Surveillance of Feral Swine (Sus scrofa) in the Western USA for Antibodies to Vesicular Stomatitis Virus, 2013-21.

Vesicular stomatitis virus (VSV) outbreaks periodically occur in livestock in the western US and are thought to originate from outside this country. Feral swine (Sus scrofa) have been identified as an amplifying host for vesicular stomatitis New Jersey virus (VSNJV) and have been used to better understand the epidemiology of this virus through serosurveillance. This study aimed to determine if antibodies to vesicular stomatitis Indiana virus (VSIV) and VSNJV were present in feral swine in the western US and to determine if seropositive animals were associated with areas of previously detected VSV in livestock. A total of 4,541 feral swine samples was tested using virus neutralization (VN); samples exhibiting neutralizing activity against one or more of the viruses were confirmed using competitive ELISA (cELISA). Eight sera exhibited neutralizing activity by VN assay and a single serum sample from an animal from Kinney County, Texas sampled in December 2019 tested positive for antibodies to VSIV by cELISA. This finding is supported by a local outbreak of VSIV in horses in the same county in June 2019. The low prevalence of antibodies against VSNJV and VSIV was unexpected but indicates that feral swine in the western US do not represent an endemic reservoir for either of these viruses.

Seroprevalence of Bovine Viral Diarrhea Virus in Wild Pigs (Sus scrofa) in 17 States in the USA.

Wild pigs (Sus scrofa) are among the most detrimental invasive species in the USA. They are damaging to crops and agriculture, pose a public health risk as reservoirs of zoonotic pathogens, and may also spread disease to livestock. One pathogen identified in wild pigs is bovine viral diarrhea virus (BVDV), a virus that causes an economically important disease of cattle (Bos taurus and Bos indicus). We sought to determine the BVDV seroprevalence in wild pigs in 17 states across the US and to determine whether age category, sex, or location were associated with a positive antibody titer. Serum samples from 945 wild pigs were collected from 17 US states. Virus neutralization assays were performed to determine antibody titers against BVDV-1b and BVDV-2a. Total BVDV seroprevalence for the study area was 5.8% (95% confidence interval [CI], 4.11-8.89). Seroprevalence across all evaluated states was determined to be 4.4% (95% CI, 2.48-6.82) for BVDV-1b and 3.6% (95% CI, 1.54-5.60) for BVDV-2a. The seroprevalence for individual states varied from 0% to 16.7%. There was no statistical difference in median antibody titer for BVDV-1b or BVDV-2a by sex or age category. State seroprevalences for both BVDV-1b and BVDV-2a were associated with wild pig population estimates for those states.

African swine fever at the wildlife-livestock interface: challenges for management and outbreak response within invasive wild pigs in the United States.

African swine fever (ASF) causes significant morbidity and mortality in both domestic and wild suids (Sus scrofa), and disease outbreaks convey profound economic costs to impacted industries due to death loss, the cost of culling exposed/infected animals as the primary disease control measure, and trade restrictions. The co-occurrence of domestic and wild suids significantly complicates ASF management given the potential for wild populations to serve as persistent sources for spillover. We describe the unique threat of African swine fever virus (ASFV) introduction to the United States from epidemiological and ecological perspectives with a specific focus on disease management at the wild-domestic swine interface. The introduction of ASF into domestic herds would require a response focused on containment, culling, and contact tracing. However, detection of ASF among invasive wild pigs would require a far more complex and intensive response given the challenges of detection, containment, and ultimately elimination among wild populations. We describe the state of the science available to inform preparations for an ASF response among invasive wild pigs, describe knowledge gaps and the associated studies needed to fill those gaps, and call for an integrated approach for preparedness that incorporates the best available science and acknowledges sociological attributes and the policy context needed for an integrated disease response.