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21st of July 2018

Science



This invasive tick can clone itself and suck livestock dry

Tadhgh Rainey has seen his share of bloodsuckers. As an entomologist at the Hunterdon County Health Services in Flemington, N.J., he’s the person to talk to about all things mosquitoes and ticks. But he had never seen anything like the infestation on a pet sheep in September 2017.

When he and his colleague entered the sheep’s enclosure, “we almost immediately got covered in ticks,” he says. “I couldn’t believe this sheep was alive.” It was covered in hundreds, maybe thousands, of ticks.

Unable to identify the ticks, Rainey sent samples to labs across the country. One went to Andrea Egizi, an entomologist at Rutgers School of Environmental and Biological Sciences in New Brunswick, N.J. Egizi analyzed the tick’s DNA, and was shocked when the identification came back as Haemaphysalis longicornis, a native of East Asia.

Known as the longhorned tick or bush tick, H. longicornis is ubiquitous in Japan, China and the Korean Peninsula. The New Jersey sheep was the first documented sighting in the continental United States, say Rainey and Egizi, who published their findings online February 19 in the Journal of Medical Entomology.

Scientists say that it is rare to find an invasive tick species in the wild. And this one seems to be spreading. It has been discovered in at least three more states — Virginia, West Virginia and Arkansas — and warnings have been issued for Maryland. 

Here are five reasons why scientists are keeping an eye on this sneaky invader.

1. This tick can clone itself.

After a female longhorned tick feeds, she will lay up to 2,000 genetically identical eggs. Two to three months later, the eggs hatch without any male fertilization, and become mini copies of their mom. It is unclear how many ticks practice this rare form of asexual reproduction called parthenogenesis; so far, scientists have found fewer than 20 that reproduce this way, out of more than 800 tick species worldwide.

The process is “pretty alarming,” says medical entomologist Neeta Connally at West Connecticut State University in Danbury. That’s because parthenogenesis happens faster than traditional mating — about six months for the longhorned tick, compared with the two-year reproduction cycle of common American ticks such as the deer tick and lone star tick.  Researchers worry that this rapid cloning could lead to heavier tick infestations in short periods of time. The female longhorned tick can focus on feeding, reproducing and traveling, without worrying about finding a mate. “She’s one of the first feminists,” jokes Allen Heath, a parasitologist at the Hopkirk Research Institute in Palmerston North, New Zealand.

2. It’s not a picky eater. Some ticks, like the rabbit tick or moose tick, have specialized hosts and won’t feed on other animals. Other ticks, like the longhorned tick, rarely meet a blood type they don’t like. The longhorned tick will chow down on any bird or mammal it can get its hooks into — including humans (SN: 11/16/13).3. It can carry human diseases.

While no human bites have been reported in the United States yet, the longhorned tick is a significant public health threat in its native East Asia. In China, Japan and Korea, the tick is a known carrier of several viruses and bacteria that can infect humans. Recently, it has been linked to a disease called severe fever with thrombocytopenia syndrome (SFTS), which causes severe hemorrhaging and has a mortality rate of more than 5 percent. 

SFTS isn’t in the United States, but researchers worry that the longhorned tick may be able to adapt to transmit local tick-borne diseases. Of particular concern is Lyme disease, but other potentially fatal diseases that cause neurological problems are also worrying, including ehrlichiosis, anaplasmosis, Rocky Mountain spotted fever and Powassan virus (SN: 9/16/17, p. 8). 

4.  It’s a big threat to livestock.

At least for now, it seems cows and sheep should be more afraid of the tick than people. The longhorned tick is great at transmitting the deadly cattle disease theileriosis. Heavy infestations of the critters have also been known to suck so much blood from a single animal that it dies, a vampiric practice called exsanguination.

“Keep an eye on your animals,” warns Denise Bonilla, an entomologist at the U.S. Department of Agriculture Animal and Plant Inspection Service in Fort Collins, Colo. Farmers in affected areas should keep their animals on tick treatments if needed, she says.

5. This tick is probably more widespread than we realize.

Researchers have no idea how the tick got to the United States, or how it’s been traveling within the country. Theories include hitching rides on birds or horses. We do know the tick had been in the country for several years before it was discovered last September. After that, a Rutgers graduate student tested an old tick from a 2013 sample found in New Jersey. It also turned out to be a longhorned tick, misidentified at the time as a native rabbit tick. The similar-looking longhorned tick and rabbit tick are from the same Haemaphysalis genus.

Egizi says she is not surprised the longhorned tick has been found in multiple places, considering it had gone undetected for years. “The more we look for it, the more we’ll find it,” she says.

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