Sodalis glossinidius prevalence and trypanosome presence in tsetse from Luambe National Park, Zambia

Abstract

BackgroundTsetse flies are the biological vectors of African trypanosomes, the causative agents of sleeping sickness in humans and nagana in animals. The tsetse endosymbiont Sodalis glossinidius has been suggested to play a role in tsetse susceptibility to infection. Here we investigate the prevalence of African trypanosomes within tsetse from the Luambe National Park, Zambia and if there is an association between S. glossinidius and presence of trypanosomes within the tsetse examined.MethodsTsetse representing three species (Glossina brevipalpis, Glossina morsitans morsitans and Glossina pallidipes), were sampled from Luambe National Park, Zambia. Following DNA extraction, PCR was used to examine the tsetse for presence of trypanosomes and the secondary endosymbiont S. glossinidius.ResultsS. glossinidius infection rates varied significantly between tsetse species, with G. brevipalpis (93.7%) showing the highest levels of infection followed by G. m. morsitans (17.5%) and G. pallidipes (1.4%). ITS-PCR detected a wide variety of trypanosomes within the tsetse that were analysed. Significant differences were found in terms of trypanosome presence between the three tsetse species. A high proportion of G. m. morsitans were shown to carry T. brucei s.l. DNA (73.7%) and of these around 50% were positive for Trypanosoma brucei rhodesiense. T. vivax, T. godfreyi, T. simiae, T. simiae Tsavo and T. congolense were also detected. No association was found between the occurrence of S. glossinidius and the presence of trypanosome DNA in any of the three tsetse species tested.ConclusionThe current work shows that T. b. rhodesiense was circulating in Luambe National Park, representing a risk for people living in the park or surrounding area and for tourists visiting the park. The differences in trypanosome DNA presence observed between the different tsetse species tested may indicate host feeding preferences, as the PCR will not discriminate between a fly with an active/resident infection compared to a refractory fly that has fed on an infected animal. This makes it difficult to establish if S. glossinidius may play a role in the susceptibility of tsetse flies to trypanosome infection.

Microbiome frequency and their association with trypanosome infection in male Glossina morsitans centralis of Western Zambia

“…The Sodalis infection prevalence observed in the present study are comparable with circa 20% reported in other morsitans group tsetse (Dennis et al, 2014;Wamwiri et al, 2013) but markedly lower than those reported in species such as Glossina palpalis palpalis (Farikou et al, 2010) with infection rate of about 55%. Previous workers also report no significant difference in infection prevalence between male and female flies (Dennis et al, 2014), indicating that our results using male flies only could be a true reflection of the population infection status.…”

“…While these results are consistent with the observations in G. pallidipes and G. palpalis palpalis (Farikou et al, 2010;Wamwiri et al, 2013), they are contradictory to the conclusions of Dennis et al (2014) who found no association between infection with Sodalis and midgut trypanosome infections in Glossina brevipalpis, G. morsitans morsitans and G. pallidipes. The dynamics of trypanosome infection are complex and may be influenced by composition of the microbiome .…”

“…Trypanosome infection rates in cattle differ with location, but average around 15% in eastern Zambia (Kubi et al, 2007;Simukoko et al, 2007;Sinyangwe et al, 2004) where G. morsitans morsitans is one of the tsetse species present. The infection rate in G. morsitans centralis from the two western areas in this study averaged 23.2%, which was much lower than the prevalence in G. morsitans morsitans from Eastern Zambia (Dennis et al, 2014). This variation may be attributed to sampling variation, trypanocide usage and host preferences among other factors.…”

“…Previous workers also report no significant difference in infection prevalence between male and female flies (Dennis et al, 2014), indicating that our results using male flies only could be a true reflection of the population infection status. The comparable Sodalis prevalence within tsetse species and difference across species indicates that there could be some species related factors that may influence its prevalence.…”

“…The presence of mixed trypanosome infections in G. morsitans centralis indicates its ability to harbour and transmit different trypanosome species, including human-infective trypanosomes. Dennis et al (2014) provide an analysis of trypanosome infection in various tsetse species in eastern Zambia, and of key interest was the high proportion of G. morsitans positive for T. brucei (73.7%, n = 137) of which about half were T. brucei rhodesiense. In the current study, all the trypanosome species detected in G. morsitans centralis belonged to the animal infective group.…”