Mosquitoes More Than Just a Pest in Other Countries, Too

Sept 13, 2001 

By Jane Brody
The New York Times

New York - In the US, it is the height of summer, and the mosquito is out and about, determined to spoil everyone's good time. 

But for millions of people, including thousands in that country each year, the mosquito is far more than a pest. For them this insect a few millimeters long and weighing a tiny fraction of a gram carries serious disease and sometimes death. 

Mosquitoes and the malaria they carry may even be the leading impediment to economic growth in the developing world. And, medical science is learning, mosquitoes are full of surprises. 

Two years ago, New Yorkers learned what Dr Andrew Spielman calls the first law of mosquitoes: expect the unexpected. 

Until August 1999, most city residents found mosquitoes just occasional summertime pests, to be endured perhaps at an evening concert in Central Park. Then came the news that, somehow or other, a native mosquito, Culex pipiens, the so-called common house mosquito that hangs out in storm sewers and sump pumps but rarely bites people, had acquired an exotic virus that could cause a fatal brain infection, West Nile encephalitis. The virus, named for its discovery in 1937 in the blood of a feverish woman in the West Nile district of Uganda, had never before been seen on this side of the Atlantic. 

'There are other viruses out there Rift Valley fever virus, Japanese B encephalitis virus, among them that could be imported,' Spielman said. 

The 2,500 known species of mosquitoes (150 of them in the US) cover the gamut of ecological niches and bite at all times of the day and night. Some, like Aedes aegypti, a transmitter of deadly dengue fever in Puerto Rico, reside in or near people's homes, making mass eradication by community wide spraying a virtual impossibility. Aedes mcintoshi, a vector of Rift Valley fever virus, which has caused huge outbreaks in the Middle East, can survive in its egg stage for decades in a desiccated desert, hatching when it rains. 

C pipiens, the mosquito that is host to West Nile in New York, seeks its blood meal in the evening. Spielman said, 'It is the mosquito in built-up areas, but it rarely bites people. 'He has encountered it covering the walls of an African hut like a living carpet, as well as in ParisŐs subway, the Ginza shopping district of Tokyo and Confucius' graveyard in China. 

But West Nile is far from the worst mosquito-borne infection now in this hemisphere. Dengue fever, relatively unknown in the West until the 1970s, when an epidemic swept through Cuba and other Caribbean countries, produces a spectrum of symptoms, the worst of which is fatal hemorrhagic fever. Aedes aegypti, a daytime biter that prefers human blood, is the principal vector of yellow fever as well as dengue. Dengue is primarily a disease of the tropics, though it threatens to invade the Southern US.