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Global commerce, travel, population and climate changes are making
parasitic diseases-including mosquito-borne diseases-an emerging
or re-emerging public health threat, according to the national Centers
for Disease Control and Prevention. CDC believes that available
reports seriously underestimate the true incidence of mosquito-borne
diseases because of under funding of state vector control programs
and failure to diagnose some diseases. The following is what are
reported about mosquito-caused illnesses.
West Nile Virus –
A flavivirus that is spread by the bit of an infected mosquito and
can affect people, horses, many types of birds and some other animals.
The virus has been present for years in Africa, West Asia, and the
Middle East. It was first detected in the United States in 1999,
but has been spreading rapidly since that time. Experts believe
that West Nile Virus is now established as a seasonal epidemic in
North America that flares up in summer and continues into the fall.
West Nile Virus is a potentially serious, even fatal, illness.
Most people who become infected with the disease will have only
mild symptoms or none at all. However, on rare occasions, West Nile
virus infection can result in a severe and sometimes fatal illness
known as West Nile encephalitis (an inflammation of the brain).
The risk of severe disease is higher for persons 50 years of age
and older. There is no evidence to suggest that West Nile virus
can spread from person to person or from animal to person.
For more information about West Nile Virus, please visit Center
for Disease Control (West Nile Virus).
- A virus transmitted
to humans by an infected mosquito, encephalitis cannot be treated
with antibiotics. It also cannot be transmitted from human to human.
The word encephalitis means inflammation of the brain. A general
name for this mosquito-transmitted virus is an arbovirus, for ar(thropod)
+ bo(rne) + virus. Arthropoda is the phylum name for invertebrate
organisms that include insects, crustaceans, arachnids and myriapods.
A potentially serious illness of the brain and central nervous
system, encephalitis is characterized by seizures, coma, paralysis
and permanent neurological damage. Sine 1964, between 150 and 3,000
cases have been reported annually in the U.S., including the St.
Louis, LaCrosse, Eastern Equine and Western Equine Encephalitis.
 - The virus causing St. Louis Encephalitis
is the most common mosquito-borne human pathogens in the U.S. Occurring
in every state, St. Louis Encephalitis is found particularly in
Florida, the Gulf Coast Region, Ohio, the Mississippi Valley, and
Western states. Outbreaks are most likely from mid-summer through
the early fall. Since 1964 the CDC has confirmed an average of 193
cases yearly. In 1990, 226 people were infected with the virus and
11 died in Florida. Fearing an outbreak in 1997, state health officials
issued an encephalitis alert, prompting Disney World and other tourist
parks to limit night activity.
St. Louis Encephalitis is transmitted among birds primarily by
Culex pipiens mosquitoes. Only being bitten by an infected mosquito
infects humans. There is no person-to-person transmission. Symptoms
include fever, headache, nausea, vomiting, convulsions and lethargy.
The state of symptoms may be abrupt onset of fever, nausea and vomiting
with severe headaches. These symptoms develop within five to seven
days after a bite by an infected mosquito. In its severe form, it
can cause seizures, coma and paralysis. The mortality rate is 10%
with most fatalities among people 60 and older. Treatment is administered
for symptoms as they occur.
- Occurring
primarily in upper Midwestern states of Minnesota, Wisconsin, Iowa,
Illinois, Indiana and Ohio, LaCrosse Encephalitis also has been
reported in the mid South Atlantic states of West Virginia, Virginia,
and North Carolina and in the Southeastern states of Alabama and
Mississippi. Some 75 cases have been reported annually in the U.S.
since 1964.
Most cases occur among children and teens under 16. Symptoms are
fever, headache, nausea and vomiting, convulsions and lethargy,
with severe cases including seizures, coma and paralysis. Some 1%
of cases result in death. Treatment is administered for symptoms
as they occur.
- A viral
infection maintained in nature by a bird-mosquito cycle similar
to St. Louis Encephalitis, Eastern Equine Encephalitis is found
in freshwater swamp areas of coastal states of the Gulf of Mexico
and the Atlantic Ocean, and in some inland mid-western locations.
CDC has reported an annual average of five cases since 1964. Mosquitoes
associated with the disease include Culex quiquefasciatus, Aedes
sollicitans and Aedes vexans.
Eastern Equine Encephalitis can infect people of any age, but young
children and infants suffer most from the disease. Symptoms begin
4-10 days after the bite of an infected mosquito, with sudden onset
of fever, general muscle pain and increasingly severe headache.
Serious cases have seizures and coma. About 35% of those infected
die, usually within three to five days from the onset of symptoms.
Children and infants who survive are frequently afflicted with varying
degrees of mental retardation and paralysis. Up to half of survivors
will suffer permanent brain damage, many requiring permanent institutional
care. Treatment is administered for symptoms as they occur.
- Found
in every state west of the Mississippi River, in southwestern Canada
and northwestern Mexico, Western Equine Encephalitis may be increasing
because of expanded irrigated agriculture in the North Platte River
Valley, which has fostered habitats and conditions favoring mosquitoes
that transmit disease. On average, 19 cases have been reported annually
by the CDC since 1964.
Culex tarsalis is the most important vector in the West. East of
the Mississippi, Culex quinquefasciatus is the suspected vector.
Birds are the major host. Causing death in about 3% of cases, epidemics
are cyclical, roughly every 10 years. The last, of 41 cases, was
in 1987. Symptoms include infections. Severe cases exhibit fever,
headache, nausea, vomiting, anorexia and malaise, followed by weakness
and altered mental functioning. Treatment is administered for symptoms
as they occur.
- Most cases
are reported in the Midwestern states of Ohio, Indiana and Wisconsin.
Rather than birds, the natural hosts of California Encephalitis
are small animals-rabbits, hares, and squirrels. Vectors are mostly
woodland mosquitoes of the Aedes genus.
- Both
humans and horses are susceptible to Venezuelan Equine Encephalitis,
but unlike the other arboviral encephalitis, victims develop high
levels of the virus in the blood. This allows mosquitoes to transmit
disease to humans or equines without the intermediate host, birds.
Vectors include species of Aedes, Culex and Anopheles.
- One of the most rapidly
expanding diseases in the world, with tens of millions of cases
annually in the tropics, dengue fever is a small but significant
risk in the United States because the two transmitting mosquito
species, Aedes aegypti and Aedes albopictus, are found here. The
CDC reports 100 to 200 cases in the United States each year. In
1996, 181 cases were reported and 45 diagnosed, according to Texas
State health officials. Heavy rains that year brought out swarms
of mosquitoes at the Mexican border. Arizona State health officials
are preparing for dengue after finding the Aedes aegypti in Tucson.
Sometimes called "breakbone fever," dengue fever's symptoms include
high fever, headaches, bodyaches, sore throat and a rash appearing
three to four days after symptoms start. The rash may not be visible
in persons with darker skin tones. Symptoms lasting five to seven
days may be followed by several weeks of fatigue and weakness. More
severe cases, in addition to fever and headaches, may show coughing
and abdominal pain. Without treatment, fatalities may reach 15%.
Treatment is administered for symptoms as they occur.
- Caused by a parasite transmitted
by infected Anopheles mosquitoes present in tropical and subtropical
countries, malaria annually affects 300-500 million people and kills
1.5 to 2.5 million, mostly children, according to the World Health
Organization. Caused by any of the Plasmodium species of protozoa,
it remains the most important human disease transmitted by mosquitoes
worldwide but is rare in the U.S. Thought to have been introduced
on the North American continent during colonial days, malaria is
not native to the U.S.
Travel-related outbreaks have occurred here after the domestic
Anopheles mosquito population was infected. The CDC reports U.S.
malaria transmission since 1986 among Hispanic immigrants and California
residents. Since 1985, about 1,000 cases of imported malaria have
been reported each year, with 66 deaths in 1986-1995. In 1996, the
U.S. had 1,800 cases.
Early stages have flu-like symptoms, seven to eight days after
infection, such as fever, chills, headache and muscle aches. If
not diagnosed and treated rapidly, malaria may cause shock, renal
failure, acute encephalitis and coma, and it can be fatal. If not
treated properly, symptoms may reappear months or years after infection.
Treatment includes antibiotics. Prevention when traveling in high-risk
areas includes anti-malarial drugs.
- Occurring in Africa
and South America, yellow fever is a rare cause of illness in travelers.
Most countries have requirements for yellow fever vaccination. Vaccinations
are required of persons reentering the U.S. from yellow fever areas.
All planes and ships are required to kill infected mosquito vectors.
The first recognized and documented importation of yellow fever
into the U.S. since 1924, involves an American who contracted the
virus while fishing on the Amazon and Rio Negro Rivers in 1996.
Returning to Tennessee, he died after six days of hospitalization.
Caused by a virus closely related to the dengue virus, and transmitted
by Aedes aegypti, yellow fever infections produce dengue-like symptoms
in humans. But the effects of yellow fever are much more severe.
Symptoms include fever, jaundice or yellowing of skin, and hemorrhaging.
The fatality rate may exceed 50% in epidemics. A safe vaccine is
available, but no treatment exists.
Mosquitoes harass and bite livestock, causing beef cattle and hogs
to fail to gain weight, and dairy cattle to decrease milk production.
Family pets and wildlife also suffer from the unrelenting attacks
of mosquitoes.
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