This article {extract} was published in Communicable Diseases Intelligence Vol 34 No 3 September 2010 and may be downloaded as a full version PDF from the Table of contents page.

Results, continued

Vectorborne diseases

A disease that is transmitted to humans or other animals by an insect or other arthropod is called a vectorborne disease. Vectors of human disease of most concern in Australia are typically mosquitoes that are able to transmit viruses or parasites to humans.

During 2008, there were 8,876 notifications of mosquito-borne diseases reported to NNDSS (5.5% of total notifications). This was a 30% increase in the number of notifications compared with 2007 (6,828). The notifiable mosquito-borne diseases include those caused by the alphaviruses (Barmah Forest virus and Ross River virus), flaviviruses (the viruses causing dengue, Murray Valley encephalitis, Kunjin, Japanese encephalitis and yellow fever—which is reported under quarantinable diseases) and malaria. Geographical location rates for vectorborne disease notifications represent the place of residence rather than the place of acquisition of infection, although in many instances this may be the same. Further information about these vectorborne diseases can be found in the National Arbovirus and Malaria Advisory Committee annual (NAMAC) 07–08 annual report.⁵⁵

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Alphaviruses

Alphaviruses are single-stranded RNA viruses that cause disease epidemics characterised by fever, rash and polyarthritis. There is a variety of mosquito vectors for Barmah Forest virus (BFV) infection and Ross River virus (RRV) infection, which facilitates the transmission of these viruses in diverse environments (freshwater habitats, coastal regions, salt marshes, floodwaters, established wetlands and urban areas).⁵⁶ In Australia, BFV and RRV are the alphaviruses of major public health significance, accounting for 87% (7,753 cases) of the total mosquito-borne disease notifications for 2008. Between 2003 and 2008 notifications ranged annually for BFV from 1,367 (2003) to 2,140 (2006), and for RRV from 2,540 (2005) to 5,651 (2008) (Figure 57).

Figure 57: Notifications of Barmah Forest and Ross River virus infections, Australia, 2003 to 2008, by month and year of diagnosis

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Barmah Forest virus infection

There were 2,102 notifications of BFV infections notified to NNDSS in 2008, which accounted for 24% of total mosquito-borne disease notifications for the reporting period. Fifty-nine per cent of BFV notifications were reported from Queensland (1,242 notifications) and 25% from New South Wales (533 notifications). BFV notifications during 2008 were 1.4 times the mean for the previous 5 years.

The highest rates of BFV notifications were reported by the Northern Territory (34.6 per 100,000 population compared with 42.3 per 100,000 population in 2007), Queensland (28.9 per 100,000 population compared with 19.8 per 100,000 population in 2007), and New South Wales (7.6 per 100,000 population compared with 8.3 per 100,000 population in 2007). Cases were reported in all jurisdictions. The national BFV notification rate in 2008 was 9.8 per 100,000 population, compared with 8.1 per 100,000 population in 2007. Notification rates for BFV varied by geographic location.

Figure 58 shows the age and sex distribution of BFV notifications. The BFV notification rate was highest amongst the 45–49 year age group (18.5 per 100,000 population). Overall, 52% of notifications reported to NNDSS were males.

Figure 58: Notification rate for Barmah Forest virus infections, Australia, 2008, by age group and sex

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Ross River virus infection

There were 5,651 notifications of RRV infections reported to NNDSS in 2008, which accounted for 63% of the total mosquito-borne disease notifications received during this period.

Notification rates varied by geographic region, but the majority of notifications in 2008 were from Queensland (50%, 2,838 notifications) and New South Wales (20%, 1,152 notifications). The national RRV notification rate for 2008 was 26.4 per 100,000 population compared with 20.0 per 100,000 population in 2007.

The age and sex distribution of RRV notifications is shown in Figure 59. The RRV national notification rate was highest in the 40–44 year age group (44.9 per 100,000 population). Overall, 47% of notifications reported to NNDSS were males.

Figure 59: Notification rate for Ross River virus infections, Australia, 2008, by age group and sex

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Flaviviruses

Flaviviruses are single-stranded RNA viruses, some of which are associated with epidemic encephalitis in various regions of the world. In Australia, the flaviviruses of public health importance are Murray Valley encephalitis virus (MVEV), Kunjin virus (KUNV), Japanese encephalitis virus (JEV) and dengue viruses (DENV).

The Sentinel Chicken Program is a surveillance scheme involving New South Wales, the Northern Territory, Victoria and Western Australia. Chicken flocks are located in strategic locations and are regularly tested for antibodies to MVEV and KUNV. This program is designed to provide early warning of flavivirus activity (excluding dengue and JEV).⁵⁷ A sentinel chicken surveillance report was published as part of the NAMAC annual report 2007–08.55

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Murray Valley encephalitis virus infection

There were 2 cases of MVEV reported to NNDSS in 2008 compared to no cases in 2007. One case was a 60-year-old male from New South Wales who recovered and the other case was a 49-year-old male from Western Australia, who died from the infection.⁵⁸

Figure 60: Notifications of dengue, Australia, 2003 to 2008, by month and year of diagnosis

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Kunjin virus infection

During 2008, 1 case of KUNV was reported to NNDSS from Queensland compared with 1 notification in 2007 from Victoria.

Dengue virus infection

There were 558 notifications of DENV reported to NNDSS in 2008 (Figure 60), of which 75% were acquired overseas. The number of cases reported in 2008 was a 78% increase in the number of cases reported in 2007 (314).

Local transmission in Australia is restricted to areas of northern Queensland where the key mosquito vector, Aedes aegypti, is present. Dengue is not endemic to Queensland, but outbreaks can occur when the virus is introduced via international travellers or residents returning home from overseas. Queensland reported 232 notifications of DENV in 2008 (41% of all DENV notifications). Locally-acquired cases represented 25% (137/558 cases) of the total number of dengue notifications for Queensland in 2008, which were mainly attributable to an outbreak of locally-acquired dengue serotype 3 in Cairns that occurred between November and December 2008.

In early 2004, 2 deaths due to dengue fever were reported in Australia. These were the first deaths attributed to dengue in over 100 years and there have been no other deaths reported since.⁵⁹

In 2008, 57% of DENV notifications were male (318 notifications) and 90% of notifications were aged between 15 and 64 years (503 notifications). The highest notification rate for males was in the 55–59 year age group (4.2 per 100,000 population) and in females was in the 20–24 year age group (4.5 per 100,000 population) (Figure 61).

Figure 61. Notification rate for locally-acquired and imported cases of dengue, Australia, 2008, by age group and sex

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Japanese encephalitis virus infections

There was 1 case of JEV notified in New South Wales in 2008 in a man who had recently travelled to Japan. This was the first JEV case notified in Australia since 2004.

Arbovirus infections (NEC)

In 2008, there were 28 notifications of arbovirus infection (not elsewhere classified or NEC). Twenty-one notifications in Queensland, 6 notifications in Victoria and 1 notification in New South Wales.

Of the Queensland notifications, 4 cases were further identified as Kokobera virus infection.

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Malaria

There were 533 notifications of malaria in Australia in 2008, compared with 568 notifications in 2007 (Figure 62). There were no locally-acquired infections in 2008. Since Australia was declared malaria free in 1981 there have been two reported locally acquired outbreaks in 1986 and 2002 respectively, with a total of 15 cases. The majority of cases were reported by Queensland (31%; 167), New South Wales (22%; 116), Victoria (20%; 105), and Western Australia (16%; 85). Queensland reported that 79 (47%) of 167 notifications were acquired in Papua New Guinea, which was similar to 2007.

Figure 62. Notifications of imported cases of malaria, Australia, 2003 to 2008, by month and year of diagnosis

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The largest number (70) of malaria notifications was in the 20–24 year age group and 69% of malaria notifications were for males (Figure 63).

Figure 63: Notifications of malaria, Australia, 2008, by age group and sex

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The infecting Plasmodium species was reported for 98% of malaria notifications in 2008 (Table 16). Of these 533 notifications, P. falciparum (43%) and P. vivax (50%) were the predominant species.

Table 16. Notifications of malaria, Australia, 2008, by parasite type and state or territory

Parasite type	State or territory									Type (%)
	ACT	NSW	NT	Qld	SA	Tas	Vic	WA	Aust
Plasmodium falciparum	2	42	13	71	11	4	26	57	226	43
Plasmodium malariae	1	2	0	2	0	1	0	3	9	2
Plasmodium ovale	0	6	0	3	0	0	0	0	9	2
Plasmodium vivax	12	65	5	82	5	3	73	20	265	50
Plasmodium species	0	1	0	9	1	0	0	2	13	2
Mixed P. falciparum and other species*	0	0	1	0	0	0	5	1	7	1
Mixed other species*	0	0	0	0	0	0	0	2	2	1
Total	15	116	19	167	17	8	104	85	531

* New South Wales, South Australia, Tasmania, Victoria, Western Australia and the Northern Territory report mixed species infections per notified case. Queensland and the Australian Capital Territory report 1 notification for each species in a mixed infection.