Malaria and toxic bacteria

Mosquitoes might be infected with all sorts of pathogens, such as viruses and bacteria. When you get stung at night, the mosquito will inject a tiny amount of their saliva, which contains a specialized, potent cocktail of molecules that numb the pain of the bite and stop the blood from clotting. But, together with that saliva, the pathogens also enter your bloodstream.

Still, some bacteria seem to have a detrimental effect on the mosquito itself.

Scientists noticed that some laboratory colonies of mosquitoes were incapable of transmitting malaria parasites[1]. These insects also harboured a few cells of a bacterium called Delftia tsuruhatensis TC1, which produces a toxic alkaloid called harmane. Bacteria-produced harmane inhibited the development of female Plasmodium falciparum parasite gametes in the mosquito gut.

Harmane was found to be a contact poison that could also cross the mosquito cuticle to kill developing malaria parasites. The data suggests that the bacteria can reduce a mosquito's parasite load by up to 73%.

Contained field trials in Burkina Faso, coupled with modeling studies, showed that the bacterium has the potential to be deployed in mosquito breeding sites as a component of malaria control.

Harmane is a heterocyclic amine found in a variety of foods, including coffee[2]. Harmane is also present in tobacco smoke[3].

[1] Huang et al: Delftia tsuruhatensis TC1 symbiont suppresses malaria transmission by anopheline mosquitoes in Science – 2023
[2] Herraiz, Chaparro: Human monoamine oxidase enzyme inhibition by coffee and β-carbolines norharman and harman isolated from coffee in Life Sciences - 2006
[3] Herraiz, Chaparro: Human monoamine oxidase is inhibited by tobacco smoke: beta-carboline alkaloids act as potent and reversible inhibitors in Biochemical and Biophysical Research Communications - 2005