Effect of wing length on the prevalence of trypanosomes in Glossina morsitans morsitans in eastern Zambia

Abstract

BACKGROUND: Tsetse fies (Diptera: Glossinidae) transmit trypanosomiasis (sleeping sickness in humans and nagana in livestock). Several studies have indicated that age, sex, site of capture, starvation and microbiome symbionts, among others, are important factors that infuence trypanosome infection in tsetse fies. However, reasons for a higher infection rate in females than in males still largely remain unknown. Considering that tsetse species and sexes of larger body size are the most mobile and the most available to stationary baits, it was hypothesized in this study that the higher trypanosome prevalence in female than in male tsetse fies was a consequence of females being larger than males. METHODS: Black screen fy rounds and Epsilon traps were used to collect tsetse fies in eastern Zambia. Measurement of wing vein length and examination for presence of trypanosomes in the fies were carried out by microscopy. Principal component method was carried out to assess the potential of wing vein length as a predictor variable. The multilevel binary logistic regression method was applied on whole data, one-method data and one-sex data sets to evaluate the hypothesis. RESULTS: Data derived from a total of 2195 Glossina morsitans morsitans were evaluated (1491 males and 704 females). The wing length variable contributed the highest variance percentage (39.2%) to the frst principal component. The variable showed signifcant infuence on prevalence of trypanosomes when the analysis was applied on the whole data set, with the log odds for the prevalence of trypanosomes signifcantly increasing by 0.1 (P = 0.032), per unit increase in wing length. Females had higher trypanosome prevalence rates than males, though not always signifcant. Furthermore, moving from females to males, wing length signifcantly reduced by 0.2 (P < 0.0001). CONCLUSIONS: We conclude that wing length is an important predictor variable for trypanosome prevalence in Glossina morsitans morsitans and could partially explain the higher prevalence of trypanosomes in females than in males. However, reasonably representative population data are required for analysis—a serious challenge with the current tsetse sampling methods. Thus, analysis combining data from mobile and stationary methods that include both sexes’ data could be useful to verify this hypothesis.