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The epidemiology of Trypanosoma vivax infections was studied at a riverside site in the Ouro-Djafoun livestock area situated in the Central African Republic during the period between July 1991 and July 1992. This paper examines the possibility that stable flies (Diptera: Stomoxyinae) were also vectors of this trypanosome species in a non-cyclic way. Previous studies have revealed that the usual cyclic transmission by the tsetse fly Glossina fuscipes fuscipes was probably not the only transmission route. At the study site, at least five species or subspecies of stable flies were encountered: Stomoxys nigra nigra (approximately 60% of the sample), S taeniata, S sitiens, S omega omega and Haematobia spp. The hypothesis that stable flies could be good vectors of T vivax in this country is supported by three main observations: i) stable flies were very abundant at the cattle resting site; ii) an estimation of the 'contact index' between the cattle and stable flies demonstrated close interactions between cattle and stable flies at this site, particularly during the rainy season, and iii) there was a good correlation (P < 0.05) between the apparent stable fly densities at the resting site and the frequency of T vivax in the cattle. The relevance of this phenomenon in terms of epidemiology and combatting T vivax-caused nagana is discussed.

Neighteen Mbororo zebu herds were monitored to evaluate the impact of a trapping campaign against Glossina fuscipes fuscipes restricted to the watering places. This programme is part of the strategy of an integrated campaign against bovine trypanosomoses in the Central African Republic. Trapping reduces the densities of G. f. fuscipes and causes trypanosome prevalence to fall. These effects are shown by the improved hematocrit values and the reduced number of trypanocidal treatments administered. The impact on productivity is more difficult to assess over a short period; nevertheless, it seems clear from the parameters calculated.

Host odours increased the trap catches of Glossina fuscipes fuscipes in cattle breeding areas of the Central African Republic. The increase was significant with zebu urine (x 1.4) and the principal reptilian host, the monitor lizard (x 1.7). The greatest effect (x 4.2) was obtained for male G f fuscipes with zebu urine when the densities of flies were low (less than 5 males per trap per day). It seems that olfactory baits in urine could improve the control of G f fuscipes by trapping. Reptile odour contains attractants that should be identified.

From 1987 to 1993, a survey on the feeding behavior of Glossina fuscipes fuscipes was conducted in the Central African Republic. A total of 556 blood-meal samples was analyzed by ELISA. According to the results, the number of blood meals from cattle was rather low (12% on average). During the rainy season, this number increased significantly and varied according to the sampling area. Along the riverine forests, this amounted to 5%, while blood meals from wild ruminants amounted to 87%. In the neighborhood of watering-places, the number of cattle blood meals reached 9-22%. Reptiles were found to be important hosts (17-35%). In all cases, man presented a non-negligible host (4-14%), similar to suidae (2-19%). The authors discuss the relevance of these results to risk of trypanosomes transmission.

In the early 1960s, the most part of the Central African Republic was located inside the distribution area of Glossina morsitans submorsitans Newst. Since the last distribution studies of this tsetse in CAR (in 1963), the number of cattle has increased from 400,000 to approximately two millions, mainly of the Mbororo zebu breed. To set up the present distribution of G. m. submorsitans a study by trapping has been carried out in 27 livestock areas, regarding about 1,200 pastoralists' settlements. Furthermore, north-south transects have been made using both trapping (with bipyramidal traps laid every 2,000 meters) and net-catching (within a car driving slowly). The result have shown the disappearance of G. m. submorsitans from the main livestock areas in the west (Bouar, Bozoum, Bocaranga, Batangafo, Bossangoa, Paoua), centre (Bossembélé, Bouca, Dékoa) and east (Bambari, Grimari, Ippy). The southern border of the distribution area has been moved upwards to the north by up to 400 kilometres in the west of the country. This important retreat is discussed. It leads to a huge increase in the pastures available for the Mbororo pastoralists. Their access is still restricted in the centre-north and in the east by wild game reserves where G. m. submorsitans remains.

The sleeping sickness focus at Nola-Bilolo in the forest region was the subject of a survey of 142 patients in order to discover their probable places of infection. Seventy of these patients had been detected by active case-finding during a survey conducted in January-February 1991; the other 12 had been discovered by passive case-finding during 1990. The sample of actively detected patients is significantly younger (average 22 +/- 3 years) than the sample detected passively (30 +/- 3 years). This survey highlights the geographical heterogeneity of transmission in the focus. The places where infection is highest are M'Poyo, which with 18% of cases forms the epicentre of the focus and the main reservoir of infecting flies, followed by Bilolo (9%), Mékara (8%), Modigui-Kouna, Ziendi and Domissili (7%). The patients, 95% of whom belong to the M'Bimou tribe, all engage in agriculture; the main activities are coffee-growing for men and the steeping of casava in the river for women. These two activities determine the main places and times of human-tsetse contact. The information obtained by listing the cases detected passively from medical registers is inadequate for locating the places of transmission. The information gathered during active case-finding campaigns by the mobile teams offers a better approach. The method used here, which is recommended, consists of matching the replies given by the patients about their points of contact with the tsetse flies, not just with their places of residence but also with their successive movements and their places of work. The rigour demanded by this kind of approach can only be ensured by a specific survey. This survey also made it possible to demonstrate substantial movements from village to village, which appear to be characteristic of this focus. The results indicate that poorly targeted vector control is likely to be doomed to failure. The study makes it possible to specify priority areas for vector control by trapping and to avoid a "blind" control strategy whereby the whole focus is swamped with traps. The latter strategy is not financially feasible for many countries of tropical Africa.

The authors review urban sites of Glossina fuscipes fuscipes in the suburbs of Bangui and propose a classification of these sites. Among them, two isolated breeding sites are characterized by a high density of tsetse and a close man/fly contact. To prevent a possible reactivation of the historical sleeping sickness focus of Bangui-Bimbo, a tsetse control programme in these two sites is necessary.