[Course of transmissible gastroenteritis on a swine-breeding farm]. / Protichane na transmisivniia gastroenterit v svinevudno predpriiatie.

Epizootiologic studies were carried out from the introduction of the transmissive gastroenteritis on the Enterprise up to the end of 1984. Clinical observations and morphologic survey were conducted on the infected animal farms. The diagnosis was based on both virologic and serologic investigations with routinely employed methods. The basic reason for the occurrence and spread of transmissive gastroenteritis on the Enterprise were shown to be omissions in the system of prevention measures with regard to infectious diseases, i. e., the functioning of farms as open units and the intense connections between them. The basic way of spreading the infection was shown to be the removal of animals from healthy to affected farms. The part played by other ways of infection transmission proved negligible, and the strict adherence to veterinary and sanitary requirements of protection guaranteed to a high extent the prevention of transmissive gastroenteritis on swine-breeding complexes and farms. It was also found that the disease assumed a stationary character on the infected farms, with periodic enzootic outbreaks in some of them associated with the nonobservance of feeding and raising technologies.

[Use of a microvirus-neutralizing reaction in diagnosing transmissible gastroenteritis (TGE)]. / Izpolzuvane na mikro-virusneutralizatsionnata reaktsiia v diagnostikata na transmisivniia gastroenterit (TGE).

A micro virus-neutralization reaction was designed and tested to detect antibodies to the virus of transmissive gastroenteritis. Use was made of a stable cell line, SPEV, and a laboratory strain of the virus that had been adapted to it. The optimal concentration values of the cell suspension and the normal calf serum contained in it were determined. A total of 90 blood serum samples from pigs were comparatively investigated for the presence of virus-neutralising TGE antibodies, the tube test being performed trough the inoculation of the cells in suspension. On the other hand, the micro virus-neutralization test was carried out in two variants: the sera were diluted via Mikrotiter micropipettes and micropipettes of the Takachi apparatus. It was found that the micro virus-neutralization test in its two variants was not inferior in terms of sensitivity to the tube test, was more readily applicable, and was less material consuming.

[Trials of peroral vaccination of newborn pigs against transmissible gastroenteritis (TGE)]. / Opiti za peroralna vaktsinatsiia na novorodeni praseta sreshtu transmisiven gastroenterit (TGE).

Experiments were carried out to apply oral vaccination to newborn pigs against transmissive gastroenteritis on a stationary swine breeding complex at the time when the disease assumed an acute course and on newly infected farms. Used was an attenuated strain an hour prior to allowing the pig to suck. It was found that such vaccination approach was innocuous. It proved effective when applied at the moment of birth both on the infected (stationary) farms and in the new foci of infection--morbidity and mortality were lowered and the body development of pigs was improved. Such vaccination was shown to produce also an antiepizootic effect if systematically used on stationary farms--clinically, there were no new epizootic outbreaks of the diseases.

[Isolation and use of a farm-specific hyperimmune serum against transmissible gastroenteritis]. / Poluchavane i prilagane na obornospetsifichen khiperimunen serum sreshtu transmisiven gastroenterit.

A specific stationary hyperimmune serum was obtained in a pigbreeding complex with a transmissive gastroenteritis infection via trifold (at a fourteen-day interval) i/m injection of sows with 5 cm3 each of undiluted virus (10(6) TCCPE50 per cm3). Tested were hyperimmunization programmes with pigs in the final fattening period. It was found that the use of undiluted virus led to the equation of sows in terms of their immunologic state and to the essential rise of the titer of humoral antibodies. In order to obtain high titer immune serum against transmissive gastroenteritis it is sufficient to proceed with the i/m injection of pigs or adult swine in the final stage of fattening at rising amounts (from 3 to 10 cm3) of attenuated virus of sufficiently high titer (10(6) TCCPE50 per cu. cm). The hyperimmune serum produced a very good prophylactic effect with newborn pigs on the same farm - the twofold oral administration of 5 to 10 cm3 on the day of birth and a couple of days later led to a drop of both morbidity and mortality rate as well as to the improvement of body development.

[Demonstration of a transmissible gastroenteritis virus by contrast immunofluorescence]. / Dokazvane na virusa na transmisivniia gastroenterit chrez kontrastniia imunofluorestsenten metod.

Tested were a number of procedures to employ the immunofluorescence method for diagnosing transmissive gastroenteritis in pigs--impression preparations, frozen cross-sectioned material, and infected cell cultures of the established cell line SPEV. It was found that immunofluorescence microscopy was a dependable method for the express diagnosis of transmissive gastroenteritis. It could be employed in its three variants. The use of impression preparations, however, did not prove as dependable as the remaining ways of applying the method, and this drawback had to be compensated for with the study of a greater number of impression preparations taken from more pigs that had contracted the disease. It was also established that most promising and effective was to apply the method with the use of cell cultures infected with suspensions of organs. Cell cultures of the established SPEV cell line infected with material that contained the virus could produce dependable positive results in immunofluorescence investigations at the 24th hour following inoculation. This method could be employed for the express diagnosis of transmissive gastroenteritis.

[Experiments to produce an attenuated strain of the transmissible gastroenteritis virus and its use as a live vaccine]. / Opiti za polchavane na atenuiran shtam na virusa na transmisivniia gastroenterit i izpolzuvaneto mu kato zhiva vaksina.

Serial passages have been performed of a field virus of the transmissive gastroenteritis to obtain an attenuated strain adapted to a permanent cell line of pig kidney, "SPEV". The strain is innocuous for test animals, for pigs of all ages, and for swine during the entire period of pregnancy. It has proved genetically stable. The strain is immunogenic for swine and pigs both under laboratory and under field conditions (in new foci and on stationary farms) and can be used as a live vaccine against transmissive gastroenteritis, either untreated or in a freeze-dried state.

[Isolation of the transmissible gastroenteritis virus in a continuous pig embryo kidney cell line]. / Izolirane na virusa na transmisivniia gastroenterit v postoiannata kletuchna liniia SPEV.

Attempts were made to isolate the virus of transmissive gastroenteritis in a permanent cell line SPEV in view of the diagnostics of the disease. Used were small intestines of pigs during the first 24 hours after the setting in of clinical symptoms. The successful isolation of the virus in a SPEV line depended on the methods employed to handle the material as well as on the ways of inoculating the cell cultures. In the conditions of the investigation most proper proved centrifugation of the organ suspensions and the suspension method of infection. The SPEV line, however, was shown to be insufficiently sensitive to isolate the virus of transmissive gastroenteritis. About 30 per cent only of the positive material could be used to demonstrate the virus following direct infection, while the study of the remaining (up to 62 per cent) material required additional passing. The SPEV line could replicate the virus after its infection with organ suspensions containing the virus, and this could be demonstrated through immunofluorescence investigations. The same method could likewise be employed in the express diagnosing of the disease. The passing of the virus strains in the SPEV line led to their attenuation. In order to retain the virulence of the strains passing should take place in nonimmune pigs or should alternate with the use of both pigs and cell cultures.

[Cultivation of the transmissible gastroenteritis virus in a continuous cell line]. / Kultivirane na virusa na transmismisivniia gastroenterit v postoianna kletuchna liniia.

Cell cultures of the permanent cell line SPEV to which the transmissive gastroenteritis virus had already been adapted were used to culture the virus and carry out the virus-neutralization test. Use was made of a cell suspension of a variable density--300 and 500 thou cells per cm3. Both variants of the cell suspension were comparatively studied in terms of growth, the production of a monolayer, susceptibility to infection, and titer of the virus obtained, using 4 test tubes with the virus at various rates of dilution which were kept under observation daily, keeping a record of the infected and noninfected cell cultures. The amount of the virus was determined by titration. It was found that the monolayer was produced more rapidly in the suspension containing 500 thou cells/cm3. In that case infection could be performed at the 24th hour. The cytopathic effect was more pronounced, and the titer of the virus obtained was higher. Successful attempts were made with the virus-neutralization test with the infection of the cell cultures in suspension. Thus, the entire procedure was shown to be labour-saving as the time for investigation of the sera was shortened.