Viral disease of horses and livestock likely to expand US range as climate changes – study

The tongue of a horse with vesicular stomatitis.
The tongue of a horse with vesicular stomatitis.

Vesicular stomatitis, a viral disease that affects horses, cattle and pigs, is expected to expand its range in the continental United States in the face of climate change, according to researchers.

Vesicular stomatitis is the most common vesicular livestock disease in North America. It is caused by the vesicular stomatitis virus, which is endemic from northern South America to southern Mexico.

The virus spreads from southern Mexico to the US through insects when conditions are right. It can also be spread by direct contact with infected animals, and by contaminated objects.

Historically, the virus has spread from endemic regions in Mexico to US locations over a two-to-three-year period, with overwintering between years. Its occurrence and expansion during incursions requires the presence of the virus, competent insect vectors, and susceptible hosts, as well as suitable environmental conditions.

While infections are rarely fatal to humans or livestock, clinical disease diagnosis in livestock is difficult to distinguish from foot-and-mouth disease, a devastating, highly contagious viral disease of livestock eradicated from the US in 1929.

Outbreaks of vesicular stomatitis result in quarantines and animal movement restrictions in horses, cattle and swine.

Dylan Burruss and his fellow researchers, writing in the journal Climate, said there is a considerable need to improve understanding of relationships among environmental drivers and patterns of disease occurrence, especially as climate change drives shifts in the range of insects and the viruses they transmit.

The study team used a big data model integration approach, combined with machine learning, to estimate the potential geographic range of vesicular stomatitis across the continental US under long-term average climate conditions over the past 30 years.

The current extent of the disease is confined to the western portion of the US and is related to summer and winter rain, winter maximum temperatures, elevation, autumn vegetation biomass, horse density, and proximity to water.

They then forecast shifts in the range of the virus using climate change projections selected from climate models that most realistically simulate seasonal temperature and rain.

Climate change scenarios that altered climatic conditions resulted in greater changes to the potential range of the disease, they said. The modeling indicated that the range of vesicular stomatitis would expand north and east.

They expected that the variable impacts of climate change across the continental US will be exacerbated with additional changes in land use and land cover. This will, in turn, affect biodiversity and water cycles that are connected to the ecology of insect vectors involved in spreading the disease.

In addition, they said, although wildlife in the current range of the virus have not been implicated as hosts, as the range expands to new locations, important wildlife species may become infected and warrant conservation measures to limit the negative effects of this disease.

Discussing their findings, the authors said their human-guided machine learning approach distilled complex information across multiple fields, and identified plausible and important long-term predictors of the geographic range of the disease.

The potential geographic extent of the disease under current climatic conditions included the observed occurrence locations from 2004 to 2016, and expanded it primarily to the northwest (Montana, Idaho, and Oregon), southwest (Arizona and Utah), as well as including large portions of Texas.

Projections from a future scenario with moderate increases in greenhouse gas concentrations predicted an eastern expansion in Oklahoma and Texas, localized reductions in the Rocky Mountains, and with less confidence, some expansion northward in North Dakota, South Dakota, and Montana.

Projections with continued increasing greenhouse gas concentrations more strongly suggest an expansion northward (North Dakota, South Dakota and Montana) as well as eastward (Nebraska, Kansas, Oklahoma and Texas).

Future climate conditions that likely modify stream flow (that is, high rainfall) and insect habitat had the potential to affect the future range the most, they said.

Expansion in the geographic distribution would have important consequences for livestock owners in these regions, they said.

Veterinarians and livestock owners in previously unaffected areas would need specific educational outreach and materials to increase awareness for the possible incursion of the disease, identify clinical signs, understand reporting requirements, and implement appropriate insect control and biosecurity in susceptible herds.

The study team comprised Burruss, with New Mexico State University; and Luis Rodriguez, Barbara Drolet, Kerrie Geil, Angela Pelzel-McCluskey, Lee Cohnstaedt, Justin Derner and Debra Peters, all with the US Department of Agriculture.

Burruss, D.; Rodriguez, L.L.; Drolet, B.; Geil, K.; Pelzel-McCluskey, A.M.; Cohnstaedt, L.W.; Derner, J.D.; Peters, D.P.C. Predicting the Geographic Range of an Invasive Livestock Disease across the Contiguous USA under Current and Future Climate Conditions. Climate 2021, 9, 159.

The study, published under a Creative Commons License, can be read here

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