Year of the Rooster

Sick tiger

2005, the Chinese zodiac’s Year of the Rooster, saw a resurgence of human deaths. By June, more than 100 laboratory-confirmed cases were reported to the WHO, with more than 50 deaths.³⁴² The year also saw the continuation of an alarming trend in the growth of H5N1’s learning curve.

The WHO’s Klaus Stöhr explained in an editorial in the New England Journal of Medicine: “Recent laboratory and epidemiologic studies have yielded disturbing evidence that the H5N1 virus has become progressively more pathogenic in poultry, has increased environmental resistance, and is expanding its mammalian host range.”³⁴³ By 2003, H5N1 had undergone more than a dozen reassortments with other influenza viruses since its re-emergence among domestic poultry in 2001, trading genes like baseball cards and forming a powerhouse H5N1 mutant known to scientists as type Z. The virus was shuffling between more than a dozen decks, picking all the best cards. The adaptations that allowed Z to survive in the ambient environment augmented the virus’s ability to infect, spread, and mutate even further. Within a year the mutant Z+ was born.³⁴⁴

Z+ led to the explosion of cases across Asia in 2004. H5N1 had slowly but surely mastered the ability to spread among chickens with supreme efficiency, flooding across poultry-raising nations. It had also gotten better at killing.

University of Wisconsin virologists were the first to show that the virus’s lethality was not limited to birds. Influenza viruses don’t typically kill mammals like mice, but in the lab. Z+ killed 100% of the test population, practically dissolving their lungs.³⁴⁵ “This is the most pathogenic virus that we know of,” declared the lead investigator. “One infectious particle—one single infectious virion—kills mice. Amazing virus.”³⁴⁶ Crystallography studies showed that on a molecular level the virus had begun structurally to look more like the virus of 1918.³⁴⁷

H5N1 began taking more species under its wing. Reports came from China that pigs were infected,³⁴⁸ raising a concern that these animals could act as additional gene “swap meets.” Since pigs can be infected with both human and avian flu, they are thought to act as “mixing vessels” for influenza viruses.³⁴⁹

Pet cats began to die.³⁵⁰ This was the first time on record that cats had ever come down with the flu. Cats had always been considered resistant to getting the disease.³⁵¹ “If avian influenza has one predictable property, it is that it is not predictable,” lamented an Ohio State University biologist. “It has made a fool of us more than once.”³⁵² The WHO wrote, “The reported infection of domestic cats with H5N1 is an unusual event in what is an historically unprecedented situation.”³⁵³

Tigers and leopards in zoos who were fed chickens from the local slaughterhouse fell ill and died.³⁵⁴ In Thailand’s largest tiger zoo, more than a hundred big cats were killed. There was evidence that the virus was able to spread from tiger to tiger.³⁵⁵ Experimental studies seem to have confirmed the suspicion.³⁵⁶ Webster’s lab discovered that ferrets could also be infected with the virus, leading to rapid paralysis and death. “Everything it does is rather frightening,” said Webster.³⁵⁷ “The outbreaks indicate that the virus has become highly pathogenic to more and more species,” reported Shigeru Omi, WHO regional director for the Western Pacific region. “The virus remains unstable, unpredictable and very versatile. Anything could happen. Judging from the way the virus has behaved it may have new and unpleasant surprises in store for us.”³⁵⁸

The feline outbreaks had researchers very concerned. The virus was getting better adapted to killing mammals. “Every species leap [by H5N1] represents a new virus mutation, increasing the chance that one will become highly infectious to humans,” explained one WHO epidemiologist.³⁵⁹ Not only was the virus getting a better feel for mammalian biology, it was beginning to learn how to spread mammal to mammal.

Because cats, unlike pigs, are resistant to human influenza, they would presumably not be able to act as mixing vessels in which viral gene shuffling could potentially form bird-human hybrid viruses like those that triggered the pandemics of ’57 and ’68. But what the cat could drag in is a facilitation of the stepwise adaptation of the avian virus towards direct human infection and transmission, as presumably occurred in the pandemic of 1918. These home and zoo outbreaks also suggest viral infection in the meat.