Spreading the fear

The only thing spreading faster than WNV appears to be the fear of the virus. The virus has been detected in 41 of the 48 contiguous states and, according to Dr. Lyle Petersen of the CDC, it is only a question of time before it becomes established throughout the country.

“We fully expect that, over time, the virus will make it to the West Coast,” Petersen said in a recent phone interview with reporters from across the country.

Petersen noted that WNV was closely related to and shares many of the same mosquito vectors as St. Louis encephalitis (SLE), which is endemic to the U.S. Because of that, he believes WNV will thrive across the U.S. just as SLE has.

According to a brochure prepared by the state of North Carolina, most people infected with WNV suffer no symptoms at all. In some, it produces flu-like symptoms and may cause swollen glands and/or rashes. Less than 1 percent of humans infected with WNV become severely ill. In these cases, an infection of the brain (encephalitis) occurs. People 50 years of age and older and people with health problems and/or immune deficiencies are most susceptible.

Wood noted that North Carolina citizens are at much greater risk from not wearing seat belts, failure to follow preventive healthcare guidelines and not receiving proper available immunization than WNV.

There is no cure for WNV. According to Petersen, most treatment for the disease is supportive, designed to relieve symptoms and lessen stress. The Associated Press reports that the Food and Drug Administration just approved the first national trial of a drug designed to combat WNV. James Rahal of the New York Hospital Queens is experimenting with the use of alpha interferon as a way of lessening symptoms and curtailing the duration of the disease. There is no conclusive data from those studies at this time.

Since the discovery of WNV in the U.S. in 1999, there have been around 35 fatalities. Many more people have died from influenza during that time.

The American Bird Conservancy believes native bird populations may be at a greater risk from this exotic pathogen than humans. According to an ABC report, “Experience with old-world WNV epidemics demonstrates that WNV poses similar, if not lesser, mortality risk to humans than the closely related, North American endemic, and bird-reservoired SLE.”

SLE has been around since the 1930s. CDC records show there were 4,478 cases of SLE between 1964 and 1968 and the average is about 128 cases a year. The mortality rate for SLE is from three to 30 percent of cases with the risk increasing with age.

The ABC is concerned that panic regarding WNV could lead to increased indiscriminate spraying of pesticides to try and control mosquitoes. The ABC report states: “Organophosphates, due to their acute and sub-lethal effects to birds other wildlife and humans, should not be used for mosquito control ... All pesticides used today in controlling mosquitoes kill important natural predators of mosquitoes to some extent ...adulticiding [spraying for adult mosquitoes] only adds to the stress placed on resident and migratory birds directly, through toxic effects ... and indirectly by reducing their food supply.”

The ABC suggests that control methods for the virus should mirror those used for SLE. That protocol calls for controlling mosquitoes in the larval stage using relatively non-toxic means. “Larvaciding of mosquitoes is the primary prevention strategy recommended by the CDC for SLE and WNV,” according to the ABC report. The report also states that case studies in New York and Florida have shown that after many years of spraying to control equine encephalitis, populations of vector mosquitoes have actually increased.

Researchers from the National Institute of Allergy and Infectious Disease and Walter Reed Army Institute have been working to perfect a vaccine for WNV. While they say they will be ready to start testing the vaccine on humans in 2002, Petersen of CDC believes it would be a number of years before any vaccine could be applied to the general population. By that time, there may be no need.

“What we don’t know is whether being exposed to the virus will cause lifelong immunity. What we do know is from related viruses, like Japanese encephalitis ... or yellow fever, that once you get infected with those viruses, you have immunity for life, and so we might expect the same thing to occur with the WNV,” Petersen said.

Petersen also noted that in areas where the virus is highly endemic, like the West Nile region of Africa, that infection is primarily in children, suggesting that people get infected at an early age then become immune.

In the meantime, Wood suggests a commonsense approach. If you’re going to be outside during peak mosquito hours, usually dusk and dawn, you may want to wear long sleeves and use mosquito repellant. Wood said the health department recommends a repellant that contains DEET – 30 percent or less for adults and 10 percent or less for children. He said residents could make their homes safer by draining standing water and cleaning clogged gutters where mosquitoes breed.

According to the N.C. Department of Health: “In most areas where mosquitoes carry the virus, less than 1 percent of mosquitoes are infected. Even if a mosquito is infected and transmits the virus to humans, less than 1 percent of those people who are infected by it become seriously ill. So, the chances of becoming severely ill from any one mosquito bite are extremely small.”