AUGUSTA – The Maine Department of Agriculture, Conservation and Forestry said Sept. 14 that a horse showing neurological signs last week in York County tested positive for West Nile Virus (WNV). The horse is currently undergoing supportive veterinary care and does not pose a threat of infection to any other animals or humans. The horse was unvaccinated against the disease.

WNV is a virus that is transmitted through the bite of an infected mosquito. One pool of mosquitoes has tested positive for WNV in York County this year. This is the first confirmed case of WNV in horses in Maine on record. WNV has been diagnosed in horses this year in nearby states such as New York.

“WNV and Eastern Equine Encephalitis (EEE), which are carried by mosquitoes, are viral diseases that cause similar signs, and are often fatal in unvaccinated horses.  Both viruses can affect human beings if they are bitten by mosquitoes that carry the viruses,” said Dr. Michele Walsh, Maine state veterinarian. “People cannot acquire WNV or EEE infection from sick animals, only from the bite of an infected mosquito.”

The Maine Center for Disease Control and Prevention (Maine CDC) and Maine DACF suggest Mainers take the following steps to protect themselves and their animals from EEE and WNV:

• Wear long sleeves and long pants
• Use an EPA approved repellent on skin and clothes
• Take extra precautions at dusk and dawn
• Use screens on your windows and doors
• Drain artificial sources of standing water where you and your animals live, work, and play
• Vaccinate horses against WNV and EEE

Both WNV and EEE viruses are carried by mosquitoes, which pick them up from infected wild birds. The viruses replicate in birds, which act as natural reservoirs for the diseases. 

Signs of the diseases in horses may include:  stumbling or poor balance, unusual behavior and lethargy. Other symptoms include head pressing, circling, tremors, seizures and eventual coma.  “WNV and EEE are preventable in horses through vaccination,” Walsh advised.  “If more than six months has elapsed since a horse has been vaccinated, a booster vaccination may be needed.” While EEE has not been detected in Maine so far in 2018, it has been detected here in recent years, and has been detected in neighboring states and provinces this year. Horse owners should contact their own veterinarians to decide if booster shots are needed. Revaccination is recommended if more than six months have passed since the last vaccination when exposure to infected mosquitoes is likely. Vaccinating horses regularly is the best way to protect them against these dangerous diseases, and is safe, effective and essential.

 “This WNV activity in mosquitoes and horses should serve as a reminder to the public that humans are at risk from this disease as well, and should take the appropriate steps to protect themselves,” said Dr. Siiri Bennett, State Epidemiologist for the Maine CDC.  Although many persons infected with WNV have no apparent illness, those who develop symptoms do so usually three to 10 days after the bite of an infected mosquito.  One in five people infected develop a fever with symptoms such as headache, body aches, joint pains, vomiting, diarrhea or rash, and most recover completely.  Less than 1 percent of people develop a serious neurologic illness such as encephalitis or meningitis, and approximately 10% of those may die.

Maine’s Health and Environmental Testing Laboratory performs arboviral testing for mosquitoes, large animals and humans.  Submission information can be found at www.mainepublichealth.gov/lab.

For more information:

Maine CDC’s arboviral website:  http://www.maine.gov/dhhs/mecdc/infectious-disease/epi/vector-borne/index.shtml

Maine’s weekly arboviral surveillance reports:  http://www.maine.gov/dhhs/mecdc/infectious-disease/epi/vector-borne/arboviral-surveillance.shtml

HETL’s submission form and information:  www.mainepublichealth.gov

Department of Agriculture, Conservation & Forestry's Animal Health website:  https://www.maine.gov/dacf/ahw/animal_health/