H5N1 bird flu has finally reached North America. This is not the long-dreaded outbreak of the virus in birds that could engulf the continent. But the lone, tragic human case shows that flu viruses that pose major threats to humanity stalk the planet even when they have not recently been making headlines.
Canadian authorities say that an otherwise healthy adult resident of Alberta visited Beijing, China, in late December, fell ill on the flight home and died in hospital a few days later. Canadian news reports say it was a female healthcare worker at Red Deer Hospital who was in her 20s.
H5N1 does not, so far, spread readily among people. None of the person’s close contacts have developed symptoms, and if they had the virus, they should have by now. This particular infection will spread no further. Still, the incident is a wake-up call: despite all the warnings, we are not keeping a very good eye on flu viruses.
Spot the sickness
The real marvel of the Canadian case is that it was diagnosed at all. James Talbot, Alberta’s chief medical officer, said on Wednesday that the patient developed symptoms on 27 December on Air Canada flight 030 from Beijing to Vancouver, then flew to Edmonton on Air Canada flight 244. Authorities are trying to contact passengers from those flights.
The patient went to hospital on 1 January and died two days later. But, says Talbot, the symptoms were fever, headache and malaise – not the respiratory symptoms typical of flu. Perry Kendall, chief medical officer of neighbouring province British Columbia, where the patient changed planes, confirmed in a news conference that the symptoms did not include coughing.
H5N1 was only revealed when the victim was tested for pathogens after death. The case was initially diagnosed as encephalitis, or brain inflammation. “That is one of the ways that H5N1 patients die,” said Talbot.
In fact some flu viruses do infect the brain, and two Vietnamese children were diagnosed with H5N1 in 2005 after dying of what was initially diagnosed as encephalitis. At the time epidemiologists worried that this might mean that many H5N1 cases were going unrecognised.
Under the radar
This may solve one riddle of H5N1. In a 2012 study, researchers found that air travellers are the main way that ordinary human flu gets around the world. Yet until now, no human traveller is known to have carried H5N1 abroad. “Best guess: the infection is rare and people who get it are poor,” says Derek Smith of the University of Cambridge, an author of that study.
But any previous travellers with H5N1 who looked like the Canadian case were probably missed. Both the US Centers for Disease Control and Prevention and the World Health Organization recommend testing for H5N1 only in patients with respiratory symptoms such as pneumonia.
H5N1 first hit the headlines in 1997, when it emerged from China’s booming poultry industry, and again from 2004 to 2007 when it migrated throughout Asia, Europe and Africa in wild birds and poultry. Attention then faded.
But the virus remains endemic in birds in China, Bangladesh, Egypt, India, Indonesia and Vietnam, and occasionally surfaces in other countries, including Cambodia last year. Infected birds cause a steady trickle of human infections, and 384 of the 648 known human cases so far have resulted in death. But then it stops: humans virtually never pass on the virus.
In 2011, however, Dutch scientists showed that H5N1 might become readily transmissible in people if it acquired as few as five crucial mutations, without any obvious loss in deadliness. Every human infection is a chance for the virus to make those adaptations.
The Canadian casualty is said to have visited only Beijing, and no poultry farms or markets. Beijing has reported only one human case of H5N1, in 2009,and no poultry outbreaks, says Marius Gilbert of the Free University of Brussels, Belgium, who has mapped H5N1 in China. Last year all of China reported only two human cases, in the south-western province of Guizhou, where an outbreak in chickens was reported on 27 December last year.
That’s a long way from Beijing. But these reports show H5N1 is alive and well in China. It could simply be unreported elsewhere – not through negligence, but because human cases may have unrecognised symptoms. And birds may have no symptoms at all – if they are vaccinated but infected or are resistant carriers, such as ducks.
Meanwhile, another bird flu in Chinese poultry, H7N9, has shown that these viruses can infect people who merely stray near live poultry markets. In March 2013 that virus started killing people in and around Shanghai.
It carries some similar genes to H5N1, also does not pass readily between humans, and is almost as lethal – 45 of the 137 cases registered by the WHO have resulted in death. But if anything H7N9 may be more worrying than H5N1. It spreads more readily from poultry to people, Chinese researchers concluded in a recent comparison. And it already carries three of the five mutations that would allow transmission in mammals.
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