A fungus that compromises the immune system of mosquitoes makes them more susceptible to spreading malaria, say researchers.
Because environmental microorganisms like fungi vary greatly from region to region, the findings may help explain why malaria is a bigger problem in some areas than others. For example, sub-Saharan Africa in 2015 was the site of 89 percent of malaria cases and 91 percent of malaria deaths.
Microbes that block the Anopheles mosquito from being infected by the parasite that causes malaria have been identified in the past, but this is the first time researchers have found a microorganism that instead appears to make the mosquito more likely to become infected with—and then spread—the disease.
“This very common, naturally occurring fungus may have a significant impact on malaria transmission: It doesn’t kill the mosquitoes, it doesn’t make them sick, it just makes them more likely to become infected and thereby to spread the disease,” says study leader George Dimopoulos, deputy director of the Johns Hopkins Malaria Research Institute.
“While this fungus is unlikely to be helpful as part of a malaria control strategy, our finding significantly advances our knowledge of the different factors that influence the transmission of malaria.”
Malaria is caused when Anopheles mosquitoes are infected with the Plasmodium parasite and go on to bite and infect healthy humans. Mosquitoes become infected when they bite and feed on the blood of humans infected with the parasite, and the cycle continues.
According to the World Health Organization, there were roughly 214 million malaria cases and about 438,000 malaria deaths around the world in 2015.
For the study in Scientific Reports, researchers isolated the Penicillium chrysogenum fungus—a member of the same family of fungi that gives us the antibiotic penicillin—from the gut of field-caught Anopheles mosquitoes and discovered the fungus compromised the mosquito immune system, allowing the malaria parasite to more easily infect them.
Researchers had hoped Penicillium chrysogenum would act like several bacteria that have been identified that actually block mosquitoes from becoming infected with the malaria parasite. Even though this fungus actually appears to worsen infections, it can still help researchers in their fight against malaria.
“We have questions we hope this finding will help us to answer, including why do we have increased transmission of malaria in some areas and not others when the presence of mosquitoes is the same?” Dimopoulos says. “This gives us another piece of the complicated malaria puzzle.”
Research in the field is necessary to see if the fungi affect mosquitoes in nature the same way they do in the laboratory.
There is as yet no effective malaria vaccine. Other strategies have focused on preventing mosquito bites, spraying insecticides to control the number of mosquitoes, and developing genetically modified mosquitoes immune from the malaria parasite.
The National Institute of Allergy and Infectious Disease, the Johns Hopkins Malaria Research Institute, and a UNCF-Merck Science Initiative Graduate Research Fellowship funded the work.