Invasive Tick Species From Asia Rapidly Spreading In CT: What To Know

CONNECTICUT — An invasive tick species from Asia is rapidly spreading in Connecticut, with numbers significantly increasing over the last several years, environmental officials and researchers said.

The Connecticut Agricultural Experiment Station has reported the first confirmed case of the invasive longhorned tick carrying Ehrlichia chaffeensis, a bacterium that causes human monocytic ehrlichiosis, marking the first such discovery in the United States.

The finding, published in the "Emerging Infectious Diseases" journal, stems from collaborative research conducted by CAES and U.S. Department of Agriculture scientists.

Longhorned ticks continue to expand to more places, including Connecticut

Since its detection in the U.S. in 2017, the longhorned tick (Haemaphysalis longicornis), originally native to East Asia, has spread to at least 21 states and the District of Columbia. Connecticut confirmed its first fully engorged, human-parasitizing specimen in 2018 in Fairfield County, with established populations following in 2020. The tick has since been found in multiple towns across Fairfield and New Haven counties, as well as individual specimens in New London and other areas.

The ticks are not large: adults are about an eighth of an inch wide, including legs, and nymphs are much smaller. They are deep copper or red in color, and have eight legs as adults.

The Asian tick is easily confused with other tick species, as its distinctive “horns” may not always be visible without a microscope.

The longhorned tick’s ability to reproduce asexually and feed on a wide range of hosts — including humans, domestic animals, and wildlife — has contributed to its rapid expansion. Its role as a potential vector for disease has raised concerns among health officials, particularly in light of new findings. A single female tick can lay up to 3,000 eggs, and this massive offspring is responsible for the tick being discovered in hordes on certain areas and on their victims.

Ehrlichia chaffeensis is primarily transmitted by the lone star tick (Amblyomma americanum) and causes ehrlichiosis, a potentially serious illness that affects white blood cells. Early symptoms include fever, fatigue, headache, and muscle aches, which can escalate into more severe complications such as kidney failure or respiratory distress if not treated promptly. There is no vaccine, and prevention relies on avoiding tick bites.

While the lone star tick has been the predominant vector for the bacterium, this new finding suggests that the longhorned tick could also play a role in its transmission. Researchers note that the tick may be capable of spreading pathogens through partial feeding behavior — where it begins feeding on one host, then continues the meal on another, potentially transmitting disease agents in the process.

Connecticut cases continue to rise

Between 2001 and 2019, reported ehrlichiosis cases in the U.S. grew from 142 to more than 2,000. Connecticut saw a rise from just two cases between 2008 and 2018 to 28 cases from 2019 through 2023. Experts suggest the disease is likely underreported and expect further increases as the tick continues to expand its range.

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“This discovery highlights the growing threat posed by invasive ticks,” said Dr. Goudarz Molaei, director of the CAES Passive Tick and Tick-Borne Disease Surveillance Program. “Raising public awareness of emerging tick-borne illnesses is critical to both human and veterinary health.”

Molaei emphasized the need for a comprehensive response to the growing tick threat, including expanded surveillance, stricter inspections at ports of entry, accurate identification of exotic ticks, effective eradication protocols, and advanced testing for both native and nonnative pathogens.

He added that mitigating the risks associated with invasive tick species must become a national priority. “We need to ensure we’re prepared not just to monitor but to respond effectively to the changing landscape of tick-borne disease transmission.”

What other diseases do they transmit?

Fortunately, it appears as though they do not transmit Lyme disease. They have been found carrying other pathogens linked to that disease, anaplasmosis, babesiosis, Bourbon virus disease, and theileriosis, though further research is needed to determine its capacity to transmit these diseases. While they're capable of transmitting diseases like Rocky Mountain spotted fever to humans and animals alike, there's not yet evidence that they've done so on a wide scale in the United States.

Research is still underway on the tick's relatively new interactions with American environments, and its disease vectors and behaviors Japan, China, Korea, and Russia are not necessarily indicative of what it will do here, officials say.

Still, Asian longhorns pose a significant and immediate threat in other ways. Most notably, they carry and transmit Theileria orientalis, a disease which causes often fatal anemia and fever in cattle.

Impact on cattle and wildlife

Researchers at Ohio State University concluded that a 2021 infestation of Asian longhorned ticks was behind the deaths of three cattle, including a previously healthy adult bull who died of severe blood loss from tick bites, according to a news release.

The bull was 5 years old and “enormous,” Risa Pesapane, the senior author of the paper published in the Journal of Medical Entomology and an assistant professor of preventive medicine at Ohio State, said in a news release.

“To have been taken down by exsanguination by ticks, you can imagine that was tens of thousands of ticks on one animal,” said Pesapane.

The ticks feed mainly on deer and raccoons but have also been found on dogs and cats, cattle sheep, goats, horses, squirrels, rabbits, skunks, opossums and groundhogs.

Range

Samples of the Asian longhorned tick have been found in 17 states. They're predominantly along the eastern seaboard, though they've ranged out to the midwest. Locations include Connecticut, New Jersey, Pennsylvania, Delaware, New York, Ohio, West Virginia, Virginia, Kentucky, Tennessee, Maryland, North Carolina, South Carolina, Georgia, Missouri, Arkansas, and Massachusetts.

Researchers estimated there were about 1 million longhorned ticks in the pasture of about 25 acres where the cattle that died had been grazing. A pesticide application in 2021 eradicated the ticks, but they returned a year later.

CAES continues to monitor the tick’s presence and encourages residents to take preventive measures to reduce the risk of bites, including using insect repellents, checking for ticks after outdoor activity, and keeping yards free of tall grass and brush.

“The good news about the ticks, though, is that most tick control agents that we currently have seemed to kill them,” Pesapane said. “Still, managing them is not easy because of how numerous they are and how easily they can come back.”

Pesticide applications have limits, though. Asian longhorned ticks hide easily in vegetation, and unless the pesticide is applied directly to the insect, they’re likely to survive.

The best recourse is to target them early in the growing season when adults become active again, but before they lay eggs.

“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.

With reporting from Michelle-Rotuno Johnson