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Department of Zoology


Why do some parasite species such as Bacillus cereus cause mild nausea and diarrhoea for 24-48 hours when others such as B.anthrasis (Anthrax) kill 90-100% of infected people within 48 hours? Understanding why parasites evolve to be harmful would be an important step in our fight to control disease. Key to understanding the harm parasites cause their hosts is understanding how parasites deal with competition from other parasites within hosts, and optimise their transmission between hosts. And its not just other parasites that the parasites have to compete with: hosts evolve resistance, leading to a host-parasite arms-race. However, these critical interactions have not been rigorously tested due to a lack of experimental systems.

My research tackles this using a powerful system of worms infected with bacteria, where the infection process is natural and I can study evolution in real time due to their short lifespans. I love this work because it may help our fight against diseases. Antibiotics are our main way of treating infection, but because of their widespread use, parasites are becoming resistant and so the drugs are less effective. The long-term aim of my research is to establish better ways of predicting and therefore preventing parasites becoming more harmful. 

Current research topics include:

  • How does multiplicity of infection affect virulence?
  • How should virulence evolve in response to the spatial structure of parasites?
  • How do various life history and demographic parameters correlate with parasite virulence?
  • How does within-host and between host parasite competition interplay and effect parasite virulence?
  • For pathogens that live in or invade via external facing host tissues (e.g. the gut), how does the host microbiota affect the evolution and virulence of pathogens?

Key Publications 

Full List of Publications


Contact Details

Group Leader

Dr Helen Leggett

Department of Zoology
University of Cambridge
Downing St


Group Members