Spread of drug-resistant malaria parasites looms large

Anopheles Freeborni Mosquito - CDC

Photo: CDC

Anopheles mosquitoes that take multiple blood meals from different people who are infected with malaria or take multiple parasite strains from a person during a single blood meal can have grave consequences — they can end up accumulating more malaria infections. Also, mosquitoes that have already been infected with one malaria parasite strain become more likely to get infected with a new strain.

The presence of more than one strain in a mosquito at any given point has some undesired outcomes. For instance, the interactions between strains inside the mosquito are such that the very presence of an existing infection “enhances the replication” of malaria parasites. The survival of mosquitoes is not impacted despite the presence of more strains and enhanced replication leading to larger population of parasites.

Besides accumulating mixed strains when feeding on different people, the mosquitoes with such mixed strains will, in turn, increase the rates of mixed infections in humans. The insects can also take multiple parasite strains from a person during a single blood meal. After all, mixed strain infections in a person are the norm in places of high malaria transmission. Different parasite strains found in the same blood meal can “freely recombine” in the gut of the mosquito.

These have great “implications for the evolution of parasite virulence and the spread of drug-resistant strains,” writes Laura C. Pollitt, the first author of a paper published recently in the journal PLOS Pathogens . Dr. Pollitt is from the Centre for Immunity, Infection and Evolution, University of Edinburgh, U.K.

Seen in context, mosquitoes taking multiple blood meals from different people or multiple parasite strains from a person during a single blood meal may end up “disproportionately” contributing to malaria transmission.

Female Anopheles mosquitoes were kept in cages and allowed to feed on mice infected with two different Plasmodium strains at predetermined times.

The experiment allowed the researchers to evaluate how the presence of a strain affected the parasites that were brought in later via another blood meal. They also examined the survival of the mosquitoes when both the strains were present at the same time.

Published in The Hindu on August 10, 2015

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