Strangles in Horses: Causes, Symptoms & Treatment

copyright Dr. Josie Traub-Dargatz, CSU

copyright Dr. Josie Traub-Dargatz, CSU

The disease known as strangles in the horse is caused by the bacteria Streptococcus equi var. equi (S. equi). Horses with strangles usually have a high fever, followed by nasal discharge and enlargement and abscessation of the lymph nodes under the jaw and in the throatlatch region. Affected horses often have a loss of appetite and may stand with their head and neck extended. Occasionally some horses develop abscessation of lymph nodes in the chest and abdomen known as “bastard strangles”.

S. equi is spread through contact with fluid draining from the abscess or nasal

secretions. The incubation period from infection to clinical signs is 3-14 days. Horses infected with Strangles do not shed the bacterium from the nasal secretions for 1-2 days after the onset of fever. If temperatures are regularly taken, new cases can be quarantined before they become infectious, limiting spread through a barn. The organism can be carried on the boots, clothes and equipment of those who have contact with an infectious animal, necessitating strict biosecurity measures to prevent spread. Most horses will shed the organism for 2-3 weeks post infection. A veterinarian can perform nasopharyngeal washes one week apart to ensure a horse is free of infection before returning him to the barn. Some horses may remain persistently infected due to bacteria harbored in the guttural pouches. These horses can shed the organism intermittently and are known as carriers. They may be the source of infection when introduced into a herd of susceptible horses. Carriers can be detected by performing nasopharyngeal washes. S. equi may persist in the environment for a few months.

Treatment of Strangles depends on the situation and severity of the disease. If antibiotics are begun as soon as the horse shows fever, lymph node abscessation may be prevented. Once a horse has lymph node involvement, antibiotics are generally contraindicated. Antibiotics at this stage may prolong the time to abscessation and resolution of the signs. Instead therapy should be directed at encouraging maturation and drainage of the abscess. Some horses develop complications that necessitate additional therapies.

Seventy-five percent of horses that have lymph node involvement and recover have a solid immunity that lasts 5 years or longer. Antibody titers can determine the strength of immunity. Vaccination should be administered on a case-by-case basis by a veterinarian depending on previous exposure and likelihood of future exposure. Horses that have had previous exposure to S. equi may develop immune mediated complications following vaccination.

Most horses that suffer from Strangles will recover without complications on their own. But to prevent the disease, all new horses or horses returning from an event where horses are comingled should be quarantined with temperatures taken daily or twice daily. New horses should be isolated for 3 weeks. Ideally, no new horses should be introduced to a farm without 3 negative nasopharyngeal washes.

Many thanks to Dr. Josie Traub-Dargatz from Colorado State University for allowing us to use her pictures.


What You Need To Know About Equine Herpes Virus Myeloencephalopathy Outbreaks

Over the last several years there have been numerous outbreaks of Equine Herpes Virus (EHM) myeloencephalopathy infections in horses. Many of the outbreaks originated at shows or events where numerous horses were stabled together for a few days.

The cause of the outbreaks is Equine Herpes Virus-1 (EHV-1). Usually the virus causes respiratory signs including fever, poor appetite, coughing, nasal discharge and lethargy. It can cause abortion and neonatal death. In rare circumstances the virus may produce neurologic signs known as myeloencephalopathy. Loss of bladder and anal tone, mild incoordination, stumbling, hindlimb paralysis, and recumbency are signs of equine myeloencephalopathy.

Transmission from one horse to another comes from direct contact (nose to nose) or by contact with infected discharges carried on boots, buckets, blankets, trailers, hands, aborted fetus etc. The incubation period (time from infection to exhibiting clinical signs) is 2-14 days. Most horses have been infected with the respiratory form before the age of 2 years. Previous infection does not protect the horse from reinfection later in life. Some horses have a carrier or latency state in which they test positive but have no clinical signs. Stress may cause a recrudescence of the disease or result in shedding of the virus.

The virus can be treated with anti-viral drugs, which will lessen the severity of clinical signs if caught in the very early course of the disease. However, treatment is usually supportive (bladder drainage, anti-inflammatory drugs, sling) until the horse recovers on it own. If the horse becomes recumbent, the prognosis is poor.

Although vaccination for EHV-1 does give some protection against the respiratory form, it does not protect against the neurologic form. Following some simple management practices while at home and away can help protect your horse from infection. New horses on the farm, or horses that are returning to the farm after co-mingling with other horses should be kept away from horses on the farm for 21 days.

While at a horse show and when returning take your horse’s temperature every day. Contact a veterinarian the first day your horse has a fever. If EHV-1 is suspected, a nasopharyngeal swab can be obtained and submitted for tests to determine of EHV-1 is to blame. Horses exposed to EHM will be quarantined for 21 days following clinical signs to prevent spread of the disease.

Equine Lyme Disease

Over one hundred horse owners/ enthusiasts gathered at the Virginia Horse Center on March 19 for dinner and an educational seminar sponsored by Blue Ridge Equine Clinic, Augusta Cooperative Farm Bureau and the Virginia Horse Center. We were delighted to see old friends, clients and to get acquainted with new friends from our horse community.

Dr. Abby Sage, VMD from Blue Ridge Equine Clinic, gave an excellentCE mtg Dr Sage presentation on Equine Lyme Disease: What We Know and What We Still Don’t Know. Although there are been a few studies on the disease, the frustrating reality is that there is still much that has not been proven scientifically about Lyme Disease in horses, which has reached epidemic levels in our region since 2009.

The disease is caused by a bacteria called Borrelia burgdorferi. It is carried by the tiny deer or black legged tick and can be transmitted throughout the year. It is difficult to be certain what the clinical signs of the disease are in the horse. When ponies were experimentally infected with the organism, none of them developed clinical signs even though the organism was recovered from the ponies at necropsy. There have only been six documented cases of Lyme Disease in the horse that have been reported in the scientific literature. However clinical signs that have been attributed to the disease are: stiff, swollen joints, anterior uveitis (moonblindness), neurologic signs, low grade fever, sensitivity to touch, lameness, weight loss, tremors, neck pain, lethargy, laminitis and pseudolymphoma. Unfortunately, these signs may be caused by many other diseases that are commonly seen. Those include anaplasma, EPM, arthritis, typing up, PSSM and many more.

Lyme test results are based on an antibody response. If the horse is infected with the organism, it will develop an antibody response. However, 40-50% of all horses in the mid-atlantic region test positive (75% in New England, where Lyme Disease was first reported) even though they have no clinical signs nor will they develop clinical signs in the future. They have been exposed, develop an antibody response but do not get sick. So a positive test does not mean that the clinical signs the horse is experiencing are definitely caused by the Borrelia organism.

So how do we know if a horse is infected with Lyme Disease? For lack of a better method, veterinarians have adopted the rules for humans the CDC uses:

* the horse must be in an endemic area

* the horse must have compatible clinical signs

* all other potential diseases must be ruled out

* the horse must have a positive test

* if the horse dies, it must have compatible pathology

Results from experiments on treating Lyme Disease have not been definitive. An experiment performed at Cornell University College of Veterinary Medicine divided 16 ponies into 4 groups of four. Horses which were infected with Lyme Disease and treated for 28 days four different ways: Doxycycline (oral form of tetracycline), ceftiofur (antibiotic in Naxcel or Excede), IV Tetracycline or with no medication (control group). The only group that showed a negative antibody test after 28 days of treatment was the IV tetracycline. However another experiment in naturally infected horses did not show a similar effect with IV tetracycline. It is not clear why these horses did not have a negative test after treatment. It may be that they became reinfected or they remain chronically infected.

Considering the results from the first treatment experiment, one may wonder why not just treat all suspected cases with IV Tetracycline? Several reasons: it’s expensive, as it requires a daily visit from the veterinarian for 30 days, horses can collapse if it is giving too quickly, it’s very irritating if it gets outside the vein, it can cause GI upset and renal failure. As you can see, it’s not a treatment decision to be made lightly in a suspected case of Lyme Disease. If you or your veterinarian suspects Lyme’s Disease a discussion about the test and treatment options should follow. Today veterinarians use Monocycline (oral tetracycline) because it is given orally and rises to therapeutic levels in the blood stream of the horse. But there is no clinical evidence confirming if it actually works or how long it should be given.

As you can see, it’s frustrating for all of us that there is so much that is still unknown about Lyme Disease: its prevalence, definitive clinical signs, how to diagnose it and best treatment method. Until more research dollars are invested in further research, the only things we know for sure are the organism that causes it and that tetracycline has some effect on it.


Why Do Horses Tie Up?

There are many names for “it”: azoturia, set fast, paralytic myoglobinuria, and chronic exertional rhabdomyolysis (ER), but most of us know “it” as tying up. It is a common muscle problem in horses with multiple causes. The most common syndromes include Polysaccharide Storage Myopathy (PSSM), Recurrent Exercise Rhabdomyolysis (RER), vitamin/mineral deficiency, electrolyte imbalance, exhaustive exercise, especially on hot, humid days.  Some horses can have chronic episodes starting at a young age when exercised lightly. Depending on the cause of tying up, keeping your horse well hydrated and fit for exercise can help reduce tying up episodes.

PSSM is a common cause of chronic tying up in Quarter Horses, Paints, snow pictureAppaloosas, Warmbloods, and Draft Breeds, although other breeds may be affected. In PSSM, horses have a genetic defect in the muscle cells which results in excessive storage of sugar known as glycogen. Most horse owners have reported that horses with PSSM have exercise intolerance. A genetic test is available for some breeds of horses that require only a hair sample or blood test. However, other breeds may need to have a muscle biopsy performed to diagnose the disorder. The diet for these horses should consist of low starch/low sugar feeds with a high fat percent.. Any change in diet should be done gradually. These horses should also have daily exercise to prevent muscle stiffness and liberal access to turnout.

Recurrent Exercise Rhabdomyolysis (RER) is another cause for chronic tying up and occurs when there is an abnormality in the way muscle cells regulate intracellular calcium. This type of tying up is not due to the calcium in the horse’s diet, but is also believed to be a genetic defect in the muscle cell. RER episodes occur with exercise or excitement, so keeping the horse calm is one part of prevention. Getting the horse conditioned to the stimuli, providing controlled daily exercise, and the least amount of time in the stall possible are the best ways to prevent RER.  A proper diet for these horses can be difficult because most are in training; they need enough calories to maintain that level without making them high strung.  Fat is a good energy source without making them “hot”.  The most common breeds with RER are Arabians, Standardbreds, and Thoroughbreds.

Tying up episodes can range from mild to severe. A horse can present with a tucked-up abdomen, excessive sweating, muscle stiffness, reluctance to move, muscle twitching in the flank, a camped-out position, back muscle pain and/or a shortened stride. Sometimes this can happen very quickly or, in the cases with RER, some Standardbreds have been known to tie up 15 minutes after exercise. If your horse presents with these symptoms, call your veterinarian and do not move the horse but keep them standing.  Offer the horse water and prevent them from getting chilled with a blanket.  In cases of significant muscle damage, myoglobin (the protein which carries oxygen in the muscle cell) may be released, resulting in red or dark colored urine. Fluids, under the direction of your veterinarian, may be required to prevent kidney damage.

A horse who chronically ties up should be examined by a veterinarian to rule out specific diseases that could be the cause.  There is still much to learn about the causes of tying up, but research continues to offer new strategies to manage this difficult condition.

Equine Enteric Coronavirus – A Newly Emerging Disease Of Horses

Cornell University’s School of Veterinary Medicine has provided current information on Equine Enteric Coronavirus, a newly emerging disease most often found in the Northeast during colder seasons.  Good information to keep in mind as you monitor your horse’s health this winter.

As always, please feel free to call us with any questions or concerns about your horse’s health:  (434)973-7947 Earlysville Clinic or (540)460-5702 Valley Division.