Bird flu’s cause, end still unknown

Wild waterfowl may be off the hook for the continued spread of bird flu, but people may be on the hook as eventual victims of the disease, experts say.

Despite Centers for Disease Control and Prevention assurances that the risk to humans is low, a University of Minnesota expert in communicable diseases is less certain.

'That's a real concern' that the latest iteration of highly pathogenic bird flu could affect humans, said Michael Osterholm, director of the university's Center for Infectious Disease Research and Policy.

'The hog industry could spin out a new virus,' said Osterholm, who has been engaged in efforts to control the spread of the disease that has hit Iowa much harder than any of the other 15 affected states.

Osterholm said he and other experts worry that H5N2 could 'reassort' with other viruses in the lungs of pigs and emerge as a new virus that could affect the health of humans.

'While there is always a chance of influenza viruses reassorting, there is no indication that this virus is likely to do so,' said Lyndsay Cole, a spokeswoman for the USDA's Animal and Plant Health Inspection Service, the lead federal agency in the effort to halt the spread of the disease.

Osterholm said the lungs of swine, which densely populate the Upper Midwest region most affected by highly pathogenic bird flu, are 'special' in that they can simultaneously host two different influenza viruses.

As the two virus strains replicate in the host, they can swap genetic material — with the possibility of a new bird flu virus able to infect mammals, including humans, he said.

Some scientists believe that reassortments among subtypes from avian and human viruses were important in producing new strains that caused human influenza pandemics in 1957 and 1968.

The Atlanta-based CDC, in a recent website post, said: 'No human infections with these viruses have been detected at this time. However, similar viruses have infected people in the past. It's possible that human infections with these viruses may occur.'

'Something else going on'

Avian flu has devastated Midwestern poultry and egg producers, causing the culling of 40 million birds, of which about 28.5 million, mostly laying hens, have been in Iowa.

In the 49 days since Iowa's first case was announced on April 14, the state has recorded 68 cases in 18 mostly northwest Iowa counties.

Gov. Terry Branstad's emergency declaration, initially scheduled to end today, has been extended to July 1 because the disease shows no sign of abating.

Both Osterholm and Hongwei Xin, director of the Iowa State University Egg Industry Center, said they believe wild waterfowl introduced the virus to Midwest domestic poultry.

'Scientists think that's how it got started. Now we begin to wonder if something else is going on,' said Xin.

One unsubstantiated hypothesis, he said, is that the virus attaches to fine particles — dust, feathers, manure — that are transmitted through the air.

While officials have strongly suspected that droppings from migrating ducks and geese were spreading the lethal virus from farm to farm, the results of research conducted by the Minnesota Department of Natural Resources ran counter to the theory.

'No human infections with these viruses have been detected at this time. However, similar viruses have infected people in the past. It's possible that human infections with these viruses may occur.'

- Centers for Disease Control, Atlanta

In a recent Website post

Researchers tested more than 3,000 samples of duck and goose feces, at least half of which was collected near bird flu infected sites, with no samples testing positive for H5N2.

That research proves only that the virus is not widespread in wild birds, according to Osterholm. It does not disprove that wild birds brought it to the Midwest or that wild birds have contributed to its spread, he said.

Osterholm called 'premature' any conclusions about how the disease is spreading.

The virus is not behaving in accordance with such established dogma as that warmer temperatures and better sanitation will contain it, he said.

Earlier predictions that summer heat would quell the virus have yet to materialize.

'Last week it was on the decline. Now it's picking up again,' Xin said.

Osterholm said data show that confined poultry with biosecurity measures in place are less vulnerable to disease than poultry raised outdoors. On the other hand, the cost is astronomical when one bird in a confinement setting gets sick and millions of others have to die.

Because of the epidemic, most of the industry's best management practices are on the table, he said.

'Everybody re-evaluates when you have an event like this,' said Iowa Agriculture Secretary Bill Northey, the state's point person on the epidemic.

Though confinement husbandry was developed as a means to raise healthier birds, 'when you can't stop an outbreak within a facility, that changes the math,' Northey said.

A USDA epidemiological team is collecting samples and conducting interviews and surveys in an effort to determine how the disease is spreading, he said.

Based on the team's findings and other information, producers will rethink the 'right size for poultry facilities and the right distance from others,' he said.

Osterholm said the threat goes beyond individual businesses, which may lose lots of money, and consumers, who will pay more for eggs and poultry. Because poultry are the most efficient converters of energy to protein, it is a world food security issue in which a substantial reduction in poultry production would adversely affect nutrition around the world, he said.

In some parts of the world, eggs and poultry are the only affordable sources of protein, Northey said.

Just as no one knows how the disease spreads, no one knows when it will end, Osterholm said.

'I wake up every day wondering that,' Xin said.

Osterholm said the North American poultry industry will have to come to grips with highly pathogenic bird flu.

'Once it gets into an area, it has just not gone away,' he said.