Effect of Wing Length on the Prevalence of Trypanosomes in Glossina Morsitans Morsitans in Eastern Zambia

Abstract

BackgroundTsetse flies (Diptera: Glossinidae) transmit trypanosomiasis (sleeping sickness in humans and nagana in livestock). Several studies have indicated that the age, sex, site of capture, starvation and microbiome symbionts, among others, are important factors influencing trypanosome infection in tsetse flies. However, reasons for a higher infection rate in females than in males still largely remain unknown. As species and sexes of tsetse flies 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 because females were larger than males.Materials and methodsBlack screen fly rounds and epsilon traps were used to collect tsetse flies in eastern Zambia. Wing vein length was measured and the presence of trypanosomes was examined by microscopy. Principal component method was carried out to determine which variables had potential to be used as predictor variables. The multilevel binary logistic regression method was applied on whole data, one-method data and one-sex data sets to evaluate the hypothesis. ResultsA total of 2,195 Glossina m. morsitans data were evaluated (1,491 and 704 males and females, respectively). The wing length variable contributed the highest variance percentage (39.15%) to the first principal component. The wing length variable showed significant influence on prevalence of trypanosomes when the whole data set was analyzed. The log odds for the prevalence of trypanosomes significantly increased by 0.123 (p = 0.032), per unit increase in wing length. Moreover, moving from females to males, wing length significantly reduced by 0.150 (p < 0.0001) and females had higher trypanosome prevalence rates than males, though not always significant. ConclusionWing length is an important determinant factor for trypanosome prevalence in G. m. morsitans and could partially explain the higher prevalence of trypanosomes in females than in males. To verify this status, however, it’s clear that, reasonably representative population data is required for analysis – a serious challenge with the current tsetse sampling methods. Nonetheless, analysis of combined data from mobile and stationary methods that includes both sexes data, could verify the status.

Wing length of tsetse caught by stationary and mobile sampling methods

“…A total of 3,585 G. m. morsitans were caught (3,191 by fly rounds and 394 by traps), (Mweempwa, 2015). Out of the 3,191, 2006 had their wing length measurements taken and out of the 2006 these, 1,223 (60.9%) met the selection criteria for this study as mentioned under data analysis sub-title.…”

“…The method used to sample tsetse populations is described in detail by (Mweempwa et al, 2015) except for use of epsilon traps (Muzari and Hargrove, 1996) and measurement of body size. In brief, black-screen fly-rounds Potts (1930) were used to capture tsetse at four locations.…”

“…The study locations were Chisulo, Kasamanda, Lusandwa and Zinaka with minimum and maximum distance apart of 10 to 30 kilometers, respectively. The degree of habitat fragmentation at these sites increased in the order Lusandwa, Zinaka, Chisulo and Kasamanda (Mweempwa et al, 2015)…”

“…Measurements read off the graticule were converted to millimeters (mm) by dividing by the magnification used. Other examinations carried out on tsetse flies included ovarian age, wing fray, infection by trypanosomes and sex ratio, covered in detail in a PhD thesis by Mweempwa, (2015).…”

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

“…The data were collected in eastern Zambia during a study on the status of tsetse populations and epidemiology of livestock trypanosomiasis in areas of varying degrees of habitat fragmentation [ 16 ]. The description of the study area, methods used to sample tsetse populations and laboratory examinations of tsetse flies were as provided in previous studies in the area [ 4 , 17 , 18 ].…”