An Asian, self-cloning tick threatens U.S. livestock | Science News for Students

An Asian, self-cloning tick threatens U.S. livestock

In its native range, this arachnid spreads dangerous human diseases
Jul 24, 2018 — 6:45 am EST
a photo of a longhorned tick adult and nymph dwarfed by the edge of a dime

Scientists have discovered the longhorned tick in four U.S. states. This species can reproduce by cloning. Here, an adult and a young tick, or nymph, are shown next to a dime.

J. Occi/Rutgers Center for Vector Biology

Tadhgh Rainey has seen plenty of bloodsuckers. He’s an entomologist — a scientist who studies insects — at the Hunterdon County Health Services in Flemington, N.J. He knows all about mosquitoes and ticks. But he had never seen anything like the September 2017 infestation on a pet sheep.

As he and a 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 the ticks. (By the way, ticks are arachnids, not insects.)

Rainey couldn’t identify the species. So he sent samples to labs across the United States. One went to Andrea Egizi. She’s an entomologist at Rutgers School of Environmental and Biological Sciences in New Brunswick, N.J. When she analyzed its DNA, she was shocked to learn it was a native of East Asia.

This bush or longhorned tick has a long name too: Haemaphysalis longicornis (HEE-muh-fih-SAAL-is Lon-jih-KOR-nis). It can be found all over Japan, China and the Korean Peninsula. That unlucky New Jersey sheep was the first reported sighting of the tick in the continental United States, say Rainey and Egizi. They described their finding online February 19 in the Journal of Medical Entomology.

It’s rare to find a new immigrant tick species in the wild, scientists say. And this one seems to be spreading. It has so far also turned up in Virginia, West Virginia and Arkansas. People in Maryland are now on the lookout. 

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

1. This tick can clone itself.

After a female longhorned tick eats, she can lay up to 2,000 eggs. All have the exact same DNA as their mom. Two to three months later, the eggs hatch without any male fertilization. They grow into exact mini copies of their mom.

This rare way of reproducing without the genetic influence of a male is called parthenogenesis (Par-then-oh-JEN-eh-sis). Of the world’s more than 800 tick species, fewer than 20 appear able to reproduce this way.

Neeta Connally is a medical entomologist at West Connecticut State University in Danbury. She finds this process of reproducing is “pretty alarming.” Why? It creates a new generation of young far faster than with traditional mating. Longhorned ticks can reproduce in just six months. By contrast, common American ticks, such as the deer tick and lone star tick, need two years.

Researchers worry that this rapid cloning could lead to heavier tick infestations in short periods of time. The female longhorned tick doesn’t need to worry about finding a mate. She can focus on feeding, traveling and making more babies.

2. It’s not a picky eater.

Some ticks, such as the rabbit tick or the moose tick, specialize in just one type of host. They won’t feed on other animals. The longhorned tick is different. It rarely meets a blood source that doesn’t look appetizing. It will chow down on any bird or mammal it can get its hooks into — including humans.

3. It can carry human diseases.

No human bites have been reported in the United States thus far. But in its home range, this tick has proven a major public health threat. In China, Japan and Korea, for instance, it can carry any of several viruses and bacteria that infect people. Recently, this tick has been linked to a disease known as SFTS. That’s short for severe fever with thrombocytopenia (Throm-boh-sy-toh-PEE-nee-uh) syndrome. This disease causes dangerous bleeding. More than five in every 100 people who get this syndrome die from it. 

SFTS has not shown up in the United States. But researchers worry that the immigrant tick might adapt to carry the diseases that native U.S. ticks do. Lyme disease is one. Lyme disease can give people flu-like symptoms. It also leaves them with a rash shaped like a bull’s-eye. And there are potentially fatal tick diseases that can affect the nerves and brains in people. These include ehrlichiosis (Air-lik-ee-OH-sis), anaplasmosis (An-uh-plas-MOH-sis), Rocky Mountain spotted fever and Powassan virus. 

a photo of hundreds of ticks attached to the inside of the ear of a sheep
Hundreds of ticks, young and old, were found on the ear of a New Jersey sheep.
Tadhgh Rainey/Hunterdon Country Health Services

4.  It’s a big threat to livestock.

At least for now, this tick poses the greatest risk to cows and sheep. The arachnid is great at transmitting the deadly cattle disease theileriosis (Thy-LEER-ee-OH-sis). Heavy infestations of the critters have also been known — like a vampire attack — to suck so much blood from a single animal that it dies.

“Keep an eye on your animals,” warns Denise Bonilla. She’s an entomologist at the U.S. Department of Agriculture Animal and Plant Inspection Service in Fort Collins, Colo. If farmers in affected areas are already giving their animals anti-tick medications, they should keep doing it, she says.

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

Researchers have no idea how and when the tick first got to the United States. They also don’t know how it’s been traveling within the country. It may, for instance, hitch rides on birds or horses.

Evidence shows the tick had already been in the United States before the New Jersey sheep infestation was discovered last September. After finding the ticks on that sheep, a Rutgers graduate student tested a tick collected in New Jersey in 2013. It also turned out to be a longhorned tick. Four years earlier, it had been misidentified as a native rabbit tick.

Considering the longhorned tick went undetected for years, Egizi is not surprised it has turned up in multiple states. “The more we look for it, the more we’ll find it,” she suspects.

Power Words

(for more about Power Words, click here)

agriculture     The growth of plants, animals or fungi for human needs, including food, fuel, chemicals and medicine.

arachnid     A group of invertebrate animals that includes spiders, scorpions, mites and ticks. Many have silk or poison glands.

bacteria     (singular: bacterium) Single-celled organisms. These dwell nearly everywhere on Earth, from the bottom of the sea to inside other living organisms (such as plants and animals).

bush     (in landscape descriptions) The name for wild lands in certain countries, especially parts of Africa and Australia.

cattle     Also known as bovines (because they’re members of the subfamily known as Bovinae), these are breeds of livestock raised as a source of milk and meat. Although the adult females are known as cows and the males as bulls, many people refer to them all, generally, as cows.

clone     An exact copy (or what seems to be an exact copy) of some physical object. (in biology) An organism that has exactly the same genes as another, like identical twins. Often a clone, particularly among plants, has been created using the cell of an existing organism. Clone also is the term for making offspring that are genetically identical to some “parent” organism.

colleague     Someone who works with another; a co-worker or team member.

DNA     (short for deoxyribonucleic acid) A long, double-stranded and spiral-shaped molecule inside most living cells that carries genetic instructions. It is built on a backbone of phosphorus, oxygen, and carbon atoms. In all living things, from plants and animals to microbes, these instructions tell cells which molecules to make.

egg     The unfertilized reproductive cell made by females.

entomology     The scientific study of insects. One who does this is an entomologist.

flu     Short for influenza. A highly contagious viral infection of the respiratory passages causing fever and severe aching. It often occurs as an epidemic.

generation     A group of individuals (in any species) born at about the same time or that are regarded as a single group. Your parents belong to one generation of your family, for example, and your grandparents to another. Similarly, you and everyone within a few years of your age across the planet are referred to as belonging to a particular generation of humans.

genetic     Having to do with chromosomes, DNA and the genes contained within DNA. The field of science dealing with these biological instructions is known as genetics. People who work in this field are geneticists.

graduate student     Someone working toward an advanced degree by taking classes and performing research. This work is done after the student has already graduated from college (usually with a four-year degree).

immigrant    (v. immigration) Someone that leaves the nation of his or her birth to live in another country. The term can also loosely be applied to a species that moves far beyond its home range.

infect     To spread a disease from one organism to another. This usually involves introducing some sort of disease-causing germ to an individual.

infestation     A parasitic community of pests, such as when wasps make their home on the porch of an abandoned house.

insect     A type of arthropod that as an adult will have six segmented legs and three body parts: a head, thorax and abdomen. There are hundreds of thousands of insects, which include bees, beetles, flies and moths.

journal     (in science) A publication in which scientists share their research findings with experts (and sometimes even the public). Some journals publish papers from all fields of science, technology, engineering and math, while others are specific to a single subject.

livestock     Animals raised for meat or dairy products, including cattle, sheep, goats, pigs, chickens and geese.

mammal     A warm-blooded animal distinguished by the possession of hair or fur, the secretion of milk by females for feeding their young, and (typically) the bearing of live young.

native     Associated with a particular location; native plants and animals have been found in a particular location since recorded history began. These species also tend to have developed within a region, occurring there naturally (not because they were planted or moved there by people). Most are particularly well adapted to their environment.

nerve     A long, delicate fiber that transmits signals across the body of an animal. An animal’s backbone contains many nerves, some of which control the movement of its legs or fins, and some of which convey sensations such as hot, cold or pain.

online     (n.) On the internet. (adj.) A term for what can be found or accessed on the internet.

parthenogenesis     An unusual form of reproduction where animals sometimes produce healthy offspring from an unfertilized egg.

peninsula     A parcel of land that is that is attached to the mainland but surrounded by water on three sides.

range     The full extent or distribution of something. For instance, a plant or animal’s range is the area over which it naturally exists.

risk     The chance or mathematical likelihood that some bad thing might happen. For instance, exposure to radiation poses a risk of cancer. Or the hazard — or peril — itself. (For instance: Among cancer risks that the people faced were radiation and drinking water tainted with arsenic.)

species     A group of similar organisms capable of producing offspring that can survive and reproduce.

symptom     A physical or mental indicator generally regarded to be characteristic of a disease. Sometimes a single symptom — especially a general one, such as fever or pain — can be a sign of any of many different types of injury or disease.

syndrome     Two or more symptoms that together characterize a particular disease, disorder or social condition.

theileriosis     An infectious disease caused by a protozoan belonging to the genus Theileria.

thrombocytopenia     A condition that leads to excessive bleeding. It’s caused by a shortage of platelets, needed for blood clotting. Symptoms include excessive bruising and a very slow clotting of the blood following some injury.

tick     A small eight-legged blood-sucking arthropod, related to spiders and mites. Although they look like bugs, these are not insects. They attach themselves to the skin of their host and feed on their blood. But in the process, they may spread any germs that could have been present in the blood of an earlier host.

virus     Tiny infectious particles consisting of RNA or DNA surrounded by protein. Viruses can reproduce only by injecting their genetic material into the cells of living creatures. Although scientists frequently refer to viruses as live or dead, in fact no virus is truly alive. It doesn’t eat like animals do, or make its own food the way plants do. It must hijack the cellular machinery of a living cell in order to survive.


Journal: T. Rainey et al. Discovery of Haemaphysalis longicornis (Ixodida: Ixodidae) parasitizing a sheep in New Jersey, United States. Journal of Medical Entomology. Vol. 55, May 4, 2018, p. 757. doi: 10.1093/jme/tjy006.