For Hong Kong there is a chilling reminder of the 2002-03 Sars epidemic in the latest - and worst yet - outbreak of Ebola, a viral disease with a mortality rate from 60 to 90 per cent. It has now swept across borders in west Africa, killing over 700 people in four countries. As with Sars, the victims include doctors, nurses and even a hygienist responsible for detoxifying protective suits worn by visitors to Ebola isolation centres.
There the similarity ends. Unlike severe acute respiratory syndrome, Ebola is not spread readily on the air by droplets from an infected person. It is spread by contact with the blood, body fluids or even sweat of infected people. The vulnerability of health workers and the extreme mortality rate are attributed to poor health-care infrastructure such as effective isolation, and the lack of secure testing facilities for dangerous samples from suspected Ebola victims. Most worryingly, the virus has now spread from isolated rural villages to urban west Africa.
There is no room for complacency elsewhere. A Liberian official who flew to Lagos, Nigeria, collapsed at Lagos international airport and died in hospital of Ebola. As virologists have pointed out, he might have gone anywhere within an incubation period of up to 21 days. It is therefore reassuring that Hong Kong's health authorities have stepped up surveillance and prepared contingency plans in the event of the Ebola virus appearing in the city.
Having jumped the species barrier, probably from fruit bats, Ebola now spreads from human to human. There is no cure or vaccine. Symptoms include fever, vomiting, diarrhoea, organ failure and internal and external bleeding. To bring the latest outbreak under control, Africa needs international help from government and non-government agencies, in addition to the coordinating role of the World Health Organisation and the brave dedication of doctors and nurses from Medicins Sans Frontieres and other health charities. Supplies of protective clothing like masks, gowns, gloves and goggles are urgently needed to reduce the risk to the lives of people who save lives. Local community leaders must be enlisted to support efforts to modify cultural attitudes and customs that impede proper health care, including suspicion of modern medicine and ritual washing of the bodies of the dead. Without international medical, material and financial help, there is a risk of an African humanitarian crisis with global health implications for international transport and the movement of people.