Malaria effects hundreds of millions of people worldwide and kills over two million people every year. It has even made an occasional appearance in North America due to introduction of new mosquito strains and travelers from malaria regions. Malaria is transmitted from an infected person to a non-infected person by the bites of the certain species of mosquito. The malarial gamete is sucked up from the infected person by the mosquito and carried in its gut until the mosquito bites an uninfected person. The bite injects the gamete into the blood stream where it travels to the kidney to mature. Neem can block the development of the gamete in the infected person. This not only prevents the infected person from developing malaria but also stops the disease from spreading.
Neem leaf extract substantially increases the state of oxidation in red blood cells, preventing normal development of the malaria plasmodia. An active ingredient in neem leaves, called Irodin A, is toxic to resistant strains of malaria, with 100 percent of the plasmodia dead in 72 hours with only a 1 : 20,000 ratio of active ingredients. In other experiments alcoholic extracts of neem leaf performed almost as well as the more refined compounds.
Two other compounds found in neem leaves called gedunin, a limonoid, and quercetin, a flavonoid, are at least as effective as quinine and chloroquine against malaria. Another molecule, gedunin, an extract of neem bark, has also been found to be effective in treating malaria.