There has been an outbreak of highly pathogenic Avian Influenza H7N7 at a free-range egg farm, at Lethbridge, near Geelong. Agriculture Victoria is responding to the incident. Avian Influenza is a serious disease of poultry, and can cause a high mortality rate in production birds. This disease was reported when a drop in egg production was observed, and high bird mortality rates occurred in one of the poultry sheds. Samples were submitted to Agriculture Victoria on 29 July 2020 where they tested positive for Avian Influenza H7. The CSIRO’s Australian Centre for Disease Preparedness confirmed the disease as highly pathogenic Avian Influenza H7N7 on 31 July 2020.
How is Agriculture Victoria responding. The affected property has been quarantined and depopulated. Movement controls are in place to stop any birds, eggs and equipment from leaving the premises. A Restricted Area of about 10 k radius is in place around the property. Agriculture Victoria will be in contact with property owners in the vicinity of the infected property and will conduct further surveillance and sampling of domestic birds in this area. A larger Control Area across a wider area, about 80 wide extending up to Ballarat, has also been created. Movement within both the Restricted and Control areas depends on the risk. Australia has previously had a small number of outbreaks of H7 Avian Influenza. These were all quickly and successfully eradicated.
Human Health. The H7N7 virus is not a risk to the public as it rarely affects humans unless there is direct and close contact with sick birds.
About Avian Influenza. Avian Influenza (AI) is a highly infectious viral disease of birds which occurs worldwide.. All Avian Influenza viruses are members of the family Orthomyxoviridae. The influenza viruses of this family are categorised into types A, B, C or D, and only influenza A viruses have been isolated from avian species. Influenza A viruses are further divided into subtypes determined by haemagglutinin (H) and neuraminidase (N) antigens. At present, 18 H subtypes and 11 N subtypes have been identified. Each virus has one of each subtype in any combination. There are many combinations of subtypes (strains) of avian influenza virus that cause infections of different severity. These range from low pathogenic or mild strains (causing ‘low pathogenicity avian influenza or LPAI), to highly pathogenic strains that are associated with severe disease and high mortality in poultry (highly pathogenic avian influenza or HPAI). H5 and H7 strains can be highly pathogenic. Chickens, ducks, geese, turkeys, guinea fowl, quail, pheasants and ostriches are included in the more than 140 species that are susceptible to avian influenza. AI virus is carried by wild birds, particularly waterfowl and shorebirds, around the world; for the most part without causing any apparent clinical disease. Wild ducks in particular can carry the virus and can then contaminate food and water supplies. Occasionally, when exposure to wild birds occurs, AI can infect domestic birds and spread rapidly. Migratory birds, predominantly shore birds and waders from nearby countries in South East Asia, can pose a risk if they harbour avian influenza infection and then mingle with, and transmit this infection to waterfowl that are nomadic within Australia. These nomadic birds can then mingle with and spread the infection to domestic birds such as poultry. It is not unusual for avian influenza virus to be detected in wild birds in Australia. Avian influenza can also spread by the movement of eggs, birds, people, vehicles and equipment between farms, and by clothing, footwear, aerosols, water, feed, litter, biting insects and vermin. There is currently no effective treatment available for birds once clinical signs of avian influenza appear. Vaccines are available for certain subtypes of the AI virus, which may protect poultry from clinical signs of disease if they subsequently become infected. However, routine vaccination for avian influenza is not permitted in Australia. Pigeons and AI. Pigeons are not particularly susceptible to AI. They can however become transiently infected with the virus and transmit the virus during this time. Infected pigeons usually display either mild or no symptoms . Birds with symptoms are usually quiet, fluffed, less active ,have a reduced food intake and show a variety of symptoms associated with respiratory distress including coughing, sneezing and a noisy respiration. Pigeons clear the virus relatively quickly and a long term carrier state does not occur. The significance for pigeon fanciers is that because pigeons can transmit the virus, pigeon movement can be restricted. In the past , both in Australia and overseas, restrictions on pigeons have ranged from totally depopulating lofts in the Restricted Area, through to not allowing the exercise of pigeons in the Controlled Area and prohibiting the release of pigeons in races where they would be expected to fly over quarantined areas. It is too early to say what will happen in this current outbreak. Decisions will be made depending on how effectively the outbreak can be controlled. As for now, pigeon fanciers should just monitor the situation. Further information can be obtained on the Agriculture Victoria website. Dr Colin Walker