The last of the three students diagnosed with novel coronavirus (Covid-19) in Kerala after returning from the epicentre of the outbreak in Wuhan in January left for home after being declared disease free on Friday, even as the World Health Organisation said data from China continues to show a decline in new cases in the country. Yet the threat of a pandemic remains high with a worldwide surge in cases with no clear link to China, which has confirmed asymptomatic transmission of the infection that has now been reported in 27 countries.
A 20-year-old woman from Wuhan who had no symptoms travelled 675 km north to Anyang and infected five relatives, Chinese scientists reported this week. After her relatives developed Covid-19 pneumonia, she was isolated but initially tested negative for the virus. Follow-up tests showed she was positive for Covid-19 despite her having a normal chest CT and being free fever, stomach or respiratory symptoms, such as cough or sore throat, according to doctors at the People’s Hospital of Zhengzhou University in Henan Province in China.
All novel outbreaks are a public health concern because humans have no immunity against a new disease. The coronavirus family of viruses cause about a third of all common colds (rhinoviruses, adenoviruses, and viruses also cause the common cold), but severe disease is caused by Sars (severe acute respiratory syndrome) and Mers (Middle East respiratory syndrome), which had a death rate of about 10% in 2003 and 30% 2012, respectively.
Genetic analyses shows Covid-19 shares 79.5% of genetic sequence with Sars coronavirus, accrding tot he journal Nature, with the two also having the same cell entry receptor that attaches to the membrane of the host cell to cause infection. Covid-19 has 96.2% homology to a bat coronavirus, but the intermediate species between bats and humans has yet to be identified. For Sars it was civet cats, for Mers it is camels.
Covid-19, however, spreads more easily than Sars or Mers, which is what is what has made it so difficult to contain, more so because new evidence shows infected people apparently healthy can also infect others. The clinical of fever and dry cough in the majority of patients, with about a third developing shortness of breath, and some reporting headache, sore throat, and diarrhoea.
The known routes of transmission are through droplets in the air by coughing and sneezing, close personal contact including touch, touching an object or surface contaminated with the virus and then touching your mouth, nose or eyes before washing your hands, and in rare cases, faecal contamination.
The incubation period (time between getting infected and showing symptoms) is reported to be 5.2 days, but it is known to last up to 14 days, which is the reason people exposed to the virus are asked to stay quarantined for at least two weeks. With new evidence proving transmission begins during the asymptomatic phase, tracking the source of the infection is increasingly getting more difficult as the infection spreads beyond 27 countries to cause localised outbreaks in communities.
Though the number of infections outside mainland China is a little over 12,000, the rate of secondary and tertiary transmission is increasing. Apart from the confirmed cases from travellers to Wuhan and on cruise ships, countries including Singapore, Japan, Thailand, South Korea and Italy and have identified clusters of locally transmitted cases.
The WHO has cautioned that despite new infections reducing in China, it’s still unclear which way the pandemic will go. With global air travel increasing 10-fold since the last Sars epidemic in 2003, countries must stay vigilant to track and contain the infection. Despite huge funding committed for vaccine development, the world is unlikely to get a vaccine before 18 months. Till knowledge gaps remain in understanding virus behaviour, old-fashioned containment measures of diagnosis, surveillance, quarantine, supportive treatment, transparent data sharing, and global partnerships are the only shield against the new infection.