Biology of malaria parasites

(credit: EviMalar, Jamie Hall, Edward Ross, Wellcome Trust)

There are several hundred species of malaria parasite (Plasmodium spp) that infect mammals, birds and a wide variety of reptiles. 

We mostly use 4 species of rodent malaria parasite to test whether evolutionary and ecological theories can explain the extensive variation in the traits underlying the virulence and infectiousness of parasites.

Specifically, we study how parasites adjust traits during infections in response to changes to the in-host environment (e.g. development of anaemia, immune responses, infection genetic diversity, drugs) to maximise fitness. 

 Rodent Malaria

The rodent malarias were collected from Central Africa in the 1960s-1970s. Like all malaria parasites, they undergo several rounds of asexual replication in a vertebrate host and sexual reproduction in a dipteran vector (often mosquitoes).

Different types of parasite life-history stages accomplish these tasks; asexually replicating stages cannot survive when taken up by a vector and sexually reproducing stages only replicate in their vector.

When an infected vector bites a host, it injects infective stages that travel into the new host's tissues (the liver in mammals) and each parasite replicates asexually. After several rounds of replication, red blood cell invading forms are released into the circulation. These blood-stage parasites also replicate asexually and disease symptoms develop (anaemia, weight loss and cerebral malaria in some cases).

For every parasite replication cycle a small proportion of these asexually produced parasites develop into male or female sexual stages (gametocytes). When a vector takes an infected blood meal the gametocytes rapidly differentiate into gametes and fertilization occurs within 30-60 minutes.

The resulting zygotes undergo a series of morphological transformations to establish infections in the vector, resulting in the formation of thousands of parasites that migrate to the salivary glands ready for transmission to new hosts.