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West Nile Virus

Introduction 

September 14, 2012
 
Joint South Dakota Department of Health and SDSU message to schools regarding WNV and fall outdoor activities and sports:
 

Protecting Athletes, Coaches, Band Members, Cheerleaders and Fans against West Nile Virus

Summer vacation is over, but the West Nile Virus season continues.  South Dakota is experiencing our worst West Nile season since 2007. As of September 5, 2012 in South Dakota:

       119 human cases of West Nile virus disease have been reported to the SD Dept of Health.

          Status:  meningitis/encephalitis 35%; fever 65%; and hospitalized 47%.

          Deaths:  2.  

          Age:  8% of cases have been school age children. 

          Gender:  male 50%, female 50%. 

Until the West Nile Virus season is over, it is essential precautions be taken to protect student athletes, coaches, band musicians, cheerleaders and fans from contracting the disease especially during late afternoon/evening practices and nighttime events.  Proper use of mosquito repellents is a MUST! 

Mosquito repellents containing these active ingredients typically provide reasonably long-lasting protection:

  • DEET,
  • Picaridin,
  • Oil of Lemon Eucalyptus,
  • IR3535, 

Research indicates repellent efficacy and duration of protection vary considerably among products and among mosquito species and are markedly affected by ambient temperature, amount of perspiration, exposure to water, abrasive removal, and other factors.  In general, higher concentrations of active ingredient provide longer duration of protection, regardless of the active ingredient.

Practice and playing fields should be sprayed for mosquitoes. 

 
 
 
August 29, 2012 CDC Briefing on Hurricane Isaac and West Nile Virus
 
 

Press Briefing Transcript

CDC Telebriefing on West Nile Virus Update

Wednesday, August 29 at Noon ET

I have taken the following excerpts from the press briefing transcript as they speak to Isaac and potential for increasing cases of West Nile Virus -  the bottom line is no dramatic increase is anticipated and  Lyle Petersen explains why they do not expect Isaac to contribute to the number of cases of WNV.

LYLE PETERSEN: And now I’d like to say a few words about Hurricane Isaac and the question of how it might affect the spread of West Nile virus. Previous experience has shown that floods and hurricanes do not typically result in increased transmission of West Nile virus. Thus, we expect Hurricane Isaac will likely have no noticeable effect on the current West Nile epidemic. Nevertheless, small increases in the numbers of West Nile cases were noted in some areas of Louisiana after Hurricane Katrina. These were thought to be due to increased outdoor exposure that occurred when houses were severely damaged and during recovery efforts. CDC has reached out to health departments in Louisiana, Mississippi, Alabama, and Tennessee to alert them of the situation and offer assistance. In light of the ongoing risk for West Nile virus infection, it's important for people to protect themselves from mosquito bites.

We encourage everyone to use insect repellent when you go outdoors, wear long sleeves and pants. Use air conditioning if possible. Empty stands water from items outside your home, such as gutters, kiddie pools and birdbaths. In response to this year's outbreak, CDC works closely with state and local health departments particularly in areas hardest hit by the epidemic. As I noted earlier, nearly half of this year's West Nile virus cases have occurred in Texas. A majority of the cases there have been in the Dallas area. CDC has had the privilege of working with the Texas department of state health services in Dallas County and other county departments to help protect people from the West Nile virus. They’ve done a great job. Dr. Lakey is going to give an update about the situation in Texas. Dr. Lakey?

ELIZABETH WEISS: Thank you so much for taking my call. I had a question about the point that was made earlier, looking at the hurricane, you said that there had historically been an uptick, is that right after? You assume because there was so much standing water, the services that might have gone to mosquito abatement may have been used elsewhere, an uptick later do you mean never or later?

LYLE PETERSEN: What has been observed in the past, we have had a lot of experience with vector-borne diseases and hurricanes and floods? What has been observed in the past that these don't really have a big impact on overall incident of disease. The reason is, because, it's because, these hurricanes and flood events tend to disrupt the entire ecology of the area and interrupt this natural transmission cycle between birds and mosquitoes. The virus normally exists in. And so, the end result is, really hurricanes and floods don't have a major impact on our virus transmission. But, naturally, before the hurricane happened, there were plenty of West Nile virus infected mosquitoes out there in the environment. And so, what happens -- what was observed in Louisiana, was, after Katrina, was that, people who were out, houses were destroyed. They were living out in the elements; there were a lot of workers out there and homeowners taking care of downed trees and the like. Outdoors and exposed to the West Nile virus-infected mosquitos already there. In some areas, where it was looked at, there was a small transient increase in West Nile virus transmission following hurricane Katrina, but if you look at the overall picture the hurricane really is not expected to have a major impact at all on what's happening across the country.

 

 
August 16, 2012
 
The cases of West Nile Virus are spreading and increasing across the country, with the Centers for Disease Control stating this is the worst outbreak in years.  The warmer winter and spring temperatures suggested by many that this could be a potentially bad year for the virus and now that is being seen in in 30 states.  The drought can also play a role in the increased number of cases as some mosquitoes such as Culex tarsalis survive in dry conditions and with spotty rains or irrigations pits, breed and can spread the virus.  These mosquitoes are also the ones called "stealth biters" -- they get you and you do not know it.  They are not like the flood water nuisance mosquitoes. 
 
Community control programs are essential but taking personal responsibility is the best way to reduce your risk of West Nile Virus.
 
  
Background
 
Although the West Nile virus mainly infects birds, it can be transmitted to humans and other animals by certain species of mosquitoes that take blood meals from both birds and humans. The bite from just one infected mosquito is all that is needed to transfer the disease.
 
 In humans, West Nile virus disease symptoms vary from no visible effect to flu-like symptoms, paralysis, or even death. All age groups are susceptible, but the elderly and those with weakened immune systems are more likely to experience severe forms of the disease. More on symptoms

Public mosquito control programs have been started in many cities and towns across the country. Even the best community mosquito control program will only reduce the risk from West Nile virus and thus wherever you live, personal protection against mosquito bites is your best safeguard.



Types of mosquitoes in the U.S. 

Since 1999, in the United States more than 60 mosquito species have been found in West Nile virus positive mosquito pools.  These are pools from which West Nile virus was isolated, West Nile RNA detected, or West Nile antigen was detected using a variety of diagnostic tests.  Although a mosquito species found positive for the virus in nature may potentially be a carrier, further tests are usually needed to determine if the species is efficient in transmitting the virus to humans.  It is important to know which mosquitoes are efficient carriers of the virus in your state or local community.   


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Why do mosquitoes bite? 

Adult female mosquitoes need blood to produce eggs and perpetuate their species. Although they can survive by feeding on sugary liquids, it is only after a blood meal that they start producing eggs. Only female mosquitoes bite. Male mosquitoes feed on sugars found in fruits and flowers.

Mosquitoes looking for a blood meal are mainly attracted to carbon dioxide in the breath, body heat, and sweat of humans. Lactic acid and numerous other scents emitted by the human skin have also been found attractive to mosquitoes. Individuals who produce more body heat, sweat, carbon dioxide, and lactic acid will be more attractive to mosquitoes.

Birds, horses, cattle, dogs, cats, rabbits, squirrels, and other animals are fed upon by mosquitoes. It is when mosquitoes bite different hosts that disease-causing microorganisms may be spread. 


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Disease-causing microorganisms mosquitoes transmit 

Flowchart: West Nile Virus Transmission Cycle from the CDC web site, click on the image to visit the site and view the full-sized version.

Arboviruses (short for arthropod-borne viruses) such as the West Nile virus, western equine encephalitis virus, and Saint Louis encephalitis virus are perhaps the most important microorganisms that mosquitoes transmit in the United States. In other parts of the world, mosquitoes are carriers of parasites that cause human malaria, filariasis, dengue fever, Japanese encephalitis, yellow fever, and others.

The West Nile virus is a disease that primarily affects birds. It may be transmitted by mosquitoes from infected birds to other hosts such as humans or horses. The West Nile virus has not been shown to be transmitted from human to human, horses to humans, or horses to horses. Thus, the West Nile virus is carried by various species of birds and spread by mosquitoes.

 


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Most effective way to prevent bites and control mosquitoes at home 

Insect repellents are recommended as the best way for one to protect themselves from mosquito bites when involved in outdoor activities.  Repellents act by making a person "undesirable" for feeding or in other words the repellent masks the gases and scents known to be attractive to mosquitoes.

DEET and Picaridin are recommended to be applied to the skin and permethrin applied on the clothing. DEET and Picaridin repel mosquitoes while permethrin actually kills mosquitoes on contact.

Using DEET or Picaridin alone or permethrin alone will not be as effective as using the two in combination. However, using DEET or Picaridin alone may be sufficient for most outdoor activities such as going to the park, mowing the lawn, gardening, or relaxing in the backyard. Individuals who will be outdoors for an extended period of time, like hunters and campers, are encouraged to use the combination of DEET or Picaridin and permethrin.

There are alternative repellents such as combinations of soybean oil, geranium oil and coconut oil and lemon eucalyptus that have been shown to repel mosquitoes, but only for short periods of time. Before using any repellent read and follow all label directions.

Mosquitoes lay their eggs in standing water. Limit the number of places around your home for mosquitoes to breed by getting rid of items that hold water. Repair broken screens and windows on your home.

 Support your community mosquito control programs.


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Last Updated:9/14/2012 2:28 PM
 

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