At first glance they may look like harmless insects, but ticks can cause nasty diseases. Not only in horses, but also in other mammals such as humans, dogs and cats. One of the diseases that can be transmitted by a tick bite is Lyme disease. Lyme disease is caused by the bacterium Borrelia burgdorferi. This is a thin, spiral-shaped bacterium with a whiptail (flagella) that makes it very mobile. The Borrelia bacterium can be transmitted via the sheep tick (Ixodus ricinus).

These ticks are mainly active in spring and summer. They need blood from a host to moult and the females also need it to lay eggs. For example, they wait in tall grass or bushes for a suitable host (horse, human, dog, etc.) to pass by. The ticks sense the host’s arrival by the body heat they radiate. The ticks then drop onto the host or climb up. They then bite in a suitable spot (preferably thin skin) and start sucking blood. The female ticks are about 4 mm in size, but can grow up to 1 cm in size after sucking blood. They are flat and dark brown, the females have a reddish brown abdomen.

Not all ticks are infected with the Borellia bacterium, about 20 percent carry this bacterium. This group contracted it by sucking blood from small (rodent) animals or birds that can carry this bacterium. The infected tick then passes the bacterium on to the next host while sucking blood. The longer a tick can bite, the greater the chance that the bacteria will be transmitted. After 24 hours the chance of infection increases rapidly, but within 24 hours the chance is small.

In horses, Lyme disease can go undetected, as not all horses will show obvious symptoms. Horses that do have symptoms may suffer from fever, weight loss, lameness, muscle aches and lethargy. In more severe cases, moon blindness (eye inflammation), meningitis or abortion can occur. In humans we can sometimes see the typical red circle around the tick bite, but we do not see this in horses. Symptoms may not appear until late, making it difficult to link to the tick bite.

It is not easy for a vet to diagnose Lyme disease. The symptoms that the horse shows could occur in various diseases and disorders. If a tick bite is known to have occurred, the vet can take a skin biopsy near the bite site and analyse it. However, a possible infection is often diagnosed with a serological examination. This involves looking at the number of antibodies against this specific bacterium. Once the disease has been diagnosed, the horse can be given a long course of antibiotics.

There are various means for people to protect themselves against ticks, but for horses there are no registered products on the market in the Netherlands. It is therefore best to check your horse regularly for ticks. Especially if you went on a trail ride in an area where sheep ticks like to live (boggy areas with shrubbery, but also dunes and heathland) it is wise to check for ticks afterwards. If you remove the tick within 24 hours, the chance of infection is smallest. Check not only your horse, but yourself as well. Found a tick? Remove it properly, using tick tweezers or pinchers. Pulling out the tick in its entirety, without damaging it, minimizes the risk of bacterial infection.