact at room temperature (20-220C) for one hour and then poured into each flask 200 ml of medium containing 2% of serum from large bovines. The culture of infected tissue is incubated at a temperature of 360C + 1.00 and in the event of the appearance of the cytopathic action of the virus in 50-70% of cells, read the first harvest of the virus-containing liquid and add the same amount of fresh maintenance medium again and incubate for another 24 - 36 hours during which the cells in the infected culture are infected at 100 S. take out all the matras with the infected culture of the tissue from the thermostat, cool to room temperature and then freeze at a temperature of (-) 10 at -200C for 20-24 hours to completely detach the cells from the glass .

The frozen culture is slowly thawed in the flasks and in the presence of pieces of ice, the suspension containing the viruses is well shaken and it is poured into the common bottle. The two harvests of the virus-containing material are brought together, mixed thoroughly and a series of vaccines is made up and distributed in the vials (liquid vaccine).

The liquid vaccine has a cyto-spathic activity titer equal to 106'0 'O6.5 and a delay of va
DCTSO / ml at least 4 months liquidity when stored at (-) 10200c. Directly before use, the vaccine is slowly thawed and shaken
The desiccated preparation has a residual humidity of up to 3 t and the titer of cytopathic activity from 10 to 10 'DCT50 / ml. The period of validity of the vaccine
DCT5O / ml lyophilized is more than a year at a storage temperature of (+) there + 200C in a dark place. Before use, the vaccine is diluted. To dilute the dried out preparation, physiological solution or tap water or Hanks solution is used.

 The vaccine series obtained is checked for sterility, safety, immunogenicity, cytopathic activity, and the dry preparation is additionally checked for residual humidity. After that, the vaccine can be used for prophylactic vaccination of lambs and kids.

 A series of vaccines can contain 150,000 to 500,000 doses to be inoculated.

EXAMPLE 3.

Vaccine safety trial.

 The natural liquid vaccine or the dry vaccine diluted with physiological solution to a necessary volume was administered subcutaneously to the 5 white mice at a dose of 0.2 ml and to two rabbits at a rate of 1.0 ml. . For the safety trial, non-immune lambs 5-10 days old were also taken and the 0.3 ml vaccine was applied to the skin of the freshly scarified upper lip. The experimental animals were observed daily for 15 days.

All animals were clinically healthy.

No pathological reactions such as refusal of fodder, increase in body temperature, depression, indigestion have been observed. In inoculated lambs, at the place of application of the preparation, transient local changes in the skin characteristic of the post-vaccination reaction have been recorded.

EXAMPLE 4.

Immunogenicity and immunity duration test for the vaccine.

 a) 50 heads of lambs aged 1 to 10 days were inoculated with the vaccine by application of 0.1-0.3 ml of preparation to the frankly scarified skin of the upper lip. Two non-immune lambs of the same age were used for control. 15 days later, the vaccinated animals and the control animals were infected with the virulent epizootic virus by application of 300 DI (infectious dose on the scarified skin of the upper lip). The animals were observed daily. Control animals (not inoculated) fell ill with the appearance of characteristic signs of lesion of the skin of the lips and the mucous membrane of the oral cavity. The reaction to the application of the epizootic virus in inoculated lambs was manifested by a short-term appearance (for 2-3 days) of small nodules directly at the site of application and then they disappeared without a trace in 5 days, and the animals remained clinically healthy.

 b) 3, 6, 9, 12 months after inoculation, the lambs were also infected with the epizootic virus.

Not all vaccinated animals were infected with the infectious ecthyma, except the lambs infected 12 months after vaccination. Local changes in the skin were recorded immediately at the place of application of the preparation, but the pathological process quickly and easily evolved in comparison with uninoculated animals. Thus, stable immunity in lambs inoculated lasts at least 9 months.

 EXAMPLE 5.

Vaccine testing in real conditions.

 For several years, more than 32 million head of lambs aged 1 - 30 days have been inoculated directly into sheep flocks. None of the inoculated animals were infected with contagious ecthyma in the period of enzootic relapse of the disease in the non-inoculated herd.

EXAMPLE 6.

Test of the vaccine in farms where the contagious ectyma has been registered.

 In these farms, each year for several years, the newborn lambs were vaccinated. No case of infection has been recorded in flocks of sheep vaccinated during the current year.

Claims (7)

 1. Live viral vaccine cultivated against contagious ecthyma of sheep breeds, characterized in that it contains a strain "La1" attenuated of the contagious ecthyma virus, deposited under N 8 obtained from the virus "of the streets" isolated in infected places from the skin of the lamb infected with contagious ecthyma, and adapted by several passages to a primary culture of skin cells of the fetus of sheep.  2. Vaccine according to claim 1, characterized in that it contains a strain "La1" attenuated N 8 adapted by 10-20 passages to the primary culture of skin cells of the fetus of sheep aged 3-3.5 months , at a temperature of + 36 to + 370C.  3. Process for the preparation of a live viral vaccine cultivated against contagious ecthyma of sheep breeds, characterized in that the strain "La1" attenuated of the virus is cultivated on a culture of skin cells of the fetus of sheep contagious ecthyma, deposited under N 8 obtained from the "street" virus, isolated in the infected places of the water of the lamb affected by the contagious ecthyma, adapted by several passages to the primary culture of cells of the skin of sheep's fetus.  4. Method for preparing the vaccine according to claim 3, characterized in that the strain "L1" N 8 adapted by 10-20 passages is used for the primary culture of cells of the calf of the fetus of sheep aged 3-3 , 5 months, at a temperature of + 36 to + 370C.  5. Method for preparing the vaccine according to claims 3 or 4, characterized in that the "L1" strain N 8 is cultivated on the primary culture of fetal skin cells at the age of 3 months in sheep, on a maintenance medium, at a temperature of + 360 C.-  6. Method for preparing the vaccine according to claim 3 to 5, characterized in that, as maintenance medium, medium N 199 containing 2% of serum from large bovines is used.  7. Method for preparing the vaccine according to claims 3 to 6, characterized in that the first harvest of the material containing the viruses is carried out during the infection of 50 - 70% of culture cells, and the second harvest virus-containing material being made 24-36 hours after the first harvest.