Infection with porcine respiratory coronavirus does not fully protect pigs against intestinal transmissible gastroenteritis virus

Eight nine-week-old specific-pathogen-free pigs which had been infected with the transmissible gastroenteritis virus (TGEV)-related porcine respiratory coronavirus (PRCV) and four uninfected littermates were challenged with TGEV. The previous PRCV infection failed to protect them against the enteric TGEV infection. Virus excretion in faeces was detected by an ELISA in all the pigs for three to six consecutive days after inoculation. Although little diarrhoea was observed, the infection extended through much of the small intestine of one of the previously infected pigs four days after inoculation. Challenge with TGEV caused a secondary neutralising antibody response. By using a peroxidase conjugate of a monoclonal antibody which recognises a specific antigenic site on TGEV, antibodies against TGEV could be distinguished from antibodies against PRCV in an ELISA blocking test.     

Antigen selection and presentation to protect against transmissible gastroenteritis coronavirus.

The antigenic structure of the S glycoprotein of transmissible gastroenteritis virus (TGEV) and porcine respiratory coronavirus (PRCV) has been determined and correlated with the physical structure. Four antigenic sites have been defined (A, B, C, and D). The sites involved in the neutralization of TGEV are: A, D, and B, sites A and D being antigenically dominant for TGEV neutralization in vitro. These two sites have specific properties of interest: site A is highly conserved and is present in coronaviruses of three animal species, and site D can be represented by synthetic peptides. Both sites might be relevant in protection in vivo. PRCV does not have sites B and C, due to a genomic deletion. Complex antigenic sites, i.e., conformation and glycosylation dependent sites, have been represented by simple mimotopes selected from a library expressing recombinant peptides with random sequences, or by anti-idiotypic internal image monoclonal antibodies. An epidemiological tree relating the TGEVs and PRCVs has been proposed. The estimated mutation fixation rate of 7 +/- 2 x 10(-4) substitutions per nucleotide and year indicates that TGEV related coronaviruses show similar variability to other RNA viruses. In order to induce secretory immunity, different segments of the S gene have been expressed using a virulent forms of Salmonella typhimurium and adenovirus. These vectors, with a tropism for Peyer's patches may be ideal candidates in protection against TGEV.     

Cell-mediated immune responses of suckling pigs inoculated with attenuated or virulent transmissible gastroenteritis virus

Two litters of suckling pigs seronegative for transmissible gastroenteritis (TGE) virus were orally inoculated with live attenuated (P115) or virulent (M5C) strains of TGE virus. A third seronegative litter (controls) was given cell culture fluids from uninfected cells. Lymphocytes were collected from blood, spleen, mesenteric lymph nodes, and Peyer patches of euthanatized pigs at 0 day and approximately weekly until 26 days after exposure and at approximately 45 days after exposure. Sera were tested for virus-neutralizing antibody titers by use of plaque reduction. Lymphocytes were tested in a lymphocyte proliferation assay for uptake of [3H]thymidine after incubation with the homologous or the heterologous strain of inactivated TGE virus or uninfected cell culture fluids. Only pigs inoculated with virulent TGE virus developed clinical signs of TGE and shed virus. However, all pigs inoculated with TGE virus seroconverted at 6 days after exposure. Responses of lymphocytes from all sources from TGE virus-inoculated pigs peaked between 6 and 14 days after exposure. Pigs inoculated with virulent TGE virus had higher lymphocyte proliferative responses and neutralizing antibody titers than did pigs inoculated with attenuated TGE virus. Cessation of virus shedding coincided with the peak of lymphocyte proliferative responses. The highest responses were with intestinal lymphocytes (mesenteric lymph nodes and Peyer patches) from pigs inoculated with virulent TGE virus. The responses of intestinal lymphocytes from pigs inoculated with attenuated virus were not significantly different from those of pigs inoculated with cell culture fluid. Lymphocytes collected from all sources, except blood from M5C-inoculated pigs, had significantly (P less than 0.05) higher responses to the homologous than to the heterologous TGE virus stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Intestinal permeability to macromolecules in piglets infected with transmissible gastroenteritis virus

The permeability of the intestine of specific pathogen free piglets was investigated by measuring the concentration of 125-I in the blood after oral administration of 125-I polyvinylpyrrolidone (125-I PVP, MW=40 000 Da) and the concentration of 131-I in the faeces after intravenous administration of 131-I porcine albumin (131-I PA, MW=68 000 Da). The tests were performed one day before and up to two days after the piglets were infected with the Miller strain of transmissible gastroenteritis (TGE) virus. Biopsies of the jejunum were taken at the end of the experiment and blood samples were taken six-hourly. The piglets became anorexic and had diarrhoea 12 hours after infection; the packed cell volume decreased and the concentrations of urea and total serum proteins increased slightly after infection. However, the marked villous atrophy was not accompanied by an increased permeability of the intestine to PVP or PA.     

Fluid therapy trials in neonatal piglets infected with transmissible gastroenteritis virus.

The main purpose of this study was to evaluate the effectiveness of an oral fluid therapy alone or combined with parenteral administration of a 5% dextrose solution to attenuate the clinical signs and the pathophysiological consequences of transmissible gastroenteritis in neonatal piglets. Eighteen two day old conventional piglets were infected with transmissible gastroenteritis virus while six others were used as controls (Group 1). At the onset of diarrhea, infected piglets were divided into three groups of six (Groups 2, 3 and 4). Piglets in group 2 were not treated and were fed a milk replacer ad libitum. Piglets in group 3 were removed from the milk replacer and placed on an oral glucose-glycine-electrolyte solution ad libitum. Those in group 4 were placed on oral fluid therapy and received a 5% dextrose solution intraperitoneally at the rate of 25 mL/kg of body weight once a day. Blood samples were collected in heparin within minutes after the infected piglets became comatose and from the controls at four or five days of age. The following variables were measured: packed red cell volume, blood pH, total plasma protein and bicarbonate, blood urea nitrogen, and plasma glucose, creatinine, chloride, inorganic phosphorus, sodium, potassium, magnesium and calcium. Vomiting and diarrhea appeared 12 to 24 hours postinoculation in the infected piglets. There was a sudden and rapid progression into a comatose and moribund state one or two days later whether the infected piglets were treated or not.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

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.     

仔猪传染性胃肠炎的防治

仔猪传染性胃肠炎是由猪传染性胃肠炎病毒引起的一种急性、高度接触性传染病。主要是经过消化道和呼吸道感染,以水样腹泻、呕吐、脱水、仔猪迅速死亡为特征。今年春季在本镇各村均有发生,有48％的饲养户的仔猪不同程度发病。     

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.     

Passive protection of piglets by recombinant baculovirus induced transmissible gastroenteritis virus specific antibodies.

Sera of pigs immunized with parts of the transmissible gastroenteritis virus (TGEV) spike (S) protein expressed by recombinant baculoviruses were tested, together with a TGEV hyperimmune antiserum, for their abilities to protect three-day-old piglets against TGEV infection. The piglets were infected with virulent TGEV and the sera were given orally 3 h before infection, together with the virus, and every 6 h postinfection during the 30 h of the experiment. Virus shedding was monitored by TGEV isolation from rectal swab samples. The sera containing antibodies induced by the complete S protein or the amino terminal half of the S protein showed protective properties, indicated by delayed onset of clinical signs and virus shedding, similar to the TGEV hyperimmune serum. Those immune sera containing antibodies induced by shorter recombinant proteins were not protective.     

Demonstration of cytotoxic lymphocytes to virus-infected target cells in pigs inoculated with transmissible gastroenteritis virus.

Lymphocytes, cytotoxic to virus-infected target cells, were induced in pigs orally exposed to transmissible gastroenteritis virus. They were studied and experiments were carried out by using autochthonous testicle cells as target cells to avoid genetic incompatibility of effector lymphocytes and target cells. Cytotoxic lymphocytes were demonstrated in Peyer's patches, mesenteric lymph nodes, spleen, and peripheral blood on postinoculation day (PID) 7. Cytotoxic activity of lymphocytes increased thereafter and reached the maximal amount at PID 21. Lymphocyte cytotoxicity was somewhat greater in lymphocytes of peripheral blood and spleen than in those of Peyer's patches and mesenteric lymph nodes after PID 14. On the contrary, lymphocyte reactivity to the viral antigen measured by lymphocyte proliferative assay was higher in Peyer's patch and mesenteric lymph node cells than in peripheral blood and splenic cells. Lymphocyte cytotoxicity was depressed by treating effector cells with anti-porcine thymocyte serum and complement. However, lymphocyte suspensions treated with anti-porcine thymocyte serum and complement were still cytotoxic to some extent against virus-infected target cells, although T lymphocytes were completely excluded by the treatment. This suggests that cytotoxic mechanism other than the direct action of cytotoxic T lymphocytes may be involved in the cytotoxicity assay systems used in the present studies. In experiments in which allogenic cells (testicle cells of siblings) were used together with autochthonous cells as targets, lymphocyte cytotoxicity was equally expressed against both autochthonous and allogenic target cells in 2 of 3 experiments. However, lymphocyte cytotoxicity was greater against autochthonous cells than against allogenic target cells in 1 of 3 experiments.     

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.     

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.     

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.