The COMBAT project: controlling and progressively minimizing the burden of vector-borne animal trypanosomosis in Africa

[Updating the northern tsetse distribution limit in Chad in the context of global change]

Background - Rationale

Tsetse flies (Diptera: Glossinidae) are obligate bloodfeeders that occur exclusively in Sub-Saharan Africa, where they are the vectors of trypanosomes causing HAT (human African trypanosomiasis) and AAT (African animal trypanosomiasis). In Chad, tsetse flies occur only in the most southern part of the country because of its favorable bioclimatic conditions. However, despite the importance of HAT and AAT in this country, very little is known about the current tsetse distribution, in particular its northern limit, which is of key importance for the surveillance of these diseases.

Material and methods - Results

A total of 217 biconical traps were deployed in 2021 and 2022 from the West to the East around the formerly known northern limit, resulting in 1,024 tsetse caught belonging to three different taxa: Glossina morsitans submorsitans (57%), G. tachinoides (39%) and G. fuscipes fuscipes (4%). In addition to the information gathered on the presence/absence of each tsetse taxon, we show a strong North-South shift of the northen tsetse distribution limit as compared to the previous works from 1966 to 1996, and a growing spatial fragmentation in more and more discrete pockets of tsetse presence.

Discussion - Conclusion

This North-South shift of the northern tsetse distribution limit in Chad is the likely consequence of the combined effect of severe draughts that affected the country, and increasing human pressure on land. This update of the tsetse northern limit will be of help to the national programmes in charge of HAT and AAT.

Limited impact of vector control on the population genetic structure of Glossina fuscipes fuscipes from the sleeping sickness focus of Maro, Chad

Tsetse flies (genus Glossina) transmit deadly trypanosomes to human populations and domestic animals in sub-Saharan Africa. Some foci of Human African Trypanosomiasis due to Trypanosoma brucei gambiense (g-HAT) persist in southern Chad, where a program of tsetse control was implemented against the local vector Glossina fuscipes fuscipes in 2018 in Maro. We analyzed the population genetics of G. f. fuscipes from the Maro focus before control (T0), one year (T1), and 18 months (T2) after the beginning of control efforts. Most flies captured displayed a local genetic profile (local survivors), but a few flies displayed outlier genotypes. Moreover, disturbance of isolation by distance signature (increase of genetic distance with geographic distance) and effective population size estimates, absence of any genetic signature of a bottleneck, and an increase of genetic diversity between T0 and T2 strongly suggest gene flows from various origins, and a limited impact of the vector control efforts on this tsetse population. Continuous control and surveillance of g-HAT transmission is thus recommended in Maro. Particular attention will need to be paid to the border with the Central African Republic, a country where the entomological and epidemiological status of g-HAT is unknown.

An Atlas of Surra in Spain: A Tool to Support Epidemiological Investigations and Disease Control

Trypanosomosis is a global animal issue, causing significant economic losses, particularly in Africa. In Spain, only one pathogenic species, Trypanosoma evansi, has been identified so far. It was first detected in a dromedary camel in the Canary Islands in 1997. Since then, numerous cases of the disease, known as Surra, have been diagnosed, prompting various studies and efforts in control and surveillance. Given the lack of a comprehensive database that consolidates the most relevant data in this area, the development of a national atlas, with a focus on the Canary Islands, to incorporate all available information on T. evansi in Spain became a necessity. For the development of the atlas, a repository was constructed, encompassing a range of datasets and documents spanning from 1997 to 2022. Information from each source, and in particular georeferenced locations and results of blood tests on animals, were extracted and integrated into a comprehensive database. A total of 31 sources were analysed, providing a total of 99 georeferenced locations and 12,433 animal samples. Out of these samples, 601 (mostly from dromedaries) were found to be positive for T. evansi. The Card Agglutination Test for T. evansi (CATT/T. evansi), a serological test, was the most commonly used diagnostic method, and it showed a higher prevalence for all tested animal species. Positive cases were mainly concentrated in the Canary Islands, specifically in the eastern islands, with isolated cases found in the province of Alicante (Iberian Peninsula). This atlas provides an overview of the history and occurrence of Surra in Spain, and it represents a valuable tool for future control initiatives and for research. Still, the need for more studies remains, especially for further testing of potential hosts other than camelids and for the examination of their potential transmission vectors.