How can I keep my horse from getting ticks/Lyme disease?

We are unfortunately seeing more ticks, and thus, more Lyme disease in our local horses. Lyme disease is caused by a spiral-shaped bacteria, (B. burgdorferi), called a spirochete. Because the spirochete is able to change its presentation to the mammalian host immune system, it can escape detection and therefore destruction by the immune system. This is also one reason that it is difficult to treat and “cure” Lyme disease. While the Deer tick is the primary transmitter of Lyme disease, other ticks can also carry it. So the best way to keep horses from getting Lyme disease is to keep ticks off of your horse. Ticks climb up tall vegetation, hold on with one side and hold out the legs on the other side of their body, grasping onto whatever comes along. Keeping vegetation in and around pastures mowed short will help keep the number of ticks down. As for your horse itself, applying Permithrin-containing insect repellants, especially on the legs, tail and under the jaw helps keep ticks off of your horse. Several of these come in a spot-on preparation. Fipronil spray works well too. Keeping your horse’s tail trimmed (banged) or tied up can also help. Some folks use Guinea hens to reduce the tick population, as these fowl love eating ticks.

It takes about 24 hours from the time a tick gets onto your horse until it can transmit Lyme disease, so checking your horse daily and removing any ticks that you find is important. Don’t squeeze them: use a tick remover (Cabela’s sells a nifty one), or remove the tick using tweezers by grasping the tick’s head. If your horse develops a severe reaction to a tick bite, contact us to discuss treatment or testing options.

Lyme Disease Prevention

1. Keep ticks off of your horse: insect repellants, environmental management Keeping vegetation in and around pastures mowed short will help keep the number of ticks down. As for your horse itself, applying Permithrin-containing insect repellants, especially on the legs, tail and under the jaw helps keep ticks off of your horse. Several of these come in a spot-on preparation. Fipronil spray also works well. Keeping your horse’s tail trimmed or tied up can also help.
2. Remove any ticks found on your horse at least once daily! It takes about 24 hours from the time a tick gets onto your horse until it can transmit Lyme disease, so checking your horse daily and removing any ticks that you find is important. Don’t squeeze them: use a tick remover (Cabela’s sells a nifty one).
3. Vaccination: While there is no “approved” Lyme vaccine for horses, anecdotal evidence suggests that the dog vaccine is very effective in horses. We will therefore be offering this vaccine to our equine patients. The recommendation for initial vaccination is one dose on day one, one dose 3 weeks later and a third dose at 3 months. Vaccination is then recommended every 6 months. We conduct reduced cost Lyme vaccination clinics each late winter and late summer to ensure that your horse is vaccinated several weeks before the seasonal rise in tick numbers, thus helping to give your horse the best immunity against Lyme disease. Contact us for details and be sure to check your email in late winter and late summer for clinic dates.
   Below is the mechanism by which the recombitec Lyme vaccine works.
   Osp stands for outer surface proteins. OspA and B are expressed when the spirochete is attached to the tick’s mid-gut. OspC is expressed when the spirochete is connected to mammalian tissue. OspE is expressed when the spirochete is in early stage of infection. OspF is expressed when the spirochete is in late stage of infection.
   The spirochete can also change its shape to three different forms and hide within cellular folds. When the tick begins feeding the warmth of the ingested blood meal causes OspC to be up regulated and OspA and OspB to be down regulated. The genetic expression of OspC proteins allows the organism to leave the mid-gut and enters the hemolymph and then the salivary glands. The OspC enters the host to cause Lyme disease. When the tick falls off the host OspC reverts to OspA and OspB. The vaccine produces OspA antibodies which kill the spirochete within the gut of the tick before there is a shift of production, therefore prevents transmission from the tick to the host of a virulent organism.

Lyme Diagnosis

Lyme disease is the “great imitator”; it resembles other diseases, and is often a fall back diagnosis after ruling out other problems/diseases. Signs may include:

• Ill-defined lameness (shifting limb lameness, waxing & waning lameness)
• Muscle pain (horse seems whole-body sore, muscles painful to palpation, stiffness)
• Increased skin sensitivity (dislikes grooming)
• Behavioral/Personality changes (can mimic gastric/intestinal ulcer symptoms)
• Poor Performance
• Anterior Uveitis (inflammation of the interior of the eye)
• Joint swelling (occasionally)
• Neurologic signs (rarely)

Lyme Testing

Lyme Multiplex test
The Equine Lyme Multiplex assay is a blood test based on three antigens, called outer surface proteins (Osp), of B. burgdorferi. Various research studies have shown that Osp antigen expression changes on the bacterial surface in response to tick feeding and again after infection of a warm-blooded host, such as horses, or humans In response to infection, horses develop antibodies to these Osp proteins and testing for antibodies to specific Osp antigens can assist in the diagnosis of infection and Lyme disease.  The test can be used to determine infection, vaccination status and follow up to determine treatment success.

1. OspA – positive values for antibodies to OspA are typically observed in vaccinated horses. OspA is expressed while B. burgdorferi persists in the tick mid-gut and also while the bacteria are cultured in-vitro. During infection of mammalian hosts, the bacteria down-regulate OspA. Therefore, antibodies to OspA are generally undetectable after natural infection in most non-vaccinated horses. Low positive, transient antibody values to OspA can sometimes be detected 3 weeks after infection 12.
2. OspC – is a valuable indicator of early infection with B. burgdorferi. Antibodies to OspC are detected as early as 3 weeks after infection. Antibodies to OspC decline after 7-11 weeks and become undetectable by 4-5 months after infection 12,14.
3. OspF – is an indicator of chronic infection. Antibodies to OspF are detectable by 5-8 weeks after infection and are maintained at high levels afterwards. Researchers at Cornell observed a very high agreement between antibodies to OspF and C6 as robust markers for infection 12,14. Horses with positive antibody values to OspF and negative antibody values to OspC are considered to be infected with B. burgdorferi for at least 5 months (Fig. 3).

If a tick is found on your horse, it can be sent in for B. burgdorferi PCR.  PCR for Anaplasma can be performed simultaneously if requested.

Lyme Treatment

Horses with clinical signs and a confirmed serological antibody titer to B. burgdorferi are treated with either oral administration of doxycycline or minocycline for 30-45 days, or i.v. oxytetracycline for 30 days, or a combination of oxytetracycline i.v. for a variable period, followed by an oral doxycycline or minocycline treatment for a total treatment time of 30-60 days. The duration of treatment is empirical and based on experience. Very few adverse reactions are reported to treatment; the most common side effect was soft manure (B. Wagner and A. Grice: Summary of the Lyme Disease Table Topic – 57th Annual Convention, AAEP, San Antonio, TX, 2011).