Mosquitos and horses: EEE (Animal Science Update)
Over the summer we will work through a few hot topics, mosquitos, ticks and more grazing topics for my column.
In this column I will touch on some things dealing with mosquitos and Eastern equine encephalitis, commonly referred to as EEE (usually said as “Triple-E”).
There is an old fact sheet on the Rutgers NJAES website (https://njaes.rutgers.edu/pubs/) that I am attempting to update, and these are some excerpts from it.
However, the updated version is not public quite yet. EEE is a virus disease of wild birds that is transmitted to horses and humans by mosquitoes.
The virus is found in states along the eastern seaboard, gulf coast, and northern Midwest.
New Jersey represents a major focus for the infection with some form of documented viral activity every year and in every county.
The virus responsible for EEE attacks the central nervous system of its host and horses are particularly susceptible to the infection.
Onset is abrupt and horse cases are almost always fatal. The American Association of Equine Practitioners reports “75–95 percent (usually within two or three days of onset of signs).”
Symptoms include unsteadiness, erratic behavior, and a marked loss of coordination.
There is no effective treatment and seizures resulting in death usually occur within 48-72 hours of an animal’s first indications of illness.
The EEE virus occurs naturally in a wide variety of wild songbirds. EEE virus normally appears in local bird populations shortly after the nesting season is over in the spring.
Mosquitoes transmit the infection from bird to bird during the early summer months and infections usually peak sometime in August.
When mosquito populations are high, however, transfer from birds to horses and/or humans is possible. In a typical outbreak year, horse cases begin to appear in animals in mid-summer.
All equine cases are the result of mosquitoes which have fed on infected birds and then feed on horses.
Professional vaccination is the only method available to protect horses from the disease.
Vaccinations should be administered by a licensed veterinarian to assure that viable vaccine is utilized, and injections are properly administered.
Mistakes in vaccination protocol by well-meaning horse owners can result in ineffective protection in an animal that was thought to be risk free.
All too frequently, owner vaccinated horses develop overt cases indicating that the animal was improperly vaccinated or was vaccinated with vaccine that had lost its protective properties. Properly administered vaccinations are effective for only one year; thus, booster shots are required on an annual basis. Newly vaccinated animals require a two-shot series administered two to four weeks apart before protection can be guaranteed.
Foals should be revaccinated during summer to ensure protection during the first year of life. It is recommended in the face of a fall epidemic, horses vaccinated in March should be boostered later in the season.
A sick horse is an indication that the virus is present in local mosquitoes. If there is a positive horse case of EEE homeowners should contact their county mosquito control agency and make them aware of the situation. To find your county agency see: https://www.nj.gov/dep/enforcement/pcp/bpo-mfagencies.htm. Mosquito control personnel are familiar with the EEE cycle and have the expertise to reduce the mosquitoes that function in the cycle. Eliminating water-holding containers from your property (buckets, tires and other receptacles) will reduce mosquito breeding in the immediate vicinity.
Horse troughs provide excellent mosquito breeding habitat and should be flushed out at least once a week to reduce mosquitoes near the paddock area. Work with your county mosquito control agency and point out any wetland habitats that may have produced the mosquito responsible for the infective bite.
Suspect horse cases should be reported to your veterinarian as soon as possible. Your veterinarian will diagnose the infection and take blood or tissue samples for confirmation.
Euthanasia may be necessary because the disease is fatal in unvaccinated animals. The veterinarian will probably request the brain since brain tissue is the only certain way to confirm the diagnosis. Some horse owners are reluctant to report suspect cases for fear of quarantine. There is no quarantine for EEE and nonreporting only postpones the mosquito control activities that could protect other horses on your farm and the immediate vicinity.
Stay healthy and safe everyone! Happy Return to Riding!
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