Vectors, Viruses and Victims
From American Scientist:
Mosquitoes live brief but busy lives feeding on nectar and plant sugars. The females must also find human or animal blood to feast on in order to produce eggs and continue the life cycle, so they live rather longer than the males—several weeks rather than several days. Frail though individual mosquitoes appear, historically they have shown an impressive propensity to travel. Sometimes they have been stowaways on ships traveling to other continents, carried aboard in water casks and drinking vessels. On arrival in new lands they have exploited the ecological changes—deforestation, canal building, rice cultivation, urban water storage and deficient drainage—brought about by their obliging human hosts. Despite occasional suspicions that mosquitoes were up to no good, most human observers before 1900 were remarkably unaware of the insects’ true role. They were inclined to regard mosquitoes as a nuisance—often a prodigious one—rather than the death-dealing menace they actually were. The creatures’ frailty belied their fatality.
As accomplished environmental historian J. R. McNeill brilliantly demonstrates in Mosquito Empires, for nearly 400 years the human history of the Americas, from the northern shores and interior plains of South America through the islands of the Caribbean to the southeastern corner of the present-day United States, was governed by the activities of “imperial mosquitoes”—both the Anopheles species that were the vector for malaria and more especially Aedes aegypti, which harbored lethal yellow fever virus. His central argument is that when Europeans first established themselves in the Americas in the 16th century, they had an epidemiological advantage in that the diseases they brought with them (such as smallpox, measles, mumps and whooping cough) caused devastation among indigenous populations. But in the 17th century, migrant mosquitoes such as Aedes aegypti were introduced to the Americas, largely through the mechanism of the transatlantic slave and sugar trade, with ships serving as “super-vectors, efficiently moving both mosquito and virus from port to port.” Once new diseases such as yellow fever made the crossing from West Africa, transported by mosquitoes or traveling in the blood of their victims, then the disease ecology of the Americas was profoundly transformed. Major demographic and environmental changes were also taking place—hundreds of thousands of slaves were imported, and forests were cut down for fuelwood used to boil sugar. The once benign Caribbean became a “giant sinkhole” of suffering humanity.