Bird flu: Is this the revenge of the rooster?

Today, the chicken is perhaps the most widely domesticated fowl, raised extensively and commercially for human consumption.

No one really knows when man first started eating chickens, but it would not be an exaggeration to say that he liked what he tasted; so much so that chickens have become the second most widely consumed meat in the world today.

Wherever in the world you may be, you can be sure that there will be plenty of chicken recipes to choose from.

However, the fowl industry isn't without its problems. Bird influenza outbreaks occur sporadically, affecting millions of chickens, and mass culling is usually carried out to prevent further spread of the disease.

It is said that the first recorded avian influenza virus was identified in Italy in 1878 as a serious disease of chickens.

Originally known as Fowl Plague, it was responsible for several outbreaks among poultry.

It was only in 1955 that the cause of Fowl Plague was found to be an avian influenza virus.

Despite the millennia-long human-chicken connection, it has only been relatively recently that this connection has taken a twist with the emergence of what is commonly known as bird flu in humans.

Types of influenza viruses

Flu infections in humans are quite common. In fact, the flu is one of the most common causes of human respiratory infections.

Such infections can be especially dangerous in susceptible populations - infants, the elderly and those with chronic diseases.

In general, there are three types of influenza viruses: A, B and C, with A mainly infecting humans and animals, and B only circulating among humans. C infections are generally mild and rarely reported.

Influenza A viruses can be subdivided into different types depending on the combinations of different surface proteins, namely, haemagglutinin (H) and neuraminidase (N).

Altogether, there are 18 H subtypes and 11 N subtypes, making all sorts of permutations possible in the virus.

Birds are the primary natural reservoir for most influenza A viruses.

As such, these cause infections in birds, with the more virulent types, known as highly pathogenic avian influenza (HPAI), causing severe disease that result in high death rates.

The milder forms of the virus are called low pathogenic avian influenza (LPAI).

The primary risk factor for human infect-ion with a bird flu virus appears to be direct or indirect exposure to infected poultry, dead or alive, or even contaminated environments, such as markets.

From birds to humans

Awareness of bird flu exploded when in 1997, a highly virulent strain, H5N1, was found in humans in Hong Kong.

This avian virus has since spread to other continents, and has even become entrenched in the poultry populations of some countries.

Various other forms of bird flu outbreaks in humans have also been reported, such as the H7N7 and H9N2 viruses, and scientists are concerned about possible mutation of these viruses that could lead to human-to- human spread.

Currently, the H7N9 bird flu in China has resulted in at least 29 deaths since an outbreak was first reported in December.

The Spanish flu of 1918 has been cited as the most devastating epidemic in recorded world history, killing somewhere between 20 and 40 million people.

Recent research has suggested that the flu was actually a mutated form of the H1N1 avian flu virus.

The research, conducted by scientists who analysed the structure of gene samples collected from victims of the disease, found subtle alterations to a protein molecule that allowed it to move from birds to humans, and with devastating effects.

Preventing outbreaks

According to the World Health Organisation (WHO), "to date, although human-to-human transmission of these viruses is thought to have occurred in some rare instances when there had been very close and prolonged contact between a very sick patient and caregivers such as family members, there has been no sustained human-to-human transmission".

Whether a future pandemic will occur is unknown.

However, measures have to be taken to reduce this risk, and controlling the disease in the animal source is critical to decreasing this risk.

Controlling the circulation of bird influenza viruses in poultry is essential to reducing the risk of human infection, hence the culling of affected birds when detected, despite the huge economic costs.

In addition, those in affected areas should maintain strict personal, food and environmental hygiene, such as washing their hands often with soap and water, and following good food safety and hygiene practices.

WHO advises that travellers to countries with known outbreaks of bird flu should avoid poultry farms, contact with birds or entering areas where poultry may be slaughtered.

Because birds are a natural reservoir of influenza A viruses, it's impossible to eradicate the virus.

Hence, the need for vigilance and surveillance so that any infection in birds is detected quickly and dealt with effectively.