As the West Nile Virus high season gets well under way in the US, there are increasing reports of infected mosquitoes and clean up operations, together with a step up in county and state health officials urging residents and businesses to eliminate standing water on their properties.

According to the Centers for Disease Control and Prevention, 27 states have reported human cases of West Nile Virus this year. Two areas that have been in the news these past few days are Massachusetts and Los Angeles, California.

Earlier this week the Department of Public Health in Massachusetts announced three counties now have mosquitoes carrying either the West Nile Virus or another mosquito-borne disease, Eastern equine encephalitis (also known as sleeping sickness or triple E), according to a report in the Boston Globe.

West Nile Virus was found in mosquitoes in pools in Essex County (in Salem and Swampscott) and Norfolk County (in Weymouth).

Mosquitoes carrying Eastern equine encephalitis were found in two pools in Plympton in Plymouth County.

Massachusetts public health officials are said to have increased monitoring of mosquitoes and urged the public to step up their use of mosquito repellent and drain off all standing water, the preferred breeding ground for mosquitoes.

Meanwhile in Panorama City in the San Fernando Valley in Los Angeles County, California, there is a big clean up operation to clear a one mile creek known as the Pacoima Wash, where fourteen samples of WNV carrying mosquitoes have been found, said the Los Angeles Times yesterday. Bulldozers have been called in to clear the tall grasses.

Local residents are urged to notify the authorities of any pools of stagnant water in the area. The situation is not without irony, since Pacoima means “running water” in Native American.

While most of the WNV cases in Los Angeles County this year have been traced to San Fernando Valley, county officials say the problem is county wide because birds can also carry the virus and they fly much longer distances than mosquitoes. In fact the mosquitoes pick up the virus from feeding on infected birds and then they infect humans when they bite them.

So far WNV has been detected in 19 dead birds and 33 pools of mosquitoes in the county of Los Angeles, said the LA Times.

California has seen a significant increase in human cases of WNV this year compared to last year, and five Californian residents have died from the disease, two from Kern County which neighbours Los Angeles.

Governor Arnold Schwarzenegger has pledged a 1.35 million dollar emegency fund for WNV, and California State Senator Dean Florez, D-Shafter, said he wants to see more funding in next year’s budget so that the problem is tackled more proactively.

The majority of people who are bitten by a WNV carrying mosquito have no symptoms, and about 1 in 5 will have mild to moderate symptoms 3 to 14 days after being bitten.

However about 1 in 150 people who are bitten become seriously ill with symptoms such as headache, stiffness in the neck, high fever, apathy, convulsions, tremors, feeling disoriented and weak in the muscles, loss of vision, numbness, and rarely, paralysis and coma.

There is a small risk that the disease leads to brain and nervous system damage, and this risk is greater for the over 50s.

Mosquitoes are on the move during dawn and dusk, so if you have to go out at these times, wear long sleeved shirts and long pants, and cover any exposed skin with a recommended repellent. Also, fasten door and window screens and repair any holes and tears.

All the health authorities in the areas affected are urging residents to check their back yards and gardens for standing water. An inch of water in a forgotten flower pot warming in the sun a couple of days after rain is a most attractive breeding site for a mosquito.

Click here for more information about West Nile Virus from the CDC.

Click here for an earlier article “West Nile Virus Bites Deep in California” (6th August).

Written by: Catharine Paddock