Encephalitis is an inflammation of the
brain
Encephalitis has many different causes including
viruses, bacteria, parasites, and toxins. When encephalitis
is caused by a virus transmitted by arthropods such
as mosquitoes or ticks, it is known as arboviral
(short for arthropod-borne) encephalitis.
In the U.S., arboviral encephalitis is
usually caused by viruses transmitted by mosquitoes
There are four main causes of arboviral encephalitis
in the U.S. These include eastern equine encephalitis,
western equine encephalitis, St. Louis encephalitis,
and LaCrosse encephalitis. In 1999, there was an
outbreak of West Nile encephalitis in the New York
area; West Nile virus is closely related to St.
Louis encephalitis virus and is found commonly in
Africa, Asia, and the Middle East.
These arboviruses, which are usually found in birds
or small rodents, are transmitted to humans by the
bite of an infected mosquito carrying the virus;
they are not spread directly from human to human.
Arboviral infections are most common in the summer
and early fall. In Maryland, human cases of arboviral
encephalitis rarely occur; there were no reported
cases in the 1990’s.
Most people who are infected with an arbovirus
either do not get sick or have mild symptoms
For those few people who do develop symptoms, those
symptoms usually begin 5 to 15 days after a bite
from a mosquito carrying the virus. A small percentage
of infected people develop encephalitis or meningitis
(inflammation of the tissues that cover the brain
and spinal cord); symptoms may include:
- High fever
- Disorientation
- Seizures
- Headache
- Personality changes
- Coma
- Neck stiffness
- Weakness or paralysis
- Other brain problems
Young children and the elderly are most likely
to have severe illness. There are no proven treatments
for arboviral encephalitis. Most people recover
from the illness, but permanent brain problems and
death can occur.
Steps you can take to prevent mosquito
bites and arboviral encephalitis:
- Remove standing water around your home; as
little as one-half inch of water will support
dozens of mosquitoes. Remove or turn over buckets,
bottles, and other containers; discard old tires
or drill drainage holes in tires used for playground
equipment; clean rain gutters; store canoes, wheelbarrows,
and plastic wading pools upside down; flush birdbaths
and the bottom of plant holders twice a week;
remove pet food and water dishes that are not
being used; adjust tarps (over pools, boats, etc.)
to eliminate standing water; fix dripping faucets.
- Wear clothing that covers the arms, legs, and
feet whenever you are outdoors.
- Use mosquito repellents sparingly on exposed
skin. An effective repellent will contain 20%
to 30% DEET (N,N-diethyl-meta-toluamide). Higher
concentrations may cause side effects, particularly
in children. Avoid applying repellents to the
hands of children and do not use repellents on
children under 3 years of age. Follow package
instructions carefully.
- Spray clothing with repellents containing permethrin
or DEET as mosquitoes may bite through thin clothing.
- Minimize outdoor activities at dawn, dusk,
and in the early evening when mosquitoes are most
active.
- Inspect window and door screens and repair
any holes found.
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