APPLICATION OF BIOLOGICAL AND MOLECULAR TECHNIQUES TO THE DIAGNOSIS AND CONTROL OF AVIAN INFLUENZA AND OTHER EMERGING POULTRY PATHOGENS
Location: Exotic and Emerging Avian Viral Diseases Research Unit
Title: Epidemiology of HPAI in wild birds in Mongolia
Submitted to: Wildlife Disease Association Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: May 28, 2009
Publication Date: August 2, 2009
Citation: Gilbert, M., Joly, D.O., Karesh, W.B., Brown, J.D., Stallknecht, D.E., Spackman, E., Swayne, D.E., Cardona, C. 2009. Epidemiology of HPAI in wild birds in Mongolia [abstract]. Abstracts of the Wildlife Disease Association Annual Meeting, August 2-6, 2009, Vancouver, British Columbia, Canada. p. 61.
INTRODUCTION. Since its emergence in 1997 and subsequent re-emergence in 2003, a highly pathogenic strain of avian influenza (HPAI) virus (AIV) subtype H5N1 has affected humans, domestic poultry, and wildlife across Eurasia and Africa. Prior to 2005, outbreaks in wild birds were sporadic and thought to relate to spillover from infected domestic poultry. The situation changed dramatically in April 2005, with the onset of an outbreak of HPAI H5N1 in wild migratory water birds at Qinghai Lake in northern China. We conducted sampling in Mongolia to test the hypotheses that a) wild birds could move HPAI H5N1 long distances, and b) HPAI H5N1 can become endemic in wild bird populations. Mongolia was ideal as there are very few domestic poultry in that region, thus the presence of HPAI could only be explained by introduction by migratory birds during their migration.
MATERIALS AND METHODS. Birds were captured using species appropriate methods. Tracheal, cloacal and/or oropharangeal swabs were collected and stored in viral transport media. Faecal samples were collected opportunistically in areas with single species. Samples were frozen in the field using liquid nitrogen either immediately post collection or within six hours. Total RNA was extracted with a procedure optimized for cloacal swab samples. The RNA was screened for AIV by real-time RT-PCR (rRT-PCR) using the USDA standard. All rRT-PCR positive samples were processed for virus isolation in embryonated chicken eggs and were tested for H5 subtype virus by the USDA H5 rRT-PCR test.
RESULTS. Over a three year study period (2006-2008), faecal, oropharyngeal, and cloacal samples were obtained from live birds of species across geographically isolated sites. In 2005, a die-off of birds (n = 116, 9 species) was reported at Erhel Lake, and during a subsequent investigation we were able to isolate HPAI H5N1 from one of four carcasses suitable for necropsy (a whooper swan). In addition the Mongolian government reported isolates from three whooper swans and one bar-headed goose. No further isolates of HPAI H5N1 were detected.
DISCUSSION. The isolation of H5N1 in wild birds in an area where there are no domestic birds, strongly suggests that at least one species of migratory bird is able of carrying the virus over long distances and introducing it to new waterfowl populations. We note that this species is as yet unidentified. Aside from one isolation of HPAI H5N1 by the Mongolian government in the spring of 2006, there was no further evidence the presence of the virus in Mongolian wild birds, suggesting that the virus did not become endemic in the Eurasian flyway.