REPLICATION, DIFFERENTIATION, GROWTH AND THE VIRULENCE OF TRYPANOSOMA-BRUCEI INFECTIONS

This study had 2 objectives: first, to investigate how the processes o f slender form replication, of differentiation from dividing slender t o non-dividing stumpy forms, and of stumpy mortality, combine to deter mine the initial (acute-phase) growth rate of Trypanosoma brucei popul ations; second, to determine how acute-phase growth rates influence pa rasite densities during the subsequent, chronic phase of infection. Du ring the acute phase, slender and stumpy populations both grew approxi mately exponentially, the latter more slowly than the former. Mathemat ical models showed how this difference in slender and stumpy growth ra tes can be explained in terms of heterogeneous replication and differe ntiation rates. Stumpy life-expectancy was determined for one stock an d found to be age-dependent with a half-life of 48-72 h, much larger t han observed population doubling times of 5-10 h. A comparison of clon ed stocks showed that the highest parasite densities during the chroni c phase were associated with the highest acute-phase growth rates of b oth the whole parasite population and of the subpopulation of slender forms. By contrast, high chronic-phase parasitaemias artificially prod uced following rapid syringe passage were associated with low acute-ph ase growth rates of slender forms. Syringe-passaging is a laboratory p rocedure which selects for virulent parasites, but these parasites beh ave differently from naturally virulent stocks.