Avian influenza in suphanburi province, Thailand: assessment of transmission dynamics and interventions in the local poultry sector.

Abstract

This dissertation provides a review of avian influenza, with specific regard to highly pathogenic avian influenza (HPAI) H5N1, a description of the Thai poultry system and the country's experiences with influenza outbreaks, and discussions of both poultry and human exposure to and infection with HPAI H5N1. In addition, four research manuscripts provide insight into the relationship between influenza A, including HPAI H5N1, and poultry and human health in rural Suphanburi Province, Thailand. A major goal of this work was to learn more about the management of free-grazing duck (FGD) flocks in Thailand and their role in avian influenza virus maintenance and transmission. FGD have been associated with highly pathogenic avian influenza (HPAI) H5N1 outbreaks and may be a viral reservoir. In July-August 2010, the influenza exposure of Thai FGD and risk factors thereof were assessed. Sera from over 6000 FGDs were analyzed to detect antibodies to influenza A nucleoprotein (NP) and hemagglutinin H5 protein. Eighty-five percent were seropositive for influenza A. Of the NP-seropositive sera tested with H5 assays 39% were H5 ELISA-positive and 4% suspect. Twelve per cent of H5 ELISA-positive or suspect ducks had H5 titers ≥1:20. Risk factors for influenza A seropositivity include older age, poultry contact, flock visitors and older purchase age. Flocks had H5 virus exposure as recently as March 2010, but the last HPAI H5N1 outbreak in Thailand was in 2008, highlighting a need for FGD surveillance. This dissertation also includes an investigation of the seroprevalence of and risk factors for antibodies to HPAI H5N1 in poultry owners. Seroprevalence was 6.3%, and single persons and those working with farmed chickens were at increased risk of seropositivity. Poultry owners reported limited use of personal protective equipment during all activities and inconsistent hand washing practices after carrying poultry and gathering eggs. Lastly, this dissertation includes the description and results of an agent-based model (ABM) of the local Thai poultry sector which was built to simulate contacts among FGD flocks and persons that own poultry and conduct poultry-related activities. Using this model, opportunities for the transmission and control of HPAI H5N1 in this setting were identified.