Results, continued
Vectorborne diseases
Notifications
During 2007, there were 6,823 notifications of mosquito-borne diseases reported to NNDSS (4.6% of total notifications). This was a 20% decrease in the number of notifications for 2006 (8,606). 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 discussed under quarantinable diseases) and malaria.
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 and Ross River virus, which facilitate the transmission of these viruses in diverse environments (freshwater habitats, coastal regions, salt marshes, floodwaters, established wetlands and urban areas).52 In Australia, Barmah Forest virus (BFV) infection and Ross River virus (RRV) infection are the alphaviruses of major public health significance, accounting for 87% (5,919 cases) of the total mosquito-borne disease notifications for 2007. Between 2002 and 2006 (Figure 50), notifications ranged annually for BFV from 910 (2002) to 2,142 (2006), and for RRV from 1,459 (2002) and 5,547 (2006). In 2007, there were 1,716 notifications of BFV and 4,203 of RRV.
Figure 50. Notifications of Barmah Forest and Ross River virus infections, Australia, 2002 to 2007, by month and year of onset
Chikungunya
Chikungunya virus is a member of the alphavirus genus in the family Togaviridae. It belongs to the Semliki Forest virus complex and is therefore closely related to Ross River and Barmah Forest. It is found epidemically in many parts of South East Asia and in Africa. Chikungunya causes illness characterised by an abrupt onset of fever, rash and severe joint pain (chikungunya is Bantu of the Makonde people of south-east Tanzania for 'that which bends up', reflecting the bent over appearance of those with severe joint pain). The acute disease lasts 3–10 days, but convalescence may include prolonged joint swelling and pain lasting weeks or months. It has clinical similarities to dengue, including occasional cases with haemorrhagic manifestations. Deaths are rare.53
In Australia, the known competent vectors for chikungunya virus Aedes aegypti occur in northern Queensland and Aedes albopictus are found on Cocos, Christmas and the Torres Strait Islands. Other Australian mosquitoes could be possible vectors, but there are no data on the competence of these at present.
There have been known imported cases of chikungunya virus into Australia from viraemic travellers during the recent epidemic in the Indian Ocean. Outbreaks in near neighbours such as Indonesia and Papua New Guinea, where we have more travel origins could feasibly increase the numbers of viraemic travellers and hence introduce the disease. Continued Australian military presence in South East Asia also provides a likely entry route.
Northern Australia has suitable climate and environment parameters for the introduction of chikungunya. The National Arbovirus and Malaria Advisory Committee (NAMAC) considered and advised CDNA on 23 January 2008 that with the increased number of infected cases to Australia, and the possibility of local transmission, the number of cases of chikungunya in Australia will increase. NAMAC has initiated action, through the CDNA, to make chikungunya a nationally notifiable disease.
Barmah Forest virus infection
There were 1,716 notifications of BFV infections notified to NNDSS in 2007, which accounted for 25% of total mosquito-borne disease notifications for the reporting period. Forty-eight per cent of BFV notifications were reported from Queensland (n=826) and 33% from New South Wales (n=572). BFV notifications during 2007 were 1.3 times the mean for the previous 5 years.
The highest rates of BFV notifications were reported by the Northern Territory (42.3 cases per 100,000 population compared with 62.9 cases per 100,000 population in 2006), Queensland (19.8 cases per 100,000 population compared with 23.6 cases per 100,000 population in 2006), and New South Wales (8.3 cases per 100,000 population compared with 9.4 cases per 100,000 population in 2006). Cases were reported in all jurisdictions except for Tasmania. The national BFV notification rate in 2007 was 8.2 cases per 100,000 population, compared with 10.3 cases per 100,000 population in 2006. Notification rates for BFV varied by geographic location (Map 8). These locations represent the place of residence of a notified case and not the place of acquisition of infection. For 2007, the highest regional BFV notification rate was reported in the Litchfield Shire of the Northern Territory (74.7 cases per 100,000 population).
Map 8: Notification rates for Barmah Forest virus infection, Australia, 2007, by Statistical Division of residence and Statistical Subdivision for Northern Territory
Figure 51 shows the age and sex distribution of BFV notifications. The BFV notification rate was highest amongst the 45–49 year age group (15.8 cases per 100,000 population). A similar number of males and females were notified to NNDSS with BFV.
Figure 51: Notification rate for Barmah Forest virus infections, Australia, 2007, by age group and sex
Ross River virus infection
There were 4,203 notifications of RRV infections reported to NNDSS in 2007, which accounted for 62% of the total of mosquito-borne disease notifications received during this reporting period.
Cases of RRV infection reported to NNDSS varied by geographic region but the majority of notifications in 2007 were from Queensland (51%, n=2,137) and New South Wales (20%, n=841). These locations represent the place of residence of a notified case and not necessarily the place of acquisition of infection. Map 9 shows that the highest rates of notifications were reported in the Finniss area of the Northern Territory (406 cases per 100,000 population) and the Kimberley region of Western Australia (303 cases per 100,000 population). Five of the top 10 rates of RRV notification by region in Australia occurred in the Northern Territory in 2007. The national RRV notification rate for 2007 was 20 cases per 100,000 population compared with 26.6 cases per 100,000 population in 2006.
Map 9: Notification rates for Ross River virus infection, Australia, 2007, by Statistical Division of residence and Statistical Subdivision for the Northern Territory
The age and sex distribution of RRV notifications is shown in Figure 52. The RRV national notification rate was highest in the 40–44 years age group (35.8 cases per 100,000 population). Overall, 48% of notifications reported to NNDSS were males.
Figure 52: Notification rate for Ross River virus infections, Australia, 2007, by age group and sex
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 network involving New South Wales, the Northern Territory, Victoria and Western Australia. The 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).54 A sentinel chicken surveillance report was published as part of the National Arbovirus and Malaria Advisory Committee Annual Report 2006–07.55
Murray Valley encephalitis virus infection
There were no cases of MVEV infection reported to NNDSS in 2007, compared with 1 case reported in 2006 in Western Australia.
Kunjin virus infection
In October 2007, 1 case of KUNV was reported to NNDSS in Victoria compared with 3 notifications of KUNV in 2006. Further investigations resulted in the reclassification of the diagnosis as West Nile virus. This is the first report of a laboratory confirmed West Nile virus (New York 99) infection imported into Australia.
Dengue virus infection
There were 314 notifications of DENV infection reported to NNDSS in 2007 (Figure 53) including 268 notifications of overseas acquired dengue virus infection. In Australia, imported cases of DENV are reported each year with occasional local transmission. Local transmission is restricted to areas of northern Queensland where the key mosquito vector, Aedes aegypti, is present. The number of cases reported in 2007 was a 68% increase in the number of cases reported in 2006 (n=187).
Figure 53: Notifications of dengue (locally-acquired and imported cases), Australia, 2002 to 2007, by month and year of diagnosis
Queensland reported 120 (38%) notifications of DENV in 2007. An outbreak of locally-acquired dengue serotype 3 occurred in Townsville between February and April 2007. Locally-acquired cases represented 15% (46/314) of the total number of dengue notifications for 2007. Map 10 presents 44 of 46 notifications that were acquired locally and able to be represented geographically (2 cases, a resident of Brisbane and Darwin acquired their infection in Townsville).
Map 10: Notification number and rate of locally-acquired dengue virus infection, Australia, 2007
In early 2004, 2 deaths were reported in Australia due to dengue fever. These were the first deaths attributed to dengue in over 100 years.56
In 2007, the highest notification rate for DENV occurred in the 25–34 years age range and the 50–54 years age group (Figure 54). The highest rate for males was in the 45–49 years age group (22 cases) and in females in the 25–29 years age group (22 cases). Fifty-two per cent of DENV cases were male (n=163) and 91% of cases were aged between 15 and 64 years (n=287).
Figure 54: Notification rate for dengue (locally-acquired and imported cases), Australia, 2007, by age group and sex
Japanese encephalitis virus infections
There were no human cases of JEV notified in Australia in 2007. The last JEV notification was reported by Queensland in February 2004 when a 66-year-old male acquired JEV in Papua New Guinea.57 There have been 9 other cases of JEV reported to NNDSS since 1995, although JEV was not nationally notifiable until 2001.57 Four of these 9 notifications were reported in Torres Strait Islanders from the Badu Island community.57 The other locally acquired JEV case was reported in a resident from the Cape York Peninsula, Queensland.57 The remaining 4 cases were reported as acquired from overseas countries.57
Flavivirus infections (NEC)
There were 22 flavivirus infection (not elsewhere classified) notifications during 2007; notified by Queensland (n=18) and Victoria (n=4).
There were 3 Kokobera virus notifications from Queensland in this category.
Malaria
There were 567 notifications of overseas acquired malaria in Australia in 2007, compared with 772 notifications in 2006 (Figure 55). There were no reports of locally acquired malaria in 2007. The majority of cases were reported by Queensland (34%), Victoria (20%), New South Wales (17%) and Western Australia (15%). Queensland reported that 87 of 193 notifications were acquired in Papua New Guinea.
Figure 55: Notifications of malaria, Australia, 2002 to 2007, by month and year of onset
The largest number (n=70) of malaria notifications was in the 20–24 years age group (Figure 56). Sixty-five per cent of malaria notifications were for males.
Figure 56: Notifications of malaria, Australia, 2007, by age group and sex
The infecting Plasmodium species was reported for 97% of malaria notifications in 2007 (Table 18). Of these 567 notifications, P. falciparum and P. vivax were the predominant species.
Table 18: Notifications of malaria, Australia, 2007, by parasite type and state or territory
Parasite type |
State or territory | Aust | Type (%) |
|||||||
|---|---|---|---|---|---|---|---|---|---|---|
| ACT | NSW | NT | Qld | SA | Tas | Vic | WA | |||
| Plasmodium falciparum | 2 |
32 |
24 |
88 |
17 |
10 |
39 |
51 |
263 |
46 |
| Plasmodium malariae | 0 |
2 |
0 |
2 |
0 |
0 |
3 |
3 |
10 |
2 |
| Plasmodium ovale | 1 |
2 |
0 |
5 |
0 |
0 |
4 |
6 |
18 |
3 |
| Plasmodium vivax | 7 |
58 |
5 |
98 |
7 |
3 |
63 |
12 |
253 |
45 |
| Plasmodium species | 2 |
3 |
0 |
0 |
0 |
0 |
0 |
11 |
16 |
3 |
| Mixed P. falciparum and other species* | 0 |
0 |
0 |
0 |
0 |
1 |
4 |
0 |
5 |
1 |
| Mixed other species* | 0 |
0 |
0 |
0 |
0 |
0 |
0 |
2 |
2 |
0 |
| Total | 12 |
97 |
29 |
193 |
24 |
14 |
113 |
85 |
567 |
|
* New South Wales, South Australia, Tasmania, Victoria and Western Australia report mixed species infections per notified case. Queensland, the Northern Territory and the Australian Capital Territory report 1 notification for each species in a mixed infection.
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Communicable Diseases Surveillance
This issue - Vol 33 No 2, June 2009
NNDSS Annual report 2007
Communicable Diseases Intelligence