Human Settlements Theme Report

Australia State of the Environment Report 2001 (Theme Report)
Lead Author: Professor Peter W. Newton, CSIRO Building, Construction and Engineering, Authors
Published by CSIRO on behalf of the Department of the Environment and Heritage, 2001
ISBN 0 643 06747 7

Liveability: human well-being (continued)

Environmental health (continued)

Vector-borne diseases

Several vector-borne diseases are notifiable in Australia to the National Notifiable Diseases Surveillance System (NNDSS). These include both mosquito-borne arboviral diseases and malaria. The vector-borne arboviral diseases covered by the NNDSS are Barmah Forest virus and Ross River virus (known to cause epidemic polyarthritis), encephalitis (caused by Murray Valley encephalitis and Kunjin viruses), Japanese encephalitis and dengue fever. Table 42 presents the number of notifications of vector-borne diseases in Australia from 1991 to 1998.

Table 42: Notifications of vector-borne diseases in Australia, 1991-1998. [HS Indicator 8.2]
Infection Year
  1991 1992 1993 1994 1995 1996 1997 1998
Arboviruses (NEC)A 199 303 578 587 67 52 18 81
Barmah Forest virusB - - - - 756 837 704 558
Dengue fever 46 366 690 17 34 43 210 557
Malaria 790 712 688 703 625 849 746 705
Ross River virus 3532 5630 5428 3974 2602 7823 6683 3094

AIncludes Murray Valley encephalitis, Japanese encephalitis, Kunjin, Kokabera and Stratford viruses. B Until 1995, Barmah Forest virus was included in arbovirus infection (not elsewhere classified).

Source: DHAC(2001).

Ross River virus follows a seasonal pattern, with peak notifications in the wet season or summer months. The epidemic activity is commonly associated with heavy rainfalls and flooding, or with high tides inundating salt marshes and coastal wetlands. In general, epidemic activity is more often observed in temperate areas, with sporadic cases in other areas, whereas in tropical north-eastern Australia transmission occurs throughout the year (Mackenzie et al. 1998).

Barmah Forest virus has been reported from all states and territories in Australia, except Tasmania. In 1998, low rates of disease were reported in Victoria, the ACT and South Australia. The Northern Territory had the highest rate of 11 per 100 000 population, followed by Queensland with a notification rate of 10 per 100 000 population. Peak activity is seasonal, usually occurring from January through to April (Thomson et al. 1999). Notifications of Barmah Forest virus infection have decreased in recent years.

Dengue fever is not endemic in Australia, but epidemics have been reported several times since 1990. These have often been cases of importation by tourists or returning residents. No deaths have been attributed to dengue as the underlying cause in Australia since 1967. The potential for local transmission of dengue is confined to an area in Queensland corresponding to the geographic range of its mosquito vector Aedis aegypti (Mackenzie et al. 1998). However, increased rainfall could favour the spread of the vector into both the Northern Territory and New South Wales (Ewan et al. 1991).

Other arboviruses There were 81 notifications of arboviruses, not elsewhere classified, in Australia in 1998 (Thomson et al. 1999), predominantly from Queensland (52%) and Victoria (43%). These include Murray Valley encephalitis, Japanese encephalitis, Kunjin, Kokabera and Stratford viruses. Following outbreaks in the Torres Strait in 1995, the first case of Japanese encephalitis on the Australian mainland was reported in Queensland in March 1998. Around the same time, a further case of Japanese encephalitis was confirmed in the Torres Strait. Arbovirus transmission cycles in Australia, in relation to the environment, are understood poorly. The public health response to the threat of increased activity of these viruses therefore should include further research into the ecology and other environmental conditions that facilitate these outbreaks (Mackenzie et al. 1998).

Malaria Australia remains free from endemic malaria, but hundreds of imported cases occur each year among travellers returning from endemic areas. Strict malarial surveillance and prompt public health action is therefore important to prevent local transmission of the disease, particularly in northern Australia where environmental conditions favour transmission of malaria, were it to be reintroduced (Thomson et al. 1999). During the period 1979-1998, there were 22 deaths from malaria, an average of about one death every year.

Legionnaire's disease

Legionnaire's disease or legionellosis is a rare form of pneumonia caused by Legionella bacteria, including Legionella pneumophila and Legionella longbeachae. The bacteria are found naturally in soil and water, and are widespread in the environment. They have been found in lakes, rivers, creeks, springs and other bodies of water and soils. In recent years cases associated with the use of potting mix have been reported. Legionella is also found in manufactured systems such as cooling towers associated with air-conditioning and industrial systems, as well as in warm water systems where the temperature is kept between 20C and 45C, such as spa baths. These systems often provide conditions or environments that allow the bacteria to breed in large numbers. Outbreaks of disease often happen when air-conditioning cooling towers become contaminated with the bacteria, as was the case with the outbreak at the Melbourne Aquarium in April 2000 in which around 100 people were infected and four died. This was the largest outbreak of legionnaire's disease ever recorded in Australia.

Legionellosis is notifiable in all states and territories in Australia, and includes notifications of infections caused by all Legionella species (over 20 species). Table 43 presents the number and rate of notifications for legionellosis in Australia from 1991 to 2000.

Table 43: Notifications of legionellosis, Australia, 1991-1998. [HS Indicator 7.12]
Notifications Year
  1991 1992 1993 1994 1995 1996 1997 1998 1999 2000
Number 110 185 178 179 160 192 161 271 260 473
Rate (per 100 000 population) 0.6 1.1 1.0 1.0 0.9 1.0 0.9 1.4 1.4 2.5

Source: National Notifiable Diseases Surveillance System.

Notifications of legionellosis have increased in recent years. The number more than doubled between 1991 and 2000.

There is no vaccine available against legionnaire's disease. As Legionella is widespread in the environment, eradication of the bacteria is impossible. Therefore, control measures must be in place to prevent the growth of the bacteria in cooling towers, warm water systems and spas, including regular maintenance and chemical treatment. In the event of an outbreak, victims require prompt treatment.