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Mosquito Borne Diseases

West Nile Virus

According to the CDC β€œthe best way to avoid West Nile Virus is to prevent mosquito bites.”

West Nile virus is a potentially serious disease that is transmitted to humans by mosquitoes. Every year hundreds of cases are reported, and possibly many hundreds more go undiagnosed or misdiagnosed. West Nile virus did not emerge in the United States until 1999.

West Nile Facts:

  • West Nile virus (WNV) is a single-strand RNA virus of the family Flaviviridae, genus Flavivirus, spread from birds to mosquitoes to humans.
  • West Nile was first isolated in Africa in 1937.
  • West Nile virus first appeared in the United States in 1999, which is an important milestone in the evolution of the virus.
  • West Nile virus cannot be spread from human to human. (Mother to fetus or through breast milk transmission is still being evaluated).
  • Symptoms usually appear 3-14 days after being bitten by an infected mosquito.
  • Individuals over age 50 are more likely to develop the severe form of the disease.
  • Blood donations are screened for West Nile virus before being distributed.
  • West Nile virus can kill birds, though most survive infection. If you find a dead bird, do not handle it. Contact the St. Louis County Health Department at 314-615-0650.
  • Pets can also become infected with West Nile virus.
  • Horses can become infected. The horse mortality rate is 40%. According to the CDC, there is a vaccine available from veterinarians for horses.

West Nile Virus Symptoms
Serious symptoms may last several weeks and neurological effects may even become permanent. Treatment should be sought immediately if these symptoms are exhibited:

  • Headache
  • High Fever
  • Neck stiffness
  • Stupor
  • Disorientation
  • Coma
  • Tremors
  • Convulsions
  • Muscle weakness
  • Loss of vision
  • Numbness
  • Paralysis

Milder symptoms may last for a few days to several weeks.

  • Headache
  • Fever
  • Body aches
  • Nausea
  • Vomiting
  • Swollen lymph glands
  • Rash on the chest, stomach and back

Diagnosis of West Nile Virus
Diagnosis is based on the presence of the disease in the locality (any recent travel should be noted to your physician) and the presence of symptoms. West Nile virus or other arboviral disease should be strongly considered when patients over 50 develop unexplained encephalitis or meningitis during mosquito season. Blood tests may confirm the presence of the disease, though prior infections or recent vaccinations can produce false positive results. When the disease is extremely serious, a spinal tap or brain imaging may be taken.

Treatment of West Nile Virus
There is no specific course of treatment for West Nile virus. Most cases resolve themselves with no treatment. Even the most severe cases are typically treated only with supportive therapy such as intravenous fluids and painkillers. Interferon is being investigated as a treatment and shows some promise.
More information can be found at CDC

Arboviral Encephalitides

Arboviral Encephalitides are viruses that are maintained in nature through vertebrate hosts and blood feeding arthropods like mosquitoes. These viruses can cause encephalitis which is a dangerous inflammation of the brain. It is among the most serious conditions linked to mosquitoes.

The diseases of major concern in the U.S. for mosquito-borne encephalitis are:

  • Eastern Equine Encephalitis
  • Approximately one-third of all people with clinical encephalitis caused by EEE will die from the disease and of those who recover, many will suffer permanent brain damage.
  • La Crosse Encephalitis
  • La Crosse (LAC) encephalitis was discovered in La Crosse, Wisconsin in 1963. Since then, the virus has been identified in several Midwestern and Mid-Atlantic states. Most cases of LAC encephalitis occur in children under 16 years of age.
  • St. Louis Encephalitis
  • The leading cause of epidemic flaviviral encephalitis is St. Louis encephalitis (SLE) virus. SLE is the most common mosquito-transmitted human pathogen in the U.S.
  • West Nile Virus Encephalitis
  • Following bird migration, the virus is presently extending westward, and by April 2003, virus activity had been detected in 46 states and the District of Columbia.
  • Western Equine Encephalitis
  • Missouri has not had any confirmed cases of WEE since 1964

These viruses can invade the Central Nervous System and cause encephalitis. At that point, the disease can take a deadly course. Even those who survive are often left with permanent neurological damage. Age plays a factor, with the very young and the very old more likely to experience permanent brain damage or death.

Symptoms of vector-borne encephalitis.

  • Initial mosquito bite
  • Clumsiness
  • Confusion
  • Fever
  • Headache
  • Memory loss
  • Mood changes
  • Muscle weakness
  • Seizures
  • Stiff neck
  • Stupor
  • Vomiting

Diagnosis of encephalitis.
The underlying virus may be identified by a blood test or other diagnostic procedure. Diagnosing its development into encephalitis may be accomplished via spinal tap, EEG, or brain imaging.

Treatment of encephalitis.
No currently available medication “cures” encephalitis. Rather, treatment is supportive, dealing with relieving the associated swelling of the brain, loss of automatic breathing functions and other symptoms or complications.

Preventing encephalitis.
Since encephalitis is caused by a variety of infections, there is no single vaccine for it. Nor is there any commercially available vaccine for many of the initiating pathogens. The U.S. CDC recommends taking preventive measures against mosquito and tick bites.
More information can be found at http://www.cdc.gov/ncidod/dvbid/arbor/arbdet.htm