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

Cornelius Mweempwa,Kyoko Hayashida,Kalinga Chilongo,Boniface Namangala

doi:10.1186/s13071-021-04907-y

Abstract

BackgroundTsetse flies (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 influence trypanosome infection in tsetse flies. 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 flies was a consequence of females being larger than males.MethodsBlack screen fly rounds and Epsilon traps were used to collect tsetse flies in eastern Zambia. Measurement of wing vein length and examination for presence of trypanosomes in the flies 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.ResultsData 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 first principal component. The variable showed significant influence on prevalence of trypanosomes when the analysis was applied on the whole data set, with the log odds for the prevalence of trypanosomes significantly increasing by 0.1 (P = 0.032), per unit increase in wing length. Females had higher trypanosome prevalence rates than males, though not always significant. Furthermore, moving from females to males, wing length significantly reduced by 0.2 (P < 0.0001).ConclusionsWe 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.Graphical abstract

Highlights

In a study by Hargrove [2], age structures determined from samples of tsetse flies caught using different methods differed significantly in six out of ten pair comparisons in G. m. morsitans and in all ten pair comparisons in G. pallidipes, and the differences were attributed to increased flight activity with age
This study showed that wing length was among the important factors that influenced prevalence of trypanosomes in G. m. morsitans
Because of the sampling bias inherent in individual methods with respect to wing length [4], analysis of the one-method data set did not show the importance of wing length as an important predictor variable for prevalence of trypanosomes; the influence of the variable on prevalence seemed suppressed in the analysis

Summary

Introduction

Tsetse flies (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 influence trypanosome infection in tsetse flies. Sampling tsetse flies involves the use of stationary and/or mobile techniques These techniques are known to display inherent biases toward certain sections of populations, e.g. toward particular species, sex, age group and pregnancy stage [2, 3]. Some studies have been carried out to identify factors that influence rates of trypanosome infection in tsetse flies and these factors include age [5], sex and site of capture [6], starvation [7] and microbiome symbionts [8, 9] among others

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