To identify the origin of an unknown virus, scientists need to find out the pathogen that caused the disease and the animal carrier, that is, the natural host of the virus, according to Dr Zhao Guoping, an academician of the Chinese Academy of Sciences.
Tracing the origin of the virus pathogen requires scientific evidence, including the biological evidence provided by etiology, clinical medicine and epidemiology and the molecular biological evidence provided by genetic sequencing and antibody detection, according to Dr Zhao.
The epidemiological investigation of the origin of an infectious disease usually starts from the contact history of the first infected patient, or "patient zero", which is even more difficult to confirm.
It is challenging to trace COVID-19 patient zero as it involves a large volume of complicated data, and the early cases might include asymptomatic infections short of medical records, said Liu Peipei, an expert at the Chinese Center for Disease Control and Prevention.
Jin Qi, head of the Institute of Medical Biology at the Chinese Academy of Medical Sciences, said patient zero has not been confirmed for the 1918 influenza pandemic, AIDS or the H1N1 flu that broke out in 2009.
