Caractérisation génétique des populations de Glossina palpalis palpalis (Robineau-Desvoidy, 1830) à l’aide des marqueurs de l’ADN mitochondrial : importance dans le développement des stratégies de lutte contre la maladie du sommeil

Abstract

Human African Trypanosomiasis remains a public health problem. In 2018 WHO estimated that 65 million people were at risk of contracting the disease. Improving the knowledge on entomology, ecology and genetics of insect that are vectors of parasites is essential to successfully fight against the diseases caused by them. Sleeping sickness does not escape this logic: the entomology and ecology knowledge of tsetse fly species, trypanosomes vectors, would be used to identify places and period of the year when the probability of parasite transmission is the highest; and therefore the places where the fight against the disease can be carried out first. The genetics of tsetse populations could help to identify populations that are isolated or not for their effective control. The transmission risk index TRI (r) of Laveissière et al. (1994), modified by Grébaut et al. (2004) was used to determine the risk levels of risk of transmission of the parasite (trypanosome) in the sleeping sickness foci of Bipindi Cameroon, while evaluating the influence of spatio-temporal parameters on this transmission. For this, two comparative studies were conducted during two different seasons (July and March). The gene flow within and between geographically separated populations of Glossina palpalis palpalis from Cameroon, the Democratic Republic of Congo (DRC) and Côte d'Ivoire has also been estimated. The demographic history of these populations has been determined, and the phylogenetic relationships between individuals of this subspecies have been assessed. These parameters being important in the establishment of effective control strategies for sleeping sickness. The value of haplotype diversity H in DRC was two times greater than the value obtained in Cameroon and three times the value observed in Ivory Coast. Nucleotide diversity Πn were six times smaller in Ivory Coast than in RDC and in Cameroon. A significantly higher density of Glossina palpalis palpalis was observed in July, but the highest infection rates were observed in March. Among the successfully identified blood meals, 66.7% came from humans and 33.3% from pigs. The highest transmission risk index was observed in the Lambi village. The assessment of the TRI shows that the risk was higher in July and near perennial water sources. The genetic analyses involved a total of 418 Glossina palpalis palpalis, of which 258 were sampled in Cameroon, precisely in Bipindi, Campo, Fontem and Bafia, 100 in Azaguié and Nagadoua in Ivory Coast and 60 from Malanga in the DRC. The variation at three concatenated mitochondrial markers namely COI, COII-TLII and 16S2 was examined. Thirty four haplotypes were found, of which 30 were “rare”, since each was present in less than 5% of the total number of individuals. No haplotype were shared among Cameroon, Ivory Coast and DRC populations. The value of haplotype diversity H in DRC was two times greater that the value obtained in Cameroon and three times greater than that observed in Côte d'Ivoire. Nucleotide diversity πn were six times smaller in Ivory Coast than in the DRC and Cameroon. The fixation index FST of 0.88 showed a high genetic distance between Glossina palpalis palpalis populations from the three countries. That genetic distance was correlated to the geographic distance between populations. We also found that there is a substantial gene flow between tsetse flies from locations separated by over 100 km in Cameroon and between tsetse flies from locations separated by over 200 km in Ivory Coast. Demographic parameters suggest that the tsetse flies of Fontem (Cameroon) had reduced in population size in the recent past. Other Central African populations are made up of permanent large populations. In Ivory Coast population more investigations are required in order to better understand the demographic history of tsetse flies populations. Phylogenetic analysis confirms that Glossina palpalis palpalis originating from the Democratic Republic of Congo is genetically divergent from the two other countries as already published in previous studies.