BOX 2-3 Environmental Eyesore or Mosquito Nursery?
Both! Discarded tires are an eyesore to most, but to some mosquitoes they offer an ideal location to deposit their eggs. Aedes aegypti and Ae. albopictus, both vectors of diseases such as dengue fever, viral encephalitis, and yellow fever, prefer to lay their eggs in water that collects in containers. Discarded tires, which hold water no matter in what position they land and which do not typically harbor predators like fish or frogs, are perfect incubators for the eggs of these mosquitoes. And each year, the United States throws away a quarter of a billion tires and imports several million (mostly from Japan) to be retreaded and resold.
Not only do the mosquitoes find homes in discarded tires, but they also find transportation. When old tires are transported around the country by truck, mosquito eggs often go with them. Eggs then hatch hundreds of miles from where they were laid, and populations of adult mosquitoes can establish themselves in areas they might never have reached. Ae. albopictus actually "hitchhiked" to the United States in 1985 from Japan in a shipment of used tires. Already, this species has established itself as a resident.
Tires are not the only human-made accommodations favored by mosquitoes. Any container that holds water—an empty beer or soda can, a bucket, or flowerpot—that is left outside during the warm spring and summer months is an attractive egg-laying site for a female mosquito. Some mosquitoes will even breed indoors in a moist container in a basement, garage, or shed if given the opportunity. This is in part why aerial spraying of pesticides is not an effective way to control mosquitoes; the insects usually lurk (and lay their eggs) in damp hiding places that the chemicals cannot reach.
Thus, as innocuous as they may seem to many, discarded items like old tires and empty aluminum cans may play a role in the initiation and spread of mosquito-borne disease. Eliminating human-made breeding sites is a simple, logical way to reduce the chances of such disease.
by the dengue virus's four serotypes. Scientists do not expect that a vaccine will be available in the next 5 to 10 years.
Immunosuppression, a weakening of the immune system, can be caused by a number of factors, including the following: