The Shelby County Health Department has warned of what could be the longest West Nile virus season on record. Mosquitoes in zip codes 38109, 38122, 38134, and 38135 have already tested positive for the disease.
So, should we steel ourselves for a pandemic?
Probably not, according to Dan Sprenger, manager of vector control for Memphis and Shelby County.
"We've had West Nile virus every year since its introduction in 2002," Sprenger said. "We average about five to 15 human cases each year, and usually there are one or two deaths a season — generally people of more advanced age. In the scope of things, driving a car is certainly more risky than getting West Nile virus."
Birds are most affected by the disease; human and pet populations are less susceptible.
Still, vector control is anticipating a higher number of cases because of the longer spring and summer seasons. Without the efforts of vector control, Sprenger says mosquitoes and mosquito-borne illnesses could be a lot worse.
"Part of what we're trying to do is abate and inform," Sprenger said. "If we didn't, [West Nile] would hit people blindside."
West Nile virus first appeared in the New York City area in 2001 and spread across the country and North America. In some cities — Memphis is one — the virus comes back every year.
Vector control handles this yearly recurrence through meticulous surveillance. Collecting mosquitoes at 163 operational sectors throughout Shelby County, vector control sends the sample mosquitoes to the state for testing.
The state looks for cases of both West Nile virus and a similar disease, the St. Louis encephalitis virus. Both are transmitted by house mosquitoes, however, St. Louis encephalitis is a bit more virulent than West Nile. Memphis hasn't seen a case of it in over 20 years. West Nile, on the other hand, has been diagnosed in about 40 Shelby County patients since 2002.
Since the West Nile virus first appeared, vector control has moved away from simple pest control to a more advanced approach to controlling both pest mosquitoes and disease-carrying mosquitoes. A funding change helped facilitate this shift: In 2005, the source of funding for vector control switched from the Shelby County general fund to a fee tacked onto Shelby County residents' utility bills. This consistent source of funding has helped fund a larger-scale surveillance of arthropod-borne diseases — an addition to the insecticide spraying routine already in place. According to Sprenger, this represents a more unified approach to the mosquito problem in Shelby County.
All the same, Sprenger says that vector control can only do so much to stop mosquito infestation and disease. Residents are equally responsible for keeping the mosquito population under control.
"When we find out the zip codes in which we've found the disease, it's a small portion of that zip code that actually has it in their area, but it's an easy way to communicate with the public," Sprenger said. "Passing on information empowers people to change their behavior."
Residents must be vigilant about wearing DEET insect repellant and staying indoors during peak mosquito time (around sunset). Residents should get rid of any standing water in which mosquitoes might lay their eggs. Birdbaths should be refreshed frequently as well as pet water bowls. Sprenger also notes that standing water can collect in unlikely places, like rubber tires, which he considers one of the worst offenders for creating mosquito habitats.