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Germ warfare: Hong Kong’s never-ending fight against viruses

Since the fatal outbreak of Sars in 2003, Hong Kong has been battling to keep a succession of diseases at bay. Sarah Lazarus examines the readiness of the city’s defences against ever-evolving strains of viruses

 

On February 21, 2003, Liu Jianlun, a doctor from Guangdong province, travelled to Hong Kong and checked into Kowloon’s Metropole Hotel. He was feeling under the weather. Eleven days later he died in hospital. Severe acute respiratory syndrome (Sars) had arrived in Hong Kong.

Sars created shock waves because it was so deadly and because it brought a chilling fact into sharp focus – that nature is constantly producing new diseases and no one is safe from them. Presently, two viruses are sounding alarm bells among infectious disease experts.

One is a new strain of bird flu, H7N9, the other is Middle East respiratory syndrome (Mers), a close relative of the Sars virus.

“If we look at the numbers from earlier this year, we can see that H7N9 spread at unprecedented speed,” says Professor Malik Peiris, chair of virology at the University of Hong Kong. As the scientist who discovered the Sars virus, he knows only too well what havoc a new virus can wreak.

As for Mers, says Peiris: “If it mutates to become more virulent, the outlook isn’t good.”

 

THE HUMAN RACE HAS been plagued by infectious diseases since nomadic people first came together to form settled farming communities, around 10,000 years ago. Viruses and bacteria took advantage of the large number of people and animals living together. They multiplied and prospered and there has been an arms race between them and us ever since. Every time human ingenuity finds a way to stamp out the germs, they evolve a new strategy to outfox us.

In the final quarter of the 20th century it looked as if people were finally gaining the upper hand. An impressively long list of infectious diseases – including polio, smallpox, diphtheria and measles – had been banished from much of the world thanks to vaccination campaigns and modern medicines. But Sars shattered any illusion of safety.

Battalions of pathogens are lurking in forests, hiding out in caves and spreading stealthily through farms, ready to ambush us at any time. In recent decades a startling number of diseases have burst into existence, among them HIV, Nipah virus, West Nile virus and mad cow disease.

The agents of many new diseases are viruses and new viruses make formidable enemies. They evolve at dizzying speed, resisting antiviral drugs and evading vaccines. Our immune systems have evolved strategies to protect us, but the viruses are often one step ahead and able to attack with tremendous power. While older diseases such as measles and rubella are rarely fatal now, the victims of new viruses have alarmingly high mortality rates.

The vast majority of new viruses spring from the animal kingdom. At some point, the animal virus develops the ability to jump to people. This is what happened with the Sars virus, which started off in horseshoe bats, hopped over to civet cats and then made the fateful leap to humans. In the case of Sars, a global pandemic was averted, but it’s still too early to tell what impact H7N9 and Mers will have on the world.

Bird flu erupted onto the scene in Hong Kong in 1997, when a strain called H5N1 jumped from poultry to people for the first time. Eighteen people were hospitalised, of whom six died. The Hong Kong government, fearing a major epidemic, took a bold move and destroyed every chicken in the territory. The virus has since expanded its reach to 64 countries, wiping out tens of millions of birds and infecting hundreds of people, but there have been no further human cases in Hong Kong.

The H7N9 strain originated in wild birds and crossed over to domesticated chickens, ducks and pigeons. The first human case was reported in the mainland in March. To last month, it has infected 137 people, killing 45. Almost all the victims had visited live poultry markets or had had close contact with live birds shortly before they became ill. H7N9 causes severe pneumonia, poisons the blood and triggers multiple organ failure. The World Health Organisation has labelled it an “unusually dangerous virus”.

“Compared to earlier strains, it’s in a different league in terms of the ease with which it passes from birds to people,” says Peiris. “Its unique biology shows us why. The virus has special proteins on its outer surface which allow it to attach to human cells with a vice-like grip. So once it gets into the human body it grows like a bomb. And unlike H5N1, which caused infected birds to sicken and die and was therefore easy to spot on farms and in markets, this new strain doesn’t produce any symptoms in poultry. It’s silent and invisible – unless you test a bird for the H7N9 virus there are no indications that it’s carrying it.”

Following the spring outbreak, the virus beat a retreat over the summer and no new cases were reported. This wasn’t reassuring though – bird flu follows a seasonal pattern, just like human variants, and experts are concerned that the disease will come storming back this winter.

Peiris was involved in a study carried out in Shanghai in May in which antiviral drugs were administered to 14 severely ill bird-flu patients.

“Most patients responded well to the drugs, but in two cases the patients’ ‘viral load’ didn’t reduce,” he says. “Genetic tests showed that the virus had developed resistance not only to Tamiflu, but to all the antiviral drugs we have available. This was extremely disturbing.”

Given that we cannot rely on drugs to save lives, perhaps the most important strategy is to tackle bird flu at source.

Secretary for Food and Health Dr Ko Wing-man is responsible for keeping bird flu out of Hong Kong. He has a good track record; as deputy director of the Hospital Authority during the H5N1 outbreak in 1997 he was instrumental in the initiative to cull the territory’s chickens.

“It wasn’t an easy decision because of the complex logistics of the operation and the expense of compensating farmers and poultry workers, but the truly difficult decision was what to do next.”

After the cull, the government made plans to close down all chicken farms and live poultry market stalls in Hong Kong, but was stymied by strong resistance from both the poultry industry and the local community.

“In southern Chinese culinary culture, a freshly slaughtered chicken is considered vastly superior to a frozen or chilled chicken, and many thought the practice of buying live chickens should be preserved to maintain Hong Kong’s status as a haven for good food,” says Ko. “We couldn’t carry out our plans in full, but we were able to reduce the size of the industry considerably.”

While it was once common to see chickens scratching around the backyards of village houses in the New Territories, Hong Kong’s chickens are now confined to the 30 remaining poultry farms.

“The small size of the industry has allowed us to introduce stringent biosecurity measures,” says Ko. “We have upgraded all the facilities, introduced better cleaning and hygiene technology and provided poultry workers with protective gear. We also conduct regular inspections.”

Mainland farms that produce chickens for sale in Hong Kong are just as tightly controlled and can only operate under licence by the city’s authorities.

“Chickens are sampled from each imported batch and tested for both the H5N1 and H7N9 bird flu viruses,” says Ko. “The chickens are only transferred to the wholesale market at Cheung Sha Wan once the tests come back negative.

“We have also introduced new regulations on the retail side. Chickens are no longer allowed to stay in the markets overnight. At the end of each day those which haven’t been sold are slaughtered and frozen for sale.

And a system of regular rest days, on which the chicken stalls are closed and deep-cleaned, has also been implemented.”

Peiris fully supports these measures although, in an ideal world, he would like to see all of the live poultry markets closed.

“Closing them is without doubt the most effective measure in terms of eliminating the risk of human infection. If the markets remain open then the next best strategy is to remove the birds every night and enforce rest days. Then, if any birds are infected, the virus can’t be passed on indefinitely – the chain of transmission will be broken.”

For now, Hong Kong’s defence strategies are keeping the H7N9 virus at bay – but for how long can we remain a fortress? Flu viruses are notorious for undergoing rapid genetic changes. The big fear is that H7N9 will acquire the capability for person-to-person transmission. If that happens it could become unstoppable.

There has been only a single recorded probable case of one person catching H7N9 from another. In March, an elderly man in Jiangsu province was admitted to hospital with bird flu. He had picked up the disease on one of his regular visits to a live poultry market. The man’s daughter cared for him at his bedside until his health deteriorated and he was transferred to intensive care. Six days after her last contact with her father, the daughter developed flu symptoms. Both patients died within a fortnight of each other. Investigations revealed the daughter had not had contact with live poultry and that the virus which killed her was the same one that had attacked her father.

Although not absolutely proven, it is thought highly likely that the daughter caught the virus from her father.

“The virus still can’t transmit easily between people,” says Peiris.

“Other close contacts of the patient didn’t catch it, so clearly it’s not running rampant. But this case shows just how close the virus is to attaining full capability.

“There are other clues that point to this conclusion. H7N9 is unique amongst bird flus in that it mounts a twin attack on the human body.

The earlier strain, H5N1, penetrates deep into the lungs, where it causes pneumonia, but from there it is unable to transmit to other people. H7N9 attacks both the lungs and the upper airways. Like the common cold, it could potentially be passed from person to person when they cough and sneeze, releasing hordes of viruses into the air.”

If H7N9 makes this critical leap, it could easily snowball into a largescale pandemic and the government would have to muster its forces quickly in order to repel it. With the reliability of antiviral drugs in question, the other weapon in the medical armoury is vaccination. Since the outbreak in the mainland this year, teams in various countries have been working to create an effective vaccine and one should become available soon.

Vaccines aren’t a fail-safe solution, however. In the event of a pandemic, huge quantities would be required and their manufacture would have to be scaled up rapidly. This is difficult in the case of influenza vaccines because they are usually grown in hens’ eggs, a process that takes months.

Another issue is that a vaccine has to maintain its effectiveness against a virus that is constantly mutating. The vaccine would require periodic updating and scientists and manufacturers might find it hard to keep pace.

But while bird flu is giving infectious disease experts a headache, Mers is causing them even greater anxiety. Very little is understood about this virus, which first appeared in the Middle East last year. Its original source has not been confirmed, there is no vaccine for it and there is no cure.

What is certain is that it is extremely potent. Of the 157 people known to have been infected with Mers, 66 have died – a terrifying death rate of 42 per cent.

Peiris is collaborating with scientists in the Middle East to try to unravel the mystery.

“We know that the virus originated in an animal, so we are working to pinpoint which one. Viruses related to Mers have been detected in bats, but it’s unlikely they passed it to people directly. The virus probably travels via another animal.”

The prime suspect is the camel. The “ships of the desert” are also sources of meat and milk in the Middle East, so they are plausible intermediaries.

“Most camels have high levels of antibodies – proteins produced by the body to fight infections – to a virus which is either Mers itself or something very similar,” says Peiris. “This shows they suffered an infection earlier in their lives.

“It raises a red flag, but it isn’t definitive proof. What we need is to find an animal with an active virus to see if we can match it to the strain found in humans. But even if that happens, it doesn’t prove that the camel is passing the virus directly to people. It’s not clear cut and until this is resolved we are limited in the action we can take to prevent further outbreaks”.

Another unsettling feature of Mers is that although most of its victims caught the disease from animals, about 20 were infected by another person.

“It’s one step on from H7N9 in that regard,” says Peiris. “Clearly it is limited in its capability to transmit that way or we would have seen an exponential spread, but every time it jumps from one person to another it has the chance to acquire that strength.”

Hong Kong’s border authorities have surveillance procedures in place to stop anyone with infectious diseases coming into the territory undetected.

“All of Hong Kong’s border crossings are equipped with infrared scanners that test body temperatures,” says Ko. “Anyone with a fever will be examined by medical staff and if a disease like bird flu or Mers is suspected, the person will be swiftly isolated and tests conducted. Within a few hours we will know the results and will give appropriate treatment.”

There is, however, always the possibility of someone arriving prior to the onset of symptoms and spreading the disease before their condition is known.

After Sars, there was massive investment in the infrastructure needed to deal with this scenario – a positive legacy of a terrible tragedy.

A state-of-the-art infectious disease facility was built at Princess Margaret Hospital in Kwai Chung, and the Centre for Health Protection – which is responsible for co-ordinating the control of infectious diseases – was established. Hong Kong is well supplied with experts such as Peiris and all medical staff in public hospitals are trained in the management of infectious diseases.

There is no doubt that Hong Kong’s authorities, having learnt many lessons from Sars, are capable of mounting a vigorous defence against outbreaks of infectious disease but, in the age of global travel, germs are travelling further and faster than before, invading rich countries and poor. As a major international travel hub, with high population density, Hong Kong is extremely vulnerable.

“There is no room for complacency,” Peiris cautions. “We must remain vigilant and stay on our guard – nowhere more so than in our interactions with animals, because that is where the threats of the future will come from.”

Whether it arrives in the form of bird flu, Mers or a virus that doesn’t yet exist, an infectious disease pandemic at some point in the future is a very real and very scary possibility.

 

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