West Nile Virus Outbreak Worst in U.S. History

A Culex pipiens, the common house mosquito, the species most likely to carry West Nile virus. (Photo by Nazim Khir)


ATLANTA, Georgia, August 22, 2012 (ENS) – A mosquito bite can kill, and this year 41 Americans have found that out the hard way as they lost their lives to the mosquito-borne disease West Nile virus.

Forty-seven of the 50 states have reported West Nile virus infections in people, birds or mosquitoes, according to the federal Centers for Disease Control and Prevention, CDC, in Atlanta.

A Culex pipiens, common house mosquito, the species most likely to carry West Nile virus. (Photo by Nazim Khir)

A total of 1,331 cases of West Nile virus disease in people have been reported to CDC – the highest number of West Nile virus cases reported through the third week in August since West Nile virus was first detected in the United States in 1999.

About 75 percent of the cases have been reported from five states in a north-south strip through the center of the country – Texas, Oklahoma, Mississippi, Louisiana and South Dakota – almost half of all cases have been reported from Texas.

The Texas Department of State Health Services, DSHS, says the higher than usual number of human West Nile cases in the state this year is due to the warm winter and recent rains, particularly in the North Texas region.

Texas has more than 640 state-confirmed cases of West Nile illness so far this year, including 23 related deaths.

Over the past 10 years, 49 cases on average were reported to DSHS by this time each year, ranging from a low of just three cases in 2011 to a high of 171 cases in 2006.

Most at risk this year is Dallas County, where 10 people have died.

“The disease poses an immediate public health threat to Dallas County. We need to use all possible tools, including aerial spraying, to fight this outbreak,” said Dr. David Lakey, DSHS commissioner. “Aerial spraying is a very effective and safe way to kill adult mosquitoes in large, densely populated areas.”

spray plane
Plane sprays for mosquitoes carrying West Nile Virus in Dallas, August 19, 2012 (Photo by neutronman61)

DSHS contracts with Clarke, a private environmental products and services company, for aerial application of a mosquito control product called Duet, which is labeled and approved by the U.S. Environmental Protection Agency for use in outdoor and residential areas.

Duet is a synthetic pyrethroid mosquito control product that mimics a naturally occurring substance found in chrysanthemums. The active ingredients are in the same chemical family as products currently being used for ground spraying in the Dallas area. The product is applied at very low concentrations, less than an ounce per acre, by small, twin-engine aircraft flying 300 feet above the ground overnight.

The EPA has said that pyrethroids do not pose a significant risk to wildlife or the environment. Still, some Dallas residents fear the chemical could harm their children, pets, and useful insects such as honey bees.

For people concerned about exposure during aerial spraying, health officials suggest that they minimize exposure. Avoid being outside, close doors and windows and consider keeping pets inside during spraying. If skin or clothes are exposed, wash them with soap and water. Rinse homegrown fruits and vegetables with soap and water before eating. Because the chemical breaks down quickly in sunlight and water, no special precautions are suggested for outdoor swimming areas.

West Nile virus is worse this year than ever before even in states other than the five most affected, such as Pennsylvania where seven human cases have been reported.

“There are more infected mosquitoes, and the infection rate is much higher,” said Amanda Witman, spokeswoman for the Pennsylvania Department of Environmental Protection. “We are also coming into a time of year when the population is at its strongest, posing the biggest risk to human health.”

Many people who are bitten by an infected mosquito won’t get sick, but many others will, warns the CDC.

The reasons one person becomes severely ill from diseases mosquitoes carry and another does not are not entirely known, which is why the CDC advises everyone to use mosquito repellant whenever they are outside, and especially between dusk and dawn.

“Put a few bottles or packets of repellent around – in the car, by the door, in a purse or backpack,” the agency advises.

CDC recommends the use of repellents containing active ingredients that have been registered and approved by the U.S. EPA for efficacy and human safety when applied according to label directions.

Use insect repellent that contains DEET, picaridin, IR 3535, or oil of lemon eucalyptus, a natural oil extracted from the leaves and twigs of the lemon-scented gum eucalyptus plant, and PMD, the chemically synthesized version of oil of lemon eucalyptus.

The EPA characterizes the active ingredients DEET and picaridin as “conventional repellents” and oil of lemon eucalyptus and IR3535 as “biopesticide repellents,” derived from natural materials.

The national nonprofit group Beyond Pesticides advises, “When compared to the ‘pure’ oil of lemon eucalyptus, PMD showed far superior repellent activity under laboratory conditions. PMD has also shown remarkable ability to repel mosquitoes when compared to DEET – the most popular synthetic commercial insect repellent which has been linked to serious adverse effects, especially in children.”

In addition, the EPA recommends using products containing permethrin on clothing, shoes, bed nets, and camping gear, but not directly on the skin. “Permethrin is highly effective as an insecticide and as a repellent,” the agency says.

mosquitoes breeding
Mosquitoes breeding in a discarded jar full of water (Photo courtesy CDC)

To reduce the risk of being bitten by mosquitoes, health officials recommend that poeple limit outdoor activities between dusk and dawn when mosquitoes are most likely to bite and wear long pants and long-sleeved shirts while outside.

“Make sure you have good screens on your windows and doors to keep mosquitoes out,” the CDC advises. “Get rid of mosquito breeding sites by emptying standing water from flower pots, buckets and barrels. Change the water in pet dishes and replace the water in bird baths weekly. Drill holes in tire swings so water drains out. Keep children’s wading pools empty and on their sides when they aren’t being used.”

Since 1999, when West Nile virus was first discovered in the United States, more than 30,000 people across the country have been reported as getting sick.

Most often, West Nile virus is spread by the bite of an infected mosquito. Mosquitoes become infected when they feed on infected birds. Infected mosquitoes can then spread the virus to humans and other animals when they bite.

West Nile virus is not spread through casual contact such as touching or kissing a person with the virus.

People typically develop symptoms between three and 14 days after they are bitten by the infected mosquito.

There is no specific treatment for West Nile virus. In milder cases, people experience symptoms such as fever and aches that pass on their own, although even healthy people have become sick for several weeks. In more severe cases, people usually need to go to the hospital where they can receive intravenous fluids, help with breathing and nursing care.

The CDC advises that people over the age of 50 are more likely to develop serious symptoms of West Nile virus if they do get sick and should take special care to avoid mosquito bites.

Copyright Environment News Service (ENS) 2012. All rights reserved.

Continue Reading