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Currently, dengue is the most important viral disease transmitted by mosquitoes afflicting humans in a world context. Clinical symptoms range from mild fevers, to a severe and potentially life threatening haemorrhagic disease. Source reduction of the breeding habitats of the major mosquito vector, Aedes aegypti, is the best form of control.
The normal cycle of dengue infection is considered to be human - mosquito - human. From feeding on an infected and viraemic human, the female mosquito is able to transmit the dengue virus after an incubation period of 8-10 days wherein virus infection, replication and dissemination result in infection of the salivary glands making the mosquito infective for life.
In Australia epidemics of dengue occurred in the late 19th century and early 20th century. Australia was considered to be free of local dengue following 1955 (when there had been a large outbreak in Townsville), but in 1981 a major outbreak with an estimated 3,000 infections occurred in northern Queensland, presumably initiated by an infected traveller.
In Australia, there are three possible vectors: Ae. aegypti, whose distribution is restricted to Queensland; Ae. scutellaris, which is present in north Queensland and is a known vector of dengue in Papua New Guinea; Ae. katherinensis, which is found in northern Queensland, the Northern Territory and northern Western Australia but appears to be not an effective vector. Additionally, Ae. albopictus, poses a threat to Australia. It is an important vector that has been introduced from Asia to many countries, as eggs or larvae transported in artificial container habitats such as used motor vehicle tyres, and water barrels on ships. If it was introduced to Australia it is likely it could readily establish and present a threat for dengue transmission.
It is assumed that Ae. aegypti is the vector of greatest concern because of its distribution and close association with humans. Ae. aegypti is predominantly a day-biting mosquito whose larvae may be found almost exclusively in clean water in man-made containers such as water-barrels, rainwater tanks, wells, vases, tyres, bottles, tins, and most other water-holding containers found in the domestic environment. Although the species is currently restricted to Queensland, there are past records of Ae. aegypti being found in NSW, the NT and WA.
Dengue is a debilitating infection of comparatively short duration with a high attack rate but a low fatality rate. The so-called 'classical' Dengue Fever (DF) form usually affects older children and adults with fever, violent headache, and severe pains in the muscles and joints following an incubation period of 5-8 days, and lasts about 4-7 days; recovery is generally complete although convalescence may be long. A more severe form, Dengue Haemorrhagic Fever (DHF), involves internal bleeding and is sometimes associated with severe shock (the Dengue Shock Syndrome (DSS)), and occurs most frequently in infants and young children.
Dengue virus occurs as four serotypes, designated DEN 1, 2, 3 and 4; each has been involved in both uncomplicated dengue and in cases with haemorrhagic syndrome.
A variety of blood tests are used to demonstrate the presence of specific antibodies to Dengue virus. Blood samples should be taken during the acute and convalescent phases of the illness, and a fourfold rise in antibody levels will confirm the clinical diagnosis.
No specific antiviral treatments exists nor is there any vaccine available. For patients with DHF or DSS, treatment is supportive.
Restricting the availability of potential breeding habitats for Ae. aegypti will help to reduce mosquito densities and therefore reduce the possibility of disease transmission. All containers capable of holding water in the domestic environment can provide habitat for the larval stage of the mosquito and this includes water-barrels, rainwater tanks, wells, vases, tyres, bottles, potplants saucers and tins.
Personal protective measures include: avoiding known mosquito infested areas, especially at dawn and dusk when mosquitoes are most active; ensuring that houses are adequately fly screened (with small mesh); using insect repellents that contain the chemical DEET, and reapplying it regularly; and wearing long sleeved shirts and pants.
Boughton, C.R. (1996). Australian Arboviruses of Medical Importance. Royal Australian College of General Practitioners, Melbourne, pp 67.
Gubler, D.J. (1988). Dengue. in Monath, T. (ed). The Arboviruses: Epidemiology and Ecology, Volume II. CRC Press, Florida, pg: 233-261.
Gubler, D.J. and Kuno, G. (eds). (1997). Dengue and Dengue Hemorrhagic Fever. CAB International. Cambridge.
Assoc. Prof. Richard C. Russell and Stephen L. Doggett
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