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.     

Effects of ambient temperatures on clinical and immune responses of pigs infected with transmissible gastro-enteritis virus

Two- to three-months-old pigs infected with transmissible gastroenteritis (TGE) virus showed no clinical response when housed at 30°C, but comparable infected pigs exposed to temperature changes from 30°C to 4°C following infection showed typical signs of TGE. Development of TGE-specific immune responses, as measured by blastogenic response of tissue lymphocytes, occurred at 3 days post-inoculation (DPI) in pigs held at 30°C, but not until 7 DPI in infected pigs held under the adverse conditions.Immunosuppression with corticosteroids resulted in a fall in circulatory T cells, lowering of non-specific blastogenic response of circulatory lymphocytes, and clinical signs of disease when immunosuppressed pigs were infected with TGE virus and held at 30°C. It is suggested that clinical responses to TGE virus infection may be affected by the influence of ambient temperatures on the immune responses of pigs.     

Age Dependent Resistance to Transmissible Gastroenteritis of Swine (TGE) II. Coronavirus Titer in Tissues of Pigs After Exposure

Coronavirus titers were compared in various tissues of three-day old and 21-day old pigs after exposure to the virus of transmissible gastroenteritis (TGE). Pigs in both groups that did not die from TGE were necropsied at intervals from one to 15 days post-exposure, and their tissues assayed for viral content. Viral titers were much higher in the small intestines of the younger pigs. Viral isolations were obtained from several tissues of the younger pigs but only from the small intestines of pigs infected at 21 days of age. Levels of viral neutralizing antibodies in the serums of both age groups were comparable at similar post-exposure intervals.     

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.     

Immunity of swine to Ascaris suum

Swine were hyperimmunized to Ascaris suum by giving multiple oral inoculations of embryonated eggs. Sera and lymphocyte lysate from these pigs were administered parenterally to 4-week-old pigs. The latter animals were no more resistant to larval migration than control pigs receiving sera or lymphocyte lysate from non-immunized pigs. Other pigs were infected with transmissible gastroenteritis (TGE) virus, allowed to recover and challenged with embryonated ascarid eggs. They likewise were no more resistant to ascarid larval migration than control pigs.     

Concurrent porcine rotaviral and transmissible gastroenteritis viral infections in a three-day-old conventional pig.

A 3-day-old suckling pig with diarrhea was necropsied, and immunofluorescent microscopic examination of the small intestinal mucosa, together with immune electron microscopic examination of the large intestinal contents, provided a presumptive diagnosis of a concurrent infection with transmissible gastroenteritis (TGE) virus and porcine rotavirus. Immunofluorescent microscopic, immune electron microscopic, and serologic data obtained from gnotobiotic pigs experimentally inoculated with the large intestinal contents of the suckling pig confirmed this diagnosis. Two gnotobiotic pigs, convalescent from previous TGE viral infections, became infected with porcine rotavirus only. However, another gnotobiotic pig, convalescent from a previous porcine rotaviral infection, became infected with TGE virus only, following inoculation with the large intestinal contents of the suckling pig.     

Transmissible Gastroenteritis in Feeder Swine: Clinical, Immunofluorescence and Histopathological Observations

Eight feeder swine (four to six months of age) were inoculated orally with 200,000 to 500,000 pig infectious doses (PID) of the Purdue strain of transmissible gastroenteritis (TGE) virus. Biopsies obtained from their small intestines were examined histopathologically and by fluorescent antibody tissue section technique at intervals that included 24, 48, 72 and 96 hours postexposure, and similar examinations were carried out at necropsy 168 hours postexposure. Evidence of virus infection was demonstrated in all segments of the small intestine except the upper duodenum and the viral antigen was found only in the cytoplasm of the absorptive cells covering the villi. Although six of the eight pigs failed to show clinical signs of TGE, typical microscopic lesions of villous atrophy with replacement of columnar absorptive cells by cuboidal cells were observed in seven pigs, and TGE virus antigen was demonstrated in the intestinal cells of four of eight pigs during the first week postexposure. The infection was usually mild to moderate and focal in the pigs without clinical signs of the disease and more severe and extensive in the pigs with clinical signs of the disease variable in severity. It was concluded that TGE virus probably replicated in all feeder swine exposed, and that the presence or absence of clinical signs of TGE in these pigs was related to the severity and extent of the villous atrophy and columnar cell replacement induced in their small intestines.     

Cross-protection studies between feline infectious peritonitis and porcine transmissible gastroenteritis viruses

Cross-protection studies between the feline infectious peritonitis (FIP) and the porcine transmissible gastroenteritis (TGE) viruses were conducted in cats, pigs and pregnant gilts. Cats vaccinated with TGE virus developed neutralizing antibodies against TGE virus and low titer antibody against FIP virus detected by an indirect fluorescent antibody technique but were not protected against a virulent FIP virus challenge. Baby pigs and pregnant gilts vaccinated with FIP virus did not develop detectable antibodies to TGE virus. Nevertheless, it appeared that vaccination of swine with FIP virus conferred some immunity against TGE virus infection. Seventeen-day-old pigs vaccinated with two doses of FIP virus had a 67% survival rate following a virulent TGE virus challenge, and 75% of the 3-day-old pigs suckling either FIP or TGE-virus-vaccinated gilts survived virulent TGE virus infection in contrast to 0% survival of baby pigs suckling unvaccinated gilts.     

Upper respiratory infection of lactating sows with transmissible gastroenteritis virus following contact exposure to infected piglets.

Ten breeding sows were left in direct contact with their newborn piglets that had been experimentally infected with transmissible gastroenteritis (TGE) virus. All sows became infected with the virus. The sows developed fever and showed mild clinical signs of the disease for a few days. The sows excreted virus in the nasal secretion, feces, and milk during the acute febrile phase of illness. Virus was isolated from the nasal secretion of one sow as early as 20 hours after contact exposure to the infected piglets. At necropsy, the virus was more frequently isolated from the tissues of the upper respiratory tract than from small intestines; this finding indicated that the TGE coronavirus replicated in the upper respiratory tract and induced an acute respiratory infection in susceptible adult swine. Neutralizing antibody was present in the sera 8 sows after 12 to 36 days during the convalescent period. From these results, we conclude that susceptible sows in direct contact with ill piglets can become infected and by excreting virus can serve as a source of TGE virus for other susceptible pigs on the premises.     

Efficacy of vaccination of sows with serologically related coronaviruses for control of transmissible gastroenteritis in nursing pigs

Three groups of pregnant sows were vaccinated at 8 and 2 weeks before parturition with tissue culture-adapted feline infectious peritonitis (FIP) virus, porcine transmissible gastroenteritis (TGE) small-plaque (SP) virus from a persistently infected cell line, or noninfected cell culture fluids (controls). Pigs nursing vaccinated sows were orally challenge exposed with virulent TGE virus when they were 1 to 3 days old. The morbidity of the nursing pigs was 48% in the SP-TGE group, 82% in the FIP group, and 93% in the controls. The survival rate among the nursing pigs was 77% in the SP-TGE groups, 48% in the FIP group, and 14% in the controls. Virus-neutralizing antibodies of immunoglobulin A were detected in colostrum and milk of the SP-TGE group, but not in the FIP or control groups.     

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)     

Quantitative transmissible gastroenteritis virus shedding patterns in lactating sows.

To test the role of sows in spreading transmissible gastroenteritis (TGE), 11 sows were intravenously, intranasally, or intramammarily inoculated with virulent virus within 5 days of farrowing. Six of the sows were separated from their offspring, and 5 were allowed to nurse their litters. All sows became clinically ill with sign of anorexia, depression, and fever that persisted until postinoculation day 4 or 5. They shed virus through milk, nasal secretions, and feces, with individual variations occurring in degree and duration of shedding in the 1st week after inoculation. Of 40 pigs separately fed milk samples from the 6 inoculated sows, 19 pigs (47.5%) became sick in 24 to 40 hours, and virus was isolated from them at necropsy. Of 43 pigs in the 5 litters that nursed exposed dams, all became sick with typical signs of TGE, and 29 (67.4%) died in 2 to 9 days. Sows given the single intramammary inoculation of virus developed statistically significant higher levels of TGE virus-neutralizing antibodies than did sows inoculated intravenously or intranasally.     

Transmissible Gastroenteritis in Feeder Pigs: Observations on the Jejunal Epithelium of Normal Feeder Pigs and Feeder Pigs Infected with TGE Virus

Light and electron microscopy findings in the jejunal mucosa of the normal feeder pig and feeder pigs infected with transmissible gastroenteritis (TGE) virus are reported. Villi in the mid jejunum of the normal feeder pig were elongated, finger shaped and covered with a layer of columnar absorptive cells with a well developed and regular brush border. Severe lesions of villous atrophy were present in all jejunal segments of feeder swine killed 96 hours post infection with TGE virus. Atrophic villi were covered by flat to cuboidal cells with a poorly developed brush border in some areas. In other segments, cells varied in appearance from sub-columnar to columnar type of near normal appearance.

The ultrastructure of the jejunal absorptive cells in the normal feeder pig was found to be similar to that described for the jejunal cells of other adult mammals. There were no significant indications of high pinocytotic activity. The epithelial cells covering the atrophic villi of TGE infected pigs had a fine structure similar to that described for the crypt cells, ranging in appearance from very immature to moderately differentiated cells. Microvilli were very short, decreased markedly in number and irregular in arrangement. The terminal web was poorly developed. Strands of rough endoplasmic reticulum were markedly diminished and an increase in free ribosomes was noted. The significance of these observations in explaining pathogenesis of TGE in feeder pigs is discussed.

     

Isolation of transmissible gastroenteritis virus from pharyngeal swabs obtained from sows at slaughter.

A virologic survey was conducted to determine the frequency of transmissible gastroenteritis (TGE) virus infection in farm-raised sows. Pharyngeal swab specimens collected in an abattoir were examined for TGE virus by inoculation onto swine-testes cell culures. The virus was detected in 61 (3%) of a sample of 2,058 Iowa sows after slaughter. All TGE viral isolates, given orally to 2- or 3-day-old pigs, caused acute gastroenteritis and in some cases death. All pigs that recovered from illness had serum antibody to TGE virus.     

Identification of porcine transmissible gastroenteritis virus in house flies (Musca domestica Linneaus)

Transmissible gastroenteritis (TGE) virus was detected in house flies (Musca domestica Linneaus) by staining with specific fluorescent antibody. The flies were collected within a swine confinement facility in which TGE was enzootic. Laboratory-reared flies were infected experimentally with TGE virus and the virus was recovered from the insects for 72 hours after infection. The TGE virus was identified both by the fluorescent antibody technique and by isolation in cell culture. The nature of plaque formation in cell monolayers inoculated with the virus passaged through flies changed from a large plaque (4 mm or greater in diameter) to a small plaque (1 mm in diameter) over the period. Large plaques were observed early after infection and were attributed to TGE virus mechanically carried by the flies. Small plaques occurred 8 to 12 hours after infection and were considered to be produced by virus replicated in the dipterous cell.     

Evaluation of an enzyme-linked immunosorbent assay for the detection of transmissible gastroenteritis virus antibodies

An enzyme-linked immunosorbent assay (ELISA) using a detergent-solubilized antigen of purified virus was developed for detection of antibody against porcine transmissible gastroenteritis (TGE) virus in swine serum. The ELISA demonstrated antibody responses in pigs immunized intramuscularly with the attenuated TO-163 strain of TGE virus and in pigs orally infected with the virulent Shizuoka strain of the virus. The results of the ELISA were well correlated with those of the neutralization test. These results indicate the usefulness of the ELISA as a serological tool for TGE virus antibody.     

Studies on Transmissible Gastroenteritis of Swine I. The Isolation and Identification of a Cytopathogenic Virus of Transmissible Gastroenteritis in Primary Swine Kidney Cell Cultures

Two virus isolates from transmissible gastroenteritis (TGE) of swine were adapted to grow in primary swine kidney cells. Growth of the virus was indicated by the resistance of the infected cells to the cytopathic effect of a virus diarrhea virus of cattle, and by the development of large round cells on the cell sheet.

Evidence that these virus isolates were TGE was obtained by the development of signs of the disease followed by death of exposed SPF pigs, or the resistance of the recovered pigs to further signs of disease when they were exposed to virulent TGE contained in virus bearing intestinal tissue.

The in vitro and in vivo serum neutralization tests, along with staining of infected cells by fluorescein conjugated TGE antiserum, gave further indication of the specific nature of the virus growing in the cell cultures.

     

猪伪狂犬病野毒感染的临床诊断、血清学调查以及控制措施

目的为某规模化猪场猪伪狂犬病病毒野毒株感染防控工作提供科学的免疫防控方案。方法对某发病猪群（采用Bartha-K61经典毒株疫苗进行了猪伪狂犬病免疫）进行流行病学调查,并采用ELISA方法检测其猪伪狂犬病gB抗体和gE抗体水平。结果根据调查、解剖和血清抗体检测结果,初步确诊该发病猪群为猪伪狂犬病野毒感染。通过采取紧急免疫伪狂犬病HB2000毒株疫苗、调整免疫程序和配合药物治疗等措施,育肥猪死亡率从2.56%降低至0.60%;除了4周龄及12周龄猪群外,其余猪群伪狂犬病野毒抗体水平全部下降;种公猪、8周龄、10周龄、14周龄猪群伪狂犬病野毒抗体阳性率均为0。结论Bartha-K61经典毒株疫苗并不能提供完全的保护力,通过紧急免疫与流行毒株同源性较高的HB2000毒株疫苗,加强生物安全管理工作,能够有效控制猪伪狂犬病野毒感染。     

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.     

Solid phase immune electron microscopy for diagnosis of transmissible gastroenteritis in pigs

A serological trapping technique is described for detecting transmissible gastroenteritis (TGE) virus in faeces. The technique involves the coating of electron microscope grids with protein A and specific TGE virus antiserum. Optimal conditions for performing this solid phase immune electron microscopy technique were a concentration 250 micrograms ml-1 of protein A; 1:100 diluted rabbit anti-TGE virus hyperimmune serum for coating the grids and overnight incubation with virus samples. The possibility of detecting coronavirus in crude faeces was highly improved with solid phase immune electron microscopy, compared with conventional negative staining electron microscopy, by specific trapping of virus and prevention of adsorption of contaminants. The sensitivity of the method was evaluated by coded investigation of a dilution series of stock virus mixed with different pools of faeces. The improvement of virus detection in faeces by solid phase immune electron microscopy, compared with standard electron microscopy was at least 100-fold. Faecal shedding of coronavirus by pigs infected with virulent and attenuated strains of TGE virus was studied. Virus detection in faeces by a standard electron microscopy technique was not practical, since the virus was obscured by a large quantity of debris in the faeces. By using solid phase immune electron microscopy, however, the aspect of the specimens on the grids improved so much that, in addition to more common immunofluorescence, the technique might be useful as a diagnostic test for TGE. Virus was detected in daily faecal samples from one or two days after experimental infection with virulent TGE virus, until death in five out of eight animals. Unlike immunofluorescence, solid phase immune electron microscopy may be used for diagnosis in living animals.