Avian Influenza Viruses, Australia | CDC EID

EID Journal Home > Volume 16, Number 12–December 2010
Volume 16, Number 12–December 2010
Research
Surveillance and Analysis of Avian Influenza Viruses, Australia

Philip M. Hansbro, Comments to Author Simone Warner, John P. Tracey, K. Edla Arzey, Paul Selleck, Kim O'Riley, Emma L. Beckett, Chris Bunn, Peter D. Kirkland, Dhanasekaran Vijaykrishna, Bjorn Olsen, and Aeron C. Hurt
Author affiliations: The University of Newcastle, Newcastle, New South Wales, Australia (P.M. Hansbro, E.L. Beckett); Department of Primary Industries, Attwood, Victoria, Australia (S. Warner, K. O'Riley); Orange Agricultural Institute, Orange, New South Wales, Australia (J.P. Tracey); Elizabeth Macarthur Agriculture Institute, Menangle, New South Wales, Australia (K.E. Arzey, P.D. Kirkland); Australian Animal Health Laboratories, Geelong, Victoria, Australia (P. Selleck); Department of Agriculture, Fisheries and Forestry, Canberra, Australian Capital Territory, Australia (C. Bunn); Duke-NUS Graduate Medical School, Singapore (D. Vijaykrishna); Kalmar University, Kalmar, Sweden (B. Olsen); Uppsala University, Uppsala, Sweden (B. Olsen); and World Health Organization Collaborating Centre for Reference and Research on Influenza, Melbourne, Victoria, Australia (A.C. Hurt)

Suggested citation for this article

Abstract
We investigated carriage of avian influenza viruses by wild birds in Australia, 2005–2008, to assess the risks to poultry industries and human health. We collected 21,858 (7,357 cloacal, 14,501 fecal) samples and detected 300 viruses, representing a detection rate of ≈1.4%. Rates were highest in autumn (March–May) and differed substantially between bird types, areas, and years. We typed 107 avian influenza viruses and identified 19 H5, 8 H7, and 16 H9 (40% of typed viruses). All were of low pathogenicity. These viruses formed clearly different phylogenetic clades to lineages from Eurasia or North America, suggesting the potential existence of Australian lineages. H7 viruses were similar to highly pathogenic H7 strains that caused outbreaks in poultry in Australia. Several periods of increased detection rates (numbers or subtypes of viruses) were identified. This study demonstrates the need for ongoing surveillance to detect emerging pathogenic strains and facilitate prevention of outbreaks.

Shorebirds (Charadriiformes) and wild waterfowl (Anseriformes) represent the major natural reservoirs of avian influenza viruses (AIVs). These birds can carry all 16 hemagglutinin (HA) and 9 neuraminidase (NA) subtypes (1); the viruses typically cause asymptomatic infections in these hosts. Studies in Europe and North America demonstrated the following: AIV carriage is highest in autumn but may also be high in spring; prevalence among shorebirds and ducks is increased during their northward and southward migrations, respectively; and distribution, prevalence, and subtypes involved vary from year to year (2,3). Interspecies transmission of AIV in several species of wild birds has been documented; however, the most frequent adaptation of these viruses occurs in domestic gallinaceous poultry.

The respiratory tract of poultry and gastrointestinal tract of waterfowl are replication sites for AIVs, and poultry are incubators for the progression of low-pathogenicity avian influenza (LPAI) virus into highly pathogenic avian influenza (HPAI) virus (4–6), usually through the acquisition of polybasic amino acids at the HA cleavage site. HPAI, particularly HPAI (H5N1), may induce up to 100% deaths in poultry and cause substantial economic losses (4,7–9). Strains that are highly pathogenic in gallinaceous species may cause a range of clinical signs in other avian species, from mild illness to highly contagious and fatal disease. H5 and H7 AIVs have the propensity to become HPAI and thus are a significant risk to the poultry industry. These subtypes and H9 have also caused disease and death in humans. Subtype H5N1 first caused outbreaks in wild migratory waterfowl in the People's Republic of China in 2002 and in domestic poultry in Hong Kong Special Administrative Region, China, in 2003 (10). The World Health Organization has since confirmed 433 human cases of avian influenza (H5N1) with 262 deaths (11).

AIVs may be transported by infected migratory birds (12–14). Shorebirds and waterfowl usually survive infection, and transmission by migratory waterfowl over long distances within Asia and between continents has been documented (15–17). Nevertheless, the role of migratory birds in the distribution and transmission of AIVs remains controversial. Managing the potential threat of transport of AIVs by wild birds requires appropriate surveillance programs that assess the occurrence, subtypes, and pathogenicity of isolates that the birds carry.

Australia is isolated by sea, and shorebirds make up the majority of long-distance migratory birds that visit the continent (3 million/year [12]). These birds breed in Siberia (May–July) and stop off throughout Asia (April–May, July–September) in areas where HPAI (H5N1) epizootics have recently occurred (e.g., Vietnam, Thailand, Hong Kong, China, Indonesia) (18). Most arrive in Australia in spring (August–September) and depart in autumn (March). Shorebirds are known to carry a variety of AIVs, including subtype H5N1 (1). Wild waterfowl, such as ducks, geese and swans are common in Australia. However, they do not migrate out of Australia in large numbers, although they do undertake intracontinental movements and occupy the same habitats as migratory shorebirds. Collectively, these factors provide an environment that allows the assessment of the import of AIVs by migratory birds and transmission to, and distribution by, local waterfowl.

Until recently, only small and historical studies of AIVs have been undertaken in Australia (14,19–22). No outbreaks of HPAI H5 viruses have been identified, despite the close proximity of Indonesia, where AIV (H5N1) is endemic and outbreaks frequently occur. Five outbreaks of HPAI have occurred in Australia; all outbreaks were caused by H7 viruses. In all cases of disease, transmission of LPAI H7 from wild birds and subsequent mutation to HPAI after serial passage in chickens was considered the probable source (13,23,24). Nevertheless, the source of infection in wild birds has not been identified. Therefore, surveillance for AIVs is needed in Australia in localities where large numbers of migratory shorebirds and waterfowl occur in close proximity to poultry operations (13). We examined the occurrence and subtypes of AIVs carried by migratory shorebirds and waterfowl in southeast Australia over a 4-year period.

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Suggested Citation for this Article

Hansbro PM, Warner S, Tracey JP, Arzey KE, Selleck P, O'Riley K, et al. Surveillance and analysis of avian influenza viruses, Australia. Emerg Infect Dis [serial on the Internet]. 2010 Dec [date cited].
http://www.cdc.gov/EID/content/16/12/1896.htm

DOI: 10.3201/eid1612.100776

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Philip M. Hansbro, Research Centre for Asthma and Respiratory Disease and Hunter Medical Research Institute, David Maddison Clinical Sciences Building, Cnr King and Watt Streets, Newcastle, NSW 2300, Australia; email: philip.hansbro@newcastle.edu.au