For the first time in 50 years, a new tick species has arrived in the United States — one that in its Asian home range carries fearsome diseases.
The Asian long-horned tick, Haemaphysalis longicornis, is spreading rapidly along the Eastern Seaboard. It has been found in seven states and in the heavily populated suburbs of New York City.
At the moment, public health experts say they are concerned, but not alarmed.
Although domestic American ticks are a growing menace and transmit a dozen pathogens, no long-horned ticks here have yet been found with any human diseases. In Asia, however, the species carries a virus that kills 15 percent of its victims.
For now, the new arrivals are considered a greater threat to livestock.
Known in Australia as bush ticks and in New Zealand as cattle ticks, long-horned ticks can multiply rapidly and suck so much blood from a young animal that it dies. The ticks bloat up like fat raisins until their tiny legs are barely able to support them.
After a blood meal, females can lay hundreds of fertile eggs without mating.
“One tick can crank out females in fairly large numbers,” said Thomas Yuill, a retired pathobiologist at the University of Wisconsin, Madison, who was one of the first to raise alarms about the invaders.
The first long-horned tick was found last summer in western New Jersey. This summer they were collected in public parks and a golf course in Bergen, Union and Middlesex counties in New Jersey, and in wooded and grassy areas of New York’s Westchester County.
They were reported in Pennsylvania for the first time last week, and have been sighted in Arkansas, North Carolina, Virginia and West Virginia.
They were found feeding on horses, dogs, deer, a calf, a sheep and an opossum. They do bite humans, but it is not clear how often.
People should use the same precautions they do against domestic ticks, experts said, such as using repellents and checking for ticks after walking through woods or tall grass.
Tadhgh Rainey, an entomologist at the public health department of Hunterdon County, N.J., found the first long-horned ticks in the country last August, when a woman who had been shearing her pet Icelandic sheep came to his department with ticks on her hands and wrists.
“I thought she’d have a few,” Mr. Rainey said in an interview. “But she was covered in them, easily over 1,000 on her pants alone.”
Most were young nymphs about the size of dust specks. “She had a change of clothes in her car, so we put her clothes in the freezer to kill them,” Mr. Rainey recalled.
The ticks didn’t match any North American pests, and initially he could not identify them. The woman’s 12-year-old sheep was penned alone and had never traveled, so where they came from remained a mystery.
A month later the woman called again to see if he had figured out what they were, and Mr. Rainey drove out to see the animal for himself. “A minute after we entered the paddock, even before I touched the sheep, I was covered in ticks,” he said.
The sheep was weak from blood loss, so he gave the owner some insecticidal livestock wash. The grass around the paddock was later cut and the area sprayed in an effort to eliminate the outbreak.
Andrea Egizi, an entomologist at Rutgers University, finally identified the longhorns by DNA analysis. Her lab has now tested more than 100 specimens found in New York and New Jersey.
Thus far, Dr. Egizi said, none have any of the pathogens causing the six diseases she screens for: Lyme disease, relapsing fever, babesiosis, anaplasmosis and two varieties of ehrlichiosis.
The Centers for Disease Control and Prevention lab in Fort Collins, Colo., has screened about 100 long-horned ticks for three dangerous viruses — Powassan, Heartland and Bourbon — and all came up negative, said Ben Beard, the agency’s deputy director of vector-borne diseases.
The lab now has 10 live long-horned ticks and is feeding them to create a colony, Dr. Beard said. That will take about a year, and then researchers can determine whether they can transmit Rocky Mountain spotted fever and other diseases.
In East Asia, long-horned ticks do carry pathogens related to Lyme and others found in North America. But the biggest threat is a phlebovirus that causes S.F.T.S., for severe fever with thrombocytopenia syndrome. (Thrombocytopenia means abnormally low levels of platelets, which help the blood clot; a severe drop triggers internal bleeding and organ failure.)
However, the syndrome is not found in Australia or New Zealand, earlier stops for the long-horned ticks as they spread from Asia. In those countries, they cause babesiosis and theileriosis in cattle but are mostly “of nuisance value” to humans, said Dr. David Thomson, a veterinarian in Queensland, Australia.
It’s not clear that the S.F.T.S. virus, which is related to the Heartland virus found in a number of American states, could get established in this country, because its transmission cycle is unknown — it may need more than one host.
(Although West Nile virus, for example, is transmitted to humans by mosquitoes, they first get it from birds, because humans do not build up enough of the virus to pass on.)
It’s not known when or how long-horned ticks reached the United States, nor why the species is spreading so fast now.
They bite birds, but Mr. Rainey said he suspected they originally arrived on a large animal. As far back as 1960, he said, the ticks were found on a horse held in quarantine.
One collected in 2013, Dr. Beard said, was misidentified until recently as a rabbit tick, which is also in the Haemaphysalis genus.
In theory, just one female could have produced all the long-horned ticks spreading in the country through asexual reproduction. But Dr. Egizi said she has found three mitochondrial DNA lineages, meaning at least three females arrived.
Although experts said having a new invader is unsettling, they worry more about deer ticks, lone star ticks and other established species whose ranges are growing as winters get warmer.
Cases of the illnesses they transmit — everything from Lyme disease to alpha-gal syndrome, an allergy to red meat — are rapidly increasing. Even in Asia, only about 1 percent of long-horned ticks have the S.F.T.S. virus; in parts of this country, 25 percent of deer ticks carry Lyme disease.
“The jury’s still out on how big a threat this is,” Dr. Beard said. “But we think it’s a very important question to address.”
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