Shedding Light on the Epidemiology of Senecavirus A

September 24, 2019 — 

Vesicular diseases have been on the radar of animal health governmental agencies and industries around the world due to their high socio-economic impact. Unfortunately, there are viruses that induce vesicular lesions that resemble these high impact diseases. Senecavirus A is an example. [Source: National Hog Farmer 10 September 2019]

SVA has been around for at least three decades but it was not until 2014-15 that this virus started drawing more attention as outbreaks of the swine vesicular disease were reported in the United States and Brazil. This virus that belongs to the Picornaviridae family, in which the foot-and-mouth disease virus is also a member, has been associated with vesicular disease and neonatal mortality in breeding herds in different countries.

Clinically, the vesicles this virus causes are indistinguishable from those caused by other vesicular diseases (e.g. FMD, vesicular stomatitis). Therefore, making a prompt diagnosis is key to rule out economically devastating diseases that would trigger a set of events dedicated to contain and eliminate a vesicular reportable disease and thus maintain continuity of business.

Currently there are many unanswered questions with regards to the occurrence of SVA and yet, outbreaks of the disease continue to occur sporadically in breeding and finishing sites but also in pigs that have recently arrived at the slaughter plant. Data on the proportion of pig farms exposed to SVA is scarce in the United States; therefore, a study was designed to shed light on how widespread this virus is in our industry together with understanding which factors can be associated with exposure to SVA. This National Pork Board-funded study aims to estimate the proportion of SVA-exposed breeding and finishing sites by collecting blood samples from 100 sow and 100 growing pig farms.

Production companies and swine clinics were invited to participate in this national SVA prevalence study. Within each herd, 30 blood samples have been collected randomly across parities in sow farms and from pigs 20-weeks old or older in growing pig farms. Samples collected are being tested with an indirect immunofluorescence assay for SVA antibodies at the University of Minnesota Veterinary Diagnostic Laboratory. Participating practitioners are also being asked to fill out a farm characteristics survey that will allow us to determine herd-level risk factors associated with the presence of SVA antibodies.

The sample collection phase is reaching the end as samples originating from 186 pig farms located in 16 different states have been collected and tested for SVA antibodies. Preliminary serologic test results show that out of 5,583 samples, 268 (4.8%) have tested positive. Positive samples are clustered in 17 out of 91 (18.7%) sow herds and seven out of 95 (7.4%) growing pig herds that have had at least one positive sample. The proportion of animals with SVA antibodies within each farm ranged from 3.3% to 100%, with an average of 37.2% among all farms with positive samples. Out of the 16 represented states, seven had at least one farm with positive samples.

The risk factor analysis being performed will be crucial to better understand the underlying key components toward SVA infection and transmission among farms. Different farm characteristics such as herd size, proximity to other farms, as well as commonly practiced procedures such as carcass rendering, and many different biosecurity practices will be assessed regarding their association with having a positive farm.

This study contributes to the understanding of the epidemiology of SVA in the country. The virus appears to be present in the U.S. swine industry at a low level; however, at a low prevalence the virus continues to be a source of concern as SVA cases continue to occur and generate stress and production disruptions on production systems and packers as every time there is a case a disease investigation is conducted to rule out foreign animal diseases. Further understanding transmission and occurrence will lead to unveiling epidemiological properties that will aid in the development of prevention and control measures.