Longitudinal patterns of trypanosome infections in red-spotted newts

Longitudinal data on Trypanosoma diemyctyli infections in individual red-spotted newts, Notophthalmus viridescens, were collected over a 5-yr period. Many newts (37%) retained infections throughout their adult lives and only 4.5% appeared to lose infections following their initial autumn sample. Individual infection levels were higher at their first sample as compared to their second sample. Newts of known age were transplanted between leech-free and leech-infested ponds. The time course of infection between previously exposed and unexposed individuals was similar when both were caged in a leech-infested pond. Previously infected individuals maintained stationary chronic levels for 3 mo in both leech-infected and leech-free ponds. The trends observed in these longitudinal data suggested that transmission by leeches is necessary for infection, that continued transmission does not significantly alter the dynamics of infrapopulation growth and stasis, and that constraints on trypanosome population growth occurred at the host individual level.