Longhorned tick arrival shows need for surveillance

Longhorned ticks are new to North America. They can carry infectious diseases.  |  New Jersey Department of Agriculture photo

Ticks come in two basic varieties. The so-called “hard ticks” are from the family known as Ixodidae and are characterized by a hard plate on their backs. Soft ticks (family Argasidae) lack this hard, protective plate and are usually more oval or pear-shaped.

Ticks can carry a variety of infectious diseases and can infect humans, cattle, sheep, dogs, cats and other species with infections often caused by bacteria or viruses that the ticks spread when feeding on a host.

An exotic tick species new to North America has now appeared in a number of states in the United States.

The tick was first identified on a sheep farm in New Jersey and has also been seen previously on imported animals and materials in U.S. ports.

It is known as the longhorned tick (Haemaphysalis longicornis) and was previously thought to be native to China, Korea and Japan and has also been established in New Zealand and Australia. The longhorned tick is a hard-tick species and has now been identified in Arkansas, Maryland, New Jersey, New York, North Carolina, Pennsylvania, Virginia and West Virginia.

Although many of these identifications have been recent in 2017 and 2018, a tick taken from a dog in New Jersey in 2013 has now been identified as the longhorned tick as well. It appears that the tick has become established in the U.S. and is spreading.

Like other ticks, the longhorned tick can potentially carry various infectious diseases but to date, those identified in North America have not been found with pathogens.

However, these ticks can cause significant problems in livestock even if not spreading infectious diseases. The female tick of this species can multiply asexually and does not need to mate to produce eggs. Like many tick species, they overwinter as immature larvae and climb up vegetation to wait for a host. They then attach to a host, feed for a number of days, and eventually drop off.

The larvae then molt into the nymph stage, which often overwinters to the following spring, at which point they can molt to the adult stage after a blood meal on a host.

The nymph stage is very small and can be difficult to identify without a microscope. The adult tick can be pea sized, once it has had a blood meal.

These ticks have been known in Australia and New Zealand as bush ticks or cattle ticks. They are prolific, and infested animals can carry a high number.

Heavily infested animals can become weak from blood loss especially in younger animals and probably reduce productivity in older animals.

The longhorned tick is known to infect cattle and sheep and can infect a variety of wildlife species. They also infect birds and can migrate to other areas through migratory birds.

The longhorned tick has not been identified in Canada yet, but it appears that it could spread further in North America.

A recent study funded by the Beef Cattle Research Council and carried out by Agriculture Canada scientists in Lethbridge updated the tick distributions for Western Canada and demonstrated that the Rocky Mountain tick is still prevalent in British Columbia, Alberta and western Saskatchewan. The American dog tick is more prevalent in Saskatchewan and Manitoba and the ranges of the two ticks do overlap in southern Saskatchewan.

Tick-borne diseases of cattle occasionally seen in Canada include lyme disease caused by a bacteria known as Borrelia burgdorfeia, anaplasmosis caused by a rickettsial bacteria, Anaplasma marginale, and tick paralysis caused by salivary neurotoxins produced by some tick species.

The longhorned tick may have potential to spread to Canada and may also have the potential to carry some bacterial or viral diseases to livestock and humans.

It is an example of how diseases and pests can move from one country to another and why we need to have surveillance systems in place to identify and manage these new risks.

John Campbell is a professor in the department of Large Animal Clinical Sciences at the University of Saskatchewan’s Western College of Veterinary Medicine.

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