Ticks pose health risks for people and animals

While the lyrics of Brad Paisley’s song Ticks may seem like a cheesy pick-up line, checking for ticks is actually not a bad idea.

Ticks are external parasites that are most closely related to spiders and can live on birds and mammals.

Anecdotally, this year seems to be a good one for ticks. Weather has an important impact on the number of ticks, with wet years associated with higher numbers. Tick lifecycle lengths vary between species and geographical location.

In northern climates, such as Western Canada, most ticks cycle annually, while in tropical countries, many species will complete several lifecycles per year.

Other factors that affect tick density include the number of hosts a tick requires for its lifecycle and whether or not several life stages can feed on the same species.

In Western Canada, ticks become active in late April, taking blood meals on various hosts as they develop through their lifecycle. This feasting gradually tapers off into later summer with most species hibernating over the long winters.

Egg, larva, nymph and adult are the four lifecycle stages each tick completes. Tick larvae have three pairs of legs while nymphs and adults have four. At the adult stage, female ticks can lay thousands of eggs.

Ticks are attracted to their hosts by breath and temperature. Most ticks spend less than 10 percent of time on the host animal, taking a quick blood meal before dropping off and molting into the next life stage.

There are several species of ticks in Western Canada including wood ticks and the blacklegged tick in Manitoba and British Columbia.

In addition, migratory birds are estimated to transport between 50 and 175 million ticks each year into Canada.

The moose tick, dermacentor albipictus, is fairly uncommon in that it is a one-host tick. All three life stages occur on the same host. Then females lay eggs in the environment. This adaptation allows ticks to successfully parasitize animals that travel great distances. Despite its name, moose ticks can also infest cattle and horses.

Ticks can pose health risks if they bite people and animals. Anaplasmosis is one of many infections transmitted by ticks. This disease of ruminants, including cattle, sheep, goats, deer and elk, is caused by the microscopic blood bacteria anaplasma marginale.

Anaplasmosis is characterized by severe anemia, jaundice and sometimes death.

Ticks transmit this bacterium when they sequentially bite an infected animal followed by one that is susceptible to infection.

Interestingly, the bacteria can actually replicate within the tick, which improves its chances of causing infection when the tick bites again.

Biting flies, needles and other equipment with blood contamination can also transmit anaplasma. Anaplasmosis is rare in Canada. Most recent cases were seen in beef cattle from Manitoba.

Recent changes at the Canadian Food Inspection Agency have downgraded this disease from a reportable disease to one that is immediately notifiable. This means the CFIA will no longer conduct anaplasmosis surveillance and outbreak investigations.

Laboratories that diagnose cases will have to report the numbers to the CFIA so information will still be collected about the disease’s frequency.

Anaplasmosis in horses and people is caused by a different species than cattle, anaplasma phagocytophilum. Infection in horses appears to be rare in Western Canada, with only two horse cases reported.

Black-legged ticks are important transmitters of the bacteria that cause Lyme Disease. These ticks are found in parts of Manitoba and British Columbia, however, with climate change, their range is expected to expand north and west into Sask-atchewan and Alberta.

In addition to infectious diseases, ticks can present other health risks, including chronic blood loss, irritation, secondary infections and hide damage, which can culminate in substantial production losses.

Tick treatments for livestock in-clude a variety of dips and pour-ons. Vaccines are used elsewhere to control trick-transmitted diseases.

Zebu cattle (Bos indicus) are resistant to ticks, a quality that has been used to control the impact of tick-associated diseases in Asia, Africa and Australia.

Ticks on livestock, horses and pets can be removed by gentle traction and in some provinces, they can be submitted for identification and testing.

Dr. Jamie Rothenburger is a veterinary pathology resident at the Western College of Veterinary Medicine, University of Saskatchewan. Twitter: @DrJamieR_Vet



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