Experts Concur: West Nile Virus Here to Stay, More Widespread Than Any Had Expected

January 10, 2003

CHICAGO -- At the fourth annual Clarke West Nile Virus Conference, experts in mosquito control, vertebrate entomology and disease prevention from around the country agreed that the explosive growth of the West Nile Virus in 2002 will result in a continued presence of West Nile around the country.

"2002 was an explosion of the West Nile Virus -- the largest recorded outbreak of mosquito-borne disease in the western hemisphere," said Dr. Charles Apperson, professor of entomology at North Carolina State University in Raleigh. "The question is not whether the virus will return in 2003, but rather what areas will have the most severe outbreaks."

At the seminar, sponsored by Clarke Mosquito Control, experts agreed that the virus would be present in every area of the country by the end of 2003. "Bird migration patterns are a huge indicator of one way the virus spreads from localized areas to more widespread regions," said Dr. Robert McLean of the National Wildlife Research Center, U.S. Department of Agriculture. "Birds are hosts for the virus, and when mosquitoes feed on birds infected with the virus, they are able to replicate that virus and pass it on to other hosts, including humans."

From 1999 to 2001, the country's cases of West Nile Virus totaled 149 with 19 fatalities. In 2002 alone, more than 3,850 cases and 232 fatalities were reported. In addition, "more than a million birds succumbed to this disease in 2002, easily," said McLean.

Though it's almost impossible to predict where West Nile will be most prevalent, the ability of the virus to "overwinter" in mosquitoes may lead to positive mosquito pools earlier in the warmer months. An area that confirmed the presence of West Nile in 2002 may find that 2003 brings earlier confirmations of the presence of the virus, as the disease may not need to be reintroduced, said McLean.

West Nile Virus, a disease mainly impacting birds, horses and humans, was also found in a number of different species, including brown bears, goats, reindeer, dogs and squirrels. In addition, the introduction of human-to-human transmission through organ transplants, blood supply and mother/infant transmission provided new clues on how the virus spreads. "With the quantity of West Nile cases in 2002, we were able to further categorize how the virus affects humans," said Apperson. "West Nile Virus manifested itself primarily in two categories: West Nile Fever and West Nile Meningoencephalitis."

According to Apperson, West Nile Meningoencephalitis affected about 70 percent of patients in 2002, and tended to be seen more in older patients. West Nile Meningoencephalitis is categorized by symptoms in the central nervous system, including swelling of the brain and meninges (covering of the brain), and has a 6 percent fatality rate. West Nile Fever is categorized by mild flu-like illness (headache, sore throat, backache, myalgia, arthralgia, fatigue), fever, frontal headache, abdominal pain, vomiting, rash and conjunctivitis.

"There's no way to treat the disease of West Nile at this time, we can only treat the symptoms," said Apperson. "The only way that we can have an impact on the spread of the disease is by reducing mosquito populations."

The seminars, with an audience of mosquito control officials from hundreds of municipalities, also focused on suppression of the disease through mosquito control, using the latest in surveillance and testing technology and mosquito control products.

"Not every community can hire a dozen PhDs to analyze their mosquito populations and test for the virus in laboratory conditions," said Dr. Leon Robert, an associate professor of tropical public health at the Uniformed Services University of the Health Sciences in Bethesda, Maryland. "Both time and budget can limit what a city or county can do. We want to offer new tools and ways that communities can do a scientifically solid program without having to make a city decide between mosquito control and say, police protection."

Robert pointed to new technologies like the VecTest(R) rapid test for West Nile that reduces the long turn-around time that an outside lab requires to determine the presence of the disease. "When West Nile is confirmed in mosquito pools, communities need to be able to act quickly to address the situation."

Jim McNelly, northeast operations manager for Clarke Mosquito Control, adds that the Center for Disease Control and Prevention provides a blueprint for appropriate response to West Nile. "The key to minimizing an outbreak of West Nile Virus is surveillance and larviciding, and when appropriate, adulticiding," said McNelly. "Officials who follow the guidelines closely do the best job in reducing the impact to their community."

The Clarke West Nile Seminar is the fourth annual seminar devoted to better understanding the transmission, impact and control of the disease for local government officials. Clarke Mosquito Control has been at the forefront of the mosquito control industry since 1946, offering services, products, equipment and education that aid in the control of mosquito populations.

Source: Clarke Mosquito Control