Scientists have discovered that transmission of the malaria
parasite via the mosquito regulates its ability to cause disease
and therefore affects the severity of the
illness.
This is because parasite gene expression changes during
transmission through mosquitoes, which changes the type of immune
response generated in a mammal host. This, in turn, reduces
parasite growth and associated disease.
The team also identified parasite genes that may play a role in
inducing an effective immune response, and therefore controlling
the malaria parasite. By identifying these potential targets of
effective anti-malaria immunity, the findings could help drive the
development of an effective vaccine.
The work was led by Jean Langhorne of the MRC's National
Institute for Medical Research (now part of the Francis Crick
Institute) and carried out in collaboration with the
Wellcome Trust Sanger Institute in
Cambridge.
Malaria is caused by five species of protozoan parasites called
Plasmodium. These parasites are spread to people through the bites
of infected mosquitoes.
Laboratory studies to investigate the malaria parasite in the
blood are usually done by injecting Plasmodium-infected blood
directly into mice. However, for this study the researchers
developed an efficient method to transmit the parasites through
mosquitoes, by infecting mice via mosquito bites - mirroring the
normal way people are infected in real-life.
Dr Langhorne explained: "Our study shows that the complex
interaction between the parasite and the mosquito vector determines
the severity of disease caused by the malaria
parasite.
"These findings will influence the ways in which experimental
malaria research is performed, and therefore the outcomes of
immunity and pathogenesis studies, and shift our focus towards
understanding the role of the mosquito vector and the natural route
of transmission in the pathogenesis of
malaria.
"This opens up exciting new avenues of research that could help
identify protective immune mechanisms and their targets and thus
advance the development of an effective anti-malaria vaccine. This
work therefore has enormous implications for our long-term goal of
malaria control and eradication."
The paper, Vector transmission
regulates immune control of Plasmodium virulence, by Philip
Spence, William Jarra, Prisca Lévy, Adam Reid, Lia Chappell,
Thibaut Brugat, Mandy Sanders, Matthew Berriman and Jean Langhorne,
is published in Nature.