August 15, 2002
Tests Verify Scotland County Horse Has West Nile Virus
No one liked mosquitoes to begin with, but the rapid spread of the deadly West Nile Virus (WNV) has more and more people arming themselves with bug spray and fly swatters as they head outdoors to enjoy the summer.
The disease had been isolated to the Eastern Hemisphere until 1999 and had not made too many headlines until this summer when the first fatalities from the viral infection were reported. Six states and the District of Columbia have reported human cases of WNV.
WNV made its first appearance in Scotland County last week. DVM Larry Wiggins diagnosed a horse in Scotland County with the disease on Wednesday, August 7.
According to Wanda Parrish of the Scotland County Veterinary Clinic, the tests on the horse returned from the University of Missouri lab as a positive for West Nile Virus. Parrish said the horse was still under observation. She added that the clinic had also sent a dead bluejay found near the site, for testing for WNV.
West Nile virus is spread by the bite of an infected mosquito, and can infect people, horses, many types of birds, and some other animals.
Most people who become infected with West Nile virus will have either no symptoms or only mild ones.
On rare occasions, West Nile virus infection can result in a severe and sometimes fatal illness known as West Nile encephalitis (an inflammation of the brain). The risk of severe disease is higher for persons 50 years of age and older.
There is no evidence to suggest that West Nile virus can be spread from person to person or from animal to person. However experts do recommend wearing gloves or double plastic bags when handling dead birds to be disposed of.
The chance of becoming ill from a mosquito bite is extremely small. According to the Missouri Health Department much less than one percent of mosquitoes actually carry WNV and even if an infected mosquito bites a human, less than one percent of persons bitten by a virus carrying bug will become severely ill.
In 2002 there have only been 145 confirmed cases of WNV in humans. These cases have mostly been confined to Louisiana (85) and Mississippi (41) where all eight fatalities attributed to the disease have been reported. Texas has reported 13 human cases and both Illinois and Alabama have had two confirmed cases. Indiana and the District of Columbia have each confirmed one case of the virus in humans.
Cases of WN virus disease in horses have been documented, either by virus isolation or by detection of WN virus-neutralizing antibodies in 1999, 2000, and 2001.
Approximately 40% of equine WN virus cases results in the death of the horse. Horses most likely become infected with WN virus in the same way humans become infected, by the bite of infectious mosquitoes.
In locations where WN virus is circulating, horses should be protected from mosquito bites as much as possible. Horses vaccinated against eastern equine encephalitis (EEE), western equine encephalitis (WEE), and Venezuelan equine encephalitis (VEE) are NOT protected against WN virus infection. A West Nile virus vaccine for horses was recently licensed, but its effectiveness is unknown.
Horses infected by WN virus develop a brief low-level viremia that is rarely, if ever, infectious to mosquitoes. There is no reason to destroy a horse just because it has been infected with WN virus.
Data suggest that most horses recover from the infection. Treatment would be supportive and consistent with standard veterinary practices for animals infected with a viral agent.
Information for this story was provided by the Missouri Department of Health and the Centers for Disease Control and Prevention.
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