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Q&A examines complexities of bird flu

by Anissa Anderson Orr

W. Paul Glezen, MD

Constantly changing and adapting to its environment or host, the influenza virus exemplifies Darwinism at its most dangerous. Researchers and medical professionals keep a close eye on this chameleon-like infectious agent in both humans and animals, tracking it down most recently in chicken farms in Gonzales, Texas.

W. Paul Glezen, MD, a professor of molecular virology and microbiology at Baylor College of Medicine in Houston and an epidemiologist at the Influenza Research Center, explains the workings of this hardy virus and its effect on humans and animals. The center is conducting research on high potency vaccines for the elderly and a nasal spray vaccine for children.

No humans have contracted flu from the chickens in Texas. What circumstances would have to happen for a human to contract this disease?

Glezen: The virus could mutate to allow the virus to attach to human cells lining the nasal passages, as one possibility. Another possibility is the simultaneous infection of a human with an avian virus and one of our currently circulating human viruses. The co-infection might lead to a reassortment of the two viruses with progeny that would have the surface proteins of the avian virus, which would be new for humans, and other properties that allow the virus to infect humans.

Many flu strains seem to start in poultry, like the strains in China. What exactly happens when the flu "jumps" from animals to humans?

Glezen: Influenza A viruses commonly infect aquatic birds, such as wild ducks and geese. These birds are not sick but may spread the virus to domestic poultry. The avian flu outbreaks in chickens and turkeys can be severe, causing 30 percent to 100 percent mortality in the flocks. In China and Southeast Asia, the current A(H5N1) strains can occasionally jump from sick chickens to humans producing an often-fatal pneumonia. So far, this virus has not spread from human to human. That would mean that a new pandemic virus has arisen. A(H5N1) viruses have never been known to spread in human populations before.

What is the difference between the flu virus in animals and that of humans?

Glezen: The main difference is the attachment protein, called sialic acid moiety, on the lining of the respiratory tract. Birds have one structure and humans another. The avian flu viruses attach best to avian respiratory mucosa (membranes lining the respiratory tract) and the human flu viruses best to human respiratory mucosa. The problem is that flu viruses are changeable and can mutate to allow transmission between species.

How quickly does the flu virus mutate? Is it a hardier virus than other infectious diseases?

Glezen: The virus is changing constantly. It adapts to the immunity of the population so that even if last year’s virus infected you, you may not be immune to the virus that shows up next year. Influenza A viruses change faster than influenza B viruses.

What are we still learning about the flu?

Glezen: We are learning more about the ability of flu viruses to change and to produce new pandemic viruses. Research is in progress to find better methods for producing vaccines in a shorter time period.

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