Ticks and Lyme disease in horses
Lyme disease as a result of a tick bite has unfortunately become widely known in recent years. It is an increasingly well-known phenomenon not only in humans, but also in horses, dogs and to a lesser extent in cats.
Lyme disease is one of the diseases transmitted by a tick, but a major German study has shown that the spirochete (spiral-shaped bacterium) “Borrelia Burgdorferi sensu lato complex” is also found in the DNA of mosquitoes.*
We even see (young) animals that inherit Lyme from the mother.
Lyme disease as a result of a tick bite has unfortunately become widely known in recent years. Not only in humans, but also in horses, dogs and, to a lesser extent, cats, it is an increasingly familiar phenomenon. Lyme disease is one of the diseases transmitted by a tick, but a major German study has shown that the spirochete (spiral-shaped bacterium) “Borrelia Burgdorferi sensu lato complex” is also found in the DNA of mosquitoes.*
We even see (young) animals that inherit Lyme from the mother.
Disease symptoms are often vague and can vary widely, which is why Lyme disease is known as the “chameleon” among diseases. Therefore, detecting Lyme can be very difficult.
With the help of a blood test, the horse’s antibodies against Borrelia (Lyme) can be measured. The antibodies against Borrelia are not produced immediately. Therefore, the disease can often only be detected after 3 to 8 weeks and in some cases not at all, because antibodies are not always produced.
However, this test cannot show whether the horse has had recent contact with the disease and the symptoms are caused by Lyme disease.
Lyme disease
Lyme disease is the most well-known disease that can be transmitted by, among other things, ticks.
Lyme disease is caused by a bacterium: Borrelia burgdorfi. This bacterium is found, among other things, in the saliva of an infected tick. But today we know that mosquitoes, fleas and lice can also transmit these bacteria. Because ticks often go undetected or too late, symptoms are also not recognized and detected until it is already a chronic problem.
The absence of an Erythema Migrans after a tick bite (the familiar red circle) does not mean that there is no infection, often you can’t even see it through the fur in animals.
Borrelia is very good at disguising and hiding. Lyme disease is therefore also the chameleon among diseases, which makes its detection incredibly difficult.
Symptoms in Lyme disease
The clinical manifestations of the disease are associated with non-specific symptoms in both humans and animals. The following symptoms can be seen: varying lameness, stiff thick joints, fever, tender muscles, chronic weight loss, lethargy, behavioral changes and neurological signs. The complaints can be very diverse.
The very diversity of symptoms sometimes makes diagnosis difficult. Too often, the focus is placed on a specific complaint and more extensive examination reveals that there are other complaints and that the underlying problem is Lyme. In practice, our experience is that Lyme in horses likes to “nest” in the lower back. Because of the neurological symptoms, it can cause a (mild) atactic appearance.
Some horses with Lyme have typical external features; (slightly) underweight, skimpy in muscling, a distended belly, floppy tail tone, and a somewhat sunken “pointy butt.” Often animals are also more depressed, anxious or aggressive.
The ticks
Lyme disease is not caused by a parasite, but by a bacterium, Borrelia burgdorfi, among others. This bacterium is transmitted by ticks, among others. Depending on where the tick is found, up to 75% of the ticks can be infected with the Lyme bacteria. Because ticks often go undetected, symptoms are also noticed late and not discovered until it is already a chronic problem.
A number of ticks occur in the Netherlands. The most common tick is Ixodes Ricines.
Ixodes Ricinus
The life cycle takes between two and three years. During this period the larvae, nymphs and ticks do not spend more than 3 weeks on the three different hosts. The rest of the time is spent on the forest floor.
Active adult ticks are generally a bit higher in the vegetation to be able to sit on a passing horse. Ticks are most active in spring and fall.
The Ixodes ricinus tick can transmit the bacteria Borrelia burgdorferi. Research by the University of Wageningen showed that in 2006 average 23.6% of the Dutch ticks were infected with the Borrelia bacteria. The female is usually larger, so it is soon discovered. The male does not suck blood and therefore cannot transmit diseases.
The theory that the risk of Lyme borreliosis is many times lower when the tick is properly removed within 24 hours is now well outdated.
Dermacentor
Other important ticks are Dermacentor ticks. These normally live in somewhat warmer areas, but have also been seen occasionally in the Netherlands in recent years. The adult ticks are particularly active in the spring and fall. This tick prefers to live on vacant areas around cities and on neglected pastures. This tick is the transmitter of the disease babesiosis.
The tick bite and communicable diseases
Ticks are often mainly found on the lower legs, abdomen, groin and chest. The tick can damage and irritate the skin there. Sometimes it is also painful. After the bite, a scab can form, sometimes it is even warm, swollen and sensitive. The tick bite itself often does little harm. Problems can arise when diseases are transmitted by the tick. Lyme disease ( Borrelia burgdorferi), Babesiosis and Ehrlichiosis are tick-borne diseases.
What to do with a tick bite
It is very important to check your horse carefully when you have been in a place with a lot of ticks, such as in a forest.
When the tick has been removed, it can be sent for examination to determine which tick it is and which infection the tick may be carrying. It is also important to remember the location of the tick, as this may be important for further investigation.
Removing a tick
To remove a tick, use a tick hook or tick tweezers intended for this purpose. Removing a tick with this avoids pinching the body of the full-grown tick and often leaving the head attached. Anesthesia with alcohol is undesirable, because a tick can then empty its stomach contents. Tick removal tools are available at the practice.
All diseases resulting from a tick bite
Lyme disease
Lyme is caused by, among other things, Borrelia burgdorferi, a pathogen that resembles a bacterium.
Ehrlichiosis
The tick Ixodes ricinus can transmit the blood parasite Anaplasma phagocytophilum. Equine ehrlichiosis causes a clinical picture with fever, poor eating, lethargy, muscle pain, fluid under the abdomen and thick hind legs. The horses sometimes don’t want to walk, and can be atactic. Mild anemia can be seen in the blood, as well as a shortage of platelets and a shortage of granulocytes. Horses younger than 3 years old become less ill from this infection than older horses. The disease can be detected with a blood smear and by demonstrating an increase in the antibodies.
Often the horses recover themselves within 7 to 21 days. The disease can also be more serious. Then an antibiotic treatment is necessary and the horse needs supportive treatment.
Babesiosis or Piroplasmosis
A condition that we see more and more is Piroplasmosis or Babesiosis. The tick that transmits this disease has also been seen in the Netherlands in recent years. In addition, the tick can enter our country by transporting horses from abroad. The condition is caused by the blood parasites Babesia caballi and Theileria equi. These parasites are located in the red blood cells. The incubation period is 5 to 21 days. In the first stage, infected horses show a high fever, severe anemia, chest tightness, yellow mucous membranes and fluid retention. Subsequently, there may be weight loss, fluctuating fever, fluctuating appetite and reduced performance.
The diagnosis can be made by blood smear and an increase in the antibodies in the blood can be seen from two weeks after the infection. The parasite itself can also be found with a special test (PCR). Treatment consists of giving the drug imidocarb, which kills both types of blood parasites. In case of severe anemia, a blood transfusion is sometimes necessary.
Diagnosis
Red spots and rings that can develop after an infection do not always occur and are therefore not indicative of infection. In addition, these are often difficult to see in an animal’s fur.
With the help of a blood test, the horse’s antibodies against Borrelia (Lyme) can be measured. The antibodies against Borrelia are not produced directly. Therefore, often the disease can only be detected after 3 to 8 weeks and in some cases not at all, as antibodies are not always produced.
However, this test cannot show whether the horse has had recent contact with the disease and the symptoms are caused by Lyme disease. They may have had contact with Borrelia and thus have antibodies in their blood without showing any symptoms. An acute infection can be detected when no antibodies were found on the first blood draw and antibodies were found on the second blood draw.
Tests are also being developed in which the presence of Borrelia itself can be demonstrated. This requires, for example, a biopsy of the skin at the tick bite or of a joint. The sensitivity of this test is not yet well known in the horse. The diagnosis is only certain when it is known that the horse has been infected with ticks, the horse shows (multiple) symptoms, the test is positive, other disorders are excluded and the horse responds well to the treatment. When the blood test is negative, it does not mean that there is no contamination, as it can be a false negative.
Therapy
Thanks to years of experience and research, it is now possible to treat Lyme. With this, it can be controlled, but Lyme will never disappear completely. Therefore, it is also very important to establish a treatment plan that includes relapse prevention.