FRIDAY, July 15, 2005 (HealthDay News) -- The West Nile virus has started its annual drive across the nation, hitting Western states hardest and claiming the life of one elderly Missouri man.
So far this year, 11 states have reported 25 cases of human West Nile virus-related illness, including the fatality, according to research released in Friday's weekly journal by the U.S. Centers for Disease Control and Prevention (CDC).
The toll so far doesn't compare to last year at the same time, when there were 108 cases in about 10 states, according to CDC spokesman Tom Skinner.
But despite the smaller numbers this year, officials say they can't yet tell how severe a year this is likely to be.
"It's certainly too early to project what kind of season this is going to be," Skinner said. "West Nile virus is here to stay, and we will see cases across the country each and every year."
And the current numbers may be misleading.
"There's always a bit of a lag between what is reported to CDC and what is actually out there," added Dawn Wesson, an associate professor of tropical medicine at Tulane School of Public Health and Tropical Medicine in New Orleans.
"Often cases are in the process of being diagnosed, testing is being done and follow-up testing, and it's not reported until there is a double confirmation," she said.
For example, Wesson said that in Louisiana there have been a couple of cases that were not listed in the CDC report.
August and September are considered peak months, where health officials usually expect to see more activity.
"Things are going to start rolling soon, but it is kind of a leap to make any predictions," said Stephen Higgs, Ph.D., associate professor in the department of pathology at the University of Texas Medical Branch, Galveston. "There are no surprises here at the moment."
Since it first appeared in North America in 1999, West Nile virus has made its way across the continent and is now found in virtually every contiguous state. Since that time, according to the CDC, about 15,000 humans have been infected with the virus and more than 650 people have died.
Last year alone there were 2,539 human cases and 100 deaths, according to the CDC.
West Nile virus is normally passed from an infected mosquito to a bird, and then from the bird to other mosquitoes. The mosquitoes then pass the virus on to humans.
The greatest concentration of cases reported in this week's issue of the CDC's Morbidity and Mortality Weekly Report was in the West. Arizona had three cases, California two, Colorado seven, South Dakota five and New Mexico two. Georgia, Indiana, Kansas, Missouri, Ohio and Texas each had one case.
According to Wesson, there have been big jumps in the proportion of mosquitoes and dead birds testing positive for West Nile in Louisiana. "A month ago, we were getting maybe 30 to 40 percent of mosquitoes, and now it's over 80 percent," she said. "There's amplification going on."
Of the cases reported to the CDC, 19 (79 percent) of the 24 cases for which data were available occurred in males. The median age of people infected was 45 years, although the range was 17 to 80. They became sick from May 14 to June 30.
The one fatality appears to be that of a 70-year-old man in northeast Missouri, according to an Associated Press report. State health officials said that he died June 14 and that West Nile likely contributed to his death even though the man had other medical problems.
In addition, the CDC reported, seven blood donors who appeared to have West Nile virus were reported to authorities. Five of these were in Texas and one in Arizona.
In the non-human realm, 281 dead corvids (members of the crow family) and 96 other dead birds with West Nile infection have been reported from 16 states this year. Infections have also been reported in horses in 11 states and a total of 439 West Nile virus-positive mosquito pools have been reported in 13 states.
The bottom line for humans is that it's time to start adding on protection, experts said.
"First and most important, remove any standing water where mosquitoes are likely to breed," Skinner advised. "And wear repellant and long-sleeved clothing."
This year, in addition to the standard DEET-containing products, the CDC has also endorsed products containing oil of lemon eucalyptus and Picaridin.
Unfortunately, these types of precautions against West Nile are now a fact of life in the U.S., Higgs said. "The basic precautions are going to hold forever, because I don't think this is going to go away."
For more on how you can protect yourself from the West Nile virus, visit the CDC.