Equine Vaccination Overview

EQUINE VACCINATION RATIONAL .......

Eastern Equine Encephalomyelitis (EEE)

--An acute, often fatal, viral disease of horses, humans, pheasants, and partridge.

--It occurs seasonally as it is carried by mosquitoes. EEE may occur whenever mosquitoes are present in your area.

--Symptoms are depression,fever poor appetite, and behavior changes, leading to generalized weakness,ataxia,paralysis, and usually death.

--Vaccination..foals starting at 3-4 months of age,with boostering 3 weeks later; annual shots thereafter are satisfactory, preferably in the spring.

Western Equine Encephalomyelitis (WEE)

--A potentially fatal viral disease of horses, mules, donkeys,and humans.

--It occurs seasonally like EEE, mosquitoes are the vector.

--The reservoir is infected birds which keep the virus in the area from year to year. The mosquito acquires the virus by taking a blood meal from infected birds.

--Symptoms may be no more than a transient fever, decreased appetite and depression. If the virus penetrates the brain,then neurologic signs will be seen and death may result.

--Vaccination..foals at 3-4 months, with booster in three weeks. Adults are protected by a yearly booster, preferably in spring.

Tetanus

--A bacterial disease of all mammals, with horses being the most susceptible.

--The disease usually occurs after a puncture wound, obstetrical complications,post castration infection,and umbilical infection. A nail puncture to the hoof is a very common cause of tetanus.

--The bacteria causing the disease-Clostridium tetani is a normal inhabitant of the gastrointestinal tract and is therefore abundant in feces. The disease is found worldwide.

--The disease may take days to several months to develop with shorter incubation periods being most common.

--Symptoms include spasm and paralysis of voluntary muscles (lock jaw),prolapsing of the third eyelid. A stiff "sawhorse" stance is common. Walking becomes difficult and loud noises can precipitate convulsions.

--Death is usually secondary to respiratory paralysis.

--Vaccination..foals usually at birth with tetanus toxoid, followed by revaccination at 3 months and boosterlng 3 weeks later. Annual boosters are adequate thereafter

Rabies

--A viral disease affecting the central nervous system. There are no definitive tests which can confirm the disease while the horse is alive.

--The disease is transmitted most often from the bite of a wild carnivore (skunk, fox, bat, raccoon). Not all bites from infected carriers will necessarily transmit the disease. Infection depends on the concentration of the virus in salivary secretions. The length of incubation is extremely variable relating to the proximity of the bite to the central nervous system, (i.e.; bites to the head and neck are manifested much faster than bites to the legs). Some reports indicate the disease may not become apparent for as long as one year after a bite.

--Symptoms are extremely variable, with possible signs including colic,lameness,ataxia,paresis,incontinence,inability to chew and many more. Most horses appear dull and depressed, than those showing excitement and aggression.

--Diagnosis can only be made by post mortem examination of the brain.

--Vaccination..foals at three months followed in three weeks by a booster. Adults are revaccinated annually.

Strangles (Streptococcus Equi)

--A bacterial disease caused by Streptococcus equi. This disease affects only horses and their relatives, (donkeys,zebras,etc.) The classic disease is manifested by mucopurulent (pus and mucous) nasal discharge and submandibular lymphadnopathy(swollen lymph nodes under the jaw).

--Affected horses often run a fever and go off feed due to an irritated pharynx and throat.

--The swollen lymph nodes often rupture and drain pus. The pus discharged is grossly contaminated with the Streptococcus equi organism and can spread the disease to other horses through contaminated stalls, water buckets, and troughs, etc.

--During fly season, flies will land on a draining abcess, then move to the muzzle or eyes of another horse, spreading the disease.

--The organism is extremely susceptible to penicillin, and the disease course can be drastically reduced in many cases by administering penicillin.

--Penicillin treatment does not cause bastard strangles, as was once thought, according to recent research at the University of Pennsylvania.

--Complications associated with this disease include pneumonia, pleuro-pneumonia,intra abdominal and thoracic abscess formation, gutteral pouch empyema, myocarditis and abscess formation in other parts of the body.

--Mortality.can occur in 2% to 10% of the cases in a particular barn if infected with virulent forms of the organism.

--Vaccination for this disease is not 100% efficatious,but horses which do contract the disease do not develop the serious pathologic signs seen in unvaccinated horses.

--Vaccination..foais at 3 months followed by one or two boosters at 3 week intervals and every 6 months thereafter. Some social barns with rapid turnovers of horses may need to vaccinate 3 to 6 times per year.

Equine Rhinopneumonitis (Equine Herpes Virus) (EHV-I)

--EHV-1 or "Rhino" as it is commonly called, causes respiratory disease,

abortion in mares, and occasionally paralysis (herpes myelitis,if the viris attacks the central nervous system).

--The viris is transmitted by inhaling viris contaminated aerosol droplets.

--EHV-1 is a particular problem in young horses under three years of age, but can affect any age horse.

--Symptoms include fever,depression, and a clear nasal discharge, which can change to a purulent discharge when complicated by secondary bacterial infection.

--Death is rare in the respiratory form of the disease, however when EHV-I affects the central nervous system horses may die or have to be humanely destroyed.

--Vaccination..foals at three months followed by a booster three weeks later,then every four months.

--It is suggested only the killed form of the vaccine should be used. The modified live form has reportedly precipitated abortion on some farms.

--New research suggests that there may be two or more subtypes of EHV-I, with a specific type of abortion and a specific type causing CNS or respiratory forms. However, there is apparent antigentic crossover so one vaccine covers both subtypes.

Equine Influenza

--"Flu" in the equine has somewhat similar symptoms to that of humans with cough,fever,decrease in appetite,and muscle soreness --Coughing is the most obvious sign.

--Secondary bacterial infection is a common sequela of the disease.

--Horses infected with the disease should be rested one to three weeks and treated with antibiotics if secondary bacterial infection arises.

--Mortality is rare in this disease if the infected horses are allowed to convalesce properly.

--However,horses which are trained or raced while still sick have been known to become severely debilitated and die.

--Vaccination..foals at three months with three week booster, every 3-4 months thereafter.

Potomac Horse Fever (PHF)

--This disease is caused by an Ehrlichia organism called Ehrlichia risticii, which causes acute enteric (intestinal) disease in horses. The disease was first recognized in Maryland near the Potomac River in 1979. Outbreaks seem to follow rivers and is also prevalent in lake areas.

--Spread of the disease is by one or more biting insects (arthropods),but to date no definitive vector has been recognized.

--The disease usually presents initially with mild depression and lack of appetite,along with temperature elevation.

--Gut sounds are noticeably decreased or totally absent.

--Within 24 to 48 hours the horse develops profuse watery diarrhea.

--Laminitis develops in about 25X of the cases and is often the secondary manifestation which may necessitate humane destruction of the horse.

--Some horses may show only the depression,and decreased appetite for 2 days, and then return to normal spontaneously.

--Horses which develop diarrhea need intense fluid therapy to maintain hydration, often for as long as 10 days.

--The Erhlichia organism is sensitive to intravenous tetracycline therapy. This is especially effective when administered prior to the onset of diarrhea.

--Since the diarrhea caused by PHF cannot be differentiated from diarrhea caused by Salmonella or enterocolitis the veterinarian is playing a guessing game by using tetracycline because it can exaggerate the symptoms of salmonella or enterocolitis.

--The mortality rate of horses developing PHF has been reported in ranges between 17% and 36%.

--Even some vaccinated horses have developed the PHF diarrhea,and necessitated both fluid and tetracycline therapy but the majority of vaccinated horses develop either "complete" or "partial" immunity to the disease, and that makes the

vaccination of value.

--Vaccination..foals at 3 months followed by booster in 3 weeks and every six months thereafter. Adults-2 shot booster 3 weeks apart with a booster every six months.

Equine Viral Arteritis(EVA)

--A viral disease causing fever,lacrimation(runny eyes),limb edema weakness,diarrhea,and abortion.

--Blood studies indicate the disease infection to be much more prevalent than is readily apparent by clinical signs.

--There is no good treatment for EVA other than supportive therapy (fluids,anti-biotics,non-steroidal anti-inflammatories).

--This is an especially significant disease on breeding farms, because stallions are reported to shed the virus in semen for life.

--Vaccination is not on the routine list,and some areas require permission by the state veterinarian to vaccinate.

--Use of the vaccine on selected horses (breeding stock), which are being sent in the high risk areas where active cases are being reported (recently Kentucky~ Arizona, and "unofficially" Minnesota) is suggested.

-- Leprospirosis

--One of several diseases known to cause "moonblindedness" in horses, and on rare occasions, abortion in the broodmares, along with other clinical diseases.

--At this time there is no approved vaccine for use in equine, and there are some cases where moonblindedness was precipitated by the vaccine used on horses.

--Some practitioners feel vaccinating for leptosplrosis is of value, Experts at several Veterinary Colleges have recommended not vaccinating horses at this time.

--Summary

It is suggested that horses in social environments (horses going to shows, in sale barns, barns with large populations, breeding farms, and race horses)~ should be vaccinated according to the mentioned protocols; This would

include encephalomyelitis, tetanus, strangles, rhinopneumonitis, influenza, and Potomac Horse Fever.

"Backyard'' horses which are never in contact with others may do very well with only encephalomyelitis, tetanus, and PHF, and possibly rabies if they are outside in areas where skunks and other vectors are prevalent.

It should be pointed out that there are a few other viral diseases which affect equines for which no vaccine is available {adenovirus and rhino virus). These diseases can mimic rhinopneumonitis and influenza symptoms.

Also, environmental factors such as dusty or moldy hay and stalls with high ammonia levels due to improper cleaning can lead to horses having chronic coughs and a generalized decrease in respiratory natural defense mechanisms.

Stressful environments can also lead to apparent vaccination failure. Stress may be created during crowding, travel, inhumane training methods, poor nutrition and many other factors. These factors can cause a depression of immunity and subsequent development of clinical disease even though the horses are vaccinated.

Large farms benefit from isolating new arrivals for 3 weeks to one month. If this is not possible, having new horses vaccinated at home at least three weeks prior to arrival may also be beneficial.