To better understand how the influenza virus has the ability to infect multiple species and to jump from species to species, one must understand the Influenza viruses type A and type B. The function to jump species is of particular concern with Avian Influenza (H5N1).

Outbreaks of influenza H5N1 occurred among poultry in eight countries in Asia (Cambodia, China, Indonesia, Japan, Laos, South Korea, Thailand, and Vietnam) during late 2003 and early 2004. By March 2004, the outbreak was reported to be under control. Beginning in late June 2004, however, new deadly outbreaks of influenza H5N1 among poultry were reported by several countries in Asia (Cambodia, China, Indonesia, Malaysia [first-time reports], Thailand, and Vietnam). It is believed that these outbreaks are ongoing. Human infections of influenza A (H5N1) have been reported in Thailand, Vietnam and Cambodia as of May 2005. It is important to emphasize that the Asian outbreak has been in back yard poultry farms not commercial settings.

Influenza A infects multiple species besides humans (e.g., birds, swine, horses, whales and seals). Subtypes differ because of certain proteins on the surface of the virus, hemagglutinin [H] and neuraminidase [N]. There are 16 different H subtypes and 9 different N subtypes of influenza A viruses. The current human subtypes are: H1N1, H1N2 and H3N2. The virus can have low pathogenic or high pathogenic effects on an infected person or animal. For example H9N2 doesn't cause mortality in domestic chickens but H7 and H5 strains do. Birds serve as reservoirs for new subtypes of H1 and H15.

Humans are the only host for influenza B. Influenza B causes less mortality than influenza A, and it is only associated with regional outbreaks (endemics) vs. a pandemic (outbreak over a wide geographic area and affecting a large portion of the population).

Avian influenza is an infection caused by a subtype of the influenza A virus (H5N1). These flu viruses occur naturally among birds. Wild birds worldwide carry the virus in their intestines, but usually do not get sick. Infected birds shed flu virus in their saliva, nasal secretions, and feces. However, Avian Influenza is very contagious and can make some domesticated birds including chickens, ducks, and turkeys, very sick and kill them. Avian Influenza virus does not usually infect humans.

Several cases of human infection with Avian Influenza viruses have occurred since 1997. Susceptible birds and humans become infected when they have direct contact with contaminated excretions or surfaces that are contaminated with excretions. It is believed that most cases of Avian Influenza infection in humans have resulted from contact with infected poultry or contaminated surfaces.

As the Avian virus affects the respiratory and the gastrointestinal systems of birds, the virus can be shed in respiratory and gastric secretions. In cool temperatures and low humidity the virus has the potential to live for weeks. Therefore, given the right environment the virus can live in water and on surfaces for some time.

Disinfection of surfaces is an important public health measure. Most common disinfectants and detergents have shown to be effective. Hand washing is one of the most important measures to keep from getting sick and from spreading germs to others. Therefore, proper hand washing with soap and water or hand rinses is essential to remove any trace of germ or dirt. For first responders, Personal Protective Equipments (PPE) such as N95 particulate respirators, protective impermeable gowns, and disposable gloves are recommended as well as human influenza vaccination. Additionally, hand washing and consultation with healthcare providers before and after potential exposures to determine the need for chemoprophylaxis are essential.

Symptoms of Avian Influenza in humans have ranged from typical flu-like symptoms (fever, cough, sore throat and muscle aches) to eye infections, pneumonia, severe respiratory diseases (such as acute respiratory distress), and other severe and life-threatening complications.

There are currently no vaccine to protect humans against the H5N1 virus that is being seen in Asia and parts of Eastern Europe. However, vaccine development efforts are under way. Studies suggest that the prescription medicines approved for human flu viruses would work in preventing Avian Influenza infection in humans. However, flu viruses can become resistant to these drugs, so these medications may not always work.

There are two classes of influenza antiviral medications: adamantanes and neuraminidase inhibitors. The Avian Influenza H5N1 has shown resistant to adamantnes (Amantadine or Rimantadine) but not to neuraminidase (Tamiful/Oseltamivir- oral or Relenza/Zanamivir-inhaled). The optimal dose and duration of treatment with these drugs are uncertain. Antiviral treatment of influenza is most effective for early treatment of uncomplicated cases. Studies still need to be done to prove that they work.

The H5N1 virus does not usually infect humans. In 1997 however, the first case of spread from a bird to a human was in Hong Kong. Since that time, the death rate for these reported cases has been about 50%. Most of these cases occurred from contact with infected poultry or contaminated surfaces. So far, spread of H5N1 virus from person to person has been rare and spread has not continued beyond one person.

During an outbreak of bird flu among poultry (domesticated chicken, ducks, turkeys), there is a possible risk to people who have direct contact with infected birds or surfaces that have been contaminated with excretions from infected birds. In such situations, people should avoid contact with infected birds or contaminated surfaces, and should be careful when handling and cooking poultry. For more information about avian influenza and food safety issues, visit the WHO website at http://www.who.int/foodsafety/micro/avian/en/.

The current risk to Americans from the H5N1 Avian Influenza outbreak in Asia is low. The strain of H5N1 found in Asia has not been found in the U.S. There have been no human cases of H5N1 flu in the U.S. It is possible that travelers returning from affected countries in Asia or Eastern Europe could be infected if placed in favorable circumstances. Since February 2004, medical and public health personnel have been watching closely to find any such cases.

Because all influenza viruses have the ability to change, scientists are concerned that the H5N1 virus could one day be able to infect humans and spread easily from one person to another. Criteria for a pandemic strain are:

• New influenza A subtype in humans
• Little or no immunity in the population
• Causes clinical illness
• Sustained person to person transmission

The last key factor, sustained person to person transmission, as not yet been met. Because these viruses do not commonly infect humans, there is little or no immune protection against them in the human population. No one can predict when a pandemic might occur. However, experts from around the world are watching the H5N1 situation in Asia and Eastern Europe very closely and are preparing for the possibility that the virus may begin to spread more easily and widely from person to person.

In February 2004, CDC provided U.S. health departments with recommendations for enhanced surveillance ("detection") in the U.S. of Avian Influenza A (H5N1). Follow-up messages were sent to the health departments about how to detect (domestic surveillance), diagnose, and prevent the spread of Avian Influenza A (H5N1). CDC also recommended measures for laboratory testing for H5N1 virus and currently advises that travelers to countries with known outbreaks of influenza A (H5N1) avoid poultry farms, contact with animals in live food markets, and any surfaces that appear to be contaminated with feces from poultry or other animals. CDC is taking part in a number of pandemic prevention and preparedness activities involving many national and international agencies and organizations.

NASA has a team of expert physicians and occupational health professionals who have established an ongoing line of communication with the experts at CDC and are preparing an Agency response plan to the potential threat from Avian Influenza. In case of a pandemic NASA would follow any large public health measures (such as isolation or quarantine) that the CDC might impose.

• Hand Hygiene
• Avian Influenza
• Avian Influenza Outbreaks
• Travelers' Health