Hot Dry Weather And Home Foreclosures Blamed For Rise In West Nile Virus In California

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Main Category: Infectious Diseases / Bacteria / Viruses
Also Included In: Water - Air Quality / Agriculture;  Neurology / Neuroscience;  Tropical Diseases
Article Date: 25 Jul 2007 - 8:00 PDT

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Health authorities who reported a second death this year in the state of California, due to infection by West Nile Virus (WNV), have blamed hot dry weather and home foreclosures for the higher prevalence of the illness compared to last year.

An 85 year old man from Kern County, in Central Valley, California, became the state's second victim of the disease, which is spread by mosquitoes that have fed on WNV infected birds. The first victim to have died of WNV related illness in California this year was an elderly woman, who was also from Kern County.

According to a report in the Los Angeles Times, California health officials said the number of people in the state reported to have contracted WNV related illnesses in 2007 so far is 36, compared with 16 cases by the same time last year. The total number of cases in the whole of 2006 in the state was 278 people infected and 7 deaths.

The main reason for the increase, they suggest, is the hot dry weather. The West Nile season runs from July to September, and hot dry weather creates ideal conditions for the virus-carrying mosquito which likes to breed in warm stagnant water. The mosquito is far less active when the weather is wet and cold.

Another cause being suggested for the increase in mosquito numbers this year is the higher number of homes that have been foreclosed, leaving swimming pools full of stagnating water for the pregnat female mosquitoes to lay their eggs in.

West Nile Virus (WNV) belongs to the virus family Flaviviridae, which is part of the Japanese encephalitis (JE) antigenic group of viruses. Found mostly in tropical and temperate parts of the world, WNV infects mainly birds, but it is also found in humans, horses, dogs, cats, chipmunks, skunks, bats, squirrels, and domestic rabbits. Infections in humans are mostly via mosquitoes that feed on infected birds.

People at highest risk of getting ill from WNV are adults over 50 and anyone who has ever received a solid organ transplant, says the US Centers for Disease Control and Prevention (CDC) public information flyer on WNV.

The risk of becoming seriously ill with WNV is about 1 in 150, and possibly even lower than this because many people don't realise they are infected and don't report it. Serious illness occurs when the brain or surrounding tissue becomes inflamed, due to West Nile encephalitis or West Nile meningitis.

Symptoms of severe WNV illness include: headache, high fever, stiff neck, mental confusion, weak muscles, tremors, convulsions, coma, and paralysis.

Symptoms can last for several weeks, and neurological damage could be permanent, so anyone with these symptoms should see a doctor straight away.

The CDC advises people to protect themselves against WNV and reduce opportunity for the mosquito to breed by:

• Applying insect repellent. Before you go outside, apply an EPA-registered insect repellent such as those containing DEET, picaridin or oil of lemon eucalyptus. Read the label find out if you can apply any of these directly onto your skin or just your clothes. Permethrin sprayed on clothing provides protection through several washes, but don't use it directly on your skin and don't spray it under clothing.
• Covering up. Wear long sleeve shirts, long pants and socks sprayed with repellent while outdoors.
• Avoiding being outside when mosquitoes are active. Many mosquitoes bite between dusk and dawn, so limit time outdoors during these hours, or if you can't, then make sure you use repellents and protective clothing.
• Mosquito proofing your home. Make sure door and window screens are secure and don't have tears, drain all standing water to reduce breeding sites in back yards, balconies, patios, plant pots, clean pet drinking water bowls, cover up wells and water butts, clear gutters and check neighbours do the same.

WNV first showed up in North America in 1999 in New York City (believed to have been brought in by an air passenger) and has since spread throughout the US and from about six years ago, Canada as well.

Surveillance of WNV relies on sampling mosquitoes trapped in the environment, blood samples taken from wild birds and testing the brains of dead birds found by animal control organizations and members of the public.

Before screening for WNV was introduced in 2002, over 1,000 cases of donated blood tainted with WNV were reported, and some 30 people are believed to have contracted WNV from blood transfusions.

According to the CDC's 2007 WNV Surveillance Chart, the following states have reported avian, animal or mosquito WNV infections: Arizona, Arkansas, California, Colorado, Connecticut, Delaware, Florida, Idaho, Illinois, Indiana, Kansas, Louisiana, Minnesota, Mississippi, Missouri, Nebraska, New Jersey, New Mexico, New York, North Dakota, Ohio, Oklahoma, Oregon, Pennsylvania, Puerto Rico, South Dakota, Tennessee, Texas, Utah, Virginia, and Wisconsin.

Human cases have been reported to the CDC this year from: Alabama, Arizona, Arkansas, California, Colorado, Idaho, Illinois, Iowa, Kansas, Minnesota, Mississippi, Nebraska, Nevada, North Dakota, South Dakota, Texas, Utah, Virginia, and Wyoming.

Click here for public information flyer about WNV and how to protect against infection (CDC, PDF reader required).

Click here to see Progress of the West Nile Virus in the United States (wikipedia).

Click here to find out more about WNV in California (government site).

Written by: Catharine Paddock
Copyright: Medical News Today
Not to be reproduced without permission of Medical News Today

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