CORVALLIS — Although summer may be winding down, the threat of West Nile virus in Oregon appears to be increasing, putting humans and some animals at risk.
The Oregon Health Authority has confirmed two human cases of West Nile virus in Oregon this week. The affected adults are from Coos Bay and Malheur County. These are the first two confirmed human cases since 2009 in Oregon. The highest number of infected humans occurred in 2006, with 73 confirmed cases.
Most infections are mild, with fever and flu-like symptoms, but severe infections may cause encephalitis (inflammation of the brain), and rarely, death.
According to public health officials, the veterinary diagnostic laboratory at Oregon State University, which provides testing for the state, is reporting the highest levels of West Nile virus activity in mosquitoes since 2009.
The lab has confirmed the virus in 58 different “pools” of mosquitoes — of which 55 were located in Malheur County. In contrast, only three pools of West Nile virus were confirmed last year in Oregon, and four in 2010. In some previous years however, over 1,000 pools of mosquitoes were found carrying the virus.
Emilio DeBess, Oregon Health Authority veterinarian, said West Nile virus typically peaks around Labor Day weekend. He recommends the following precautions for Oregonians:
n Eliminated sources of standing water that are a breeding ground for mosquitoes, including watering troughs, bird baths, clogged gutters and old tires;
n Protect yourself when outside, especially at dusk or dawn when mosquitoes are most active, by using repellants containing DEET, oil of lemon, eucalyptus or Picardin, following application directions;
n Wear long-sleeved shirts and long pants in mosquito-infested areas;
n Make sure screen doors and windows fit tightly and are in good repair.
The virology section of the state’s diagnostic lab has also confirmed West Nile virus in one horse in Klamath County, and in a crow from Malheur County. Certain birds are known carriers of West Nile virus.
“Infected crows, ravens, jays and other members of the corvid family are considered ‘reservoirs’ and will carry very high viral loads of West Nile,” said Donna Mulrooney, OSU lab supervisor. Mosquitoes biting infected birds will then be infected with the virus and carry it on.
“Horses, on the other hand, are known as ‘dead-end’ hosts,” added Mulrooney. “They don’t carry enough of a viral load to infect mosquitoes if bitten. However, the danger to horses is real. Anywhere from 30 to 50 percent of horses infected with the West Nile virus will die.”
More information on West Nile virus is available from the Oregon Health Authority.