Tribpedia: West Nile Virus

The West Nile Virus is a mosquito-borne disease whose effects can range from unnoticed to, in rare cases, lethal. Following a wetter-than-usual spring and early summer in parts of the state, 2012 saw a spike in incidence, especially in North Texas, with Dallas County alone reporting (as of Aug. 23) 10 deaths out of 288 cases –– with the typical peak period of August and September ongoing. Statewide, the Department of State Health Services (DSHS) reported 640 cases across 57 counties, resulting in 23 deaths (there is a lag between county and state reports; actual numbers may be higher). This year’s outbreak in Texas –– the nation’s worst –– is high, but DSHS numbers indicate there were more deaths on fewer cases in 2006, while 2003 (the worst year so far) saw 439 cases in 86 counties, resulting in 40 deaths. August rains and continuing high temperatures threaten to put both the incidence and the death toll for 2012 at an all-time high.


The virus, so named because it was first isolated in the West Nile district of Uganda in 1937, made its first recorded U.S. appearance in New York City in 1999, and has since shown up all across the nation. One of a group of flaviviruses, the West Nile strain is closely related to the St. Louis encephalitis virus. It is transmitted to humans by mosquitoes that have bitten infected birds. Most people who are exposed to the virus never know it; about 20 percent of those infected develop the milder form of the disease, known as West Nile fever. Symptoms may include abdominal pain, diarrhea, fever, headaches, lack of appetite, muscle aches, nausea, rashes, sore throat, swollen lymph nodes and vomiting, lasting for three to six days.

In about one in 150 cases, the virus crosses the blood brain barrier, resulting in West Nile encephalitis, West Nile meningitis, or West Nile meningoencephalitis. The Center for Disease Control explains the differences: “Encephalitis refers to an inflammation of the brain, meningitis is an inflammation of the membrane around the brain and the spinal cord, meningoencephalitis refers to inflammation of the brain and the membrane surrounding it, and poliomyelitis refers to an inflammation of the spinal cord.” Symptoms can include disorientation, high fever, acute stiffness in the neck, muscle weakness, stupor, tremors, convulsions and paralysis. About one in 10 of those cases results in death.  Populations most at risk to the West Nile virus include people with compromised immune systems, the very young and the elderly. Experts recommend that people experiencing any of these symptoms should see a doctor immediately.

There is no vaccine against the virus. The first step to take is to avoid mosquito bites ––  the Harris County Mosquito Control Division reports 90 percent to 95 percent of the mosquitoes tested in the Houston area carry the virus. Preventive measures include using insect repellents that contain DEET, wearing long-sleeve and brightly colored clothing, staying inside at dawn and dusk and draining pools of standing water. After officials declared a public health emergency in Dallas County, aerial spraying was made an option for Dallas-area cities, with several communities approving ahead of the Aug. 15 deadline, despite health concerns from some residents. Spraying began on August 16.

On August 20, in neighboring Tarrant County, officials announced two more deaths –– both persons in their 80s, bringing that county's total number of cases to 250. North of Tarrant and Dallas counties, which mostly contain the metropolitan sprawl of Dallas/Ft. Worth, Denton county, with one of the highest incidence rates in the state, declared a health emergency on August 22nd, offering aerial spraying to towns to augment ground spraying already underway.

On July 6, 2012, scientists from several Texas medical schools published a paper detailing the results of a years-long study conducted on 139 people who had been infected with the virus. Fully 40 percent were found to have developed chronic kidney disease (CKD) –– including patients who had the milder West Nile Fever, long thought to have no long-term effects. Doctors are advised to be aware of this troubling and long-term complication when treating patients.

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