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2020/04/07 16:24

武漢爆發肺炎是過去26年,蝙蝠身上病毒引起的第6起傳染病,其他5起: Hendra in 1994, Nipah in 1998, SARS in 2002, MERS (Middle East respiratory syndrome) in 2012, and Ebola in 2014. 本次冠狀病毒96%相同於雲南馬蹄蝙蝠身上的冠狀病毒。蝙蝠或動物本身不是問題,它們只是自然、正常的生活著,人類去接觸它們才是問題。如此狀況繼續下去,下一次的傳染病爆發,只是時間問題。現在全球急於針對本次冠狀病毒研究解藥與疫苗,長期須對所有具危險性的冠狀病毒,開發一體適用的解藥與疫苗。

By January 7 the Wuhan team determined that the new virus had indeed caused the disease those patients suffered—a conclusion based on results from polymerase chain reaction analysis, full genome sequencing, antibody tests of blood samples and the virus’s ability to infect human lung cells in a petri dish. The genomic sequence of the virus—now officially called SARS-CoV-2 because it is related to the SARS pathogen—was 96 percent identical to that of a coronavirus the researchers had identified in horseshoe bats in Yunnan, they reported in a paper published last month in Nature. “It’s crystal clear that bats, once again, are the natural reservoir,” says Daszak, who was not involved in the study.

In 2004, an international team of scientists takes blood and swab samples from bats at night in order to discover potential bat-borne pathogens. Credit: Wuhan Institute of Virology

The genomic sequences of the viral strains from patients are, in fact, very similar to one another, with no significant changes since late last December, based on analyses of 326 published viral sequences. “This suggests the viruses share a common ancestor,” Baric says. The data also point to a single introduction into humans followed by sustained human-to-human transmission, researchers say.

Given that the virus seems fairly stable and that many infected individuals appear to have mild symptoms, scientists suspect the pathogen might have been around for weeks or even months before the first severe cases raised alarm. “There might have been mini outbreaks, but the virus burned out” before causing havoc, Baric says. “The Wuhan outbreak is by no means incidental.” In other words, there was an element of inevitability to it.

Although the Wuhan outbreak is the sixth one caused by bat-borne viruses in the past 26 years —the other five being Hendra in 1994, Nipah in 1998, SARS in 2002, MERS (Middle East respiratory syndrome) in 2012, and Ebola in 2014—“the animals [themselves] are not the problem,” Wang says. In fact, bats help promote biodiversity and the health of their ecosystems by eating insects and pollinating plants. “The problem arises when we get in contact with them,” he says.

The researchers found that the new coronavirus enters human lung cells using a receptor called angiotensin-converting enzyme 2 (ACE2). The scientists have since been screening for drugs that can block it. They, as well as other research groups, are also racing to develop vaccines and test promising candidates. In the long run, the team plans to develop broad-spectrum vaccines and drugs against coronaviruses deemed risky to humans. “The Wuhan outbreak is a wake-up call,” Shi says.



Tracking cases through mutations

Bedford’s lab has been using genetics to track the new coronavirus, known as SARS-CoV-2, since the first U.S. cases started to multiply in Washington State in February and March. Back then, public health officials focused on tracking patients’ travel histories and connecting the dots back to potentially infected people they’d met along the way.

Meanwhile, Bedford and his team turned to unlocking the virus’s genetic code by analyzing nasal samples collected from about two dozen patients. Their discovery was illuminating: By tracing how and where the virus had changed over time, Bedford showed that SARS-CoV-2 had been quietly incubating within the community for weeks since the first documented case in Seattle on January 21. The patient was a 35-year-old who had recently visited the outbreak’s original epicenter in Wuhan, China.