There may be a new combatant in the fight against malaria. Scientists from Johns Hopkins University Bloomberg School of Public Health and Malaria Research Institute have discovered a symbiotic bacteria living in the midgut of some mosquitos that inhibits the growth of the malaria parasite. In tests, the Enterobacter bacterium strain known as Esp. Z was shown to have the ability to kill 99% of the malaria causing parasites.
The world health implications of this discovery are huge. Malaria kills nearly 800,000 people a year. In 2008, there were 247 million cases of malaria and nearly one million deaths – mostly among children living in Africa. In Africa a child dies every 45 seconds of Malaria where the disease accounts for 20% of all childhood deaths.
The human malaria parasite Plasmodium falciparum enters the mosquito when it feeds off an infected human. In the mosquito’s midgut the parasite encounters many obstacles to its development including human blood-derived factors, the mosquitos’ own innate immune responses, and resident microbiota. Although most of the parasites are killed in the mosquito it only takes the survival of a small number to continue the cycle of transmission back to humans.
Dr. George Dimopoulos and his colleagues conducted their research using bacteria isolated from Anopheles arabiensis populations of wild mosquitoes collected in southern Zambia. They discovered that the way that the Plasmodium parasite is destroyed by the Esp. Z bacteria is a rather roundabout mechanism that may lead to longstanding and effective preventative measures against the disease. The Esp. Z bacteria does not directly attack the malaria parasite. Because of this it does not produce an immune response from the parasite and therefore is left alone to continue its deadly (to the parasite) and beneficial (to humans) work. The researchers found the secret to its effectiveness in a byproduct produced by the microbe during its replication. Reactive oxygen species (known as free radicals) produced by the Esp. Z bacteria were discovered to inhibit the development of the Plasmodium parasite. Dependant on the concentration of the Esp. Z present, up to 99% of the parasites failed to mature in the mosquito’s midgut. To verify that these free radicals were indeed the cause of the death of the parasites, antioxidants were supplemented with the bacteria in cultures. In cultures where vitamin C was added the parasites continued normal development even in the presence of reactive oxygen species producing Esp. Z.. And again in cultures where another potent antioxidant, reduced glutathione, was added with the Esp. Z, development occured on a normal basis. In cultures where Esp. Z was absent the addition of vitamin C had no affect on the parasite numbers, indicating that the the free radicals were causing the death of the parasite.
Although this study was conducted with Esp. Z isolated from a single collection of mosquitoes in Zambia made during one rainy season, 25% of the insects collected harbored the strain. The results may have long reaching effects. The question begs, “Might it be possible to increase the populations of Esp_Z or other naturally inhibitory bacteria by manipulating the makeup of the midgut microbial flora in wild mosquitoes as a way to control malaria worldwide by stopping the disease before it starts?”