Utah health, agriculture, wildlife and mosquito-control experts are painfully aware that West Nile virus cases tend to explode the year after it first appears in a state.
In Utah, that means the upcoming mosquito season could be brutal if residents don't take precautions.
"We have reason to be concerned there will be a fair number of cases this year," said Dr. Scott Williams, state Department of Health executive director. He said although there are ways to slow down the spread and protect against it, officials do not believe they can prevent it entirely.
West Nile is carried by mosquitoes and spread to birds. Infected mosquitoes can pass the virus to humans and horses, as well. People can also, on rare occasion, receive the virus from a blood transfusion or transplant, mother to baby in the womb or through a needle stick.
Monday, officials from various agencies gathered at the health department to brief reporters on what to expect when the mosquitoes that can carry West Nile virus become active, expected to start about mid-May. Human cases are likely to appear around July 1 and peak in August, but sometimes human cases occur before the virus is otherwise found in the horse and bird population that usually precedes human infection.
There are key points for Utahns to keep in mind. First, the chance of getting West Nile virus is very small. Of those who are bitten by an infected mosquito, 80 percent will show no symptoms. Nearly 20 percent will have symptoms of West Nile fever, including headache, fever, muscle aches, nausea and vomiting, eye pain, etc., but will usually make a complete recovery in three to six days.
More problematic are the small number of people who will show the neurological symptoms: meningitis, encephalitis or acute flaccid paralysis from spinal cord damage. That's about one in 150 people who are infected. Ten percent of those with neurological symptoms will die, or about one in 1,000 infected people, said Dr. Robert Rolfs, state epidemiologist.
Those most at risk are 50 and older. Treatment of the virus is merely supportive. There is no human vaccine, though at least one is being developed and could be available in a few years.
Despite the fact that most people will not become ill from infection, Rolfs said he has become "a little less comfortable saying it's a mild, flu-like illness."
The core message public health officials want to drive home is that infection is largely preventable. People will likely have no problem if they get rid of standing water in their yards, repair screens, keep yards cleared of tall grasses and debris and wear clothing and an appropriate dose of DEET-containing mosquito repellent during the dusk-to-dawn hours when the mosquitoes (in Utah it's culex pipiens and culex tarsalis) that carry the virus are out. Adults can use up to a 35 percent concentration of DEET, children 10 percent. Infants under 2 months old must not use DEET.
"We want to encourage people to be outdoors. We don't want people to run and hide. But use mosquito repellent and get rid of standing water," said Michelle Korth, an epidemiologist with the state health department.
Some people are even putting "bat houses" in their yards so the bats will eat mosquitoes.
Mosquito abatement district teams are already out trying to eradicate mosquito populations, said Gary Hatch of the Davis Mosquito Abatement District. They also trap mosquitoes, which are then tested for the virus.
Agriculture folks are encouraging vaccination of horses, because those who received it have survived the virus, said Department of Agriculture spokesman Larry Lewis. Nationally, 15,000 horses were infected in 2002, a number that dropped below 5,000 last year in large part because of vaccination.
Health officials are keeping an eye on the surveillance of sentinel chicken flocks throughout the state, because they are early harbingers of the virus' arrival, though they don't actually become ill. Other surveillance includes mosquitos, dead birds, horses and, of course, humans.
The Division of Wildlife Resources is watching bird populations and preparing to collect dead birds of types that are particularly vulnerable to the virus for testing. Besides their fragility, they are spread the virus geographically. Those birds include corvids (magpies, ravens, jays and crows), raptors (hawks) and owls, said Kris Fehlberg, Division of Wildlife Resources. This year, they're bringing the established bird-banding stations into the effort.
Last year, West Nile virus debuted in nine Utah counties, but eight of the "unaffected" counties had little or no testing, so it may have been more widespread, Rolfs said.
On a map showing infection, Utah in 2003 looked very much like Colorado had the year before: minor presence of the virus, with two in-state acquired human cases, along with six Utahns who got the virus elsewhere. In Colorado, the year after its slow start, there were 2,943 reported human infections and 54 deaths.
In Utah the virus last year was found in mosquito populations in Uintah and Utah counties, in a dead bird in Grand County, and in sentinel chicken flocks in Duchesne, Emery and Carbon counties. Six counties found horses with the virus: Sanpete, Millard, Wayne, Duchesne, Uintah and Emery.
Local health departments will take the lead in dealing with human infections, with help from the state, said state spokeswoman Jana Kettering. More information is available online at www.health.utah.gov or at www.cdc.gov.