Horses (and their Human Caretakers) at Risk for Mosquito-borne Illnesses

Two mosquito-transmitted viral diseases that infect horses have arrived in New Hampshire: Eastern Equine Encephalomyelitis (EEE) and West Nile Virus (WNV).

Horses infected with EEE may run fevers, show signs of depression, lose their appetites, become weak, go blind, lose coordination, and have convulsions. In some cases, horses may show no signs at all before dying.

Horses infected with WNV show similar symptoms—through they often have no fever—or have no symptoms at all. As of this writing, there have been no confirmed New Hampshire cases of West Nile in horses in 2005.

Vaccinations are available for horses for both of these diseases and we strongly encourage horse owners to consult their veterinarians to develop an appropriate vaccination program.

Human health concerns
Recent reports of two horses stricken with EEE in southern New Hampshire, and two suspected human cases, along with the first report of a dead bird infected with WNV, have also raised concerns about threats to human health.

The federal Centers for Disease Control (CDC) reports that healthy adult humans who become infected by either virus will likely experience mild, flu-like symptoms, such as fever or headaches. Very young children, the elderly or people with weakened immune symptoms can become very ill from either disease.

Very few mosquito species are capable of transmitting either EEE or WNV. Those that can pick up the virus by biting infected birds. The infected mosquitoes may then transmit the virus by biting horses or humans. As of this writing, there have been no confirmed human cases of either EEE or WNV in New Hampshire this year. The New Hampshire season for risk of these viruses runs from June through October.

Protection from mosquito bites
Protection from mosquito bites is the best preventative for humans. You can decrease the chances of both you and your animals being exposed to WNV and EEE by decreasing exposure to adult mosquitoes:

• Use mosquito repellant that contains DEET, picaridin, or oil of lemon eucalyptus when working or playing outdoors, especially around dawn and dusk.
  
  
• Prevent large populations of mosquitoes by removing any potential sources of water in which they can breed.
  
  
• Dispose of any water–holding containers, including discarded tires. Drill holes in the bottom of containers that are left outside and might collect water.
  
  
• Clean clogged roof gutters on an annual basis.
  
  
• Turn over wading pools or wheelbarrows when not in use, and do not allow water to stagnate in birdbaths. Aerate ornamental pools or stock them with fish.
  
  
• Clean and chlorinate swimming pools that are not in use and be aware that mosquitoes can breed in any puddle that lasts more than four days.
  
  
• Thoroughly clean livestock–watering troughs on a monthly basis.

If you have questions about either WNV or EEE in horses, contact your veterinarian.

For more information about the risk of WNV and EEE to humans:

• Fact Sheet on Eastern Equine Encephalitis
• Centers for Disease Control & Prevention Eastern Equine Encephalitis Information’
• Fact Sheet on West Nile Virus
• Centers for Disease Control & Prevention West Nile Virus information
• Citizens can also call the WNV/EEE information line at: 866/273-NILE (6453) for answers to questions about WNV or EEE.

By Lisa Townson, UNH Cooperative Extension 4-H Specialist