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West Nile Virus 2012. Hype or Threat?

 Is West Nile virus 2012 a serious public health concern or matter of media hype? 

The Centers for Disease Control and Prevention (CDC) tell CNN that the recent 2012 West Nile Virus outbreak is the largest ever seen in the United States.  Read CNN: West Nile outbreak largest ever.

Really? Worse by geographical distribution? By total number of cases? Fatalities? Not according to the CDC's Statistics, Surveillance, and Control Archive its least not yet.

West Nile Virus (WNV) has hit the mainstream media in a big way over the last weeks of August, 2012. The virus is being dramatically portrayed as spreading, seemingly out of control, from state to state. As of this publication date, the Centers for Disease Control and Prevention (CDC) is reporting 1,118 human cases of WNV with 41 deaths attributed to the mosquito-borne disease. Going by these (most recent as of posting) numbers, the 2012 WNV situation is actually fairly average when guaged against previous years.  See How does 2012 WNV measure up to past years below.

Is the CDC intentionally contributing to the hype or are we missing something?

CDC categorizes WNV into broad groups; neuroinvasive and non-neuroinvasive disease. In other words, a severe form (neuroinvasive) that produces meningitis or encephalopathy and a less severe form. The 2012 data-to-date demonstrate that 56% of WNV cases are neuroinvasive, with 44% non-neuroinvasive or less severe.

Signs and Symptoms
As many as 80% of people infected with WNV will have no symptoms at all. Few may have mild symptoms resembling other viral illness such as influenza. One out of every 150 people infected with WNV go on to develop severe disease  - high fever, various neurological abnormalities, and weakness that may last several weeks. Neurological effects may be permanent.

How does 2012 measure up to past years? 
2012. An average year for WNV?
Looking back at the CDC data from 2011 to 2006 we find some interesting (albeit less dramatic) numbers. For that six-year period there were a total of 11,708 cases of WNV and 477 fatalities. That's an average of 1,951.3 cases/yr and 79.5 fatalities/yr. making 2012 look like an average year (of the last 6 years) for WNV.

Interestingly, the CDCs archived statistics 2003 would reign supreme as the worst outbreak ever. In 2003 there were 9862 reported cases of WNV and 264 deaths spanning 46 states.

According to the CDC West Nile Virus homepage:
  • People over 50 at higher risk to get severe illness. People over the age of 50 are more likely to develop serious symptoms of WNV if they do get sick and should take special care to avoid mosquito bites. 
  • Being outside means you're at risk. The more time you're outdoors, the more time you could be bitten by an infected mosquito. Pay attention to avoiding mosquito bites if you spend a lot of time outside, either working or playing. 
  • Risk through medical procedures is very low. All donated blood is checked for WNV before being used. The risk of getting WNV through blood transfusions and organ transplants is very small, and should not prevent people who need surgery from having it. If you have concerns, talk to your doctor. 
Vector control. Key to prevention or hazard trade-off?
The main countermeasure against WNV is to kill the mosquito that carries the virus by way of pesticide use. Substances such as malathion and parathion have been used. Both are organophosphate-based chemicals that can produce illness and cause reactions similar to chemical weapon nerve agents at toxic doses. More recently, the pesticide Zenivex has been used. Zenivex E4 is a skin and eye irritant that contains petroleum distillates and poses an aspiration pneumonia hazard. The NFPA rating is Health: 2 Fire: 2 Reactivity: 0. Zenivex has an oral toxicity LD50>5,000 mg/kg and an inhalational toxicity of LC50>2mg/L (4-hour).

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