ORF3a deletion in field strains of porcine-transmissible gastroenteritis virus in China: A hint of association with porcine respiratory coronavirus.

Porcine-transmissible gastroenteritis virus (TGEV) is a pathogenic coronavirus responsible for high diarrhoea-associated morbidity and mortality in suckling piglets. We analysed the TGEV ORF3 gene using nested polymerase chain reaction and identified an ORF3a deletion in three field strains of TGEV collected from piglets in China in 2015. Eight TGEV ORF3 sequences were obtained in this study. Phylogenetic tree analysis of ORF3 showed that the eight TGEV ORF3 genes all belonged to the Miller cluster. CH-LNCT and CH-MZL were closely correlated with Miller M6, while CH-SH was correlated with Miller M60. These results thus indicate that the existence of Miller, as well as the Purdue cluster, in Chinese field strains of TGEV. Furthermore, we found the first evidence for a large deletion in ORF3 resulting in the loss of ORF3a, previously reported in porcine respiratory coronavirus, in three field strains (CH-LNCT, CH-MZL, and CH-SH) of TGEV. The results of the present study thus provide important information regarding the underlying evolution mechanisms of coronaviruses.

Prior infection of nursery-age pigs with porcine reproductive and respiratory syndrome virus does not affect the outcome of transmissible gastroenteritis virus challenge.

Thirty-six specific-pathogen-free pigs were weaned at 2 weeks of age and separated into 4 treatment groups (A-D, 9 pigs/group). Treatment groups B and D were infected with porcine reproductive and respiratory syndrome virus (PRRSV), whereas groups A and C remained uninfected. Two weeks later, 1 pig from each group was necropsied to assess gross lung involvement, and then the remaining group D PRRSV-infected pigs and the group C uninfected pigs were challenged at 4 weeks of age with transmissible gastroenteritis virus (TGEV) to determine if prior infection with PRRSV increased the severity of TGEV disease after challenge. One hundred percent morbidity but no mortality occurred in pigs following challenge. Clinically, pigs of both groups C and D were similar in terms of onset and severity of diarrhea. The serum antibody response to TGEV and the amount and duration of TGEV shedding after challenge was similar for both groups. Only a few pigs in each group had a transient fever postchallenge, and both group C and group D pigs began to recover and to gain weight at or near the end of the first week postchallenge. It was concluded that the clinical course of TGEV disease was not markedly affected by infection of pigs with TGEV 2 weeks after they had been infected with PRRSV.

Natural infection with the porcine respiratory coronavirus induces protective lactogenic immunity against transmissible gastroenteritis.

Our objective was to evaluate the level of passive protection against transmissible gastroenteritis (TGE) among 57 newborn piglets nursing from seven seropositive sows previously naturally infected with porcine respiratory coronavirus (PRCV). After challenge exposure we observed mortality rates of 44% for litters of seven PRCV-infected sows, 40% for litters of four sows orally immunized with the attenuated TGEV strain Nouzilly, and 91% for litters of seven seronegative susceptible sows. A blocking ELISA with two appropriate monoclonal antibodies distinguished serological responses of PRCV-infected sows from those of TGEV-immunized sows. The results suggest that natural infection of the sow with PRCV may induce a degree of protective lactogenic immunity against TGE.

Effect of chlorpromazine on experimental diarrhoea in just-weaned piglets.

In just-weaned piglets (n = 30, 3-4 weeks) diarrhoea (100%) and vomiting (66%) were provoked by inoculation with transmissible gastroenteritis virus and enterotoxigenic E. coli strains (O149: K91: K88ac; LT, STa and STb enterotoxin positive). This combined infection resulted in a mortality of 71% within 7 days. During this period animals revealed a decrease in body weight, in arterial pressure, in leukocyte count, in plasma pH and in plasma lactic acid concentrations, and an increase in heart rate and in total plasma protein concentration. In shocked and expiring piglets an increase in haematocrit and a decrease in base excess and actual bicarbonate were observed. Chlorpromazine, administered intramuscularly on 3 successive days following the dual infection in 8 K88ac susceptible pigs, in a dosage of 2 and 1.5 mg/kg.24 h, somewhat retarded the appearance of severe diarrhoea and suppressed vomiting. These beneficial effects, however, did not result in an increased survival.

Pathophysiology of diarrhoea induced by a combined infection with transmissible gastroenteritis virus and enterotoxigenic Escherichia coli in newly-weaned piglets and the effect of flurbiprofen treatment.

In newly-weaned 3-4 week old piglets (n = 29) diarrhoea (100%) and vomiting (65%) were induced by inoculation with transmissible gastroenteritis virus and enterotoxigenic E. coli strains (0(149):K91:K88ac; LT, STa and STb enterotoxin positive). This combined infection resulted in pronounced mortality within 7 days. During this period the piglets had decreases in body weight, arterial pressure and leucocyte count and increases in heart rate and in total plasma protein concentration. The plasma pH and lactic acid concentration decreased, whereas the values for pO2, pCO2 and frequency of respiration did not change significantly. No significant changes in the serum concentrations of potassium, chloride or calcium were observed, whereas sodium concentration revealed a transient increase. In shocked and dying piglets an increase in haematocrit was observed, whereas base excess and bicarbonate concentration decreased. Flurbiprofen, a potent non-steroidal anti-inflammatory drug, administered intramuscularly on 3 successive days following the combined infection at a dosage of 1 mg/kg/12 h was without beneficial effect on diarrhoea or mortality.

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.

Determinants of diarrhea in viral enteritis. The role of ion transport and epithelial changes in the ileum in transmissible gastroenteritis in piglets.

To understand mechanisms of viral diarrhea further, we studied ileal ion transport in vitro in relation to mucosal changes and epithelial differentiation in transmissible gastroenteritis in piglets, an invasive viral enteritis thought to involve mainly proximal intestine. In infected pigs, at the height of diarrhea, short-circuited ileal epithelium failed actively to transport Na+ and Cl-, and there was a defect of glucose-mediated Na+ transport. The Cl- secretory response to theophylline remained intact. Conductance measurements indicate that paracellular permeability may be reduced and transcellular transport may be altered. A mucosal lesion was observed at the time of the transport changes, characterized by villus blunting, crypt hyperplasia, and immature crypt-type enterocytes on the villus epithelium, deficient in disaccharidase and (Na+, K+)ATPase activity but rich in thymidine kinase. Consideration of the major determinants of diarrhea in this invasive enteritis must take into account not only altered mucosal function and differentiation but also the extent of intestinal involvement, including the ileum, a major site of fluid absorption in the intestine.