Bird Flu: The Next Pandemic?

On October 24, 2005, health officials in Thailand confirmed that a 7-year-old boy who had been hospitalized on October 19 had fallen ill from avian influenza (commonly called “bird flu”) caused by the virus H5N1. The boy’s father had died of the same disease on the day the boy was hospitalized.

Also in October 2005, health officials confirmed that birds infected with bird flu had been identified in Turkey and Romania, showing that the deadly bird flu virus had reached eastern Europe. In the United Kingdom, veterinarians confirmed that an imported parrot, still in quarantine, was infected with a highly pathogenic strain of H5 avian influenza. The bird was destroyed, as were other birds it could have infected.

In Thailand, 1.3 million health workers and volunteers set out to destroy chickens showing signs of disease and refer people to health clinics. The European Union imposed a ban on importing exotic birds and declared bird flu a “global threat.”

At the same time, health officials rushed to reassure people that the H5N1 virus, deadly to birds, was not capable of infecting humans on a widespread scale, and that few, if any, cases of human-to-human transmission of the virus have occurred. Aware of the negative economic impact on the poultry industry, leaders in assorted countries rushed to reassure people that eating poultry was safe.

How concerned should you be about bird flu? Here’s a brief overview of what you need to know about avian influenza.

What is Avian Influenza?

Avian influenza is a disease of birds caused by different strains of the type-A influenza virus. The disease is infectious – that is, it spreads easily between birds. Fifteen subtypes of type-A influenza viruses are known to infect birds. Infected birds show a wide range of symptoms, which vary from slight illness to severe, quickly-spreading, fatal disease.

How Does Avian Influenza Spread?

Avian influenza spreads easily between birds. Although avian influenza can infect all birds, some birds are more susceptible to type-A influenza viruses than others. Most wild birds carry type-A influenza viruses in their intestines but rarely fall ill from them. Avian influenza is common in wild migratory waterfowl, especially wild ducks.

Domestic birds such as turkeys and chickens can be infected if they come into contact with infected wild waterfowl other migratory birds. The virus also spreads through live bird markets.

Infected birds can spread through saliva, nasal secretions, and feces. If an infected bird survives, it excretes the virus for 10 days after other signs of illness go away. In addition to spreading easily between birds, the virus can contaminate equipment such as vehicles, feed, cages, or even clothing worn by poultry workers.

Why Are Health Officials Concerned?

Generally, avian influenza viruses only infect birds and pigs. The virus subtypes that cause birds to fall ill don’t contain the “keys” they need to infect humans. But in 1997, health officials in Hong Kong documented 18 cases of infection in humans by a subtype of avian influenza virus known as H5N1. Of the 18 people infected, 6 died. As of October 24, 2005, 121 people had been infected by the H5N1 virus, and 62 of those people had died.

All reported cases of human infection with the H5N1 virus have occurred in Asia. However, the recent identification of avian influenza in migratory birds in European countries including Germany, Turkey, Romania, and Croatia, has raised concerns that the virus will spread aggressively beyond Asia.

How Could the H5N1 Virus Cause Widespread Infections in Humans?

Type-A influenza viruses are good at adapting to whatever host is available. All type A influenza viruses are capable of changing rapidly, and the H5N1 virus is especially good at it. Some epidemiologists (physicians who specialize in tracking the ways that diseases start and spread) believe that all influenza type-A viruses began as avian influenza and gradually developed the ability to infect humans and other species.

Viruses can change rapidly because of two processes: antigenic drift and antigenic shift.

Antigenic Drift

Most organisms contain a built-in “proofreading” and error-correcting system that ensures that when they reproduce, genetic material is replicated accurately. Influenza viruses lack this mechanism, so errors in replication go uncorrected. Thus, as influenza viruses replicate, their genetic material constantly changes. These changes, while usually small, are permanent. The new strain that emerges is called an antigenic variant. The process is called antigenic drift.

Health officials constantly monitor changes in human influenza viruses caused by antigenic drift. Each year, the composition of influenza vaccine is adjusted to reflect these small changes in the genetic composition of the influenza virus.

Antigenic Shift

A second property of viruses has public health officials worried: different subtypes of influenza A viruses are able to exchange, or reassort, genetic materials. The resulting virus contains a new combination of genetic material, part from both parent viruses. This process, called antigenic shift, can lead to dramatic changes in a virus from one generation to another.

Antigenic shift is the process that allows viruses to gain the ability to infect other species. Public health experts are concerned that the H5N1 virus might, through the process of antigenic shift, pick up a key piece of genetic material that will allow it to infect humans and spread easily between people.

A Ticking Clock

There’s yet another reason for concern: experts agree that the world is due for another influenza pandemic. An influenza pandemic is defined by the Centers for Disease Control as “a global outbreak of disease that occurs when a new influenza A virus appears or ‘emerges’ in the human population, causes serious illness, and then spreads easily from person to person worldwide.” The virus spreads easily, because the influenza A subtype is new and people have not developed resistance to it. The immune system is unable to recognize and fight off these viruses.

Many researchers agree that another pandemic is inevitable, and right now, H5N1 looks like the most likely potential culprit. Experts cannot predict exactly what will happen if the H5N1 virus causes an influenza pandemic, but they agree that the consequences are likely to be grave. The Centers for Disease Control predicts that in the United States alone, a medium-level pandemic could cause 89,000 to 207,000 deaths, 314,000 to 734,000 hospitalizations, 18 to 42 million outpatient visits, and illness in another 20 to 47 million people. A medium-level influenza pandemic could affect from 15 to 35 percent of the population, and the cost could reach $71.3 to $166.5 billion.

Worldwide, the potential outlook is even more grim. The World Health Organization (WHO) predicts that even a low-level influenza pandemic could lead to the deaths of 2 to 7.4 million people. As many at 150 million people could die in the worst-case scenario projected by the WHO.

Symptoms of Avian Influenza in Humans

The early symptoms of avian influenza are much like those seen in other respiratory illnesses: coughing, sore throat, sneezing, runny nose, fever, and general aches and pains. The signs and symptoms are similar to the common cold and illness caused by human influenza viruses. Severe respiratory distress secondary to viral pneumonia has been seen in several fatal cases.

Who is Most at Risk?

According to the WHO, people who have direct contact with infected poultry or objects and surfaces contaminated by their droppings are most at risk. Slaughter, de-feathering, butchering, and preparation of poultry for cooking are thought to be the most risky activities.

Influenza takes its greatest toll on the elderly, young children, people with chronic respiratory disease, heart disease, and those whose immune systems are compromised. All of these populations would be at great risk should an avian influenza pandemic occur. However, the majority of those who have died after infection with the H5N1 virus have been young, healthy adults. This may be because these people had greater exposure to poultry.

Can Avian Influenza Be Prevented or Treated?

The WHO recommends that infected flocks should be killed to reduce the chance of human infection with the H5N1 virus. According to the WHO, rapid action in Hong Kong during the 1997 outbreak, during which 1.5 million chickens, ducks, and geese were slaughtered, may have averted a pandemic.

At present, there is no vaccine that can prevent infection with the H5N1 virus. The ordinary flu vaccine does not provide protection against avian flu. After a new subtype emerges, it requires at least four months to produce significant quantities of a new vaccine that could provide protection against that subtype.

The antiviral drugs oseltamivir and zanamivir, if given at exactly the right time, may treat and prevent infection with the H5N1 virus. However, these drugs are costly and available only in limited supplies. Health experts also warn against using the drugs preventatively, because the virus may develop a resistance to the drugs, rendering them ineffective if an influenza pandemic does occur. The H5N1 influenza virus identified in Asia in 2004 and 2005 is resistant to the two other available antiviral drugs, amantadine and rimantadine.

Protecting Yourself

The WHO and the United States Centers for Disease Control list the following recommendations for preventing the spread of avian influenza from person to person:

• Practice good hygiene and health habits.
  
  
  • Wash hands thoroughly after using the bathroom, shaking hands with other people, or handling chicken, turkey, or other fowl.
    
    
  • If you are experiencing flu-like symptoms – coughing, congestion, runny nose, fever – do not go to work, church, school, or other public places.
    
    
  • Avoid contact with people who are sick.
    
    
  • Cover your mouth and nose with a tissue if you sneeze. If no tissue is available, use the crook of your elbow.
    
    
  • Keep your hands away from your eyes, mouth and nose.
    
    
• Get a flu shot. While the flu shot won’t protect you from the avian flu, it reduces the chance the H5N1 virus will use your body as the “mixing ground” to combine genetic material with the human influenza virus.
  
  
• Poultry workers should be protected by proper clothing and equipment, and receive antiviral drugs as a preventative measure.
  
  
• People who live in countries where H5N1 has been identified and outbreaks have occurred should avoid contact with migratory or wild birds that are dead or show signs of disease.
  
  
• Travelers to areas affected by H5N1 outbreaks should stay away from live animal markets and poultry farms.
  
  
• Eat only properly-cooked chicken, turkey, and other fowl. According to WHO, avian flu virus is killed by heat, so properly-cooked fowl does not pose a health risk.
  
  

For more information, see:

United States Centers for Disease Control
http://www.cdc.gov/flu/avian/

World Health Organization
http://www.who.int/csr/disease/avian_influenza/avian_faqs/en/