SARS virus is mutating, fear doctors
15:55 16 April 03
NewScientist.com news service
A cluster of SARS patients in Hong Kong with unusual symptoms has prompted concern that the virus causing the disease is mutating. Doctors fear the changes are making the disease more severe.
Scientists in Hong Kong are now urgently sequencing key genes from recently isolated coronaviruses to reveal any changes. New Scientist has learned that the changes in symptoms mirror those already seen when animal coronaviruses have mutated.
Microbiologist Yuen Kwok-yung, at the University of Hong Kong, said on Wednesday that the 300 patients from a SARS hot spot, the Amoy Gardens apartment complex, were more seriously ill than patients who acquired the infection elsewhere.
The Amoy Gardens patients are three times as likely to suffer early diarrhoea, twice as likely to need intensive care and less likely to respond to a cocktail of anti-viral drugs and steroids. Even medical staff who caught the infection from Amoy Gardens patients are more seriously ill, Yuen said.
Gut and lung
The comparison of the symptoms is continuing, says John Tam, a microbiologist at the Chinese University of Hong Kong. "But at the same time we are studying the genetic sequences of the viruses involved in both outbreaks. The presence of a mutation leading to an altered tissue preference of the virus cannot be discounted at the moment," he told New Scientist.
The much higher rate of diarrhoea in Amoy Garden cases supports the idea of an altered tissue preference, meaning a viral strain that can attack the gut as well as the lungs.
This switch mirrors effects seen in several animal coronaviruses. A bovine gut coronavirus, with some genetic sequences similar to the SARS virus, can also cause severe pneumonia in cattle. And in the 1980s, a pig gut coronavirus suddenly mutated into a respiratory infection in pigs.
These switches involved mutations in the viral genes coding for the spike proteins, which form the protruding halo that gives coronaviruses their name. Luis Enjuanes and colleagues at Spain's National Centre for Biotechnology in Madrid have switched the pig virus from a mild respiratory infection to a virulent gut infection solely by changing the spike protein gene. Ominously, the gut form replicated much faster.
Pinning down
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So scientists are likely to look for changes to the spike protein gene in the virus infecting Amoy Gardens patients. "It may require a lot of sequence work," Malik Peiris, of Hong Kong University, told New Scientist.
But the complete genetic sequences of two virus samples isolated early in the SARS epidemic, now released by Canadian and US researchers, will make it easier to pin down any subsequent changes.
The fears of viral mutation came as the death toll from SARS reached 161, with nearly 3600 reported infections in countries all over the world. On Wednesday, the World Health Organization officially named the new coronavirus as the cause of SARS, based on work reported by New Scientist on 2 April.
And health officials have expressed further concern about the under-reporting of cases in China, where SARS originated. Officially, the capital Beijing has 40 SARS cases. But, after gaining access to two military hospitals, the WHO's Alan Schnur said: "I would guess the range would be between 100 and 200 probable cases in Beijing." In total, about a thousand people are under observation in the city.
Debora MacKenzie |
