Aquatic invasive species and emerging infectious disease threats: A One Health perspective

An estimated 60-75% of the world's infectious diseases of humans are zoonotic, infecting both humans and other animals. Many are vector-borne, relying on transmission by mosquitoes and biting flies that are aquatic for much of their lifespan. Others rely on aquatic molluscs, fishes, or other aquatic animals for completion of their transmission cycles, and others develop and thrive in diverse freshwater environments outside any host. While such diseases remain firmly endemic in many areas, new outbreaks of infectious diseases associated with freshwater have occurred throughout the world, and many others have spread to new locations. This may involve introduction of aquatic vectors into locations where the disease was previously unknown, as in the recent occurrences of mosquito-transmitted diseases such as West Nile Virus in North America, dengue fever in southern Europe, Chikungunya virus in the Caribbean and South America, and dirofilariasis in Central and Eastern Europe. Such a pattern is also possible with such major human pathogens as Schistosoma blood flukes and food-borne trematodes, through introduction of aquatic host snails from long-established foci in other areas. Alternatively, waterborne pathogens may be introduced directly, leading to disease outbreaks such as the cholera disaster still unfolding in Haiti. Accidental or intentional introduction of pathogens or their aquatic vectors and hosts are among the primary concerns that affect international trade, travel, and global health security. These concerns are compounded by the prospect of warming climate, potentially resulting in primarily tropical diseases encroaching into historically subtropical or temperate regions. Thus, we must be prepared for the possibility of geographic spread of diseases into areas where they have not occurred, or reintroduction into areas where they once occurred but have been eliminated through control measures. For example, North America and Europe are at risk for reintroduction of such major tropical diseases as malaria and yellow fever, and thus must come under increasing scrutiny, starting with surveillance of freshwater systems for both established and potentially invasive vector and host populations. This critical perspective paper briefly reviews selected previous cases in which aquatic invasive species have contributed to infectious disease emergence, re-emergence, or increase, and proposes One Health strategies for integrating human, animal, and environmental monitoring and surveillance to better prepare for or prevent geographic spread of major human health threats associated with aquatic systems.