Malaria: Coming soon to an airport near

you!

Tropical Diseases in the Global Village

You too can get tropical diseases without leaving the comfort of your own home.

• What accounts for the geographic restriction of some diseases?

• How do diseases move into new areas?

• Are tropical diseases really diseases of economic underdevelopment?

Malaria has been with us for a long time

now

10,000

BC

mummies

DNA evidence

The A- African variant of G-6-PD may date as far back as 11,760 years ago

When did malaria come to the New World?

• with Columbus or the slave trade– no documented blood polymorphisms

associated with malaria resistance in the Amerindians, so malaria is recent

– Ravenel’s extinction hypothesis: eradication of the original natives of the Caribbean islands and coastal plain was caused by malaria

Did malaria arrive twice?

• P. simium in New World monkeys looks like Asian P. vivax

• New World P. vivax is distinct from both– DNA– vector specificity

Conclusion:

• malaria entered the New World twice– once > stable transmission in

monkeys– once > stable transmission in man

How is transmission established?

mosquito

man

bite first host

bite second host

Factors that influence transmission

mosquito

man

bite first host

bite second host

susceptible vector species

Factors that influence transmission

mosquito

man

bite first host

bite second host

vector longevity

Factors that influence transmission

mosquito

man

bite first host

bite second host

biting preferences

Factors that influence transmission

mosquito

manbite first host

bite second host

infected reservoir

Factors that influence transmission

mosquito

manbite first host

bite second host

available to vector

Colonial America

• malaria was well established in Connecticut by 1650

• Charleston, SC, was almost abandoned in 1680 because of the intensity of malaria transmission

Eradication in the north

• 1900: Staten Island, NY, one in five residents has malaria

• 1901: Port Authority gives $50,000 to Alvah Doty to drain the marshes

• 1908: Staten Island is malaria-free

Malaria and the New Deal

• ecological degradation of major river basins in the South– deforestation– erosion– uncontrolled floods

• 1933: 150,000 cases of malaria, 5,000 deaths annually in Tennessee R. basin

TVA: Power and Public Health

• 21 dams, 600,000 acres of lakes• mosquito control teams

– periodically raise and lower water levels

– speed water flow in canals– clear aquatic vegetation

• 1942: 50,000 malaria cases annually, 600 deaths

DDT

• 1943: widescale aerial application• 1952: malaria eradicated• 1962: Silent Spring

Will malaria return?

• reappearance of infected hosts– immigrants from endemic regions– returning military personnel

• transmission from a single marine to 35 campers in the California Sierras

Will malaria return?

• introduction of new efficient vectors– 1930: Anopheles gambiae introduced

into Brazil by a French naval vessel; epidemic malaria, 16,000 deaths

– malaria vectors brought to Guam by military aircraft during WWII and Viet Nam war; outbreaks in 1966 and 1969

Airport Malaria: The case for disinsection

• between 1969 and 1999– 26 cases in France– 17 cases in Belgium– 14 cases in the UK– 4 cases in Germany– 4 cases in the US