Wild Birds and Increased Transmission of Highly Pathogenic Avian Influenza (H5N1) among Poultry, Thailand

Juthatip Keawcharoen,Hans Heesterbeek,Thanawat Tiensin,Jan Van Den Broek,Annemarie Bouma,Albert D.M.E Osterhaus

doi:10.3201/eid1706.100880

Abstract

Since the outbreaks of highly pathogenic avian influenza (HPAI) subtype H5N1 virus, wild birds have been suspected of transmitting this virus to poultry. On January 23, 2004, the Ministry of Public Health in Thailand informed the World Health Organization of an avian influenza A (H5N1) outbreak. To determine the epidemiology of this viral infection and its relation to poultry outbreaks in Thailand from 2004 through 2007, we investigated how wild birds play a role in transmission. A total of 24,712 swab samples were collected from migratory and resident wild birds. Reverse transcription PCR showed a 0.7% HPAI (H5N1) prevalence. The highest prevalence was observed during January-February 2004 and March-June 2004, predominantly in central Thailand, which harbors most of the country's poultry flocks. Analysis of the relationship between poultry and wild bird outbreaks was done by using a nonhomogeneous birth and death statistical model. Transmission efficiency among poultry flocks was 1.7 X higher in regions with infected wild birds in the given or preceding month. The joint presence of wild birds and poultry is associated with increased spread among poultry flocks.

Highlights

Since the outbreaks of highly pathogenic avian influenza (HPAI) subtype H5N1 virus, wild birds have been suspected of transmitting this virus to poultry
192 samples were positive for subtype H5N1, resulting in an overall prevalence of 0.78%
Prevalence differed significantly among the group of wild bird species (p

Summary

Introduction

Since the outbreaks of highly pathogenic avian influenza (HPAI) subtype H5N1 virus, wild birds have been suspected of transmitting this virus to poultry. To determine the epidemiology of this viral infection and its relation to poultry outbreaks in Thailand from 2004 through 2007, we investigated how wild birds play a role in transmission. Millions of domestic poultry died from the effects of the disease or from culling efforts to control the spread of the virus [1,2,8,9]. The spread of the HPAI (H5N1) virus from Southeast Asia to Russia, Europe, and Africa was assumed to originate from a virus source at Qinghai Lake, People’s Republic of China [6,10]. In Thailand, 7 waves of HPAI (H5N1) virus outbreaks have occurred since January 2004. Additional insight on the basis of quantitative data into the role of wild birds would be necessary to further develop control measures and surveillance programs

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