magazine, June 2000
West Nile virus
killed seven people in New York City last summer. Does an infected
bird found downtown last fall mean Baltimore is next?
On the afternoon of October14, bustling
traffic on the 300 block of East Lombard Street, in the
heart of the city's business district, slowed as it made its way
around officers from the Baltimore City Health Department who were
gingerly removing the carcass of an American crow. Although the
foot-long specimen resembled hundreds of others that had been picked
up in years past, this crow was different. This crow had the government
A public health alert had arisen 200 miles to the northeast: Earlier
in the summer, New York City had experienced an outbreak of lethal
West Nile encephalitis virus – a disease never before seen
in the Western Hemisphere. More than 60 people had become ill with
brain infections, and seven people had died. At the direction of
the Centers for Disease Control and Prevention (CDC) in Atlanta,
Georgia, state and local health departments along the East Coast
were asked to step up surveillance of birds and other wildlife.
The virus had been found in animals in New York, Connecticut and
New Jersey. And since it was carried by mosquitoes, it was critical
to know how far the disease might have spread.
So, like dozens of other dead animals found on Baltimore’s
streets and alleys that summer, the Lombard Street crow was warpped
in two plastic bags, packed with ice, and shipped by UPS to the
National Wildlife Health Center in Madison, Wisconsin.
Within days, the laboratory tests came back positive. West Nile
encephalitis had come to Baltimore.
The rapid movement of a previously unheard-of virus
from Europe to New York to the streets of downtown Baltimore offers
a rare and alarming opportunity for infectious disease experts at
Johns Hopkins and University of Maryland -- who typically travel
to remote and inhospitable areas of the world -- to study an emerging
It is “very uncommon” for a potentially major disease
to appear in our own backyard, says geographic medicine specialist
Robert Edelman, MD, director of the Traveler’s Health Clinic
at the University of Maryland. “Everyone realizes the potential
for this,” says Edelman. “The chances that [West Nile]
has spread down here are very, very good.”
That’s the bad news. The West Nile virus causes encephalitis,
an inflammation of the brain that can, in extreme cases, result
in permanent brain damage and death. Common symptoms include fever,
stiff neck, mental confusion, and, in the case of severe infection,
The good news is that most people who are bitten by an infected
mosquito will not become sick. Although the elderly tend to be more
susceptible to the disease, West Nile “causes illness only
in a small proportion of individuals,” says Edelman. “Even
if they do get sick,” he explains, “most people will
Right now, there’s no way to know how serious an issue West
Nile encephalitis is for Baltimoreans. But there’s enough
reason for concern that we should know about the disease –
and what to do about it.
the most common urban mosquito in North America and a vector
for the West Nile virus.
According to the CDC, more than 30 new infectious diseases
have been identified since 1973, including legionnaires disease,
toxic-shock syndrome, the human immunodeficiency virus (HIV), and
now, West Nile encephalitis.
An emerging disease, explains Edelman, is one that was not previously
recognized, one that enlarges in a known territory, or moves into
a new territory. The viruses and bacteria that cause emerging diseases
aren’t literally new, but had been festering in some remote
spot until an animal or human gave them an opportunity to travel.
While the HIV virus that causes acquired immune deficiency syndrome
(AIDS) wasn’t identified until the 1980s – it was a
kind of virus, a retrovirus, which until then wasn’t thought
to infect humans – further research has shown that the virus
has been around in humans and primates for decades.
The last major disease to emerge in the United States was hantavirus,
a genus of at least 14 viruses that erupted in 1993 among impoverished
Navajo in the “Four Corners” region of Arizona, Utah,
Colorado, and New Mexico. In May of 1993, several healthy Navajo
youth died of a mysterious pulmonary illness. The agent responsible
for the disease, hantavirus, is transmitted by breathing air contaminated
with rodent feces. A mild winter and wet spring produced an abundant
food supply that allowed the population of mice and rats to multiply
dramatically in the Southwest.
There have been 238 cases of hantavirus pulmonary syndrome and
nearly 100 deaths in the U.S. through February 2000, according to
the CDC. Although hantavirus has been found in all 48 contiguous
states, the disease has not grown into a major public-health problem
because the conditions under which it flourishes are not common.
Fortunately, Baltimore, whose humid climate is very different from
the arid Southwest’s, doesn’t have many rats that are
infected with the disease.
What we do have is mosquitoes.
Diseases emerge in areas of the world where different populations
of humans, animals and viruses mingle, says Donald Burke, MD, professor
of the Vaccine Research Center at Johns Hopkins. Usually, viruses
are choosy about the hosts they infect. There are animal viruses
and there are human viruses, but rarely do they pass from one species
to another. However, in certain places around the world –
the tropics, African rainforests, Hong Kong – humans and wildlife
co-exist in close proximity, with animals coming and going through
human settlements, and humans hunting wild meat.
In those cases, viruses that are adapted to humans have a chance
to mix and swap genes with viruses that are adapted to other animals,
leading to new hybrids that can cross from species to species. “An
animal-adapted virus recombines with a human-adapted virus,”
explains Burke. Under the right conditions, there can be an “exchange
of genetic material between human and animal microbes that allows
accelerated evolution of the organism.”
This scenario – the adaptation of a simian virus to humans
– is likely how HIV emerged from Africa years ago. The human
T-lymphocyte, an essential component of the immune system, was not
at the time known to be vulnerable to an infectious agent like HIV.
But it is. In fact, viruses are very receptor-specific, and for
every receptor in the body – and there are hundreds of thousands
of different kinds – there exists the potential for a virus.
The white blood cell was an untapped market for viruses, an opportunity
waiting to happen.
“There are lots of animal pathogens, many of which do not
have a corresponding established human infection,” says Burke.
“The AIDS virus is a good example of something that was not
recognized in humans until the early 1980s. This kind of thing is
probably occurring with lots of different organisms.”
than 30 new infectious diseases
have been identified since 1973
Several alarming infectious diseases have emerged from the tropical
rain forests in recent years – the painful and deadly Ebola
virus, which nearly escaped from a Reston, Virginia, animal facility
in 1989; dengue fever, which has rapidly spread through the Caribbean
and Central America; and now West Nile encephalitis.
Originally identified in the 1930s, the West Nile virus
has been responsible for sporadic cases of disease in Africa, Asia
and Europe for decades. Outbreaks of West Nile occurred in the western
Mediterranean and southern Russia in the early 1960s, Belarus and
Ukraine in the 70s and 80s, Romania in 1996-97, the Czech Lands
in 1997, and Italy in 1998. The last major outbreak of West Nile,
in Bucharest, Romania in 1996-97, caused more than 500 bases of
But U.S. residents didn’t pay attention to the disease until
the summer of 1999, when West Nile erupted in a residential neighborhood
in Queens, New York. Initially identified as the more common St.
Louis encephalitis, lab testing later proved the virus to be West
West Nile is carried by mosquitoes that thrive in densely populated
urban areas and is able to cause illness in several different kinds
of animals, apparently crossing species with ease. West Nile has
been found in about 20 species of bird – particularly the
common American crow – as well as horses, dogs and cats.
“When you see that kind of behavior, moving from one species
to another,” says Burke, “that has all the earmarks
of an emerging infection.”
The crow found in Baltimore marks the most southern point in the
United States to which West Nile is known to have traveled. Public
health officials and infectious disease experts from around the
world will be watching the mid-Atlantic closely, Baltimore in particular,
to assess how far West Nile may have spread since last summer.
On scenario is that the Baltimore crow is a bellwether that West
Nile is creeping further south, heading toward the warmer climate
similar to its African origins. “Our great fear is that it
will move south,” says Edelman. “That’s a big
mystery. We don’t know what’s going to happen.”
Last summer, federal, state and local health agencies launched
a massive response to West Nile, monitoring mosquito traps and dead
animals to identify traces of the disease. Other than the Baltimore
crow and some birds found in New Jersey, no other infected bird
has been found outside of the New York City area, according to Linda
Glaser, wildlife disease specialist at the U.S.G.S. National Wildlife
Health Center in Madison, Wisconsin. The last infected bird was
a red-tailed hawk in Westchester County, New York, that died in
However, monitoring of trapped mosquitoes revealed that West Nile
had “overwintered,” surviving the cold weather in New
York. If West Nile lived through the winter in New York, says Glaser,
the virus could also have survived in Maryland. Nobody knows whether
West Nile will be a problem this year until the weather warms up
and mosquitoes become active again.
“There is a threat,” says Edelman. “Whenever
you have mosquito transmission [of disease], you have potential
for large-scale problems. But that doesn’t mean there will
be large-scale illness.”
The absence of West Nile in mosquitoes caught in Maryland to date
is not particularly reassuring, says Jeff Roche, MD, acting state
epidemiologist in the disease control division of Maryland’s
health department. “We’re not discounting the fact that
there could be endemic disease in Maryland from West Nile virus,”
In Maryland, three state agencies are involved in efforts to control
the threat of West Nile. The Department of Natural Resources is
monitoring signs of disease in birds and other wildlife. Mosquito-control
efforts are under the direction of the state Department of Agriculture.
Responding to the potential human health risks of West Nile is the
jurisdiction of the Department of Health and Mental Hygiene. The
State of Maryland established a West Nile hotline – 888-584-3110
– that will be staffed 24 hours a day, seven days a week.
Though scientists are concerned about a threat to public health,
they can’t help butt be intrigued by this rare chance to study
an emerging disease close to home. “This may be one of those
fascinating times when we may be seeing the emergence of an important
new disease,” says Roche.
We’ll be hearing more about West Nile as the virus settles
in and finds its way around the new neighborhood. “We’re
going to have to get used to it,” says Edelman. “The
problem with these things is that once [emerging diseases] are ensconced,
the general rule is that they stay around for a while. We’re
going to have our hands full with West Nile.”
Reducing Risks of West Nile Virus
• Stay indoors
at dawn and dusk, when mosquitoes are most active.
• Wear long-sleeved
shirts and long pants when outdoors.
• Apply insect
repellent sparingly to exposed skin. An effective repellent has
20 to 30 percent DEET. High concentratins of DEET may cause side
effects, particularly in children.
• Spray clothing
with repellent containing permethrin or DEET, as mosquitoes may
bite through clothing.
B and "ultrasonic" devices are not effective in preventing
Source: Centers for Disease Control and Prevention
UPDATE: West Nile was reported in four states
in late 1999. Within three years the virus spread from coast to
coast to all but four of the lower 48 states. There were 3,852 confirmed
cases of West Nile infection and 241 deaths during 2002. In Maryland
there were 31 cases of West Nile -- including the nation's first
in utero transmission from mother to baby -- and at least
two deaths in 2002.
Nile Home Page
Centers for Disease Control and Prevention
From Medline, sponsored by National Library of Medicine and National
Institutes of Health
on West Nile Virus
Fact sheet from the National Institute of Allergy and Infectious
Nile -- Publications and Links
From National Institute of Allergy and Infectious Disease
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Copyright 2000, 2003 Bruce Goldfarb. All rights reserved.