DiseasesP r e v e n t i o n s e r i e s

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associated with travel, intense training and competition makes horses more susceptible to infection, and they are also more likely to encounter the virus at shows, events and other venues with large, transient equine populations housed in close quarters.

Fortunately, several vaccines against equine influenza are available that, when combined with some common-sense hygiene measures, keep most horses healthy. For best results, incor-porate the following measures into your flu-prevention plan.

P R E V E N T I O N By Melinda Freckleton, DVM, with Christine Barakat

INFLUENZA

Here’s how to protect your horse from this common equine upper respiratory infection.

Precise statistics aren’t avail-able, but one thing’s certain: Influenza is one of the most common upper respiratory

infections to strike horses.Particularly at risk are young horses

who haven’t previously been exposed to the flu virus and have no natural immunity to it. In addition, the stress

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PRIMARY DEFENSE: VACCINATION

Vaccination may not prevent influ-enza in every horse, but it can reduce the severity of illness in those who do get sick. Three types of equine influ-enza vaccine are available. Which one is best for your horse, and on what schedule, is a decision best made with your veterinarian:

Inactivated-virus vaccines contain multiple strains of the influenza organ-ism, including those most likely to be

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in circulation when they are produced. Most of these vaccines require two or three initial injections several weeks apart, followed by boosters annually.

A modified-live virus vaccine is ad-ministered intranasally, with the aim of stimulating immunity at the site where the influenza pathogen enters the body. The vaccine is typically effective after the first administration, and protection lasts as long as six months.

A recombinant vaccine combines a small segment of genetic material from the influenza virus with canarypox vi-rus (which does not replicate in mam-mals). The vaccine is initially given in two doses, five weeks apart, then an an-nual booster.

Even after an outbreak of equine in-fluenza starts in your area, it may not be too late to vaccinate. The protocol will depend on the horse’s vaccination sta-tus, the product used and the nature of the local incidence. Your veterinarian will know the best protection strategy.

SECONDARY DEFENSE: HYGIENE PROCEDURES

1. Limit contact between unfamiliar horses. Allowing strange horses

to “greet” each other by touching noses is a bad idea for several reasons. Not only can it lead to squealing, nipping and pawing, but a nasal secretion car-rying the influenza virus can be passed from one horse to another. Horses can be contagious without looking sick, so there’s no way to know which ones might be infected.

2. Don’t use communal water troughs or buckets. Many bacte-

ria and viruses, including influenza, can live in water for hours or even days. If an infected horse drinks from a com-munal trough, each one who follows could pick up the virus. Bring your own water buckets to an event and do not lend them to other competitors.

3. Don’t share equipment. The in-fluenza virus can survive on

tack and tools for many days and be passed from horse to horse. Use your own equipment when on the road, and if you must borrow an item in a pinch, first wash it with a disinfecting soap or clean it with an antibacterial wipe.

4. Isolate potentially contagious horses. Ideally, new horses or

those returning after a trip would be quarantined for at least 14 days in a separate structure with their own care-takers and equipment. Horses already on the farm who become sick would be similarly isolated. Of course, such measures aren’t always possible, but get as close to that ideal as you can. At a minimum, put the horse in your most isolated stall and turn him out alone. Feed and handle him last, after caring for the other horses, then shower and change to avoid carrying the virus on your hands or clothes.

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IN FOCUS: Equine influenza Definition: infection of the upper respiratory tract with the orthomyxovirus equine influ-enza A type 2. (The term “flu,” however, is often mistakenly applied to any upper respiratory infection.) Transmission: The virus is passed from horse to horse pri-

marily through direct contact or nasal secretions. The virus can also be transferred indirectly, via surfaces, water buckets, tack and tools, and it can linger in the air for a few hours, par-ticularly in humid weather. Signs: coughing, fever, lethargy and nasal discharge. Some infected horses show no signs of illness. Diagnosis: Most cases of equine influenza are diagnosed based on clinical signs, the

horse’s recent history and by ruling out other similar-looking diseases (such as the respira-tory form of equine herpesvi-rus), but a definitive diagnosis can be made through a blood or nasal swab test. Treatment: The only treat-ment for influenza is supportive care. This may include medica-tions to lower fever. Fresh air is also important because in-fluenza can irritate the airways, and the additional stress may

trigger a recurrence of long-term respiratory conditions, such as heaves. Finally, rest is key to recovery. Plan on giv-ing a horse at least one week off for every day of fever, for a minimum total of three weeks. Severely affected horses may need several months of rest to fully recover. If your veterinar-ian suspects a bacterial infec-tion has taken hold during the course of influenza, he may also prescribe antibiotics.

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P R E V E N T I O N By Laurie Bonner with

Melinda Freckleton, DVM

STRANGLES

1. Vaccinate at-risk horses. Two strangles vaccines are available,

a killed-organism version (injectable) and a modified live organism (intrana-sal) preparation. Neither product offers complete protection against the dis-ease, but they will reduce the severity of signs in a horse who does become ill. Immunity does not last long; the vac-cination must be repeated every six to 12 months. In addition, if a horse who already has high levels of antibodies is vaccinated, he is at increased risk of a serious and sometimes fatal immune malfunction called purpura hemorrhag-ica. For these reasons, vaccination is

THIS HIGHLY CONTAGIOUS

DISEASE IS EASY TO CONTROL WITH BASIC

PRECAUTIONS.

Strangles---an infection of the lymph nodes caused by Streptococcus equi bacteria--- is generally not fatal, but it

can make a horse miserable and pos-es a real challenge for his caretakers. Strangles can strike any horse, but those between the ages of 4 months and 5 years are most susceptible and most likely to become more severely ill. The disease is passed by both direct contact with other horses and by indirect con-tact with contaminated surfaces. The good news is that you can take steps to reduce your horse’s chances of picking up strangles:

PROTECTION: The intranasal strangles vaccine contains a modified live organism.

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IN especially if they have come from auc-tions, racetracks or other crowded, stressful venues, keep them separated as far as possible from current resi-dents for at least two full weeks.

3. Maintain separate housing for frequent travelers. Contact

with other horses increases the risk of exposure to pathogens, and travel itself is stressful and lowers natural immunities. If you have horses you take to shows regularly, maintain separate housing for them at home that keeps them away from those who rarely leave the premises. If space is at a premium, keep the fre-quent travelers separate for at least a few days while you monitor them for signs of illness.

4. Use separate gear for each horse. The bacteria that cause

strangles can survive six to eight

weeks in water and on wood surfaces, and the disease can easily be passed from horse to horse with shared grooming tools, buckets, tack and other items. It’s a good idea to keep a separate set of tools and equipment for each horse, especially if any fall into at-risk categories. Disinfect tools periodically by scrubbing them in a mild bleach solution and laying them in bright sunlight to dry.

5. Educate visitors about touch-ing unknown horses. A

person who walks down the barn aisle touching every nose can eas-ily spread disease by hand. Be sure regulars in your barn understand the consequences of unguarded contact with all of the horses. Politely worded signs posted in prominent places may serve as good reminders, espe-cially if your barn frequently hosts casual visitors.

IN FOCUS: STRANGLES Definition: highly conta-gious infection of the lymph nodes, usually of the head, caused by Streptococcus equi bacteria. The abscesses may become so large that they obstruct the airway, hence the term “strangles.” Causes: S. equi is passed directly from horse to horse or indirectly through contact with contaminated surfaces, includ-ing fences, buckets, feeders,

tack and tools. People can carry the bacteria on their skin and clothes, too. Signs: Initially, infection causes high fever, depression, appetite loss and a thin, watery nasal discharge that soon be-comes thick and yellow; some swelling may be evident around the lymph nodes between the jawbones and near the throat. After seven to 14 days, the swellings become large, painful, hard abscesses that are likely to eventually break, draining thick, yellow pus either through

the nostril or a breach in the skin. Diagnosis: Physical exami-nation, with consideration of exposure to other animals, will point toward strangles. A bac-terial culture or PCR0 analysis of the nasal secretions confirms the presence of S. equi. Treatment: Supportive care–including stall rest and soft, easy-to-swallow food–is often the only treatment neces-sary, especially in milder cases. If the abscesses impair breath-ing or the fever rises above

103.5 degrees, more intensive treatment, including antibiot-ics, tracheostomy and surgical drainage, is needed.

A rare and serious com-plication, known as bastard strangles, occurs when S. equi bacteria travel from the upper respiratory lymph nodes and form abscesses in the lungs, brain or other unusual sites. Rupture of these abscesses, which can occur weeks after the initial strangles infection seems to be resolved, can have fatal consequences.

recommended primarily for:• young horses, including weanlings• those who travel frequently to

shows or other places where they will encounter large numbers of other horses

• those in areas where strangles oc-curs persistently

• pregnant mares, to increase the antibodies they will pass to their foals in the colostrum

Ask your veterinarian for guidance. An antibody titer is available which can determine whether an individual already has a high level of immunity against strangles.

2. Quarantine new arrivals at the farm, especially horses with an

unknown history. A horse exposed to strangles can incubate the infection for as long as 10 to 12 days before the first signs of illness develop. When new horses are brought to the farm,

E q U U S6 P r e v e n t i o n s e r i e s • d i s e a s e s

Pigeon fever, also called dryland distemper or false strangles, is not the most se-rious disease that can affect a horse. But the huge, raised

swellings it can cause---12 or more inch-es across, in some cases---are painful for him and alarming to see, especially if you’re not sure what is causing them.

The swellings are large pus-filled abscesses under the skin, which can take more than a week to mature and erupt and much longer to heal fully. It can take months for a pigeon fever outbreak to run its course through a herd, and in 3 to 4 percent of cases, complications are fatal.

P R E V E N T I O N By Laurie Bonner with Melinda Freckleton, DVM

PIGEON FEVER

Once limited to arid regions,

this bacterial infection is moving

into other parts of the country. Here’s

how to protect your horse.

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Southern California and the Southwest, but it has been spreading both north-ward and eastward. So no matter where you are, it’s worth learning how to identify the infection and take steps to protect your horse. Here’s what you need to do:

• Keep paddocks clear of manure. The bacterium that causes pigeon fever, Corynebacterium pseudotuberculosis, thrives in soil contaminated with manure, especially in hot, droughty conditions. When horses roll or lie down in paddocks or churn up clouds of bacteria-laden dust, the organisms may enter wounds, insect bites or other

Corynebacterium pseudotuberculosis

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breaks in the skin. Picking up manure regularly will help reduce the bacterial populations in the soil.

• Protect against flies. Houseflies, stable flies and horn flies have all been found to be carriers of C. pseudo-tuberculosis during outbreaks, so it’s possible that they may transmit the in-fection from horse to horse. Fly sheets and judiciously applied repellents will help keep flies away from turned-out horses. Composting manure or remov-ing it from your property also helps keep fly populations down.

• Keep wounds clean. Check your horse daily for nicks and sores, and treat any that you find with a

disinfecting cleanser labeled for use on small wounds. After the area is cleaned, applying a layer of ichtham-mol or an over-the-counter anti biotic ointment will help speed healing while preventing flies from contacting the exposed tissues. Bandaging, when possible, will also help keep insects away from sores until they can heal.

• Isolate infected horses. The pus that drains from a pigeon fever abscess is loaded with bacteria that can easily persist in the soil and infect other horses. Move infected horses as far away from others as possible. The abscesses near the surface of the skin will rupture and heal on their

own, but having them drained by a veterinarian will help contain the infection.

• Quarantine new horses. Horses may carry pigeon fever for three to four weeks before showing signs, and the shipment of carriers around the country may be contributing to the spread of the infection beyond its former boundaries. When bringing new horses onto your property, keep them isolated from resident horses long enough to be sure they are not incubating any infections. House new-comers in a separate barn or pen as far as possible from other horses for at least three weeks.

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Definition: bacterial in-fection that creates purulent abscesses. The disease takes three forms: External ab-scesses form under the skin or in the musculature. Internal abscesses form within the internal organs, usually the lungs, liver, spleen or kidneys. Ulcerative lymphangitis affects the lower legs. Signs: External abscesses

create distinct large swellings that can reach 12 inches in diameter, often on the chest, but also under the belly, on the genitals, or on virtually any other part of the body; only about 25 percent of horses with this form show signs of systemic illness. Internal ab-scesses cause fever, weight loss, colic, coughing, lethargy and other signs of illness. Ulcerative lymphangitis is characterized by swelling of the lower leg and the formation of nodules that ultimately open and drain pus,

usually along lymph tracts. Causes: Corynebacterium pseudotuberculosis bacteria penetrate the horse’s skin, either through physical contact between contaminated dirt and open wounds or via bites from flies carrying the pathogen. Diagnosis: observation of abscesses visible under the skin or within the muscles. Culture of fluids extracted from an abscess is needed to posi-tively identify the organism. Ultrasound may be needed to locate abscesses deep within the musculature or internal

organs. A blood test is avail-able that can aid in detection of internal infections. Treatment: External ab-scesses that do not interfere with breathing, swallowing or movement can be allowed to mature and drain on their own, but a veterinarian may choose to lance them. Hot compresses may speed maturation of the abscess, and anti-inflammatory medica-tions can relieve pain. Internal abscesses and ulcerative lym-phangitis require aggressive treatment with antibiotics.

IN FOCUS:

Pigeon fever

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Minimizing your horse’s exposure to ticks can help reduce his risk of contracting this difficult-to-diagnose disease.

Although named after the New England town where it was first identified, Lyme disease

is a threat to horses in many parts of the United States. The spiral-shaped bacterium Borrelia burgdorferi that causes the disease is carried by ticks commonly found in the Northeast, upper Midwest and West Coast.

B. burgdorferi infection can cause inflammatory reactions throughout the body, leading to a variety of clini-cal signs. Horses with Lyme disease may have stiff joints, mild fevers, chronic weight loss, eye inflamma-tion, laminitis, muscle tenderness, sensitive skin or any combination of these problems. As a result, it’s noto-riously difficult to diagnose.

Only about 10 percent of horses bitten by infected ticks develop clini-cal signs of Lyme disease, but the condition can be debilitating. That means it’s worth spending the time to minimize the risk of infection. If you live in an endemic area, you won’t be able to keep every tick off your horse, but here are a few steps you can take to reduce his exposure to the organ-ism that causes Lyme disease:

P R E V E N T I O N By Christine Barakat with Melinda Freckleton, DVM

LYME DISEASE

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1. Keep your pastures short and tidy. Ticks crawl up tall blades of grass

and brush to latch onto passing hors-es. Keeping turnout areas mowed to a height of five inches will make it more difficult for them to hitch a ride.

2. Use repellents even after fly sea-son. Look for products that are

labeled to work against ticks as well as flies. Ticks are most likely to transmit B. burgdorferi during the late summer months and well into fall---until tem-peratures drop below freezing---so con-tinue to use the product even after flies are no longer a problem.

3. Reduce your rodent population. The white-footed mouse is an

important reservoir for B. burgdorferi.

Eliminate old woodpiles, haphazard-ly stored blankets or other potential habitats for varmints on your property. Sweeping the grain room daily will also help keep rodents away.

4. Check your horse for ticks daily and be prepared to remove

them. Ticks crawl around on a horse’s body for a few days before biting, so keep an eye out for them during your grooming sessions. Pay particular attention to the area under the throat-latch and around the ears as well as the underside of the neck and belly; these are all locations where ticks are more likely to attach. Even if the one you find is already feeding, it’s not too late. Studies have shown the bacteria are not transmitted for 36 to 48 hours, so you

still have time to prevent infection. If you do find a feeding tick, use tweezers to grasp it gently at the head, as close to the skin as possible. Lift it straight up and away from the skin. Do not squeeze---this could send the fluids into your horse’s bloodstream. Kill the tick by submerging it in alco-hol and seal it in a tight container.

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IN FOCUS:

Lyme disease

Definition: infection with the bacterium Borrelia burg-dorferi, which is transmitted to horses via two species of Ixodes spp. ticks, variously known as deer ticks, bear ticks or black-legged ticks. Signs: fever, muscle stiff-ness, joint inflammation (partic-ularly in larger joints), mild and

transient lameness, behavioral changes, hypersensitivity. Diagnosis: Because the signs of Lyme are vague and as many as 50 percent of horses in endemic areas may carry anti-bodies to the bacteria, diagnosis is difficult. Testing options are improving but are still imperfect. Most veterinarians rule out other

possibilities before settling on a diagnosis of Lyme. Treatment: a course of antibiotics, usually tetracycline and doxycycline. Because treat-ment carries the risk of several side effects, including laminitis0 and kidney damage, it is typi-cally reserved for horses show-ing clinical signs of disease.deer tick

white-footed mouse

What about a vaccine?Although no equine vaccine against

Lyme disease is currently available, you may have heard that the canine vaccine can be used to protect horses. Some veterinarians in high-risk areas may recommend this option, but only on a case-by-case basis after weighing the risks and benefits.

E q U U S1 0 P r e v e n t i o n s e r i e s • d i s e a s e s

WS P R E V E N T I O N By Laurie Bonner with

Melinda Freckleton, DVM

RHINOPNEUMONITIS

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This respiratory disease spreads easily, but you can take steps to protect your horse.

Rhinopneumonitis (rhino) is a highly contagious respiratory infection that causes a variety

of signs including nasal discharge, congested breathing, fever, lethargy, loss of appetite and cough. The sever-ity of the illness may range from barely noticeable to quite severe, and most horses recover readily.

However, the viruses that cause rhino---equine herpesvirus type 1 (EHV-1) and type 4 (EHV-4)---can sometimes take a dangerous turn. EHV-1 infections may cause abortion---a sudden outbreak can cause every mare in a herd to lose her pregnancy. Certain strains of EHV-1 and -4 are also capable of infecting a horse’s central nervous system, and he may develop neurological disease with signs ranging from muscle weakness, a flaccid tail and urine dribbling to full paralysis and recumbency.

EHV-1 spreads from horse to horse through direct nose-to-nose contact,

from contact with infected surfaces, and via airborne droplets from the breath of an infected horse. The virus can also be carried on people’s hands and clothes. Most horses are exposed to the virus at some point in their lives and build up a natural immunity---the illness is likely to be more severe in younger horses who are newly exposed than in mature adults. Once exposed, almost any horse can become a latent carrier---one who can shed the virus and spread infection without showing signs of illness. Because EHV-1 is so ubiquitous, pre-venting rhino completely isn’t possible. But you can take steps to protect your horse and to limit the spread of the disease when an outbreak does occur:

1. Consider vaccination. The American Association of Equine

Practitioners recommends vaccina-tion against EHV only for those horses most at risk of exposure to the virus. Generally, that means horses who travel frequently to shows or other crowded events as well as those who remain at home but are exposed to the travelers. Pregnant mares are also routinely vac-cinated, both to avert “abortion storms” and to confer immunity to their foals. Other horses on breeding farms may be vaccinated for added protection of the mares. Talk to your veterinarian about your horse’s risk of exposure, especial-ly if your circumstances have changed since you last discussed vaccinations. Be aware, too, that the vaccine for EHV

E q U U S1 1 P r e v e n t i o n s e r i e s • d i s e a s e s

will not necessarily prevent a horse from developing rhino, but it may reduce the severity of his illness. Vaccination may also reduce the amount of virus the ill horse sheds, decreasing the risk to others around him.

2. Prevent close contact with strange horses. Keep your horse well away

from others at shows and on trails. Nose-to-nose contact easily spreads the virus, but EHV is also transmitted on micro-scopic water droplets from the breath of an infected horse, so eight to 10 feet is an ideal distance.

3. Avoid shared water and equipment. EHV survives for hours or days in

water troughs and on hard surfaces. Use your own water buckets instead of com-munal troughs when you travel with your horse, and do not swap tack or tools with others at shows or events. At home, make sure each horse in your care has his own set of buckets,

tack and grooming tools. One handy way to keep things straight is to assign each horse his own color, and use multicol-ored electrical tapes to tag items.

4. Wash your hands after working with each horse. You can carry

EHV on your clothes and hands for four to six hours after exposure to a horse who is shedding the virus. Make it a habit to wash or sanitize your hands when moving from horse to horse as you go about your chores. A few well-placed bottles of hand sanitizer in the barn can make this habit more conve-nient. If you frequently have visitors in your barn, post signs asking people not to go down the aisle touching every friendly face.

5. Isolate newcomers to the farm. A horse who has been recently ex-

posed to EHV can incubate the infection for up to 12 or 14 days before showing any signs of illness, and he may pass

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INthe virus to others during that time. Keep a new arrival at your farm away from the resident herd for at least two weeks, especially if he came from an auction or another crowded, stress-ful place. If you don’t have a separate barn, designate an end stall as a quar-antine area, and use fans to direct the airflow out the door and away from the other stalls. Turn the isolated horse out into a separate area that does not share a fence with your resident herd. It’s also a good idea to have separate housing for horses who travel fre-quently, at least during the show sea-son, to prevent them from bringing the virus back to the “homebodies.”

6. Use your thermometer. Take the temperatures of all traveling

horses twice daily. Start at least three days before you leave and continue for at least five days after your trip. Call your veterinarian should you discover any fevers.

Definition: highly con-tagious respiratory disease caused by herpesviruses (EHV-1, EHV-4). In rare cases, some strains of these herpesviruses also cause potentially fatal neurological complications. Causes: EHV passes from horse to horse through direct nose-to-nose contact, from

contact with infected surfaces, and via airborne droplets from the breath of an infected horse. Signs: nasal discharge, congestion, fever, lethargy, loss of appetite, cough. Mares may abort or deliver a weak, inviable foal. Horses with the neurologi-cal form may become recum-bent and/or have hindquarter

weakness, flaccid tail and de-creased anal muscle tone. Diagnosis: observation of signs. To confirm the diagno-sis, a veterinarian may collect a nasal swab and/or blood sample for laboratory tests to detect the virus. This may be done to identify the particular strain of EHV that has infected the horse. Treatment: supportive care,

including intravenous fluids, anti-inflammatory drugs and antiviral drugs. Those with the neurological form may require additional measures. Horses with EHV need to be isolated from others. Most horses re-cover fully with no long-term repercussions, even from the neurological form. Those who become recumbent have the poorest prognosis.

IN FOCUS: Rhinopneumonitis