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 Outbreak preparedness & control

Avian Influenza (bird flu)

"While avian influenza caused by highly pathogenic virus strains have sometimes been shown to infect man, this disease should not be confused with human influenza, a common human disease. However, avian influenza under certain circumstances could pose a serious threat to humans." (World Health Organisation for Animal Health, OIE).


PPHSN Advice on Avian Influenza (bird flu) H5N1 and H7 from the human health perspective -
2 December 2005

  General information    

Avian influenza, or bird flu, is a viral infection caused by influenza virus type A that 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, 6 of whom died.

To date, the clinical symptoms of the illness caused by H5N1 in humans are based on the reported cases from Asian countries. The incubation period has mostly been from 2 to 4 days but has stretched to 8 days. Most patients have initial symptoms of high fever >38°C and cough, but diarrhea, vomiting, abdominal, pain, pleuritic pain, and bleeding from the nose and gums have also been reported early in the course of illness in some patients. Especially, watery diarrhea without blood or inflammatory changes appears to be more common than in influenza due to human viruses and may precede respiratory symptoms by up to one week. Symptoms of lower respiratory track infection develop early in the course of the illness: shortness of breath and respiratory distress are commonly found, with clinical manifestations of pneumonia--which seems to be primary viral pneumonia--and radiographic changes. The disease progresses to an acute respiratory distress syndrome, with multiorgan failure, and a high fatality rate among hospitalised patients. Common laboratory findings are: leukopenia, particularly lymphopenia, and mild-to-moderate thrombocytopenia. The virus is more often found in pharyngeal than in nasal samples, with sometimes high viral loads. Most cases so far have been linked with exposure to poultry, with several household clusters suggestive of human-to-human transmission through intimate contact. Although no asymptomatic infections has been found in Vietnam and Thailand through surveys, mild cases have been detected through intensified surveillance of contacts more recently in Northern Vietnam [1].

During an outbreak in poultry, in the Netherlands in 2003, H7N7 subtype seems to have caused mainly conjunctivitis, although influenza-like illnesses were reported, as well as the death of a veterinarian. On 30 March 2004, a patient from British Columbia presented with conjunctivitis and 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 successive human infection can also occur, and lead to a strain 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 20 October 2005, has spread to other Asian, and more recently European countries namely: Cambodia, China, Indonesia, Japan, Lao People’s Democratic Republic, Thailand, Viet Nam, Mongolia, Southern Russia, Romania and Turkey. To date (29 November 2005), human infections caused by H5N1 have been documented only in Viet Nam, Thailand, Cambodia, Indonesia and China resulting in 68 deaths out of 133 confirmed cases.

Poultry includes all birds that are commonly reared for their flesh, eggs or feathers, and they include chickens, ducks, geese, turkey and guinea fowl. Droppings of 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. Around October, some migratory birds from Asia migrate to the South Pacific to spend the northern hemisphere winter months there, and return north around March. Therefore, given the current spread of HPAI, the Pacific is in danger of infection from the southerly migration.

Migratory birds undoubtedly transfer virus from one geographic region to another. The main reservoir are often wild birds such as ducks, which may easily pass the viruses on to domestic poultry. It is important therefore to minimise contact between domestic poultry and wild birds, 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:

o    Freezing and refrigeration does not substantially reduce the concentration or virulence of viruses on contaminated poultry products.

o    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.

o    Recommended practices of thorough cooking significantly reduce the potential of transmission. 

o    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. 

o    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): like, 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.
  Travel Advice

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 thoroughly well-cooked poultry products.

See also WHO advice for people living in areas affected by bird flu or avian influenza at: http://www.who.int/csr/disease/avian_influenza/guidelines/advice_people_area/en/

  Antiviral drugs and Vaccines

 

  • Besides intensive medical attention, Oseltamivir, registered and commonly known as “Tamiflu®”, is the main antiviral treatment for bird flu in humans. Zanamivir (Relenza®) is another effective treatment. However, these drugs only have an effect if given within two days of the onset of the illness. Even then, they may not be 100% effective.

 

  • Other antiviral drugs, M2 inhibitors namely amantidine (Symmetrel®) and rimantidine (Flumadine®) are active against influenza A but not influenza B. A(H5N1) was found to be resistant to these drugs from the genetic sequencing of human cases in Viet Nam and Thailand.

 

  • Human vaccines against H5N1 are being developed, but their capacity to prevent a pandemic is yet to be established: it is uncertain that they will protect against the H5N1 virus if it mutates and adapts to humans. Researchers are carefully monitoring the situation to ensure that if the virus changes into a strain that is more infective for humans, they can start to develop a vaccine specifically for that strain.

 

  • 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. This practice is highly regulated.

 

  Avian Influenza updates and more information

For on-going avian influenza updates, please refer to:

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]).

 

The PPHSN Influenza Specialist Group
Updated by SPC on 2 December 2005


[1] Reference :http://content.nejm.org/cgi/content/full/353/13/1374

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