Héctor Puente

and 10 more

Global emergence and re-emergence of Porcine epidemic diarrhea virus (PEDV), an Alphacoronavirus which causes a highly contagious enteric disease, have led to several studies addressing its variability. The aim of this study was to characterize the infection of weaned pigs with Swine enteric coronavirus (SeCoV) -a chimeric virus most likely originated from a recombination event between PEDV and Transmissible gastroenteritis virus, or its mutant Porcine respiratory coronavirus-, and two PEDV G1b variants, including a recently described recombinant PEDV-SeCoV (rPEDV-SeCoV), as well as to determine the degree of cross-protection achieved against the rPEDV-SeCoV. For this purpose, forty-eight 4-week-old weaned pigs were randomly allocated into four groups of 12 animals; piglets in groups B, C and D were orally inoculated with a PEDV variant (B and D) or SeCoV (C), while piglets in group A were mock inoculated and maintained as controls. At day 20 post-infection all groups were exposed to rPEDV-SeCoV; thus, group D was subjected to a homologous re-challenge, groups B and C to a heterologous re-challenge (PEDV/rPEDV-SeCoV and SeCoV/rPEDV-SeCoV, respectively) and group A was primary challenged (-/rPEDV-SeCoV). Clinical signs, viral shedding, microscopic lesions and specific humoral and cellular immune responses (IgG, IgA, neutralizing antibodies and IgA and IFN-γ-secreting cells) were monitored. After primo-infection all three viral strains induced an undistinguishable mild-to-moderate clinical disease with diarrhea as the main sign and villus shortening lesions in the small intestine. In homologous re-challenged pigs, no clinical signs or lesions were observed, and viral shedding was only detected in a single animal. This fact may be explained by the significant high level of rPEDV-SeCoV-specific neutralizing antibodies found in these pigs before the challenge. In contrast, prior exposition to a different PEDV G1b variant or SeCoV only provided partial cross-protection, allowing rPEDV-SeCoV replication and shedding in feces.
Respiratory disease in weaned pigs is a common problem in the field, with a complex aetiology of both viruses and bacteria. In the present study, we investigated the presence of eleven viruses in nasal swabs collected from nurseries (fifty-five clinical outbreaks) under the suspicion of swine influenza A virus (swIAV) by cough and fever. The other ten viruses included influenza B (IBV) and influenza D viruses (IDV), Porcine reproductive and respiratory syndrome virus (PRRSV), Porcine respiratory coronavirus (PRCV), Porcine cytomegalovirus (PCMV), porcine circoviruses 2 (PCV2), 3 (PCV3) and 4 (PCV), Porcine parainfluenza 1 virus (PPIV1) and Swine orthopneumovirus (SOV). Twenty-nine swIAV-positive cases and twenty-six cases of swIAV-negative respiratory disease were primarily established. IBV, IBD, PCV4 and PPIV1 were not found in any case, while PRCV, SOV, and PCMV were more likely to be found in swIAV-positive nurseries with respiratory disease ( p<0.05) although, globally, PCV3, PRRSV, and PCMV were the most frequently detected agents on herd level. At an individual level, the prevalence of different viruses was: swIAV 48.6%; PRCV 48.0%; PRRSV 31.6%; SOV 33.8%; PCMV 48.3%, PCV2 36.0%; and PCV3 33.0%. Beyond that, it was common to find animals with low Ct values (< 30) for all agents except for PCV2 and PCV3. When analysed the association between different pathogens, PRCV was the one with the most associations. It positively interacted ( p < 0.05) with swIAV and SOV but was negatively associated ( p < 0.05) with PRRSV and PCVM. Besides these, swIAV and PRRSV were negatively related (p < 0.05). Further analysis of suckling pigs showed that circulation of PRCV, PCMV, SOV, and PCV3 started in the maternities, suggesting a role of the sows in the transmission. Overall, our data may contribute to a better understanding of the complex aetiology and the epidemiology of respiratory disease in weaners. This is the first report of SOV in Spain.

Ivan Díaz

and 7 more

The aim of the present study was to evaluate the duration of protective immunity against Porcine epidemic diarrheoa virus (PEDV). To that, a two phases study was performed. In the first phase, 75 four-week-old pigs (group A) were orally inoculated (0 days post-inoculation; dpi) with a European PEDV G1b strain and 14 were kept as controls (group B). The second phase started five month later (154 dpi), when animals in group A were homologous challenged and animals in group B were challenged for first time. Clinical signs, viral shedding and immune responses were evaluated after each inoculation, including the determination of antibodies (ELISA and viral neutralisation test, IgA and IgG ELISPOTs using peripheral blood mononuclear cells and lymph node cells) and the frequency of interferon-gamma (IFN-γ) secreting cells. During the first phase, loose stools/liquid faeces were observed in all group A animals. Faecal shedding of PEDV occurred mostly during the first 14 days but, in some animals, persisted until 42 dpi. All inoculated animals seroconverted for specific-PEDV IgG and IgA, and for neutralizing antibodies (NA). At 154 dpi, 77% of pigs were still positive for NA. After that, the homologous challenge resulted in a booster for IgG, IgA, NA, as well as specific-PEDV IgG, IgA and IFN-γ secreting cells. In spite of that, PEDV was detected in faeces of all pigs from group A, indicating that the immune response did not prevent reinfection although the duration of the viral shedding and the total load of virus shed was significantly lower for previously challenged pigs (p<0.05). Taken together, the results indicated that, potentially, maintenance of PEDV infection within an endemic farm may occur by transmission to and from previously infected animals and also indicates that sterilising immunity is shorter than the productive life of pigs.