Mosquitoes Know No Borders: Surveillance of Potential Introduction of Aedes Species in Southern Québec, Canada

Current climatic conditions limit the distribution of Aedes (Stegomyia) albopictus (Skuse, Diptera: Culicidae) in the north, but predictive climate models suggest this species could establish itself in southern Canada by 2040. A vector of chikungunya, dengue, yellow fever, Zika and West Nile viruses, the Ae. Albopictus has been detected in Windsor, Ontario since 2016. Given the potential public health implications, and knowing that Aedes spp. can easily be introduced by ground transportation, this study aimed to determine if specimens could be detected, using an adequate methodology, in southern Québec. Mosquitoes were sampled in 2016 and 2017 along the main roads connecting Canada and the U.S., using Biogent traps (Sentinel-2, Gravide Aedes traps) and ovitraps. Overall, 24 mosquito spp. were captured, excluding Ae. Albopictus, but detecting one Aedes (Stegomyia) aegypti (Skuse) specimen (laid eggs). The most frequent species among captured adults were Ochlerotatus triseriatus, Culex pipiens complex, and Ochlerotatus japonicus (31.0%, 26.0%, and 17.3%, respectively). The present study adds to the increasing number of studies reporting on the range expansions of these mosquito species, and suggests that ongoing monitoring, using multiple capture techniques targeting a wide range of species, may provide useful information to public health with respect to the growing risk of emerging mosquito-borne diseases in southern Canada.

Interaction of Mycobacterium ulcerans with Mosquito Species: Implications for Transmission and Trophic Relationships

ABSTRACT Mycobacterium ulcerans is the causative agent of Buruli ulcer, a severe necrotizing skin disease that causes significant morbidity in Africa and Australia. Person-to-person transmission of Buruli ulcer is rare. Throughout Africa and Australia infection is associated with residence near slow-moving or stagnant water bodies. Although M. ulcerans DNA has been detected in over 30 taxa of invertebrates, fish, water filtrate, and plant materials and one environmental isolate cultured from a water strider (Gerridae), the invertebrate taxa identified are not adapted to feed on humans, and the mode of transmission for Buruli ulcer remains an enigma. Recent epidemiological reports from Australia describing the presence of M. ulcerans DNA in adult mosquitoes have led to the hypothesis that mosquitoes play an important role in the transmission of M. ulcerans. In this study we have investigated the potential of mosquitoes to serve as biological or mechanical vectors or as environmental reservoirs for M. ulcerans. Here we show that Aedes aegypti, A. albopictus, Ochlerotatus triseriatus, and Culex restuans larvae readily ingest wild-type M. ulcerans, isogenic toxin-negative mutants, and Mycobacterium marinum isolates and remain infected throughout larval development. However, the infections are not carried over into the pupae or adult mosquitoes, suggesting an unlikely role for mosquitoes as biological vectors. By following M. ulcerans through a food chain consisting of primary (mosquito larvae), secondary (predatory mosquito larva from Toxorhynchites rutilus septentrionalis), and tertiary (Belostoma species) consumers, we have shown that M. ulcerans can be productively maintained in an aquatic food web.