Bug-free Bugs

Taming mosquitoes with bacteria
Mosquitoes are arguably the most dangerous animals on earth. Mosquito-borne pathogens cause many diseases, including malaria, dengue fever, and yellow fever. They transmit disease to […]

Art by Anna Pouncey

Mosquitoes are arguably the most dangerous animals on earth. Mosquito-borne pathogens cause many diseases, including malaria, dengue fever, and yellow fever. They transmit disease to more than 700 million people annually, killing millions. Malaria alone kills 780,000 every year, more than 2% of deaths worldwide. However, a novel technique is currently being researched which does not aim to eradicate the mosquitoes, but rather render them harmless.

To achieve this, scientists propose to prevent pathogens from infecting mosquitoes using a harmless bacterium called Wolbachia. When fed blood infected with dengue virus, mosquitoes artificially infected with Wolbachia had no detectable virus particles except when given an artificially high dose. Additionally, when given Chikungunya (a virus which causes similar symptoms to dengue fever) infected blood, only 12% of Wolbachia infected mosquitoes had detectable virus particles after four days, compared to 75% for uninfected mosquitoes. There is also evidence of Plasmodium (malaria) inhibition by Wolbachia.

The mechanism of action for this reduced pathogen load is currently the subject of research. Two possibilities have been identified that, combined, are believed to suppress the pathogens. First, Wolbachia is known to initiate the innate immune system of the mosquito, allowing the immune system to attack other invaders. Second, Wolbachia may compete for scarce resources with the pathogens, preventing pathogens from replicating inside the mosquito.

Unlike most bacteria Wolbachia live inside the mosquitoes’ cells and are inherited from mother to offspring rather than being transmitted horizontally between individuals. Wolbachia also have evolved the ability to spread into a population by manipulating the hosts’ reproduction: infected male mosquitoes cannot reproduce with uninfected females, giving infected females an advantage. As a testament to their spreading ability, Wolbachia naturally infect over half of all insect species tested.

Could this natural biological control agent spell an end to mosquito borne disease? Upcoming field trials will hopefully mirror the laboratory results and may finally provide us with an effective means of combating mosquito-borne pathogens.

About Marcus Blagrove

Marcus Blagrove is a DPhil student in Zoology at Green Templeton College.