Questions About Eastern Equine Encephalitis and …

1 Questions AboutEastern EquineEncephalitisand HorsesIntroductionEastern Equine Encephalitis (EEE) andwestern Equine Encephalitis (WEE) virus infec-tions occur in horses and other equids in Louisi-ana. Eastern Equine Encephalitis (EEE) is morecommon and tends to occur in outbreak diseases are transmitted to horses andhumans by mosquitoes that have fed on infectedwild birds. The EEE virus was first identified inmosquitoes in Louisiana in 1951 nearPonchatoula in Tangipahoa Parish. The virus isactive in horses to some degree every virus attacks the central nervous systemof its host. Unvaccinated horses are particularlysusceptible to the infection. The disease appearswithin five days after mosquitoes transmit thevirus to the horse. Onset of clinical signs of EEEare abrupt, and affected horses die within threedays. Signs of EEE in horses include fever; asleepy appearance; some muscle twitches of thehead, neck, shoulder and flank; and a weak,staggering gait.

2 Affected animals are soon down,unable to stand. There is no effective fatality rate is 90 percent or higher. Ananimal that survives may have permanent does EEE come from?EEE occurs in nature in a wide variety ofsongbirds. Blood samples from New Jersey birds,where most of the research on EEE has beendone, indicate that the blue jay, tufted titmouse,chickadee, catbird and cardinal are most ofteninfected. Although these birds do not develop thedisease, they maintain high levels of the EEEvirus. They are considered reservoirs in thedisease melanura is the primary mosquitospecies that transmits the virus from bird to mosquito inhabits marshes and woodedwetlands and rarely feeds on people or , the EEE virus normally exists in arather secluded environment where it does notpose an immediate threat to horses or emus susceptible toEEE and WEE?An exotic species sometimes grown inLouisiana, the emu is susceptible to EEE andWEE.

3 The emu infected with EEE virus developsa fatal intestinal disease characterized by bloodydiarrhea. Emu owners need to be aware that aninfected emu is a source of virus to be spread bymosquitoes. A person should not skin an infectedemu or contact the bloody stool. The emu devel-ops a nervous system illness when infected withWEE virus. Emus should be vaccinated annuallyfor EEE and causes an EEEoutbreak in horses ?There are two possibleexplanations for EEE out-breaks in horses, and both areprobably responsible in partduring epidemic years. Onefactor involves mother nature, and the other isrelated to health management of the of EEE from birds to horsesand people can occur when mosquito populationsare high. In this situation, mosquito species otherthan Culiesta melanura become involved in thetransmission cycle of the EEE virus. Since theseother mosquitoes are more likely to feed onpeople and horses, it gives the EEE virus a meansof escape from the bird reservoir and from themore secluded habitats of Culiseta are usually the first to become infectedbecause they are normally housed in rural areasand they have a much greater exposure to potential for an outbreak of the diseasein horses may correspond to the number ofunvaccinated animals present.

4 It is unusual to seeEEE in a horse that has received the initial vac-cine series and timely boosters. During an out-break, most people have their animals vaccinatedbut then fail to follow up with annual boostershots the next year or so. Two or three years afterthe last outbreak, the population of unvaccinatedanimals has increased considerably, and anotheroutbreak is do horses get EEE?Horses become infected when they are bittenby a mosquito carrying the EEE time of the year does EEEinfect horses?EEE cases in horses usually begin to appearin mid to late summer and increase into the 1998, following a warm winter, infected horseswere seen in south Louisiana beginning in earlyspring. The outbreak continued to spread northduring the summer. In Louisiana, outbreaks ofEEE in horses tend to occur at two- to is the best way to protect myhorse?Annual vaccination of all horses and otherequids is recommended.

5 Horses vaccinated forthe first time must receive an injection of EEE-WEE combined vaccine followed by a seconddose of the vaccine three to four weeks two-dose series is essential to establish aneffective immune response. A booster shotshould be given in the spring each year thereaf-ter. If an outbreak of EEE or WEE occurs in thearea in late summer or fall, a second booster should be vaccinated at 4, 5 and 6months of age (three doses total) to ensureprotection. Another booster should be given insix months and annually are available from various handling and administration of vaccineare essential to ensure adequate protection. Anoverall health program for horses is recom-mended. It would include vaccinations adminis-tered by a should I do if my horsedevelops symptoms?It is important to find out the cause of theillness. Other diseases and poisoning may havesimilar symptoms or clinical signs.

6 The veteri-narian may want to obtain blood samples to sendto a diagnostic laboratory to test for EEE. Ra-bies, Equine infectious anemia (EIA), equineleucoencephalomalacia (moldy corn poisoning),liver failure, Equine protozoan myelitis (EPM),botulism, West Nile Virus and other conditionsmust be considered. If the animal dies, a thoroughautopsy may be necessary to confirm the cause of2illness. In some cases, removal of the brain forlaboratory analysis may be all that is in horses does not require a is important to confirm the diagnosis of EEE soother horse owners can be told of the need tovaccinate their humans contract EEE directlyfrom infected horses?No, the EEE virus isnot passed from horses tohumans by contact withbody fluids or in otherways. Furthermore, it isnot spread from horse to horse either. EEE-infected horses generally do not have enoughvirus in their blood to infect mosquitoes.

7 Thehorse is described as a dead-end host. EEE isacquired only from mosquitoes that have fed oninfected birds. An infected horse does not pose adisease threat to its human owners. It does indi-cate that the virus is present in the local birdpopulation and that local mosquitoes are transmit-ting the do humans get EEE?Humans can become infected when they arebitten by a mosquito carrying the EEE EEE represent a serioushealth threat to humans?Human cases of EEE are rare, but they canoccur during an outbreak year. The disease pro-duces serious illness, and the probability ofrecovery is less than 50 percent. In overt cases(cases where infection actually develops intodisease), the virus produces an illness that beginswith headache and stiff neck. As the diseaseprogresses, the patient can fall into coma, withdeath as a likely outcome. Recovery is possible,but individuals who recover usually have braindamage.

8 Children appear to be more susceptiblethan adults. The good news is that most humanswho are bitten by infected mosquitoes abort theinfection in the early stages and recover with noevidence that they ever had the disease. The overtto inapparent ratio of Encephalitis in New Jersey,where most of the research on EEE has beendone, is estimated at one overt case for every 23individuals bitten by infected mosquitoes. Peoplewho live near acid water swamps and in closeproximity to ponds filled with emergent vegeta-tion are at increased risk from mosquitoes thattransmit is the best way to protect myfamily if my horse contracts EEE?No human vaccine is available for routineuse, so avoiding mosquitoes is the best protectionwhere EEE is present. In parishes with mosquitocontrol districts, these agencies should be madealert. Mosquito control personnel are familiarwith the EEE cycle and have the expertise toreduce the mosquitoes that transmit the as well as horse owners can takemeasures to reduce the threat of , avoid mosquito-infested areas and useinsect repellent when exposure is water-holding containers from yourproperty (buckets, tires and other receptacles)will reduce mosquito breeding in the immediatevicinity.

9 Horse troughs provide excellent mos-quito breeding habitat and should be flushed atleast once each week to reduce mosquitoes nearthe paddock area. The use of residual insecticidesfor treating mosquito resting areas around homesand livestock premises is helpful, thank Dr. Wayne Crane and Rutgers University forallowing us to quote from parts of their publication on Christine Navarre, Associate Professor, Veterinary ScienceDr. Jack Baldwin, Professor, EntomologyLouisiana State University Agricultural CenterWilliam B. Richardson, ChancellorLouisiana Agricultural Experiment StationDavid J. Boethel, Vice Chancellor and DirectorLouisiana Cooperative Extension ServicePaul D. Coreil, Vice Chancellor and DirectorPub. 2834 (online only)10/05 in furtherance of Cooperative Extension work, Acts of Congress of May 8 andJune 30, 1914, in cooperation with the United States Department of Agriculture.

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