What are the health risks of mammalian orthoreovirus (MRV) and porcine adenovirus (PAdV)? With that question, US researchers aimed to unravel some relevant pig health questions.
The recently-published results suggest that both MRV and PAdV can infect pigs and contribute to general enteric disease, but that these viruses are not associated with severe or unique clinical signs.
The outcome will help professionals better understand diagnostic findings, according to a review of the study by the Swine Health Information Center (SHIC), located in Manhattan, KS, USA. The centre also funded the study. The review stated: “These findings suggest that both viruses circulate in swine populations, with evidence pointing toward intestinal shedding or prior exposure rather than widespread active disease in routine tissue submissions.”
The study was led by Dr Wenjun Ma, attached to the University of Missouri. Both viruses have been known to be present in pigs around the globe, but data for US herds were limited. In the research set-up, the team therefore first needed to establish whether the viruses were indeed present in US swine herds and, if so, whether they posed health risks.
Is mammalian orthoreovirus present in US pig herds?
Using RT-qPCR, the team tested 794 lung, intestinal, blood and faecal samples from 18 states throughout the US for evidence of both viruses. The set also included 3 lung samples from Mexico. In total, 29 of 786 (3.69%) swine lung tissue samples were positive for MRV, while 1 in 8 (12.5%) gut samples were positive for MRV.
Additionally, the team tested 481 serum samples from pigs in the US using an ELISA test. In total, 60% were seropositive.
The report stated that “active MRV infection was infrequently detected in field tissue samples, whereas prior exposure to MRV was common in the sampled swine population.”
Is porcine adenovirus present in US pig herds?
Similarly, zooming in on PAdV, the team screened 576 swine samples by PCR, including 516 lung samples and 8 intestinal samples, as well as 52 faecal samples collected from a Missouri swine farm. The team reported that all 8 intestinal samples were negative for PAdV, whereas 1 of 516 (0.02%) lung samples and 6 of 52 (11.5%) faecal samples were PCR-positive. The team failed to isolate the virus from the 7 PCR-positive samples.
In the report, one can read that: “These findings indicate that PAdV was not detected in the lung or intestinal tissue samples examined and that the positive faecal and lung PCR results did not provide confirmed evidence of live PAdV infection.”
Pathogenicity and transmissibility
The other question the researchers had hoped to answer was whether the viruses – individually or together – could lead to disease and spread it. The team put together healthy pigs 3 to 4 weeks old with pigs infected with MRV, PAdV or both. The team wrote, “Pigs infected with the virus developed mild clinical signs, including diarrhoea and fever, and viral genetic material was found in intestinal tissues of infected pigs and contact pigs.”
The team therefore concluded, “Overall, these findings indicate that both viruses can infect pigs, but that co-infection did not produce significantly more severe clinical disease under these conditions.”
The team also concluded, “Neither virus was associated with severe or clearly distinct disease in this study.”