A study in virulence

A comparison of the severities of coronavirus outbreaks so far

Less than a month after a novel coronavirus struck the picturesque Chinese city Wuhan in Hubei province, the first set of scientific results on the deadly virus shows its eerie similarity to the SARS pathogen that swept the world 17 years ago, infecting more than 8,000 people and killing 774 in 17 countries.

The World Health Organisation’s January 30 situation report says there are 7,818 confirmed cases globally in 19 countries with 170 deaths. China bears the brunt as there are only 82 confirmed cases in 18 countries with no death outside the communist country. The disease shows no signs of abatement and spreads due to international travel.

Preliminary data from Wuhan indicate similarities between the first 41 cases of 2019 novel corona-virus and SARS. The 2019 novel coronavirus (2019-nCoV) appears to cause similar symptoms such as the severe acute respiratory syndrome and the risk of spreading from person to person and between cities.

Closely related

A new genetic analysis of 10 genome sequences of 2019-nCoV from nine patients in Wuhan finds that the virus is most closely related to two bat-derived SARS-like coronaviruses. The study was published in Lancet.

Comparing the 2019-nCoV genetic sequence with a library of viruses, a team of researchers from the China-based Shandong University, Shandong First Medical University and Shandong Academy of Medical Sciences found that the most closely related viruses were two SARS-like coronaviruses of bat origin — bat-SL-CoVZC45 and bat-SL-CoVZXC21 — which shared 88% of the genetic sequence.

The scientists found 2019-nCoV was genetically little distant to the human SARS virus (which shared about 79% of the genetic sequence) and the Middle East respiratory syndrome (MERS) virus (which shared about 50% of the genetic sequence).

Studying the spike protein of the virus (how it binds, then enters human cells), the authors report that 2019-nCoV and human SARS virus have similar structures, despite some small differences. As a result, they suggest that 2019-nCoV might use the same molecular doorway to enter the cells as SARS (a receptor called ACE2), but note that this will require
confirmation.

Based on their data, the authors say that it seems likely that the 2019-nCoV causing the Wuhan outbreak might also be initially hosted by bats and transmitted to humans via a currently unknown wild animal sold at the Huanan Seafood Market.

Currently, six coronaviruses (seven including 2019-nCoV) are known to cause diseases of the respiratory tract in people, but only SARS and MERS have resulted in large outbreaks of fatal illness to date.Currently, there are no specific coronavirus antiviral drugs or vaccines with proven efficacy in humans.

The first hint came from an analysis of the first 41 patients — admitted to a Wuhan hospital between December 16, 2019, and January 2, 2020 — who were infected with laboratory-confirmed 2019-nCoV.

Combing clinical records, laboratory results, and imaging findings with epidemiological data, the authors reported that on an average, patients were middle-aged (median age 49 years), most had visited Huanan Seafood Market (66%, 27 patients), and were men (73%, 30 patients). Like SARS, the majority of cases affected healthy individuals, with less than a third of cases occurring in people with underlying chronic medical conditions such as diabetes (20%, 8 patients), high blood pressure (15%, 6), and cardiovascular disease (15%, 6).

Similarly, 2019-nCoV infections presented with a broad range of symptoms.

All patients admitted to hospital had pneumonia and most had a fever (98%, 40 patients), cough (76%, 31), and fatigue (44%, 18). Over half of the patients experienced shortness of breath (dyspnoea; 55%, 22), whilst headache (8%, 3) and diarrhoea (3%, 1) were rare.

“Despite sharing some similar symptoms with SARS (fever, dry cough, shortness of breath), there are some important differences, such as the absence of upper respiratory tract symptoms (rhinorrhoea [runny nose], sneezing, sore throat) and intestinal symptoms, such as diarrhoea which affected 20-25% of SARS patients,” explains lead author Bin Cao from the China-Japan Friendship Hospital and Capital Medical University, China.

Approximately one in three patients developed acute respiratory distress syndrome (29%, 12 patients) or were admitted to intensive care (32%, 13 patients), and six died.

Cytokine storm (overproduction of immune cells) occurred in critically ill patients, but more research is needed to understand how it impacts the immune system, the researchers report in Lancet.

“It is hard to understand the mortality rate associated with this new virus currently, as we are only detecting severe cases in the initial stages of the epidemic, rather than the milder or asymptomatic cases,” explains co-author Lili Ren from the Chinese Academy of Medical Sciences and Peking Union Medical College, China.

Poorly understood

Even though classic public-health measures brought the SARS pandemic to an end, the factors associated with transmission of SARS-CoV — ranging from self-limited animal-to-human transmission to human super-spreader events — remain poorly understood nearly 20 years later, according to an account published in the January 23 issue of the JAMA.

In another Lancet paper, a team studied a family of seven people who presented the hospital with unexplained pneumonia. They identified 2019-nCoV in five members who had recently visited Wuhan, and in one other family member who did not travel with them.

Only a child, who was reported by their mother to have worn a surgical mask for most of the stay in Wuhan, was not infected.

Importantly, another child was infected with 2019-nCoV, but showed no clinical symptoms — suggesting that individuals may be able to spread infections in the community without knowing that they are infected.

“Our findings are consistent with person-to-person transmission of this new coronavirus in hospital and family settings, and the reports of infected travellers in other countries,” says lead scientist Kwok-Yung Yuen from the University of Hong Kong-Shenzhen Hospital.