NOMADIC MOVEMENTS AND INFECTIOUS DISEASE TRANSMISSION: TACKLING HIGHLY PATHOGENIC AVIAN INFLUENZA VIRUSES ALONG THE FREE-GRAZING DUCK MOVEMENT NETWORK IN VIETNAM

摘要

The presence of free-grazing ducks (FGD) has consistently been shown to be associated with highly pathogenic avian influenza (HPAI) outbreaks in South-East Asia. To provide a quantitative evaluation of their role and generate control recommendations,various stakeholders involved in the Vietnamese FGD production system were interviewed and a risk assessment model of HPAI transmission developed. These activities highlighted that duck flocks are transported extensively across district and province boundaries with almost one third of the grazing sites being located outside the province of residence. The mean probability of HPAI transmission between an infected flock to at least one susceptible flock during a grazing cycle was estimated at 0.28 (95% CI= 0.17 - 0.52). Transmission via indirect contacts during transport was identified as the most likely transmission route. Increasing vaccination coverage or increasing frequency of transport vehicle disinfection were identified as the two most effectivestrategies for decreasing the transmission risk.