The Asian longhorned tick most likely began invading the United States years ago. Now found in nine states, the tick may soon occupy a large swath of eastern North America as well as coastal regions of the Pacific Northwest, according to research published Thursday in the Journal of Medical Entomology.
"This tick can bite humans, pets, farm animals and wildlife," said Ilia Rochlin, author of the study and an entomologist and researcher associated with the Rutgers University Center for Vector Biology.
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Until recently, this species was found only in China, Japan, Korea and southeastern Russia as well as in parts of Australia, New Zealand and the Pacific islands. Then, in 2017, the first established Asian longhorned tick population was discovered in New Jersey, followed by detections in Virginia, West Virginia, Pennsylvania, North Carolina and Arkansas.
Although the tick is capable of causing infectious disease, no cases of illness, either in humans or in animals, have been reported in the United States.
"There is a good chance for this tick to become widely distributed in North America," Rochlin said. "Mosquito control has been very successful in this country, but we are losing the battle with tick-borne diseases."
Unusual reproductive abilities
Dina M. Fonseca, director of the Center for Vector Biology, a Rutgers professor of entomology and co-author of a previous report published by the US Centers for Disease Control and Prevention, explained the Asian longhorned tick's strange capacity to reproduce asexually.
"These ticks are parthenogenetic, which means that females create diploid eggs (with a full set of the mother's DNA) that develop into adults without needing the DNA of a male," she wrote in an email. (Fonseca did not contribute to the new study.)
Of nearly 700 species of "hard" ticks -- of which the Asian longhorned tick is one -- only a handful are known to be parthenogenetic. "So it is a rare ability but not exceptional," said Fonseca. This unusual method of creating clones means it is possible for the tick to cause "massive" infestations of its hosts. "We have seen very large numbers on livestock as well as on dogs."
One of the diseases Asian longhorned ticks can transmit is severe fever with thrombocytopenia syndrome, a hemorrhagic illness that has recently emerged in China, South Korea and Japan, according to the previous CDC report.
This syndrome, which also causes nausea, diarrhea and muscle pain, results in hospitalization for most patients and leads to death for up to nearly a third of those infected. This possibility is a concern because a close relative of the illness, the Heartland virus, circulates in Midwestern and Southern states, Rochlin noted.
In Australia and New Zealand, the Asian longhorned tick has transmitted theileriosis to cattle. Also called "bovine anemia," the illness causes lethargy, lack of appetite and, in pregnant cows, spontaneous abortion or stillbirth. "In some regions of New Zealand and Australia, this tick can reduce production in dairy cattle by 25%," the CDC report says.
'Where could it go or where could it be?'
Because the tick has been found in widely separate regions of the United States, Rochlin believes that it "has been present in the United States for a number of years" and is likely to gain additional ground. For his new study, he modeled likely habitats in North America.
He looked at climate data from Asia, Australia and New Zealand where the tick is established and then compared that with climate reports for North America.
The most suitable habitat for the tick included coastal areas as far north as New Brunswick and Nova Scotia to as far south as Virginia and North Carolina, Rochlin found. On the West Coast, the coastal area where the tick is likely to survive ranged from southern British Columbia to Northern California.
Large inland swaths might also become home to this tick: from northern Louisiana to Wisconsin and into southern Ontario and Quebec, as well as westward into Kentucky, Tennessee and Missouri, his study showed.
Asian longhorned ticks can become "very abundant" in favorable habitats, Rochlin said. "Coupled with the aggressive biting behavior of this species and its potential for carrying human and animal pathogens, this species represents a significant public health concern."
Putting the Asian longhorned tick in perspective
Erika Machtinger, an assistant professor of entomology in Pennsylvania State University's College of Agriculture, said what's "wonderful" about the new study is that it gives the "information everybody's wanting to know: Where could it go, or where could it be?"
Machtinger, who was not involved in the new research, said she likes to "put these scary new things in perspective. The Zika virus was one of those."
"When you think about the native pathogens that we have here that are a problem, Zika virus was a blip on the radar," Machtinger said of Zika concerns in mainland United States during 2016. The native pathogen of Lyme disease infects about 320,000 people every year and "can cause mortality. It can cause serious debilitating affects," she said. "That's a problem. This [tick] is something we need to be aware of and continue to monitor, but people don't need to be afraid of this."
Because there have been few instances of this tick feeding on humans, the bigger concern may be cows and other veterinary issues, Machtinger said. Still, she did not downplay the threat entirely because this is the first introduction of an invasive tick that the United States has seen in 80 years, she said.
Very similar to the rabbit rick, the bird tick and other native species, the Asian longhorned tick was "overlooked for quite a few years," said Machtinger, who believes that it may have been here since 2010 or even earlier. "That's the important piece: It's here, but it's been here," she said. "And it's not going to take over the northeast or eastern part of the US quickly if it does build up numbers."
Although its ability to clone itself means a tick can easily produce a couple thousand eggs, "so can our native black-legged ticks," Matchinger said. Ultimately, she said, the Asian longhorned tick may be no more scary than some native species.
Rochlin said this tick species infiltration of the United States "strengthens the need to develop a comprehensive strategy for tick control and tick-borne disease prevention." He added the best defense for those who are worried is to practice "the usual precautions against tick bites recommended by the CDC," such as treating clothing and gear with products containing 0.5% permethrin and checking your body for ticks after being outdoors.
Machtinger advised, "be diligent in protecting yourself and your animals." And, if you happen to find a tick you've never seen before, bring it to a veterinarian or a university and ask for help.
"We rely on our community scientists," she said. "We rely on folks who are out there and find weird things on their animals that they haven't seen before to bring it [in] and say, 'Where can I get this identified? Can you help me?' "
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