Results, cont'd

Vectorborne diseases

A disease that is transmitted to humans or other animals by an insect or other arthropod is known as 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 2009, there were 8,232 notifications of mosquito-borne diseases reported to NNDSS (3.5% of total notifications). This was a 7% decrease in the number of notifications compared with 2008 (8,876). The notifiable mosquito-borne diseases include those caused by the alphaviruses (Barmah Forest virus and Ross River virus), flaviviruses (dengue, Murray Valley encephalitis, Kunjin, Japanese encephalitis and yellow fever) and malaria. Yellow fever is reported under quarantinable diseases. 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) annual report 2008–09.⁶⁸

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Alphaviruses

Alphaviruses are single-stranded RNA viruses that cause disease epidemics characterised by fever, rash and polyarthritis. There are a variety of mosquito vectors for Barmah Forest virus (BFV) and Ross River virus (RRV), which facilitate the transmission of these viruses in diverse environments (freshwater habitats, coastal regions, salt marshes, floodwaters, established wetlands and urban areas).⁶⁹ In Australia, BFV and RRV are the alphaviruses of major public health significance, accounting for 76% (6,272 notifications) of the total mosquito-borne disease notifications for 2009. Between 2004 and 2009, notifications ranged annually for BFV from 1,100 (2004) to 2,133 (2006), and for RRV from 2,538 (2005) to 5,652 (2008) (Figure 64).

Figure 64: Notifications of Barmah Forest and Ross River virus infections, Australia, 2004 to 2009, by month and year of diagnosis

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Barmah Forest virus infection

There were 1,486 notifications of BFV infections notified to NNDSS in 2009, which accounted for 18% of total mosquito-borne disease notifications for the reporting period. Fifty-four per cent of BFV notifications were reported from Queensland (799 notifications) and 24% from New South Wales (359 notifications). BFV notifications during 2009 were 0.9 times the mean for the previous 5 years.

Cases were reported in all jurisdictions. The highest rates of BFV notifications were reported by the Northern Territory (52.0 notifications per 100,000 population) and Queensland (18.1 notifications per 100,000 population). Cases were reported in all jurisdictions. The national BFV notification rate in 2009 was 6.8 notifications per 100,000 population, compared with 9.8 notifications per 100,000 population in 2008. Overall, 55% of BFV notifications reported to NNDSS were males.

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Ross River virus infection

There were 4,786 notifications of RRV infections reported to NNDSS in 2009, which accounted for 58% of the total mosquito-borne disease notifications received during this period. The majority of notifications in 2009 were from Queensland (45%, 2,154 notifications) and New South Wales (19%, 912 notifications).

The highest rates of RRV notifications were reported by the Northern Territory (189.9 notifications per 100,000 population) and Queensland (48.9 notifications per 100,000 population). Cases were reported in all jurisdictions. The national RRV notification rate for 2009 was 21.9 notifications per 100,000 population compared with 26.4 notifications per 100,000 population in 2008. Overall, 47% of RRV notifications reported to NNDSS were males.

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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 Programme 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 DENV and JEV).⁷⁰ A sentinel chicken surveillance report was published as part of the NAMAC annual report 2008–09.⁶⁸

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Murray Valley encephalitis virus infection

During 2009, 4 notifications of MVEV were reported to NNDSS. The 2 MVEV notifications from Western Australia involved a resident of Broome (March 2009) and a resident of Port Hedland (May 2009). Both these cases survived their illness but have long term neurological deficits.⁷¹ The 2 MVEV notifications from the Northern Territory both died as a result of their illness. The 1st case was a long term resident from the Batchelor area (March 2009) and the other was a Queensland resident holidaying at Channel Point (May 2009). Health warnings were given both before and after the cases, with warnings based on vector numbers, rainfall, historical risk periods and/or detections of seroconversions in sentinel chicken flocks. During 2008, 4 notifications of MVEV were reported to NNDSS.

Kunjin virus infection

There were 2 notifications of KUNV reported to NNDSS in 2009, one from Queensland and one from the Northern Territory compared with 1 notification in 2008 from Queensland.

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Dengue virus infection

There were 1,402 notifications of DENV infection reported to NNDSS in 2009 (Figure 65), of which 66% were locally acquired (922 notifications) and 34% (480 notifications) were acquired overseas. The number of cases reported in 2009 was a 150% increase in the number of cases reported in 2008 (562).

Figure 65: Notifications of dengue virus infection, Australia, 2004 to 2009, by month and year of diagnosis

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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 occur when the virus is imported via international travellers or residents returning home from overseas. Queensland reported 1,036 notifications of DENV in 2009 (74% of all DENV notifications). Locally-acquired cases represented 66% (922) of the total number of dengue notifications in 2009. These were attributed to outbreaks of locally-acquired dengue, involving all 4 serotypes, in north Queensland.

One dengue associated death was reported in March 2009. The last time death due to dengue fever was reported was in early 2004, when 2 deaths were reported in Australia. The latter were the first deaths attributed to dengue in over 100 years.⁷²

In 2009, the largest number (99) of dengue notifications was in the 40–44 years age group and 53% were males (Figure 66).

Figure 66: Notifications of dengue, Australia, 2009, by age group and sex

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Japanese encephalitis virus infection

There were no notifications of JEV reported to the NNDSS in 2009 compared with 1 notification of JEV in New South Wales in 2008. This case was in a man who had recently travelled to Japan and was the first JEV notification in Australia since 2004.

Arbovirus infections (NEC)

In 2009, there were 26 notifications of arbovirus infection (not elsewhere classified or NEC). There were 23 notifications in Queensland and three in Victoria. Overall, 58% of NEC notifications reported to NNDSS were males.

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Malaria

Malaria is a serious acute febrile illness which can be transmitted from person to person through the bite of an infected mosquito. It is caused by a parasite called Plasmodium that includes 5 species – vivax, falciparum, malariae, knowlesi and ovale.²¹ There were 526 notifications of malaria in Australia in 2009, compared with 529 in 2008 (Figure 67). There were no locally-acquired infections in 2009. Since Australia was declared malaria free in 1981 there have been 2 reported locally-transmitted outbreaks in 1986 and 2002 with a total of 15 cases. The majority of notifications in 2009 were reported by Queensland (35%, 185 notifications), Victoria (21%, 113 notifications), New South Wales (18%, 92 notifications), and Western Australia (16%, 82 notifications). Queensland reported that 51 of 185 notifications (28%) were acquired in Papua New Guinea.

Figure 67: Notifications of malaria (imported cases), Australia, 2004 to 2009, by state or territory and month and year of diagnosis

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The largest number (59) of malaria notifications was in the 20–24 years age group and 71% of malaria notifications were for males (Figure 68).

Figure 68: Notifications of malaria, Australia, 2009, by age group and sex

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The infecting Plasmodium species was reported for 96% of malaria notifications in 2009 (Table 17). Of these 526 notifications, P. falciparum (42%) and P. vivax (48%) were the predominant species. New South Wales notified the first case of a fifth species, Plasmodium knowlesi, acquired in Indonesian Borneo.⁷³

Table 17: Notifications of malaria, Australia, 2009, by parasite type and state or territory

	State or territory
Parasite type	ACT	NSW	NT	Qld	SA	Tas	Vic	WA	Aust	Type (%)
Plasmodium falciparum	2	43	2	74	13	4	33	47	219	42
Plasmodium knowlesi	0	1	0	0	0	0	0	0	1	0
Plasmodium malariae	0	1	1	2	1	0	3	1	9	2
Plasmodium ovale	0	4	0	3	0	0	2	3	12	2
Plasmodium vivax	1	41	9	91	15	1	71	24	253	48
Plasmodium species	0	0	0	15	1	0	2	2	20	4
Mixed P. falciparum and other species*	0	1	2	0	2	0	2	5	11	2
Mixed other species*	0	1	0	0	0	0	0	0	1	0
Total	3	92	14	185	32	5	113	82	526

* 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.