Sheep and cattle-killing disease carriers never take a break
Some pests don't disappear in winter, as previously supposed

Date:
July 3, 2023
Source:
University of California - Riverside
Summary:
Bluetongue virus, an incurable cattle and sheep-killing disease,
is spread by tiny flies once thought to disappear in winter. New
research demonstrates that though they are harder to find when
it's cold, they remain active.


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FULL STORY ========================================================================== Bluetongue virus, an incurable cattle and sheep-killing disease, is
spread by tiny flies once thought to disappear in winter. New research demonstrates that though they are harder to find when it's cold, they
remain active.

Bluetongue virus is common in cattle throughout most of the United
States, particularly in the southwestern U.S. with nearly 20% of some California cattle herds infected. Due to concerns about spread of this
virus, exports of U.S.

cattle and cattle products to parts of Europe and Asia have been
restricted to prevent contamination.

However, not all infected animals die. The main symptoms are elevated temperatures, lethargy, a sore area above the hooves, and some bleeding
around the mouth. All ruminants are susceptible, including goats and
deer as well as cattle and sheep.

"The tongue, especially in sheep, can turn blue from enlargement with
blood," said Alec Gerry, UC Riverside entomology professor and study
co-author.

Biting midges, flies so small they're also called no-see-ums, are
responsible for transmitting the virus. However, the typical adult midge
lives for fewer than 30 days.

"There's been a question about how bluetongue virus persists through
the winter months to make it to the next season," Gerry said. "Our
study looked at adult activity in winter, doing collections on only the
warmest days each week - - something entomologists do not typically do." Previous studies found few flies active during winter in California. One
theory about the midges posited that they die in colder months, and that
the virus- carrying midges are somehow reintroduced from a tropical place
with warm winters. Another theory suggested that no-see-um activity is
not dormant in winter, but surveillance methods aren't robust enough to
catch their reduced activity and ongoing transmission of bluetongue virus.

Convinced the latter theory was correct, the research team commenced
trapping on the warmest days, every two weeks, for three years. "And we
caught them every time," said Xinmi Zhang, a Scripps College entomologist
who led the study while a Ph.D. student in Gerry's lab at UCR.

By changing up typical insect collection practices, the researchers
discovered midges continue to be active on the warmest days. This finding
is described in a Journal of Medical Entomology paper, and in a new blog
post for the Entomological Society of America.

"Not only are the midges more active on those warm days, but the fact
that we found younger adults suggests they are developing through the
winter months," Gerry said. "There is no break in the normal life cycle." Though this study did not find active virus in winter, another study
conducted in California's Central Valley did find virus during this
time period. Taken together, the two studies show virus transmission is
likely ongoing.

Given that there is no specific treatment for Bluetongue and no natural
enemy of the midges that has been identified to help reduce their numbers, Gerry said the findings should support improved methods for managing
virus transmission such as application of insect repellants to ruminant
animals during winter when biting midge activity is at its lowest point
during the year.

California cattle are acclimated to the strain of the virus circulating locally, so they are don't suffer bad reactions. However, that could
easily change. "If a new strain is imported somewhere that didn't have
it before, the animals' reactions could be severe. This could result in
big economic impacts," Zhang said. During an outbreak of Bluetongue in
northern Europe in 2006, thousands of cows died.

"It's so important to have a better understanding of these insects'
behavior.

And now, we do."
* RELATED_TOPICS
o Plants_&_Animals
# Veterinary_Medicine # Virology # Cows,_Sheep,_Pigs
# Microbes_and_More # Bird_Flu_Research # Animals #
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o Fly o Bighorn_Sheep o Ranching o Pandemic
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Story Source: Materials provided by
University_of_California_-_Riverside. Original written by Jules
Bernstein. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Xinmi Zhang, Alec C Gerry. Host-seeking activity of adult Culicoides
sonorensis (Diptera: Ceratopogonidae) during winter in southern
California, USA, and assessment of bluetongue virus overwintering.

Journal of Medical Entomology, 2023; DOI: 10.1093/jme/tjad049 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2023/07/230703133012.htm

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