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Returned travellers from Bali behind spike in chikungunya virus infections

Chikungunya virus infection is a mosquito-borne acute illness caused by the chikungunya virus, a member of the Alphavirus group, which also includes Ross River and Barmah Forest viruses. Chikungunya virus is endemic in many tropical regions of the world, reflecting the distribution of Aedes aegypti and A. albopictus mosquitoes, the same vectors that transmit dengue viruses. Chikungunya virus is not endemic in Australia, although there is potential for transmission in northern Queensland (A. aegypti) and the Torres Strait Islands (both species), where these mosquitoes are established.

From the early 2000s, major outbreaks of chikungunya virus infection were reported in Southeast Asian, South Asian and Indian Ocean island countries, including Indonesia, Malaysia, Reunion, Seychelles, and India. An increased number of chickungunya outbreaks worldwide has resulted in numerous reports of imported infections among travellers recently returned from these and other countries.

Chikungunya virus infection became a notifiable disease in Western Australia in May 2008. Between 2008 and 2012, an average of 6 chikungunya cases were notified per year (range: 2–10 cases), with infection acquired in a number of countries, mostly in Southeast Asia (Figure 1).

This year, however, there has been a dramatic increase in notifications of chikungunya virus disease, with 51 cases reported to September. This increase is attributable wholly to an increase in the number of cases acquired in Bali, Indonesia. Of the 51 cases notified to date, most were females (70%, n=58) and the median age was 45 years (range: 10–74 years). The vast majority of cases (92%, n=47) reported recent travel to Indonesia, and among these, 94% (n=44) had been to Bali. The remaining 4 chikungunya cases in 2013 acquired their infections in Papua New Guinea (n=2), Singapore (n=1) and an unspecified location in Southeast Asia (n=1). Official data on the incidence of chikungunya virus in Bali are lacking, however, one local newspaper report indicated an increase in transmission of the disease in early 2013.

Chikungunya virus infection should be considered among travellers returning from Bali and other endemic regions with febrile illnesses. Signs and symptoms of chikungunya virus infection include fever, rash and arthralgia affecting multiple joints, as well as headache, nausea, vomiting and conjunctivitis. Typically, the fever lasts for 2 days and ends abruptly. Other symptoms, however, last for several days, and joint pains may persist for months. The incubation period ranges from 2 to 12 days but is usually 3 to 7 days. The differential diagnosis in a returned traveller includes measles, rubella, leptospirosis, scrub typhus malaria, typhoid fever and other arthropod-borne viral infections, such as dengue virus. Serological and in some instances polymerase chain reaction (PCR) testing for chikungunya virus infection is available via WA pathology laboratories.

Given the large number of Western Australians who visit Bali, doctors should advise any patient planning travel to the island – or other endemic areas – of the risks of mosquito-borne diseases, particularly dengue fever and chikungunya virus infection.

This advice should include taking precautions to prevent mosquito bites by applying insect repellent, wearing long, light-coloured, loose-fitting clothing and sleeping in screened accommodation. It should also highlight that the mosquitoes that transmit chikungunya and dengue viruses bite during the day and prefer shady, indoor locations.

* 1 January to 30 September 2013

Figure 1 – Notifications of chikungunya virus infection in Western Australia, by country of acquisition and year, May 2008 to September 2013

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