Healthy as a… an encyclopedia of horse illnesses |

Healthy as a… an encyclopedia of horse illnesses

EHV can cause abortion in mares and upper respiratory tract disease in foals. Photo by Deanna Licking

It’s been said that the cheapest part of owning a horse is the purchase price. The Equine species though large and powerful, can be extremely delicate and susceptible to a myriad of problems.

VESICULAR STOMATITIS (VS): Is very contagious affecting horses, livestock, wildlife and humans. It is viral and reportable, once it’s confirmed the affected premises will be quarantined to reduce the spread of the disease, until 14 days from the onset of the last case. Blister like lesions can develop on the tongue, mouth lining, lips or nose and sometimes on the coronary bands, udder or sheath. Once suspected, a blood test is used to confirm the disease. The virus is spread by insects and direct contact.

The incubation period from exposure to first signs range from two to eight days, a fever may develop first as blisters form; one obvious sign is drooling or frothing at the mouth and not eating. The disease generally runs its course in two weeks, but may take up to two months for all the sores to heal. Live virus can be isolated from the lesions for up to a week after they first appear, during this time it is highly contagious. Soft feed may help reduce mouth discomfort, and anti-inflammatory medications used as comfort measures.

STRANGLES OR EQUINE DISTEMPER: (Streptococcus Equi): Is infectious and contagious, characterized by abscesses of the lymphoid tissue of the upper respiratory tract. It is transmissible through direct contact and fomites. It can survive up to four weeks outside the host under ideal circumstances. The incubation period is three to fourteen days and the first sign is a fever (103-106F). The horse will exhibit nasal discharge and depression, in rare cases infected horses can develop brain abscesses. Keep ill horses in a warm, dry and dust free environment. Warm compresses can help abscesses to mature and once ruptured flush with iodine for several days until discharge ceases. The attack rate is reduced by 50% in horses vaccinated.

RHINOPHEUMONITIS/ EQUINE HERPES VIRUS (EHV): nine strains of EHV have been identified worldwide, but EHV 1, 3, and 4 pose the most serious health risk for domestic horses.

EHV-1: can cause four manifestations of disease in horses, including neurological form, respiratory disease, abortion and neonatal death.

EHV-3: Causes a venereal disease called coital exanthema that affects the external genitalia but doesn’t affect fertility.

EHV-4: Causes nonfatal upper respiratory tract disease in foals and sometimes abortion and neurological disease.

EHV is a common DNA virus that occurs in horses worldwide. EHV-1 is contagious; spread by direct contact between horses and shared equipment. The virus can survive from seven days to a month in the environment. Cleaning and disinfecting everything that comes in contact with infected horses is extremely important.

After infection, the incubation period can be from 24 hours to six days or longer. EHV-1 causes a two-phase fever peaking on day one or two and again on day six or seven, often with nasal and eye discharge, but little coughing. Neurological disease appears suddenly and progresses rapidly, reaching its peak within 24 to 48 hours. Signs include: nasal discharge, incoordination, hind limb weakness, loss of tail tone, lethargy, urine dribbling, head tilt, leaning against fence or wall for balance, and inability to rise.

Diagnosis by a veterinarian includes, nasal swab and blood test to detect virus. Infected premises are quarantined for 21 to 28 days after the last new infection. Ill animals are treated with anti-inflammatory drugs and sometime IV fluids. Antibiotics can be used to treat secondary infections but they have no effect on EHV itself. The best protection is vaccination and biosecurity measures.

EQUINE ENCEPHALOMYELITIS (SLEEPING SICKNESS): There are three main strains, Eastern, Western and Venezuelan Equine Encephalomyelitis. It is caused by Alphaviruses, carried by birds and rodents and transmitted by the bite of infected mosquitoes; unvaccinated horses are the most susceptible.

Symptoms cause non-specific clinical signs and often affect the central nervous system: fever, severe depression (Sleeping Sickness), behavior changes, impaired vision, circling or head pressure, muscle twitches, inability to swallow, paralysis, convulsions and death. Supportive care is the only treatment, survival rates for horses with Eastern and Venezuelan are very low, but survival rates with Western can be as high as 70-80 percent. Vaccination is the most effective at preventing the disease, along with eliminating mosquito breeding areas.

EQUINE INFECTIOUS ANEMIA VIRUS (EIA): it is non-contagious but transmitted by blood-feeding insects, but also by blood contaminated equipment. The incubation period is 15 to 45 days or longer and progresses through three clinical phases. First signs are fever, depression and poor blood clotting, all of which are often mild and easily overlooked. This is followed by a prolonged period of recurring episodes of fever, anemia, muscle weakness and loss of condition. The intervals between episodes can range from days to months, the symptoms subside within a year but the horse becomes an inapparent carrier. The Coggins blood test is the most common testing method, seropositive horses must be quarantined and reactor horses must be euthanized or quarantined for life. Annual Coggins testing of all horses, controlling insects and good hygiene is recommended.

WEST NILE ENCEPHALOMYELITIS: Is inflammation in the brain or spinal cord. This viral disease is transmitted primarily by mosquitoes from a bird host. The infection rate in horses is low around 10 percent but the mortality rate is high around 50 percent. Symptoms include: discomfort or lameness, low-grade fever, muzzle twitching, impaired vision and lack of coordination. A blood test is necessary for diagnosis. Treatment includes supportive care and anti-inflammatory drugs. Most horses that recover will return to normal in one to six months. Preventive vaccination is the most effective.

EQUINE INFLUENZA: Is highly contagious and spreads rapidly among susceptible horses, generally ones under age five. It is rarely fatal except in weak animals. Transmission is by inhalation of respiratory secretions, with an incubation of one to three days. A high fever, clear nasal discharge, swollen lymph nodes and a dry cough. Depression, loss of appetite and weakness are often seen. The signs last less than three days in uncomplicated cases but the cough may persist for weeks. Mild cases recover in two to three weeks but severe ones may take up to six months. The diagnosis is made by testing nasal and throat secretions. Generally rest and supportive care are all that is needed, with a week of rest for every day of fever with a minimum of three weeks rest. Nonsteroidal anti-inflammatory drugs and antibiotics may be used to treat a long lasting high fever.

Prevention includes good hygiene and isolating new horses from the herd for two weeks. There are also vaccinations available, with a booster recommended every six months.

EQUINE RABIES: An acute viral infection of the nervous system. Once signs appear it is fatal. Transmission is through the bite of an infected animal, in horses the virus can be in the body for days or months before signs develop. Two major forms of rabies are seen, the “Mad Dog” syndrome: horses show rapidly developing signs of distress and extreme agitation, rolling, biting, striking, unmanageability and self-inflicted wounds.

The “Paralytic” form involves paralysis of the throat and jaw, excessive salivation and inability to swallow. People can become infected when examining the mouth or giving medication with bare hands. The only diagnosis is a laboratory analysis of the euthanized animal. Annual vaccination is the best preventive measure.

TETANUS (LOCKJAW): Is a toxic reaction to the toxin produced by the bacteria Clostridium Tetani in dead tissue, with horses and humans being the most susceptible. The bacteria is found in the soil and intestinal tracts and introduced into the body through deep puncture wounds. The incubation period varies from one day to several weeks, averaging around 10-14 days. Localized stiffness, often of the jaw and neck muscles, the hind limbs and region of the wound. General stiffness, followed by spasms and sensitivity to touch become evident. The spasms and stiffness will become worse. About 80 percent of them will die but those that survive will take two to six weeks for recovery. Supportive care and keeping in a dark stall with feed and water high enough so that they don’t have to lower the head can help. Immunization is recommended annually.

Information sourced from Merck Vet Manual at

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