It is a highly contagious viral disease caused by Influenza Type A viruses which generally affects poultry birds such as chickens and turkeys. There are many strains of the virus – some of them are mild and may merely cause a low egg production or other mild symptoms among chickens, while others are severe and lethal.

Wild aquatic birds such as ducks and geese are the natural reservoir of “Influenza A” viruses and the central players in the ecology of these viruses.

Many birds carry the flu without developing sickness and shed it in their droppings. Since birds excrete even while flying, they provide “a nice aerosol of influenza virus, shedding it all over the world”, in the words of American virology professor Vincent Racaniello.

From water birds, many of whom migrate and travel long distances, the viruses are thus further spread to poultry and terrestrial birds. Sometimes, the virus jumps over to mammals such as pigs, horses, cats and dogs.

No, it does not. Generally, people coming in close contact with infected alive or dead birds have contracted the H5N1 bird flu, and it does not usually spread from person to person, as per the WHO. There is also no evidence, the WHO says, that the disease can be spread to people through properly prepared and cooked poultry food. The virus is sensitive to heat, and dies in cooking temperatures.

H5N1 is severe and deadly – around 6 out of 10 confirmed cases in humans have led to deaths (though the actual mortality rate may be lower due to under-reporting of asymptomatic cases).

If the virus mutates and becomes easily transmissible from person to person, say by altering its shape to grab human cells much more effectively, it can potentially cause a pandemic.

Also, flu viruses are more prone to mutation because they have a segmented genome. All known strains of flu – including the seasonal flu and the pandemic flu – have jumped from birds to humans in this way.

In India, no case of bird flu in humans has been detected so far, according to the Union health ministry. The department of animal husbandry has reported 25 episodes of H5N1 bird flu in poultry in 15 states from 2006 (when the first outbreak occurred in Maharashtra and Gujarat) till 2015. It has also been detected in crows.

Unlike in birds, where it generally infects the gut, the avian influenza attacks the respiratory tract of humans and may cause severe respiratory illnesses such as Pneumonia or Acute Respiratory Distress Syndrome (ARDS). Its early symptoms include fever, cough, sore throat, and sometimes abdominal pain and diarrhoea.

Antiviral drugs, especially oseltamivir, improve the prospects of survival in humans, according to the Union health ministry. The ministry advises people working with poultry to use PPEs and follow hand hygiene. In the US, the FDA approved a vaccine for the H5N1 virus in 2007.

Among poultry birds, vaccination strategies advised by the World Organisation for Animal Health can be used to prevent the flu, and the Organisation recommends eradicating the highly pathogenic avian influenza (HPAI) at its source to decrease the disease in avian species and further human infections.