Chikungunya fever is another tropical, mosquito-born disease. It's endemic in Southeast Asia, India and great parts of Africa.

The Asian tiger mosquito is one of several vectors for chikungunya.

Chikungunya is a virus which was discovered in 1953, first documented in Thailand in 1958. Most of the population in Indochina is probably immune against the disease. Though, tourists and travellers from other world regions are usually not immune. The disease is spreading out to the southern parts of Southeast Asia. In the last years there were considerable numbers of cases of chikungunya in Indonesia, Malaysia, the Philippines, Burma/Myanmar, Cambodia and Thailand, certainly also in Singapore. Between 2001 and 2003 there was a chikungunya epidemy on Java. In May 2009 there was an outbreak in Trang / Thailand, in 2012 in parts of Cambodia with 1,500 reported cases. Chikungunya appeared the first time in Cambodia in 1961.

Chikungunya is transfered by various kinds of mosquitoes, including the aggressive Asian tiger mosquito (Stegomyia albopicta, or aedes albopictus), which transferes dengue fever and a number of other diseases as well. Other vectors of the chikungunya virus are primates and rodents.

Recently a virus mutation happened, which is particularly well transfered by the Asian tiger mosquito. It's pathogenicity is higher than those of the other, older variations.

The outspread of the Asian tiger mosquito in the last years, also into south Europe, is supposed to be responsible for the chikungunya epidemy in summer 2007 in Ravenna, Italy. Possibly the disease will spread out into more regions in Europe and north America in the next years.

The chikungunya virus is very vector-adaptable and therefore transfered by various kinds of mosquitoes; the Asian tiger mosquito is only one of them, anopheles (the malaria-transfering mosquito) another, together with culex and mansonia mosquitoes. Since anopheles mosquitoes (malaria) are night-active and the tiger mosquitoes (dengue) are day-active, chikungunya transfering mosquitoes cover day and night activities. That makes a potential infection risk around the clock, particularly in the time around dawn and dusk.

Usually the disease is not transfered directly from human to human, though there are allegedly proofed exceptions reported. Pregnant women can transfer chikungunya to their unborn children, as happened in a case in the provincial hospital in Trang / Thailand in the end of May 2009. At this time there was an outbreak of chikungunya in Trang which spread out over other parts of Thailand, particularly infecting military troops in the south of the country.

After an incubation period of three to seven (maximum two to twelve) days the victim gets high fever together with severe limb pain and high touch sensitivity. The fever lasts normally some few days, in average three days. Other symptoms are muscle pain, rash, slight photophobia, internal bleedings, noise and gum bleeding, headache, fatigue, eye-inflammation and stomach problems.

An Asian tiger mosquito (aedes albopictus, potentially a chikungunya and dengue vector), seen in Kampot, Cambodia. Though, this specimen is missing the characteristical white line on it's back. Aedes albopictus can easily be mistaken with other subspecies of the kind. Image by Asienreisender, 2013

Usually the disease eases off after one or two weeks without treatment and no harm remains. Afterwards the patient is immune against it for the rest of his life. There are asymptomatic courses in with the patient does not show the listed symptoms.

Generally it's observed that the recovery from the disease depends on the patients age. Younger people recover (much) faster than middle-aged. Older people suffer longest.

In some cases long-term complications occur. The symptoms can reappear over months or, very seldom, over (up to two) years. Particularly limb pain over longer periods are reported. Also liver inflammations, heart inflammations, neurological problems, encephalitis or even brain damages can appear. Though, a hemorraghic course of the disease, in contrast to dengue, is seldom.

Typically for chikungunya is a certain sensitivity of one or both wrists for pressure.

For a reliable diagnosis a laboratory test is required, where a virus isolation can be done. The disadvantage is that the test requires a high safety level and takes one to two weeks until completion.

Another test (RT-PCR) is identifying chikungunya-specific genes and can be completed in one to two days.

A serological diagnosis shows results in two to three days, but is not as reliable as the others.

Nevertheless, it's not easy to differentiate chikungunya from dengue, because both diseases appear in similar areas and show familiar symptoms, including the antibodies in the blood.

Since chikungunya is a disease which appeared (until recently) exclusively in poor, developing countries, there was no promising market for a medical treatment. Research for a vaccine or a medicine therefore was small.

So, when it comes to therapy it looks pretty similar as it does for dengue. Abatement of symptoms by applying pain relievers (paracetamol is mostly recommendet, by no means aspirin!) is most what can be done.

Prevention against chikungunya includes the measurement against mosquitoes in general: repellents, mosquito nets, destruction of their breeding places... A vaccination is not available yet, but might be developed within the next years.

In 1981 reportedly two liters of concentrated chikungunya virus were stolen from a laboratory for biological warfare in Fort Detrick, USA. The amount would be sufficiant to overkill, theoretically, the global population. The information on the theft was coming to the public due to a whistleblower in 1986.