Avian influenza is commonly known as bird flu. It is a form of influenza that infects wild migratory fowls and domestic birds - chickens, turkeys and ducks. There are a number of varieties of avian influenza. Wild migratory birds - ducks, geese, gulls and cormorants etc. are the natural hosts (reservoirs) pf these viruses.

They carry the viruses in their intestines, but usually do not get sick from them. They may sometimes fall sick only mildly. The virus is however contagious and deadly to domesticated birds like chickens, ducks and turkeys and can kill them within one to two days. Some virulent strain of bird flu can also cause serious disease and death in wild migratory birds.

It happened at Quinhai lake reserve in western China in early May 2005 killing about 5000 bar-headed geese. H5N1 strain was the culprit. These attractive and glorious birds are the winter visitors to Myanmar and Eastern India from Siberia and central Asia. The wild migratory fowls visit our Loktak Lake, the largest fresh water lake in NE India and other water bodies in winter between November to February.

Avian flu is a sub-type of influenza A viruses. Influenza virus is divided into three types - influenza A, B and C. Influenza B & C can infect only human. They are mild and less virulent. C cannot produce any ailment. Influenza A can infect humans, birds, pigs, horses, seals, whales and other animals.

In the recent outbreak of bird flu in Asian countries, H5 N1, had jumped species to some exotic animals and birds like leopard, cat, pheasant, heron, crane, parrot and falcon.

H5N1, is having a field day to roll through chicken population far too long to mutate and become lethal enough to jump species and ultimately could inflict natural host like migratory ducks & gees. It is a worrisome trend.

Influenza A viruses are divided into sub-types based on 2 surface proteins. They are spike-like protein substances known as Haemaglutinin (HA) and Neuraminidase (NA). There are 16 different HA sub-types and 9 difference NA sub-types.

Many different combinations of H and N are possible. There are therefore 144 (16x9) possible combinations of A virus flus. All subtypes of flu A viruses can be found in birds. They generally do not infect humans, even though they can do so. Avian flu subtypes are H5 H7 and H9 etc. H5 is the most pathogenic (virulent) one. H7 is less virulent.

Human flu viruses are those subtypes that occur widely in humans. They are only three known subtypes of human flue viruses. They are H1N1, H1N2, and H3N2. Some genetic parts of current human flu came from birds originally.

H5 N1 virus does not typically infect humans. In 1997, however, the first instance of direct bird-to-human transmission of bird flu virus (H5N1,) was documented during an outbreak of avian Influenza among poultry in Hong Kong. The virus caused severe respiratory illness in 18 people, of whom 6 died. The Government culled (slaughtered) all of its chickens -1.5 million of them. That stopped the outbreak, but the strain (H5N1) still continues.

In most instances when bird flu (H5N1 strain) jumps species from infected chickens to a human, the result in a "dead end" infection. The transmission of infection ends there. There is no further progression/transmission of the disease from person to person. H5N1 is not so efficient in transmission.

Nonetheless, there is strong evidence of person-to-person. Transmission in 1 or 2 cases. In September 2004, the mother of an 11 -year old bird flu victim in Thailand died of H5N1 after catching infection from her daughter. She was never exposed to infected birds. This rare case of limited person-to-person transmission is giving concern to all.

Mutation in the virus could increase the efficiency of human-to-human transmission. Another ominously dreaded phenomenon is likely to happen in the near future is when a person is suffering from common influenza (human influenza), and he happens to be infected by bird flu (H5N1) also at the same time, then the 2 different virus genes would mix in the lung cell of the person.

It will be followed by a rearrangement and re-assortment of 8 nucleic acid genome segments between different viruses. Simply put, swapping of genes takes place between bird virus and human virus. An entirely new viral strain would be formed.

The new virus would inherit most of the genes (nucleic acid) from the human virus and H & N from the avian virus which are highly antigenic. It would be a monster, super and rogue virus. The human beings do not have any kind of immunity against such altogether newly transformed virus strain.

They can easily infect human and transmit the disease from person to person rapidly like a wild fire.

WHO has sounded alarm bell for imminent bird flu pandemic in the conference held in Geneva on 9th November, 2005. The experts opined that the pandemic would be worse than that of 1918 Spanish pandemic which claimed about 50 million lives.

How does bird flu spread amongst birds and human?

Infected wild fowls shed flu viruses in their saliva, nasal secretions and faeces. They can do so for about 1-2 months. Even small quantities of bird droppings carry a large load of the viruses. Just 1 gm of infected materials can infect millions of poultry.

The virus is highly contagious and fatal to the domesticated poultry like chicken, turkey 'and ducks. They become infected when they have contact with contaminated excretion or contaminated surfaces. The risk of transfer of infection is maximum when domestic birds (ducks) roam freely or use a common source of water supply with migratory bird.

The virus can survive in the water for 4 days at 22° C and more than 30 days at 0° C. It can survive at cool temperature in contaminated manure for at least 3 months. H5N1 virus can remain sticking to the ruffled-feathers of the infected chicken which is smeared with excreta.

When the person handles the chicken, the virus can be inhaled directly. Or the virus can be transferred to the hands of the persons, and when he touches nose, face etc, the virus is inhaled. Frequent hand washing with soap can prevent infection.

The inhaled virus adheres to and invades the epithelial cells of respiratory mucosa. The highly charge protein spikes H and N can swiftly plough through the inner linings of respiratory tract leaving behind a trail of destruction. Ulceration and destruction of mucosa follow resulting in sub-mucosal haemorrhage.

The more virulent the strain, the greater the amount of epithelial cell destruction and the more severe the pathological changes and the clinical manifestations. Ultimately the bronchial lumen is filled with blood and mucous excretion. Massive pulmonary haemorrhagic oedema occurs, and the patient dies of respiratory failure.

Asian scenario:

Outbreak of highly pathogenic avian influenza (H5 N1,) swept across 10 countries in Asia from mid 2003 to 2005 killing about 150 million chickens, 62 human lives with staggering economic loss. The countries are China, Cambodia, Indonesia, Laos, South Korea, North Korea, Thailand, Vietnam, Malaysia and Japan. Up to this latest outbreak, all the human deaths resulted from infected chickens.

In the early part of the epidemic almost all the countries except Japan and South Korea handled the crisis ineptly. Tendency to denial and cover-up due to ignorance about the disease, official stonewalling, insufficient money and manpower to implement preventive measures etc. gave ample opportunity to H5N1, to circulate amongst the chicken population and mutate. Vietnam & Indonesia are fairly poorly. Vietnam recorded highest victim of 42 and both countries are declared endemic zones. Thailand acted promptly and contained the epidemic.

The picture is in sharp contrast in Europe where the same strain took a foothold starting from Romania followed in close heel by Turkey, England, Croatia, Germany and Russia in October and November 2005. No human casualty so far. All the countries acted promptly to contain the epidemic. They enjoyed the advantage of learning from Asian experience besides being developed EU countries.

Clinical features in human beings:

Typical flu-like symptoms with temperature' hovering around 39°C. Muscles pain, sore throat, cough, sore eye (conjunctivitis), prostration and respiratory distress. Breathing difficulty is the most prominent feature in most patients. Children are more vulnerable to the disease.

Among a few patients, the virus may affect central nervous system, muscles, liver and guts. In Vietnam, a 4 year old boy presented with diarrhoea, encephalitis died in 2004. Encephalitis can occur as a result of direct virus invasion of the brain.

Symptoms in birds:

H5N1 is highly pathogenic to poultry - chickens, ducks and turkeys. It can kill chickens within 24 to 48 hours. In acute form, dullness, drowsiness, cyanosis of combs, wattles and oedema of face are seen. Central Nervous system symptoms like tilting of head, tremors and paralysis may be present. Diarrhoea in some cases is also present.

The disease may also occur in a mild form due to less virulent strain like H7. In the mild form, it causes ruffled feathers and reduced production of eggs. Bird flu may start as a mild illness but after some months, due to changes in the virus, the disease may become serious and rapidly kill nearly all the affected birds. The present strain H5N1 is a virulent one.

Treatment:

Anti-viral drug Oseltamivir (Tamiflu) is effective. It is Neuraminidase (NA) inhibiter. Recommended for 18 years and above. For prophylaxis above 13 years.

Role of vaccine:

Vaccine is essential tool for the control of influenza, particularly avian virus. There is at present no specific vaccine to prevent bird flu in human beings. Vaccine preparation trial at the National Institute of Allergy and Infections diseases (NIAD) in collaboration with Centre for Disease Control (CDC) Atlanta, USA against H5N1 and H9N2, two specific avian viruses that have significant pandemic potential are in the final stage. However, human influenza vaccine is recommended for people at risk and general people at the time of outbreak of bird flu. Influenza vaccine is available in India.

While it may not prevent H5N1, it will help to prevent re-assortment and thereby reduce the risk of human to human transmission. It may also prevent the occurrence of severe forms of the disease. The people who should be considered for influenza vaccination are those person who are likely to come in contact the infected material.

They include staff who visit the field in the affected countries, laboratory workers who come in contact with the infected material, people working in the poultry farms and in markets where poultry is sold.

Control measures at personal and community levels:

During an epidemic, avoid going to poultry farms and markets where chickens are sold. This infection affects predominantly the respiratory tract (breathing passage) and it is acquired by inhalation of the virus. There is greater risk of getting bird flu while handling infected birds or infected eggs than eating these foods. If the food is well cooked, there is hardly any risk of getting bird flu. Frequent and thorough hand washing is to be observed to help wash out the virus from the hands.

While handling possibly infected birds, shoes should be covered by shoe cover to avoid contaminated droppings. Gown, face mask and goggles should be used. Ears should also be covered fully. Killing of all infected birds. Disposal of carcasses and all products and cleaning and disinfection of farms with formalin, iodine compounds and spraying with oxidizing agent like sodium dodecyl sulphate etc are to be enforced.