National Audubon Society
Notes from the Science Committee: Frequently Asked Questions
Most of us have heard or read about avian influenza (also called avian flu and bird flu) and its possible impacts on domestic livestock. There are also concerns that the genuine possibility of the development of strains of these viruses could pose serious health threats to humans. We have reviewed many sources, some of which are listed below. Following are some answers to the most commonly asked questions:
Is Avian Flu a New Type of Flu?
No, avian influenza was first identified more than 100 years ago during an outbreak in Italy. Since then, the disease has cropped up at irregular intervals in all regions of the world. In addition to the current outbreak in Asia, recent epidemics have occurred in Hong Kong in 1997-1998 and 2003, in the Netherlands in 2003, in the Republic of Korea in 2003, and in British Columbia in 2004. During 2006 avian flu viruses were detected in birds and cats in continental Europe. Avian influenza remains a serious veterinary and public health problem in Indonesia, Bangladesh and Vietnam. Avian influenza viruses infect chickens, turkeys, pheasants, quail, ducks, geese, and guinea fowl, as well as a wide variety of wild birds, including shorebirds and gulls. Migratory waterfowl – most notably wild ducks – are the natural reservoir hosts of avian influenza viruses, and these birds are also the most resistant to infection. The avian influenza viruses belong to the type A influenza virus, of which there are many different subtypes. These subtypes differ because of certain proteins on the surface of the virus (hemagglutinin [HA] and neuraminidase [NA] proteins). There are 16 different HA subtypes and 9 different NA subtypes. Many different combinations of HA and NA proteins are possible. Each combination is a different subtype. All subtypes of influenza type A viruses can be found in birds. However, when we talk about “bird flu” viruses, we are referring to those subtypes that continue to occur mainly in birds. They do not usually infect humans, even though they can and sometimes do. When we talk about “human flu viruses” we are referring to those subtypes that occur widely in humans. There are only three known subtypes of human influenza viruses (H1N1, H2N2, and H3N1). Most likely the human influenza viruses originated from birds. Influenza viruses are constantly changing, and they can adapt over time to infect and spread among humans (and pigs). Get more detailed information on the influenza viruses and how they change over time as well more information on influenza pandemics.
Is bird Flu Normally Fatal to Birds?
The many subtypes of avian influenza viruses that occur worldwide cause varying degrees of clinical illness in poultry. Chickens and turkeys are particularly susceptible to epidemics of rapidly fatal influenza. Influenza viruses infecting poultry can be divided into two distinct groups on the basis of their ability to cause disease. The highly pathogenic viruses cause high mortality in infected poultry, sometimes up to 100 %. All other virus subtypes cause a much milder, primarily respiratory, disease. Only those viruses that cause mild disease in poultry have been isolated from wild birds and, under natural conditions, are not known to cause disease in these species.
How is Avian Influenza Spread?
The avian influenza viruses behave quite differently in birds than in mammals. In birds the viruses propagate in both the intestinal and respiratory tracts. The viruses are primarily shed in the feces, but also in saliva and nasal secretions. The principal mode of transmission among birds is therefore fecal-to-oral via contaminated food and water. Avian influenza viruses can remain viable at moderate temperatures for long periods in the environment and can survive indefinitely in frozen material. In mammals (humans, pigs, horses) influenza virus infection is usually restricted to the respiratory tract, and the symptoms for uncomplicated influenza illness are constitutional and respiratory signs. This may be complicated by secondary bacterial infection, especially in the elderly, young children and individuals with compromised immune systems, resulting in severe, life-threatening pneumonia. In the recent epidemic of avian H5N1 influenza in Southeast Asia, examples of intestinal and central nervous system symptoms have also been recorded in human patients.
Can Birds be Infected at Bird Feeders?
Yes, at least theoretically, because of the fecal route of excretion of the virus and its ability to stay viable and infectious at low temperatures – usually the very time of year when we are most diligent about feeding our backyard birds. However, with passerines being the most common visitors to bird feeders, and the frequency of infection in these species being very low indeed, the risk may safely be considered remote. Of much more concern are other easily transmitted infections such as salmonellosis (a bacterial infection), avian pox and various fungal infections. It is important, therefore, to clean feeders frequently and disinfect them with bleach or vinegar at least once a month.
Are Possibly-Infected Wild Birds a Danger to Humans?
There is evidence from the ongoing avian influenza epidemic in Southeast Asia that humans might have become infected by swimming in waters contaminated with fecal material from ducks and geese. Also, people working in environments with high concentrations of infected poultry — farms and live-bird markets, for example — have been infected through exposure to high concentrations of virus-containing fomites. However, in general, the host-range barrier of the influenza viruses is such that avian influenza viruses do not replicate well in mammals, including pigs, horses and humans. Likewise human influenza viruses do not grow well in birds.
Can Avian Flu be Transmitted from One Person to Another?
Until recently, this was not known to occur. However, several instances of likely transmission have now been documented in the ongoing avian influenza epidemic in Southeast Asia. Of greater concern is the possibility that the viruses, through repeated contact, become “adapted” to humans. The most dangerous scenario would be that of a human becoming simultaneously infected with avian and human influenza viruses. This would allow the two viruses to exchange genetic material, thereby “humanizing” the avian influenza virus. Such an event could lead to unprecedented virulence and pandemicity. To date this has not happened in the ongoing epidemics in Southeast Asia, but the World Health Organization (WHO) and national health organizations, including the USA Centers for Disease Control (CDC) are constantly vigilant to the possibility and are monitoring the situation closely. For further information refer to their websites, listed below.
Should I be Cautious if I Encounter a Dead Bird?
Yes, but not necessarily because of avian flu. The vast majority of birds that are found dead have died of causes other than diseases communicable to humans. If you need to move a dead bird, use precautions such as wearing gloves or using a long-handled shovel or other tool to move the bird. If you need to handle the bird, bag it tightly. In light of the West Nile virus endemicity in the US, we recommend that you contact your local public health department if you find a dead bird, especially crows, jays, or raptors. In Seattle and King County contact the Environmental Health Services Division.
Where Can I Get More Information About Avian Flu?
There are numerous Avian Flu information sites:
- Department of Health and Human Services
Avian Influenza Q & A, UN Food and Agricultural Organization
- Birdlife International
- Veterinary Medicine, UC Davis
Avian Influenza Outbreaks, UN Food and Agricultural Organization
- World Health Organization
- US Department of Agriculture
For information specifically relevant to the influenza situation in the USA, refer to the CDC website and links listed there. From October through May, surveillance information is updated each week, and can be found on the Flu Activity Page of the CDC website. The site also includes international surveillance data of relevance to those intending to travel. In addition, periodic updates regarding influenza are published in the MMWR Weekly.