The American Plague - Molly Caldwell Crosby [109]
In the United States, the cycle had taken a different turn. There were no cases of jungle yellow fever, no forest-dwelling monkeys giving refuge to the virus; it was not a yearly occurrence. Instead, there was only a series of urban epidemics when the virus exploded on a population.
The cycle would not be broken until the mosquito’s breeding places were destroyed. In Memphis and elsewhere, it happened through the invention of the sewer system and elimination of private cisterns and privies.
Massive campaigns against Aedes aegypti essentially wiped out the mosquito from Central and South America, and the U.S. government promised to do the same. In their book Mosquito, Andrew Spielman and Michael D’Antonio wrote that there was a sense of irony to the situation: “After all, America had gone to war with Spain, in part, because of the danger of yellow fever spreading from Cuba into nearby lands.” Now that Latin America had the same concerns about the United States, there was opposition to the idea. North Americans did not welcome the intrusion of government employees trampling through yards and hunting mosquito larvae. What’s more, the Environmental Protection Agency banned the use of DDT. As a result, Aedes aegypti never fully left the United States; if its presence today was not already known, it was brought to our attention with recent outbreaks of dengue in Texas.
Over time, mosquitoes have proven their evolutionary dexterity, adapting to insecticides and building a resistance. Once again, the striped house mosquito now flourishes in cities throughout South America, Central America and the southern United States. Its lyre-marked body and striped legs swarm around potted plants, gutters and rain-filled watering cans. A homebody, the domestic aegypti prefers human habitations, houses, boats and fresh water. But this was not always the case.
Hundreds of years ago, Aedes aegypti lived only in the jungles of Africa, where it hovered around tree trunks to lay its eggs in pools of rainwater. Its range was short; the mosquito preferred to stay in one general place, close to the trees. As man traveled into the interior of Africa, the mosquito made its evolutionary leap: It adapted to human life. Rather than tree trunks, it first sought water casks, then standing water around homes, and in modern times, oddly enough, it has adapted to tires. The dark interior and the water that clings to the inside of a tire mimic the hollows of a tree trunk. Scientists believe that the world’s mass of discarded tires in urban settings has recreated the atmosphere of those ancient jungles in Africa.
Aedes aegypti is not the only mosquito to have made the journey from tree holes to tires. The Asian tiger mosquito, Aedes albopictus, is relatively new to the United States. The tiger mosquito arrived in 1983 in a shipment of tires from Asia. The large, striped mosquito is very similar in appearance to its aegypti cousin, but true to its name, the tiger mosquito is a more voracious feeder. As a vector the tiger mosquito has been known to carry dengue, encephalitis and yellow fever in other countries. It has yet to transmit disease in the United States. The tiger mosquito, hardy and determined, has proliferated in North America, even crowding out some of its aegypti neighbors. Nature has a dark sense of humor though: The first Asian tiger mosquito on this continent was found hovering in Elmwood cemetery in Memphis, Tennessee.
In recent years, vaccine usage for yellow fever has fallen off. The problem is a lack of education and funds sufficient for the dissemination of the vaccine. Surveillance is also minimal. As a result, in the 1970s, outbreaks of yellow fever began once again, creating what is known as the “yellow fever belt” in Africa. The World Health