It was the height of summer 2022 when the calls started coming in. Dozens of dead deer suddenly littered rural properties and park reserves, alarming the public and inconveniencing landowners. According to Urbana Park District officials, it was Epizootic Hemorrhagic Disease (EHD), a midge-borne viral disease that appears in the state’s whitetail deer populations every few years. And when susceptible deer are infected, they die within days.
Now, University of Illinois scientists have found genetic variants in deer associated with the animals’ susceptibility to EHD.
“This is the first time that this gene has been fully sequenced in white-tailed deer. This is important because without the sequences there is no starting point to do research,” says Alfred Roca, co-author of the study and professor in the Department. of Animal Science, part of the College of Agricultural, Consumer and Environmental Sciences (ACES) at the U of I.
The team sequenced the Toll-Like Receptor 3 (TLR3) gene, a protein that crosses the 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 DNA called single nucleotide polymorphisms (SNPs). Two of the SNPs were significantly more frequent in uninfected deer.
“Because we found mutations in TLR3 more frequently in EHD-negative animals, we believe that deer carrying these mutations are less susceptible to EHD,” says co-author Yasuko Ishida, researcher at the Department of Animal Sciences from the University of the Island.
This finding is rooted in the likelihood that many Illinois white-tailed deer will be exposed to EHD in their lifetime, but only some will die from the disease.
In many areas, epidemics occur every 3 to 5 years, when environmental conditions favor the life cycle of virus-carrying midges. The midges spend their larval stages in the mud under ponds and puddles where deer drink during drought conditions. As these water sources dry up, usually in late summer, the midges’ muddy habitat is exposed and adult flies emerge to bite and infect deer. The cycle can be interrupted locally by driving rain or a cold snap, which is why epidemics do not occur every year.
The researchers point out that EHD is not transmissible to humans or pets through midge bites or eating infected deer meat.
Although wildlife managers can do little to disrupt the cycle and prevent outbreaks in natural habitats, the team says it’s still useful to understand the genetic basis of disease. Theoretically, deer in captive herds could be sampled to characterize the level of vulnerability to EHD, and wild herds could be sampled during hunting and EHD outbreak seasons, informing managers and the public of the risks future.
“The value of this research is that it helps inform the public about PEM. She helps him understand not just what the disease will look like, but potentially how bad an outbreak will be in a particular area. Sometimes it helps to know what to expect,” says study co-author Nohra Mateus-Pinilla, a veterinary wildlife epidemiologist with the Illinois Natural History Survey, with adjunct appointments at the Department of Animal Sciences, in the Department of Natural Resources and Environmental Sciences at ACES and in the Department of Pathobiology.
Given the episodic nature of the disease, it is unlikely to re-emerge as a serious outbreak in Urbana Parks any time soon. But it’s a growing threat to upstate areas, including Chicagoland. Another recent study by Mateus-Pinilla, Roca and others shows that the disease is slowly but steadily moving north into Illinois. The researchers aren’t sure if this is due to climate change or more reporting, but it’s clear that EHD isn’t limited to rural Illinois.
“It is very complicated to respond to an outbreak of EHD because there are often a large number of deer found dead near water. People don’t know what to do when this happens, but we encourage the public to report potential EHD outbreaks to their local IDNR. wildlife biologist for surveillance and future study of the disease,” says Jacob Wessels, who completed research as part of his master’s degree and is now a conservation police officer with the Department of Natural Resources of the Illinois.