|New Jersey Horse Health News|
In the last issue of the NJ Horse Health News two horse diseases were reviewed: Equine Infectious Anemia (EIA) and Rabies. In this issue, two diseases of horses are again featured: Equine Encephalomyelitis and Lyme disease.
Many owners are now asking the question: "With such a mild winter, what diseases do I need to watch out for in 1998? The two diseases featured in this issue are high on our list for possible increased prevalence in NJ this year. The insects which spread encephalomyelitis (mosquitos) and Lyme disease (ticks) have been seen in our state virtually throughout the 1997-98"winter" months. NJ horse owners should immediately plan on aggressive preventive measures to control mosquito and tick exposure to their horses and make sure that all of their horses have been adequately vaccinated for encephalitis.
In this issue the NJ Association of Equine Practitioners (NJAEP) has outlined encephalitis vaccination protocols for NJ horses of all possible ages. Now is the time (if you didn"t do it after reading the last NJHHNews) to review your horse health records, consult with your vet, and update any overdue vaccines. If you've put this task on a "back burner", now is the time to take action. Remember, the cost of preventive medicine is minimal as compared to the cost of disease... especially when the cost may include the life of your horse.
~NEWSLETTER EDITOR ~
~ A Viral Disease Spread by Mosquitos ~
Viral encephalomyelitis (or encephalitis) is a potentially fatal disease of New Jersey horses. The eastern equine encephalitis (EEE) virus is usually first found in our local mosquito population in July of each year. This virus infects horses by way of a bite from an EEE-carrying mosquito. Mosquitos pick up this virus by taking a blood meal from a wild bird that has the virus circulating in its blood. Wild birds are nature's reservoir for this virus.
Unvaccinated horses exposed to the EEE virus by infected mosquitos will develop neurological signs of disease. People may also become infected if a mosquito carrying the EEE virus bites a human instead of a horse. Once infected, a horse or human cannot directly spread the disease to other hosts. An infected mosquito is always the cause of the spread of this disease!
Disease Surveillance: The identification of an encephalitis positive horse means that there are mosquitos carrying the virus in the vicinity of the sick animal. Regulations in NJ require that veterinarians report any suspect equine encephalitis cases immediately to the New Jersey Department of Agriculture (NJDA). In this way, the NJDA can work with the reporting veterinarian to ensure that all necessary diagnostic tests are conducted. If a positive horse is then identified, the NJDA will provide information to the New Jersey Department of Health so that a disease alert can be issued to area residents.
Disease in Horses: Horses infected with the eastern equine encephalomyelitis virus develop neurological disease when the virus reaches the brain tissue (encephalo-) and/or spinal cord (-myelitis). Horses may be depressed, weak, develop a fever and head press. Symptomatic treatment with appropriate drugs will have no effect on these signs of disease. In general, infected horses progressively appear to be blind, go down, thrash and kick or paddle, and convulse. The course of this disease is fast and heartbreaking to watch. Most owners elect euthanasia before there is a final diagnosis due to the severe suffering of the animal and extremely poor prognosis for survival.
Disease Diagnosis in the Horse: While examination of the blood for antibodies to the encephalomyelitis virus may sometimes provide a diagnosis of infection, examination of the brain tissue for virus isolation is the only definitive method of diagnosing this disease. Sick horses suspected to have viral encephalomyelitis should always have blood taken for lab analysis of antibody levels. Horses which die or are euthanized should have brain tissue tested for the presence of encephalomyelitis virus and rabies. Other diseases which may affect the brain and/or spinal cord of the horse and mimic encephalomyelitis and rabies disease may include: leukoencephalomalacia (moldy corn poisoning), meningitis, herpes virus, protozoa, aberrant worm migrations, abscesses, and poisoning.
Human Health Concerns: Following identification of a positive equine encephalitis case in our state, the New Jersey Department of Health issues public health alerts (newspaper, radio) warning residents to minimize their exposure to mosquitos. Preventive measures which are recommended for NJ residents include:
Vaccination is the first line of defense to prevent viral encephalomyelitis disease in NJ horses. After that, these same preventive measures should apply to the horse... as well as the owner!
The New Jersey Association of Equine Practitioners (NJAEP) recommends that all horses, ponies, donkeys and mules be vaccinated for at least the eastern and western strains of equine encephalitis. Both viral strains are found in the US. The eastern US has the eastern strain of virus, the western US has the western strain and the Midwestern US has both. One additional strain of encephalomyelitis virus occasionally comes north into the US from Mexico and Central America: Venezuelan. NJ horses which do extensive traveling around the US should be vaccinated for all three strains of virus!
Annual vaccination of adult horses in NJ for viral encephalomyelitis should be performed in the Spring of each year: late March or early April. Adult horses being vaccinated for the first time will need to be given a booster vaccine two to four weeks after the first vaccination. Horses with only one initial vaccination will not be adequately protected against infection by the virus. A two-shot series is required initially to stimulate a protective immune response.
NJ foals born in the late Spring to vaccinated pregnant mares should be vaccinated minimally at three, four and six months of age, and again at one year. (In Florida, where mosquitos are found year-round, the State Veterinarian recommends that all foals be vaccinated at two months of age, followed by monthly vaccines until six months of age, and then every six months thereafter!) Although most companies which manufacture encephalomyelitis vaccines recommend annual boosters after the first two-shot series, most companies also recommend re-vaccination of horses in the face of a disease outbreak. Some manufacturers recommend vaccination every six months in areas where mosquitos are found year-round. (Keep this in mind!)
Equine practitioners keep track of equine encephalomyelitis reports in NJ and surrounding states. When a positive horse is identified in a practice area, veterinarians alert their clients and recommend immediate vaccine boosters. Remember, the cost of a vaccination is far less than the cost of trying to save an infected horse. As a matter of fact, over 90% of encephalomyelitis horses will die. Of those horses which are intensively treated and do survive, there is no guarantee that they will return to full use or "come back to normal".
Researchers at Rutgers University support the equine industry of New Jersey through research projects and outreach programs as part of their land-grant school mission. This past February, the Annual Horse Management Seminar was held on the Cook College Campus, sponsored by Rutgers Cooperative Extension, the NJ Horse Council and the Equine Advisory Board of the New Jersey Department of Agriculture. The day-long seminar attracted horse breeders, trainers, and owners from across the state. Seminar topics included Equine Protozoal Myeloencephalitis (EPM): Epidemiology, Diagnosis and Treatment and Alternative Therapies for General Horse Care and Management. Researchers from The Ohio State University and Neogen Corp. reviewed the evolution of information and current thinking on EPM, while members of the New Jersey Association of Equine Practitioners (NJAEP) lectured on alternative medical therapies including acupuncture, chiropractics, and homeopathy. The Rutgers 1999 Horse Management Seminar is tentatively scheduled for February 21st. Mark your calendars now!
Two scientists in the Department of Animal Sciences at Rutgers, Professor Karyn Malinowski and Assoc. Professor Ken McKeever, have provided an update on their equine research projects for the NJ Horse Health News (see below). Dr. Malinowski has been studying the effects of somatotropin (growth hormone) on horses of different ages and uses, while Dr. McKeever has been working on the effects and detection methods in horses of another hormone, erythropoietin. Here's a capsule report onsome ongoing work:
In recent years there has been much interest by scientists, and the general public, in the use of somatotropin (growth hormone) for use in both animals and humans. Currently, many farmers are using bovine somatotropin (bST) to increase milk production in dairy cows. Also, human medicine has used somatotropin supplements in children deficient in growth hormone and as a supplement for geriatric patients to improve their quality of life.
Dr. Malinowski and her colleagues at Rutgers have been working with a pharmaceutical company to evaluate the use of a recombinant equine somatotropin (reST) in geriatric horses. In one study, 16 mares between the ages of 20 to 26 years, were given a daily injection of reST as either a low dose, high dose, or placebo (control). After six weeks of treatment, it was found that the horses receiving the reST showed an increase in feed efficiency and the potential of having higher numbers of white blood cells to fight infection. Although there was no significant weight gain in the treated mares, researchers reported an appearance of increased muscle definition which was supported in a second twelve-week study using reST injections.
To date, the results of research done at Rutgers show the potential for beneficial effects of somatotropin on the immune system of the horse. Further studies are planned by Dr. Malinowski, including testing an orally active somatotropin and its application for use in horses to speed healing after illness, surgery or injury. Dr. Malinowski also plans on studying the effects of this drug on geriatric horses to improve their quality of life.
For more information, readers may contact Dr. Malinowski c/o Dept. of Animal Science, Cook College, 84 Lipman Dr., New Brunswick, NJ 08901-8725 or Malinowski@aesop.rutgers.edu.
Erythropoietin is a naturally occurring hormone produced by the kidneys in response to low blood oxygen caused by illnesses such as anemia, hemorrhage, or high altitude. This hormone stimulates the production of red blood cells in the bone marrow, thus increasing the oxygen carrying capacity of the blood. Currently, there are synthetic injectable forms of this hormone used in human medicine, referred to as EPO. While EPO is used to treat life-threatening cases of anemia in humans, it has found its way into the horse industry and has been used illegally as a performance enhancer. This is a major concern to horse owners, veterinarians, and racing officials interested in maintaining the integrity of racing as a sport.
Misuse of this drug has become a major health concern in the horse industry. Many reports and publications have warned of life-threatening side effects following the use of EPO in horses. Most prominent of the observed side effects is a severe anemia which may develop in 30 to 40% of horses treated with EPO... the exact opposite of the desired outcome! This anemia is the result of production of antibodies to both the drug and the horse's own erythropoietin. The probability of this reaction occurring in the horse even appears to increase with each administration of EPO!
Dr. McKeever is currently working with the NJ State Police Racing Commission Laboratory to develop a test to detect the illegal use of erythropoietin in horses.
Readers may contact Dr. McKeever c/o Dept. of Animal Science, Cook College, 84 Lipman Dr., New Brunswick, NJ 08901-8725 or McKeever@aesop.rutgers.edu.
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People and dogs are susceptible to infection with the tick-borne agent which causes Lyme disease. Can horses also become infected with this agent and become clinically sick?
Yes! Lyme disease (or "Borreliosis") is caused by a bacterial spirochete called Borrelia burgdorferi. This agent is transmitted by a species of tick called Ixodes, commonly called the "deer tick". These ticks are found throughout New Jersey, as is the disease in people and dogs. Horses do not appear to be as susceptible to the disease as people and dogs, however. Lyme disease in horses has been reported in NJ by equine practitioners over the past ten years. What are the clinical signs of Lyme disease commonly seen in horses?
Clinical signs of this disease in horses appear to be quite variable including (but not limited to) one or more of the following:
Multiple organ-systems of the horse may be directly affected by this spirochete, so that wherever the organism causes the most damage may be where clinical signs of disease are found (like arthritis when the bacteria is in a joint and hepatitis when it is found in the liver). In addition, there may be variations in the severity of disease from horse to horse following exposure to this spirochete. Some of the variation in clinical signs appears to be related to the response of the horse's immune system to the presence of the spirochete. While some horses appear to tolerate infection with this organism and demonstrate no signs of illness, other horses may be infected and clinically sick. There's a lot yet to learn about this disease in horses!
How is Lyme disease diagnosed in horses?
In people, Lyme disease is called the "great imitator". The same may be said of trying to diagnose this disease in horses. In the horse, Borrelia burgdorferi may cause clinical signs of disease which resemble other diseases or the organism may be present and cause no clinical signs of disease. In addition, this spirochete is extremely difficult to isolate from a live horse. So, in order to diagnose a horse with Lyme disease, common causes of the clinical signs of disease must first be eliminated.
After ruling out other possible causes of disease, veterinarians use blood tests to determine exposure of a horse to the Borrelia burgdorferi spirochete. This is done by checking for antibodies in the serum. Two different types of lab tests are used to measure the level of serum antibodies to Borrelia burgdorferi: the ELISA and Western blot. Most horses need to have both blood tests performed in order for a veterinarian to determine whether the horse has been exposed to Borrelia burgdorferi or has other antibodies which may interfere with this test.
Once antibodies are identified in the blood of a horse showing signs of Lyme disease, there is still no guarantee that the clinical signs of disease are being caused by Borrelia burgdorferi. The presence of antibodies means that the horse has been exposed to or vaccinated for this organism. If no other cause of disease is identified, a sick horse would then be treated with appropriate antibiotics to kill Borrelia burgdorferi spirochetes. Follow-up blood tests are needed to determine if the level of antibodies to the spirochete are decreasing. Decreasing antibody levels and diminishing signs of Lyme disease in a horse undergoing treatment indicate that the therapy is having a positive effect against this bacteria.
Is there a Lyme disease vaccine approved for use in horses?
No! Currently, there is no USDA approved Lyme disease vaccine for use in horses. Some horse owners have elected to vaccinate their horses using one of three Lyme disease vaccines approved for use in dogs. However, there is no research or clinical information to support the use of any dog vaccine for Lyme disease prevention in the horse. In fact, use of the vaccine will make interpretation of the diagnostic tests more difficult should this disease be suspected. In addition, researchers have reported finding the spirochete organism in clinically ill horses who had previously been given the dog vaccine! Insect control is probably the best method of preventive medicine for horse owners to decrease their horses= exposure to ticks. Talk with your veterinarian and ask for some recommendations on appropriate insecticides to use on your horse to minimize contact with ticks.