Detection of antibody against transmissible gastroenteritis virus of pigs by indirect immunoperoxidase antibody test

Immunoperoxidase intibody (IPA) test was developed for detecting antibody against transmissible gastroenteritis (TGE) virus of pigs. The IPA antibody titers in sera collected in the field from 82 pigs were approximately seven times higher than those obtained in a serum-neutralization test. The correlation between the TGE antibody concentrations in the IPA and serum neutralization tests was positive (r = +0.74). The IPA tests appears to have the potential for routine laboratory use for serologic diagnosis of TGE.     

Infection of pigs with transmissible gastroenteritis virus from contaminated carcases

Sixteen 6-month-old pigs were exposed to transmissible gastroenteritis (TGE) virus by placing them in close contact with piglets infected at 1 week of age. Fourteen of the older pigs were slaughtered between 1 and 5 d after exposure to infection and their carcases dressed in simulated abattoir conditions. Samples of muscle, bone marrow and carcase lymph nodes were stored at -25 degrees C for at least 30 d and then homogenised and fed to groups of 1-week-old and 3-week-old pigs. Four of 12 one-week-old pigs died and TGE virus was isolated from intestinal contents of one of these. All pigs of both age groups developed neutralising antibody to TGE virus over the ensuing 4 w. The results indicate that carcases from pigs infected with TGE virus can represent a source of infection for susceptible pigs given access to them.     

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.     

Comparison of two methods for detection of transmissible gastroenteritis virus in feces of pigs with experimentally induced infection

An indirect, double-antibody sandwich-type ELISA for detection of transmissible gastroenteritis virus (TGEV) was developed, using a solid phase of rabbit hyperimmune serum and a pool of 3 antipeplomer monoclonal antibodies to trap and to detect the virus, respectively. The technique was used to detect viral antigen in feces of pigs that had been infected with the virulent Miller strain, the attenuated Purdue strain, or the Erica strain (a Dutch field isolate) of TGEV. The results were compared with those of a solid-phase immunosorbent electron microscopy (SPIEM) technique for virus detection. Both techniques detected shedding of virulent virus in feces obtained from pigs on the first or second day after infection, and virus excretion continued for 6 to 8 consecutive days. Virus shedding started later in pigs infected with the attenuated Purdue strain of TGEV and lasted only 2 to 4 days. In comparison with the 2 virulent strains, infection with the attenuated strain appeared to be limited to a smaller portion of the small intestine. Of 242 fecal specimens that were tested by use of ELISA and SPIEM, 119 had positive results in both tests. Additionally, virus could be detected by ELISA in 21 and by SPIEM in 16 specimens. Fecal specimens obtained from pigs before infection always reacted negatively by ELISA for TGEV antigen; there was no cross-reactivity with fecal specimens containing porcine rotavirus or porcine epidemic diarrhea virus. The ELISA and SPIEM were found to be specific and sensitive for the detection of TGEV in feces.     

Oral transmission of transmissible gastroenteritis virus by muscle and lymph node from slaughtered pigs

A study was conducted in the USA to determine whether transmissible gastroenteritis (TGE) virus could be transmitted from carcases of slaughtered pigs. Transmissible gastroenteritis virus was transmitted to 6-day-old piglets by dosing with homogenates of muscle and lymph node collected from 500 clinically normal pigs at the time of slaughter. All piglets in 2 separately housed litters showed clinical signs of TGE with 5 piglets dying within 10 d of oral dosing with homogenates. Transmissible gastroenteritis virus was isolated from 2 of these piglets and all piglets developed TGE antibody. Transmissible gastroenteritis virus was not isolated in tissue culture from muscle and lymph node homogenates, but was isolated from 4 (0.8%) of 500 tonsil samples collected from the same pigs. A survey of 250 serum samples provided an estimate of the prevalence of slaughtered pigs with TGE antibody of 34.8% in the sample population. The results indicate that carcases of some pigs from TGE endemic areas contain viable TGE virus, and that there would be a substantial risk of introducing TGE virus into Australia by the importation of uncooked pig meat from these areas.     

Detection of duck plague virus by reverse passive hemagglutination test

A reverse passive hemagglutination (RPHA) test was developed to detect duck plague virus (DPV). The technique used sheep erythrocytes stabilized with formaldehyde and pyruvaldehyde and coated with immunoglobulin G (IgG) containing anti-DPV antibody prepared from antiserum produced in sheep. Optimum coating of stabilized erythrocytes occurred at 25 C and pH 4.0 with a concentration of IgG of 20-40 micrograms/ml and a 90-min incubation period. The coated cells were stable for 40 days when stored at 4 C or for at least 4 months (the longest period tested) when frozen at -70 C or -196 C. The RPHA test was conducted at 25 C and read after 3 hours. The high specificity of the test is indicated by the absence of cross-reactions with heterologous virus strains, with specimens prepared from normal duck livers, and with normal chicken embryo chorioallantoic fluid, as well as by the inhibition of hemagglutination only with DPV antiserum. The RPHA test detected six strains of DPV in all virus-containing specimens as well as the immunofluorescence (IF) test did; however, conventional plaque assays (PA) failed to detect virus in five specimens that contained three non-plaque-forming strains of DPV. The mean quantity of DPV that could be detected in the RPHA test was 25 plaque-forming units or 65 fluorescent units per ml. Although the RPHA test was less sensitive than either the PA or the IF test, there was a positive correlation in the titers of DPV antigens between all three tests. The RPHA test is a rapid, simple procedure that is sufficiently sensitive for diagnostic detection of DPV in acute infections, especially in tissues of ducks dying of the disease.     

Intestinal phospholipase B activity in pigs inoculated with transmissible gastroenteritis virus

Intestinal phospholipase B activity in pigs inoculated with transmissible gastroenteritis (TGE) virus was studied. Phospholipase activity was quantified by measuring the hydrolytic release of free fatty acids in homogenized intestinal tissue incubated with lysophosphatidylcholine. An increase in enzyme activity was observed in the cranial and caudal portions of the ileum and jejunum in pigs killed 3, 6, and 8 days after inoculation with TGE virus. Seemingly, phospholipase B may be part of the host immune response against TGE viral infection.     

Financial impact of transmissible gastroenteritis in pigs

The financial impact of an epizootic of transmissible gastroenteritis in pigs was evaluated in a California sow herd through estimating growth, feed, and profit functions. Two groups of pigs were studied: pigs born before and surviving the epizootic (epizootic [E] pigs), and pigs born after the epizootic (postepizootic [PE] pigs). Short-term profits were maximized at 165 days for both groups of pigs, ranging from $47.14 for female E pigs to $60.32 for male PE pigs. Accordingly, it was concluded that pigs surviving or born shortly after a transmissible gastroenteritis epizootic are profitable to raise, if raised under management conditions similar to those in the study herd.     

Enzootic pneumonia in feeder pigs: Association with transmissible gastroenteritis virus infection

Infection with transmissible gastroenteritis virus (TGEV) was present in some pigs on arrival at a feeder pig farm and was well established three weeks later. TGE infection preceded Mycoplasma hyopneumoniae infection, which was not detected until three weeks after arrival. Severe lesions of enzootic pneumonia were observed at the end of the fattening period.     

Lesions of transmissible gastroenteritis virus infection in experimentally inoculated pigs suckling immunized sows

Intestinal lesions of transmissible gastroenteritis (TGE) virus infection in conventionally reared pigs suckling either nonvaccinated, vaccinated, or previously infected sows were studied by scanning electron microscopy, light microscopy, and immunofluorescent microscopy for TGE viral antigen. Pigs were inoculated with virulent TGE virus when they were 5 or 21 days old and were euthanatized shortly after the onset of diarrhea or 96 hours after inoculation if no diarrhea developed. Pigs inoculated when they were either 5 or 21 days old and suckling nonvaccinated sows developed severe lesions, including swelling and necrosis of enterocytes and severe villus atrophy. Pigs inoculated when they were 5 days old and suckling sows vaccinated with attenuated vaccines developed less-severe villus atrophy, and those suckling sows immunized by exposure to nonattenuated TGE virus developed moderate or no villus atrophy. Pigs inoculated when they were 21 days old and suckling sows vaccinated with attenuated vaccines had severe villus atrophy, whereas those suckling sows immunized by exposure to nonattenuated virus had more-moderate villus lesions. Villus atrophy was inhibited to various degrees in pigs suckling immunized sows, depending in part on the antibody titer in the colostrum and milk.     

Mild transmissible gastroenteritis in pigs suckling vaccinated sows

A strain of transmissible gastroenteritis (TGE) virus of low virulence was isolated from 14-day-old pigs suckling sows vaccinated with an attenuated TGE vaccine. Diarrhea developed in suckling pigs approximately 14 days after farrowing in 4 farrowings; however, none of these pigs died from diarrhea. Diarrhea ceased after the 4th farrowing, when vaccination of sows was discontinued. Experimentally, both the field isolate and the vaccine strain were infective and in some instances lethal for 2-day-old pigs exposed orally; however, neither strain was as virulent as the Purdue strain.     

Pathogenicity of an attenuated strain of transmissible gastroenteritis virus for newborn pigs.

The pathogenicity of a cell culture-attenuated strain of transmissible gastroenteritis virus for newborn pigs was investigated. Newborn (1- to 2-day-old) pigs were orally given 2 x 10(6) plaque-forming units of attenuated virus. All pigs developed mild diarrhea, but deaths did not occur. As determined by immunofluorescence and villous atropy, infection of the small intestine was limited to the caudal 50 to 66%. Fluorescing cells and atrophic villi were seen from 2 to 3 days until 6 to 7 days after exposure. Attenuated virus-exposed pigs produced circulating virus-neutralizing antibodies detectable as early as 5 days after exposure. By contrast, all pigs orally given 1 x 10(2) pig infective doses of virulent transmissible gastroenteritis virus developed severe diarrhea, and almost all of those not killed died within 2 to 5 days after exposure. In the latter pigs, the entire length of the small intestine, except for the first 4 to 5 cm, was infected with virus by 24 to 36 hours after exposure.     

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.