Dermacentor albipictus

Dermacentor albipictus (the winter tick or moose tick) is a large reddish-brown to gray-brown tick. In Canada, D. albipictus is found in all provinces and territories, appearing as far north as the southern Yukon.


Summary

Dermacentor albipictus (the winter tick or moose tick) is a large reddish-brown to gray-brown tick. In Canada, D. albipictus is found in all provinces and territories, appearing as far north as the southern Yukon. Dermacentor albipictus is a one-host tick with all stages of the life cycle (larvae, nymphs and adults) feeding on the same host. Adult female ticks drop from the host and lay eggs in the environment. A larva develops within each egg, which hatches. The life cycle continues when these larvae find a suitable host, on which they moult through the nymph stage and become adults.

These ticks are most often found on wildlife including moose, deer, elk and bison although horses and cattle that share pasture with these wild species are also often infested. Coyotes and wolves can also acquire these ticks while preying or scavenging on infested ungulates. Dermacentor albipictus ticks are seasonal in their activity with larvae attaching to their hosts in the early fall. The ticks will moult twice on the host sometime during the winter and adults drop off the hosts the following spring.

Horses and cattle with light to moderate infestations generally do not display any clinical signs. Hair loss and possibly clinically significant blood loss may be seen in heavy infestations. Dermacentor albipictus can cause severe disease in moose, elk and caribou in Canada, especially in the late winter and spring with one of the most obvious clinical signs being hair loss resulting from grooming and rubbing to relieve the irritation caused by the adult ticks, anaemia resulting from blood-feeding by the ticks, and weight loss resulting from interference with feeding. Moose with major hair loss are often referred to as “ghost moose’ because the areas of hair loss appear pale grey, rather than the normal dark brown of the hair. Tick numbers and the severity of disease in moose vary from year to year, but the reasons for this have not been fully identified.

Carbaryl (SEVIN®) is the only product approved in Canada for the treatment of D. albipictus in horses and cattle. Dermacentor albipictus may be found incidentally feeding on people. It is not known to transmit agents that may cause disease in people.

More information on D. albipictus can be found on the Canadian Cooperative Wildlife Health Centre website: http://www.ccwhc.ca/wildlife_health_topics/winter_tick/wintertick.php

Taxonomy

Phylum: Arthropoda
Subphylum: Chelicerata
Class: Arachnida
Subclass: Acaria
Superorder: Parasitiformes (Anactinotrichidea)
Order: Ixodida (= Metastigmata)
Family: Ixodidae

Among the arthropods, ticks are most closely related to mites and spiders. Hard ticks of veterinary importance in Canada include Rhipicephalus sanguineus, Dermacentor andersoni, D. variabilis, and various Ixodes spp., including I. scapularis and I. pacificus, the vectors of Borrelia burgdorferi - the cause of Lyme disease.

Note: Our understanding of the taxonomy of helminth, arthropod, and particularly protozoan parasites is constantly evolving. The taxonomy described in wcvmlearnaboutparasites is based on that in the seventh edition of Foundations of Parasitology by Larry S Roberts and John Janovy Jr., McGraw Hill Higher Education, Boston, 2005.

Morphology

Dermacentor albipictus, the winter tick, is a large (unfed adult females are 5-7 mm long, fed females can be twice as large) reddish-brown to gray-brown tick. The larvae have six legs while the nymphs and adults having 8 legs. It is an ornate tick, has festoons, distinctive eyes and the basis capituli is rectangular. It is similar in appearance to the other Dermacentor species ticks found in Canada differentiated primarily by its seasonal occurrence and by the size and shape of the goblet cells within the spiracle plates. Confirmation of identification is usually carried out in a diagnostic laboratory.

Host range and geographic distribution

The winter tick is most often found on wildlife including moose, deer, elk and bison although horses and cattle that share pasture with these wild species are also regularly infested. Dermacentor albipictus will feed on coyotes and wolves although it is thought that they acquire ticks incidentally while preying or scavenging on infested ungulates.

This tick is found throughout the United States and is found in all provinces and territories of Canada appearing as far north as the southern Yukon. The geographic distribution appears to be spreading north.

Life cycle

Dermacentor albipictus is a one-host-tick. Larval ticks attach to the host in the fall and remain on the same host until they are engorged adults. Tick eggs in the environment hatch sometime in August or September and the larval "seed-ticks" ascend vegetation, gather into clusters and wait for an appropriate host to brush against the grass or branch to which they are attached. The larval ticks feed and moult to nymphs in October and November. Nymphs feed and moult to adults between January and March. Adults are present as early as February and by May most engorged females have fallen off the host into the environment. Eggs are laid in leaf-litter in June and will hatch in August or September.

Dermacentor albipictus life cycle

Epidemiology

The primary requirement for tick infestation appears to be sharing habitat in some way with a population of large wild mammals –usually moose, elk or deer. Ticks are generally acquired on pastures frequented by these ungulates. Dermacentor albipictus ticks are seasonal in their activity with larvae attaching to their hosts in the fall. Climatic factors such as temperature, wind, moisture levels and snow cover will affect tick activity in the fall. Larval tick survival is also affected by abiotic factors such as temperature and moisture levels.

Pathology and clinical signs

Horses and cattle with light to moderate infestations of ticks generally do not display any clinical signs. The large engorged female ticks are easily observed in late winter and early spring on infested livestock. Animals may be pruritic around the bite sites. Hair loss and perhaps clinically significant blood loss may be seen in heavy infestations. 

Note: Dermacentor albipictus can cause disease, even severe disease, in moose, elk and caribou in Canada, especially in the late winter and spring. One of the most obvious clinical signs is hair loss, and affected moose are sometimes referred to as "ghost moose". 

Diagnosis

If large numbers of ticks are present then owners may observe engorged ticks on their livestock. Engorged female Dermacentor albipictus are quite large and easy to recognize. They will be the only engorged ticks found on horses and cattle in Canada in late winter and early spring. The services of a diagnostic laboratory may be helpful in confirming this diagnosis.

Treatment and control

Carbaryl (SEVIN®) is the only product approved in Canada for the treatment of winter tick in horses and cattle.

Additional information on the product mentioned is available from the Compendium of Veterinary Products (Twelfth Edition, 2011), or from the manufacturers.

Public health significane

D. albipictus may incidentally be found feeding on people. It is not known to transmit agents that may cause disease in people
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