Understanding the role of coinfection in disease and infection control.

Coinfection, where two or more parasite species infect a host at the same time, is the norm in most human populations, particularly in developing countries. When parasites coinfect they often interact with one another, changing within host infection dynamics and between host transmission. This joint assault on the host, can also lead to changes in disease severity severe disease and alter the efficacy of anti-parasite treatment strategies. Despite how common and important coinfection is, we still know very little about how human parasites interact during coinfection. This PhD will determine the effects of coinfections, among three common and important human parasites, by following infections, health and treatment effects through time in very young children from Uganda.

Most coinfection studies are carried out in school aged children or adults, who will generally have had a substantial history of infections. Each of these past infections will prime the host immune response and alter host health, in different ways, masking or skewing the relationships observed during current coinfections and making it very difficult to determine the true effects of the parasite species upon one another. Very young children offer a better, and very understudied, cohort in which to examine coinfection because they lack a significant infection history. By following individual children through their early years, we will observe the order and severity of new infections, allowing us to compare and contrast parasite dynamics in singly infected and coinfected hosts and associate this with child health. Further, as any child found with an infection must be treated, we can also observe natural experiments, enabling us to see how different infections respond to treatment in the presence or absence of other parasite species.

The overall project aim is to determine the interspecific relationship between three important and common infections, malaria, schistosomes and giardia and to evaluate the effects of coinfection combinations versus single infections on host health and parasite control strategies. This aim will be achieved through three key objectives:

1. Determine infection dynamics and health in Ugandan children in the 0 to 36-month age range, by longitudinal sampling a cohort of children in an established field site to assess parasite prevalence, intensity and child health.
2. Assess the effect of coinfection on parasite control by comparing control efficacy between children with different infection histories.
3. Develop a within-host model of the interactions among the parasite species (with structure determined from statistical analysis of data collected in objective 1) and use this to examine the effects of potential control strategies on host health and parasite transmission potential, validating the model through the data obtained in objective 2.