A Nasty Parasite
Charles Lavern, a French army surgeon in Algeria in 1880, first described malaria parasites in the red blood cells of humans. Several years later, Sir Ronald Ross observed developing parasites in the intestines of mosquitoes and provided the first major evidence that mosquitoes were acting as vectors, or vehicles, to spread disease. Ross succeeded in demonstrating the life cycle of the parasites of malaria in mosquitoes.
Human malaria is caused by four main species of the Plasmodium parasite:
A vector is a vehicle for moving a disease-causing organism from one host to another. Mosquitoes were vectors for malaria by helping to spread it from human to human.
A disease is endemic when it is constantly present in a community or among a group of people.
Malaria kills one child every 30 seconds. A total of 800,000 children under the age of five die from malaria every year, making this disease one of the major causes of infant and juvenile mortality. The disease is also responsible for a substantial number of miscarriages and low-birth-weight babies.
Transmission: Mosquito Marauder and a Deadly Cycle
Malaria parasites are transmitted by the female anopheles mosquito. There are about 380 species of this type of mosquito, but only about 60 species can transmit disease. The parasites can only live within female mosquitoes and can be transferred only to humans. The parasites have a complex life cycle that is split between the human host and the mosquito vector. The process of malaria transmission occurs this way:
A sporozoite is a slender, spindle-shaped organism that is the infective stage of the malaria parasite. It is the result of the sexual reproductive cycle of the parasite, which occurs inside the mosquito.
Malaria is not common in the United States, but people who travel to parts of the world where it is endemic need to protect themselves by taking antimalarial medication and trying to avoid mosquito bites by using repellent, netting, and so on.
The parasites must spend about two weeks in the mosquito to undergo further life cycle changes before they can infect humans again. When the mosquito feeds on another human, the parasites are injected into a new host. This mosquito can transmit the infection only if she sucks more blood from an uninfected person before she dies.
Excerpted from The Complete Idiot's Guide to Dangerous Diseases and Epidemics © 2002 by David Perlin, Ph.D., and Ann Cohen. All rights reserved including the right of reproduction in whole or in part in any form. Used by arrangement with Alpha Books, a member of Penguin Group (USA) Inc.