Chikungunya is a Makonde (Bantu) word meaning "that which bends up", describing the contorted posture of patients suffering from the illness. It is caused by an arbovirus transmitted by mosquitoes of the genus aedes, like Dengue Fever. The symptoms are also similar to Dengue (fever, nausea, rash and joint pain) but chikungunya is significantly less dangerous (unlike Dengue, it does not develop into haemorrhagic fever), and not life-threatening except for those with existing serious health problems. A minority of patients have to spend a few days in hospital.The acute phase only lasts a few days but joint pain and weakness can persist for weeks or even months in some patients.

The outbreak was most serious on the neighbouring island of Reunion in the summer. It has since begun to decline and is expected to decline further as the southern winter sets in with cooler and dryer weather. But with as many as 3000 new cases per week in May, the epidemic in Reunion is far from over. Some 200,000 out of Reunion's population of 770,000 have already had the disease.

On Mauritius, infections are at a much lower level, with around 6000 cases confirmed so far. Most of the cases have been concentrated around Mahebourg (near the airport but on the opposite side of the island from Flic en Flac) and other areas on the east coast. One case was diagnosed in Hong Kong in a visitor who had returned from Mauritius in March. A HKU professor who stayed in Tamarin (near Flic en Flac) in April 2006 encountered very few mosquitoes, while a HK family who stayed in a resort in May encountered no mosquitoes at all.

The likelihood is that new infections will decline to a low level by June/July but there will still be some degree of risk in visiting Mauritius. The incubation period is typically 4-7 days: that is, symptoms begin suddenly between 4 and 7 days after being bitten by an infected mosquito. In the unfortunate event of being infected during the field trip it is therefore likely that the patient would be back in HK when the symptoms begin. Painkillers such as paracetemol and acetominophen are recommended, but not aspirin.

The virus cannot be transmitted directly beween people. However if an infected person is bitten the same mosquito could infect others nearby. It is therefore important to keep patients away from mosquitoes.

There is currently no vaccine or specific treatment, and vaccines are still at an experimental stage. So the focus is on prevention by avoiding mosquito bites. Campaigns to fumigate and eradicate breeding places have been under way in Mauritius, where malaria was successfully eradicated some years ago. This poster from the Mauritian Ministry of Health and Quality of Life says in creole: "Protect you(rself) against mosquitoes to avoid the transmission of disease... keep your environment clean".

The mosquito responsible is aedes aegyptii a close relative of aedes albopictus, the "Asian tiger mosquito" found in Hong Kong, both being identified by the black and white stripes along the body; a. aegyptii carries yellow fever, dengue fever and chikungunya in Africa, while a. albopictus carries dengue in Hong Kong, Singapore and Southeast Asia.