Search

Understanding the dynamics of schistosome infections is problematic because direct measurements of worm burden are not possible. Hitherto, the relative intensity of infection has been estimated by the number of parasite eggs excreted. Egg excretion is assumed to have a consistent relationship with worm burden with duration of infection. We have tested this assumption in Schistosoma mansoni- and S. haematobium-infected populations by looking at the relationships between a circulating parasite antigen, egg excretion level, host age, and parasite density. The study was carried out in two populations because experimental models suggested that S. haematobium but not S. mansoni suffers immune-mediated reduction of fecundity. The results were consistent with this observation, showing that S. mansoni egg output remains stable irrespective of host age or infection intensity while S. haematobium has a substantially reduced egg production with host age. This information is fundamental to understanding the immunology and epidemiology of human schistosomiasis and thus practical approaches to disease control.

The transmission of the human African trypanosomiasis (HAT) infection, also known as human sleeping sickness, depends on environmental factors operating at the mega-, macro-, and micro-scale levels. However, at the latter level T.b. rhodesiense parasite undergoes metacyclic development processes, controlled by its evolution, regulatory and mediation factors. Selective pressures acting on host-parasite interactions are thought to influence the genetics of the parasite and its hosts. In retrospect, the phenotypic difference responsible for the change in fitness of the parasite is complicated, since natural variation in a phenotype may be maintained by frequency-dependent selection, with species-specific fitness dynamics. Although little evidence exists on aspects of mutualism o f trypanosomes, it is possible that synergistic interactions among pathogens may be involved in the complex of phenotype variations. This paper considers the underlying dynamics with reference to the endemicity of the infection in Lambwe Valley ecosystem.