Emerging issue: New invasive tick species
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.
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 survivalLonghorned 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 hostsHumans, cattle, sheep, goats, pigs, chickens, cats, dogs, rodents, birds, and many wildlife animal species.
Parthenogenesis and life cycleLonghorned 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.