Invasive ticks are spreading without any males

Adult female Asian longhorned ticks attached to vegetation and waiting for a host to come by. (Credit: Jim Occi)

The invasive population of Asian longhorned ticks in the United States likely began with three or more self-cloning females from northeastern Asia, according to a new study.

Asian longhorned ticks outside the US can carry debilitating diseases. In the US and elsewhere they can threaten livestock and pets. The new study in the journal Zoonoses and Public Health sheds new light on the origin of these ticks and how they are spreading across the country.

“While additional samples from the tick’s native range are needed to pinpoint more exactly the source of the US introduction, our data suggest that they came from one or more locations in northeastern Asia—either through a single introduction of at least three ticks or as multiple introductions from different populations,” says lead author Andrea M. Egizi, a visiting professor in the entomology department at Rutgers University-New Brunswick and a research scientist with the Monmouth County Tick-borne Diseases Laboratory that the Rutgers Center for Vector Biology hosts.

In 2017, the Rutgers Center for Vector Biology and other researchers detected an infestation of the Asian longhorned tick (Haemaphysalis longicornis), which is native to East Asia, in New Jersey. It was the first time established populations of this species had been detected in the US. Subsequent investigations found the tick to be widespread in the eastern US. Researchers discovered it has been present in New Jersey since at least 2013.

Although this species transmits serious illnesses to people and animals in other countries, experts don’t know whether the tick populations in the United States will make people sick, according to the US Centers for Disease Control and Prevention.

The species has two forms: one with males and females, and one with self-cloning females that lay eggs without needing to mate, a process called parthenogenesis. The self-cloning form, free from the need to look for mates, is especially likely to thrive and spread. A single female can establish a fast-growing population. This type entered Australia and New Zealand in the early 1900s, and now causes significant losses in the cattle industry.

The researchers enlisted about 25 collaborators at 20 institutions to get samples of Asian longhorned ticks across the US and internationally, and used gene sequencing to detect genetic similarities and differences among various populations.

Their findings indicate that at least three individual ticks, from self-cloning populations, were brought to the United States, which explains why all adult Asian longhorned ticks found in the US so far have been female. Overall, US ticks are more likely to have come from an East Asian country (or countries) than from Australia and New Zealand.

As part of the study, the US Department of Agriculture Animal and Plant Health Inspection Service, Veterinary Services found evidence that these ticks traveled within the United States on wildlife as well as through the transport of pets or livestock.

“One thing we uncovered is the ease with which pets, especially dogs, can accidentally help ticks cross international borders and state lines,” says senior author Dina M. Fonseca, a professor and director of the Center for Vector Biology.

“Many countries require dogs to be treated for ticks and other parasites before entering the country, but the United States does not. We urge greater awareness of this issue to prevent future exotic tick introductions.”

Source: Rutgers University