by It was the summer peak in 2022 when the calls started coming in. The dead deer suddenly littered rural properties and park preserves, scaring the public and inconveniencing landowners. According to Urban Park District officials, it was Epizootic Hemorrhagic Disease (EHD), a tick-borne viral illness that appears in white-tailed deer across the state every few years. And when susceptible deer are infected, they die within days.
Now, University of Illinois scientists have discovered gene variants in deer that are associated with the animals’ susceptibility to EHD.
“This is the first time that this gene has been completely sequenced in white-tailed deer. This is important because without the sequences, there is no starting point to do any kind of research,” says study co-author Alfred Roca, professor in the department. of Animal Sciences, as 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 lines the membranes of intracellular organelles in immune cells and helps recognize double-stranded RNA (dsRNA) viruses. When a dsRNA virus, like the one that causes EHD, enters the cell, TLR3 activates the host’s first line of immune defenses, triggering inflammation and triggering the rest of the immune system.
When the team sequenced TLR3 from EHD-infected and uninfected deer, they found many 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 often in EHD-negative animals, we think that deer with these mutations are less at risk of EHD,” says co-author Yasuko Ishida, a research scientist in the Department of Animal Sciences at U of I
That conclusion is rooted in the likelihood that many white-tailed deer in Illinois will be exposed to EHD during their lifetime, but only a few will die from the disease.
In many areas, outbreaks occur every 3-5 years, when environmental conditions favor the life cycle of the whales that carry the virus. The whales spend their larval stages in the mud under ponds and ponds where deer drink during drought conditions. As those water sources dry up, usually in late summer, the whales’ muddy habitat is exposed and the adult flies emerge to bite and infect deer. The cycle can be locally disrupted by drenching rains or cold spells, which is why outbreaks do not occur every year.
The researchers emphasize that EHD is not transmissible to humans or pets through louse bites or eating infected deer meat.
While there is little wildlife managers can do to interrupt the cycle and prevent outbreaks in natural habitats, the team says it is still helpful to understand the genetic basis of the disease. In theory, deer in captive herds could be sampled to characterize the level of vulnerability to EHD, and wild herds could be sampled during hunting seasons and EHD outbreaks, informing managers and the public about future risk.
“The value of this research is that it helps to inform the public about EHD. It helps them to understand not only what the disease looks like, but the severity of a potential outbreak in an area where Sometimes there’s value in knowing what to expect,” says study co-author Nohra Mateus-Pinilla, a wildlife veterinary epidemiologist at the Illinois Natural History Survey, with adjunct appointments in the department Animal Sciences, in the Department of Natural Resources and Environmental Sciences in ACES, and in the Department of Pathobiology.
Given the episodic nature of the disease, another major outbreak in Urbana’s fields is unlikely anytime soon. But it is a growing threat to northern regions of the state, including Chicagoland. Another recent study by Mateus-Pinilla, Roca, and others shows that the disease is slowly but steadily moving north in Illinois. The researchers don’t know if that’s due to climate change or greater reporting, but it’s clear that EHD isn’t limited to rural Illinois.
“Responding to an EHD outbreak is very complicated as large numbers of dead deer are often found near water. People don’t know what to do when that happens, but we encourage the public to report possible EHD outbreaks report to their local IDNR. wildlife biologist to monitor and study the disease in the future,” says Jacob Wessels, who completed the research as part of his master’s degree and is now a conservation police officer with the Illinois Department of Natural Resources.
