Putting the Bite on West Nile Virus

What Colorado’s Mosquito Control Districts are Doing to Ensure You Don’t Get Sick

According to the Centers for Disease Control, Colorado had more than 300 reported cases of West Nile Virus in 2013. Dr. Richard Nunamaker, a board member at Delta County Mosquito District No. 1, and a retired research entomologist who has spent most of his career studying insect-transmitted pathogens, considers it to be “a very serious threat in this state.” He points out that despite significant differences in population, “Colorado was second only to California in the total number of human cases of West Nile Virus.”

According to CDC statistics, almost all of Colorado’s cases occur between early July and late September. Last year August had the most activity with 125 reported cases. Teyler Hurst, District Manager at Alamosa Mosquito Control District, notes that the disease “fluctuates in intensity but never goes away. Studies are being done on the relation of winter temperatures and the intensity of West Nile Virus. What they are showing is that with warmer winters West Nile is more prevalent, and with harsher/colder winters West Nile is less prevalent. So with the 2013 winter being relatively warmer than normal, our 2014 West Nile Virus should be on the rise.”

West Nile Virus is predominantly transmitted to humans through mosquito bites. The virus normally cycles back and forth between mosquitoes and birds, but mosquitoes can also transmit it to humans, horses, and other animals. Fortunately, it does not develop with enough virulence in mammals to be transmittable back to mosquitoes the way it does with birds.

West Nile can also be transmitted through blood transfusions, though this is extremely rare. Despite that, a Colorado man died from West Nile Virus in 2012 after receiving a transfusion with infected blood.

According to the CDC, most infected people will not develop symptoms, while 20% will develop mild symptoms, such as fever, headache, body aches, nausea, vomiting, and swollen lymph nodes. Milder symptoms last a few days to several weeks, which resolve on their own without need for medical treatment.

Only 1 in every 150 people infected with West Nile will develop severe symptoms. These symptoms include high fever, headache, neck stiffness, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness, and paralysis. Severe symptoms usually last several weeks, but their neurological effects may be permanent. People with severe symptoms require medical attention which includes fluids and rest, though there is no specific treatment for West Nile Virus. Dr. Nunamaker reminds us that there are still a lot of questions regarding West Nile Virus, such as whether it may persist in the body’s central nervous system and whether infection may lead to an autoimmune disease.

The best advice is to simply avoid West Nile by exercising preventative measures during summer months. The CDC encourages the use of insect repellents containing DEET, picaridin, IR3535, and oil of lemon eucalyptus or para-menthane-diol. Some of the best protection can come simply from wearing long sleeves and pants while outdoors, especially from dusk to dawn, when mosquitoes are most active.

Districts should equip employees who work outdoors with adequate protective clothing and the proper mosquito repellents. Alamosa Mosquito Control District requires their staff to wear long sleeves, pants, and other appropriate personal protective equipment at work. This is a great example of an employer taking proactive steps to protect its team from transmission.

Who is at Highest Risk?

While everyone is at some risk, those who work outdoors have the highest risk. People over the age of 50 and anyone with a weakened immune system should take extra precautions against West Nile Virus. Anyone who believes that they have been infected or shows severe symptoms should seek medical attention.

Mosquito control districts are working hard this season to protect the community from the West Nile Virus. For example, Alamosa Mosquito Control District has a mosquito trapping network that is running constantly. The district catches mosquitoes and tests them for West Nile twice a week. If a mosquito tests positive for West Nile Virus, the district posts surveillance personnel to keep watch on areas within a 3 mile radius of the site. They deploy insecticides that target the mosquito both in larval and adult stages. The district can reduce the mosquito population of the affected area by 95% and prevent an outbreak of disease.

Delta County Mosquito Control District No. 1 also uses vector controls as a primary means of combating West Nile. The district pairs these efforts with communications to media outlets to inform the public of ways in which they can help to reduce mosquito populations.

What Else Can My District Do?

Make sure that your district’s buildings have screened windows and doors in order to keep out mosquitoes. Inspect screens for tears and repair or replace them immediately. You can reduce mosquito breeding sites by emptying standing water from flower pots, buckets, and barrels.

Park and Recreation districts can drill holes in playground equipment such as tire swings in order to let accumulated water drain out. These districts should also keep recreational items such as children’s wading pools empty when not in use. The Colorado Department of Public Health and Environment also encourages individuals, businesses, and districts to stock permanent ponds or fountains with fish that eat mosquito larvae and to avoid overwatering lawns or gardens to prevent the accumulation of standing water.

Finally, keep an eye out for dead birds. Birds can die from the West Nile Virus, and dead birds are a possible indication of an outbreak. Anyone who finds dead birds should not handle them with bare hands, and report them to a county health department or to the Colorado Department of Public Health and Environment. Based on your tip, they may conduct an investigation and take appropriate action.

The Colorado Department of Public Health and Environment as well as the Colorado Communicable Disease Epidemiology Program can be reached at 303-692-2700.

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