00000000DF is most prevalent in adults, while DHF is more prevalent in children. In 1975, 64.7 per cent of dengue cases were in the under 15 years age group, but in the peak year of 1982 only 42.5 per cent of cases were in this age group. Similarly for mortality, 51.4 per cent of deaths in 1982 occurred in people over 15 years, whereas in the past it was rare for adults to die of dengue disease. The disease has been showing a milder spectrum with less mortality since 1984. The decline in mortality can be attributed to increased awareness of the disease, early medical attention and changing patterns of the disease. More deaths have occurred among the Chinese and this can be attributed to their lifestyle, customs and beliefs, which delay them from seeking proper medical attention and referral.

00000000The two vectors of dengue in Malaysia are A. aegypti and A. albopictus. Aedes aegypit is a domiciliary mosquito and is found both inside and outside the home. It is usually associated with DHF in urban settings. Aedes albopictus, a local species, is prevalent in peri-urban areas and is associated with dengue fever.

00000000The density of the vector mosquitoes is related to climatic conditions and the habit of storing water. Aedes aegypti prefers clean clear water with low oxygen partial pressure e.g. rainwater. The Aedes premise index and the Breteau or container index are used to monitor the density of mosquitoes for preventive actions. Periodic house inspections and entomological surveys carried out under existing law (Destruction of Disease Bearing Insect Act, 1975) have not generated useful indices. Outbreaks tend to occur in areas with high Aedes densities. However, areas with low Aedes indices (of five per cent or less) are not exempt.

Data from WHO/WPR 1997

Australia

00000000Aedes aegypti is believed to have become established in northern Australian settlements in the 1860s. Lumley and Taylor(27) documented regular epidemics of dengue, commencing in 1873 when eight clinical cases were imported into Sydney from Mauritius. Local transmission was probably first recorded from Townsville in 1879 but the outbreaks on the Charters Towers gold fields during 1885 - 1886 are better remembered because of their extensiveness and the description by Hare(28) of what is considered to be the first DHF case. By 1926, clinical dengue had been reported in four Australian states, coincident with the distribution of A. aegypti. Lumbey and Taylor(27) reported on the large outbreak of dengue in 1941 - 1944, which spread from Queensland to New South Wales due to the movement of armed services personnel. From 1954 - 1955, north Queensland was stricken by DEN-3 virus and some 15 000 of 40 000 residents of Townsville were infected(29). In ensuing years, A. argypti was reduced and this led to the decline of dengue in the country.

00000000From 1981 - 1983, there was an upsurge of dengue activity in Queensland. Breteau indices of over 100 were not uncommon, a level said to be twice that of the high risk category for yellow fever(30). It has been estimated that at least 3000 infections of DEN-1 occurred in 19 north Queensland towns. In Cairns, it was noted that 13 of 98 patients showed some haemorrhagic manifestations but these were not severe enough to be classified as DHF. A control programme has been mounted against the mosquito vector but the possibility still exists that the other dengue serotypes will be introduced into Australia.