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Take note of the invasive, exotic Asian longhorned tick

By Mike Catangui, Ph. D

U.S. counties report westward expansion of tick suspected of spreading theileriosis caused by Theileria orientalis Ikeda genotype protozoan parasite of cattle
longhorned ticks
Fig. 1. Adult female (right) and nymphal stage (left) Asian longhorned ticks (Haemaphysalis longicornis) placed on top of a dime for scale. (Photo: James Gathany; Anna E. Perea/USCDC)


After first being detected on an Icelandic sheep on August 1, 2017, in Hunterdon County, New Jersey, the Asian longhorned tick (ALT) has now been found (as of November 2021) in 18 states in the U.S. It is already known to occur in Hawaii and other Pacific island nations.

The Asian longhorned tick (Haemaphysalis longicornis) [Fig. 1] is now considered the likely vector of Theileria orientalis Ikeda genotype protozoan parasite of cattle in Virginia and West Virginia (Dinkel et al., 2021). Both the parasite (Theileria orientalis Ikeda genotype protozoan) and the vector (Haemaphysalis longicornis tick) are brand new records for cattle in these states.

The mortality rate for theileriosis in infected cattle can vary from one to five percent (Dinkel et al., 2021); Theileria orientalis Ikeda genotype is not considered harmful to humans (VMCVM, 2021).

According to Dinkel et al. (2021), the disease symptoms of cattle infected with Theileria orientalis Ikeda genotype include erythrocyte destruction leading to anemia and hypoxia. Severely affected animals often exhibit pyrexia, weakness, pallor, and increased heart and respiratory rates; abortion is common although transplacental transmission of the parasite from cows to calves is only observed in 10 percent of cases. A polymerase chain reaction (PCR) test is available to confirm theileriosis Ikeda genotype.

Longhorned ticks can multiply very fast by cloning themselves and can cause exsanguination (severe loss of blood) if allowed to multiply unabated in infested animal hosts. They are capable of reducing milk production in dairy cattle by up to 25 percent. Known hosts are humans, cattle, sheep, goats, pigs, poultry, cats, dogs, rodents, birds, and many wildlife animal species.

Current distribution in the U.S. (as of November 2021)

[See Fig. 2]


Oil-based and water-based on-animal fly sprays may be able to effectively control longhorned ticks on cattle and horses.

Although effective against ticks on cattle, endectocides (anthelmintic or deworming products containing the active ingredient doramectin, eprinomectin, ivermectin, or moxidectin) are currently not labeled for use against ticks on cattle in the U.S. (Davey et al., 2005). However, cattle veterinarians may be able to prescribe endectocides for “extra-label application” against ticks on cattle.

Endectocides are systemic anthelmintics (dewormers) belonging to the macrocyclic lactone group that are also labeled for use against cattle grubs, blood-feeding lice, mange mites, horn flies, and other parasites of cattle. Reference MWI Animal Health pest control product charts on

Producers need to consult with their veterinarians and MWI Animal Health representatives before using endectocides on cattle. Prior to using any product mentioned in this article, carefully read and follow all available instructions, warnings, and safety information made available by the product’s manufacturer.

MWI Technical Services: On the front lines of tick control

In late 2017, the United States Department of Agriculture’s National Veterinary Services Laboratories (NVSL) confirmed the presence of the Asian longhorned tick in the United States.

In fall 2018, MWI Technical Services Entomologist and Parasitologist Manager, Dr. Mike Catangui, PhD, started “sounding the alarm” about the Asian longhorned ticktheileriosis issue, “way before the industry press picked up the news,” he says.

Less than three years later, MWI and Catangui were involved in designing a tick control program for owners grazing cattle in the West Virginia-Pennsylvania-Virginia region.

Catangui was called in to advise on products and control after an MWI veterinary client reached out to his Territory Manager, MaryAnn Wetmore. The veterinarian’s client, a farm owner in Pennsylvania, had cattle that didn’t look well, even though a deworming program was in place.

“The veterinarian was specifically looking for options on how to control the Asian longhorned tick vectors,” says Catangui. “The affected herd was located across the border from West Virginia. It already lost four cows and one calf due to the suspected theileriosis vectored by the numerous suspected Asian longhorned ticks on the herd.”

Through a collaboration facilitated by the internet, including emails, videos, and a video conference Catangui hosted with the group, they worked out a solution that included equipment and insecticide products available from MWI.

“We presented tick control options — spraying the herd with on-animal sprays and using endectocides as extra-labeled products (endectocides are not labeled for ticks but several scientific publications indicate that it can be an effective option),” says Catangui.

The producer already used an endectocide dewormer in the 2021 grazing season. Upon examination, the veterinarian and owner reported there were, indeed, significantly fewer ticks in the cattle treated with this product.

Q: Why should producers remain vigilant about the ALT?

Catangui: “Cattle theileriosis, caused by Theilaria orientalis Ikeda genotype protozoan parasites and vectored by the new invasive Asian longhorned tick can become a very serious pest of cattle in the US. Mortality rate is estimated to be about 5 percent of infected cattle; cattle theileriosis caused by Theilaria orientalis is known to cause fetal loss, abortion, and neonatal calf death in other parts of the world (Dinkel et al., 2021).”

Q: What should producers know about products that control ticks?

Catangui: “In general, hard-bodied ticks, such as the Asian longhorned tick, can be controlled by using water-based or oil-based on-animal sprays already familiar to cattle producers for controlling flies and lice on feedlots, pastures, and dairy farms. On-animal sprays can contain natural pyrethrins or synthetic active ingredients; there are over 30 products to choose from. No special permits or license is necessary except for using restricted-use products.

“It remains to be seen whether insecticidal products delivered through pour-ons, backrubbers, dusters, automatic misting systems, or aerosols can effectively control the Asian longhorned ticks on cattle. Endectocides are currently not labeled for use against ticks but there are several research publications that indicate that they can be effective against hard-bodied cattle ticks (Davey et al., 2005). If a producer wants to use any of the available endectocide products as an injection or pour-on, a prescription for “extra-label” use of the product is needed from a licensed veterinarian.”

Map of U.S. counties that show the westward expansion of the invasive tick species
Fig. 2. U.S. counties (shaded in dark blue) show the westward expansion of the invasive tick species Haemaphysalis longicornis to over 130 counties across 18 states, including Arkansas, Connecticut, Delaware, Georgia, Hawaii, Kentucky, Maryland, Missouri, New Jersey, New York, North Carolina, Ohio, Pennsylvania, Rhode Island, South Carolina, Tennessee, Virginia, and West Virginia. (Map created by MWI Animal Health from USDA-APHIS, 2021, data.)

Creating awareness for the Asian longhorned tick (ALT):

  • This tick is native to eastern China, Japan, the Russian Far East, and Korea. It is an introduced/ established exotic species in Australia/New Zealand and several western Pacific Region island nations.
  • Morphologically, the ALT looks very similar to the Brown dog tick and is often misidentified, according to the Tick Research Lab of Pennsylvania.
  • Asian longhorned ticks are light brown in color. Adult females grow to the size of a pea when engorged with blood.
  • In the US, the ASL has been found in or near counties with large horse, cattle, and sheep populations.
  • Dr. Kathy Simmons DVM, Chief Veterinarian of the National Cattlemen’s Beef Association (NCBA), says that state animal health authorities and individual cattle producers must remain vigilant to control the spread of this invasive, exotic tick as there is no federal program for tick control or eradication in place.
  • Simmons points out that controlling and managing the tick is important because of its mobility. Since being found on a sheep in August 2017 in New Jersey, the tick has been found in 18 states [see Fig. 2].
  • Dr. K. Fred Gingrich II, DVM, Executive Director of the American Association of Bovine Practitioners (AABP) says veterinarians and producers need to be aware of ALT. If you do find ALT, report it to your state veterinarian, he advises. According to NCBA, USDA and state animal health officials have a procedure for veterinarians to identify and report ticks.
  • To protect against infestations, producers should frequently inspect their cattle, complete regular tick treatments, and consult their veterinarian about what preventative products to use [see Control section in this article].

Challenges to ALT control and management:

  • Tiny size makes detection difficult — nymphs can be the size of a sesame seed
  • Asexual reproduction with many eggs: An adult female doesn’t need a mate to produce about 2,000 eggs in two to three weeks, so the spread of this tick is faster. It can be spread by both domestic and wild species, including birds
  • Resiliency to live in environment without a suitable host: Larvae can survive on the ground and vegetation unfed for 217 days, nymphs for 263 days, and adult females for 249 days
  • The ALT prefers warm places on both humans and animals. On cattle, pay extra attention to ears, groin, and underbelly. On humans, check for ticks under armpits, behind the knee, in hair or around groin.
  • Producers need to report any sightings of unusual looking ticks or infestations to their veterinarian.
  • Although many ticks can look alike to the naked eye, the following suspicious tick encounters are characteristic of ALT, according to Ohio State University Extension:
    • Observing unusually high numbers (hundreds to thousands) of ticks or little “spiders” on animals or equipment
    • Being swarmed by ticks upon entering a field
    • Observing clusters of ticks on the tips of vegetation (may look like clumps of seeds)
  • According to USDA, the ALT prefers tall grasses and wooded areas.

MWI can assist with tick identification

MWI Technical Services can help with identifying and documenting the occurrence of Asian longhorned ticks in the US. Tick specimens may be placed in a zip top bag with collection information (location, host species, date) and placed in a freezer for future identification. Tick specimens may also be placed in a sealed plastic pill bottle containing a rubbing alcohol preservative.

Please contact your veterinarian or MWI territory manager if you see numerous or larger numbers of ticks infesting your cattle and other farm and companion animals.

About The Author

Mike Catangui, Ph. D

Entomologist, Parasitologist
MWI Animal Health
View Bio