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
Superorder: Parasitiformes (Anactinotrichidea)
Order: Ixodida (= Metastigmata)
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.
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.
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.
Pathology and clinical signs
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".
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.