SARS-Like Virus Infecting More People Spurs Hunt for Source

A new virus related to the one that caused SARS a decade ago was reported in an 11th person this week, spurring scientists to find the source of the lethal germ.

The latest case, identified in the U.K., was probably the result of human to human transmission and increases the need for countries to watch for unusual patterns of respiratory disease, the World Health Organization said yesterday. The infected person hadn’t traveled recently and is related to a person whose infection was announced Monday.

The source of the pathogen, a coronavirus that emerged as recently as April, hasn’t yet been discovered, frustrating efforts to curb its spread. Cases in humans provide opportunities for the virus to mutate and become more easily transmissible among people, potentially setting off a pandemic like the Severe Acute Respiratory Syndrome that sickened more than 8,000 people, killing 774, in 2002 and 2003.

“The low number spread over a long period suggests that sporadic jumping from animals to human is the most likely explanation,” said Yuen Kwok-yung, chairman of infectious diseases at the University of Hong Kong’s department of microbiology.

Previous cases were reported in Saudi Arabia, in areas around Jeddah and Riyadh, and in Jordan and Qatar. Genetic evidence indicates the virus is most closely related to a coronavirus found in bats, the WHO said in November.

Wildlife Reservoir

That link suggests that bats would be “the most likely wildlife reservoir,” said John Mackenzie, a Melbourne-based virologist who helped investigate SARS as leader of a WHO delegation to China. “Challenges exist about gaining the wildlife samples to explore which might be carrying the virus,” he said.

“It’s important to know the source so at least you have some indication of what the risks are and to what extent that risk exists,” said Mackenzie, who is an honorary professor of microbiology at the University of Queensland. “The evidence now suggests that the chances of an outbreak like SARS is unlikely - - it doesn’t seem to transmit that readily.”

Of the 11 confirmed cases of human infection notified to the WHO since April 2012, five have been fatal. The latest case is being treated in an intensive care unit, the Geneva-based agency said in a statement yesterday.

Undetected Cases?

“The fact there are still new cases occurring is a concern because pathogens can change and emerge genetically to become more transmissible over time,” said Raina MacIntyre, professor of infectious diseases epidemiology at the University of New South Wales. “If human-to-human transmission is occurring, another possible explanation could be that there are many more undetected cases.”

Screening blood tests have found no signs of existing or previous infections among the general population in Saudi Arabia, Yuen said, citing informal information available on the Internet.

“This again suggests that the virus is not transmitted at a low level in the human population, but that a new viral infection recently entered the human population,” he said in an e-mail today.

Coronaviruses encompass a family of germs that cause illnesses ranging from the common cold to SARS, which was far more transmissible than the new virus currently appears, according to the WHO.

Cluster Watch

The Geneva-based United Nations agency recommends clusters of severe acute respiratory infections, especially in health-care workers, be thoroughly investigated, regardless of where in the world they occur, it said yesterday.

“This new development does justify the measures that were immediately put into place to prevent any further spread of infection and to identify and follow up contacts of known cases,” said John Watson, head of the U.K.’s Health Protection Agency’s respiratory diseases department, in a statement yesterday.

“To date, evidence of person-to-person transmission has been limited,” Watson said. “Although this case provides strong evidence for person to person transmission, the risk of infection in most circumstances is still considered to be very low.”

The emergence of the new pathogen shows why outbreak surveillance, notification and response systems can’t be “disease-specific,” said William Aldis, an assistant professor of global health at Bangkok’s Thammasat University and a former WHO representative to Thailand.

“Otherwise we will forever be looking for the last infectious agent or vector, not the next one,” Aldis said in an e-mail. “We need to support outbreak surveillance and response systems coherently, not disease-by-disease.”

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