Roger D. Woods

Evidence for a porcine respiratory coronavirus, antigenically similar to transmissible gastroenteritis virus, in the United States.

A respiratory variant of transmissible gastroenteritis virus (TGEV), designated PRCV-Ind/89, was isolated from a swine breeding stock herd in Indiana. The virus was readily isolated from nasal swabs of pigs of different ages and induced cytopathology on primary porcine kidney cells and on a swine testicular (ST) cell line. An 8-week-old pig infected oral/nasally with the respiratory variant and a contact pig showed no signs of respiratory or enteric disease. These pigs did not shed virus in feces but did shed the agent from the upper respiratory tract for approximately 2 weeks. Baby pigs from 2 separate litters (2 and 3 days old) also showed no clinical signs following oral/nasal inoculation with PRCV-Ind/89. In a third litter, 5 of 7 piglets (5 days old) infected either oral/nasally or by stomach tube developed a transient mild diarrhea with villous atrophy. However, virus was not isolated from rectal swabs or ileal homogenates of these piglets, and viral antigen was not detected in the ileum by fluorescent antibody staining even though the virus was easily recovered from nasal swabs and lung tissue homogenates. Swine antisera produced against PRCV-Ind/89 or enteric TGEV cross-neutralized either virus. In addition, an anti-peplomer monoclonal antibody, 4F6, that neutralizes TGEV also neutralized the PRCV-Ind/89 isolate. Radioimmunoassays with a panel of monoclonal antibodies indicated that the Indiana respiratory variant and the European PRCV are antigenically similar.

Lack of protection in vivo with neutralizing monoclonal antibodies to transmissible gastroenteritis virus

Abstract Monoclonal antibodies (Mabs) specific for the E1 and E2 surface glycoproteins of the transmissible gastroenteritis virus (TGEV) of swine were examined either alone or in combination to evaluate their potential value in protecting neonatal pigs against a lethal dose of TGEV. Cesarean-delivered colostrum-deprived (CDCD) piglets were given one pre-challenge dose of Mab and an equal dose of the same Mab at each successive feeding after challenge. In vivo challenge results demonstrated that neither Mabs given individually nor combinations of the Mabs were able to protect neonatal pigs against a lethal dose of TGEV. However, in parallel experiments, polyclonal antibodies from immune colostrum or serum were protective.

Nucleotide sequence of coronavirus TGEV genomic RNA: evidence for 3 mRNA species between the peplomer and matrix protein genes

Abstract The region of the TGEV genome between the E1-matrix protein gene and the E2-peplomer protein gene has been sequenced from a cDNA clone. The consensus recognition sequence, 5 ′AA TT CTAAAC was found upstream from 3 large open reading frames. In coronaviruses these homologous recognition sequences are involved in the initiation of transcription suggesting that there are 3 mRNA species in this region of the TGEV genome. Northern blot analysis and nuclease S1 mapping confirmed the presence of 3 mRNA species between mRNA 3 encoding the E2-peplomer protein and mRNA 6 encoding the E1-matrix protein. The 5′ regions of these 3 mRNAs encode potential polypeptides of predicted molecular weight; 7859, 27744 and 9287, respectively. The potential translation product of ORF B (27744 Da) is considerably larger than previously reported and could be difficult to distinguish by size from the E1-matrix protein.

Complement-Dependent Neutralization of Transmissible Gastroenteritis Virus by Monoclonal Antibodies

Monoclonal antibodies (MAb) to each of the 3 major structural proteins of transmissible gastroenteritis virus (TGEV) of swine were compared as to their virus neutralizing activity in the presence or absence of guinea pig complement. MAbs to the peplomer protein had neutralizing activity for TGEV with or without complement and the titers were similar in either case. MAbs to the matrix protein had neutralizing activity for TGEV only in the presence of complement. Antibodies to the nucleocapsid protein were without neutralizing activity with or without complement. High concentrations of guinea pig complement, but not swine complement, had neutralizing activity for TGEV even in the absence of any known TGEV antibodies.

Differentiation between Transmissible Gastroenteritis Virus and Porcine Respiratory Coronavirus Using a cDNA Probe

A plasmid, pG3BS, containing a cDNA clone from the 5′ coding region of the peplomer glycoprotein gene appears to be specific for enteric transmissible gastroenteritis virus (TGEV) strains and for live-attenuated TGEV vaccines. This cDNA probe is used to differentiate porcine respiratory coronavirus (PRCV) isolates from TGEV field and vaccine strains by a slot blot hybridization assay. Probe pG3BS also hybridizes to canine coronavirus (CCV) RNA but does not hybridize to antigenically related feline infectious peritonitis virus (FIPV) RNA. The RNAs of 13 enteric TGEV isolates from the United States, Japan, and England, 4 US-licensed live-attenuated TGEV vaccines, and antigenically closely related CCV were detected by pG3BS. The RNAs of FIPV and 3 US isolates of PRCV did not react with pG3BS but were detected by a TGEV-derived plasmid, pRP3. Pigs infected with either PRCV or TGEV test serologically positive for TGEV antibody by the serum neutralization test. Characterization of the virus circulating in a swine herd by the pG3BS probe will differentiate between an enteric TGEV and a respiratory PRCV infection.

Immunization of pregnant gilts with PRCV induces lactogenic immunity for protection of nursing piglets from challenge with TGEV

Abstract The level of passive protection against transmissible gastroenteritis virus (TGEV) was evaluated by experimentally infecting 12 pregnant gilts with different doses of porcine respiratory coronavirus (PRCV) and challenging their litters at 4 days of age. An overall survival rate of 70% was found for piglets nursing the 12 PRCV-infected gilts, compared to a 16% survival rate for piglets of nine uninfected control gilts. Six of the PRCV-infected gilts had adequate levels of immunity to resist infection with TGEV following the challenge of their litters. These six completely immuned gilts also solidly protected their litters from TGEV as shown by a 96% piglet survival rate through weaning at 3 weeks of age. The results suggest that respiratory infection with PRCV induces a substantial degree of protective lactogenic immunity against TGEV.

Transmissible Gastroenteritis Coronavirus Carrier Sow

A sow infected with virulent transmissible gastroenteritis virus (TGEV) shed virulent virus in her feces for 18 months. The virus was isolated from rectal swabs beginning 2 days postexposure (PE) and continued at irregular intervals. Virus shedding was detected on 24 separate occasions. The titer of the virus shed ranged from < 1 x 10(2) pfu/ml to 7.2 x 10(3) pfu/ml, while the duration of the shedding ranged from 1 to 5 consecutive days. Inoculation of 3-day-old piglets with TGEV isolated from the sow proved the virus was virulent throughout the study. Virulent TGEV was isolated from the spleen, mesenteric lymph nodes, and the liver of the sow 544 days PE. This study demonstrates an apparently healthy sow can be a reservoir and shed virulent TGEV for an extended period of time.

Partial passive protection with two monoclonal antibodies and frequency of feeding of hyperimmune anti-transmissible gastroenteritis virus (TGEV) serum for protection of three-day- old piglets from a TGEV challenge infection

Passive protection experiments were conducted to determine the frequency and amounts of hyperimmune antiserum needed to block a transmissible gastroenteritis virus (TGEV) challenge infection and to identify monoclonal antibodies that are partially protective against TGEV. Hyperimmune antiserum or monoclonal antibodies were added to milk at each feeding or at selected feedings when the amount of antiserum was reduced. Three-day-old piglets were challenged with virulent virus that had been preincubated with antiserum or monoclonal antibodies. The results indicated that supplementing antiserum every other day was not efficacious for protection. Supplementing even small quantities of hyperimmune antiserum (0.5 ml) at least once a day in most cases was sufficient for piglet survival but did not prevent morbidity. Increasing the amount (>2 ml) and providing antiserum 3 times/day completely blocked the TGEV challenge infection. Two monoclonal antibodies were discovered that also provided passive protection for baby pigs. One monoclonal antibody, 5G1, had a high neutralizing titer, and the other, 6C4, was more effective in neutralizing and binding to virulent TGEV than to attenuated TGEVs. Both of these monoclonal antibodies were partially effective as supplements in milk for passive protection. Furthermore, these monoclonal antibodies were useful for boosting the efficacy of TGEV-neutralizing colostrum, which by itself was ineffective. These results show that other antigenic sites, different from the 4-well characterized epitopes on the S glycoprotein of TGEV, also are important for passive protection.