Malaria parasites found in mosquitoes around Washington, DC, infecting at least 2 people

Every year, over a thousand people in the United States fall ill with malaria. In 2005, 1,528 cases were reported to the Centers for Disease Control. (In most places in the world, only about 1 in 10 cases of malaria are reported to health authorities. That ratio is probably different in the United States, but there probably still is significant underreporting, so we can safely assume there’s more malaria in the United States than this data would suggest.)

Most of these malaria cases are in people who have been infected elsewhere. The pheomenon is thus called “imported malaria.” But while these imported cases toss and turn on their beds, the Anopheles mosquitoes that still thrive across the country can and do pick up their parasites, which they then can spread to others, re-igniting local transmission.

In 2002, two teenagers from Loudon County, Virginia came down with vivax malaria. The teenagers lived about half a mile away from each other, and one visited the neighbors of the other, so it is conceivable that the same infected mosquito bit both people. In response, public health officials sprayed pesticides over the area.

But where were the infected mosquitoes? They were found not just in Loudoun County, but also 30 miles away in Fairfax County and 70 miles away in Montgomery, Maryland. The three outbreaks of parasitized mosquitoes form a triangular vise around Washington, DC. Clearly, sufficient numbers of people are importing malaria into the area to infect a range of mosquitoes. Whether the insects infected others besides the two reported cases remains unclear.

For more

LL Rovert et al, “Plasmodium-infected Anopheles mosquitoes collected in Virginia and Maryland following local transmission of Plasmodium vivax malaria in Loudoun County, Virginia