Swine flu: alert, not yet alarmed

THE pigs are finally taking their revenge. Back in 1918, when the deadly Spanish flu was sweeping the world, experts noticed something odd: pigs were getting sick as well. It was the first time that influenza had been identified in pigs, and it coincided with the second wave of the pandemic in humans. It was clear: the H1N1 virus had been transmitted from human to pig.

Since then, the poor old porkers haven't been able to shake it. The virus has jumped from swine to swine, mutating and evolving every season, occasionally jumping back into humans, much of the time doing nothing more than rustling up a few antibodies, other times causing illness. In 1976 it killed a US army recruit, sparking a country-wide scare but no pandemic.

And now, 90 years on, a new strain of H1N1 swine flu is spreading across the world, a distant descendant of that original devastating virus.

The new flu is showing some ancestral features. For instance, experts wonder why this new swine flu appears to prefer infecting the young. In Victoria, for example, almost all those infected so far are under 30.

The 1918 pandemic was unique in that the risk of death was higher in those younger than 65 than those older — more than 99 per cent of the 50 million deaths were in the under-65s. Nearly half those who died were aged 20 to 40. This is unusual, because "normal" flu poses the biggest risk to the elderly and chronically ill. As with the modern swine flu, experts conjecture that a similar flu strain may have circulated before, leaving antibodies in older generations.

History is important in understanding why the prospect of an influenza pandemic was recently described by World Health Organisation director-general Dr Margaret Chan as one of "the big three global crises" alongside the financial crisis and climate change.

History had given us experience of how bad it could be. But it had also led us astray, Chan admitted.

"We were expecting, and fearing, that the highly lethal H5N1 avian virus (bird flu) would spark the next pandemic," she told the WHO health assembly on Friday. "But our most pressing concern is with the new H1N1 virus.

"For the first time in history, we are watching the conditions conducive for the start of a pandemic unfold before our eyes. On the one hand, this gives us an unprecedented opportunity. The world is alert and on guard as never before. On the other hand, this gives us a dilemma.

"Scientists, clinicians, and epidemiologists are capturing abundant signals. But we do not have the scientific knowledge to interpret these signals with certainty. We have clues, many clues, but very few firm conclusions."

The world's current pandemic plans, including Australia's, were written after the bird flu scare. If bird flu had spread like swine flu has, governments now would be shutting schools more quickly, and we would be advised to start stocking up on non-perishable foods and making plans to care for our young and elderly relatives.

Swine flu was "changing the rules", Chan said. It was spreading widely, but hitting softly. The WHO has already changed its criteria for defining a pandemic, putting less emphasis on the simple geographical spread of the disease.

But just because swine flu caused less sickness, we should not drop our guard, Chan said. "First, this is a very contagious virus. We expect it to continue to spread to new countries and continue to spread within countries already affected. Here, we have little doubt.

"Second, this is a subtle, sneaky virus. It does not announce its presence or arrival in a new country with a sudden explosion of patients seeking medical care or requiring hospitalisation. In fact, most countries need a sudden explosion of laboratory testing to detect its presence and follow its tracks."

Chan predicted that once swine flu was widespread and circulating in the general community, countries must expect to see more cases of severe and fatal infections — though she did not, at present, expect a sudden and dramatic jump in severe illnesses and deaths.

Though general flu has started to decrease in the US, there are still higher levels of flu-like illness than is normal for this time of year. The country's Centre for Disease Control is still predicting there will be more cases, more hospitalisations and more deaths associated with this new virus in coming weeks. Already the virus has been identified in 6552 people in the US, causing nine deaths.

That makes the US the world headquarters of the virus, with more than twice the number of cases as Mexico, where it is thought to have originated (though one theory has it that the virus was circulating unspotted in Southern California before it broke out in Mexico). It has spread to 42 countries, and particularly seems to be taking off in Japan and Spain. The virus is confirmed to have killed 75 Mexicans, many more than any other country. The only other countries to have tied the virus to deaths are the US, Canada (one) and Costa Rica (one).

Countries are reacting in different ways. In Australia, schools are a particular focus of concern and action. New York and Texas had some of the earliest suspected swine flu cases outside Mexico, and schools were closed by a combination of government action and community fear as parents kept their children home. Then two weeks ago New York had its first swine flu-related death: a 55-year-old vice-principal at a Queens school. The death set off a second wave of school closures: more than 30 shut their doors across the city.

In Australia, school closures have been the topic of sometimes fierce debate, with the Government being accused of both overreaction and slow response as the virus took hold in schoolyards.

Five schools have been closed, two in South Australia and three in Melbourne. Most states, including Victoria, are now telling parents to keep children out of school for a week after any overseas travel. But Health Minister Nicola Roxon said yesterday that all cases in Australia had exhibited mild symptoms.

"We do know that we have human-to-human transmission here in Australia," she said. "We do have a growing number of cases with no known contact to those who have travelled overseas. We do have another 40 people that are currently being tested today, but these numbers are going to keep growing."

While experts concur that it's unlikely we can stop the spread of swine flu, containment is still important, because it slows the virus and lessens the chance of a dangerous mutation, according to Victoria's Department of Human Services.

With normal, seasonal flu, thanks to flu shots and the usual background of infection, a community will have an established resistance to the disease. But a new virus can run amok because the immune system does not recognise it. As it stands, the virus does not seem particularly severe in the level of illness it causes, so a wide spread is not a catastrophe. But if it mutates into a more severe form, it becomes very dangerous, hence the extreme efforts to contain it.

"Up to now, the new virus has largely circulated in the northern hemisphere, where epidemics of seasonal influenza should be winding down," Chan said.

"We need to watch the behaviour of H1N1 very carefully as it encounters other influenza viruses circulating during the winter season in the southern hemisphere.

"The current winter season gives influenza viruses an opportunity to intermingle and possibly exchange their genetic material in unpredictable ways."

In other words, as the northern hemisphere warms up and Australia starts to shiver, the world will be looking south for clues as to the next stage of this potential pandemic.

There's another reason why experts worry about swine flu. Professor Anne Kelso, director of the WHO's flu research centre in Melbourne, explains that the seasonal H1N1 influenza that circulated in Australia last year was almost entirely resistant to the antiviral drug Tamiflu, which makes up the bulk of government antiviral stockpiles around the world. If the two viruses meet, their bastard child could be just as infectious, more virulent, and resistant to much of the world's antiviral medicine: a worrying combination.

ONE final question is puzzling the world's growing ranks of armchair flu experts: Is it really swine flu? Unlike bird flu, there is no concrete evidence that it was caught from an animal.

Professor Kelso's team has analysed the virus' genes, comparing them to known virus gene sequences stored in public databases. It found the new virus is a combination of two known strains of flu known to be circulating in pigs: one of them itself a combination, dating back to the 1990s, of swine, human and avian flu.

It is possible, though unlikely, that the two viruses combined in a human rather than a pig.

So those in the know, keen not to offend our long-suffering porcine friends, will insist on referring to it by its true name: "swine lineage" influenza.

Nick Miller is health editor for The Age