Lyme disease – is it dangerous for horses?

The pathogens that cause Lyme disease are bacteria of the genus Borrelia, of which there are various strains. Borrelia bacteria can hardly survive in the environment and therefore always require a host organism such as ticks, certain small rodents, or even humans or our pets.

In Germany, depending on the geographical location, 28 to 40% of all ticks are infected with Borrelia. The pathogens are transmitted to horses or dogs through tick bites, whereby it is assumed that, as in humans, transmission only occurs 24 hours after the tick bite. After infection, the pathogen spreads throughout the organism and, shortly thereafter, changes its surface structure to protect itself from the animal's immune cells and continue to multiply.

Since the migratory redness described in humans around the tick bite is rarely detected in horses due to their coat, clinical signs are usually only noticed when the disease is already chronic. The literature describes a clinical picture of Lyme disease based exclusively on case studies from different countries, but there is no common method of detection.

The symptoms described are very varied and rather unspecific. Affected animals may show chronic emaciation, intermittent and recurrent lameness, laminitis, joint swelling, muscle tension, skin and eye changes, and behavioral changes. Shortly after transmission, the pathogens can infect the central and peripheral nervous system, which can lead to severe nerve damage. The consequences are muscle wasting, coordination disorders, and neck pain.

It is often very difficult for veterinarians to diagnose Lyme disease. A detailed preliminary report from the owner, knowledge of any tick infestation, and the geographical location are important clues and, in conjunction with the clinical symptoms, can lead to an initial suspected diagnosis. Furthermore, diseases with similar symptoms, such as equine Cushing's syndrome, must be ruled out.

Further blood tests are advisable if only to rule out other diseases with certainty. However, a simple Borrelia antibody test in the blood cannot be used as proof of an acute disease. It only indicates that the animal has had contact with the pathogen and that the immune system has responded to it. A second, special test can be used to determine which specific antigens (=foreign substances) the detected antibodies are directed against. Performing both tests in succession is known as a two-stage test and, according to current knowledge, provides the most meaningful results.

Only specific antibody test procedures that detect the antibodies that indicate a chronic infection and also allow a distinction to be made between vaccinated and infected animals are meaningful. The veterinarian can perform this test in the practice using a rapid test, but these antibodies are only measurable 5 to 8 weeks after infection and remain constantly high in an infected horse. The response to antibiotic therapy can also further support the diagnosis.

Antibiotic therapy should only be administered to horses once a definitive diagnosis has been made. The earlier treatment is started, the better the chances of success. However, as borreliosis in horses is usually only detected in its late stages, treatment can be very lengthy and require a great deal of commitment on the part of the animal's owner.

In order to eliminate all forms of the pathogen, treatment with a special, high-dose antibiotic must be continued over a very long period of time. Due to the pathogen's ability to evade the animal's immune system, it cannot be completely eliminated and deterioration or relapses cannot be ruled out despite treatment. Killing the pathogen can release toxins that can cause the symptoms of the disease to worsen at the beginning of treatment.

The most important preventive measures include daily grooming and checking the horse for ticks and removing them. Regular maintenance of pasture areas can also reduce the risk of infection. In addition, various tick repellent products can be used on horses. Your veterinarian will be happy to advise you on the most suitable product.

In risk areas, a dog vaccine against Lyme borreliosis can be used in horses. Your veterinary practice can also advise you on this.

To remove the tick correctly and completely, always use tick tweezers or a tick card. Use these to grasp the tick as close to your horse's skin as possible. Pull the tick out slowly without twisting or squeezing it. If the tick is squashed or stressed by prolonged manipulation, it will release more saliva and thus more pathogens. If the tick's mouthparts or head remain stuck in the skin after removal, this can lead to inflammation or allergic reactions.

Then thoroughly disinfect the bite area and your hands. Dispose of the tick by burning it or wrapping it in paper towel and crushing it. Alternatively, you can simply pin it between two strips of adhesive tape. Then dispose of it in the household waste. If you want to know whether the tick is infected with Borrelia or other pathogens, send it alive in a well-sealed plastic bag by post to a special laboratory.

Observe your horse for signs such as fever, fatigue, or lameness over the next few weeks. If you suspect an infection, contact your veterinarian immediately.