West Nile risk low
MICHAEL JAMISON of the Missoulian
KALISPELL - Chances are, if a mosquito carrying the West Nile virus is
going to find you, it will likely do so in the next few weeks.
Of course, chances are, that won't happen at all.
"All of the evidence shows late July and August are the weeks of most
concern," said Jim Murphy, health specialist with the Montana
Department of Public Health and Human Services.
By way of example, Murphy pointed to 2003, the year West Nile hit
Montana hardest and killed four people. In June that year, he said, one
case was reported. Then came five in July, 137 in August, 39 in
September and finally two in October.
Given a time lapse of a week or two between the bite and symptoms, he
said, it's clear the greatest risk comes in late July through August.
But just how big is that risk?
"We want people to be aware," Murphy said of the mosquito-borne virus,
"but we don't want them to go nuts. Summer's short enough in Montana;
get out and enjoy it."
Enjoy it, perhaps, in long sleeves and with screens in the windows.
Enjoy it with gutters and birdbaths cleared of standing water. Enjoy it
away from the buggiest spots, and indoors during the buggiest hours.
"Reduce your risk along the way," Murphy said. "That's our message."
But the message, he admits, must be tempered by a healthy dose of risk
In 1999, when West Nile virus first hit America's popular
consciousness, it came in the form of a surprise attack on New York
City. Health officials responded with helicopters, spraying neurotoxins
over neighborhoods to kill the mosquitoes. Media responded with glaring
headlines and images of dead birds.
When winter finally came and knocked back the insects, seven people
Less widely reported was the fact that during that same year, more than
2,000 New Yorkers died of the flu. In fact, Americans were 10 times
more likely to be struck dead by lightning in 1999 than to die from
West Nile virus.
Chances of West Nile killing you in 1999, it turns out, were about one
in 41 million.
As the virus increased its range across the country in subsequent
years, the risks likewise increased. Last summer, about 100 died from
West Nile nationwide. That's a one in 2.9 million risk.
By comparison, the National Safety Council reports that about 500
Americans - one in every half-million - die in their beds each year,
accidentally strangled by their own covers.
A whopping 1,600 - or one in 180,000 - fall fatally down their stairs.
More than 6,000 die crossing the street.
Which only goes to prove that if you can make it out of bed, down the
steps and to the corner bus stop, mosquitoes are pretty much the least
of your worries.
A rational assessment of risk, then, hints that the hype about West
Nile has been bigger than the threat.
Researchers at the National Safety Council think that's in part because
mosquitoes are so random in their blood-sucking urges, in part because
media tend to report the uncommon rather than the common, and in part
because West Nile still seems so new. New means unknown, and unknowns,
we all know, come shrouded in fear.
"Possibly the most newsworthy thing about West Nile virus is merely
that it is new," the Safety Council reports, "not that it is an
unusually large 'big picture' threat to public health."
But, the council admits, the dynamics of group fear often tend to trump
reason. Following the Sept. 11, 2001, attacks, for instance, air travel
tanked, with empty seats common for several months. People had taken to
their cars, afraid to fly.
But between October and December of that year, a National Safety
Council study shows the number of fatal car wrecks climbed by more than
1,000 over the same period from a year before.
People know they're 1,000 times more likely to die on the way to the
airport than during the flight, know they're 10,000 times more likely
to die of any random cause on any given day than to win the lottery,
but still they choose car over airliner, stopping along the way to pick
up a chance at the Powerball.
Once we get used to the risks - obesity, car wrecks, crossing the
street - we finally come to take them for granted, replacing fear with
something more reasonable.
But according to the Safety Council, that hasn't happened yet with West
The great irony is, part of what makes the virus so scary is that it's
so unknown, and part of what makes it so unknown is that it's so
First, you need to be in an area with lots of mosquitoes. It also helps
if those mosquitoes are a fairly well-infected population.
But even then, it's only one of 150 mosquito species - Culex pipiens -
that really tends to carry West Nile. And only the females are a
problem, because the males don't bite. (Female mosquitoes need protein
from blood to help their eggs develop.)
In a worst-case scenario, less than 1 percent of the local mosquito
population will be affected.
And even if one of those bugs finds you, you'll probably never know it.
More than 99 percent of people infected don't actually get sick. Of the
1 percent who do, only a small fraction get seriously ill. And of that
small fraction, an even smaller fraction will die.
After adding up all the risk factors, the National Safety Council
report concluded that "neither panic in the streets nor blase
inattention and inaction will be the antidote."
Murphy agrees, pointing out that the good news is the risk is small.
The better news is the risk can be easily mitigated. And the best news
is that the risk appears to be diminishing with time.
According to the Montana health department, "in many states, the number
of human West Nile cases has gradually declined over time as people and
animals develop immunity from infection." It's like the chicken pox:
Once you're exposed, you're pretty much immune for life.
By way of example, Murphy points to Montana's experience. West Nile
arrived, so far as we can tell, in 2002, when a horse in the town of
Shepherd got sick.
That year, two people were diagnosed, but no one died.
The following year, the virus took hold of a very susceptible
population, and 228 were diagnosed. Four people died in 2003.
But then came 2004, and the number of cases dropped back to six, with
no deaths. It was a classic infectious disease spike - from two to 228
to six cases, in a short three years.
Often, the spike persists for two summers, but Murphy thinks a cool
2004 season kept bug numbers low. The risk remains, he said, for
another big year.
And, he said, some populations remain at still higher risk, even if
that risk is relatively low. Older folk, for instance, need to pay
particular attention. Of the four fatalities in 2003, all were between
the ages of 64 and 84, "and 90 percent of our hospitalizations were
people over age 50," Murphy
In addition, the virus seems not to have spread equally yet across the
"This has not really jumped the Continental Divide," Murphy said.
Even in the red-hot summer of 2003, Missoula County had zero cases,
which is exactly how many were reported in Flathead, Lake, Lincoln,
Mineral, Granite, Ravalli and Sanders counties.
Meanwhile, the Billings hospital was overflowing.
When the virus jumps the mountains - and everyone's certain it already
has, to a degree - then western Montana could see a spike of its own.
"And of course," Murphy said, "that's where our population is."
Fortunately, public health officials have a pretty good idea of what to
expect from West Nile when it arrives. Unlike the general population,
for whom the virus is new and unknown, health officials have known West
Nile for decades.
It's a bird disease, Murphy said, a "flavivirus," common to Africa,
West Asia and the Middle East; it has made stops all across Europe.
Spread by the mosquitoes that feed on both migrating birds and people,
the virus has been found in more than 130 avian species.
It's name comes from the West Nile District of Uganda, where it was
first diagnosed in 1937. Then in Egypt in the early 1950s and Israel in
1957. There, doctors learned it could cause swelling around the brain,
even killing the patient.
By the 1960s, pathologists had tracked it to France, where it was
infecting and sometimes killing horses. (An equine vaccine has since
been developed, but there is no similar immunization for people.)
But even with all that history to fall back on, experts were baffled
when it slipped into New York City six years ago. People reported
fevers, stiff necks, headaches, confusion, weakness and seizures.
Yet it wasn't until flamingoes and bald eagles started toppling from
their perches at the Bronx Zoo that pathologists put the pieces
With no vaccine and no cure, however, there was little they could do
for those few early patients. Viruses, unlike their microscopic cousins
the bacteria, remain notoriously tough to combat.
Equipped with neither legs nor wings, microbes have evolved clever ways
of getting around. Some inspire a sneeze to travel from host to host.
Not a few employ the services of the mosquito.
It's a great shuttle, a mainline that bypasses the body's defenses
straight into the bloodstream, which is why so many disease-causing
microbes - malaria, yellow fever, dengue fever, encephalitis - have
chosen the mosquito as their travel agent.
Early antibiotics looked like the silver bullet in the fight against
microbes, prompting U.S. Surgeon General William Stewart to announce in
the early 1960s that "the time has come to close the book on infectious
diseases. We have basically wiped out infection in the United States."
But bacteria and viruses evolve quickly, and soon they armored
themselves with antibiotic resistance.
Today, new strains of old bugs are proving Stewart wrong, and his
optimism has been replaced by common concern. Currently, the AIDS agent
HIV is dissolved to naught by a mosquito's metabolism, but what happens
if the virus mutates its way around that little obstacle?
And while the pharmaceutical industry has not developed an entirely new
antibiotic in at least a couple of decades, the pesticide industry has
certainly been busy killing mosquitoes.
In fact, part of the West Nile risk-reduction strategy proposed by
federal health officials calls for judicious use of pesticides such as
malathion, the same nerve poison sprayed over New York City back in
1999. Some 200 reported being sickened from the spraying, but while
seven died of West Nile, none succumbed to the chemical warfare.
Malathion is from the organophosphate family of pesticides, some of
which are powerful neurotoxins. But in fact, the U.S. Environmental
Protection Agency says that although such pesticides come with some
risk, the chances for real health trouble are slim - far, far slimmer
even than the chances of dying from West Nile.
Same goes for DEET, the EPA says, which doesn't kill mosquitoes, but
surely keeps them at arm's length. Developed by the Army in the late
1940s, DEET has been on the civilian market since 1957.
Since then, concerns have arisen regarding prolonged use, especially
among kids, but no strong evidence has emerged regarding long-term
It is, like all else, a matter of risk assessment.
In Canada, officials have banned products containing more than 30
percent DEET. Here in the states, we advise against using it on small
kids, against putting it on hands or near eyes, in mouths, over cuts,
atop sunburns. We also advise washing it off as quickly as possible.
Some now suggest that DEET newly combined with sunblock might pose
problems, as the lotion may result in more skin absorption than the
It is, all recognize, a poison, but then so is most everything if used
in excessive amounts.
So far this year, Murphy said, West Nile has yet to appear on the
state's radar, and only 25 cases have been reported nationwide. But the
season is just heating up, he said, "and people do need to be aware."
"They don't need to be scared, they don't need to lock themselves
inside, but they do need to be aware," Murphy said. "The world is full
of risks. That's just the way it is."
Reporter Michael Jamison can be reached at 1-800-366-7186 or
Copyright © 2005 Missoulian