St. Louis Encephalitis
- St. Louis encephalitis is a serious viral
disease that is spread by infected mosquitoes.
- It is one of several mosquito-borne virus
diseases that can affect the central nervous
system and cause severe complications and
death.
- St. Louis encephalitis is found throughout
the United States.
- There is no specific treatment for St. Louis
encephalitis.
- Prevention centers on controlling mosquitoes
and avoiding mosquito bites.
What is St. Louis encephalitis?
St. Louis encephalitis is a major mosquito-borne
disease in the United States. It is one of a
group of mosquito-borne virus diseases that
can affect the central nervous system and cause
severe complications and even death. Other similar
diseases are eastern equine encephalitis, western
equine encephalitis, and LaCrosse encephalitis.
What is the infectious agent that causes
St. Louis encephalitis?
St. Louis encephalitis is caused by the St.
Louis encephalitis virus, an arbovirus. Arbovirus
is short for arthropod-borne virus.
Arboviruses are a large group of viruses that
are spread by certain invertebrate animals (arthropods),
mainly blood-sucking insects. In the United
States, arboviruses are usually spread by infected
mosquitoes. Birds are often the source of infection
for mosquitoes, which can sometimes transmit
the infection to animals and, in rare cases,
people.
Where is St. Louis encephalitis found?
St. Louis encephalitis is found throughout
North, Central, and South America, and the Caribbean,
but is a major public health problem mainly
in the United States. The virus is found throughout
the country, but periodic outbreaks and epidemics
have occurred in the Mississippi Valley and
Gulf Coast, the western states, and Florida.
How do people get St. Louis encephalitis?
The St. Louis encephalitis virus has a complex
life cycle involving common birds (sparrows,
finches, blue jays, robins, doves) and specific
types of Culex mosquitoes that feed mainly
on birds. Humans and other mammals are not an
important part of the life cycle of the virus.
Sometimes, however, people who live in or visit
an area where the virus lives can be infected
by the bite of an infected mosquito. After infection,
the virus invades the central nervous system,
including the spinal cord and brain.
What are the signs and symptoms of St. Louis
encephalitis?
Symptoms are usually mild and include fever,
headache, tiredness, and dizziness. In its more
severe form, the disease can cause convulsions
and death.
How is St. Louis encephalitis diagnosed?
Diagnosis is based on tests of blood or spinal
fluid.
Who is at risk for St. Louis encephalitis?
Anyone can get St. Louis encephalitis, but
some people are at increased risk of severe
disease:
- Elderly persons
- Persons living in crowded, low-income areas
- Persons who work outside or participate
in outdoor recreational activities in areas
where the disease is common
What is the treatment for St. Louis encephalitis?
There is no specific treatment for St. Louis
encephalitis. Antibiotics are not effective
against viruses, and no effective anti-viral
drugs have been discovered. Care of patients
centers on treatment of symptoms and complications.
How common is St. Louis encephalitis?
St. Louis encephalitis is the most common human
disease caused by mosquitoes in the United States.
Since 1964, there have been about 4,440 confirmed
cases of St. Louis encephalitis, with an average
of 130 cases per year. Up to 3,000 cases have
been reported during epidemics in some years.
Many more infections occur without symptoms
and go undiagnosed.
Is St. Louis encephalitis an emerging infectious
disease?
Yes. The virus was first isolated in 1933 during
an epidemic in St. Louis, Missouri, and has
re-emerged often in epidemics in the United
States. The largest outbreaks in 15 years occurred
in 1990 in Florida and Texas. The risk of exposure
is increasing in urban areas as deteriorating
inner cities create new habitats for mosquitoes.
How can St. Louis encephalitis be prevented?
There is no vaccine to prevent St. Louis encephalitis.
Prevention centers on public health action to
control mosquitoes and on individual action
to avoid mosquito bites. To avoid being bitten
by the mosquitoes that cause St. Louis encephalitis:
- If possible, stay inside between dusk and
dark. This is when the mosquitoes are most
active in their search for food.
- When outside, wear long pants and long-sleeved
shirts.
- Spray exposed skin with insect repellent.
This fact sheet is for information only and
is not meant to be used for self-diagnosis or
as a substitute for consultation with a health-care
provider. If you have questions about the disease
described above, consult a health-care provider.
