An Integrated Approach To Buruli Ulcer Transmission Studies: From Aquatic Environments To Human Infection

Buruli ulcer (BU) is a debilitating skin infection usually of impoverished tropical rural populations. BU is caused by Mycobacterium ulcerans (MU), a pathogen described as a non-tuberculous mycobacteria (NTM). The exact mode of transmission of BU is not known and involvement of insect vectors including mosquitoes, animal and small mammal reservoirs and aerosols in transmission and dispersal has been proposed. A holistic approach to studies that involve NTM is proposed especially in transmission and control studies. This study related human MU infections to MU types in identified risk areas and establishing sources of human infections. Water body type preferences of members of the two most implicated insect families in BU transmission, Family Belostomatidae (Hemiptera: Heteroptera) and Family Naucoridae (Hemiptera: Heteroptera) collected from water bodies in Ghana and Cote d’Ivoire were also related to their probability of being involved in transmission of BU. Four BU endemic communities (Bepotenten, Sukuumu, Monia-Gyaman and Wromanso) in the Amansie Central District of the Ashanti Region of Ghana were selected for the study. Two hundred and twenty-four (224) questionnaires administered proportionally to population were used to elicit responses to water use and areas of contact, BU knowledge, animal contact and infection status. Ground truthing of the four communities and the capturing of geographical information allowed the reconciliation of questionnaire water contact points and the subsequent mapping to reveal all surface water contact points. M. ulcerans from environmental sources was detected using 16S rRNA and then IS2404 detections. M. ulcerans genetic material from both human BU cases and identified environmental sources were VNTR (viable number tandem repeats) typed at four loci (VNTR targets: MIRU1, Locus 6, ST1 and Locus 19. Swimming and bathing (p=0.04) in risk environments and the capture of squirrels (p=0.04) were associated with an increased in the risk of acquiring BU in the study communities (OR= 3.28 and OR=5.85 respectively). Rigorous activity in infected water was found to increase the risk of infection laying credence on a direct trauma infection route for M. ulcerans. VNTR typing of MU from human BU disease and environmental samples revealed localized infection with inhabitants mostly being infected from community associated water bodies. Four main VNTR types were detected in human disease MU based on number of copies of four loci: MIRU1, Locus 6, ST1 and Locus 19. These were ‘W’ (1,1,2,1), ‘X’ (1.1.2.2), ‘Y’ (1,2,2,1) and ‘Z’ (1,2,2,2) in the copy number order MIRU1, Locus 6, ST1, Locus 19. The ‘Y’ VNTR type was common to all communities being detected in human as well as environmental samples and is therefore the profile causing the most infections in the study communities. A total of 125 and 321 individual Naucoridae (Hemiptera: Heteroptera) and Belostomatidae (Hemiptera: Heteroptera) respectively were classified to at least genus level. Eight species of the Naucoridae were identified; Ctenopocoris africanus (Leach, 1815), Aneorocoris insolitus (Montandon, 1897), Laccocoris limicola (Stal, 1855), Laccocoris spurcus congoensis (Poisson, 1949), Neomacrocoris bondelaufa (Sites, 2015), Neomacrocoris vuga (Sites, 2015), Naucoris obscuratus (Montandon, 1913) and Neomacrocoris usambaricus (Montandon, 1913). Differences in habitat preference of the Naucoridae were observed. Naucoris spp and Laccocoris spp showed the least preference for lotic water bodies (p<0.05). Four genera of the family Belostomatidae; Abedus, Diplonychus, Lethocerus and Benacus, were identified in collections from 82 water bodies in Ghana and 7 water bodies in Cote d’Ivoire. Abedus spp were the most abundant and most widely distributed. Belostomatidae showed no preference to type of water flow (p=0.2068). The integrated approach of the study offered complementary information, observations and deductions which together enabled verifiable conclusions to be drawn on the transmission of the environmental mycobacterium. The use of few communities facilitated a more concentrated search for risk areas and their link to BU infections in the study communities. A study involving a higher number of communities in a similar geographical range is recommended. In insect transmission studies, individual species competence should be considered and generalizations minimized as species preferences to habitat are important especially in studies involving NTMs.

Source: KNUST