Dominique Cuisance

A phyto-sociological analysis of the distribution of riverine tsetse flies in Burkina Faso.

Abstract.  In Burkina Faso, Glossina palpalis gambiensis Vanderplank and G. tachinoides Westwood (Diptera: Glossinidae) are the main cyclic vectors of trypanosomiasis. The vegetation type along river banks is an important factor determining the distribution and abundance of these tsetse. The following work investigated the relation between the plant species present (including the disturbance level) and tsetse distribution and abundance, using three ecotypes, described by P.C. Morel in 1978. These were the Guinean, Sudano‐Guinean and Sudanese gallery forests. In the Mouhoun River basin, these three ecotypes are found successively from upstream to downstream. Berlinia grandiflora, Syzygium guineense and Cola laurifolia and finally Acacia seyal and Mitragyna inermis were the best indicators for the Guinean, Sudano‐Guinean and Sudanese gallery forest ecotypes, respectively, as suggested by Morel. However, other species such as Pterocarpus santalinoides and Mimosa pigra were not ecotype specific. Trap catches confirmed that G. palpalis and G. tachinoides are predominant in Guinean and Sudanese gallery forests, respectively, and that both species are well represented in the Sudano‐Guinean ecotype. Tsetse densities dropped significantly in disturbed Sudano‐Guinean and Sudanese gallery forest sites. However, this was not the case for both species in Guinean or for G. tachinoides in half‐disturbed Sudanese gallery forest sites, confirming their high resilience to human‐made changes. The importance of a detailed consideration of riverine ecotypes when predicting tsetse densities is discussed.

Polymerase chain reaction as a diagnosis tool for detecting trypanosomes in naturally infected cattle in Burkina Faso

African animal trypanosomoses constitute the most important vector-borne cattle diseases in sub-Saharan Africa. Generally it is considered that there is a great lack of accurate tools for the diagnosis of the disease. During a trypanosomosis survey in the agro-pastoral zone of Sideradougou, Burkina Faso, 1036 cattle were examined for trypanosomes using microscopy. The PCR was applied on a subset of 260 buffy-coat samples using primers specific for Trypanosoma congolense savannah and riverine-forest groups, T. vivax, and T. brucei. Parasitological examination and the molecular technique were compared, showing a better efficiency of the latter. In the near future, the PCR is likely to become an efficient tool to estimate the prevalence of African trypanosomoses in affected areas.

Microsatellite markers for genetic population studies in Glossina palpalis (Diptera: Glossinidae)

Little is known about tsetse intraspecific variability and its consequences on vectorial capacity. Since isoenzyme analyses revealed little polymorphism, microsatellite markers have been developed for Glossina palpalis gambiensis species. Three loci have been identified and showed size polymorphisms for insectarium samples. Moreover, amplifications were observed in different species belonging to palpalis group. These molecular markers will be useful to estimate gene flow within G. p. gambiensis populations and analyses could be extended to related species.

Comparison of the susceptibility of different Glossina species to simple and mixed infections with Trypanosoma (Nannomonas) congolense savannah and riverine forest types

Abstract Teneral Glossina morsitans mositans, G.m.submorsitans, G.palpalis gambiensis and G.tachinoides were allowed to feed on rabbits infected with Trypanosoma congolense savannah type or on mice infected with T.congolense riverine‐forest type. The four tsetse species and subspecies were also infected simultaneously in vitro on the blood of mice infected with the two clones of T.congolense via a silicone membrane. The infected tsetse were maintained on rabbits and from the day 25 after the infective feed, the surviving tsetse were dissected in order to determine the infection rates.

Microsatellite DNA markers reveal genetic differentiation among populations of Glossina palpalis gambiensis collected in the agro-pastoral zone of Sideradougou, Burkina Faso

Intraspecific genetic variability of Glossina palpalis gambiensis in the area of Sideradougou, Burkina Faso, was studied using polymorphic microsatellite DNA markers. This genetic study was combined with other epidemiological information on the same tsetse: bloodmeal identification, dissection of tsetse and molecular characterization of the trypanosomes detected. There was significant genetic differentiation among flies caught only a few kilometers apart, within the same riverine habitat. These distinct subpopulations were also differentially infected by trypanosomes. In part of the study area, a Factorial Correspondence Analysis undertaken on the genotypes allowed us to detect a Wahlund effect, suggesting the presence of tsetse originating from different source populations coming from two distinct drainage systems. The apparent structuring of populations of G. palpalis gambiensis is discussed relative to appropriate strategies to control African Trypanosomosis.

The changing distribution of two riverine tsetse flies over 15 years in an increasingly cultivated area of Burkina Faso

Changes in the distribution of two riverine tsetse flies, Glossina tachinoides Westwood and Glossina palpalis gambiensis Vanderplank are described in an agro-pastoral area of Burkina Faso subject to increasing human population pressure and land use change. Two similar entomological surveys (one trap every 100 m, 120 km of river) were conducted in 1981 and 1996. Changes in tsetse distribution were compared to land use changes through high resolution remote sensing imagery (LANDSAT, SPOT). There was a close relationship between proximity of crops relative to riverine forest and the density of Glossina. Where fields encroached on riverine vegetation, tsetse populations declined. Where the geomorphological structure was not well suited to agricultural activity, riverine vegetation and tsetse fly populations were relatively unaffected, even with intense agricultural activity nearby. In contrast, increased human activity and higher cattle densities in the surrounding savannah areas were associated with increased tsetse numbers. The results demonstrated a wide diversity of tsetse distribution and habitat within a few kilometres in an agro-pastoral landscape in West Africa.

Intraspecific variability in natural populations of Glossina palpalis gambiensis from West Africa, revealed by genetic and morphometric analyses

Glossina palpalis gambiensis Vanderplank (Diptera: Glossinidae) from West Africa (Senegal and Burkina Faso) were analysed for microsatellite DNA polymorphisms and size of the wings. In the overall sample a strong heterozygote deficiency was found at two polymorphic microsatellite loci. It led to a highly significant value of Fis (within‐sample heterozygote deficit) in the western zone of Sideradougou area in Burkina Faso. Genetic differentiation was significant on a macrogeographic scale, i.e. between tsetse coming from Senegal and Burkina Faso. Wing measures also differed between these two countries; flies from Senegal appeared to be smaller. Microsatellite loci further allowed differentiation of populations of G. palpalis gambiensis trapped on the same hydrographic network a few kilometres apart. The results are interpreted as indicating that further investigations will allow the study of genetic variability of tsetse flies in relation to the dynamics of transmission of human and animal trypanosomoses.

Molecular characterization of trypanosome isolates from naturally infected domestic animals in Burkina Faso

A total of 33 trypanosome cryostabilates isolated from domestic animals (bovine and dogs) were analysed using the polymerase chain reaction (PCR). The PCR was undertaken on diluted and treated buffy coat solutions according to an easy protocol of purification, using primers specific to Trypanosoma (Nannomonas) congolense of Savannah, Riverine-Forest, Kilifi and Tsavo types, T. (N) simiae, T. (Trypanozoon) brucei and T. (Duttonella) vivax. The results showed a lack of PCR sensitivity when target solutions were simply diluted, probably a reflection of the inaccuracy of the dilution procedure at very low trypanosome numbers. Nine mixed infections were found in purified samples whereas only three were detected in diluted crude solutions. T. congolense Savannah-type was present in all stabilates. Double infections involving this type with the Riverine-Forest type, T. vivax or T. brucei, were found. One stabilate was found to be infected with the three trypanosome types, namely T. congolense Savannah and Riverine-Forest genotypes and T. vivax. No infection attributable to T. congolense Kilifi and Tsavo types or T. simiae was detected in these stabilates. This work confirmed the abundance of mixed infections in the field, which could not have been detected by the classical parasitological methods. Amongst the T. congolense infections, the Savannah genotype was found to be predominant over the Riverine-Forest type; that could be a consequence of differences in genotype virulence in cattle. The detection of T. congolense Riverine-Forest type in vertebrate hosts living in wet areas could be confirmation of the suspected affinity of relationships between this taxa and the riverine forest tsetse fly species.

Trypanosome characterization by polymerase chain reaction in Glossina palpalis gambiensisand G.tachinoidesfrom Burkina Faso

Abstract. Following the discovery of four cases of African human trypanosomiasis, an entomological survey was conducted along the Mouhoun river in southwest Burkina Faso to collect Glossina palpalis gambiensisand G.tachinoides.Among 226 flies dissected, 4.87% (eleven individuals) were infected in midgut or proboscis, but never in the salivary glands. Polymerase chain reaction analysis was undertaken, and was able to characterize all the proboscis infections, and half of the midgut infections. Only Trypanosoma simiaeand T. vivaxwere found in the organs of infected flies, in single or mixed‐species infections. Ten more flies, negative with parasitological examination, were tested with Trypanozoonprimers and remained negative. The epidemiological significance of the absence of T.bruceigroup infections in wild tsetse populations and the presence of T.simiaein G.p.gambiensisare discussed.

Monitoring the developmental status of Trypanosoma brucei gambiense in the tsetse fly by means of PCR analysis of anal and saliva drops

Teneral Glossina palpalis gambiensis (Diptera: Glossinidae) were infected with a culture of procyclic forms of Trypanosoma brucei gambiense using a single-bloodmeal membrane feeding technique. The infection was monitored by analysing the saliva (mature infection) and anal drop (midgut infection) of each fly at different post-infection times both by microscopic observation and polymerase chain reaction (PCR). Amplification revealed many more positive anal drops than microscopy. The monitoring showed that the installation of T. b. gambiense in Glossina took place at least 11 days after the infection and that maturation occurred after 29 days. It also reflected precisely the parasitic status of each tsetse fly as determined by the dissection, microscopic examination and PCR amplification of the midguts and salivary glands 47 days post-infection. Twice as many tsetse flies with mature salivary glands infection were revealed by PCR than by microscopic examination, but the two techniques gave exactly the same results regarding the proportion of flies with midgut infection. This study also demonstrated the ability of natural non-infective procyclic forms of T. b. gambiense, to colonise the midgut and subsequently establish in the salivary glands of G. p. gambiensis.