Malaria-Blocking Microbe Discovered Living In Some African Mosquitoes

A high-magnification image shows the mouth of Anopheles mosquito, a key vector of the pathogen that causes malaria in humans. Photowind/Shutterstock

A microbe present in wild populations of Kenya’s Anopheles mosquito – a key vector of malaria – has been shown to block the transmission of malaria from insects to human, suggesting it may be a natural method to control the potentially fatal disease. The newly identified microbe, called Microsporidia MB, is among the first known to affect malaria transmission in mosquitoes.

Despite being preventable and curable, malaria kills more than 400,000 people each year and is particularly burdensome to the continent of Africa where more than 9-in-10 cases and deaths occur annually, according to the World Health Organization. The life-threatening disease is transmitted to people through bites of female Anopheles mosquitoes infected with Plasmodium parasites. The Centers for Disease Control and Prevention notes that infection can be difficult to recognize and lead to death if not treated within 24 hours of symptom onset.

Researchers at the International Centre of Insect Physiology and Ecology in Kenya and the University of Glasgow collected adult female mosquitoes from two sites in Kenya and conducted a series of experiments to determine the number of individuals carrying the microbe and whether it was passed on to their offspring. Mosquitos with the microbe did not harbor malaria parasites in nature or in experimental infections in the lab, according to findings published in Nature Communications.
 
Furthermore, Microsporidia MB was shown to block transmission without appearing to harm its host in what researchers note is a symbiotic relationship, meaning the two organisms live together without causing the other obvious harm. Broader dissemination of the microbe into wild mosquito populations may limit the capacity of the disease to spread, which could become a “novel vector management strategy” as more of the insects eventually carry the symbiont.  
 
The newly identified Microsporidia MB is among the first known microbes shown to affect malaria transmission in mosquitoes. University of Glasgow

"The bodies of animals are inhabited by microbes which are either detrimental or have neutral or beneficial symbionts,” said study author Dr Jeremy Herren in a statement

"Healthy insects often have microbial symbionts inside their bodies and cells. These symbionts can have major effects on the biology of their hosts, and our team is trying to learn more about this type of microbe in insects that are important to human health."

In Kenya, the rainy season lasts from April to June with periods of short rains between November and December, providing laying grounds for female mosquitoes to deposit their eggs in standing water. Similarly, the prevalence of the microbe was also seen to increase after rains. Wild-caught females were also made to induce egg-laying to determine whether the microbe could be transmitted to their offspring, further suggesting the microbe can be passed from a female to her offspring at high rates without killing or harming the host.

“We are already using a transmission-blocking symbiont called Wolbachia to control dengue, a virus transmitted by mosquitoes,” said study co-author Steven Sinkins, from the MRC-University of Glasgow Centre for Virus Research. “The Microsporidia MB symbiont has some similar characteristics, making it an attractive prospect for developing comparable approaches for malaria control.”

Researchers note that further studies are needed to determine how the microbe may be used to control malaria, particularly in larger mosquito populations. Such results will provide information to determine how researchers might “disseminate Microsporidia MB for malaria control.”  

Weekly precipitation values given are shown in dark blue while light blue bars indicate the prevalence of observed Microsporidia MB. Overall, between 6 and 8 percent of female mosquitoes were found to be infected with Microsporidia MB at two sites in Kenya. Nature Communications

 

 

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