*Drs. Kathleen Crandell and Bryan Waldridge are with Kentucky Equine Research in Versailles, Ky.
Vector-borne diseases are caused by bacteria, viruses or protozoa that are transmitted by ticks, mosquitoes and other insects.
Disease agents typically cycle between vectors and animals. When vectors bite people rather than the typical animal hosts, diseases may spread to humans.
Two common vector-borne diseases diagnosed in people are Lyme disease and West Nile virus (WNV). Both of these diseases can also compromise the health of horses.
Lyme disease is caused by the bacterium Borrelia burgdorferi and is spread by certain species of ticks. The disease is most commonly diagnosed in the northeastern U.S. as well as in Minnesota and Wisconsin.
Clinical signs of Lyme disease in horses can be extremely vague and include lameness in multiple legs, enlarged joints, fever and behavioral changes. A definitive diagnosis of Lyme disease can be difficult to obtain and involves testing for high antibody levels against B. burgdorferi. Laboratories that offer specialized tests for antibodies against Lyme disease are more reliable and can differentiate exposure to B. burgdorferi from active infection.
There currently is no approved equine vaccine against Lyme disease. Control of Lyme disease in horses primarily involves tick avoidance, insect repellents and checking horses for attached ticks. Usually, Lyme disease is treated with tetracycline antibiotics and supportive care, although nutritional support can assist in the recuperative effort.
Nutritional support aims to promote immune response, reduce inflammation and offset possible adverse gastrointestinal effects from antibiotics.
The benefits of omega-3 fatty acids have been detailed extensively. Boosting immunity is just one advantage of supplementing with omega-3 fatty acids, so this seems like a natural choice for an immune-suppressed horse.
Another advantage is a reduction in inflammatory responses. In fact, omega-3 fatty acids reduce arthritic pain and can potentially decrease the dose of anti-inflammatories used for joint pain.
Choose omega-3 products that have been derived from fish oil as these contain direct sources of eicosapentaenoic acid and docosahexaenoic acid, two long-chain omega-3 fatty acids. Marine-derived products such as fish oil should be deodorized and flavored. Products that have been deodorized and flavored are much more palatable to horses. Check with the manufacturer to be sure that the products have undergone these processes.
Lyme disease also has been recognized as a possible cause of neurologic dysfunction in horses, such as muscle loss, unsteady gait and facial nerve paralysis.
Vitamin E is recommended for equine neurologic diseases for its immune-boosting and anti-inflammatory properties. Not all vitamin E supplements are the same, so look for a natural vitamin E product (d-alpha-tocopherol, not dl-alpha-tocopherol).
In a trial conducted at Kentucky Equine Research, bioavailability was greatest with a natural vitamin E product that used a process known as nano-dispersion to deliver the nutrient throughout the body. Natural water-soluble forms of vitamin E have been shown to significantly increase the alpha-tocopherol concentration in the cerebrospinal fluid. Selenium is often discussed hand-in-hand with vitamin E because it, too, is essential for proper immune function.
Arthritis, lameness and swollen joints can be signs of Lyme disease. To bolster joint health, supplements that supply a synergistic blend of glucosamine hydrochloride and chondroitin sulfate provide broad-spectrum support. Hyaluronic acid supplements can also be helpful for improving lubrication of the joint, decreasing joint inflammation and increasing the comfort of the horse.
Other useful nutrients or additives include vitamin C, alpha-lipoic acid, magnesium and, possibly, the B vitamins.
Because Lyme disease is often treated, in part, with antibiotics, it is very important to keep horses eating and to avoid gastrointestinal problems such as diarrhea. Yeasts and probiotics help keep the hindgut in optimal working order.
Horses treated with any antibiotic should be observed for inappetence or loose manure; if either of these occur, discontinue use of the antibiotics and call a veterinarian.
Forage should be available at all times, and, when possible, horses on antibiotics should be allowed to graze at pasture or in paddocks.
WNV is spread by mosquitoes. Cases of mosquito-borne diseases such as WNV, eastern equine encephalomyelitis (EEE) and western equine encephalomyelitis tend to occur more in the late summer and early fall.
The American Association of Equine Practitioners recommends vaccination against WNV and EEE as part of a core vaccination program. Vaccination is very effective for reducing the incidence of WNV and EEE. Horses are much more likely to survive WNV than EEE with early recognition and treatment; about 70% of horses affected with WNV survive with appropriate therapy.
So far in 2013, the Centers for Disease Control & Prevention has reported two veterinary cases of WNV and 14 veterinary cases of EEE, mainly in the southern U.S.
The main goals when feeding horses with neurologic diseases are to supplement vitamin E and ensure that the horses continue eating a good-quality, balanced diet.
Many horses with neurologic disease will have impaired balance and gait abnormalities that prevent them from being turned out. If it's safe for the horse and handlers, some hand grazing allows access to fresh grass and serves as physical therapy for the horse.
Horses with neurologic diseases often have trouble balancing, especially when they lower their heads. Feeding hay in haynets or placing feed on top of a straw bale makes it easier for neurologic horses to eat. Neurologic horses are sometimes reluctant to move around their stalls, so it is important to keep hay, feed and water near each other and the horse if the horse has difficulty moving around.
Horses with severe neurologic deficits may require slings to stand. Horses in slings should be offered feed and water when they are comfortably standing or when they are lying on their chests.
Some neurologic diseases such as botulism can affect the horse's ability to grasp and swallow feed. In these cases, the horse may need to be fed soft mashes or be fed by nasogastric tube. In some instances, total parenteral nutrition — which is supplying an intravenous mixture of amino acids, glucose, lipids, vitamins and minerals — is necessary during convalescence.
Several equine neurologic diseases have been shown to be caused by vitamin E deficiency or to improve with vitamin E supplementation. Many veterinarians prescribe vitamin E supplementation for the treatment of equine neurologic diseases because of its neuroprotective effects.
The usually recommended dose of nano-dispersed natural vitamin E for horses with neurologic disease is 5,000-10,000 international units by mouth every 24 hours. This is approximately 10-20 times the dietary requirement for a 1,100 lb. (500 kg) horse.
Each horse should be treated as an individual — certainly from a nutritional point of view but also from a medical standpoint. A strong working relationship with a veterinarian and a nutritionist will help horse owners determine what is best for an individual horse.