Friday, March 07, 2003

Connecticut quarantines 4.7 million chickens for avian influenza:
Gresczyk would not disclose the name of the farm, but the apparent outbreak occurred at Kofkoff Egg Farm, said Michael Darre, a state poultry specialist and animal science professor at the University of Connecticut. The farm controls more than 90 percent of the state's egg market and produces 12 million eggs every week.
Thus proving the value of factory farming.

Meanwhile, a really scary bug in HK [Science]

Last month in Hong Kong, a 33-year-old man died and his 9-year-old son fell seriously ill after contracting an avian influenza virus from a source that remains mysterious.

Initial genetic sequencing suggests that the virus may be descended from one found in wild birds. If so, it could be difficult to contain. In all previously known cases of an avian flu jumping to humans, the source is believed to have been poultry. But "this virus hasn't been seen in domestic poultry," says Robert Webster, director of the World Health Organization's (WHO's) collaborating laboratory on animal influenza at St. Jude Children's Research Hospital in Memphis, Tennessee. However, authorities have not ruled out the possibility that the virus came from chickens on a relative's farm in mainland China.

Most flu viruses are adapted for a particular group of animals, although pigs can mix and match viruses from birds and humans. And on seemingly rare occasions, flu viruses have jumped the species barrier from other animals to humans. The last two human influenza pandemics, or worldwide flu epidemics, were caused by viruses that incorporated both human and avian flu genes. Because humans have no immunity to many strains of avian influenza, such viruses have deadly potential if they acquire the ability to infect human cells and move easily from one human host to another. However, Hong Kong health officials say that thus far there is no indication that the latest avian virus can spread from person to person.

All the same, WHO has declared an influenza alert, and its collaborating laboratories have moved into high gear. "We don't know what the consequence of this virus will be. I wouldn't trust it," says Webster. He points out that in the most similar case known--an avian influenza virus that jumped from chickens to humans in 1997, infecting 18 people in Hong Kong and killing six--there was a 6-month lag between the first death and those that followed.

Further complicating the current case is the fact that the Hong Kong family had recently visited relatives who keep chickens in Fujian Province in mainland China. The man's 8-year-old daughter died from an undiagnosed respiratory infection while there. And the deaths in this family coincide with an unidentified virus sweeping nearby Guangdong Province, infecting more than 500 people and killing at least seven. Researchers aren't sure if the family has the same illness as those in Guangdong. Webster says the nature of the Guangdong outbreak is still unknown, but "WHO has a team investigating there now."

The virus in the 1997 avian flu outbreak, labeled H5N1 for the particular forms of its surface molecules ("H" stands for hemagglutinin and "N" for neuraminidase), didn't spread beyond those who'd had direct contact with infected birds. All 1.4 million chickens in Hong Kong were slaughtered with the hope of stamping out the virus (Science, 16 January 1998, pp. 324 and 393). But despite the massive slaughter, the virus survived--perhaps in backyard poultry or in other domestic or wild bird hosts--and has continued to evolve. The latest virus, also an H5N1 subtype, is believed to be its most recent descendant.

And it ain't just the birds [also Science]
It seems that after years of stability, the North American swine flu virus has jumped onto an evolutionary fast track, churning out variants every year. Changes in animal husbandry, including increased vaccination, may be spurring this evolutionary surge. And researchers say that the resulting slew of dramatically different swine flu viruses could spell danger for humans, too. The evolving swine flu "increases the likelihood that a novel virus will arise that is transmissible among humans," says Richard Webby, a molecular virologist at St. Jude Children's Research Hospital in Memphis, Tennessee....

Most genetic changes in the flu viruses--human, pig, and bird--are small and subtle point mutations in the virus's RNA. Less common but more alarming are sudden, wholesale changes that replace entire genes and are more likely to circumvent the immune system. This process, called genetic shift, is exactly what is now occurring in North American pigs. Thus, the latest swine influenza virus is a curious hybrid: The genes that code for its coat proteins derive from classical swine influenza, but half of its internal genes have been snatched whole from avian and human viruses.

The structure of the influenza virus lends itself to such radical changes. The virus is made of eight single-stranded segments of RNA that together code for 10 proteins (see illustration). If two or more different viruses infect the same host cell, they can swap segments, creating new viral types....

The "classical" swine influenza virus discovered in 1931 is an H1N1 virus, related to the H1N1 that caused the 1918 pandemic. But in the past 5 years, a quick succession of progeny, which now include at least three additional virus subtypes and four genotypes, have all but supplanted that classical swine virus in North American pigs.

The first new virus, the one that struck the North Carolina hogs in 1998, was an H3N2; in this case, genes had crossed from human viruses to pig viruses. By late 1999, the novel viruses could be found wherever there were pigs in North America and so were presumably spread by cross-country transport. Webby and St. Jude colleague Robert Webster, together with Olsen and others at UW Madison, traced these viruses' evolutions. They found both "double reassortant" viruses, with human and swine flu genes, and "triple reassortants," containing genes from human, swine, and avian influenza viruses....

In the past decade, big swine producers have gotten bigger, and many small producers have gone out of business. The percentage of farms with 5000 or more animals surged from 18% in 1993 to 53% in 2002, according to Rodger Ott, an agricultural statistician at the National Agricultural Statistics Service in Washington, D.C. Having more pigs under one roof makes it more likely that a rogue virus can take hold. "With a group of 5000 animals, if a novel virus shows up, it will have more opportunity to replicate and potentially spread than in a group of 100 pigs on a small farm," Rossow says. On the other hand, pigs in outside pens, as is common on small farms, can be exposed to the droppings of migratory waterfowl, which may contain infectious viruses; large-scale confinement agriculture may prevent such exposure, points out Liz Wagstrom, director of veterinary science at the National Pork Board in Clive, Iowa.

Another crucial change has been the recent wide-scale vaccination for swine influenza. In less than a decade, vaccination has become the norm for breeding sows, which in turn pass their maternal antibodies on to their progeny. In 1995, swine flu vaccination was so new that the National Swine Survey conducted by the United States Department of Agriculture didn't bother to assess its extent. In 2000, the same survey showed that 44.1% of breeding females received a vaccine. Today, more than half of all sows are vaccinated against both H1N1 and H3N2 viruses, says Robyn Fleck, a veterinarian at Schering-Plough, one of the nation's three producers of swine influenza vaccine. But the vaccine is not protecting against all new strains. "We're seeing clinical disease in vaccinated pigs," says Rossow. Flu is also showing up in piglets thought to be protected by maternal antibodies passed on from vaccinated sows, such as those on the Minnesota farm.

Widespread vaccination may actually be selecting for new viral types...

It gets worse, so much worse, but in the interest of supporting the Digital Millennium Cpoyright Act and The American Academy for the Advancement of Science, I'm going to truncate the story here. Both stories written by Bernice Wuethrich, by the way.


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