Horse jabs urged as mosquito season begins

Mosquitoes like this female Aedes (Ochlerotatus) sp.,
A female Aedes (Ochlerotatus) sp. mosquito,

Horse owners in Delaware are being advised to make certain their animals’ vaccinations are current to protect against the threat of two potentially fatal mosquito-borne diseases.

The advice comes as warmer weather signals the start of the mosquito season.

Unvaccinated horses suffer most severely from both West Nile Virus (WNV) and Eastern Equine Encephalomyelitis (EEE), which are spread by mosquitoes and can be fatal, Delaware state veterinarian Heather Hirst said.

Hirst, who heads the Delaware Department of Agriculture’s poultry and animal health section, said: “Vaccination is a simple and cost-effective way of preventing these diseases – far cheaper than treating them.

“Horse owners should take full precautions to keep their horses safe, and be on the alert for signs of infection.”

Both horses and humans can contract WNV and EEE if bitten by a mosquito carrying the virus, but it is important to note that the viruses cannot be transmitted between horses or from horses to people.

The viruses normally exist in a cycle between mosquitoes and birds, but occasionally EEE can be transmitted from mosquitoes to mammals. Delaware’s last confirmed equine case of EEE was in 2005, and its last confirmed equine case of WNV was in 2003.

The Mosquito Control Section of the Delaware Department of Natural Resources and Environmental Control monitors for both diseases statewide.

It began spraying for mosquitoes in mid-March, treating wooded wetlands near populated areas in all three counties.

Hirst said horse owners should contact their veterinarian immediately if they suspect their horse may be showing signs of WNV or EEE, which both include fever, anorexia, head pressing, depression or personality change, wobbling or staggering, weakness, blindness, convulsions, muscle spasms in the head and neck, or hind-limb weakness.

Owners should consult with their veterinarians about the WNV and EEE vaccinations, as well as vaccinations for herpesvirus (rhinopneumonitis), influenza, rabies and tetanus, among others, Hirst said.

Horse owners can also help during mosquito season by keeping horses inside during dawn and dusk, which are peak mosquito times, and using topical insect repellents labeled for use on horses, Hirst said.


Beginning in June, the public’s help will be sought in monitoring for the presence of WNV by reporting sick or dead wild birds of certain species that may have contracted the virus. Sick or dead crows, blue jays, cardinals, robins, hawks or owls, and clusters of five or more sick or dead wild birds of any species, should be reported to Mosquito Control’s two offices: Glasgow, for northern Kent County and New Castle County, (302) 836-2555; or Milford, for southern Kent County and Sussex County, (302) 422-1512. Bird specimens should have been dead for at least 24 hours and not appear to have died or been killed by other obvious causes.



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