Chikungunya and dengue fever are both viral infections spread by the Aedes mosquito.
The viruses are transmitted from human to human by the bites of infected female mosquitoes.
A mosquito carrying either virus can infect more than a dozen people in its lifetime.
The Aedes aegypti is more likely to spread dengue and the Aedes albopictus, the chikungunya virus. However, both types of mosquitoes can spread both diseases.
Both diseases are on the rise.
Chikungunya, which is endemic in Africa and the Indian subcontinent, was unknown here until 2008, when Singapore had its first locally transmitted case. A major outbreak followed, with 690 people coming down with it that year and another 343 the following year.
But the National Environment Agency broke the chain of transmission, resulting in only three to six locally infected cases annually for the past three years.
So far this year, 186 people have been infected here.
Dengue fever, a more familiar adversary, is also rampant this year, with the number of cases hitting 8,001 as of yesterday. This is about 50 per cent higher than the 4,632 cases seen in the whole of last year. There were 5,330 cases in 2011.
A person can be infected with both diseases at the same time.
Associate Professor Leo Yee Sin, clinical director at the Communicable Disease Centre, said: "Having one disease does not protect against getting the other."
Dr Mukund Doshi, a specialist in internal medicine at Parkway East Hospital, said cases have been documented in Africa where patients have been infected with both dengue and chikungunya at the same time. He does not know if there are any such cases here.
Symptoms for chikungunya and dengue are almost identical - high fever, headache, eye ache, joint pain, rashes and lethargy.
Several methods can be used for diagnosis. Blood tests can detect the dengue virus or chikungunya virus in the blood during the first few days of infection, or antibodies against the viruses subsequently.
The test to check for the virus is done if doctors suspect that the patient has either dengue or chikungunya infection.
The fatigue that is caused by both viral diseases can last weeks and even months.
In some cases, the joint pain caused by chikungunya may persist for several months, or even years.
Chikungunya is rarely fatal, but dengue can be.
In 2005, 14,000 people fell sick with dengue and 25 died. So far this year, no one has died from dengue.
Currently, no vaccine is available for either dengue or chikungunya. Some dengue vaccines are being tested but they have not been approved yet, said Dr Doshi.
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