Biology subjects

Salou, E.

Publications and source records attributed to Salou, E..

3 recordsLinked to original sources

bioRxiv2025

Modelling framework to demonstrate elimination of a vector population: tsetse elimination in Chad

Every year, over 700 000 people, particularly children under five, die from vector-borne diseases worldwide. Effectively controlling current endemics and preventing new outbreaks requires an integrated approach that can lead to the elimination of both vectors and diseases. In the last two decades, integrating medical interventions and vector control has significantly reduced the incidence of Gambian Human African Trypanosomiasis (gHAT), with the World Health Organization validating eight countries as having eliminated the disease as a public health problem. However, elimination of the tsetse vector has not been confirmed, leaving the possibility of re-emergence. We developed a five-step modelling framework to assess vector elimination by calculating: (i) the probability of vector capture; (ii) the probability of observing a series of zero catches, even without actual elimination; (iii) the probability of natural elimination; (iv) the probability of failing to detect a rebound; and (v) the reinvasion risk. Our case study is g-HAT in Mandoul, Chad and the elimination of G. fuscipes fuscipes. We used vector control from 2014 to 2025 with no tsetse detected since 2018. We cannot yet conclude, with more than 90% confidence, that tsetse has been eliminated from Mandoul, nor that any remnant population will be naturally eliminated. However, since vector control was stopped in April 2025, we estimate that with continued sampling over the next two years, and no tsetse detected, elimination could be demonstrated with 99% confidence. Our multi-step modelling framework can be applied to other vectors, providing policymakers with clear guidelines for ongoing and future efforts. Significance StatementThe World Health Organisation has set the elimination of transmission of several neglected tropical vector-borne diseases, including human African trypanosomiasis (sleeping sickness), as a target for 2030. We show that deliberate elimination of tsetse, the vector, is feasible and can be demonstrated. We draw on our large-scale intervention in Mandoul, Chad where 3000 insecticide-treated Tiny Targets were deployed between 2014 and 2025, with no tsetse detected since 2018. While small undetected remnant populations cannot be entirely excluded, they would rapidly rebound in the absence of control, rendering them detectable. If no tsetse are caught over the next two years, it will confirm elimination. This illustrates a pathway for assessing and achieving vector elimination as a cornerstone of disease eradication.

ecology↗

bioRxiv2021

Molecular epidemiology of Animal African Trypanosomosis in southwest Burkina Faso

BackgroundAnimal African Trypanosomosis (AAT) is a parasitic disease of livestock that has a major socio-economic impact in the affected areas. It is caused by several species of uniflagellate extracellular protists of the genus Trypanosoma mainly transmitted by tsetse flies: T. congolense, T. vivax and T. brucei brucei. In Burkina Faso, AAT hampers the proper economic development of the southwestern part of the country, which is yet the best watered area particularly conducive to agriculture and animal production. It was therefore important to investigate the extend of the infection in order to better control the disease. The objective of the present study was to assess the prevalence of trypanosome infections and collect data on the presence of tsetse flies. MethodsBuffy coat, Trypanosoma species-specific PCR, Indirect ELISA Trypanosoma sp and trypanolysis techniques were used on 1898 samples collected. An entomological survey was also carried out. ResultsThe parasitological prevalence of AAT was 1.1%, and all observed parasites were T. vivax. In contrast, the molecular prevalence was 23%, of which T. vivax was predominant (89%) followed by T. congolense (12%) and T. brucei s.l. (7.3%) with a sizable proportion as mixed infections (9.1%). T. brucei gambiense, responsible of sleeping sickness in humans, was not detected. The serological prevalence reached 49%. Once again T. vivax predominated (86.2%), but followed by T. brucei (9.6%) and T. congolense (4.2%), while 34.6% of positive samples tested positive for at least two trypanosome species. Seven samples, from six cattle and one pig, were found positive by trypanolysis. The density per trap of Glossina tachinoides and G. palpalis gambiensis was about three flies. Conclusions/SignificanceOverall, our study showed a high prevalence of trypanosome infection in the area, pointing out an ongoing inadequacy of control measures. Authors summaryIn Burkina Faso, like in most countries of sub-Saharan Africa, Animal African Trypanosomosis (AAT) is hampering economic development. It was therefore important to investigate the extent of trypanosome infections after years of control. This study examined circulating trypanosomes in domestic animals using parasitological, molecular and serological tools in southwest Burkina Faso. The prevalence levels observed show that the known epidemiological situation in the region has not really changed. The trypanosome species usually found in the area such as T. congolense, T. vivax and T. brucei s.l. have remained the same, with a stronger presence of T. vivax. The low occurrence of tsetse fly and the predominance of T. vivax attests to the role of the mechanical vectors in maintaining the disease. Although no cases of T. brucei gambiense infection was encountered in the animals examined, trypanolysis tests suggest that there are contact cases in this historical focus of sleeping sickness. Efforts are therefore necessary to reduce or even eliminate the trypanosome burden, and the data provided by this study can assist the decision making.

microbiology↗

bioRxiv2019

Larviposition site selection mediated by volatile semiochemicals of larval origin in Glossina palpalis gambiensis

Tsetse flies (Diptera: Glossinidae) are the cyclical vectors of trypanosomes, the causative agents of African animal trypanosomosis or nagana in animals and human African trypanosomosis or sleeping sickness in humans. Tsetse flies are K-strategist species with the deposition of a single larva at 10 days intervals in specific sites. As larviposition site selection will strongly impact reproductive success, it is obvious that the selection of larviposition sites is not random and is under strong selective processes, probably mediated by specific cues as suggested by the existence of an aggregation factor in the Morsitans and Fusca groups. This study aimed to highlight the existence of an aggregation effect in the Palpalis group and to test for its chemical nature. We studied the larviposition site selection of Glossina palpalis gambiensis according to the presence of conspecific and heterospecific larvae buried in substrates in different settings. Three sets of experiments were performed with either individual or grouped (n = 50) gravid females, and with physical access to substrate or not. In both individual and grouped larviposition experiments, females selected significantly more often trays conditioned by larvae (P<0.005), either conspecific or heterospecific even in the absence of physical contact with the substrate. These results highlight the first evidence for larviposition site selection mediated by volatile semiochemicals of larval origin in Glossina palpalis gambiensis. However, these compounds seem not to be species-specific and therefore offer new avenues for the behavioural manipulation of these vectors and for the development of new vector control tools targeting gravid females.\n\nAuthor summaryLarviposition site selection in tsetse flies is govern by several biotic and abiotic factors that lead to an aggregation effect of larvae. Among those, larvae are suspected to produce chemicals that drive females to breeding site but little information is available. This study aimed to highlight the existence of an aggregation effect of larval origin in the Palpalis group and to test for its chemical nature. Through behavioural larviposition choice experiments, we showed that females of Glossina palpalis gambiensis deposit their larvae significantly more often in trays conditioned either by conspecific or heterospecific larvae, even in the absence of physical contact with the substrate. These results highlight the first evidence for aggregation effect in Glossina palpalis gambiensis mediated by volatile semiochemicals of larval origin. Isolation and identification of these chemicals should offer new avenues for the behavioural manipulation of these vectors and for the development of new vector control tools targeting gravid females.

animal behavior and cognition↗