Malaria in the United States

• On average, 1,500 cases of malaria are reported every year in the United States, even though malaria has been eliminated from this country since the early 1950's.
• First- and second-generation immigrants from malaria-endemic countries returning to their "home" countries to visit friends and relatives tend not to use appropriate malaria prevention measures and thus are more likely to become infected with malaria. 
• Between 1957 and 2011, in the United States, 63 outbreaks of locally transmitted mosquito-borne malaria have occurred; in such outbreaks, local mosquitoes become infected by biting persons carrying malaria parasites (acquired in endemic areas) and then transmit malaria to local residents.
• Of the species of Anopheles mosquitoes found in the United States, the three species that were responsible for malaria transmission prior to elimination (Anopheles quadrimaculatus in the east, An. freeborni in the west, and An. albimanus in the Caribbean) are still widely prevalent; thus there is a constant risk that malaria could be reintroduced in the United States.
• During 1963-2011, 97 cases of transfusion-transmitted malaria were reported in the United States; approximately two thirds of these cases could have been prevented if the implicated donors had been deferred according to established guidelines.

Malaria Worldwide

• 3.3 billion people live in areas at risk of malaria transmission in 106 countries and territories.
• The World Health Organization estimates that in 2010 malaria caused 216 million clinical episodes, and 655,000 deaths.
• An estimated 91% of deaths in 2010 were in the African Region, followed by the South-East Asian Region (6%), and the Eastern Mediterranean Region (3%). About 86% of deaths globally were in children.

Biology, Pathology, Epidemiology

• Among the malaria species that infect humans, Plasmodium vivax and P. ovale can develop dormant liver stages that can reactivate after symptomless intervals of up to 2 (P. vivax) to 4 years (P. ovale).
• Pregnant women have increased susceptibility to Plasmodium falciparum malaria; in malaria-endemic countries, P. falciparum contributes to 8-14% of low birth weight, which in turn decreases the chance of a baby’s survival.
• After a single sporozoite (the parasite form inoculated by the female mosquito) of Plasmodium falciparum invades a liver cell, the parasite grows in 6 days and produces 30,000-40,000 daughter cells (merozoites), which are released into the blood when the liver cell ruptures. In the blood, after a single merozoite invades a red blood cell, the parasite grows in 48 hours and produces 8-24 daughter cells, which are released into the blood when the red blood cell ruptures.
• Under the microscope, Plasmodium knowlesi can resemble either P. falciparum or P. malariae.  Thus PCR is often required to confirm infection.

Other Facts

• Four Nobel prizes have been awarded for work associated with malaria: to Sir Ronald Ross (1902), Charles Louis Alphonse Laveran (1907), Julius Wagner-Jauregg (1927), and Paul Hermann Muller (1948).
• Two important currently used antimalarial drugs are derived from plants whose medicinal values had been noted for centuries: artemisinin from the Qinghao plant (Artemisia annua, China, 4th century) and quinine from the cinchona tree (South America, 17th century).