Sunday, September 2, 2012

West Nile Virus Outbreak

"About 80% of people infected with the virus have no symptoms. Those who do usually start to feel sick 3 to 14 days after being bitten by an infected mosquito. Most people who get sick develop West Nile fever. Symptoms include fever, headache, fatigue, body aches, muscle pain, joint pain, and chills. More than half of sick people report a rash. Symptoms usually last for 3 to 6 days but some people have been sick for weeks."
The West Nile virus outbreak of the summer of 2012 is on track to be the worst ever in the United States. Health officials said earlier this week that there have been 1,118 reported cases of the disease reported in 38 states, including 41 deaths.

Forty-eight states have seen some sort of West Nile virus activity, be it in people, birds or mosquitoes; the only exceptions are Alaska and Hawaii. Since the first time West Nile Virus was detected in 1999, there has never been as many reported cases through the third week in August.

Dr. Dr. Lyle Peterson, director of the division of vector-borne infectious diseases at the Centers for Disease Control, told reporters on Wednesday that the country is in the midst of "one of the largest West Nile outbreaks ever seen."

But why is that? Why are some areas, such as Dallas County in Texas, being hit especially hard?

Texas accounts for about half of cases in the entire country. Dallas County alone has 270 cases of West Nile virus, with 11 deaths. Previously, from 2003 through 2011, Dallas County only saw 10 total West Nile deaths.

"We don't really know why it's worse this year than in previous years" Peterson said Wednesday. However he noted that the unseasonably hot weather from the mild winter and early spring and summer may play a role.

Three experts interviewed by HealthPop agree that this year's weather is likely a driving force in the current outbreak.

Dr. David J. Dausey, chair of the public health department at Mercyhurst University in Erie, Pa. and director of the Mercyhurst Institute for Public Health, said higher temperatures and fluctuations between rainfall and drought provide ideal conditions that have biological impact on mosquitoes, thereby increasing the chances of a West Nile outbreak.

He contends that the mild winter the country experienced, followed by the early spring, extended the mosquito season past when they typically would have died in the winter. That allowed mosquitoes to repopulate themselves quickly come spring. Also, for a spring and summer that's seen high temperatures and drought across the country, the warm weather speeds up the life-cycle of the mosquito, allowing them to reach a biting age quicker, Dausey said.

High temperatures also speed up the multiplication of West Nile virus within a mosquito, said Dausey, and humidity actually stimulates them to bite. At the same time, high temperatures are driving birds into populated, urban areas in search of water, with the mosquitoes following them closely behind. All these conditions, he said, may be contributing to the 2012 West Nile virus outbreak.

But why is Texas experiencing such an influx in cases?

"Well in Texas, the severity of the drought was probably greater than anywhere else in the United States," said Dr. B. Graeme Lockaby, associate dean of research and professor at the School of Forestry & Wildlife Sciences at Auburn University in Alabama. His team just received a $240,000 grant to study the link between poor water quality and increases in the mosquito populations responsible for West Nile Virus, known as the Culex mosquito. He hopes the research will lead to improvements in risk prediction models for a West Nile outbreak.

Lockaby said during a drought, there is a greater likelihood to have polluted water because, as water evaporates, pollutants remain. Therefore in an area like Texas where there are ponds and urban streams that may be polluted to begin with, the water reduction and subsequent pollutant and sewage increases stimulate growth of nutrient-rich bacteria that provide conditions where Culex mosquitoes thrive.

Dausey concurs, noting that on the surface it may look like there's less dry water. But underground sewers and catch basins that contain stagnant water also provide the nutrient-rich conditions mosquitoes seek. He also speculates that the economic and housing crisis may play a role in some urban areas, if people have abandoned homes with swimming pools or other sources of stagnant water, allowing mosquitoes to breed.

What may be more frightening is that drought conditions may also lead to an increase in other mosquito vector-diseases, said Lockaby.

Dausey agreed that in the future Americans may see malaria resurface, for which the country is likely unprepared. He said officials should have been able to predict a West Nile virus outbreak this year because of this interaction between mosquito biology and the weather, and preventative efforts should have been in place all year.

More than 30,000 people in the U.S. have come down with the West Nile virus since 1999, according to the CDC. Mosquitoes get the virus when they feed on infected birds, and then pass it through bites to to humans and other animals .

About 80 percent of people who are infected with the virus won't show any symptoms, but for 20 percent they may develop a fever, headache, body ache, vomiting, swollen lymph glands or a skin rash, what officials refer to as "West Nile fever" or "non-neuroinvasive" West Nile.

But about one in 150 however will develop severe illness, which may result in high fever, neck stiffness, convulsions, vision loss, paralysis, coma and other neurological effects that may be permanent - or even death. That's called neuroinvasive West Nile virus. People over 50 and those with compromised immune systems are at the highest risk.

More information:
» Journal of American Medical Association Article

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