The influence of urban livestock-keeping on the epidemiology of mosquito-borne zoonotic flaviviruses in Hanoi city of Vietnam

In rapid urbanizing cities, the high density of livestock populations in close vicinity to humans, and high mosquito vector abundance have provided suitable conditions for transmission of mosquito-borne zoonotic flaviviruses, that cause several million cases of human disease annually. This thesis explores the urban livestock-keeping in Hanoi and its potential influence on the epidemiology of flavivirus infections. Four major components were investigated: livestock development of the city, knowledge and practices of local people on mosquito-borne diseases (MBDs), mosquito vector abundance, and risk factors for flavivirus exposure in animals. The analyses of the livestock development policy, animal data and key informant interviews showed that the livestock production system of Hanoi had increased in line with the governmental policy during 2014 to 2018. However, some major challenges were identified such as the high proportion of small-scale livestock farms, animal diseases, and a slow progress of translocation of livestock farms out of the urban areas. A cross-sectional study was conducted in 513 households in six districts of Hanoi (two urban, two peripheral, and two peri-urban). Knowledge and practices were evaluated; mosquitoes and larvae inside and outside the houses were collected and identified; blood samples of pigs and dogs were tested by a West Nile virus competitive enzyme-linked immunosorbent assay (cELISA), a kit that allowed for detection of antibodies against several flaviviruses of different animal species. JEV-specific antibodies were confirmed by plaque reduction neutralization test (PRNT). Logistic regression models using seropositivity of households as the outcome were built to identify significant risk factors. A low level of knowledge and preventive practices against zoonotic MBDs in community was indicated in the study. Among 12,861 adult mosquitoes and 2,427 larvae collected, Culex mosquitoes were the most abundant (93.01%), followed by Anopheles (3.82%), Mansonia (1.21%), Armigeres (1.18%) and Aedes mosquitoes (0.78%). In contrast, Aedes genus larvae were prominent at 87.02%, followed by Culex spp. (12.2%). There was a positive association between pig-keeping and Culex mosquitoes (p<0.001). In total, 475 dogs and 636 pigs were tested by a cELISA. The overall flavivirus seroprevalences in dogs and pigs were 70.7% and 88.5%, respectively. The PRNT results for a subset of 50 dog sera (34 positive, 6 doubtful and 10 negative samples by cELISA), and 50 pig sera (26 positive, 6 doubtful and 18 negative samples by cELISA) showed a lower proportion of JEV-specific antibodies (28 positives for dog samples, and 13 positives for pig samples). In conclusion, this thesis shows associations between livestock-keeping and risks of mosquito-borne zoonotic flavivirus infections to humans in Hanoi.Formas, grant number 2016-0036