Lesson 6

Important Equine Diseases

Equine diseases are either spread horse-to-horse (contagious), or spread by a vector (a host spreads the disease, for example, a mosquito). This lesson covers some of the common equine diseases. It is not necessary to be able to diagnosis the diseases (that’s up to your vet), but being familiar with the common equine diseases will benefit horses under your care.

CONTAGIOUS EQUINE DISEASES

Equine Influenza Virus (Flu)

This is a very contagious disease. When it shows up in a barn area, it is very difficult to prevent exposure to all horses in the area. The equine influenza virus (EIV) is an “endemic” – a disease that can be contracted at any time. Explosive epidemics (an outbreak that occurs suddenly and in greater numbers than normal) occurs every several years. Only Australia, New Zealand and Iceland are equine influenza-free.

Transmission - The disease is spread through horse to horse contact, ---aerosol, shared water, feed, where horses congregate. The virus can be carried in the air from a cough or sneeze for up to 30 feet.

Symptoms- High fever 103 -106 F, (39-41 C), off feed, dull or depressed, cough, runny nose.

Treatment – Rest, alleviate stress, bad weather, overcrowding, hauling. Prevent secondary bacterial infections.

Prevention - Vaccinate at least annually. In high risk cases (horses that travel), vaccinate well prior to event or every 3 months. Intranasal vaccine may prove to offer longer immunity (possibly up to 9 months.)

Equine Herpesvirus (EHV) or Rhinopneumonitis (Rhino)

The equine herpesvirus is also a very contagious disease and is an endemic. There are two types: EHV-1 and EHV-4. There is a mutant of EHV-1 recently described that has a higher mortality rate. EHV-1 can cause abortion in broodmares.

Transmission - Same as Influenza.

Symptoms - Usually milder than flu, but very similar. Less commonly seen are neurological symptoms which may include: incoordination or paralysis. Rhino can be fatal.

PREGNANT MARES - Uncomplicated abortion or stillbirth (last trimester).

The mare can carry the virus in system. (EHV-1)

Treatment-- Rest. Keep from stress. Neurological symptoms require vet care. Aborting mares usually have no after effects.

Prevention – Vaccinate with a modified-live virus vaccine at least annually. (Prestige, Calvenza, Innovator) There is one modified-live vaccine (Rhinomune) that will help prevent the development of respiratory disease induced by EHV-1 and EHV-4.

Pregnant mares - killed virus vaccine. (Pneumabort K and Prodigy) Vaccination a must at third, fifth, seventh and ninth months.

None of the vaccinations are 100% effective. Vaccinated horses that contract EHV may have less severe symptoms. At facilities with confirmed EHV-1 booster vaccinations should be given to all horses.

Equine Viral Arteritis (EVA)

This disease is similar to Rhinopneumonitis, but much less prevalent, can also cause abortions. Not life-threatening to healthy adult horses.

Transmission – same as EHV and EIV, through exposure to respiratory secretions.

Symptoms – fever, depression, swollen glands (udder in mares, scrotum in geldings and stallions), edema, weepy runny eyes, nasal discharge, abortion in unvaccinated broodmares.

Treatment – supportive care. Euthanasia is recommended for foals that contracted the disease in-vitro (foaled with it).

Prevention - Vaccine is available, may be used in special circumstances, not for use in pregnant mares. Isolate new horses for 3-4 weeks, and practice good management procedures.

Strangles—Distemper

Cause: Bacteria - Strep equi

Transmission- Very contagious. Spores can live in soil for years. Spread by direct contact (horse to horse). Easily spread by attendants or handlers via clothes and hands; spread by contaminated tack, buckets, horse trailers and other inanimate objects. Sharing common water buckets troughs and feeders. Insects that get the nasal discharge or drainage from ruptured lymph nodes on their bodies can spread it. Survival rate of the virus is high when in areas that are damp, protected from sunlight and direct contact with disinfectants is avoided . There is a two to three-week incubation period.

Symptoms - Lymph glands under jaw or throat area enlarge, painful, hot, abscess. The horse goes off his feed, thick nasal discharge, cough. The horse will have difficulty swallowing or breathing ( strangles). Lymph glands abscess and burst.

Treatment-- Penicillin. Let abscess rupture before Penicillin administered, if possible. Good sanitary practices.

Prevention – Vaccine may cause complications - abscess formations at injection site, produce clinical disease. The question is always is the vaccine worse than disease? There is a new intranasal (Pinnacle IN) treatment which is effective, with fewer side effects. Quarantine the horse; avoid contact, good preventative measures

It is estimated 75% of the horses that recover from the disease have possible lifetime immunity. .

Bastard strangles - abscess formation in other areas of body than the submandibular (between the jaw bones) and/or retropharyngeal (at the back of the throat) lymph nodes.

EQUINE DISEASES SPREAD BY A VECTOR

Encephalomyelitis (Sleeping Sickness)

(EEE, WEE, VEE (up from Mexico)

Several types of encephalomyelitis depending on geographic location: Eastern Equine Encephalomyelitis (EEE), Western Equine Encephalomyelitis (WEE) and Venezuelan Equine Encephalomyelitis (VEE).

EEE: in the United States: eastern, southeastern and some southern states. Also found in Central and South America, and the Caribbean.

WEE: in the United States: western and mid-western states, variants have been found in the northeast and southeast states. Also found in Canada and Mexico.

VEE: no cases in the United States reported in the last 35 years. Primarily found in South America and Central America.

Cause - Virus

Transmission - Mosquito born disease. Bird - mosquito- horse or man. No horse to man transmission except for VEE, which can be transmitted by the moisture in the breath.

Symptoms - Fever, depression, incoordination, staggering, paralysis. May result in death.

Treatment - Intense veterinary care.

Prevention: At least annual vaccination. Preferably spring and fall.

Tetanus (Lockjaw)

Cause -- Bacteria “toxin”, or wound infection (navel). Bacterial spores found in soil and manure.

Symptoms-- About 7-10 days after wound infection, the horse will show stiffness of limbs and neck. There will be stumbling, erect ears. The third eyelid will be evident especially when the horse is excited. The horse may have a stiff “sawhorse” appearance. Death is possible.

Treatment -- Antitoxin, Penicillin, dark quiet surroundings, good nursing care. Put cotton in ears to reduce sensitivity to sound.

Prevention - Tetanus toxoid annually, after the initial two-dose vaccination series (4-6 week span between the two initial vaccinations). Good immunity. The annual vaccination will help build an immunity to tetanus.

American Association of Equine Practitioners broodmare and foal recommendations:

Pregnant mares previously vaccinated against tetanus: Vaccinate annually 4 to 6 weeks before foaling, both to protect the mare should foaling-induced trauma or retained placenta occur and to enhance concentrations of colostral immunoglobulins.

Pregnant mares unvaccinated against tetanus or of unknown vaccinal history: Administer a 2-dose primary series of tetanus toxoid with a 4 to 6 week interval between doses. Revaccinate 4 to 6 weeks before foaling.

Foals of mares vaccinated against tetanus in the pre-partum period: Administer a primary 3-dose series of tetanus toxoid beginning at 4 to 6 months of age.  A 4 to 6 week interval between the first and second doses is recommended. The third dose should be administered at 10 to 12 months of age.

Foals of unvaccinated mares or mares of unknown vaccinal history: Administer a primary 3-dose series of toxoid beginning at 1-4 months of age with 4-week intervals between doses. Serologic data indicates that a 3-dose initial series produces a more consistent anamnestic response in all foals, regardless of the age at which the series is initiated.  Tetanus antitoxin is indicated to provide passive immunity in situations where a foal is born to a non-vaccinated mare and is at risk of tetanus infection.

Tetanus antitoxin – used when immunity is questioned – for example if the wounded horse was not vaccinated with tetanus toxoid within the past 12 months. Takes effect almost immediately, but only remains in the system for approximately 10 days. Slight risk of “serum hepatitis” after administration of the antitoxin due to it being an equine serum product – this is very rare, but needs to be acknowledged.

Equine Infectious Anemia (EIA)

Cause - Virus

Transmission - Biting flies. Seen in about 1% of population, mostly in wet areas of country, which is why it is also known as swamp fever. Contaminated needles and syringes.

Symptoms - ACUTE --fever, depressed, weak, decreased appetite, could die within 2 or 3 days.

CHRONIC- -very poor condition, anemic, jaundice, limb edema (stocking up)

INAPPEARENT CARRIER - unthrifty or normal in appearance. Carries the virus in the blood.

Prevention -- No Vaccine available at this time in U.S. State Regulations require a negative Coggins test. AGID or ELISA (false positives?). Quarantine or slaughter. Always get a second test if first is positive.

Equine Protozoal Myloencephalitis (EPM)

(Neurological disease caused by protozoa which is carried by the opossum and is shed in opossum droppings.)

Transmission--The horse eats fecal contaminated feed and gets infected with the protozoa, which travels to the brain and spinal cord.

Symptoms-- In-coordination and hindquarter muscle atrophy, tilting of the head, leaning against a solid object for stability, muscle wasting (atrophy) and paralysis (especially in the muscles of the face), trouble swallowing, sweating.

Treatment – anti-protozoal drugs, supportive care with antioxidants (vitamin E) and anti-inflammatory drugs. The drugs used have side-effects, monitoring the horse is critical. Total recovery is not high, relapse is common.

Prevention – A vaccine is available for endemic areas. Control of opposum, skunks and other possible transmitters. Keep feed in a room or container that cannot be accessed by animals. Maintain a clean stable to prevent the attraction of rodents. Do not feed horses on the bare ground. Remove dead animals quickly to discourage scavengers. Maintain clean water receptacles at all times.

Potomac Horse Fever

Cause-- Equine monocytic ehrlichiosis caused by Neorickettsia risticii – originally found along rivers of the east coast (Potomac River), but has spread to other areas. Spread by adult caddisflies (Trichoptera), mayflies (Ephemeroptera), damselflies (Odonata, Zygoptera), dragonflies (Odonata, Anisoptera), and stoneflies (Plecoptera). The horses inadvertently consume the insects by eating contaminated forage or drinking water that is harboring the immature insects.

Symptoms – The horse goes off feed, depressed, mild fever, mild colic (will go from no gut sounds to severe diarrhea in 48 hours), and infected pregnant mares may abort. Many horses founder and many die.

Prevention – Stable horses during the night and turn off lights so the insects are not attracted to the barn. Do not allow horses to drink from ponds, streams, swamps or other bodies of water. Vaccinate in endemic area (none of the current vaccines state they will prevent abortion).

West Nile Virus (WNV)

Cause - The virus starts in the bloodstream of birds and is spread by mosquitos. Mosquitos acquire WNV in blood meals from infected birds and pass it on to other birds, animals, and people. Non-infected mosquitos that feed on an infected horse or human have not demonstrated the ability to ingest enough of the virus to transmit it to other animals or humans; therefore, horses and humans are considered “dead end hosts.” It is the leading cause of arbovirus encephalitis (inflammation of the brain) in horses.

Symptoms – fever, weakness and/or paralysis of hind limbs, lack of coordination and stumbling (most commonly described symptom), walking in circles, change in behavior (depression or excitability), anorexia (off feed), lower lip hangs or droops, muscles twitching, grinding teeth, inability to swallow, head pressing, colicky appearance, excessive sweating, disorientation, convulsions, weakness, impaired vision, and possible total paralysis.

Prevention – vaccines are available. Eliminate breeding areas for mosquitoes – drain swamps, remove reservoirs where standing water may accumulate (unused stock tanks, flower pots, buckets, old tires, unused swimming pools). Aerate (keep water moving) in water holding vessels, drain and clean water tanks every couple of days. Use spray or fly sheets to protect horses. Bring horses in before dusk when mosquitos are at their most active. Eliminate roosting and nesting areas for birds. (Report any dead birds, especially crows to your veterinarian.)

Treatment – Supportive care: fluids. Anti-inflammatory drugs may help. Horse must be kept in an area so it does not hurt itself. Most horses will recover, but a few will not return to full normal function.

Rabies

Cause - a virus transmitted by a dog, skunk, raccoon or coyote bite. Horse is usually exposed when bitten by the infected animal.

Symptoms – may not show symptoms for several weeks to months after exposure. Symptoms are similar to other diseases, for example EPM, WNV, EHV and botulism poisoning. Symptoms may be: a change in behavior, difficulty swallowing, staggering or lack of coordination, pressing head against walls, biting at the bite location, sensitivity to light, low fever. As the disease advances the infected animal may become vicious.

Prevention - Vaccinate yearly against rabies. Secure stable area against wild animals, don’t leave feed out that will attract animals, vaccinate pets.

Treatment – none: euthanasia is the humane step to be taken immediately.

* Rabies is zoonotic – it can be spread to humans from animals. Care must be taken if you suspect the horse has rabies.

African Horse Sickness

AHS is primarily found in Africa. Outbreaks have occurred in the Middle East, Egypt, Arabia, India, Spain and Portugal.

Cause – the virus orbivirus. Spread by insects (mosquitoes, midges and ticks).

Symptoms – (disease has four forms: pulmonary, cardiac, mild and mixed). Fever, depression, respiratory distress, colic, conjunctivitis, edema under the skin of head and neck, congested mucous membranes. Horses may stand with legs spread and neck stretched out.

Prevention – vaccination, Quarantine and slaughter of infected horses. Control insects that spread the disease.

Treatment –Supportive care. Recovery depends on which form the horse has. Euthanasia in horses that show no signs of recovering.

Other

Valley Fever - Fungal pneumonia. Dust, found in Arizona, no vaccine, difficult to cure.

Ringworm - Fungal skin disease. Very contagious and can be transmitted by combs, saddle pads, brushes, bridles, etc. Treat with tamed Iodine, Clorox 10%, Nolvasan. There is no vaccine.

Warts – virus; usually seen in young horses. Usually self limiting. Clears up in 2 to 3 months. Most often seen on muzzle and lips. Spread by contact.

Lyme Disease - Tick born bacterial disease. Mountainous areas. Polyarthritis, fever, lethargy, depression, Possible death or forever lame. Vaccine is available, used regionally.

Rodococcus Equi - Dust pneumonia in foals. Bacterial. Generally there are lung abscesses. Serum is available for preventions, but are new and expensive. Treat with Erythromycin & Rifampin. This is a stubborn disease.

EQUINE VACCINES AND VACINATION SCHEDULES

Vaccines are available for the following Equine diseases:

1. Eastern equine encephalitis.

2. Western equine encephalitis

3. Venezuelan equine encephalitis

4. West Nile encephalitis

5. Equine influenza injectible and Intranasal –(AVERT)

6. Equine Rhinopneumonitis Upper-respiratory and abortion) Calvenza –intranasal or injectable protects against the respiratory diseases of Influenza and Rhinopneumonitis

7. Equine viral arteritis (upper-respiratory and genital types)

8. Tetanus (toxin and antitoxin)

9. Botulism

10. Strangles Injectible bacterin and new Intranasal (PINNACLE)

11. Potomac horse fever

12. Lyme disease

13. Rabies

Click Here for American Association of Equine Practitioners recommended vaccines for adult horses chart.

Click Here for American Association of Equine Practitioners recommended vaccines for foals chart.

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