Movement and contact patterns of long-distance free-grazing ducks and avian influenza persistence in Vietnam.

Anne Meyer,Thu Van Nhu,Scott Newman,Tung Xuan Dinh,Timothée Vergne,Thuy Thi Thanh Nguyen,Long Thanh Pham,Dirk Udo Pfeiffer

doi:10.1371/journal.pone.0178241

Abstract

Presence of ducks, and in particular of free-grazing ducks, has consistently been shown to be one of the most important risk factors for highly pathogenic avian influenza outbreaks which has compromised poultry production in South-East Asia since the early 2000s and continues to threaten public health, farmers’ livelihood and food security. Although free-grazing duck production has been practised for decades in South-East Asia, there are few published studies describing this production system, which is suspected to play an important role in the maintenance of avian influenza viruses. This study aimed at describing quantitatively the long-distance free-grazing duck production system in South Vietnam, characterising the movement and contact patterns of the duck flocks, and identifying potential associations between farming practices, movement and contact patterns and the circulation of avian influenza viruses. We conducted interviews among stakeholders involved in the free-grazing duck production system (duck farmers, transporters and rice paddy owners) in combination with a virological cross-sectional survey in South Vietnam. Results show that both direct and indirect contacts between free-grazing duck flocks were frequent and diverse. The flocks were transported extensively across district and province boundaries, mainly by boat but also by truck or on foot. A third of the investigated flocks had a positive influenza A virology test, indicating current circulation of avian influenza viruses, but none were positive for H5 subtypes. The age and size of the flock as well as its location at the time of sampling were associated with the risk of influenza A circulation in the flocks. These findings should be considered when developing risk assessment models of influenza virus spread aimed at informing the development of improved biosecurity practices leading to enhanced animal health, sustainable animal production and reliable income for farmers.

Highlights

For over a decade, regular outbreaks of highly pathogenic avian influenza (HPAI) have occurred in poultry throughout South-East Asia, in spite of large-scale vaccination campaigns, as implemented in Vietnam and Indonesia, and stamping-out interventions [1, 2]
All duck flocks had been vaccinated against HPAI subtype H5N1 virus at least once, using either a
The use of the free-grazing duck production system has been on the decline in SouthEast Asia for the last three decades as a result of intensification of agricultural production, increasing cost of labour and increasing pesticide use [34], the Free-grazing duck (FGD) system is still widely

Summary

Introduction

Regular outbreaks of highly pathogenic avian influenza (HPAI) have occurred in poultry throughout South-East Asia, in spite of large-scale vaccination campaigns, as implemented in Vietnam and Indonesia, and stamping-out interventions [1, 2]. The presence of ducks was regularly shown to be strongly associated with the distribution of H5N1 outbreaks in Vietnam [4,5,6] and in the wider region [7,8,9,10,11]. This has been linked with the occurrence of both asymptomatic avian influenza virus infection [12, 13] and excretion [14] in domestic ducks. While formal live bird markets have been prohibited in the Mekong region, it is likely that there is continuing informal live bird trading activity, but it is recognised that this alone cannot explain the continuing circulation of avian influenza in South Vietnam

Objectives

Methods

Results

Discussion

Conclusion