Equine Lyme disease is a growing concern for horses in North America, especially during the summer months when tick bites are more common.

Lyme disease is primarily caused by infection with Borrelia burgdorferi, a bacteria that is carried by ixodid, or hard-bodied, ticks. [1] You may recognize this tick by its more popular name, the black-legged or deer tick (Ixodes scapularis).

While tick prevention is common practice for many of us that own dogs and/or outdoor cats, it has not historically been a concern for horses. However, this is changing as tick populations continue to expand.

Lyme disease often targets the muscles and can lead to lameness in horses. [2] However, when a horse presents as lame, Lyme disease is not usually the first thought, making for a sometimes tricky diagnosis.

Horses affected by Lyme disease can also experience chronic weight loss, fever, muscle tenderness, poor performance, joint issues and behavioural changes such as depression.

Not all tick bites will lead to infection with B. burgdorferi. but in the cases that do, treatment may require a course of antibiotics over several months. Treatment can be expensive which is why prevention is so important.

This article will discuss the growing tick populations in North America, diagnosis and symptoms of Lyme disease in horses, treatment as well as how to prevent this condition in your horse.

Lyme Disease and Ticks in North America

The black-legged tick is found throughout the southeastern and southcentral regions of Canada. It can be found in the provinces of Manitoba, Ontario, Quebec, New Brunswick and Nova Scotia, as well as along the West Coast in British Columbia. [3]

Human cases of Lyme disease in Canada increased by more than 18-fold from 2009 to 2019, reflecting the increasing range of the black-legged tick.

In the United States, the black-legged tick is found across central and eastern states with a huge range covering all the way from Texas to Maine. [4]

A northward spread of the black-legged tick to northern states as well as southern and central Canada has been documented and climate change has been thought to play a role in this spread. [5]

Tick Life Cycle

The black-legged tick follows a three-host life cycle that can take between 2-3 years to complete. Below is the typical life cycle for a black-legged tick.

At each stage, any animal or human can be the host and the tick can attach and feed on multiple different hosts or individuals. [6]

Lyme Disease Tick Life Cycle | Mad Barn Canada

  1. Adult females lay eggs, usually in the fall, after feeding on a host. The eggs hatch and spend the winter in the larval stage.
  2. In the spring, the larvae attach to a small rodent, such as a squirrel.
  3. After spending spring and summer feeding on the first host, larvae fall off the first host and molt into nymphs in the fall. They then spend the winter in the nymph form.
  4. The following spring, the nymphs attach to the second host, often a small mammal or rodent.
  5. The nymphs then fall off the second host in the fall and spend the winter in the adult form.
  6. The next spring, adults often seek a larger host, like a horse, cow or human. The adults then feed and mate on the third host, completing the life cycle.

The tick can pick up the bacteria, B. burgdorferi, from any of the hosts it feeds on. It can then transmit that bacteria when it attaches to a new host.

It will often take approximately 12-24 hours for the tick to transfer the bacteria after it has bitten the host. The key to reducing the chance of infection with Lyme disease is to remove the tick quickly.

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