Maine tick experts are keeping an eye out for the Asian longhorned tick, a foreign tick species that can reproduce without mating and has been documented as close as Connecticut.
Reported for the first time in the United States in 2017, this tick species has now established populations in at least 12 states, all of which are in the northeastern half of the country.
“It’s certainly something that is on every tick researcher’s radar here in the eastern United States,” said Griffin Dill, who manages the Tick Lab, located in the new UMaine Cooperative Extension Diagnostic and Research Laboratory in Orono. “This species seems to primarily reproduce through parthenogenesis, which makes its ability to increase its population size rapidly an important factor.”
Parthenogensis is a form of asexual reproduction in which growth and development of embryos occur without fertilization by sperm. Female Asian longhorned ticks can lay eggs, which will develop and hatch on their own. Because of this, a single female tick can establish a fast-growing population.
The Asian longhorned tick is known to carry and transmit a variety of dangerous diseases in its home range in Asia, but those diseases have yet to be documented in the Asian longhorned tick populations found in the U.S. However, there is a concern that the species could pick up and transmit diseases that already occur in the U.S. in other tick species, such as anaplasmosis, babesiosis and Powassan virus.
“There are a couple of pathogens in Asia that they are believed to transmit that are closely related to pathogens we have here, so it’s possible,” said Dill. “But from what we’ve seen so far in other states, [the tick’s] risk to humans is thought to be relatively low at the moment. And we haven’t seen indication that it’s able to contribute to the transmission of Lyme disease.”
In the U.S., East Asia and other areas where this tick has been found, such as New Zealand and Australia, it is considered to be a serious threat to livestock such as cattle and sheep. Major infestations can cause stress on an animal, reducing its growth and production. And in some cases, infestations can kill animals due to blood loss.
“From limited studies that have been done on this species, they do seem to prefer feeding on animal hosts as opposed to humans,” Dill said.
A new study in the journal Zoonoses and Public Health, published earlier this month, investigates the origin of this tick species and how they are spreading across the country.
Researchers gathered samples of Asian longhorned ticks across the U.S. and internationally, then used gene sequencing to compare various populations. The results indicate that at least three individual ticks from self-cloning populations were somehow transported to the U.S., and this explains why all adult Asian longhorned ticks found in the U.S. so far have been female. With Asian longhorned ticks that reproduce through parthenogenesis, male offspring are rare.
(In Asia, male Asian longhorned ticks do exist in some populations where they participate in reproduction.)
The study also found that these “original” ticks most likely came from East Asia.
While the first established Asian longhorned tick population in the U.S. was documented in New Jersey in 2017, researchers believe the species had been flying under the radar in the country for several years.
“There’s a whole lot we don’t know about it,” said Chuck Lubelczyk, vector ecologist at Maine Medical Center Research Institute. “Right now, the states where it’s occurring tend to be doing a lot more research on it [than other states], and I think a lot more research is going to be done on it as time goes by. It’s a public health issue that’s been introduced to the country and we weren’t really talking about it before it arrived here. We were kind of unprepared for it.”
It’s believed that the tick species can easily be spread by wildlife, as well as the transportation of livestock and domestic animals, such as dogs.
“There are some pretty good regulations in place in terms of livestock transport,” Lubelczyk said. “But it certainly speaks to people needing to be vigilant about tick control medicines for their dogs and other domestic animals.”
In the U.S., Asian longhorned ticks have been collected from deer, dogs, raccoons, cats, opossums and a number of other warm-blooded animals, as well as a variety of birds, according to data collected by the U.S. Department of Agriculture. They’ve also been found feeding on people.
Because of the wide geographical range that the species already inhabits, Lubelczyk believes it could survive Maine’s climate, even the state’s cold winters.
“At least in southern Maine, I don’t think it’d have a problem,” Lubelczyk said. “How it would do up in northern Maine? I don’t have a guess.”
Moving forward, tick experts ask that Maine people be on the lookout for this invasive tick species; however, they’re difficult to identify. Adults are plain brown but can look similar to brown dog ticks and rabbit ticks, both of which live in Maine.
Researchers from the Maine Tick Lab and Maine Medical Center Research Institute are looking for Asian longhorned ticks, as well as the lone star tick (which has been found in Maine, but not yet in breeding populations), when conducting on-the-ground tick surveillance throughout the state.
In addition, they receive information about tick populations in Maine from the public sending tick samples to the Maine Tick Lab in Orono. The lab identifies these tick samples for free, and for an additional fee of $15 will test deer ticks for three common diseases they carry: Lyme disease, babesiosis and anaplasmosis. For more information, visit extension.umaine.edu/ticks.