A seroepizootiologic study of five viruses in a swine-evaluation station.

This serologic study was done to gain information on the spread, maintenance, and effect upon performance of five porcine viruses. Blood samples were taken from two groups of 8- to 11-week-old pigs from a large number of Indiana swine herds in a performance-testing station 1 week after entry, 7 weeks after entry (one group only), and at slaughter. The sera were tested by indirect fluorescent antibody tests for antibodies to transmissible gastroenteritis virus (TGEV), swine influenza virus (SIV), hemagglutinating encephalomyelitis virus (HEV), porcine adenovirus (PAV), and pseudorabies virus (PRV). Seroconversions to TGEV, HEV, and PAV occurred in a group of pigs entered in May and slaughtered in August (group 1). In the group that was entered in October and slaughtered in January (group 2), pigs developed antibodies to SIV, HEV, and PAV, but not to TGEV. Only 1 of the 434 pigs tested had antibodies to PRV, and there were no seroconversions to this virus. The only statistically valid effect of infection on performance was found in group 1 pigs, which had seroconverted to TGEV during the first 7 weeks of their stay. These pigs gained 0.077 kg less per day than pigs that did not develop antibodies to TGEV during that period. The pattern of serologic reactions was indicative of a relatively slow spread of these viruses in the groups. We interpret this as supporting the concept that a relatively slow spread of these viruses through large groups of pigs kept under conditions that are less than optimum for virus spread may be an important means of their interepizootic survival.

An indirect fluorescent antibody test for antibodies to transmissible gastroenteritis of swine.

The indirect fluorescent antibody test was modified to provide a rapid technique for the detection, screening and titration of antibodies to transmissible gastroenteritis of pigs. Large numbers of slides containing transmissible gastroenteritis antigen were prepared by planting mixtures of infected and uninfected swine testicular cells onto multiwelled teflon-coated slides. After overnight incubation, about one-half of the cells in each well were infected which provided contrast to aid in detecting specific fluorescence in the presence of varying degrees of background staining. Following fixation, antigen slides were stored at -20 degrees C until used. The indirect fluorescent antibody test was compared to the virus neutralization test in both the screening and titration of swine sera containing transmissible gastroenteritis antibodies. The test was found to be sensitive and reliable and to offer certain advantages over the virus neutralization test.

Lesions of the gastrointestinal tract of pigs infected with transmissible gastroenteritis.

Gross, subgross and histological lesions were studied in 103 pigs infected with transmissible gastroenteritis virus and killed at daily intervals for 14 days. Twenty-three pigs served as controls. Thirty-six pigs were given colchicine four hours prior to being killed in order to determine the mitotic activity in the gastrointestinal tract. The gross lesions consisted of dehydration, excessive milk curd in the stomach, focal hemorrhage in the submucosa of the diverticulum ventriculi of the stomach, fundic and pyloric congestion in severly dehydrated animals and thinning of the small intestinal wall. The major subgross lesion was a marked shortening of the villi in the lower duodenum, jejunum and ileum within 24 hours after exposure to the virus. Regrowth of the villi became evident on about the sixth day after infection. Histological examination of the small intestine revealed that the villus-height/crypt-depth ratio in the jejunum was reduced from 7:1 in normal pigs to less than 1:1 in infected pigs. Villous atrophy was less severe in the proximal duodenum and ileum. Cells covering the atrophic villi were flatened or cuboidal and did not have well defined brush borders. Inflammatory changes in the gastrointestinal tract were minimal at all stages of infection. Goblet cell numbers increased slightly in the recovery stage of the disease and small numbers of mononuclear cells accumulated in the lamina propria during regrowth of the villi. The number of metaphase nuclei in the small intestinal crypts of infected pigs was greater than in normal pigs.

Diagnosis of transmissible gastroenteritis in pigs by means of immunofluorescence.

THE FLUORESCENT ANTIBODY (FA) TEST FOR THE DIAGNOSIS OF FIELD OUTBREAKS OF TRANSMISSIBLE GASTROENTERITIS (TGE) IN BABY PIGS WAS COMPARED TO OTHER AVAILABLE MEANS INCLUDING: virus isolation by inoculation of test pigs, intestinal lesions especially villous atrophy, and clinical observations. Immunofluorescent tests were done on frozen sections of the small intestine and it was possible to make a specific diagnosis within two hours after collecting samples. The results obtained with the FA test compared favorably with virus isolation from infected tissues. It was considered a more advantageous procedure as long as infected pigs were in a relatively early phase of the disease. Because of the variability of the lesions as related to the stage of infection, pathologic diagnoses were less satisfactory. Field diagnoses made on the basis of clinical signs were least reliable.