Infection: Avian Influenza

Definition
Description
Demographics
Causes and Symptoms
Diagnosis
Treatment
Prognosis
Prevention
The Future
For more information

Definition

Avian influenza, or bird flu, is a form of flu caused by a strain of the influenza A virus that ordinarily affects only birds. Avian influenza is considered a zoonosis because it can be transmitted from animals to humans. It is also considered an emerging disease because it has been identified as a major public health problem within the last twenty years and threatens to get worse in the near future.

Wild birds carry many types of the influenza A virus in their digestive tract but do not usually get sick from it. Infected wild birds can, however, infect chickens, turkeys, and other domesticated birds through contact with their nasal secretions or droppings. The infection can be spread by contaminated bird feed, water, or soil as well as by direct contact between

wild birds and domesticated poultry. There are two subtypes of avian flu in birds: a relatively mild form that causes symptoms such as feather loss and a severe form that can kill entire flocks of chickens, geese, or turkeys within forty-eight hours.

Most cases of avian flu in humans as of 2008 have occurred in farmers or other people who were exposed to sick birds. There are very few cases of human-to-human transmission of this form of influenza. The primary reason for concern is that one specific form of the flu virus that causes avian flu—H5N1—could cause widespread sickness and death if it mutates into a form that can spread easily and directly from human to human. It was a different form of the influenza A virus (H1N1) that caused the flu pandemic of 1918–1920, which took the lives of millions of people worldwide.

Description

Avian influenza is similar to seasonal influenza. The person develops a cough, a fever, an inflammation of the tissues lining the eyelid, a runny nose, and a headache. The incubation period in humans varies between two and seventeen days, with five days being the most common length of time. In fatal cases, the patient begins to have trouble breathing and may cough up blood about five days after symptoms of illness appear. Death usually results from viral pneumonia.

Some patients also have abdominal pain, vomiting, and bloody diarrhea in addition to respiratory symptoms.

Demographics

The first cases of bird flu in humans were reported in Hong Kong in 1997. Of the eighteen people taken ill, six died from the infection. The disease has spread westward among the bird populations of Asia, Europe, and northern Africa, with cases of human illness following. In Europe, however, there have been instances of infected birds discovered without any cases of human disease. As of September 10, 2008, the World Health

Organization (WHO) reported that 387 confirmed cases of avian influenza in humans have occurred since 2003; more than half of the patients died.

There have been no confirmed cases of avian influenza caused by the H5N1 subtype in the United States in either birds or humans as of September 2008. There were, however, outbreaks of a different flu virus among American poultry in 2003 and 2004. Given the fact that the broadened spread of any subtype of flu virus increases the danger to public health in all countries around the world, many researchers think that it is only a matter of time until the H5N1 type of avian flu reaches the United States.

The risk factors for getting bird flu are not completely understood, although contact with infected birds or their droppings appears to be the single most important factor.

• People of all races and both genders appear to be equally likely to be infected.
• According to WHO, people between the ages of ten and thirty-nine are most likely to die from avian flu if they become infected.
• As of 2008, 50 percent of reported cases have been in people twenty years of age or younger; 40 percent of cases have been reported in people between twenty and forty years of age.

Causes and Symptoms

The cause of avian influenza in humans is a variant of the H5N1 influenza virus that has somewhat adapted itself to infecting people. There is some evidence that the same strain that infects birds also infects pigs and can jump the species barrier into humans from pigs as well as birds.

Avian influenza may affect the lower airway in humans more severely than seasonal influenza. The most common symptoms are:

• Fever above 100.4°F (38°C)
• Cough
• Sore throat
• Difficulty breathing
• Headache
• Conjunctivitis (inflammation of the tissues lining the eyelid)

Diagnosis

Diagnosis of suspected cases of avian flu was complicated until 2006 because samples of the patient's throat secretions had to be sent to state

health laboratories or the Centers for Disease Control and Prevention (CDC) in Atlanta, Georgia, for analysis. In February 2006, however, the Food and Drug Administration (FDA) approved a new test for diagnosing strains of bird flu in people who might have the virus. The test is called the Influenza A/H5 (Asian lineage) Virus Real-time RT-PCR Primer and Probe Set. The test gives results within four hours.

Treatment

The CDC recommends two antiviral drugs, Tamiflu and Relenza, for treating any suspected case of bird flu in the United States. It is not known, however, whether the H5N1 influenza virus might become resistant to these drugs. In addition, the drugs must be taken within two days of the appearance of symptoms to be fully effective. Two experimental antiviral drugs were being tested in Russia and China in 2008, but neither had yet become available in the United States.

Patients with a severe case of avian influenza may need to be placed on a respirator. In addition, public health officials currently recommend that patients suspected of having avian flu should be placed in isolation to reduce the risk of the infection spreading to other people.

Prognosis

Avian influenza in humans is a serious disease, with a mortality rate close to 60 percent. There is little information available about the long-term effects of the illness on survivors.

Prevention

There was no effective vaccine against avian influenza that was available to the general public in late 2008, although some were undergoing clinical trials. One of the difficulties of producing a vaccine against this type of flu in large quantities is that the virus is so powerful that it cannot easily be cultured in chicken eggs, which is the usual method for making vaccines. In June 2008, the New England Journal of Medicine reported on an experimental vaccine that produced a satisfactory immune response in 75 percent of the subjects who were injected with it. The vaccine appeared to be safe for widespread use in humans and could be made in cell cultures rather than in eggs.

Until an effective vaccine for avian flu is available, the most important preventive measures people can take are to wash their hands

frequently and avoid open-air markets, raw or undercooked eggs or poultry, and close contact with live poultry when visiting Asia or other countries where cases of avian flu have been reported. Travelers may also want to ask their doctor about getting a flu shot before they take their trip. Standard flu shots will not prevent bird flu, but they can protect people against being infected with seasonal flu.

The Future

Because of the potential disaster of an avian influenza pandemic, researchers are working on developing new antiviral medications and effective vaccines as quickly as possible. No one knows if or when the H5N1 virus will mutate into a form that can be easily transmitted from one person to another. Public health officials around the world are hoping that they will be prepared if that mutation does occur.

SEE ALSO Influenza; Pneumonia; Severe acute respiratory syndrome

WORDS TO KNOW

Avian: Pertaining to birds.

Emerging infectious disease (EID): A disease that has become more widespread around the world in the last twenty years and is expected to become more common in the future.

Pandemic: A disease epidemic that spreads over a wide geographical area and affects a large proportion of the population.

Zoonosis (plural, zoonoses): A disease that animals can transmit to humans.

For more information

BOOKS

Goldsmith, Connie. Influenza: The Next Pandemic? Minneapolis, MN: Twenty-First Century Books, 2007. Chapter 6 is about avian influenza.

Grady, Denise. Deadly Invaders: Virus Outbreaks around the World, from Marburg Fever to Avian Flu. Boston, MA: Kingfisher, 2006.

Siegel, Marc. Bird Flu: Everything You Need to Know about the Next Pandemic. Hoboken, NJ: Wiley, 2006.

WEB SITES

Center for Food Safety and Applied Nutrition (CFSAN). What Consumers Need to Know about Avian Influenza. Available online at http://www.cfsan.fda.gov/~dms/avfluqa.html (updated October 19, 2006; accessed September 14,

2008). This page provides basic information about the safe preparation of foods containing eggs or poultry.

Centers for Disease Control and Prevention (CDC). Avian Influenza (Bird Flu) Home Page. Available online at http://www.cdc.gov/flu/avian/ (updated May 7, 2007; accessed September 13, 2008).

KidsHealth. Bird Flu (Avian Flu). Available online at http://www.kidshealth.org/kid/health_problems/infection/bird_flu.html (updated February 2007; accessed September 14, 2008).

Mayo Clinic. Bird Flu (Avian Influenza). Available online at http://www.mayo-clinic.com/health/bird-flu/DS00566 (updated July 11, 2008; accessed September 13, 2008).

National Institute of Allergy and Infectious Diseases (NIAID). What Are Seasonal Flu, Avian (Bird) Flu, and Pandemic Flu? Available online at http://www3.niaid.nih.gov/topics/Flu/understandingFlu/DefinitionsOverview.htm (updated November 28, 2006; accessed September 14, 2008).

National Library of Medicine (NLM). Avian Influenza or Bird Flu. Available online at http://www.nlm.nih.gov/medlineplus/tutorials/avianflu/htm/index.htm (accessed September 14, 2008). This is an online tutorial with voiceover; viewers have the option of a self-playing version, a text version, or an interactive version with questions.

Public Broadcasting Service (PBS). American Experience: Influenza 1918. Available online at http://www.pbs.org/wgbh/amex/influenza/index.html (accessed September 14, 2008). Web site includes a transcript of the television program, a timeline and interactive maps, and reflections by a present-day scientist on the possibility of another pandemic.