Aedes albopictus mosquito feeding
On 26th April 2013 2 cases of Chikungunya Fever were reported in The Cairns Post (1). The patients involved had both recently returned from Papua New Guinea and the cases are thought to have been imported. “Phew!” I hear you say; “Although it does expand the list of differential diagnoses of the febrile returned traveller, it doesn’t directly impact my overall practice as I work in Brisbane/ Sydney/Melbourne” (delete as applicable).
Unfortunately that is untrue. If we look at the history and natural history of Chikungunya Fever it will become apparent that it is a disease that we will be seeing more of.
Chikungunya virus (CHIKV) is an arthropod-borne virus, of the genus Alphavirus, which is transmitted to humans by virus-carrying Aedes mosquitoes. It was first described during an outbreak in Tanzania in 1952. The name ‘chikungunya’ derives from a root verb in the Makonde (Bantu) language, meaning “that which bends up” (similar to the colloquial “breakbone fever” for Dengue Fever, they also share vectors).(2)
From its initial range in Southern Tanzania and Northern Mozambique, Chikungunya has spread through East Africa, The Middle East, India, S.E. Asia and Indonesia. The disease was detected in Vanimo in Sundaun Province in Papua New Guinea in Feb 2012. Throughout 2012 it spread slowly east. The disease was in Lae by December 2012. From Lae it has spread dramatically and is now found in most cities in PNG including an outbreak of over 300 cases in one area of Port Moresby in April 2013.(3)
The important thing to note is that CHIKV is transmitted by Aedes mosquitos. Both Aedes aegyptii and Ae albopictus have been found in Australia and are able to breed there.
Ae aegyptii is the domestic vector for Dengue. Ae aegyptii has previously had endemicity throughout the Eastern States and in SW Australia. Ae aegyptii was found as far south as N NSW until 1948 and in WA until 1970. The range is now confined to Qld with a small area of NT.(4) Climate changes are likely to extend that range considerably. (Figure 1)
Figure 1: Present and historical range of Aedes aegyptii mosquito.Taken from ref 4.
Ae albopictus is found in the Torres Strait and has been found in imported tires in docks throughout Australia. Ae albopictus is even more concerning as it has more tolerance to cold and environmental modelling suggests it could thrive as far south as Melbourne should it get a foothold and a breeding population within the Australian mainland.(5) (See Figure 2)
Both Aedes species are day biting mosquitos that favour shady places to roost and find human habitations very congenial.
Chikungunya Fever has a presentation very similar to malaria or Dengue Fever with high fever, myalgia/arthralgia, headaches and prostration. Unlike malaria and dengue there are no common fatal complications. The concern with CHIKV infection is that the arthralgia can persist for months, or even years, after the disease has defervesced, leading to a significant morbidity.
For more information about the febrile traveller and exotic tropical maladies, come to EMCore Fiji 2014.
- New cases of mosquito-borne chikungunya disease found in Cairns. Damon Guppy, Cairns Post. Friday, April 26, 2013
- WHO Factsheet, Chikungunya. Factsheet No 327. 2008
- Personal correspondence with national dept health disease reporting PNG.
- The Extinction of Dengue through Natural Vulnerability of Its Vectors. Williams CR, Bader CA, Kearney MR, Ritchie SA, Russell RC – PLoS Negl Trop Dis 2010
- Aedes (Stegomyia) albopictus – a dengue threat for southern Australia?; Richard C Russell et al. Commun Dis Intell 2005;29:296–298.