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Transmissible gastroenteritis in neonatal dogs: experimental intestinal infection with transmissible gastroenteritis virus.

Fourteen neonatal dogs (4 through 11 days of age) were exposed orally to the Purdue strain of transmissible gastroenteritis (TGE) virus, and six dogs of similar age were noninoculated controls. Clinical signs of enteric disease did not develop. Both exposed and control dogs had normal fecal passages and appetite throughout the experiment. Jejunal epithelium from dogs euthanatized at 12, 24, 48, and 96 hours and at 10 days after exposure did not exhibit morphologic alterations detectable by light microscopy. Electron microscopic examination indicated that jejunal epithelial cells contained TGE viral particles as early as 12 hours after dogs were exposed. There were no apparent morphologic alterations or signs of desquamation of virus-infected cells, however. Results of pig transmission studies indicated that viable TGE virus was in jejunal tissue of the dogs as early as 12 hours and as late as 10 days after exposure to the virus.

Animals

Vaccination of newborn pigs with an attenuated strain of transmissible gastroenteritis virus.

Clinical signs of transmissible gastroenteritis were not observed in newborn pigs orally inoculated with the high-passaged vaccinal transmissible gastroenteritis virus (TO-163 strain). Vaccinal viral multiplication in digestive tract of newborn pigs fed colostrum before inoculation and kept at 21 to 22 C was diminished, but was not diminished in those fed colostrum and kept at 10 to 11 C. Other groups of newborn pigs inoculated with the attenuated vaccinal virus and kept at 18 to 22 C or at 31 to 34 C were challenge exposed with virulent intestinal virus on the 1st, 2nd, . . ., or 6th postinoculation (PI) days. In the groups kept at 18 to 22 C, 2 of 7 inoculated pigs challenge exposed with virulent virus on the 3rd PI day, 4 of 7 pigs exposed on the 4th PI day, and all of the pigs exposed on and after the 5th PI day survived the exposure. In the groups kept at 18 to 22 C, the attenuated vaccinal virus was distributed mainly in the respiratory organs and lymphatic tissues. On the contrary, in the groups kept at 31 to 34 C, all of the pigs died in 2 to 5 days after challenge exposure, and the attenuated vaccinal virus was scarcely detected in any of the pigs.

Animals

[Transmissible Gastroenteritis in Swine (author's transl)].

Transmissible gastroenteritis or TGE is a virus diarrhoea which occurs in pigs of all ages and is associated with high mortality rates in the young piglets. Growth of virus in the columnar epithelium of the small intestine causes atrophy of the intestinal villi, malabsorption, watery diarrhoea and dehydration. Faecal excretion of virus usually continues up to fourteen days after infection but chronic carriers have been found to occur. TGE is self-limiting on the majority of pig-breeding farms but the virus may persist in particular conditions and an enzootic form of the disease will appear in this case. In typical outbreaks, the diagnosis can usually be based on clinical symptoms. When the disease runs an enzootic course, a clinical diagnosis will be out of the question. TGE should be differentiated from colibacillosis and from another virus diarrhoea, the aetiology of which is not precisely known. A rapid and correct diagnosis may be established by direct fluorescent antibody studies of frozen sections of the small intestine in infected piglets. When sows have been spontaneously infected, their offspring will be protected by lactogenic immunity. The presence of TGE antibodies of IgA class in the milk is required to ensure complete immunity of the piglets lasting for weeks on end. Intramuscular inoculation of a commercially available vaccine in sows will only stimulate the production of antibodies of the IgG class in the milk. These antibodies will merely afford short-lived immunity. The vaccine cannot prevent symptoms of disease from appearing in piglets following infection with virulent TGE virus but it does reduce mortality

Animals

Comparison of properties between virulent and attenuated strains of transmissible gastroenteritis virus.

Strains of transmissible gastroenteritis (TGE) virus possessing different pathogenicity were examined for stability to digestive enzymes and acid, and growth at various temperatures. In growth experiments, virus titer obtained at 37 degrees C were about equal between attenuated and virulent strains, but titers attained by the attenuated strain were higher at 30 degrees C. The attenuated virus multiplied at 28 degrees C, but the virulent virus did not at this temperature. The virulent virus was significantly stable to trypsin and pepsin, but the attenuated virus was inactivated rapidly by these proteolytic enzymes. No significant differences were observed in stability to acid between the attenuated and virulent strains. At different pH, both lost their infectivity more rapidly at 37 degrees C than at 22 degrees C.

Coronaviridae

The detection of transmissible gastroenteritis viral antibodies by immunodiffusion.

Precipitating antibodies against transmissible gastroenteritis viral antigens were detected by the immunodiffusion test in two transmissible gastroenteritis viral hyperimmune antisera and in antiserum prepared against haemagglutinating encephalomyelitis virus but not in sera from several species of normal animals, in antisera prepared against a variety of othet viruses and bacteria or sera from swine with bacterial enteritis. When the immunodiffusion test was compared with the virus neutralization test for the detection of transmissible gastroeneritis viral antibodies in 20 swine sera certain samples which contained high titres of virus neutralizing antibodies failed to produce precipitation while other sera were positive in the immunodiffusion test although their virus neutralizing antibody titres were relatively low. Precipitating antibodies were also detected by immunodiffusion in several samples of milk whey from a sow which had been vaccinated with inactivated transmissible gastroenteritis virus.

Animals

The postulated role of feeder swine in the perpetuation of the transmissible gastroenteritis virus.

Clinical, immunofluorescence and histopathological observations were found to be an efficient approach for the confirmation of the diagnosis of transmissible gastroenteritis in feeder swine. Two cases are reported to exemplify how feeder swine exposed to points of concentration such as holding areas, sales barns and auctions can play an important role in the epizootiology of transmissible gastroenteritis. A third field case is reported as an example of an outbreak of transmissible gastroenteritis beginning in feeder swine and then spreading to baby pigs on the farm. All baby pigs died that were born during the acute phase of the outbreak in the feeder swine. Baby pigs born shortly after the clinical signs had abated in the herd, and from sows that had been exposed orally to virulent transmissible gastroenteritis virus and vaccinated with a commercial transmissible gastroenteritis vaccine ten days before farrowing, survived. This was explained by a combination of a decrease in the amount of virus shed in the environment and the immunity induced in the sows. These observations of field outbreaks of transmissible gastroenteritis combined with recently reported experimental studies lend strong support to the hypothesis of a reservoir for transmissible gastroenteritis virus in feeder pigs. This reservoir would be based principally on the transmission of the virus on a continuous basis from the feces of recently infected pigs to susceptible pigs. Clinical signs of transmissible gastroenteritis in such pigs are difficult to recognize or absent and this contributes to the importance of the reservoir in the field.

Animal Husbandry

Recovery of transmissible gastroenteritis virus from chronically infected experimental pigs.

Transmissible gastroenteritis (TGE) virus was reisolated from pulmonary and intestinal tissues from 6 of 9 chronically infected experimental pigs (principals) necropsied 30 to 104 days after inoculation. Tissue homogenates (lung and small intestine) from the principals were prepared and inoculated into 3- to 5-day-old gnotobiotic pigs. The virus reisolated from the tissue homogenates produced a milder disease on 1st passage and a more severe disease on 2nd passage. The chronically infected experimental pigs (principals) developed serum-neutralization titers to TGE of 1:30 to 1:525. There appeared to be no relationship between serum titers and reisolation of TGE virus from the 9 principals. The persistence of virus in lung or intestine to 104 days indicates the recovered (or carrier) pig may be considered the primary source of TGE virus infection.

Animals

Small plaque variant transmissible gastroenteritis virus.

A small plaque (SP) variant transmissible gastroenteritis (TGE) virus strain that may be useful in the control of TGE in swine has been developed and tested. This strain was derived from a persistently infected swine leukocyte cell line originally infected with a virulent TGE virus. The SP viral strain was avirulent for 3-day-old susceptible pigs and pregnant gilts. The SP virus elicited protective antibody when inoculated into pregnant gilts oral/intranasally, or intramammarily, or by both of these routes. The morbidity and mortality of their passively immune suckling pigs were 62% and 14%, respectively.

Animals

Transmissible gastroenteritis of swine. Efficacy assay of an intramammary use vaccine.

TGE seronegative pregnant gilts were vaccinated by intramammary inoculations with a chemically inactivated (betapropiolactone) cell culture virus vaccine and their nursing pigs were exposed to virus at three days of age. The pig morbidity and survival rates were compared with those of pigs nursing gilts exposed orally to virulent TGE virus during late gestation and also with pigs nursing non-vaccinated seronegative sows. The morbidity rates were 100%, 19% and 19%, while the survival rates were 33%, 100% and 17% respectively. The intramammary vaccine used to vaccinate pregnant gilts in this study did not stimulate sufficient antibody response to provide an acceptable level of protection to nursing pigs against experimental challenge with virulent TGE virus. The serum, colostrum and milk TGE neutralizing antibody responses are reported.

Animals