Is coronavirus the 'Disease X' WHO warned about?

DISEASE X?: The World Health Organization cautioned years ago that a mysterious "Disease X" could spark an international contagion. The new coronavirus, with its ability to quickly morph from mild to deadly, is emerging as a contender.

SAME AS SPANISH FLU PANDEMIC? A similar pattern of inflammation noted among Covid-19 patients was observed in those who succumbed to the 1918 "Spanish flu" pandemic, said Gregory A. Poland, the Mary Lowell Leary emeritus professor of medicine, infectious diseases, and molecular pharmacology and experimental therapeutics at the Mayo Clinic in Rochester, Minnesota.

STEALTHY VIRUS: From recent reports about the stealthy ways the so-called Covid-19 virus spreads and maims, a picture is emerging of an enigmatic pathogen whose effects are mainly mild, but which occasionally — and unpredictably — turns deadly in the second week. In less than three months, it's infected about 77,000 people, mostly in China, and killed more than 2,200.

SYMPTOMS: This photo taken on February 17, 2020 shows a man (L) who has displayed mild symptoms of the COVID-19 coronavirus using a laptop at an exhibition centre converted into a hospital in Wuhan in China's central Hubei province.

PANDEMIC CHALLENGE: "Whether it will be contained or not, this outbreak is rapidly becoming the first true pandemic challenge that fits the disease X category," Marion Koopmans, head of viroscience at Erasmus University Medical Center in Rotterdam, and a member of the WHO's emergency committee, wrote Wednesday in the journal Cell.

FAST SPREAD: The disease has now spread to more than two dozen countries and territories. Some of those infected caught the virus in their local community and have no known link to China, the U.S. Centers for Disease Control and Prevention said.

REPLICATION: Unlike SARS, its viral cousin, the Covid-19 virus replicates at high concentrations in the nose and throat akin to the common cold, and appears capable of spreading from those who show no, or mild, symptoms. That makes it impossible to control using the fever-checking measures that helped stop SARS 17 years ago.

BROADER SPECTRUM OF SEVERITY: "Unlike SARS, Covid-19 infection has a broader spectrum of severity ranging from asymptomatic to mildly symptomatic to severe illness that requires mechanical ventilation," doctors in Singapore said in a paper in the same medical journal Thursday. "Clinical progression of the illness appears similar to SARS: patients developed pneumonia around the end of the first week to the beginning of the second week of illness."