If Japanese encephalitis virus (JEV) is discovered in the U.S., how big of a threat is the feral swine herd in spreading this deadly virus?
The State of Feral Pigs in the U.S.
As vectors, feral swine are competent for over 45 diseases and parasites, a major concern for any foreign animal disease including JEV, as demonstrated in Australia. Charles Taylor of the University of Georgia (UGA) Savannah River Ecology Lab and Warnell School of Forestry and Natural Resources discussed the history, management and current research on feral pigs in the U.S. during the Swine Health Information Center-sponsored JEV Symposium held at the University of Georgia Center for the Ecology of Infectious Disease.
Feral swine are one of most destructive invasive vertebrates in North America, Taylor explained in a SHIC article, costing $1.5 billion in damage in the U.S. annually. Feral swine devastation affects agriculture, forestry and property. Regional management efforts began in the 1990s with a shift in perception and management of feral pigs, Taylor said, but did not become aggressively managed on a national scale until the mid 2010s. The National Feral Swine Damage Management Program, launched in 2014, includes research, disease monitoring, tool development, communication/outreach and control measures.
Pockets of feral swine in the U.S. have developed over centuries from genetics mixed with Eurasian boars. In the 1980s and 1990s, a rapid shift in population size and distribution of feral swine ramped up. Canada’s spread of feral pigs hit harder in the 2000s. Taylor described this recent expansion in the U.S. and Canada as a “pig bomb.” Wild pigs can have up to three litters in 14 months with litter sizes ranging from six to 10 and can begin reproducing as young as six months of age.
Current estimates are 7 to 8 million wild pigs live in the U.S. alone. Recent eradication successes have been seen in Idaho, Maryland, New Jersey and New York. States nearing or reaching eradication include Iowa, Maine, Minnesota, Wisconsin, Washington and Colorado, Taylor said. However, entrenched and widespread populations exist in the south and in California.
More research is needed to advance ecological knowledge and effective management of feral swine, Taylor said. Not only are new tools needed for control of wild pigs, but best management practices are, too. He said ongoing projects include the Blackbeard Island elimination project, evaluating different models of estimating abundance, investigating effectiveness of trap types, and exploring diet and changes with seasonality.
Swine Pathogen Horizon Scan
Anna Willoughby, a UGA student working with the Center for the Ecology of Infectious Diseases, presented a swine pathogen horizon scan during the JEV Symposium. Her research revolved around four questions:
> Which bacteria should be of concern to the swine industry?
> What bacteria species will likely infect swine?
> What wildlife hosts will likely host these bacteria?
> If a bacteria species is likely to infect, will it have an impact?
The same approach could be implemented for JEV, Willoughby explained during a presentation on her on-going bacterial spill-over research in mammals. She said it will require revisiting literature to build databases and modeling approaches for all kinds of systems. Success requires knowing details on the life history of the pathogen being examined. Willoughby believes it’s possible to pull information from previous West Nile virus outbreaks to apply to JEV work.
Willoughby said in the SHIC article that 1,600 different bacterial species are hosted by mammals and her work focused on 353 North American bacteria species, creating a dataset for development of a spill-over predictive model. Yet there are 176 wild mammals with no bacteria information and 60% of known bacteria species are detected in only one host species. The vast majority of mammals are associated with fewer than five bacteria species. In North America, there are 22 mammals with a high propensity for 10 or more bacteria species and the relating 102 bacteria species are not a lab-feasible research priority.
She is partnering with SHIC to narrow down the bacteria list relevant to swine via survey of stakeholders. Participation in the first survey round was low so will be repeated for better data, she said.
Read more about JEV:
JEV: Don’t Wait Until It’s Too Late
Urgency is Key to Fighting Japanese Encephalitis Virus
JEV in Australia: A Warning Shot that the U.S. Could Be Next?
