Countermeasures for avian influenza outbreaks among captive avian collections at zoological gardens and aquariums in Japan

Abstract

Background Despite considerable environmental changes over the last 160 years, 1,2 Japan is an important transit country for a wide range of migratory avian species. It is situated on the East Asian Flyway, a principal migratory route connecting Northeast Asia with Southeast Asia. Major branches pass through the Nansei-Shoto Islands, Kyushu, Honshu, and Hokkaido into northeast Russia, and via Kyushu and the Korean Peninsula into eastern China. 3 So far, Japan has escaped the outbreaks of infectious disease that have significantly impacted bird populations in other parts of the world. 1,2,4 During these outbreaks, tens of thousands of birds become sick leading to death in extreme cases. 5 In addition to the changing avian fauna and ecosystems in Japan, a large number of captive birds are kept in over 150 zoological gardens and/or aquariums throughout the country (http://www.jaza. jp/z_map/z_seek00.html). It is therefore likely that these captive birds would also be affected if a disease outbreak occurs. Although there are numerous infectious diseases that affect both free-ranging and captive avian species, this review contains a brief overview of the situation regarding avian influenza (AI) in Japan, as well as suggestions for the implementation of countermeasures for the prevention and management of potential AI outbreaks. First described in the late 19th century, AI is a highly contagious viral disease affecting birds, especially poultry, worldwide. AI viruses are generally isolated from wild birds, particularly migratory waterfowl belonging to the orders Anseriformes and Charadriiformes, which are considered natural reservoirs of the viruses. 5 However, since 2004, highly pathogenic (HP) AI has been classified as a typical and re-emerging infectious disease of avian species by the Japanese government and the science community responsible for animal health. 1-4 Therefore, the current review provides an overview of recent changes in AI and its causative agents in both free-ranging and captive avian species worldwide, including Japan, and provides potential strategies to manage epidemic risk in facilities with captive birds or zoological collections. General characteristics of AI and its causative agents AI is caused by influenza type A viruses, consisting of negativesense, single-stranded RNA viruses belonging to the family Orthomyxoviridae. Influenza A virus genomes contain eight segments encoding 11 proteins. Segments one to six encode PB2, PB1, PB1-F2, PA, hemagglutinin (HA), nucleoprotein NP, and neuraminidase (NA) in decreasing order in size. The seventh and eighth segments encode M1, M2, NS1, and NS2. The viruses are further categorized into various subtypes based on the combination of HA (H1-H16) and NA (N1-N9) antigens. Various influenza A virus subtypes occur in wild birds, especially aquatic species, and may also infect mammals such as humans and pigs. 1,3,6 AI viruses are globally distributed and are probably prevalent in area with higher host population. 3 AI or its causative viruses have been reporte...