Emerging issue: New invasive tick species

By Mike Catangui, Ph. D

Now suspected of spreading theileriosis caused by Theileria orientalis Ikeda genotype protozoan parasite of cattle in Virginia and West Virginia
longhorned ticks
Fig. 1. Adult female (right) and nymphal stage (left) longhorned ticks (Haemaphysalis longicornis) placed on top of a dime for scale. Male longhorned ticks are rare; adult females can reproduce asexually by cloning themselves. (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 longhorned tick has now been found (as of July 21, 2021) in 16 states in the U.S. It is already known to occur in Hawaii and other Pacific island nations. The 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 (VMCVM, 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 three to nearly 90 percent; Theileria orientalis Ikeda genotype is not considered harmful to humans (VMCVM, 2021).

Longhorned ticks can multiply very fast [Fig. 2] 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. Cattle, swine, poultry, companion animals, and humans are in the host range of longhorned ticks.

Longhorn tick on sheep ear
Fig. 2. Engorged longhorned ticks (Haemaphysalis longicornis) in the ear of an Icelandic sheep in Hunterdon County, New Jersey. (Photo: Tadhgh Rainey; Hunterdon County, New Jersey Division of Health)

Current distribution in the U.S. (as of July 21, 2021)

Arkansas, Connecticut, Delaware, Hawaii, Kentucky, Maryland, New Jersey, New York, North Carolina, Ohio, Pennsylvania, Rhode Island, South Carolina, Tennessee, Virginia, and West Virginia.

Winter survival

Longhorned ticks are expected to survive U.S. winters based on where they have been found so far in the mainland. Pastured livestock may be at risk of infestation even in the northern states where ticks had not been a significant ectoparasite.

Known hosts

Humans, cattle, sheep, goats, pigs, chickens, cats, dogs, rodents, birds, and many wildlife animal species.

Parthenogenesis and life cycle

Longhorned ticks multiply by a process called parthenogenesis. A female longhorned tick can produce exact copies of itself (clones) by laying thousands of eggs that hatch and develop into ticks without being fertilized by a male tick. Ticks belonging to the Genus Haemaphysalis are so-called three-host ticks. Their general life cycle is as follows: its tick egg will hatch into a larva, crawl around vegetation, latch onto its first host, feed on the host for about a week, detach from the host once fully engorged with blood and lymph, then molt into a nymph [Fig. 1] on the ground. This nymphal tick will crawl around vegetation, latch onto its second host, feed on blood and lymph for about a week, detach from the second host, then molt into an adult female tick [Fig. 1]. This adult female tick will crawl around vegetation, latch onto its third host, feed for about a week, detach from the host, then start laying eggs in suitable areas on the ground. An adult female longhorned tick can produce about 2,000 eggs in two to three weeks. Without the presence of suitable hosts, tick larvae can survive on the ground and vegetation unfed for 217 days, nymphs for 263 days, and adult females for 249 days.

The mortality rate for theileriosis in infected cattle can vary from three to nearly 90 percent; Theileria orientalis Ikeda genotype is not considered harmful to humans (VMCVM, 2021).


Oil-based [Table 3] and water-based [Table 2] on-animal 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) [Table 1, pages 48-49] are currently not labeled for use against ticks on cattle in the U.S. (Davey et al., 2005).

Consult with your veterinarian and MWI Animal Health representatives before using endectocides on your 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.

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.

Cane, R. 2010. Haemaphysalis longicornis Neumann profile. New Zealand BioSecure Entomology Laboratory (smsl.co.nz/site/ southernmonitoring/files/NZB/Ha%20longicornis%20Profile.pdf).
Davey, R. B., J. A. Miller, J. E. George, and R. J. Miller. 2005. Therapeutic and persistent efficacy of a single injection treatment of ivermectin and moxidectin against Boophilus microplus (Acari: Ixodidae) on infested cattle. Experimental and Applied Acarology 35: 117-129.
Maryland Department of Natural Resources. 2018. First confirmed longhorned tick found in Maryland – State urges Marylanders to take precautions to protect livestock, pets, and humans (news.maryland.gov/dnr/2018/08/07/first-confirmed-longhorned-tick-found-inmaryland/).
Rainey, T., J. L . Occi, R. G. Gobbins, and A. Egizi. 2018. Discovery of Haemaphysalis longicornis (Ixodida: Ixodidae) parasitizing a sheep in New Jersey, United States. Journal of Medical Entomology 55: 757–759. United States Department of Agriculture Animal and Plant Health Inspection Service. 2018. Longhorned tick: Information for livestock and pet owners factsheet (aphis.usda.gov/publications/animalhealth/fs-longhorned-tick.pdf).
Virginia-Maryland College of Veterinary Medicine. 2020. Theileria orientalis Ikeda genotype in cattle. Virginia Department of Agriculture and Consumer Services (vitals.vetmed.vt.edu/content/dam/vitals_vetmed_vt_edu/documents/theileria-summary.pdf)

Tick identification

MWI Animal Health Technical Services can help in identifying and documenting the occurrence of longhorned ticks in the U.S. 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 MWI Territory Manager if you see numerous ticks infesting your cattle and other farm and companion animals.

About the Author

Mike Catangui, Ph. D

Entomologist, Parasitologist
MWI Animal Health
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