First Documented Bite by Asian Longhorned Tick in the U.S.

By Will Boggs MD

June 29, 2019

NEW YORK (Reuters Health) - A tick brought in by the man in New York State it bit turned out to be an Asian longhorned tick, a vector in Asia for the bunyavirus severe fever with thrombocytopenia syndrome virus (SFTSV).

"We were very surprised to document that the patient was bitten by this particular tick species which was not known at the time to even exist in our state," Dr. Gary P. Wormser from New York Medical College, in Valhalla, told Reuters Health by email. "In addition, his exposure was more in an urban environment than a rural one."

The Asian longhorned tick was first detected in the U.S. on a sheep in New Jersey that had not traveled outside the U.S. It has now been detected in 10 states.

Dr. Wormser's team reports the case of the first human recognized to have been bitten by this tick in the U.S. and presents the results of subsequent field studies conducted near his home in a report online May 31 in Clinical Infectious Diseases.

In June 2018, the 66-year-old man removed a tick attached to his right leg and brought it to the Lyme Disease Diagnostic Center in Westchester County, New York, for identification. He had not traveled outside of Westchester County within the prior 30 days and had no exposure to farm animals. He was asymptomatic at the time of the encounter and did not develop a clinical illness over the following three months.

The tick was ultimately identified as a nymphal stage Asian longhorned tick (Haemaphysalis longicornis).

Tick sampling of the patient's lawn collected a total of four H. longicornis ticks (three nymphs and one female), all on manicured lawn. Sampling of a nearby park collected 11 Asian longhorned ticks on the first date and 14 on the second (in open, cut grass exposed to direct sun, as well as in shade and taller grass adjacent to woods). Another 61 Asian longhorned ticks were recovered from a nearby trail.

These sampling findings suggest that public health messages may need to be changed, at least in certain geographic areas, to emphasize a wider range of potential tick habitats, the researchers note.

Dr. Wormser recommends keeping ticks responsible for human bites.

"If a person is anywhere near our Lyme Disease Diagnostic Center, located at 19 Bradhurst Avenue in Hawthorne, NY, and brings the tick to us as soon as possible, we can evaluate the tick to determine the species and, if it's the deer tick, how long it was on the person. No tick in our area besides the deer tick can transmit Lyme disease. And if the tick was on the person less than 36 hours, there is essentially also no risk of Lyme disease. In other geographic areas, bring the tick to the person's primary provider, an urgent care facility, or an ER, but the expertise in these facilities in identifying ticks may be more variable."

"Tick bites are very anxiety provoking," he said. "If the tick is identified as a tick that is not the deer tick, it eliminates concern about getting Lyme disease and the bite does not warrant antibiotic prophylaxis with single dose doxycycline."

"An important lesson also is that additional tick species may be emerging in geographic areas in the U.S., even in suburban New York City," Dr. Wormser said. "Whether the longhorned tick may transmit any infections to humans in the U.S. is not known at present."

Dr. Bobbi S. Pritt from Mayo Clinic, in Rochester, Minnesota, who wrote a linked editorial, told Reuters Health by email, "Wormser's report is important in that it officially documents a human bite and thus raises awareness of the potential risk that this tick poses. We definitely need to monitor the population of the Asian longhorned tick in the United States and conduct surveillance for pathogens that it may carry."

"Prevention is key," she said. "Ticks are now widespread in the United States, and many continue to expand their ranges. We also continue to discover new bacterial and viral pathogens that are transmitted through tick bite. The Asian longhorned tick is just one of many potential threats. Therefore, people need to take steps to avoid tick bites, including regular use of tick repellents when outdoors, and checking themselves and family members (including pets) for ticks when they come inside."

"Physicians can help spread this message to their patients by providing accurate information about tick bite prevention and the pathogens that ticks carry," Dr. Pritt said. "Finally, if a tick-borne disease is suspected, physicians should send specimens to laboratories that use FDA-approved tests when available and avoid tests using unproven methods or for unproven pathogens."

Dr. Ilia Rochlin from the Center for Vector Biology at Rutgers University, in New Brunswick, New Jersey, who recently reviewed pathogens transmitted by ticks, "Different tick species carry different pathogens. Some of the stages of the tick lifecycle are low risk for pathogen transmission. For example, lone-star tick larvae can be very numerous and bite people readily, but they don't transmit diseases. Yet others, such as deer tick nymphs, can harbor multiple pathogens."

"The present study illustrates this point," he told Reuters Health by email. "Asian longhorned ticks do not transmit bacterial pathogens, so the patient was prescribed doxycycline unnecessarily. These errors can be avoided with proper tick identification."

"Ticks are becoming a very significant public-health problem in many parts of the U.S. and the world," said Dr. Rochlin, who was not involved in the new report. "Physicians should familiarize themselves with different species of ticks and tick-borne pathogens, especially those endemic in the geographic area of their practice. They can find help and additional resources at state and local public-health and vector-control agencies, such as health departments, university extensions, and mosquito-control districts."

"The burden of tick-borne diseases has increased tremendously over the last few decades," he added. "Addressing each pathogen individually with a vaccine or medication will not solve the problem. Only a comprehensive and integrated approach targeting the tick vectors, as well as their main host species - deer - can lead to significant reductions in tick populations and pathogens they transmit."

Dr. Danielle M. Tufts of Columbia University, in New York City, who also was not involved in the new report, has studied the distribution of Asian longhorned ticks on Staten Island.

"I think the most alarming thing about the article is that we are finding H. longicornis biting people in the U.S.," she told Reuters Health by email. "This is the first reported case, but we know that H. longicornis has bitten at least three other people, and our field crews have been finding them on themselves this summer."

"It is important for the public to be aware of this threat," she said. "While no pathogens have been found in the H. longicornis individuals sampled to date, there is still the possibility of them acquiring pathogens in the U.S., such as Borrelia, Babesia, Rickettsia, etc."


Clin Infect Dis 2019.


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