About avian flu

A few key figures:

• In annual influenza epidemics 5-15% of the population are affected with upper respiratory tract infections. Hospitalisation and deaths mainly occur in high-risk groups (elderly, chronically ill). Although difficult to assess, these annual epidemics are thought to result in between three and five million cases of severe illness and between 250 000 and 500 000 deaths every year around the world; 
• The flu exists in three types of viruses: A, B and C;
• Flu symptoms are non-specific and can lead to complications, particularly among people 65 years and older and in children under one year of age;
• The best preventive measure against the flu is to get a flu vaccination. Vaccinations reduce flu-related deaths by 80% and hospitalisations by 50%.                                 

Among the three types of existing viruses, the A virus is found in humans and also in ducks, geese, turkeys, chickens, pigs, horses and other animals. The B and C viruses are almost exclusively human. Only influenza A viruses can cause pandemics. There have been three major pandemics in the 20th century: in 1918 – 1919, 1957, and 1968.

Flu symptoms are non-specific but can sometimes lead to serious complications, such as respiratory infections, or chronic lung conditions, heart disease, kidney dysfunction or metabolic disorders.

The vaccination is considered to be the best flu preventive measure, and is strongly recommended each year before the flu season. The vaccination’s composition depends on the strain of viruses predicted at the time of the epidemic. The vaccine has few undesirable side effects - antibodies appear within an average of two weeks following the vaccination and remain present for several months afterwards.

Three anti-viral medications can be prescribed to prevent or help combat the flu: amantadine (mantadix), zanamivir (relenza) and oseltamavir (tamiflu). These medications are not considered alternatives to the vaccination, but can possibly be used as a complementary treatment in certain cases.  

The avian flu
The avian flu is a contagious disease, caused by an A-strain flu virus that only affects birds. It occurs and is found throughout the world. Specialists believe that all birds are susceptible to this infection, but that certain species are more resistant than others.

Some key information: 

• 15 virus subtypes can be found in birds;
• To date, all highly pathogenic outbreaks are from the A group and the H5 and H7 subtypes;
• Wild waterfowl (especially wild ducks) are considered the virus’s natural reservoir – they are one of the most virus-resistant of all bird species;
• Domestic poultry flocks are however particularly susceptible and can become the object of rapidly spreading, fatal epidemics;
• The contact between these two bird groups is often at the origin of epidemics. 

Type A viruses are found in both kinds of influenza (influenza and avian influenza), are genetically unstable and in constant mutation. They are therefore well-adapted to resist the host’s (human or animal) immune system. If the genetic material of the two flu type A viruses, including subtypes, is exchanged, merges or experiences a reassortment event, a new virus subtype is created, which is different from its two « parent » viruses. An example is the H subtypes, which are epidemiologically most important, as they govern the ability of the virus to bind to and enter cells, where multiplication of the virus then occurs. The N subtypes govern the release of newly formed virus from the cells.

The virus does not spread easily from birds to humans. Contamination is borne through the air and essentially occurs after prolonged and repeated close contact in confined spaces with respiratory secretions or faeces from infected animals, either from direct or indirect contact (surfaces and/or hands contaminated by the faeces.) 

Throughout the past several years, poultry outbreaks, or avian influenza, have been the cause of several cases of human infections, sometimes very severe, but without an important, sustained human-to-human transmission of the virus.

• 1997 Hong Kong, Strain H5N1: the first instance of human infection, called the « avian flu », during which 20 people were infected and 7 people died. This coincided with an avian flu epidemic among Hong Kong’s poultry flocks. The transmission of the virus occurred after close contact between the live, infected birds and the infected people. In three days, one and a half million birds were destroyed, which brought an end to the epidemic;
• 2003 The Netherlands, Strain H7N7: 80 people infected, 1 death. All those who became infected had worked on a poultry farm;
• 2004 – November 2005 Asia (8 countries), Strain H5N1: 132 people infected and 68 deaths. It is known that this strain can pass from animals to humans. Human-to-human contamination of this strain of avian flu has not been observed.  

Before a pandemic occurs in human beings, a flu virus first circulates within an animal species. This is called an epizooty or an epizootic disease. The accused virus is not very contagious toward humans. 

As a general rule, the animal epidemic affects birds, and particularly domestic flocks. So, because of their permanent proximity to their birds, poultry farmers are the only ones exposed, and contamination occurs via the digestive rather than the respiratory track. 

If a seasonal human flu epidemic simultaneously develops, the two viral strains (animal and human) can, because of their proximity, create a new virus via the breakdown of their genetic makeup. This circumstance is rare but statistically occurs three or four times every century. From the time this occurs, considering the new character of this extremely contagious virus in humans, the harmful consequences will be very serious in terms of morbidity and mortality.

A pandemic can start when the following conditions have been met:

1) a new influenza virus subtype emerges; 
2) it infects humans; and
3) it effectively and sustainably spreads from human to human.

All prerequisites for the start of a pandemic of the H5N1 virus strain responsible for recent cases in Asia have therefore been met save one: the establishment of efficient and sustained human-to-human transmission of this virus. The risk that the current H5N1 virus will acquire this ability will persist as long as opportunities for human infections occur. These opportunities, in turn, will persist as long as the virus continues to circulate in birds - a situation that could endure for some years to come.

The virus can improve its transmissibility among humans via two principal mechanisms. The first is a “reassortment” event, in which genetic material is exchanged between human and avian viruses during co-infection of a human or pig. Reassortment could result in a fully transmissible pandemic virus, announced by a sudden surge of cases with explosive spread.

The second mechanism is a more gradual process of adaptive mutation, whereby the capability of the virus to bind to human cells increases during subsequent infections of humans. Adaptive mutation, expressed initially as small clusters of human cases with some evidence of human-to-human transmission, would probably give the world some time to take defensive action.

Source: World Health Organization

Vaccines effective against a pandemic virus are not yet available. They are produced each year for seasonal influenza but will not protect against pandemic influenza. Although a vaccine against the H5N1 virus is under development in several countries, no vaccine is ready for commercial production and no vaccines are expected to be widely available until several months after the start of a pandemic. Current global production capacity falls far short of the demand expected during a pandemic.

Because the vaccine needs to closely match the pandemic virus, large-scale production will not begin until the new virus has emerged and a pandemic has been declared. Some clinical trials are now under way to test whether experimental vaccines will be fully protective and to determine whether different formulations can economise on the amount of antigen required, thus boosting production capacity.

The two drugs mentioned previously – oseltamivir (commercially known as Tamiflu) and zanamivir (commercially known as Relenza) – are from the neuraminidase inhibitors class and may improve prospects of survival for cases of human infection with H5N1 if administered early. However, clinical data are limited. The H5N1 virus is expected to be susceptible to the neuraminidase inhibitors. In addition, substantial constraints exist, including limited production capacity and an excessively high price for many countries. At current manufacturing capacity, which has recently quadrupled, it will take a decade to produce enough oseltamivir to treat 20% of the world’s population. The manufacturing process for oseltamivir is complex and time-consuming, and is not easily transferred to other facilities.

An older class of antiviral drugs, the M2 inhibitors amantadine and rimantadine, could potentially be used against pandemic influenza, but resistance to these drugs can develop rapidly, which could significantly limit their effectiveness. Some currently circulating H5N1 strains are fully resistant to these M2 inhibitors. However, should a new virus emerge through reassortment, the M2 inhibitors might be effective.

Source: World Health Organization

General alert level:
The WHO pandemic alert remains in Phase 3: a new influenza virus is causing disease in humans but is not yet spreading easily and sustainably among them.

• The WHO does not recommend restricting travel in affected countries;
• The WHO does not recommend screening travellers coming from H5N1 affected countries;
• The WHO reminds travellers that it is not necessary to recommend flu vaccinations for travellers going to countries impacted by avian flu; the vaccination is not efficient against the H5N1 virus strain; however it is efficient for those persons who wish to protect themselves against the “human” flu.

Advice to travellers travelling to contaminated regions:

1) Avoid poultry markets, animal sales, farms, cockfights, and ornithological parks in contaminated areas;
2) Eat poultry that has been fully cooked at 70 degrees Celsius in all parts of the food: To date, no evidence indicates that infection has been caused by the consumption of properly cooked poultry or poultry products;
3) Avoid contact with surfaces and objects, which have been contaminated by animal secretions and faeces;
4) Avoid eating raw or undercooked items (poultry and egg-based products)
5) Avoid buying, keeping or bringing back a live animal from contaminated countries, especially ornamental or domestic birds;
6) Wash your hands often with soap and water or with a disinfectant solution.  

Recommendations to populations of countries experiencing outbreaks:

• Take certain precautions, particularly during slaughter operations;
• Watch for fever or respiratory symptoms in people who might have been exposed to the virus. The first signs of the H5N1 virus infection are similar to numerous other common respiratory infections;
• Avoid all contact with dead migratory birds or wild birds showing signs of the disease;
• Avoid direct contact with infected birds or surfaces and objects contaminated by their faeces or secretions. The risk of exposure is estimated highest during slaughter, defeathering, butchering and preparation of poultry for cooking.  

Countries situated along migratory paths should remain attentive to beginning signs of the disease among wild and domestic birds. Recent events indicate it is likely that some migratory birds are now directly spreading the H5N1 virus in its highly pathogenic form.  

Measures to be taken in case of epidemics in poultry farms

If an epidemic occurs within a poultry farm, measures for eradication are the following:

• Quarantine all contaminated animals;
• Destroy all infected or potentially exposed poultry;
• Rigorously treat and monitor all transportation between farms;
• Vaccinate all people who have been in contact with the birds (avoid gene exchange)
• Ensure that people involved in slaughtering the birds wear protective equipment and use antiviral prophylactics;
• Carry out quick, rigorous epidemiological investigations in close collaboration with medical and veterinary services as soon as suspicious cases emerge;
• Read the WHO’s latest recommendations on travel to areas affected by H5N1 avian influenza;
• Reinforce the surveillance networks of reference laboratories.

• Anti-viral medicine: This is a molecule that acts on one of the surface proteins and prevents the virus from replicating. Three molecules currently exist on the market. The most common, both as a cure and as a preventive measure, is Oseltamavir (commercial name: Tamiflu*). With very few side effects, this is an efficient medicine for prevention that has also demonstrated real efficiency as a cure when given to sick patients. Its efficiency depends on the essential condition that treatment be administered in the first few hours following the appearance of flu symptoms.  However, if administered more than 48 hours after the appearance of clinical signs, this molecule’s efficiency is virtually non-existent.
• Endemic: habitual persistence in a region or within a community, of a determined disease that shows up constantly or periodically.
• Epidemic: a sudden development and rapid spreading of a contagious disease in a region where it raged in a simply endemic state or within a previously unscathed community. 
• Epidemiology : the scientific study of the occurrence, distribution and determining factors of different health states and illnesses in human groups and populations, is based essentially on preventive medicine and public health. Descriptive epidemiology, whose objective is to describe the geographic, temporal and social distribution of health states, is distinguished from explanatory epidemiology, which researches the causes of health problems, clearly underlined in the descriptive phase.
• Epizooty: an illness that hits a large number of animals of the same species or different species at the same time, within a particular region or geographic area.
• Flu Syndrome: a series of signs leading one to think, in principle, that it’s the flu.
  Infectious Syndrome: a series of signs leading one to think that the cause is a microbial infection.  Serology test: an exam that looks for anti-bodies manufactured by our immune system to defend against anti-genes, or foreign agents capable of introducing an illness.  Thus, a positive serology flu test signifies that the individual was in contact with the flu virus and developed immunity to it by making these anti-bodies targeted against this virus.
• Morbidity rate: the number of ill persons, or the total of illnesses recorded during a determined period of time within a given population.
• Morbidity: a state of sickness or disease.
• Mortality rate: the total number of recorded deaths during a determined period of time, within a given population.
• Mortality: a collective word by which one indicates the number of human beings that succumb to the same illness.
• Pandemic: form of an epidemic that extends throughout an entire continent, even the entire human race.
• Symptom: a clinical sign, a fever, for example.
• Syndrome: a series of symptoms (or signs) constituting a clinical individuality without necessarily defining the cause.