Contact details

Professor Joanne P Webster

Professor of Parasite Epidemiology
Division of Epidemiology, Public Health and Primary Care

Ground Floor
Medical School
St Mary's Campus

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Professor Joanne P Webster

EPIDEMIOLOGY AND EVOLUTION OF SCHISTOSOMES: IMPLICATIONS FOR MORBIDITY AND CONTROL

In addition to our mass human chemotherapy control programmes (see SCI), one of the principle aims of our interdisciplinary complementary research  is to understand the population structure and evolution of schistosomes in relation to chemotherapy, definitive host species and epidemiological settings - as a prerequisite both to the interpretation of prevailing patterns of infection and disease, and to guiding and targeting future disease control activities.  Schistosomiasis is a parasitic disease of profound medical and veterinary importance.  With recent shifts in global health policy towards the implementation of mass chemotherapy, intensive and prolonged new selective pressures will be placed on the parasite, which may have implications for the long term success of such campaigns.  To gain an insight into the transmission and clinical processes of the disease, a detailed understanding of schistosome population genetic structure is essential.  Through the development and application, across a range of endemic countries within Africa and Asia, of novel, ethically and epidemiologically superior molecular and phenotypic tools, in combination with clinical measurements and both laboratory and mathematical simulations, we combine basic studies of how schistosome populations evolve with the much more applied issue of identifying parasite strains.  Such research will enable any changes in population structures to be monitored, potentially virulent or drug-resistant genotypes to be identified, and the effectiveness of chemotherapy where there is cross-infection with other host species to be evaluated.  The results produced are valuable in several respects, perhaps the most important being to ensure a proper understanding of the long-term dynamics of infection, and help identify where and how to focus disease control efforts.  More generally, they will contribute to understanding coevolution and the genetics of adaptation in other host-pathogen systems.

Figure 1.  Sampling S. japonicum eggs and miracidia from a water buffalo in the Philippines (photo J. Shrivastava).

Figure 2.  Unweighted Pair Group Method with Arithmetic Mean (UPGMA) phenogram clustering identifies segregation of distinctive S. japonicum allele frequencies into two main sub-groups : Humans and bovines versus domestic animals.  (from Wang, T-P, Shrivastava, J., Johansen, M.V., Z.K. Zhang, & Webster, J.P. (2006)  Int. J. Parasitol.)

Figures 3a&b.  Sampling  (a) S. heamatobium infections and (b) schistosome-associated anaemia morbidity levels in Ugandan school-children (photos SCI).