Entomological investigations carried out from 2002 to 2010 into the involvement of water bugs (Heteroptera - Hemiptera) in transmission of Mycobacterium ulcerans to humans in Côte d’Ivoire (West Africa)

Ulcer is a disease caused by a mycobacterium present in the environment: Mycobacterium ulcerans.This communicable disease occurs essentially in wet tropical regions, and in particular in west Africa where it is endemic. It is the third most common mycobacterial disease affecting humans after leprosy and tuberculosis, although it is more prevalent than either leprosy or tuberculosis in some rural areas of several countries (Benin, Côte d’Ivoire and Ghana). This has led WHO to act, and in 1998 to declare Buruli ulcer an « emerging disease » and to recognize it as a neglected tropical disease. Its development is a source of concern in Côte d’Ivoire, the country most affected in the world, with an aggregate number of 30 000 cases and more than 2000 cases detected each year. It particularly affects children living in isolated rural areas around bodies of stagnant or slowly flowing water.  In order to control the disease, it is essential fully to understand its epidemiology. In this connection, there are several hypotheses on the mode of transmission of M. ulcerans to humans. Since 1999, the involvement of water bugs belonging to the order of the hemiptera has been invoked by Portaels. In 2002, this hypothesis was confirmed by Marsollier et al. for water bugs of the genus Naucoris taken from the region of Daloa in Côte d’Ivoire, where the disease is endemic. In 2008, Portaels also found M. ulcerans in samples taken from the environment (Gerridae) in Ghana. In 2007, studies began in Côte d’Ivoire into the specific diversity, biology, ecology, ethology and role of aquatic heteroptera in the transmission of M. ulcerans to humans. Samples of aquatic heteroptera were collected each month from different aquatic environments in endemic areas of Côte d’Ivoire. The insects were identified by family, genus and occasionally species. Their distribution, population dynamics and ecological distribution in the water points investigated were correlated with human activities. Monospecific batches of water bugs were regularly composed in order to identify the molecular signatures of M. ulcerans using PCR at the bacteriology laboratory of the Institut Pasteur in Côte d’Ivoire and at the bacteriology laboratory of the Groupe d’Etudes des Interactions Hôtes-Pathogènes (Host-Pathogen Study Group) at the University Teaching hospital in Angers, France. Eighteen (18) species belonging to 8 families were identified. After the aquatic insects collected had been identified, 283 monospecific batches were composed and sent to the Institut Pasteur in Côte d’Ivoire (IPCI) for PCR. Twenty four (24) of the 283 batches i.e. 8,5% containing the following, 14 Diplonychus sp, 2 Naucoris sp, 3 Micronecta sp, 2 Ranatra fusca, 2 Anisops sp and 1 Laccotrephes ater, respectively belonging to the families Belostomatidae, Naucoridae, Corixidae, Ranatridae and Nepidae tested positive under PCR. Thirty five (35) samples of saliva were collected from specimens of the genus Diplonychus. Six of the samples (i.e. 17%) tested positive under PCR. Out of 109 other monospecific batches sent to the laboratory in Angers, France, 33 (i.e. 30%) tested positive under PCR. They comprised 11 batches of Diplonychus sp (Belostomatidae), 8 batches of Micronecta sp (Corixidae), 2 batches of Laccocoris sp (Naucoridae), 4 batches of Ranatra fusca (Ranatridae), 3 batches of Anisops sp, 1 lot de Anisops sardea et 1 lot de Enithares sp (Notonectidae), 2 batches of Plea pullula (Pleidae) and 1 batch of de Laccotrephes sp (Nepidae). Clearly, not only is Diplonychus sp the genus most commonly found, it is also that most affected by M. ulcerans. This justifies the decision to breed this genus in the laboratory since 2008, in order to improve our understanding of its biology and ethology and to standardize physical and chemical parameters so as to determine the best conditions for breeding the insect which would provide an animal model for experimental infections. We have now bred six successive generations in the laboratory. To conclude, although some aquatic heteroptera that host M. ulcerans are strictly phytophagous, (e.g. the Corixidae), the great majority of water bugs are carnivorous predators that are hosts and vectors of M. ulcerans. The absence of a reliable key for determining the family, genus and species in central and west Africa has led us to draw up an iconographic catalogue to determine the taxonomy of these insects

Détection des Signatures Moléculaires de Mycobacterium ulcerans chez les Hétéroptères aquatiques Prélevés dans les Rizières Urbaines en Côte d’Ivoire

Certaines villes de Côte d’Ivoire regorgent des rizières en activité jouxtant les habitations. Elles pourraient être des réservoirs et augmenter les risques de propagation de l’agent pathogène de l’ulcère de Buruli. Cette étude se propose de faire l’inventaire des hétéroptères aquatiques (hôtes et vecteurs de Mycobacterium ulerans) présents dans ces rizières. Ils ont été récoltés dans la végétation aquatique des rizières avec un filet épuisette de type Troubleau. Ils ont été identifiés au laboratoire sous une loupe binoculaire, à l’aide d’ouvrages d’identification. Au total, 481 spécimens, répartis en 7 familles (Belostomatidae, Ranatridae, Naucoridae, Nepidae, Corixidae, Notonectidae et Gerridae) ont été récoltés. Les Belostomatidae, avec 65,90% (n=317) ont dominé le peuplement. Les Gerridae (n=3) ont été les plus faible (p<0,001). Sur 24 espèces identifiées, Diplonychus nepoïdes (Belostomatidae) a été la plus abondante dans les rizières (p<0,001). L’indice de Shannon a varié entre 0,74 et 1,87. La richesse spécifique estimée à partir de l’indice de Margalef a donné des valeurs comprises entre 0,82 et 2,39. La composition et la diversité du peuplement ont montré que la diversité dans les rizières était faible ; mais une espèce domine. Mycobacterium ulcerans a été détectée 34 lots monospécifiques appartenant à 6 familles et 12 espèces. Dans toutes les rizières, les Belostomatidae et Diplonychus nepoïdes (Belostomatidae) ont été les plus colonisées avec respectivement 17 et 9 lots positifs. Mycobacterium ulcerans retrouvée chez les hétéroptères des rizières urbaines pourrait assurer sa dissémination vers les habitations aux alentours et augmenter le risque de contamination.   In interior of some cities in Côte d'Ivoire, active rice fields are adjacent to houses. These could be reservoirs and increase the risks of propagation of the Buruli ulcer pathogen. The aim of this study is to make an inventory of aquatic heteropterans; hosts and vectors of Mycobacterium ulerans present in these rice fields. Heteropterans were collected in aquatic vegetation of the rice fields of 8 towns with a Troubleau type net. They were identified in laboratory under a binocular magnifying glass, using identification books. A total of 481 specimens, divided into 7 families (Belostomatidae, Ranatridae, Naucoridae, Nepidae, Corixidae, Notonectidae and Gerridae) were collected. Belostomatidae, with 65.90% (n=317) dominated the stand. The Gerridae family (n=3) was the lowest (p<0.001). Twenty-four (24) species were identified and Diplonychus nepoides (Belostomatidae) was the most abundant in all rice fields (p<0.001). Shannon index ranged from 0.74 to 1.87. Species richness estimated from Margalef index gave values between 0.82 and 2.39. Stand composition and diversity showed that diversity in the rice fields was low; but one specie dominated the stand. Mycobacterium ulcerans was detected in 34 monospecific batches belonging to 6 families and 12 species. In all rice fields, Belostomatidae and Diplonychus nepoides (Belostomatidae) were most colonized with 17 and 9 positive lots, respectively. Mycobacterium ulcerans found in aquatic heteropterans in urban rice fields could ensure its dissemination from the aquatic environment to the surrounding houses and increase the risk of contamination

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Not AvailableThe stock assessment of Brachydeuterus auritus was carried out in the coastal water of Ivory Coast from January to December 2009. Monthly length frequency data were analyzed using FiSAT software and Jones’ Cohort Analysis Model for the estimation of population parameters, total biomass and Maximum Sustainable Yield (MSY). The asymptotic length (L∞) was 25.20 cm, the growth coefficient (K) was 0.58 year-1, and the calculated growth performance index (φ’) was 2.57. The total mortality (Z), the fishing mortality (F) and the natural mortality (M) were 2.01, 0.74 and 1.27 year-1, respectively. The exploitation level (E) was 0.37 while the maximum allowable limit of exploitation (Emax) was 0.85. The biomass was 2507 tons, which provided the MSY of 2079 tons. The recruitment pattern was continuous with two major peaks per year. The exploitation level (E = 0.37) and the fishing mortality approximated the precautionary target reference point (0.64 year−1) and was within the precautionary limit reference point (0.84 year−1), suggesting that the big eye grunt stock is exploited at a low rate.Not Availabl