Live bird flu virus found in victim's blood
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HELEN BRANSWELL

Canadian Press

Toronto — Live H5N1 avian flu virus can be isolated in the blood of its human victims, a finding that will be reported by Thai researchers in an upcoming issue of a scientific journal. (Peer Reviewed)

Evidence that H5N1 can spread via the bloodstream to parts of the body not normally attacked by influenza viruses confirms this particular flu strain poses special challenges for both patient treatment and infection control, experts say. It also raises theoretical questions about the safety of the donated blood system should H5N1 trigger a pandemic.

“This is the first report of a high amount of (H5N1) virus in blood in humans,” University of Ottawa virologist Earl Brown said of the findings, outlined in a letter slated for publication in the June issue of Emerging Infectious Diseases.....

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Like the biggest lout in a clan of bad neighbors, the H5N1 bird flu virus is just the worst of a large family of avian influenzas that regularly threaten poultry farms and sometimes menace human health. The bird flu that has been making headlines in recent months -- spanning the globe from Indonesia to Romania -- has been a grave concern for scientists since 1997, when it decimated chicken flocks in Hong Kong and killed six people.

While the discovery that bird flu could jump directly to humans is relatively new, avian influenzas have been troublesome for agriculture at least since 1878, when Italian poultry were beset with a disease labeled fowl plague.

Because of the way influenza viruses readily mutate and juggle genes, there are now 144 possible subtypes of influenzas that can infect birds. Out of this variety, a handful of combinations bearing names such has H5N1, H5N2, H7N7 and H7N3 regularly pose a serious risk to poultry.

Researchers fear that H5N1 could mutate into a form that transmits easily among humans, triggering a worldwide pandemic that that could kill tens of millions.

"We may sound like we are hyperventilating, but in our heart of hearts we know this is a serious possibility,'' said Dr. Andrew Pavia, director of the Task Force on Pandemic Influenza for the Infectious Diseases Society of America.

Although the H5N1 virus does not pass easily between humans, at least 116 people have contracted the virus -- nearly all from close contact with infected birds -- and 60 have died.

The 1918 Spanish flu, which caused 50 to 100 million deaths, appears to have been a bird flu that became a human virus with just a few key mutations. Pandemic flus in 1957 and 1968, which caused serious human illness, were launched when human strains picked up genes from bird strains.

Although the stakes have obviously grown higher, for decades bird flu monitoring efforts were aimed primarily at protecting commercial poultry flocks.

"Any avian influenza is bad news for a poultry house,'' said Hon Ip, director of the National Wildlife Center virology lab in Madison, Wis. "But not all of them cause the same degree of worry.''

Most avian influenzas -- such as those in wild birds -- cause few if any symptoms. But around the world, more serious, "highly pathogenic" strains emerge regularly.

Bird-killing viruses visited chicken flocks in the United States twice in the 1920s, and in 1983 caused a disastrous outbreak in Pennsylvania poultry resulting in the culling of 17 million birds.

Today an international network of biologists, affiliated with governments and the United Nations, monitors poultry flocks and wild birds for signs of flu.

Dennis Senne, a microbiologist for the National Veterinary Services Laboratories, in Ames, Iowa, said the federal avian flu monitoring program has been screening 1.3 million birds annually for antibody traces of exposure to avian influenza. The program is expanding.

"We feel we look pretty hard,'' he said. "Soon we will be approaching 3 million tests per year.''

Discoveries of deadly bird flus are relatively rare, compared to the dozens of different strains of low pathogenic influenzas biologists detect each year.

Ominously, bird flus that appear at first to be low pathogenic can evolve suddenly into a more deadly strain. That is apparently what happened in Pennsylvania in 1983, when a mild avian strain known as H5N2 suddenly turned highly contagious and lethal to birds.

UC Davis avian flu expert Dr. Carol Cardona noted that although a strain of flu may be mild for birds, it could pose a threat to humans. The only flu strains known to readily infect humans -- from families of bird flu known as H1, H2 and H3 -- are not highly lethal to birds.

Most of the deadliest bird flus come from families known as H5 and H7. "When we see an H5 or H7, even if it is a low pathogenic, we jump in with both feet,'' Cardona said.

In flocks where infection is found, all birds are killed to prevent the spread of the virus to other farms. It is a strategy that has kept bird flu largely under control in the United States.

Cardona believes the failure to cull flocks infected with H5N1 in Asia has allowed the virus to morph into a particularly persistent strain. "The thing that makes this guy in Asia so bad is that it has been there so long. It is evolving, changing, looking for new hosts,'' she said.

H5N1 comes from a line of viruses that started killing birds in China in 1996. But H5N1 viruses have caused deadly outbreaks in birds as far back as 1959, when one turned up in Scotland. Another H5N1 virus killed birds in England in 1991.

H5N1 viruses have also been detected in the United States -- but these identically named strains were low pathogenic and apparently caused no illness in birds or humans. The virus most recently left its footprint in Michigan in 2001, when turkeys routinely tested for avian flu at a processing plant tested positive for antibodies to an H5N1 strain.

According to microbiologist Senne, the virus itself was never found, and the infected birds showed no signs of illness. Nor was there any sickness at the farm they came from. No trace of the virus has been seen since in Michigan.

Living samples of an apparently harmless H5N1 virus were also found in 1986 in ducks killed by hunters at a marsh in northern Ohio. Every year at the start of hunting season, Dr. Richard Slemons of Ohio State University obtains samples from the bottoms of freshly killed waterfowl. "I ask the hunters if I can get a swab. They look at me like, 'Boy, are you weird,' '' he said.

The strain he found is called A/Mallard/Ohio/184/1986 (H5N1). "Just because it is an H5 doesn't mean that it's a problem,'' he said.

University of Minnesota veterinarian Dr. David Halvorson isolated two harmless strains of H5N1 in "sentinel ducks" in 1981 and 1985. The ducks are stocked at Minnesota lakes and regularly tested for bird flu. Avian influenzas pose a threat to the state's turkey industry -- one of the largest in the world.

Aside from their name, what these H5N1 viruses have in common with the modern lethal cousins is a similar structure of spikes on their outer surfaces. The "H" refers to the hemagglutinin protein. Scientists have found 16 different types of H proteins in the avian influenza family, identified by a succession of numbers such as H1, H2, up to H16.

Similarly, the "N" refers to a second type of surface protein, neuraminidase, of which there are nine varieties, and nine identifiers such as N1, N2, up to N9.

Flu virus names, resembling license plates, are therefore mixtures of H's, N's and numbers -- such as H5N1, H7N3, H9N2, or H7N7 -- that tell scientists what kinds of proteins appear on the outer surface of each virus.

One of the great mysteries in flu research is to find out what subtle changes can turn a relatively harmless H5 strain into a killer. It could involve mutation on the protein itself, proteins within the core of the virus, or a combination of factors.

Halvorson said that the H5N1 strains found in Minnesota may bear some resemblance to the dreaded strain on their outer surface, but are almost certainly different in other respects. Biologists have noted that avian flus in Asia are different from those in the United States, suggesting that global transfer of bird flu genes is rare.

The good news for poultry farmers in America is that even low pathogenic strains seldom infect their birds. "Over 99 percent of our flocks are free of any influenza virus,'' Halvorson said.

H9N2

Hong Kong, 2003**

H5N1

Hong Kong 1997*

H5N2

Pennsylvania, 1983

H7N2

Virginia, 2002

H5N8

Ireland, 1983

H7N4

Australia, 1997

*The feared bird flu spreading from Asia to Europe that has killed more than 60 people.

**A mild bird flu that has also sickened a small number of people but could become a pandemic strain.

What's in a virus name

Flu virus names are based on the types of hemagglutinin and neuraminidase proteins on the viral surface. There are 144 possible varieties of bird flu. Here are 10 examples of avian flu outbreaks since 1966.

H5N9: Hemagglutinin protein (16 variations), Neuraminidase protein (9 variations)

Source: Chronicle research

E-mail Sabin Russell at srussell@sfchronicle.com.

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