Trypanosoma brucei rhodesiense (Trypanosomatidae): factors influencing infection rates of a recent human isolate in the tsetse Glossina morsitans (Diptera: Glossinidae).

Abstract

Laboratory tests were conducted to evaluate the influence of several variables on infection rates of Trypanosama brucei rhodesiense in Glossina morsitans, viz., postinfection temperature, clone/isolate of parasite, age and sex of tsetses, and the presence or absence of serum in the infective blood meal. Flies evaluated histologically had infection rates of 10.9% in the midgut (MG), 6.9% in the proventriculus (PV), and 1.9% in the salivary glands (SG); flies assessed by dissection methods yielded MG, PV and SG infection rates of 24.3, 19.0, and 4.8%, respectively. No consistent differences were found in infection rates using the different isolates/clone of T. b. rhodesiense, nor were there differences between flies held at different postinfection temperatures (range limits: 15–21 °C). Analysis of the influence of age and sex indicated an interaction effect where males <24 h old had the highest rates and all other groups, males 24–48 h old and females <24 and 24–48 h old, presented comparable rates. In addition, <6-h-old flies yielded higher infection rates than 6–26-h-old flies, while chilled 24–30-h-old flies yielded intermediate rates, indicating that the negative physiological effects of aging on infection potential can be retarded by cool temperatures. Replacement of serum in the infective meal with 1% glucose in saline significantly enhanced MG infection rates in all males held at a postinfection temperature of 25 °C, although only 24–48-h-old males showed enhanced infection rates at the 20 °C postinfection temperature.