2012 West Nile Virus Update Thus far in 2012 (as of August 21), 47 states have reported West Nile virus (WNV) infections in people, birds, or mosquitoes. A total of 1118 cases of West Nile virus disease in people, including 41 deaths, have been reported to the US Centers for Disease Control and Prevention (CDC). Of these, 629 (56%) were classified as neuroinvasive disease (such as meningitis or encephalitis) and 489 (44%) were classified as non-neuroinvasive disease. WNV neuroinvasive disease affects mostly older adults, generally over 50 years old. Overall, the mortality rate among those with documented WNV infection is approximately 7%.
The 1118 cases reported thus far in 2012 is the highest number of WNV disease cases reported to CDC through the third week in August since WNV was first detected in the United States in 1999. Approximately 75 percent of the cases have been reported from 5 states (Texas, Mississippi, Louisiana, South Dakota, and Oklahoma) and almost half of all cases have been reported from Texas.
Annual flare-ups of the virus start during the summer months, but extend into the fall. Most WNV infections result in no symptoms or minor, self-limited flu-like symptoms, such as head and body aches, nausea, vomiting, and sometimes skin rash on the chest, stomach and back. About one in 150 infected people will develop severe symptoms, which may include high fever, headache, neck stiffness, disorientation, tremors, convulsions, vision loss, and paralysis. All EMS responders and fire fighters should be aware of these.
WNV is primarily a disease of birds, which act as the primary host for the virus. The virus is transmitted among the birds through mosquito bites. Humans and horses are incidental hosts; they are occasionally bitten and infected by the mosquitoes carrying the virus. Therefore, reports of dead birds usually precede infections in horses and humans. Such reports serve as a warning of possible WNV transmission in the affected area and should be forwarded for proper handling.
In 2002, additional, rare routes of WNV transmission in humans were documented for the first time. They include infections through blood transfusions, organ transplantation, breastfeeding, and transfer of the virus from a pregnant mother to her child through a placenta.
Prevention and control of WNV, and other mosquito or insect-borne diseases, is accomplished safely and most effectively through a comprehensive, integrated mosquito management program using integrated pest management (IPM) principles. IPM is based on understanding underlying biology of the insect and transmission of the disease from the insect to humans and animals. IPM employs a variety of physical, mechanical, cultural, biological and educational measures to eradicate or control insect populations. Such IPM approach to mosquito control includes:
1. Surveying standing water habitats for mosquito larva. Eliminating or larvicide treatment of standing water habitats, such as abandoned or standing tires, fresh-water catchment devices, small ponds, flower pots, stationary water buckets, etc, where the mosquitoes breed and larvae develop, is the most effective and economical way to attain long-term mosquito control. Therefore, area sanitation, such as tire removal, stream restoration, catch-basin cleaning and container removal, and application of larvicidal chemicals (larva-killing pesticides) wherever mosquito habitat removal is not feasible or possible are effective and essential parts of integrated mosquito management program. However, any larvicidal chemicals used for standing water treatment must comply with state and federal requirements and should be applied only by licensed and certified pesticide applicators and operators.
2. Eliminating adult mosquitos through use of insecticides, usually applied from the ground (fogging) or aerially. As with larvicidal chemicals, adult mosquito insecticides must comply with state and federal requirements and should be applied only by licensed and certified pesticide applicators and operators.
3. Considering mosquito control in design, construction, and maintenance of any storm water retention structures and drainage systems, and any outdoor container structures.
4. Protecting building inhabitants from mosquito exposure through repairing or installing door and window screens.
5. Educating and encouraging use of personal protective measures, such as consistent use of DEET-based skin and Permethrin-based clothing insect repellents (For current recommendations, see www.cdc.gov/ncidod/dvbid/westnile/qa/insect_repellent.htm and awareness of prime mosquito-biting hours (from dusk till dawn).
6. Mobilizing communities to adopt and participate in comprehensive mosquito control and WNV prevention programs. To be effective, such programs require participation of civic, business, health, and environmental organizations as well as private citizens and should include both educational activities and community-wide interventions, such as clean-up days to get rid of mosquito breeding sites.
The IAFF Division of Occupational Health, Safety and Medicine will continue to monitor this outbreak. However, the most up-to-date information on WNV is provided by the CDC on their WNV website.
The CDC website offers up-to-date surveillance data and outbreak maps. It also provides common sense tips and fact sheets for reducing exposure, including elimination of standing water, which acts as mosquito breeding sites, and ways to avoid mosquito bites. The CDC has also established guidelines for the surveillance, prevention and control of this virus.