Anaplasmosis in animals

Anaplasmosis is a disease caused by a bite from a tick infected with the bacterium Anaplasma. In Québec, blacklegged ticks, also called deer ticks, can transmit the disease to animals and humans. This is the same tick that spreads Lyme disease.

This species of tick is established in the south of the province. Québec’s tick populations are growing, and with them the risk of infection for both animals and humans.

There are two main forms of anaplasmosis in Canada. Granulocytic anaplasmosis is caused by a bacterium called Anaplasma phagocytophilum, and primarily affects dogs, horses and humans. Bovine anaplasmosis, caused by the bacterium Anaplasma marginale, primarily affects bovines and other domesticated and wild ruminants, but is not transmissible to people. For more details on the risk of infection in humans, visit the Anaplasmosis section of the Lyme disease page.

Dogs and horses are the domesticated animal species most likely to contract anaplasmosis. More rarely, anaplasmosis can also affect cats, bovines, sheep, goats and domesticated birds.

Small rodents like white-footed mice, deer mice, eastern chipmunks, voles and squirrels are the primary reservoirs of bacteria in wild animals. Other mammals like raccoons and opossums can carry the disease. Ticks in their earliest stages of development (larva or nymph) pick up the infection from these wild animals. In their final stage of development (adult), ticks are often abundant on white-tailed deer.

Ticks are very small mites. Their bites can easily go unnoticed.

Many infected wild and domesticated animals show few to no symptoms. Typically observed signs are fever, weakness and loss of appetite. Death is rare in any species.

In dogs

Dogs may present other symptoms like vomiting, diarrhea, coughing, difficulty breathing and joint pains. Neurological symptoms are also possible, but rare.

In horses

Horses under four years old appear to be less affected by anaplasmosis than older horses. In addition to the signs mentioned above, horses may also present with swollen legs, difficulty moving and jaundice (yellowing of mucous membranes). Neurological, cardiac, pulmonary and muscular problems are also possible, though rare.

In Québec, only a bite from an infected blacklegged tick can transmit anaplasmosis. The risk is low if the tick is attached to the skin for less than 24 hours. If the tick is attached for longer than that, the risk increases.

Ticks do not jump or fly. Generally, they wait in leaf litter on the ground, in tall grasses or in bushes until an animal or human goes by.

Before a tick feeds, it can vary in size between 1 and 3 millimetres. It can triple in size when filled with blood. It needs to feed on animal or human blood at each stage of development.

Signs of the disease generally appear one to two weeks after infection. Anaplasmosis typically lasts one week in dogs and two weeks in horses.

The disease cannot be spread through direct contact with an infected animal or an infected person. If a blacklegged tick is found on a domestic animal, that can indicate that there are other ticks in the immediate environment or in an area where the animal was found recently. This means that the animal’s owner is also likely to have come into contact with ticks and should remember to take protective measures as well.

If your animal shows signs of the disease, contact your veterinarian. With a consultation, they can make the correct diagnosis and determine if your animal requires antibiotics or other treatment

Blacklegged ticks capable of transmitting anaplasmosis and other diseases like Lyme disease can be active at temperatures of 4°C or higher. They reach their optimal level of activity at around 25°C.

This means there is a risk of contracting anaplasmosis from spring through fall. During tick season, it’s important to take steps to protect yourself and your animals. Visit the page Protect yourself and your animals from mosquito and tick bites to learn more about preventing this disease in domestic animals and humans.

What to do if you find a tick

Within two hours of returning from an outdoor activity, use a brush to check if there are any ticks on your animal. If you find one, visit the page Removing a tick if bitten to learn what steps you should take to remove it.

Professionals in Québec conduct monitoring and surveillance to reduce the risk anaplasmosis poses to animals and people.