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NEWS | July 14, 2014

The ongoing battle of the bite

By Petty Officer 2nd Class Wilson Araujo Naval Health Clinic Charleston

You may have seen the Air Force Reserve C-130 Hercules spraying for mosquitos last month. But what you probably don't know is Naval Health Clinic Charleston preventive medicine technicians are helping our Air Force teammates take the bite out of the Joint Base Charleston mosquito population.

"NHCC Preventive Medicine is in charge of surveillance; the Air force is in charge of doing testing and aerial sprays when needed," said Lt. Jessica Newman, NHCC Preventive Medicine department head.

Due to surrounding vegetation and swamp lands, the Weapons Station is susceptible to higher populations of mosquitos, according to Newman. NHCC preventative medicine technicians provide surveillance for five areas throughout the Weapons Station, setting up CDC light traps that lure and capture mosquitos so they can be counted, deciphered according to species and sex, and sent to labs to be tested.

During summer months, the preventive medicine technicians set and retrieve traps twice a week. They set the traps an hour prior to sunset when mosquitos are most active. A combination of carbon dioxide and light draws mosquitos from up to 35 meters away to the traps, where an impellor fan suctions the mosquitos into a net. The preventive medicine technicians collect the traps the following morning and place the mosquitos in a freezer overnight. The next day, the mosquitos are counted to establish a population baseline which helps determine what type of preventive measures are needed.

"Traditionally, at the beginning of summer, mosquito counts will be low," said Petty Officer 2nd Class Darius Davis, NHCC preventive technician. "As the climate gets warmer we tend to see a steady climb. Depending on the month of trapping, one trap can collect from 100 to 1,000 thousand mosquitos per single trap."

After the mosquitos are counted, the preventive medicine technicians determine the sex of the mosquitos. Males are easier to identify because they have hairy antennas, or mustaches, but female mosquitos are the sex to fear, added Davis.

"Only female mosquitos bite; they use the blood to nourish their eggs," said Davis. "The prevalence of female mosquitos could mean the population is going to multiply at a substantial rate."

The mosquitos are then placed in petri dishes, sealed in an envelope and mailed to an Air Force Entomologist at Wright-Patterson Air Force Base, who identifies the mosquitos' species in terms of disease risk which helps determine the prevalence of mosquito diseases in an area.

According to the South Carolina Department of Health and Environmental Control website, there are at least 61 different species of mosquitos in South Carolina. The most common existing or potential mosquito-borne viruses and parasites in South Carolina include West Nile virus, eastern equine encephalitis virus, La Crosse encephalitis and other California sero-group viruses, Saint Louis encephalitis virus, and dog/cat heartworm.

"Contracting any of these diseases from a mosquito is rare," said Petty Officer 2nd Class David Oba. "But because it is possible, we need measures to monitor and control the mosquito population."

So how can the average person test to see how many mosquitos they have if they don't have a trap?

"A good way to get an idea of the mosquito population in a given area is to expose your skin," said Oba. "Female mosquitoes may detect the carbon dioxide or body scent your body produces. During one of our surveillances, I rolled up my sleeve and exposed my skin for less than a minute. Within 30 seconds my arm was full of female mosquitoes trying to feed on my blood."

More than 350 compounds have been isolated from odors produced by human skins, said Oba. Many of these compounds may be attractants or many may be repellents.
"There are many ways you can repel mosquitos from your house and from your skin," said Oba. "Mosquitos are most active during the dawn and dusk, so if possible, schedule outside activities to avoid those times. Dress in light, loose-fitting clothing. If you have a deck, light it using yellow bug lights. These lights do not repel, but they do not attract mosquitoes like incandescent lights. Mosquitoes are weak fliers, so a fan can provide a low-tech solution. Citronella candles also have a mild repellent effect."

Mosquitoes need water to breed," said Oba. "If you have areas around your yard holding water, you may be breeding mosquitoes."

Female mosquitoes deposit their eggs directly on the surface of stagnant water in places such as discarded tires, ornamental pools, unused wading and swimming pools, tin cans, bird baths, plant saucers and even gutters and flat roofs. The eggs deposited on water hatch into larvae and in the hot summer months grow rapidly, become pupae, and then in four to seven days become flying adult mosquitoes.

"And the myth that a mosquito dies once it bites you is just that - a myth," said Oba. "A mosquito does not die once it bites you. How long it takes a mosquito to die after it bites you depends on the age of the mosquito."

Mosquitoes usually have an adult life span that lasts about two weeks, but some mosquito species live for as long as two months to a year.