The short-lived, worldwide epidemic of severe acute respiratory syndrome that began its streak across the globe 10 years ago, starting in February 2003, has been echoed over the past 8 months by what is so far a much more limited number of cases of a new, mysterious respiratory virus closely related to the SARS pathogen.
Mostly known so far as the "novel coronavirus" (NCoV), the new agent is very similar to the severe acute respiratory syndrome (SARS)-associated coronavirus, and by late February the new virus had been identified in 13 patients worldwide – in Saudi Arabia, Jordan, the United Kingdom, and Qatar – causing seven deaths and severe illness in five of the other six patients.
Since the World Health Organization (WHO) and other epidemiology groups first became aware of the NCoV last September, and as the number of identified cases has inched up, researchers have scrambled to gather information about the novel virus and heighten surveillance for new cases. SARS left a legacy of just over 8,000 probable cases in 29 countries, including 29 probable U.S. cases, with an overall fatality rate of 10%. After bursting on the scene in early 2003, SARS quickly flamed out, with the last handful of clinical cases ever seen identified in China in early 2004.
"It’s likely we will see more" of the NCoV. "We’ll need to cast a wide net since we now know there are a dozen cases and different clinical presentations," Dr. Larry Madoff said at the International Meeting on Emerging Diseases and Surveillance. Although almost every patient with confirmed NCoV infection has had severe illness, one U.K. patient who acquired the infection from another household member had a mild, flulike illness. The milder case "calls into question the [WHO] established case definition for this illness," said Dr. Madoff, director of epidemiology and immunization at the Massachusetts Department of Public Health in Boston and chairman of the meeting’s program committee.
In the days after Dr. Madoff made that assessment at the meeting, the WHO on Feb. 21 reported the 13th case, a patient in Saudi Arabia first hospitalized in late January who died in mid-February.
An effort to track down the origin of the NCoV led to the area surrounding the Saudi Arabian city of Bisha, home of the first identified Saudi case. Suspecting a bat origin for the virus because the SARS-associated virus had been identified as a bat virus (although initial human transmission came via a civet), and because the human isolates of the NCoV could infect several bat-cell lines in the lab, U.S. epidemiologist Jonathan Epstein, D.V.M., led a team that surveyed bats from the Bisha area last fall to see if they could find coronaviruses similar to NCoV. Researchers previously reported finding NCoV-like viruses in bats from other locations that are related to the bats that live in the Bisha area, Dr. Epstein said at the meeting.*
"Everywhere you look in bats there seem to be one or two new coronaviruses, but most bat coronaviruses are not SARS-like. The novel coronavirus is the second bat coronavirus in addition to the SARS virus to cause a human infection," said Dr. Epstein, vice president for conservation medicine at EcoHealth Alliance, an environmental medical research organization based in New York.
"Based on published evidence, there is close relatedness between the novel coronavirus and the SARS virus, but SARS uses a receptor that is deep in the respiratory tract. The novel virus uses a different receptor. It’s not clear whether the novel virus can infect mucosa or the upper respiratory tract, but if it could it might be more transmissible," Dr. Epstein said in an interview.
A report from a team of Swiss researchers published on Feb. 19 (subsequent to Dr. Epstein’s comments) reported that the NCoV (which the Swiss researchers call human coronavirus [HCoV]-EMC) grew very efficiently in vitro on human bronchial epithelial cells, and that interferon treatment cut replication of the virus in these cells (mBio 2013;4:e00611-2).
IMNG Medical Media/Mitchel L. Zoler
Jonathan Epstein, DVM
The episodes of human infection by the NCoV so far that seem to be geographically disparate also have a precedent with SARS.
The pattern of cases "suggests that the source of the infection is common or widespread," Dr. Epstein said. "It’s a challenge to identify common environmental features in the case histories of the infected patients. But with SARS there were multiple spill-over events in different regions of southeast China" when the SARS virus moved from civets into people.
"There clearly are many unknowns about the epidemiology" of the NCoV, Dr. Marjorie R. Pollack, a consultant medical epidemiologist based in New York, wrote in a recent comment on the new coronavirus (ProMed Mail, 2013;Archive Number: 20130221.1554109). "Genetic studies on this NCoV place it related to coronaviruses found in bats. But how did the jump from bats to humans occur? Is there an intermediate host animal?"