Revisiting Immunity Versus Exposure in Schistosomiasis: A Mathematical Modelling Study of Delayed Concomitant Immunity, 1998-2000

The relative contributions of acquired immunity and exposure to the distinct epidemiological patterns of human schistosomiasis has been long debated. There is considerable evidence that humans acquire immunity to infection with age, providing partial protection in adulthood. However age- and sex-related contact patterns with water bodies contaminated with infectious cercarial schistosome larvae also contribute to the epidemiological profiles of infection.

The data supported the development a novel schistosome transmission model that incorporates both partially protective immunity represented by immunoglobulin E (IgE) antibody levels specific to Schistosoma mansoni Tegumental-Allergen-Like protein 1 (SmTAL1-IgE), and host age- and sex-dependent patterns of exposure. The model was fitted using a Baysien approach to individual data on exposure to infectious cercariae, infection levels measured as eggs per gramme of faeces (epg) and SmTAL1-IgE levels. The aim was to determine the importance of immunity parameters in optimal Schistosoma mansoni transmission models.

The data is a sub-set of data from a longitudinal re-infection study held by the University of Cambridge Schistosomiasis Research Group. The data was collected between 1998 and 2000 to empirically investigate the relative roles of exposure to the infectious cercarial life stage, and the development of partial immunity, on Schistosoma mansoni re-infection levels measured on a micro-geographical scale. Exposure was derived from longitudinal water contact observations and systematic malacology surveys of the parasites’ intermediate hosts. Infection levels and SmTAL1-IgE were measured pre- and post-treatment with praziquantel. The sub-set of data is for one of the two ethnic groups who originally participated - the members of whom are now the predominant ethnic group in Lake Albert shoreline communities. To be included in the data set an individual record also had to have both a cercarial exposure score and a pre-treatment egg count.