Winter ticks feed on horses and cause hair loss

Winter ticks (Dermacentor albipictus) differ from other ticks we encounter in late spring and early summer.

They have a single-host lifecycle and as a result are unlikely to pass diseases.

Moose, deer, and elk are the most common hosts of the winter tick, which can cause the phenomenon known as ghost moose. A single moose can host more than 50,000 winter ticks, causing them to grow itchy and lose their winter coats due to excessive scratching.

Severely affected moose may lose body condition because they spend less time foraging, have greater energy demands because of poor hair coats and are more affected by the cold, wet, snowy weather. In such cases, the tick load may contribute to their death.

Elk and deer groom themselves more by licking in the early stages of infection and therefore tend to be less severely affected than moose.

Horses and cattle are incidental hosts rather than the intended host for winter ticks. At best, horses and cattle provide a poor alternative host for winter ticks. The ticks are less likely to reach the adult stage, and therefore the number of ticks per animal usually remains relatively low, up to 200 ticks according to one source, and that results in fewer problems.

Winter tick lifecycle

Winter ticks mature through four different life stages: egg, larvae, nymph and adult.

In late summer until mid-fall, tick larvae are stimulated by shortened daylight lengths and frost to climb vegetation to seek passing hosts. Larvae feed on the host and become tick nymphs (tiny immature ticks the size of a pin head) in late fall and winter. Nymphs feed on the host and become adult winter ticks.

Engorged adult female winter ticks drop off the host animal in spring to lay eggs. The eggs hatch into larvae and the cycle repeats itself annually.

The larvae, nymphs and adult ticks all require a blood meal to mature. The blood meals are intermittent, which makes any treatment more complex. Given that all three lifecycle stages occur on a single host, winter ticks are unlikely to carry diseases that may infect the host.

Winter ticksand horses

As a rural practitioner in Western Canada, I have seen two very different clinical pictures of winter ticks in horses.

The most commonly recognized problem is engorged adult winter ticks found feeding on horses. A second, less commonly recognized occurrence is that of fall or mid-winter hair loss and dermatitis caused by winter tick nymphs on horses. This can occur over the shoulders, neck, back and rump of affected horses. Younger horses and new horses on low-lying moist brush pastures seem to be more prone to this problem.

It is not clear whether the nymphs are causing this skin problem directly or whether the horses are hypersensitive to the larvae and nymphs feeding.

Unfortunately, there is currently a lack of licensed, on-label products available to treat horses for ticks and lice. While veterinarians can prescribe the use of veterinary drugs for off-label use, the same does not hold true for the use of pesticides. The lack of a suitable and effective product is a significant animal welfare problem that needs to be addressed by the Bureau of Veterinary Drugs and pharmaceutical companies. Please consult with your veterinarian for treatment options.

Although burning of pastures would be an effective measure to control the ticks, it would be difficult to achieve due to the risk of creating larger fires. The best way to reduce the likelihood of exposure of your horses to winter ticks is to alter your pasture rotation such that horses are not grazing moist, low-lying brush pastures in late August to mid-November. These are the places that moose and elk with adult ticks frequent in the spring.

To learn more about winter ticks, the Alberta Sustainable Resource Development has a winter tick fact sheet (#21). It can be accessed online at aep.alberta.ca/fish-wildlife/wildlife-diseases/documents/WinterTick-2004.pdf.

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