|
 According
to officials at the Urbana Park District, it was Epizootic
Hemorrhagic Disease (EHD), a midge-borne viral illness that pops
up in white-tailed deer populations around the state every few
years. And when susceptible deer are infected, they die within
days.
Now, University of Illinois scientists have found gene variants
in deer associated with the animals’ susceptibility to EHD.
“This is the first time this gene has been sequenced completely
in white-tailed deer. This is important because without the
sequences, there's no starting point to do any kind of
research,” says study co-author Alfred Roca, professor in the
Department of Animal Sciences, part of the College of
Agricultural, Consumer and Environmental Sciences (ACES) at U of
I.
The team sequenced the gene for Toll-Like Receptor 3 (TLR3), a
protein that spans membranes of intracellular organelles in
immune cells and helps recognize double-stranded RNA (dsRNA)
viruses. When a dsRNA virus, such as the one that causes EHD,
enters the cell, TLR3 activates the host’s first immune
defenses, triggering inflammation and priming the rest of the
immune system.
When the team sequenced TLR3 from EHD-infected and uninfected
deer, they found dozens of variable sites in the DNA known as
single-nucleotide polymorphisms (SNPs). Two of the SNPs were
significantly more common in uninfected deer.
“Because we found mutations in TLR3 more frequently in EHD-negative
animals, we think deer with these mutations are less susceptible
to EHD,” says co-author Yasuko Ishida, research scientist in the
Department of Animal Sciences at U of I.
That conclusion is rooted in the probability that many
white-tailed deer in Illinois are exposed to EHD in their
lifetimes, but only some will die from the disease.
In many areas, outbreaks occur every 3-5 years, when
environmental conditions favor the life cycle of midges that
carry the virus. The midges spend their larval stages in mud
under ponds and puddles where deer drink during drought
conditions. As those water sources dry up, usually during late
summer, the midges’ muddy habitat is exposed and the adult flies
emerge to bite and infect deer. The cycle can be interrupted
locally by a soaking rain or a cold snap, which is why outbreaks
don’t happen every year.
The researchers emphasize that EHD is not transmissible to
humans or pets through midge bites or consumption of infected
deer meat.
Although there’s not much wildlife managers can do to disrupt
the cycle and prevent outbreaks in natural habitats, the team
says it’s still helpful to understand the genetic underpinnings
of the disease. Theoretically, deer in captive herds could be
sampled to characterize the level of vulnerability to EHD, and
wild herds could be sampled during the hunting and EHD-outbreak
seasons, informing managers and the public of future risk.
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“The value of this research is that it helps inform
the public about EHD. It helps them to understand not only what the
disease will look like, but potentially the severity of an outbreak
in a particular area. Sometimes there's value in knowing what to
expect,” says study co-author Nohra Mateus-Pinilla, wildlife
veterinary epidemiologist at the Illinois Natural History Survey,
with adjunct appointments in the Department of Animal Sciences, the
Department of Natural Resources and Environmental Sciences in ACES,
and the Department of Pathobiology.
Considering the disease’s episodic nature, it’s not
likely to present as a severe outbreak again in Urbana parks anytime
soon. But it is an increasing threat to the state’s northern
regions, including Chicagoland. Another recent study by
Mateus-Pinilla, Roca, and others shows the disease has been slowly
but steadily moving northward in Illinois. The researchers don’t
know whether that’s due to climate change or greater reporting, but
it’s clear EHD isn’t restricted to rural parts of Illinois.
“It’s very complicated to respond to an outbreak of EHD because
there are often large numbers of deer found dead near water. People
don’t know what to do when that happens, but we encourage the public
to report potential EHD outbreaks to their local IDNR wildlife
biologist for the surveillance and future study of the disease,”
says Jacob Wessels, who completed the research as part of his
master’s degree and now serves as a conservation police officer with
the Illinois Department of Natural Resources.
The article, “The Impact of Variation in the
Toll-like Receptor 3 Gene on Epizootic Hemorrhagic Disease in
Illinois Wild White-tailed Deer (Odocoileus virginianus),” is
published in Genes [DOI: 10.3390/genes14020426]. Additional authors
include Nelda Rivera, Spencer Stirewalt, William Brown, Jan
Novakofski, and Alfred Roca. The research was funded by The Federal
Aid in Wildlife Restoration Project W-146 and the USDA Cooperative
State Research, Education, and Extension Service.
[Sources: Alfred Roca, Yasuko Ishida,
Nohra Mateus-Pinilla, Jacob Wessels
News writer: Lauren Quinn] |
