Outbreak preparedness & control
Avian Influenza (bird flu) H5N1
PPHSN advice on highly pathogenic avian influenza (HPAI) in Southeast Asia - from the animal health perspective
15 May 2007
The web link below gives a comprehensive overview from FAO of the avian influenza situation in Southeast Asia – mainly from a veterinary perspective.
http://www.oie.int (World Organisation for Animal Health )
http://www.who.int/ (World Health Organisation)
| Specific information for the Pacific region |
1. Importation of poultry, poultry products and other avian species
There is increasing evidence that the widespread occurrence of avian influenza (H5N1) across Asia, Europe and Africa since 2003 has primarily been due to the inability of border quarantine agencies to prevent the introduction of live birds and poultry meat from infected countries. To prevent the introduction of avian influenza to Pacific Island poultry and wild bird populations, quarantine agencies in the region must remain diligent to ensure that poultry or poultry products are not imported from infected countries. Commodities that may harbour infective virus include meat, eggs (for consumption or hatching), feathers, poultry manure and live birds (including ornamental live birds). Properly cooked poultry products do not present a risk of virus transmission. The occurrence of H5N1 infection in humans is rare and with few exceptions has been associated with close contact with infected poultry. Accordingly, quarantine restrictions on humans are inappropriate except where influenza-like signs are present and the patient has a recent history of close contact with poultry in a country where H5N1 is present.
2. Migratory birds in the Pacific region
Migratory waterfowl (primarily ducks) are generally considered to be the main reservoir host population for influenza A viruses. The majority of studies of avian influenza in waterfowl have been conducted in North America and Europe and although a number of key migratory routes (flyways) are recognised, it is unclear to what extent waterfowl populations in the northern hemisphere interact with those in the southern hemisphere. An East Asia/Australasian flyway is recognised and is most relevant to considerations of the potential introduction of avian influenza viruses into the Pacific Island region by migratory birds. Birds that use the East Asia/Australasian flyway are predominantly shorebird/wader species (e.g. sandpipers, curlews, knots and plovers). There is little data available on the potential for such species to carry and transmit highly pathogenic avian influenza viruses.
As a precautionary biosecurity measure, agriculture officials should advise poultry owners not to allow poultry to mix with wild bird populations or to use water contaminated by droppings from wild birds as drinking water for poultry.
3. Highly Pathogenic Avian Influenza (Bird Flu)
HPAI is a poultry disease; the occurrence of human infection is rare and is generally associated with close contact with infected poultry. The structure of the poultry industry in the Pacific is such that there are very few places where the density of farmed poultry could lead to conditions resembling those in Southeast Asia. Should an outbreak of the disease occur on a Pacific Island, it would most likely be recognised in the chicken population, and first indications might be a large number of dead chickens with no evident clinical signs prior to death (see FAO web pages for further details of these clinical signs).
4. Surveillance and monitoring
Passive disease surveillance, where poultry owners/managers report the occurrence of unusual disease and deaths to agricultural personnel, is generally considered to be the most effective method of early detection of HPAI, particularly in intensive commercial poultry enterprises. As its name suggests, HPAI is ‘highly pathogenic’ and will typically cause 50–100% mortality in a chicken shed; it should therefore be readily detected although in the very early stages, clinical signs in individual birds may be indicative rather than diagnostic. Diagnosis should be confirmed via the application of serology and virus detection techniques in affected and in-contact birds. Early detection may be more difficult in villages where poultry are maintained under free-range conditions and where sick birds and carcases of dead birds may be ‘scavenged’ by other animals in the village community (e.g. cats, dogs, pigs). Active public awareness and extension activities should be directed towards communities where there are significant numbers of poultry to facilitate the early detection and reporting of unusual disease occurrences.
5. Investigation of suspicious poultry deaths
Suspicious poultry deaths should be investigated and, if no reasonable cause is found, specimens collected and submitted for laboratory investigation. Rapid diagnostic tests (RDT) are available and these may enable early identification of the presence of avian influenza viruses. However, many RDT kits have been developed for use in humans and may be unsuitable for use in avian species. The reference laboratory for HPAI in the Pacific region is the Australian Animal Health Laboratory (AAHL) in Geelong, Victoria, Australia (all details are on the OIE web site). Any such investigation should be a well planned and coordinated event, requiring import permits and an IATA-compliant transport system. Any SPC member country requiring assistance with such an investigation should contact SPC's Regional Animal Health Service (contact details below).
6. Poultry Vaccination
All Pacific Island countries and territories are currently free from HPAI without vaccination. This is the most desirable status to have, as vaccination alone cannot fully protect a country’s poultry population. Generally, vaccination against AI is discouraged as it can interfere with efforts to eradicate the disease through a stamping-out policy by ‘masking’ the presence of disease. However, vaccination can be an effective tool for the control of HPAI under certain circumstances as it can significantly decrease the amount of virus being shed. All current OIE*-approved vaccines for HPAI are inactivated (killed virus) vaccines, usually with an oil adjuvant, which must be administered individually to birds on two occasions at least 28 days apart. Research is continuing into the development of genetically engineered vaccines that would deliver critical parts of the H5N1 virus genome – e.g. the haemagglutinin antigen – via a live virus vector. In contrast to inactivated vaccines, this type of vaccine potentially has the advantage of only needing to be administered once.
Vaccination, even with OIE-approved vaccines may take up to 3 weeks to confer immunity to vaccinated birds and may not fully prevent birds from becoming infected or excreting virus, although vaccinated birds rarely become sick. The vaccines are more suitable for use with chicken parent stock and layer birds, and less so for meat birds (broilers) as the life cycle of the latter tends to be very short.
* Office International des Epizooties (World Organisation for Animal Health)
Animal Health Specialist
Secretariat of the Pacific Community
Private Mail Bag
Updated on 15 May 2007
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