A horse housed near Bock, Minnesota has tested positive for West Nile Virus, reported veterinarian Dr. James Winters after the blood samples he drew from the horse confirmed the virus on Aug. 2. Bock is located between Ogilvie and Milaca in central Mille Lacs County.
A horse in Sibley County also was confirmed with West Nile Virus on Aug. 2.
West Nile Virus is regularly found in the United States, and birds serve as the primary host of the disease. Infected mosquitoes can transmit the virus from birds and then carry it to horses or people. The virus can cause encephalitis, an inflammation of the brain and spinal cord. Infected horses may or may not show neurological symptoms and many recover completely, especially with annual vaccinations.
Vaccines for horses are widely available and have been proven to be effective in preventing infection.
Steps can also be taken to reduce disease risk by reducing mosquitoes: Change water in drinking troughs every week; Mow long grass; Drain stagnant water puddles; Remove items mosquitoes use for breeding grounds, like old tires and tin cans; Place and maintain screens over windows and stable doors.
Horses and people can also be protected from mosquitoes by using repellents. Positive test results for West Nile Virus must be reported to the Board of Animal Health.
Signs and symptoms
The typical incubation period for West Nile is 2-6 days, although it can be as long as 15 days.
Most people infected with West Nile virus will be asymptomatic or experience a flu-like illness
20% of those bitten by an infected mosquito will develop the symptoms of West Nile fever
1 out of 150 people bitten by an infected mosquito will develop the more severe form of West Nile, West Nile encephalitis
West Nile fever symptoms include:
sudden onset of high fever (usually >102°F)
prominent muscle aches and weakness
rash (more commonly associated with West Nile fever than encephalitis)
swollen lymph nodes
West Nile encephalitis
Less than 1% of those infected with West Nile will develop severe neurological symptoms consistent with encephalitis or meningitis.
West Nile encephalitis symptoms include:
mental status changes
sensitivity to light
seizures (less frequent)
15% progress to coma
Acute flaccid paralysis (AFP) occurs in a small percentage of severely affected patients
The death rate among those showing symptoms of severe West Nile infection (encephalitis or meningitis) is around 10%. Most severe cases occur in elderly people.
Sources: Board of Animal Health and Minnesota Department of Health