5 Questions: Eckburg on Avian Flu pandemic

Paul Eckburg

While it has been known for some time that birds can be infected by a wide range of influenza viruses, it was only a bird problem until a person died from avian flu in Hong Kong in 1997. A particularly virulent strain has killed more than 40 people in Southeast Asia in the last year. To better understand the magnitude of the current situation, Medical Center Report writer Mitzi Baker turned to an expert on respiratory tract infections: Paul Eckburg, MD, a clinical instructor in infectious diseases and a postdoctoral researcher at the Veterans Affairs Palo Alto Health Care System.

1. What is avian flu and how do humans get it?

Eckburg: Avian influenza has received a lot of attention recently, because it has been causing a massive outbreak among poultry in Asia since the winter season of 2003-04. It is the largest such outbreak ever described, responsible for over 100 million chicken deaths with devastating effects on the poultry industry. Avian influenza viruses usually do not infect humans, because their surface attachments* (hemagglutinin, usually subtypes H5, H7 and H9) don't bind well to the human respiratory tract. However, since 1997 there have been rare cases of human infection by avian influenza, most of which have occurred in Asia where the animal reservoirs of influenza (chickens, ducks, pigs) are in close contact with humans. The current Asian outbreak involves virus subtype H5N1, and scientists are trying to determine how this avian strain infects humans and causes disease.

2.Why should we be worried about avian flu?

Eckburg: The current Asian H5N1 avian flu outbreak is particularly worrisome, because the human cases have been very severe and have occurred in previously healthy young people. Of the 55 reported cases to date, more than 75 percent have died. This is a much higher fatality rate than what is usually associated with the flu in the United States each year. Given that this avian H5N1 virus can infect humans, that it causes such a high mortality and that most people are not immune to it (this strain is not part of the human flu vaccine), there is concern that a "pandemic" could occur—with rapid spread and millions of deaths worldwide. Fortunately, this H5N1 strain has not yet demonstrated rapid and efficient person-to-person spread.

3.What are the symptoms?

Eckburg: Of the few human cases reported from Asia, the symptoms are severe and include fever, cough, body aches and diarrhea. These features are nonspecific and, aside from the severity, do not significantly differ from those of typical human flu.

4.Are there any treatments or vaccinations available for avian flu?

Eckburg: There is no widely available vaccine that protects humans against this H5N1 avian virus, but this is an active area of research. However, it is important to continue using the current human vaccine, because preventing infection from the typical human viruses (for example, H3N2) will prevent the mixing or reassortment of avian and human viruses into a dangerous strain that could spread from person to person. Some of our current flu medications will treat avian flu, in particular the neuraminidase inhibitors oseltamivir and zanamivir. But avian flu is resistant to older medications such as amantidine.

5.What can we do to prevent a flu pandemic? What is being done on chicken farms in Asia to prevent the spread of avian flu?

Eckburg: It's not a matter of "if" a pandemic will occur, but "when." Therefore, a preparedness plan is crucial, involving global and local emergency response plans, rapid vaccine development and stockpiling of flu medications (see www.cdc.gov for more detail). Extreme measures have been necessary in Asia to curtail the spread of avian flu, including rapid destruction of the entire poultry populations, disinfection of farms and removal of waterfowl from open markets. In terms of precautions for the general public, I think simple hand hygiene—for example, alcohol-based hand gels—remains critical, in addition to quickly contacting your doctor if you develop severe flu-like symptoms.

* Hemagglutinin and neuraminidase (H and N) are two proteins found on the surface of influenza type A viruses. These two proteins are important in helping the influenza virus infect humans and cause disease. They are also used for subtyping influenza A virus, as can be seen in the acronyms identifying different strains: For example, avian H5N1 and human H3N2 are subtypes of influenza A virus. Humans can also be infected by influenza types B and C. Influenza type B and two subtypes of influenza A are included in the annual flu vaccine.