Coronavirus that causes Covid-19 can produce more than 3 times as many pathogens than SARS strain, HKU study reveals

Microbiologist Yuen Kwok-yung suggested appointing an infection-control supervisor in each office and school of Hong Kong.
PHOTO: South China Morning Post

The coronavirus that causes Covid-19 can produce more than three times the amount of pathogens than the strain that caused the severe acute respiratory syndrome (SARS) outbreak in 2003, although patients may display less inflammatory and immune responses, a study has found.

The finding from the research, led by prominent Hong Kong microbiologist Yuen Kwok-yung, is the first of its kind based on tests conducted on lung tissue removed from patients. The results underlined the virality of the disease, as well as difficulties for health authorities worldwide to detect it compared to SARS.

It took about six months to contain the SARS epidemic.

But it is a much bigger challenge for the Covid-19 pandemic, which has infected more than 1.6 million people around the world and caused more than 100,000 deaths in four months. According to the World Health Organisation, some 8,098 people were infected by Sars and 774 died of it.

"There is almost no possibility of containing the virus before July," said Yuen, of the University of Hong Kong (HKU), who led the study published in scientific journal Clinical Infectious Diseases.

By infecting lung tissues, donated by six patients, with both the viruses, Yuen and his team found the new coronavirus, officially known as SARS-CoV-2, generated 3.2-fold infectious viral particles than Sars within 48 hours.

"In some cases, SARS-CoV-2 could replicate by about 100 times within 48 hours, while the Sars virus may have peaked at about 10 to 20 times of replications," Dr Chu Hin, research assistant professor from HKU's medical school, said.

Despite reproducing more efficiently, the new virus induced slower immune and inflammatory responses, according to the study. Unlike the SARS virus, the SARS-CoV-2 almost did not induce any signalling protein interferons within 48 hours, which is key in triggering the immune system to counteract against the virus.

Of 13 types of what scientists called pro-inflammatory gene markers that lead to inflammation in the lungs, the new coronavirus triggered only five, while SARS was able to trigger 11.

"The virus is like a ninja, replicating inside the body with lower interferons and inflammatory response," said Dr Jasper Chan Fok-woo, clinical assistant professor at the medical school, adding further tests could be useful in speeding up clinical trials for medications.

The lack of symptoms or only mild symptoms have made governments around the world difficult to contain Covid-19.

With 90 per cent of the population not immune, Yuen warned that the virus could continue to spread even after the summer. While social distancing and universal masking would have to be continued, he suggested appointing an infection-control supervisor in each office and school beyond July.

"You should continue to wear masks, continue to have very good personal hygiene before you enter a school or an office. You should also be tested first to make sure you don't have the virus," Yuen said, adding Hong Kong must increase the testing capacity for the virus.

"The study also showed just having 14-day quarantines were not enough. When we reopen the border, travellers may still have to be tested.

The findings also proved that a cocktail therapy by Hong Kong medical practitioners is going in the right direction to induce an immune system response, Yuen added. Doctors have been prescribing a cocktail of lopinavir and ritonavir along with interferon beta.

"It appears from our preliminary results that the beta-interferon is the backbone, the most important component of this therapy," Yuen said.

The number of cases in Hong Kong reached 1,000 on Saturday afternoon, though the daily increase has remained below 20 new cases, prompting Yuen to suggest the city may see the end of local community outbreak soon.

"The second wave of infections is already coming down, but we can't be so sure … if people go out and have gatherings, it could return. So, observe the regulations and don't gather unless necessary," he said.

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This article was first published in South China Morning Post.