Invasive Asian Longhorned Ticks Are Spreading Across the US: Researchers

Asian longhorned ticks, an invasive species reported in the U.S. for the first time in 2017, are spreading across states and need to be studied more, according to researchers. 

In Ohio, the ticks are being blamed for the deaths of three cows due to blood loss. 

Ohio State University scientists are studying the ticks and have reported on the state’s “first-known established population” in the Journal of Medical Entomology, according to a news release. 

The tiny brown ticks come from East Asia and can be “the size of a sesame seed in some life stages and pea-sized when engorged.” 

The species was first found in New Jersey in 2017. The ticks have since spread to Arkansas, Connecticut, Delaware, Georgia, Indiana, Kentucky, Maryland, Massachusetts, Missouri, New York, North Carolina, Ohio, Pennsylvania, Rhode Island, South Carolina, Tennessee, Virginia and West Virginia, according to the CDC. They are not normally found on the Western Hemisphere.

Risa Pesapane, senior author of the paper and an assistant professor of veterinary preventive medicine at Ohio State, first found one of the ticks in Ohio in 2020 on a dog. The next year, a farmer in Monroe County called to report that three cattle “heavily infested with ticks” had died. 

“One of those was a healthy male bull, about 5 years old. Enormous. To have been taken down by exsanguination by ticks, you can imagine that was tens of thousands of ticks on one animal,” Pesapane said in the release. 

At that farm, researchers collected almost 10,000 of the ticks in 90 minutes. Pesapane estimated the 25-acre pasture contained more than 1 million. 

Treating the pasture with pesticide did not stop the ticks from returning the next year. They are hard to kill with pesticides “because of their ability to hide in vegetation” and escape direct contact. 

“It would be wisest to target them early in the season when adults become active, before they lay eggs, because then you would limit how many will hatch and reproduce in subsequent years. But for a variety of reasons, I tell people you cannot spray your way out of an Asian longhorned tick infestation – it will require an integrated approach,” Pesapane said in the release. 

Another issue is the ability of the ticks to reproduce asexually. Each female can lay up to 2,000 eggs at one time. 

“There are no other ticks in North America that do that. So they can just march on, with exponential growth, without any limitation of having to find a mate,” Pesapane said. “Where the habitat is ideal, and anecdotally it seems that unmowed pastures are an ideal location, there’s little stopping them from generating these huge numbers.”

Scientists will continue to study the ticks to determine if they are harmful to humans and to develop ways to combat the spread. The ticks so far are “not deemed to be a threat to human health,” per the release. 

“They tend to favor large livestock and wildlife, such as cattle and deer,” the release states. “Just a handful of the hundred ticks from the farm screened for infectious agents tested positive for pathogens, including one, Anaplasma phagocytophilium, that can cause disease in animals and humans. Elsewhere this tick carries another pathogen, Theileria orientalis, that affects cattle, and cases of bovine theileriosis have been reported in Ohio.” 

The CDC reported an experimental study “found that this tick is not likely to contribute to the spread of Lyme disease bacteria in the United States,” though another showed it could carry the bacteria that causes Rocky Mountain spotted fever. 

CDC guidance says the ticks should be immediately removed if found on humans and animals, and that people should take precautions such as treating clothing and gear with products containing 0.5% permethrin when in areas that ticks can be found.