Background

Mosquitoes and West Nile Virus:

West Nile Virus (WNV) is a mosquito-borne flavivirus that was original from Africa, Europe and the Middle East. In 1999 WNV was first detected in the US in an outbreak in New York City. After its emergence, WNV spread all over the US causing epidemics in several urban centers.

The first human case of West Nile Virus in the state of Georgia was reported in 2001. Mosquitoes serve as vectors of the disease by biting and infecting birds and, occasionally, humans. Birds are amplifying hosts, which help the disease reproduce and pass on to other mosquitoes, which then can infect other birds or humans. 

All mosquitoes must have water in which to complete their life cycle.  They lay their eggs in places such as tree holes (that periodically hold water), tide water pools in salt marshes, sewage effluent ponds, irrigated pastures, rain water ponds, etc. Each species therefore has unique environmental requirements for the maintenance of its life cycle. The feeding habits of adult mosquitoes are quite unique in that it is only the adult females that bite man and other animals. The male mosquitoes feed only on plant juices. Over 60 species of mosquitoes have tested positive for WNV, but the most common in the Atlanta area is Culex quinquefasciatus.

Combined Sewer Overflow (CSO):

Many urban areas have combined sewer systems, in which wastewater and domestic sewage are treated together.  During normal conditions minimally treated wastewater and storm water are mixed and piped together to a treatment facility.  However, after heavy precipitation, large volumes of wastewater exceed the maximum capacity of the sewer systems and are expelled into nearby natural streams with only minimal treatment. 

The large amounts of storm water mixed with untreated sewage water constitute a major source of pathogens, solids, debris, and toxic pollutants to receiving water and represent a significant public health and environmental concern for the affected populations.

The Atlanta area contains seven CSO facilities, many of which are located in residential areas with high population densities.  The overflows potentially in these areas flood streams with high levels of nutrients and provide ideal breeding habitats for certain mosquito species.

West Nile Virus Transmission Cycle

Mosquito Life Cycle

CSO overflow into Tanyard Creek (Atlanta, Ga.)

Site Developed by Greg Decker.