The Effect of Mycobacterium ulcerans Exotoxin on Host-Seeking and Oviposition Behavior of Aedes aegypti aegypti (L.) (Diptera: Culicidae)

Abstract

Buruli Ulcer (BU), an emerging tropical disease, affects thousands of individuals throughout the world with West Africa being the most devastated area. From 2005-2010 nearly 30,000 cases were reported from this region. This disease is caused by the mycobacterium, Mycobacterium ulcerans, which unlike other species of mycobacterium produces a mycolactone that is an immunosuppressive polyketide-derived macrolide toxin that can diffuse through plasma membranes. This disease has novel clinical symptoms that consist of a painless skin ulcer. While painless, the ulcer has negative effects, such as, bone deformation, and possible secondary infections that can often lead to death. The mode of pathogen is transmission is currently unknown. This study examined if the mycolactone serves as an attractant for host-seeking behavior, as well as oviposition site choice of the yellow fever mosquito Aedes aegypti aegypti (Linnaeus) (Diptera: Culicidae), a potential vector for the pathogen. The responses of adult mosquitoes to a blood-feeder treated with one of three doses (0.05 μg/mL), (0.5 μg/mL), (1.0 μg/mL) of the mycolactone or a control (95% ethanol) were examined. The same doses and control were used to examine the responses of adult mosquitoes to an oviposition substrate as well.

It was determined that mosquitoes were more attracted (29.1%) to the blood-feeder treated with the high dose (1.0 μg/mL) compared to the control. These data indicate that the mycolactone could serve as an attractant of mosquitoes to hosts, which could result in transmission of the pathogen responsible for BU, as well as enhance the transmission of other mosquito-related pathogens such as yellow fever. It was also determined that mosquitoes were more attracted to the control (approximately 30%) compared to the low (0.05 μg/mL) or medium dose (0.5 μg/mL); however there was attraction (approximately 15%) to oviposition sites treated with the high dose. These results indicate a possible repellant effect for mosquitoes to oviposit in sites with the low and middle doses, but could be an attractant in environments with higher concentrations. Like with the attraction assay, a dose dependent response (repellence and attraction) to the mycolactone and oviposition site selection was determined. Future studies to be conducted that would provide greater insight into the role of mycolactone as an attractant would examine additional concentrations to determine the threshold that induces a shift in mosquito behavior. Additional work with the bacteria actively producing the mycolactone in combination with a host would also provide greater insight to any role in attracting potential vectors.