Virus that sickens cows, kills deer, still rare in NYS – for now

An insect-driven disease that causes high mortality in white-tailed deer, and mimics the symptoms of foot and mouth disease in cattle, is still rare in New York state, but the warming climate may increase its future spread.

In research published Sept. 28 in Transboundary and Emerging Diseases, Cornell researchers documented their extensive, statewide testing for epizootic hemorrhagic disease virus (EHDV). They found that only 0.6% of samples collected from New York cattle, sheep and goats showed antibodies for EHDV - an indicator that an animal has encountered the disease and developed some immunity against it.

"In the Southern and Southeastern U.S. where it's warmer, EHDV is widespread. We're on the cusp of where this occurs endemically, so when we have warmer, drier summers, that creates the right conditions for outbreaks here in New York," said Elisha Frye, DVM '10, associate professor of practice of population medicine and diagnostic sciences in the College of Veterinary Medicine (CVM) and the paper's first author.

Similar to ticks and Lyme disease, EHDV is spread by certain biting midges called Culicoides. Animals cannot spread the disease to each other, but must be infected by the midges. What makes EHDV especially problematic is that its symptoms - such as high fevers, mouth sores, excessive salivating and lethargy - mimic those of the more-contagious foreign animal disease foot and mouth disease, Frye said.

Foot and mouth disease is not present in the U.S., and state and federal agencies work hard to keep it that way, Frye said. When an animal is suspected of having foot and mouth disease, farm operations must be paused while animals are quarantined and tested, causing considerable cost and disruption for farmers.

In 2021, New York experienced its worst recorded outbreak of EHDV, with an estimated 1,500-2,100 white-tailed deer killed by the virus. While cattle don't die from EHDV as frequently as deer, they lose appetite because of painful mouth sores, which cause lower milk production in dairy cows and lower weight gain in beef cattle, Frye said. The researchers tested for EHDV antibodies in 5,698 samples from cattle, sheep and goats that were sent in to Cornell's Animal Health Diagnostic Center for other reasons. Of those, 34 samples tested positive for EHDV: 31 cattle and three sheep. (Sheep and goats can develop antibodies to EHDV but are rarely sickened by the disease.)

Periods of drought, which create shallow water and exposed mud, generate productive breeding grounds for midges. In regions like New York and the Northeast, periodic outbreaks are infrequent, but can be severe because the herd lacks immunity, she said.

"The fact that we found so few animals with antibodies can be good or bad. Good because we don't want this disease here, we don't want to see white-tailed deer deaths of course, and we don't want our farms disrupted by foot and mouth disease testing," Frye said. "And bad because when a population is naive like this, they have less herd immunity to protect themselves when we do have a hot, dry year and the midges come."

Frye's advice for monitoring and managing EHDV in New York includes:

• EHDV makes deer dehydrated, and they seek out water. Hikers, hunters and others who see a deer that has died near a body of water should report it to the New York State Department of Environmental Conservation, which will test the body for its cause of death;
• Dairy and beef cattle farmers whose animals seem sick, aren't eating well and especially if they're salivating a lot should call their veterinarian to have the animals tested; and
• Veterinarians who suspect an animal's symptoms suggest foot and mouth disease (such as fever, excessive salivation, or painful blisters on the mouth, nose, teats, or hooves) should report their concerns to the New York State Department of Agriculture and Markets. State and federal regulators will oversee testing.

Paper co-authors are Dr. Diego Diel, professor of population medicine and diagnostic sciences, and Krysten Schuler, associate research professor of public and ecosystem health, both in CVM; Dr. Patrick Connelly, DVM '20, state wildlife pathologist with the New Jersey Department of Environmental Protection; Jennifer Powers, lab manager at the Cornell Animal Health Diagnostic Center's (AHDC) virology lab; and Melissa Aprea, program analyst with AHDC.

The research was supported by the National Institute of Food and Agriculture's Federal Capacity Funds, managed by Cornell's Agricultural Experiment Station, based in Ithaca.

Krisy Gashler is a freelance writer for the Cornell University Agricultural Experiment Station.