RICHMOND — As Asian longhorned ticks continue to spread throughout Virginia and the United States, scientists are racing to understand how the species is expanding so fast and how they can keep a virulent parasite carried by the ticks from infecting herds of cattle.
“There’s a geographic niche for these ticks, and we are reaping that,” said Dr. Kevin Lahmers, associate lab director of Virginia Tech’s Animal Laboratory Services and a professor with the Virginia-Maryland College of Veterinary Medicine. But, he added, “We still have a lot to learn.”
Asian longhorned ticks have likely been in the U.S. since 2010, but seven cattle deaths in Virginia’s Albemarle County in 2017 found the species was carrying a new threat to livestock: a virulent form of the Theileria orientalis parasite, which can cause a disease known as theileriosis characterized by anemia, fever, jaundice, respiratory problems and weakness in cattle. In some cases, cows become so depleted that they spontaneously abort fetuses; in other cases, cattle die. Research has estimated this particular form of Theileria, known as the Ikeda genotype, causes mortality rates between 1% and 5%.
Still, variation is wide, said Lahmers. “There are herds that have zero percent mortality. And we have some that have had 25%.”
In 2019, when the Virginia Department of Agriculture and Consumer Services (VDACS) began testing cattle at sales barns and livestock auctions for Theileria, Lahmers said about 1% to 2% of cows turned up positive. That percentage has grown dramatically: While he has not yet finalized his data for publication, Lahmers said he’s seen a “10- to 20-fold increase” in positive cases.
Neither he nor VDACS have firm estimates of cattle deaths linked to theileriosis, but Lahmers said that “if we count cattle deaths and abortions, we’re probably in the thousands.”
“It spread easily,” he said. “It doesn’t cause death in the majority — similar to COVID, it’s only a problem for a few, but the way the cattle industry works, there isn’t that much margin for profit. So if you lose 5% of your herd or 5% abort … that’s enough to take you from marginally profitable to significant financial losses.”
At the same time, Asian longhorned ticks are also showing up in more Virginia counties. In 2019, they had been detected in 24 counties, largely following the spine of Interstate 81 and then stretching west into the coalfields region. By this June, the number of counties had jumped to 38.
“It seems to be the higher elevations along the I-81 corridor,” said Lahmers. “All of those counties are positive or are going to be positive soon.”
Virginia isn’t the only state grappling with the ticks. Between 2019 and April 2023, the number of states that had detected the species rose from 11 to 19, with the U.S. Centers for Disease Control and Prevention identifying it in Arkansas, Connecticut, Delaware, Georgia, Indiana, Kentucky, Maryland, Massachusetts, Missouri, New Jersey, New York, North Carolina, Ohio, Pennsylvania, Rhode Island, South Carolina, Tennessee and West Virginia, as well as Virginia.
“I’m not sure that the expansion in Virginia is any faster than anywhere else,” said Lahmers.
Scientists aren’t sure yet how the tick is managing to spread as quickly as it is, but they have identified several possible factors. One is the species’ willingness to feed on an array of animals, including migratory birds, which means they have less trouble finding sustenance to survive and reproduce. Another is the tick’s asexual method of reproduction, which allows it to reproduce without relying on a mate.
Whatever the cause, an increasing number of Asian longhorned ticks appear to be moving into Virginia’s cattle regions, and theileriosis is a growing concern. The disease has no approved treatment in the U.S., so agricultural officials are focusing on controlling tick populations. They are urging farmers to regularly inspect their herds or any new animals being added, keep cattle out of wooded areas, mow pastures, use ear tags treated with pesticides and submit tick samples to local Virginia Cooperative Extension agents.
“As there is no cure, treatment should focus on supportive measures including stress reduction, nutritional supplementation and above all, prevention in the form of tick control,” said Dr. Charles Broaddus, Virginia’s state veterinarian, in a VDACS release.
Furthermore, Lahmers warned, just because a cow tests positive for theileriosis doesn’t mean that any subsequent illness it might suffer is due to theileriosis.
Despite the spread and the concerns, Lahmers said there’s no need to panic. Most cattle survive theileriosis, and researchers are actively working to better understand the disease and its connections to the Asian longhorned tick through cooperative agreements between the state and the U.S. Department of Agriculture’s Agricultural Research Service and Animal and Plant Health Inspection Service.
In 2019, he said, “it was a Virginia problem.” But “with time, we have found out it wasn’t just a Virginia problem and it has continued to spread.”
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