Senecavirus A in pigs
Josepha DeLay, Jim Fairles, Davor Ojkic
Senecavirus A (Seneca Valley virus, SVV) has recently been associated with clinical disease in pig herds in Brazil (2014 and 2015) and in the midwestern United States (summer 2015). Testing has identified a low prevalence of infection in the US. The virus was identified at an assembly site in Canada in October 2015, but concurrent clinical disease has not yet been documented in this country. Prior to 2015, sporadic cases of SVV infection were identified in both the US and Canada.
Sows and finisher pigs infected with SVV develop cutaneous vesicular lesions on the snout and coronary bands. The lesions may progress to ulceration and sloughing of the hoof wall, and affected animals may be lame. Morbidity is high, however there is no direct mortality associated with SVV infection in older pigs, and affected pigs generally recover in 1-2 weeks. Vesicular lesions in SVV-infected pigs are clinically identical to those of several federally reportable foreign animal diseases (FADs), including foot and mouth disease (FMD), swine vesicular disease (SVD), and vesicular stomatitis of swine (VSS). In contrast to FADs, infection with SVV is not a federally reportable disease in Canada. However because of the similarity of lesions, FAD exclusion is a priority in any herd where vesicular lesions are identified, and the Canadian Food Inspection Agency (CFIA) must be notified immediately when these lesions are detected. It is imperative that pigs with any evidence of vesicular or ulcerative lesions involving snout or hooves NOT be shipped for slaughter. Presence of vesicular lesions at slaughter inspection would result in closure of the plant while FAD investigation is carried out. This would have a significant negative economic impact on the Ontario and national swine industry, as well as on individual producers.
In addition to vesicular lesions described in older pigs, recent cases in the US and Brazil have documented disease in neonatal pigs associated with high tissue levels of SVV. Clinically, there was a dramatic spike in mortality (up to 70%) among 1-4 day old neonates, with significant but lower mortality among 5-7 day old piglets. The increase was transient, resolving in 7-10 days. Vesicular lesions were present concurrently in 70% of sows; in the remaining 30% of cases, clinical disease was limited to piglets. The syndrome of neonatal pig infection has not been previously described in association with SVV, and has been dubbed ‘epidemic transient neonatal mortality’ (ETNM). Diarrhea is present in some affected piglets, and may be the result of concurrent infection with various other pathogens including rotavirus enteritis and Clostridium difficile colitis. No specific gross or histologic lesions in affected piglets have been attributed to SVV infection.
High levels of SVV have been identified in vesicle fluid from pigs with cutaneous lesions. In addition, SVV antigen and nucleic acid were identified in multiple tissues from piglets in cases of ETNM, leading to the suggestion that death is the result of acute viremia. Despite this association, Koch’s postulates have not yet been fulfilled to confirm a causal role for SVV in either vesicular disease or neonatal mortality. Features of SVV incubation, shedding, and transmission are also uncharacterized at this time. Based on information from the Brazil outbreak, SVV does appear to be highly immunogenic, with development of long-lasting immunity.
Testing for SVV is dependent on the clinical syndrome identified in the herd. For cases with vesicles, CFIA must be contacted and will direct testing in order to exclude FADs. Testing for SVV will be included in the investigation. In herds experiencing a sudden increase in neonatal mortality but WITHOUT vesicular lesions in sows or other animals, please contact the Animal Health Laboratory (AHL) for direction regarding sampling and test selection. Samples required from neonates include serum, and both formalin-fixed and fresh samples of multiple tissues (lymph nodes, tonsil, spleen, liver, lung, kidney, heart, small and large intestine, brain, and spinal cord, if possible).
The AHL, in collaboration with the CFIA National Centre for Foreign Animal Disease (NCFAD), is validating a PCR test for SVV. This test will be available in soonfor use in any situation with no clinical evidence of vesicular disease, such as environmental monitoring and neonatal mortalities. Serological testing methods are currently being evaluated at NCFAD for potential use in Canada.
Influenza A virus testing from swine
From each submission to AHL that tests positive for Influenza A virus by PCR, one sample will be selected for further typing and results of this additional testing will be reported to clients:
a. H1N1/H3N2 typing; b. Partial H gene sequencing
On unusual viruses (i.e., non H1N1/H3N2), viruses associated with outbreaks and for emergency purposes (e.g., H5/H7), whole genome sequencing will be periodically carried out. For this testing, samples will be batched to minimize the cost and the results will be reported on a cumulative basis, i.e. no individual identification of source herd.
OMAFRA will cover all test costs apart from the initial PCR.