PPHSN Advice on Avian Influenza (bird flu) H5N1 and H7
from the human health perspective
“While avian influenza caused by highly pathogenic virus strains, has sometimes been shown to infect humans, this disease should not be confused with human influenza, a common disease. However, avian influenza under certain circumstances could pose a serious threat to humans.” (World Health Organisation for Animal Health, OIE).
Avian influenza, or bird flu, is a viral infection caused by influenza virus type A, which affects mainly birds. There are 15 subtypes that can infect birds but only the highly pathogenic avian influenza (HPAI) viruses H5 and H7 can cause fatal epidemics in birds.
The first documented infection of humans with an avian influenza virus occurred in Hong Kong in 1997 when HPAI, H5N1 strain, caused an outbreak among the poultry population. Coincidentally, 18 individuals with severe respiratory diseases were confirmed to be infected by H5N1, six of whom died.
To date, the clinical symptoms of the illness caused by H5N1 in humans are based only on a few cases from Viet Nam and Thailand. The main symptoms include fever >380C, shortness of breath, and cough. Other associated clinical symptoms may include headache, tiredness, rhinitis and muscle aches and pains. Complicated presentations may include severe pneumonia, pleural effusion and shock, especially if a secondary bacterial infection superimposed. During an outbreak in poultry in the Netherlands in 2003, H7N7 subtype seemed to have caused mainly conjunctivitis, although influenza-like illnesses were reported, as well as the death of a veterinarian. As recent as 30 March 2004, a patient from British Columbia presented with conjunctivitis, which was confirmed to be caused by Influenza A subtype H7.
When a host is simultaneously infected by two different Influenza A viruses, the molecular composition of these viruses gives them the potential to recombine and to give rise to a novel type of influenza virus. Adaptive mutation of a zoonotic Influenza A virus during human infection can also occur, and lead to a strain that is transmissible from human to human. These two mechanisms could result in a pandemic.
The current widespread epidemic that started in Korea mid-December 2003 was caused by H5N1, and, as of 14 February 2004, has spread to seven other Asian countries (Cambodia, China, Indonesia, Japan, Lao People’s Democratic Republic, Thailand, and Viet Nam). To date, human infections caused by H5N1 have been documented only in Viet Nam and Thailand, resulting in 23 deaths out of 34 confirmed cases (WHO Avian Influenza A(H7) human infections in Canada update-5 April 2004).
The term poultry refers to all birds commonly reared for their flesh, eggs or feathers, and includes chickens, ducks, geese, turkey and guinea fowl. Droppings from infected birds are often highly contaminated with the virus. Contaminated saliva, eye and nasal discharges can also transmit the virus.
Public health actions recommended for the region
There are several important public health actions and preparedness measures that need to be taken with regards to avian flu in the region:
- Avoid importation of live birds from countries affected by the epidemic.
- Increase awareness of the possibility of importation of the virus by migratory birds coming from affected areas. In the current season (i.e. beginning of 2004) the birds passing through or originating from Asia are over-wintering in the South Pacific and will return north around March. Should the current HPAI outbreaks not be controlled by October, the Pacific will be in danger of infection from the southerly migration.
While migratory birds undoubtedly transfer viruses from one geographic region to another, the main reservoir will be birds such as ducks, and these may pass the viruses on to domestic poultry. It is important therefore to minimise contact between domestic poultry and wild ducks, and/or to be vigilant regarding signs of disease in poultry where such contact occurs.
- All types of birds, poultry or their products, especially from affected areas, must be thoroughly cooked before consumption. This is because:
- Freezing and refrigeration does not substantially reduce the concentration or virulence of viruses on contaminated poultry products.
- Raw eggs from infected poultry can also be contaminated with the virus. Therefore, eggs must be well cooked before eating them. Egg shells may also be contaminated, and care should be taken when handling them.
- Recommended practices of thorough cooking significantly reduce the potential of transmission.
- We must also be conscious of possible illegal items (e.g. raw poultry products of unknown origin) that may be brought into our countries.
- Good hygiene practices during handling of raw poultry products also reduce the potential of transmission.
- Frequent washing of hands with soap or detergents is strongly advised, especially as contaminated surfaces facilitate transmission of avian influenza virus.
(See also WHO’s “Avian influenza: food safety issues” at http://www.who.int/foodsafety/micro/avian/en/print.html
- All persons whose daily job involves handling live poultry and/or their raw products, especially persons involved in the mass slaughter of animals that are potentially infected with highly pathogenic influenza viruses, must be aware of the preparedness regime in order to protect them from an unexpected outbreak. Such persons should have access to personal protective equipment (PPE): such as gloves, mask, goggles, head/shoe cover, apron/gowns. Details can be found at: http://www.who.int/csr/disease/avian_influenza/guidelines/interim_recommendations/en/)
- Unexplained deaths of birds or large number of birds must be reported to a veterinary and/or health authority as soon as possible.
- Anyone, particularly children, should be strongly advised against touching any dead poultry either around or outside the home. If they do, they should change their clothes immediately, wash their bodies/hands with soap/detergents, and should be closely observed for next few days for any symptoms of flu-like illness. Take them immediately to hospital if they show any symptoms.
Persons traveling to affected areas should:
- avoid contact with live birds, as well as bird droppings and other raw or untreated bird products (e.g. feathers); especially avoid live poultry markets and farms,
- follow proper hygiene practices (especially frequent hand washing), and
- consume only thoroughly well-cooked poultry products.
See also WHO advice to international travelers at http://www.who.int/csr/disease/avian_influenza/travel_2004_02_06/en/
Antiviral drugs and vaccines
- The effectiveness of antiviral drugs against H5N1 and H7 infections in human is not yet conclusive. Some very preliminary conclusions based on the few human infections treated with neuraminidase inhibitors, zanamivir (Relenza®) and oseltamivir (Tamiflu®) (which are active against both influenza A and B viruses), implied that they should be initiated earlier in the illness rather than later. (WER no.7, 2004,65-76. >> http://www.who.int/wer/2004/en/wer7907.pdf ; MMWR 53, (05): 13 Feb 2004 p100-103. >> http://www.cdc.gov/mmwr/PDF/wk/mm5305.pdf. Oseltamivir was prescribed for the H7-conjunctivitis of a patient in Canada, and his condition resolved. These antiviral drugs are new and expensive.
- Other antiviral drugs, M2 inhibitors namely amantidine (Symmetrel®) and rimantidine (Flumadine®) are active against influenza A but not influenza B. They were found to be resistant to A(H5N1) from the genetic sequencing of human cases in Viet Nam and Thailand.
- There are NO human vaccines available against H5 and H7 strains yet. The challenge of producing new vaccines is that vaccine composition will keep on changing to match changes in circulating virus due to antigenic drift.
- Vaccination of birds against avian influenza though is used as one of the tools of controlling the avian flu outbreaks in some countries, in others (like Australia) that practice is banned.
For ongoing avian influenza updates, please refer to:
- World Health Organization (WHO) website:
- WHO Regional Office for the Western Pacific:
If you have any problem in accessing the above-mentioned web addresses or in downloading the documents, please let us know and we’ll send the information by email or fax (send a message to [email protected]).
For more information on the bird flu from PPHSN, please contact:
Dr Tom Kiedrzynski (Email: [email protected])
Dr Seini Kupu (Email: [email protected])
The PPHSN Influenza Specialist Group
Updated on 20 April 2004