06/10/2013 12:01 pm ET Updated Aug 10, 2013

Going Viral

Remember SARS -- the outbreak that shocked and terrified the world almost exactly 10 years ago? Well now another SARS-like virus has emerged. By June this year it had already attacked 34 people and killed 18 of them.

SARS (severe acute respiratory syndrome) first appeared in Foshan, Guangdong Province, China, in November 2002. Cases were confined to the local hospitals until a doctor unwittingly carried the culprit coronavirus to Hong Kong in February 2003 while on his way to a family wedding. So began the global spread of SARS coronavirus with Hong Kong International airport as its launch pad. The doctor stayed one night in the Hong Kong Metropole Hotel before checking himself into the Prince of Wales Hospital. He had severe pneumonia and died of SARS 10 days later. During his brief stay at the Metropole the doctor's virus jumped to at least 16 other guests, supposedly via a sneeze in a crowded elevator while on his way to his room on the ninth floor. This unfortunate incident spawned a large SARS outbreak among staff, students and patients at the Prince of Wales Hospital with onward spread to the community at large. It also kick started the virus's global journey, sparking outbreaks in several other countries. An infected businessman from New York staying at the Metropole carried the virus from Hong Kong to Hanoi, Vietnam, while other hotel guests took it to Canada, and Singapore.

When a rogue virus is on the loose, one priority is to figure out how it spreads between victims and stop it. With SARS coronavirus luck was on our side. Victims are not infectious before the symptoms appear and SARS viruses airborne by a cough or sneeze do not travel far. Full isolation procedures and strict quarantine for any contacts rapidly brought the local outbreaks under control, so preventing the threatened pandemic. By July 2003 it was all over -- the final toll: 8,096 cases in 30 countries with 774 deaths -- a fatality rate of almost 10 percent.

With the emergency under control the next step is to discover where a new virus came from. Only by finding its source can we hope to prevent its re-emergence. This is the job of epidemiologists -- the medical detectives.

Viruses know nothing of sexism, ageism, racism or elitism; they just infect any susceptible person who comes their way. Many can even jump across a species barrier to infect a completely different type of animal. In fact this is how we usually acquire emerging viruses -- from wild animals. And with no pre-existing resistance or immunity to guard against these new viruses, like SARS as well as HIV and bird flu, they are often quite deadly.

As viruses do not discriminate, an outbreak starting in a particular group of people can provide vital clues to the origin of the virus. In the case of SARS, many early victims in Guangdong Province were market traders and meat handlers so epidemiologists headed for local wet markets in search of the culprit virus. Here wild animals sold live for the table include beavers, rabbits and badgers as well as many types of small mammals and reptiles. Once purchased the animals are either killed and butchered there and then or dealt with later in restaurants that specialize in such delicacies.

Scientists identified SARS-like coronaviruses in several types of animal on sale, most frequently in locally farmed Himalayan palm civet cats. That seemed to be the end of the story but then came an added twist. No such virus could be found in wild civet cats, but in 2005 a SARS-like virus was isolated from Chinese horseshoe bats. Clearly the virus must have used civet cats as a stepping stone between horseshoe bats and humans -- with the bats being its true primary home.

So what facilitated the SARS virus's international travels? First, there was a delay of three months (November 2002 to March 2003) between the first cases of SARS in Guangdong Province and the Chinese Government's report of them to the World Health Organization. Second, an international network for dealing rapidly with such global threats was lacking. In the aftermath of SARS these issues have supposedly been attended to by implementation of new international rules for reporting and handling such threats. But clearly problems remain.

It took Saudi Arabian officials three months to report the first case of SARS caused by the recently emerged coronavirus in their country, now called Middle East Respiratory Syndrome Coronavirus (MERS-Cov for short). Meanwhile the virus was silently travelling. The next cases appeared in Qatar and Jordan and then in February 2013 three cases were diagnosed in the UK. These were family members one of whom had recently visited the Middle East and Pakistan, presumably returning with the virus which he then passed on to the other two. This small cluster of cases along with others in France and Saudi Arabia prove that the virus can pass directly from human to human, but, thankfully, for the moment at least this is not a very efficient process. At the time of writing MERS-Cov, like SARS coronavirus, is assumed to be a bat virus and the hunt is on to find an intermediary carrier. Since one victim owned racing camels and another ran a camel and goat farm, perhaps locally farmed animals like goats and camels or even cattle may provide the answer.

With viruses we must learn to expect the unexpected. So how can we prevent this MERS-Cov outbreak or any other emerging virus from escalating into a lethal pandemic? We need more surveillance on the ground and more international collaboration. And ideally we need to know a whole lot more about the thousands of animal viruses out there waiting to pounce. Otherwise, we are always going to be taken by surprise.