The saliva of a four-year-old boy, tested outside the Chinese capital of Beijing last week, is raising a question that the world would rather not ask: Could this be a forewarning of the next human pandemic?
In the saliva, Chinese scientists discovered an avian virus called H7N9. First reported three weeks ago, H7N9 has now emerged among people in China’s north, centre and eastern seaboard. Of 77 cases, 16 have died. Many of those infected have multiple-organ failure and brain damage. Masks are out on the streets of Shanghai, and the Chinese poultry industry has suffered losses of more than Rs.8,300 crore.
These are worrying but not unusual manifestations of a disease outbreak. But the scientific world is extraordinarily concerned because the four-year-old was the first person to be asymptomatic—he displayed no signs of infection. This means scores of people could be infected without anyone knowing it. H7N9 could even be masquerading as a common cold.
“We are concerned by the sudden emergence of these infections and the potential threat to the human population,” wrote Rongbao Gao and colleagues at China’s National Institute for Viral Disease Control and Prevention in an 11 April report published in the New England Journal of Medicine, after studying genetic, epidemiological and virological data of the three who died in March. The illness of the three victims began as a fever and cough, but their circumstances were diverse.
One was a 27-year-old butcher who did not kill birds, although he worked in a market where they were sold. The second was a 35-year-old housewife who visited a chicken market a week before she fell ill. The third was an 87-year-old man who had no known contact with birds. Gao and colleagues wrote: “An understanding of the source and mode of transmission of these infections, further surveillance, and appropriate counter measures are urgently required.”
Translated: We guess the virus is coming from birds, but we do not really know if other animals are involved. We do not know how it is transmitted. We do not know how to cure or prevent it.
In an accompanying perspective, Nancy Cox, director of the influenza division at the Centers for Disease Control and Prevention (CDC) in the US, and Timothy Uyeki, a CDC physician, explain why the latest edition of the bird flu is of such concern. “In addition to causing severe illness and deaths, the novel H7N9 viruses reported by Gao and colleagues have genetic characteristics that are of concern to public health,” wrote Uyeki and Cox.
One, the rapidly mutating virus appears to have developed the ability to reproduce in the cooler human respiratory tract, as opposed to its warmer natural habitat, the digestive system in birds. Two, this mutation has previously showed up in ferrets frequently used in flu research. Three (though Uyeki and Cox do not mention it), the mutation was also found in viruses that caused flu epidemics in 1957 and 1968.
In short, H7N9, which until last month resided quietly in birds, appears to have swiftly—and virtually undetected—transformed itself into a human virus, mutating roughly eight times as fast as a standard flu virus.
Unlike H5N1, which caused global panic in 2006 and is highly pathogenic—meaning it has a strong ability to cause disease and damage the host—the H7N9 strain, according to the latest genetic data, causes only mild disease in domestic poultry and wild birds. This means transmission to humans might occur through infected but seemingly normal poultry, a potential epidemiological nightmare because it will be hard to discern outbreak sites.
Thus far, the anxiety is under control because there appears to be no evidence of human-to-human transmission, which still hasn’t happened with the older and more notorious H5N1 strain.
The larger concern around H7N9, and indeed a variety of bird and other viruses, is the rising threat of zoonotic infections, or infectious diseases that jump from animals to people. In his new book, Spillover, science writer David Quammen explains that as predators favour particular prey, so do pathogens. And just as a lion might occasionally kill a cow instead of a zebra, a pathogen can choose a new target, leaping from some non-human animal to a person, establishing itself as “an infectious presence”. Zoonosis, says Quammen, is “a word of the future, destined for heavy use in the twenty-first century”.
Some examples of zoonotic diseases: rabies (dogs to humans), AIDS (monkeys to humans), bubonic plague (rats to humans), and the Spanish flu of 1918-1919, which sprang from a wild bird, passed through an unknown chain of domestic animals, killing with unprecedented speed as many as 50 million people—the single deadliest event in recorded human history—before “receding into obscurity”. Will H7N9 recede into obscurity without the virulence of its ancestor? Even if it does, what else is out there?
Samar Halarnkar is a Bangalore-based journalist. This is a fortnightly column that explores the cutting edge of science and technology. Comments are welcome at email@example.com.
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