Animal sentinel surveillance: evaluating domestic dogs as sentinels for zoonotic pathogen surveillance
The capacity of zoonotic pathogens to infect multiple hosts creates surveillance challenges but also provides opportunities to gather data from animal species that can be used to understand risks to human health. This thesis presents a conceptual and practical assessment of the utility of domestic dog serosurveillance for the detection and surveillance of two pathogens, influenza A and Leptospira spp. The first chapter gives a theoretical framework that can be used to explore the attributes of animal sentinels and assess their utility in different contexts. In subsequent chapters, this framework is applied in a practical assessment of the utility of a domestic dog serosurveillance approach for the detection and surveillance influenza A and Leptospira spp. at two sites in Africa. Two cross-sectional surveys of the avian and mammal populations at a site in Northern Cameroon were conducted in early 2006 to determine if H5N1 influenza A viruses had circulated in this area and in which species that presence could be detected. Serological and molecular evidence of extensive H5 virus circulation in the domestic duck population was identified. 47% of domestic ducks at the Maga site were cELISA positive for anti-influenza A antibodies and 20% were HI test positive against an H5N1 antigen. There was also evidence of exposure to H5 subtype viruses in the local dog and pig populations. At the Kibera site in Nairobi, a cohort study was established to carry out surveillance of influenza A and Leptospira spp. in the domestic dog population and cross-sectional surveys of the domestic poultry and rodent populations were completed. There was no indication of influenza A circulation in any of the animal species surveyed, indicating low risk of zoonotic influenza A infection in the human population of Kibera. In contrast, there was extensive molecular and serological evidence of the presence of Leptospira spp. in both the rodent and dog populations. 18% of 236 trapped rodents were PCR positive for kidney carriage of pathogenic leptospires and the estimated seroprevalence of anti- Leptospira antibodies in the dog population ranged from 5-36% during the course of the study, indicating high potential risk of leptospirosis infection in the human population. The results indicate that dog serosurveillance can be used as useful tool for the determination of broad-scale patterns of pathogen presence and relative levels of population exposure. However, there are limitations of the data that can be gathered from animal sentinels and the complexities introduced particularly by incomplete understanding of diagnostic test performance must be recognized. Animal sentinel surveillance may be of most use for addressing fundamental questions of what pathogens are present where. In the developing world particularly where disease burden data are still lacking, dog sentinel serosurveillance can provide essential baseline data that can be used to target future research and resource allocation.