The World Health Organisation declared Australia to be malaria-free in 1983. Since then and until recently, only one outbreak of multiple cases of malaria has been recorded on the mainland. The current issue of the Medical Journal of Australia looks at how a second outbreak of multiple cases occurred just north of Cairns in 2002.

Dr Jeffrey Hanna and colleagues from the Tropical Public Health Unit of Queensland Health in Cairns, the Queensland Institute of Medical Research and the Army Malaria Unit in Brisbane examined the circumstances surrounding the outbreak.

A 57-year-old man contracted Plasmodium vivax (P. vivax) malaria (not the life threatening strain) on a trip to Indonesia in 2001, during which time he did not take optimal measures to prevent malaria. In late September 2002, he stayed at a camping ground at Noah Beach, north of Cairns, while suffering from symptoms of malaria.

This led to an outbreak of P. vivax malaria in 10 adults who stayed at the same camping ground in the next four weeks.

"Most of the infected patients had been exposed to mosquitoes at night," Dr Hanna said.

"They were less likely than other campers to have used insect repellent appropriately. Some of the people infected exposed themselves to night-biting mosquitoes by sleeping in the open, in a tent with legs protruding outside, in a tent with damaged netting or in a vehicle with open windows. Those who used repellents appeared to be effectively protected from malaria.

"Repellents, particularly those containing diethylmethylbenzamide (DEET), appear effective in protecting people from mosquito bites for considerable periods.

"Campers in north Queensland need to be aware that they have an increased risk of mosquito-borne diseases such as Ross River virus.

"This is only the second recorded outbreak of malaria with multiple cases on the Australian mainland since the country was declared malaria-free in 1983. Both outbreaks occurred in the Daintree National Park during the dry season, when creeks are reduced to stagnant pools and high ambient temperatures increase populations of Anopheles mosquitoes, those most likely to carry malaria.

The malaria outbreak was not sustained and did not lead to further transmission, probably as the camping ground had no permanent residents and campers stayed only a few days. Once the infected people departed, there was no reservoir of infected people to infect later generations of mosquitoes.

"The parasite that caused the outbreak probably originated in Indonesia, suggesting that the outbreak near Cairns in 2002 could have been prevented if the patient had received proper treatment after he first contracted the disease in Indonesia in 2001," Dr Hanna said.

The risk of malaria is very low in Australia but it remains an important issue for travellers to malarious areas, and for clinicians and laboratories throughout Australia.

CONTACT     Dr Jeffrey Hanna 07 4050 3604 / 0408 721 092 overseas 17/12/03-31/12/03
                  Judith Tokley     02 6270 5471 / 0408 824 306