Surveillance of avian influenza viruses in migratory birds in Egypt, 2003-09

Abstract

Migratory (particularly aquatic) birds are the major natural reservoirs for type A influenza viruses. However, their role in transmitting highly pathogenic avian influenza (HPAI) viruses is unclear. Egypt is a "funnel" zone of wild bird migration pathways from Central Asia and Europe to Eastern and Central Africa ending in South Africa. We sought to detect and isolate avian influenza viruses in migratory birds in Egypt. During September 2003-February 2009, the US Naval Medical Research Unit Number 3, Cairo, Egypt, in collaboration with the Egyptian Ministry of Environment, obtained cloacal swabs from 7,894 migratory birds captured or shot by hunters in different geographic areas in Egypt. Samples were processed by real-time reverse transcriptase PCR for detection of the influenza A matrix gene. Positive samples were processed for virus isolation in specific-pathogen-free embryonated eggs and isolates were subtyped by PCR and partial sequencing. Ninety-five species of birds were collected. Predominant species were Green-Winged Teal (Anas carolinensis; 32.0%, n=2,528), Northern Shoveler (Anas clypeata; 21.4%, n=1,686), and Northern Pintail (Anas acuta; 11.1%, n=877). Of the 7,894 samples, 745 (9.4%) were positive for the influenza A matrix gene (mainly from the above predominant species). Thirteen of the 745 (1.7%) were H5-positive by PCR (11 were low-pathogenic avian influenza and two were HPAI H5N1). The prevalences of influenza A was among regions were 10-15%, except in Middle Egypt (4%). Thirty-nine influenza isolates were obtained from PCR-positive samples. Seventeen subtypes of avian influenza viruses (including H5N1 and H7N7) were classified from 39 isolates using PCR and partial sequencing. Only one HPAI H5N1 was isolated in February 2006, from a wild resident Great Egret (Ardea alba). No major die-offs or sick migratory birds were detected during the study. We identified avian influenza virus subtypes not previously reported in Egypt. The HPAI H5N1 isolated or detected indicates that migratory birds may play a role in the dispersal of HPAI virus, but a detailed mechanism of this role needs to be elucidated.