Research has shown that after a mosquito bite, malaria parasites first travel to the liver, multiply, then escape and invade red blood cells. It was previously understood that parasites in both the liver and blood needed iron to grow.
Now, a new study by researchers at Instituto de Medicina Molecular in Lisbon, Portugal, in collaboration with researchers at the Weatherall Institute of Molecular Medicine and Oxford University shows that a second mosquito bite of an individual, already carrying blood parasites, does not lead to a full-blown second infection.
The pre-existing malaria prevents secondary infection by another Plasmodium strain, the parasite responsible for malaria, by restricting iron availability in the liver of the host.
This way, the superinfection is blocked in the liver by the first infection. This protective effect is due to the blood parasites causing the parasites in the liver to be starved of iron, so that they cannot grow.
In that respect, the results challenge the biological concept that infection of distinct host cells (liver hepatocytes or red blood cells) occur independently from each other, which may also have impact in the research area of infection (beyond malaria).
In this current study, the researchers focused at how malaria parasites developed in both the liver and in red blood cells and analysed patterns of infection in mice, looking in particular at cases of 'superinfection', in which an individual already infected with malaria is later bitten by a second infected mosquito. An individual in a high risk area can be bitten by hundreds of malaria-infected mosquitoes per year, making the issue of superinfection highly relevant.
The study reveals for the first time the crucial role of iron in the development of multiple malarial infections, which has strong implications for iron supplementation used to combat anaemia in malaria-endemic regions.
Silvia Portugal, first author of the study said: "I am very happy that we were able to find such an interesting interaction occurring between different malaria parasite stages in a single host, and that this might contribute for future control of malaria."
This study has been published in the journal Nature Medicine.