Potomac Horse Fever Facts

Potomac Horse Fever Facts

Summertime, and the living is easy…for the carriers of Potomac Horse Fever (PHF). Our wet spring and recent hot weather provide favorable environments for the aquatic insects and snails that carry the bacteria and infect horses. Here are some key pieces of information about PHF that can help protect your horses:

What to look for: Common signs of horses with PHF include fever (up to 107° F), colic, diarrhea, poor appetite, laminitis (founder), depression/lethargy, swelling of the limbs and/or ventral abdomen, and pregnancy loss. A horse with PHF may show any, all, or a combination of these signs. Because prompt treatment increases the chance of successful treatment, call your veterinarian if you think your horse may have PHF.

Infection: Infection with PHF comes from contact with caddisflies, mayflies, dragonflies, damselflies, and some snails. Because horses become infected with PHF due to insects in the environment, multiple horses on a property may become infected. Although it is an infection, it is not contagious from one horse to another. However, because some contagious diseases show the same signs (fever, colic, diarrhea), it is prudent to keep any horse with these signs isolated from others until the cause of the illness can be determined. Also, some horses with PHF can have other intestinal diseases at the same time.

Treatment: Tetracycline antibiotics are used to kill the organism, and supportive care is often also needed to treat the colitis (intestinal inflammation) that results from infection. Colitis can be very serious, even fatal in horses, and treatment may be complicated and expensive. Laminitis may further complicate treatment and outcome.

Prevention: Horses most at risk are those housed within 5 miles of a stream or pond. Risk of infection can be decreased by vaccinating horses against PHF, and through some environmental management. The vaccine is not always successful at preventing infection, but horses that have been vaccinated generally experience a milder form of the disease if they do become ill. In some circumstances, it may be beneficial to booster the vaccine in late summer; a discussion with your veterinarian can help determine if this would be helpful. Because many of the insects that carry PHF are attracted to light, turning off the barn lights at night can help protect horses from becoming sick.

We have seen multiple cases of PHF in our hospital already this year, and if the hot, rainy weather continues, we are likely to have more cases. Please give our office a call if you have any questions about PHF.


A Good Biosecurity Program

 A good biosecurity program is important to protect your horse from disease. The following are some protocols you can implement to keep your horse safe. Talk to your veterinarian about biosecurity on the farm, and ensure you have a plan set up for emergencies.
When Traveling:
– Ensure your horse is up to date on vaccinations and Coggins.
– Do not use any common water buckets, feed troughs
– Do not share any of your horse’s equipment including halters, lead ropes, lip chains, and grooming tools
– Do not allow any nose to nose contact between your horse and other horses. Select a stall where your horse will not be in contact with other strange horses, choose a tack-stall strategically to isolate your horse!
– Monitor your horse closely for changes in attitude, manure consistency, temperature, or any other change.
At Home:
– Ensure all horses on the property are up to date on vaccinations and Coggins.
– Isolate any incoming horses for 2-3 weeks (i.e. no nose-to-nose contact). This will prevent them from spreading disease to others before they show any clinical signs.
– Ensure each horse has its own buckets, grooming tools and feed buckets. No sharing!
– Take steps to eliminate mosquitoes and flies (i.e. remove stagnant water, fly spray, fly predators etc.)
– Keep the end of the hose out of buckets when filling so it does not become contaminated with dirty water.
Sick Horses:
– Have materials ready and work with your veterinarian to have a (written) quarantine plan in place! Be ready the moment you suspect your horse may have an infectious disease!
– Quarantine the sick horse immediately.
– Clean and disinfect all equipment and tools which have been in contact with the horse (including muck tub and muck fork). Ensure the sick horse has its own tools and equipment. After the horse has recovered, clean and disinfect all tools again!
– Have hand sanitizer and a shallow basin to disinfect shoes available to use after touching the sick horse before coming into contact with the healthy horses.
– Call and work with your veterinarian to set up a plan specific for your horse’s disease. Some diseases are more contagious than others and will require more intensive biosecurity protocols.

What’s Wrong With My Horse’s Eye?

Eye problems are more prevalent through the summer and fall. It is important to be aware that any eye problem should be considered serious and addressed in a timely manner. Certain eye conditions can progress quite rapidly (within 24 hours), becoming so serious that the horse will need to have the eye removed or will become blind. Most eye problems look the same to the owner: swollen, closed and tearing. The following problems are most commonly encountered, and they all have different treatments.

The most common problem is corneal ulcers. This problem usually involves one eye and tearing. Ulcers begin when the surface of the cornea is damaged. Most corneal ulcers do not threaten the overall health of the eye unless they become infected with certain types of bacteria or fungus which produce enzymes that cause further destruction of the cornea. Never treat an eye without first contacting a veterinarian. Some medications contain steroids such as hydrocortisone or dexamethasone. Steroids can cause further damage if given to horses with corneal damage.

Another problem is conjunctivitis. This presents typically with both eyes involved and includes mild eyelid swelling, tearing and inflamed, red-looking conjunctiva (white portion of the eye). This can be initiated by bacteria, dust, pollen and debris in the air.

A related problem and now more commonly found in Virginia is Eosinophilic Kerititis. This causes pain, severe purities and corneal ulceration. This syndrome is thought to have immune/allergic causes, so must be differentiated from more typical ulcers. Treatment is different and often complicated.

The last condition is anterior uveitis. Anterior uveitis is a term which means that the front portion of the eye has inflammation within it. This presents in many different ways but typically includes eyelid swelling, increased pain, tearing and a discoloration or white-to-bluish hue over the cornea. It can involve one eye or both. Treatment options range dramatically depending on the severity.

So as you can see (no pun intended!), many eye issues look the same, but are treated very differently. Early and proper therapy is crucial to a positive outcome!

Taking A Closer Look: How Blood Tests Can Add To Your Horse’s Exam

There are times when your veterinarian might advise running some “bloodwork” on your horse, but why? What information is gained, and how might it help? The answer depends on the specific tests run. Obviously, there are blood tests to detect the presence of specific viruses and bacteria that cause diseases, but what about the hematology and chemistry tests?

First, an explanation of what the tests are and what they reveal. The hematology tests analyze the components of the blood, which are the red blood cells, the white blood cells, and the total solids (proteins) in the blood.   Red blood cells carry oxygen to the tissues in the body, and too few red blood cells is called anemia. Red cell numbers can fall because of a lack of production if the bone marrow is being suppressed by inflammation or other illness, loss due to bleeding somewhere in the body, or inappropriate destruction, which can occur with a number of diseases. An increase in red cells is usually associated with dehydration, but rarely, horses with liver disease produce too many red cells. White blood cells are the soldiers of the immune system, and changes in the population of white cells can indicate inflammation. Depending on the change in the white cells, your veterinarian may also gain information about the severity and nature of the inflammation.

The biochemical analysis, or chemistry, is a panel of tests that reflect the function of different organ systems of the body, and can also indicate inflammation. Information is available on a standard chemistry test about the health of the liver, kidneys, muscles, and intestines.

There are a number of situations in which hematology and chemistry can be useful in managing a horse’s health care. The most obvious case is when a horse is showing signs of illness, such as fever, cough, weight loss, loss of appetite, change in manure, etc. The information gained from the blood work can point the veterinarian toward the cause of the disease, which will determine treatment, and also give vital information about the severity of the problem, which may change the approach to treatment (at home vs.in a clinic) or the expected outcome of treatment. Periodic blood tests during treatment help the veterinarian know how the horse is responding to treatment.

Sometimes, it is helpful to run bloodwork on healthy horses. The most common reason to run blood tests on healthy horses is to monitor the health of older horses. Just as we tend to develop problems as we age, horses may develop age related problems as they grow older. Running a hematology and chemistry yearly can help to catch liver, kidney, and sometimes endocrine problems early when intervention is most likely to be helpful. Another group of healthy horses in which routine blood work can be helpful is the population of horses that are maintained on medication long term. Any medication given over time can have systemic effects, and monitoring the health of the organs with simple blood tests can catch liver or kidney problems, gastrointestinal inflammation, or anemia early, before they make the horse sick. Including blood work into your horse’s yearly exam, especially if he is older than 15 years old or on “maintenance” medication or supplements, may help your veterinarian optimize his health and well-being.

A New Reason To Hate Ticks On Horses: Equine Anaplasmosis

Equine anaplasmosis (also known as Equine Granulocytic Erlichiosis) is a tick-borne disease caused by the bacterium Anaplasma phagocytophila (formerly known as Erlichia equi), also the cause of human granulocytic erlichiosis (HGE). It was first described in horses in California in the 1960’s, but has since been reported in multiple states of the USA and in Europe. Several cases have been diagnosed in the Shenandoah Valley so far this fall.

Anaplasma phagocytophila is a bacterium that lives within blood cells and is carried by deer ticks, the same ticks that carry Lyme disease. Possible natural reservoirs of the disease include deer, rodents and birds. Horses seem to only suffer transient infection, so that they do not harbor latent disease. The disease is not contagious from one horse to another, but multiple horses on a property may be infected, depending on the local tick population.

Horses most commonly get sick with anaplasmosis in the fall to late winter. They commonly show signs of fever, loss of appetite, reluctance to move (people with the disease complain of headache and muscle pain), leg swelling, petechiation (red spots on the gums and whites of the eyes), jaundice, and lethargy. Occasionally, horses may show neurologic signs, or have trouble rising. The clinical signs are in part due to the fact that the bacteria invades some white blood cells (neutrophils and eosinophils), leading to the destruction of red blood cells, white blood cells, and platelets. Bloodwork shows low platelets, which are important for clotting the blood, and anemia.

Diagnosis can be made in several ways. The most definitive way to diagnose the disease is to look at the blood cells under a microscope to look for the presence of the bacteria inside the neutrophils. In some infections, though, only a small number of neutrophils may be affected, and therefore they may not be detected this way. Because horses mount a strong immune response to the bacteria, titer levels can be tested to confirm recent exposure.

The treatment for anaplasmosis is the administration of tetracycline, usually oxytetracycline, minocycline, or doxycycline. Some horses with mild disease may recover without treatment. Most horses recover fully, although some may relapse in 3-4 weeks. Fatality from the disease is rare. There is currently no vaccine available, so prevention is limited to tick control.

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.


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.