INDIA: Chicken death spreads (latest news

What is avian influenza?

Avian influenza, or bird flu, is a contagious disease of animals caused by viruses that normally infect birds and, less commonly, pigs. Avian influenza viruses are highly species-specific, but have, on rare occasions, crossed the species barrier to infect humans.

What is special about the current outbreak in poultry?

The current outbreaks, which began in Southeast Asia in mid-2003, are the largest and most severe on record. Never before have so many countries been simultaneously affected, resulting in the loss of so many birds.

What are the implications for human health?

The widespread persistence of the H5N1 virus in poultry populations poses two main risks for human health.

First is the risk of direct infection when the virus passes from poultry to humans, resulting in very severe disease. Of the few avian influenza viruses that have infected humans, H5N1 has caused the largest number of cases of severe disease and death.

More than half of those infected have died. Most cases have occurred in previously healthy children and young adults.

The disease caused by H5N1 follows an unusually aggressive clinical course, with rapid deterioration and high fatality. Primary viral pneumonia and multi-organ failure are common.

The second risk, of greater concern, is that the virus — if given enough opportunities — will change into a highly infectious form for humans that spreads easily from person to person. This could mark the start of a pandemic.

Where have human cases occurred?

In the current outbreak, laboratory-confirmed human cases have occurred in Cambodia, Indonesia, Thailand and Vietnam.

How do people become infected?

Direct contact with infected poultry or surfaces and objects contaminated by their faeces is considered the main route. To date, most human cases have occurred in rural or peri-urban areas where households keep small poultry flocks that roam freely, sometimes entering homes or sharing outdoor play areas with children.

As infected birds shed large quantities of virus in their faeces, risk of exposure to infected droppings or to environments contaminated by the virus are abundant.

Exposure is considered most likely during slaughter, defeathering, butchering and preparation of poultry for cooking.

Is it safe to eat poultry and poultry products?

Yes, though certain precautions should be followed in countries currently experiencing outbreaks. In areas free of the disease, poultry and poultry products can be cooked and eaten (following good hygienic practices and proper cooking) with no fear of infection.

In areas experiencing outbreaks, poultry and poultry products can be safely consumed provided these are properly cooked and handled carefully.

The H5N1 virus is sensitive to heat. Normal temperatures used for cooking (70 degree Celsius in all parts of the food) will kill the virus.

Consumers need to be sure that all parts of the poultry are fully cooked (no pink parts) and that eggs, too, are properly cooked (no runny yolks).

Juices from raw poultry and poultry products should never be allowed to touch or mix with items eaten raw as a precaution against cross-contamination.

Persons involved in cooking should wash their hands thoroughly and clean and disinfect surfaces in contact with poultry products with soap and hot water.

In areas experiencing outbreaks, raw eggs should not be used in food that will not be heat-treated like baking.

There is no evidence of anyone getting infected following the consumption of properly cooked poultry or its products, even when these foods were contaminated with the H5N1 virus.

Does the virus spread easily from birds to humans?

No. Although more than 100 human cases have occurred in the current outbreak, this is a small number compared to the huge number of birds affected and the numerous associated opportunities for human exposure, especially in areas where backyard flocks are common.

What about the pandemic risk?

A pandemic can start when three conditions have been met: a new influenza virus subtype emerges; it infects humans, causing serious illness; and it spreads easily and sustainably among humans. The H5N1 virus amply meets the first two conditions: it is a new virus for humans and it has infected more than 100.

Only the third condition has not been met: the establishment of efficient and sustained human-to-human transmission of the virus.

How serious is the current pandemic risk?

The risk of a pandemic influenza is serious. With the H5N1 virus now firmly entrenched in large parts of Asia, the risk that more human cases will occur will persist.

Why are pandemics such dreaded events?

Once international spread begins, pandemics are considered unstoppable, as they are caused by a virus that spreads rapidly by a cough or a sneeze. The fact that infected people can shed virus before symptoms appear adds to the risk.

The severity of a disease and the number of deaths caused by a pandemic virus vary greatly, and cannot be known prior to the emergence of the virus. Under the best circumstances, assuming the new virus causes mild disease, the world could still experience an estimated 2 million to 7.4 million deaths (projected from data obtained during the 1957 pandemic).

What are the most important warning signals that a pandemic is about to start?

The most important warning signal comes when clusters of patients with clinical symptoms of influenza, closely related in time and place, are detected, as this suggests human-to-human transmission. The detection of cases in health workers caring for H5N1 patients would also suggest the same.

What is the status of vaccine development and production?

Vaccines 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 vaccine is expected to be widely available until several months after the start of a pandemic.

What are the drugs available for treatment?

Two drugs (in the neuraminidase inhibitors class), oseltamivir (commercially known as Tamiflu) and zanamivir (commercially known as Relenza) can reduce the severity and duration of illness caused by seasonal influenza.

The efficacy of the neuraminidase inhibitors depends, among others, on their early administration (within 48 hours after symptom onset).

For cases of human infection, the drugs may improve prospects of survival if administered early, but clinical data are limited.

The H5N1 virus is expected to be susceptible to the neuraminidase inhibitors. Antiviral resistance to neuraminidase inhibitors has been clinically negligible so far but is likely to be detected during widespread use during a pandemic.

An older class of antiviral drugs, the M2 inhibitors, amantadine and rimantadine, could be used against pandemic influenza, but resistance to these drugs can develop rapidly and significantly limit their effectiveness.

Some currently circulating H5N1 strains are fully resistant to the M2 inhibitors. However, should a new virus emerge through reassortment, the M2 inhibitors might be effective. For the neuraminidase inhibitors, the main constraints — which are substantial —involve limited production capacity and a price that is prohibitively high for many countries.

At the present manufacturing capacity, it will take a decade to produce enough oseltamivir to treat 20 per cent of the world’s population.

Since influenza is often complicated by secondary bacterial infection of the lungs, antibiotics could be life-saving in the case of late-onset pneumonia.

Is the world adequately prepared?

No. Despite an advance warning that has lasted almost two years, the world is ill-prepared.

WHO has urged all countries to develop preparedness plans, but only around 40 have done so. WHO has further urged the countries with adequate resources to stockpile antiviral drugs nationally for use at the start of a pandemic.

Source: World Healt