Equine Science: Ticks & their Diseases - August 22, 2009

Welcome to a very different equine science blog this week. I’m currently on holiday so am unable to do a weekly news round up this week until Sunday August, 23. In the meantime, I thought I’d do a blog post about a condition and disease that is less well known: the effects of ticks on horses.

Ticks are external parasites of warm-blooded animals, such as horses, sheep and humans, that feed on blood to survive. They have 4-stages to their lifecycle but adult ticks are not parasitic – only the larvae and young ticks are harmful. Ticks lay their eggs in sheltered spots and in trees, meaning that stabled horses and those kept in wooded areas are at risk.

Image courtesy of Pearson Scott Foresman, Wikipedia Commons.

These parasites are found worldwide. Winter ticks can survive as far north as Canada; tropical ticks found in Mexico and the Caribbean and as far north as Florida and Texas. In the UK, ticks are common in East Anglia around the Thetford Forest and along the south coast new the New Forest. They are also found in other parts of Western Europe, Southern Africa and Asia.

Ears are a common area which ticks attach themselves to and one species is called the ear tick. Ticks which infest in this area may travel deep into the horse’s ear canal leading to discomfort and irritation causing the horse is persistently rub its ear or lead to headshaking. Diagnosis is usually achieved by examining the ear under sedation and treatment is usually a pesticide syringed into the ear, which many horses take objection too. Antibiotics and steroids may also be used.

Ticks also cause two common diseases in horses – Lyme disease and Piroplasmosis.

Lyme disease is caused by a bacterium carried by ticks and can be a serious problem if the disease spreads to humans. Symptoms of the disease are non-specific but can include fever, muscle soreness and stiffness in the joints and in humans are sometimes mistaken for a cold or flu. The ticks responsible for Lyme disease are usually found under the tail or in the horse’s mane and a topical pesticide is required to remove them.

The disease is common in woodland areas and is passed to horses by sheep ticks. Research by the University of Liverpool has found that many normal horses in the UK carry antibodies to Lyme disease suggesting they have been previously infected by the disease but do not show any symptoms of the illness. In other areas of the world, the infection usually results in the disease – this is likely due to different strains.

No effective vaccine exists for Lyme disease and it is better to try and avoid infection by preventing your horse being exposed to ticks. Your local environment may make this difficult, so it is important to try and spot them when grooming and removing them before infection occurs.

Image courtesy of WIkimedia commons

Piroplasmosis has occurred in Florida in the United States, although it is most serious and widespread in the Caribbean. The organism responsible for the disease attacks the horse’s red blood cells causing anaemia and the horse usually displays signs of fever, depression, oedema, weakness and can cause pregnant mares to miscarry.

Another serious problem for both horses and humans are that ticks can cause paralysis, with foals more susceptible. However, adult horses can be affected by the presence of forty or more female ticks. Tick paralysis occurs when an adult female tick feeding on the horse injects a toxin into the blood stream. Paralysis usually starts with the hind legs and moves forwards until the muscles responsible for respiration and controlling the heart are paralysed, leading to death. However, if the ticks are removed before the paralysis reaches such a severe stage the horse can make a full recovery. The ticks responsible for such paralysis are most common in eastern Australia, Southern Africa, northwestern United States and western Canada, although it can also occur in Western Europe.

References:
http://www.thoroughbredtimes.com/horse-health/1994/June/27/Ticks-an...
http://www.horseandhound.co.uk/horsecare/1370/40011.html
http://www.gopetsamerica.com/horse/health-care/ticks.aspx