Bar the occasional false blip on the medical radar, severe acute respiratory syndrome, or SARS, has turned out to be something of a non-event in South Africa (courtesy of an alert World Health Organisation), but this has not stopped the local scientific community taking at least a watchful virological interest in the disease.

Professor Lafras Steyn, head of medical microbiology in UCT's Department of Laboratory Sciences, for one, actually had a close encounter with the disease on a recent flight from Johannesburg to Cape Town. The passengers, including Steyn, had to wait patiently at the end of a Cape Town International runway (to where they'd been diverted) after a masked doctor had removed one person from the plane and was checking to see if in fact he had been infected with the SARS virus.

Fortunately, as had happened a couple of times in the country over the past few months, it turned out to be a false alarm.

SARS, most scientists agree, is caused by a new addition to the family of coronaviruses. The coronavirus - so named because of the distinctive halo of club-shaped spikes around the centre of the particles - is usually associated with hepatitis (inflammation of the liver) in mice, gastroenteritis (inflammation of the digestive system) in pigs, and respiratory infections in birds.

The coronavirus that causes SARS is but one of a number of so-called zoonotic viruses (transmitted from animals to humans, with animals still the natural reservoir) that over the past few thousand years have leapfrogged the biological divide that separates animals and humans, explained Steyn, who touched on the topic in his UCT inaugural address. It also happens to be the latest of the 25 or so new infectious agents in humans (not all caused by viruses) to have been spotted by scientists over the past three decades.

"It happens regularly," he said. "Every now and then, there's a new organism, like the human immunodeficiency virus, that jumps the species barrier."

According to Steyn's colleague, Dr Diana Hardie, a senior specialist in the Division of Virology, these relocations are, despite their regular occurrence, unwonted behaviour among viruses. "Most viruses are very host specific," she said.

"They adapt to a particular host and need very specialised requirements in order to replicate." In addition, viruses don't set out to be as virulent as they initially are in humans, Hardie pointed out. "Ultimately, it's not in their best interest to kill their hosts. "It would rather keep the host alive for longer and have more opportunity to replicate and be maintained."

So, for example, after sufficient time (usually centuries) and adaptation, the viruses end up asymptomatically in animals, elaborated Steyn. "One current theory holds that animals and pathogens kind of learn to exist together - it's a kind of co-evolution," he said.

"So many of the organisms that we have in our bodies don't cause disease because we've learnt to live with each other."

Viruses are usually at their most harmful when they find a new host, such as when they first jump from animals into humans, added Hardie. The first few human victims usually bear the brunt of the infections, but over time (a process that could take months, years or centuries, depending on the virus) begin to co-exist with the pathogens.

There are a number of reasons why viruses tend to cross the specie barrier, said Steyn. Usually, it has to do with humans moving into areas previously inhabited by animals, where they then pick up animal viruses they'd never been exposed to.

The outbreak of SARS, for instance, has been ascribed to human migration and resettlement patterns in areas of China where pigs also suffer from several severe acute respiratory syndromes. Some virologists have pinned the blame on traditional farming practices in the Chinese areas where the disease first made its appearance, places where people interact at close quarters with a menagerie of animals, including pigs, ducks and chickens.

South Africa was among the fortunate nations to have missed out on a SARS outbreak. Much of this has to do with the early warnings from WHO (something that was sadly missing after the AIDS outbreak in the information technology-barren 1980s, according to one SAPA reporter), the many tests being developed around the world, and the timeous implementation of a number of local policies.

"The key problem and the key feature of the epidemic is the high rate at which health care workers have been infected," noted Professor Gary Maartens, head of the Division of Infectious Diseases at Groote Schuur Hospital. "Initially, people weren't aware of what they were dealing with, and were not taking the proper precautions."

In South Africa, medical staff at hospitals, airports, ports and the like, have been trained and informed what to be on the lookout for, added Maartens. Other than the one unresolved case in Pretoria, all other incidents in South Africa - including the three suspected cases in Cape Town - have been non-SARS infections.

"We looked at the cases and realised that these could not have been SARS because the people had not been to the right places, or they'd been there too long ago," reported Maartens.

While quarantine is currently the best method to check the spread of the disease, many suspect that SARS infections may soon peter out. Most respiratory diseases tend to peak in the winter, and then wane come the summer (as is happening in the northern hemisphere), Hardie observed.

"We're not sure what's going to happen to SARS - whether it's going to burn itself out and that will be the end of it (we hope), or if it's going to spring up again next winter," added Maartens.

Of concern, however, is the fact that the virus has so many new hosts to choose from. "The problem is that you're dealing with a huge susceptible population," Hardie pointed out.

"With this being a new infection of humans, you have a 100% susceptible pool."

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