Glossina spp. gut bacterial flora and their putative role in fly-hosted trypanosome development

Abstract

Human African trypanosomiasis (HAT) is caused by trypanosomes transmitted to humans by the tsetse fly, in which they accomplish their development into their infective metacyclic form. The crucial step in parasite survival occurs when it invades the fly midgut. Insect digestive enzymes and immune defenses may be involved in the modulation of the fly's vector competence, together with bacteria that could be present in the fly's midgut. In fact, in addition to the three bacterial symbionts that have previously been characterized, tsetse flies may harbor additional bacterial inhabitants. This review focuses on the diversity of the bacterial flora in Glossina, with regards to the fly species and their geographical distribution. The rationale was (i) that these newly identified bacteria, associated with tsetse flies, may contribute to vector competence as was shown in other insects and (ii) that differences may exist according to fly species and geographic area. A more complete knowledge of the bacterial microbiota of the tsetse fly and the role these bacteria play in tsetse biology may lead to novel ways of investigation in view of developing alternative anti-vector strategies for fighting human--and possibly animal--trypanosomiasis.

Keywords: bacteriome; human African trypanosomiasis; interactions; trypanosome; tsetse flies.

Figure 1

Bacterial species characterized in the midgut of tsetse flies species from sub-Saharan African countries. According, respectively, to: (1) Geiger et al. (2010); (2) Geiger et al. (2011); (3) Geiger et al. (2009); (4) Lindh and Lehane (2011). Bacteria from G. f. fuscipes: ^athe species between brackets are the closest relatives according to RDPII (Maidak et al., 2001); ^bthe species underlined were identified with culture-independent methods. No bacteria were identified in G. caliginea.

Figure 2

G. palpalis palpalis infections in the Maria Teresa focus in Angola according to Geiger et al. (2009). (A) Prevalence of infection in tsetse flies; (B) frequency of occurrence for each infection type. “Multiple” names indicate the occurrence of a mixed infection.

Figure 3

G. palpalis palpalis, G. pallicera and G. nigrofusca fly' bacterial infections occurring in the different villages (Akak, Campo Beach/Ipono and Mabiogo) of the Campo focus in Cameroon, according to Geiger et al. (2011). (A) Prevalence of bacterial infection in the different tsetse fly species; (B) bacterial infection frequency per fly species and per village. “n” indicates the number of bacterial infected flies vs. the number of collected flies. “Multiple” names indicate the occurrence of a mixed infection.

Figure 4

Possible mechanism involved in the modulation, by the midgut microbiota, of the tsetse fly infection by trypanosomes.