Flu in flight
What to know about bird flu. By DeLene Beeland
With H5N1 bird flu causing an avian pandemic and spilling over into some mammals, John Lednicky’s phone keeps ringing with people needing information. Lednicky, Ph.D., a research professor in the PHHP department of environmental and global health, a member of the UF Emerging Pathogens Institute, and an expert on viruses, shares what we know about bird flu now.
Bird flu is spreading from birds to mammals. We’ve seen outbreaks before, but what is different now?
One thing that is different now is that we are seeing H5N1 in birds in the mainland of the U.S., and the number of affected birds is significant. This did not happen to a great extent in prior years when we would read about it causing infection on chicken or duck farms in other countries. Here in Florida, we have had a mass kill off of vultures, eagles and shorebirds. And it has affected the poultry industry. On recent trips outside of Gainesville, I’ve noticed a lot of dead buzzards and crows, and I suspect it’s avian influenza.
But we need to understand what that term means because almost all influenza is, in fact, bird flu. It’s just that some of them cause high mortality events only in poultry flocks or birds, while others can cause illness in people.
How is it being transmitted from birds to mammals to people?
In birds, it is mostly oral-to-fecal routes. Ducks, for example shed a lot of virus into water when they poop, and other ducks may be feeding near them. And that is likely how it mostly gets transmitted between ducks and other waterbirds. In poultry flocks, oral-fecal transmission occurs, but the birds also shed the virus in oral, nasal and eye secretions, and may transmit the virus animalto- animal when there is close contact between a sick and healthy animal. Predatory birds and scavenging birds can acquire an H5N1 infection when they eat an infected bird or the carcass of a bird that died of H5N1 infection.
But between mammals is different. In Asia, people buy live birds at markets, where they are plucked. The plucking has been shown to aerosolize virus from the feathers. Or birds poop in crowded markets. And there may be fans or air currents in the markets that move that airborne virus around. People may breathe it in.
Dr. John Lednicky
Mindy Miller
We also think that mammals can get the virus from eating infected birds. There is evidence from studies of zoo animals, such as tigers, that were fed H5N1-infected chicken meat. These animals typically developed severe pneumonia, but mammals infected with H5N1 can develop brain disease. This should not be surprising, as many birds affected with H5N1 display signs of brain disease and succumb to it. In mammals, I suspect it may enter the body through the olfactory bulb, either after inhaling virus or when eating infected meat. But there may be other ways. It should be noted that H5N1 can cause systemic disease; it can adversely affect the kidneys, brain, liver and intestinal tract, for example, and should not be considered just a pathogen of the lungs.
How much of a threat is bird flu to people right now?
It is not easily transmitted between people right now. Think about how many birds have died, but only a few people have been infected. Here in the U.S., the threat is still low. But what we are most worried about is where the virus binds. The H5N1 viruses typically bind to cell receptors that are in the lower lungs, where they interact with what are called alpha-2,3 receptors. These are found on bird cells. Whereas human influenza viruses typically interact with alpha-2,6 receptors that are found in the upper respiratory tract, such as your upper lungs or nasal passages. There are some influenza viruses that can infect multiple receptors, both alpha-2,3 and alpha-2,6. If we have H5N1 that can now interact equally well with both, we would be in big trouble.
But the good news is that we have a medication called Tamiflu (oseltamivir) that works well and is an antiviral for flu. It does not prevent infection, but once the virus makes copies of itself inside a cell, it prevents those copies from getting out. This allows the immune system to sweep up the infected cells and it shortens the length and severity of infection.
