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In the present paper the exponential and ordinary dichotomies for linear periodic differential equations with impulses are investigated. [ABSTRACT FROM AUTHOR]

An indirect variant of the enzyme linked immunosorbent assay with the classic form of swine fever has been worked out. The test makes it possible to assess the level of antibodies with a great number of animals over a short period of time with no special equipment. The method has proved promising in taking prophylactic measures.

Attempts were made to modify the hemadsorption method used in the demonstration of the African swine fever virus. Use was made of fourteen strains of the virus with known hemadsorption properties and infectious titers, which were replicated in leukocyte cultures of swine blood, in three variants: (a) at direct infection of the cultures without changing the medium; (b) at infecting with changing the medium and adding erythrocytes to the new medium; and (c) infecting the cultures with changing the medium and adding 0.2 cm3 2 per cent erythrocyte suspension to each test tube at the 16th hour following infection. It was shown that in its third variant the hemadsorption method yielded most clearly expressed results, and all suspective fields were eliminated, the result being recorded as early as the second hour after the addition of erythrocytes, i.e., at the 18th hour following the infecting of cultures. With the third modification of the method no phagocytosis of the present erythrocytes effected by the emerging macrophages, which is common for the other two variants, could take place.

Pigs vaccinated with the lapinized K strain were studied by the immunofluorescence method, through bioassay on rabbits, and histopathologically. It was found that virus K is retained up to the 12th day post vaccination. If later on the presence of a virus was demonstrated it was believed that a wild virus participated. The virus was found in the spleen, lymph nodes, tonsils, and occasionally in the kidneys. Histologically, there were changes in the central nervous system under the form of nonsuppurative meningoencephalitis, dystrophic and fibroblastic proliferations in the kidneys, and necrobiotic and necrotic areas in the liver. They proved analogous to the changes found in spontaneously affected pigs; it was believed that there was no difference in the tropism of the vaccinal and the wild virus of swine fever. The results obtained improve the laboratory diagnostics of the classic form of swine fever.

Studies were carried out on the first grippe epizootic in pigs in Bulgaria. The affected animals showed a rise in temperature (40.5 to 41.8 degrees C), loss of appetite, abdominal type of respiration, and noisy and painful cough. The infection ran its course with a picture typical of a virus disease which did not respond to broad-spectrum antibiotic treatment. On an average the duration of the clinical course lasted 4 to 5 days, affecting almost all swine on a pig breeding farm, with single death cases. The morphologic changes observed in animals killed for diagnostic purposes were typical of a grippe infection. Isolated was a grippe virus A (Antimovo) 1/80/H3N2) the preliminary typisation of which showed close relation to strain A (victoria) 3/75/H3N2/. Serologic investigations using double blood samples from the affected pigs in double immunodiffusion test and hemagglutination-inhibition test demonstrated the etiologic role played by the isolated grippe virus.

Studies were carried out on morphologic changes in 27 pigs experimentally infected with a virulent virus of the African swine fever and in 61 pigs that has spontaneously developed the acute form of the disease. A description and 11 colour plates are given of the characteristic gross and microscopic lesions, consisting of strongly mainfested hemorrhagic diathesis, two-to fourfold enlargement of the spleen, and two-to threefold enlargement of the stomach, liver, mesenterial, kidney, and sternal lymph nodes. The digestive tract was shown to be thoroughly involved, most pronounced being the changes in the stomach and the large intestine. It was demonstrated that the basic histologic changes were localized in the central lymphoreticular system--spleen and lymph nodes, consisting in dystrophic and necrotic lesions of the lymphocytes (karyorrhexis and karyopycnosis), the reticular cells, and the cell elements of the blood vessels. A comparison is made with the morphologic changes in the case of classic swine fever, stating the most essential differences between the lesions in the two forms of the disease.

In the treatment of spleens and lumph nodes of rabbits infected with strain K, with the use of freon 113 the virus was freed from proteins up to 92-96 per cent. The infective power of the purified virus proved equal to that of the initial non-purified virus proved equal to that of the initial non-purified virus, and this points to the full extraction of the virus itself. The antigenic properties of the purified virus were demonstrated through agar gel precipitation with normal and hyperimmune sera of pigs and rabbits and indirect immunofluorescence methods. This method of purification yields a virus that can be used in more precise immunologic studies as well as in the study of the morphology of the classic swine fever virus.

Investigations were carried out on the presence of carriers and the excretion of the virulent swine fever virus in pigs vaccinated with the lapinized vaccine strain K. On the 15th, 25th, and 35th day following injection with the virulent virus a pig was killed each time and material was taken for morphologic studies and immunofluorescence microscopy. The results of the investigations were negative except for two pigs the cerebrum of which showed perivascular, slightly to moderately expressed lymphoid-cell agglomerations as well as a weakly manifested perivascular edema. Material of the killed animals was used to infect unvaccinated susceptible pigs in which the presence of the virus had not been demonstrated. No clinical and morphologic data or immunofluorescence microscopy demonstration proved the presence of a virus upon exposure of animals to pigs that were injected with a virulent virus. Hematologic studies revealed leukopenia, lower percent of hemoglobin, and a drop in the erythrocyte count following injection with the virulent virus. After a certain period of time this condition was overcome. These experiments showed that when a virulent virus gains access to pigs that have become immune after vaccination with the K vaccinal strain of the swine fever virus does not persist longer than the seventh day and does not cause the development of latent or a clinically manifested infectious process.

Attempts were made to immunize suckling pigs against classic swine fever. The pigs were treated orally, originating from sows which were immunized on the 30th-40th and the 90th-100th day of pregnancy, as well as from sows which were vaccinated one month prior to impregnation. A Bulgarian lapinized K vaccine and a Soviet LK-VNIIVViM cell culture were used (immunization being carried out 1-2 hours before the newborns were allowed to suck) at the rate of 150 doses for both vaccines. It was demonstrated that the application of a live vaccine, which was patterned as cited above, eliminated the inhibiting action of colostral antibodies and induced stable postvaccinal immunity. However, the effectiveness of the immunity conferred depended on the vaccine used in each specific case. The Soviet vaccine, in which the amount of the virus per vaccinal dose was five times as much, was shown to be more appropriate to the needs for oral immunization of suckling pigs of sows that were immune to classic swine fever than the lapinized K vaccine.