This article {extract} was published in Communicable Diseases Intelligence Vol 31 No 1 March 2007 and may be downloaded as a full version PDF from the Table of contents page.

Results, continued

Vectorborne diseases

Notifications

During 2005, there were 4,935 notifications of mosquito-borne diseases reported to NNDSS. 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 and Japanese encephalitis) and malaria.

Alphaviruses

Alphaviruses are RNA viruses which cause disease epidemics characterised by fever, rash and polyarthritis. In Australia, Barmah Forest virus and Ross River virus are the alphaviruses of major public health significance. There are a variety of mosquito vectors for Barmah Forest virus and Ross River virus that facilitate the transmission of these viruses in diverse environments (freshwater habitats, coastal regions, salt marshes, floodwaters, established wetlands and urban areas).¹⁹

Barmah Forest virus infection

Case definition – Barmah Forest virus infection Only confirmed cases are reported. Confirmed case: Requires isolation of Barmah Forest virus, OR detection of Barmah Forest virus by nucleic acid testing, OR IgG seroconversion or a significant increase in antibody level or a fourfold or greater rise in titre to Barmah Forest virus, OR detection of Barmah Forest virus-specific IgM.

There were 1,319 notifications of Barmah Forest virus (BFV) infection notified to NNDSS in 2005, which accounts for 27% of total mosquito-borne disease notifications for the reporting period. Fifty-two per cent of BFV notifications were reported from Queensland (n=680) and 34% from New South Wales (n=448). BFV notifications during 2005 were 1.3 times the mean for the previous 5 years.

The highest rates of BFV notifications were reported by the Northern Territory (25.1 cases per 100,000 population), Queensland (17.2 cases per 100,000 population), and New South Wales (6.6 cases per 100,000 population). The national BFV notification rate was 6.5 cases per 100,000 population, which was the second highest since 1999.

There was a peak in the BFV notification rate in the Northern Territory (82.8 cases per 100,000 population) during April 2005 and this was almost 4 times the peak notification rate observed in May 2004 (Figure 49). Queensland reported a peak BFV notification rate in May 2005 (32.1 cases per 100,000 population), whereas New South Wales reported a peak BFV notification rate in April 2005 (10.6 cases per 100,000 population). These were slight increases over the peak notification rates in the previous season.

Figure 49. Notification rate of Barmah Forest virus infections, select jurisdictions, 1999 to 2005, by month and year of onset

The highest rate of BFV infection in 2005, was reported in the Mid-North Coast area of New South Wales (67.5 cases per 100,000 population, Map 7).

Map 7. Notification rate of Barmah Forest virus infections, Australia, 2005, by Statistical Division of residence

Figure 50 shows the age and sex distribution of BFV notifications. The BFV notification rate was highest amongst the 45–54 year age range (11.4 cases per 100,000 population), and the male to female ratio was 1:1. Males in the 50–54 year age group had the highest age-specific rate (11.8 cases per 100,000 population). The highest age-specific BFV notification rate in females was in the 40–44 and 45–49 year age groups (11.7 cases per 100,000 population).

Figure 50. Notification rate of Barmah Forest virus infections, Australia, 2005, by age group and sex

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Ross River virus infection

Case definition – Ross River virus infection Only confirmed cases are reported. Confirmed case: Requires isolation of Ross River virus, OR detection of Ross River virus by nucleic acid testing, OR IgG seroconversion or a significant increase in antibody level or a fourfold or greater rise in titre to Ross River virus, OR detection of Ross River virus-specific IgM.

There were 2,544 notifications of Ross River virus (RRV) infection reported to NNDSS in 2005, which accounts for over one half (52%) of the total mosquito-borne disease notifications received in 2005.

The largest contributors to RRV notifications in 2005 were Queensland (46%, n=1,179) and New South Wales (23%, n=585). The highest rates of infection were reported by the Northern Territory (103.1 cases per 100,000 population), Queensland (29.7 cases per 100,000 population), and Western Australia (15.5 cases per 100,000 population). The national RRV notification rate for 2005 was 12.5 cases per 100,000 population.

Map 8 shows that the highest rate of RRV infection in 2005 was in the Northern Territory (122.4 cases per 100,000 population) and Mackay in Queensland (107.9 cases per 100,000 population).

Map 8. Notification rate of Ross River virus infections, Australia, 2005, by Statistical Division of residence

RRV infection notifications in the Northern Territory peaked in February 2005 at 319.5 cases per 100,000 population (Figure 51). This was a 52% reduction from the peak notification rate from January 2004. Queensland reported a peak notification rate for RRV in March 2005 at 99.6 cases per 100,000 population, which was almost a 40% reduction from the peak notification rate in March 2004 (251.6 cases per 100,000 population).

Figure 51. Notification rate of Ross River virus infections, select jurisdictions, 1999 to 2005, by month and season of onset

The age and sex distribution of RRV notifications are shown in Figure 52. The national notification rate was highest in the 45–49 year age group (22.8 cases per 100,000 population) and the highest BFV notification rate in males (21.4 cases per 100,000 population) was also observed in this age group. The highest notification rate in females was recorded in the 45–49 year age range (25.1 cases per 100,000 population).

Figure 52. Notification rate of Ross River virus infections, Australia, 2005, 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 (MVEV), Kunjin (KUNV), Japanese encephalitis virus (JEV) and dengue viruses (DENV).

The Sentinel Chicken Programme is a surveillance network involving New South Wales, the Northern Territory Victoria and Western Australia, and is designed to provide early warning of increased flavivirus activity.²⁰ Antibodies to MVEV and KUNV are detected in sentinel flocks located in four Australian states. Sentinel chicken surveillance reports from previous seasons have been published,^21,22,23 and the latest report has been published as part of the National Arbovirus and Malaria Advisory Committee Annual Report 2005–06.²⁴

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Murray Valley encephalitis virus infection

Case definition – Murray Valley encephalitis virus Only confirmed cases are reported. Confirmed case: Requires isolation of Murray Valley encephalitis virus, OR detection of Murray Valley encephalitis virus by nucleic acid testing, OR IgG seroconversion or a significant increase in antibody level or a fourfold or greater rise in titre to Murray Valley encephalitis virus, OR detection of Murray Valley encephalitis virus-specific IgM in cerebrospinal fluid in the absence of IgM to Kunjin, Japanese encephalitis or dengue viruses, OR detection of Murray Valley encephalitis virus-specific IgM in serum in the absence of IgM to Kunjin, Japanese encephalitis or dengue viruses. This is only accepted as laboratory evidence for encephalitic illnesses. AND Non-encephalitic disease: acute febrile illness with headache, myalgia and/or rash, OR encephalitic disease: acute febrile meningoencephalitis characterised by one or more of the following: 1. focal neurological disease or clearly impaired level of consciousness, 2. an abnormal computerised tomograph or magnetic resonance image or electrocardiograph, 3. presence of pleocytosis in cerebrospinal fluid, OR asymptomatic disease: Case detected as part of a serosurvey should not be notified. Confirmation of laboratory result by a second arbovirus reference laboratory is required if the case occurs in areas of Australia not known to have established enzootic/endemic activity or regular epidemic activity.

There were 2 cases of MVEV infection reported in 2005. In March 2005, a case of MVEV was reported in a 30-year-old male from Normanton, Queensland. The second case of MVEV disease was also reported in March 2005 in a 3-year-old boy from a community in Arnhem Land who was transferred to Royal Darwin Hospital for treatment. The boy had a relatively mild illness and made a complete recovery. The boy’s community was located near an extensive freshwater wetland with numerous water birds and frequent high numbers of common banded mosquitoes Culex annulirostris and Culex palpalis: 2 vectors of MVEV.

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Kunjin virus infection

Case definition – Kunjin virus Only confirmed cases are reported. Confirmed case: Requires isolation of Kunjin virus, OR detection of Kunjin virus by nucleic acid testing, OR IgG seroconversion or a significant increase in antibody level or a fourfold or greater rise in titre to Kunjin virus, OR detection of Kunjin virus-specific IgM in cerebrospinal fluid, OR detection of Kunjin virus-specific IgM in serum in the absence of IgM to Murray Valley encephalitis, Japanese encephalitis or dengue viruses. This is only accepted as laboratory evidence for encephalitic illnesses. AND Non-encephalitic disease: acute febrile illness with headache, myalgia and/or rash, OR encephalitic disease: acute febrile meningoencephalitis characterised by one or more of the following: 1. focal neurological disease or clearly impaired level of consciousness, 2. an abnormal computerised tomograph or magnetic resonance image or electrocardiograph, 3. presence of pleocytosis in cerebrospinal fluid, OR asymptomatic disease: case detected as part of a serosurvey should not be notified. Confirmation of laboratory result by a second arbovirus reference laboratory is required if the case occurs in areas of Australia not known to have established enzootic/endemic activity or regular epidemic activity.

There was one notification of KUNV from Queensland during 2005, in a 48-year-old female with an onset in February 2005.

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Dengue virus infection

Case definition – Dengue virus Only confirmed cases are reported. Confirmed case: Requires isolation of dengue virus, OR detection of dengue virus by nucleic acid testing, OR IgG seroconversion or a significant increase in antibody level or a fourfold or greater rise in titre to dengue virus, proven by neutralisation or another specific test, OR detection of dengue virus-specific IgM in cerebrospinal fluid, in the absence of IgM to Murray Valley encephalitis, Kunjin, or Japanese encephalitis viruses, OR detection of dengue virus-specific IgM in serum, except in North Queensland. In North Queensland, dengue virus-specific IgM in serum is acceptable evidence ONLY when this occurs during a proven outbreak. AND A clinically compatible illness (e.g. fever, headache, arthralgia, myalgia, rash, nausea, and vomiting, with a possible progression to dengue haemorrhagic fever, dengue shock syndrome or meningoencephalitis). Confirmation of laboratory result by a second arbovirus reference laboratory is required if the case occurs in previously unaffected areas of Australia. Currently North Queensland is the only area with the potential for indigenous (epidemic) dengue virus in Australia.

During 2005, there were 218 notifications of dengue virus infection reported to NNDSS, of which Queensland reported 115 notifications (53%). The only locally acquired notifications were reported by Queensland (n=74), while other jurisdictions reported imported cases from overseas or from unknown sources. Queensland reported a peak in DENV notifications in March 2005 (n=49). This was much lower than in the previous 2 years (Figure 53).

Figure 53. Notifications of dengue (locally-acquired and imported cases), select jurisdictions, January 1999 to December 2005, by month and year of onset

The Queensland notifications resulted from outbreaks that peaked in March in the Torres Strait Islands, and in May in Townsville. A summary of identified outbreaks of locally-acquired cases is shown in Table 13.

Dengue serotype 4 was the major serogroup circulating in Queensland during these outbreaks.

Table 13. Outbreaks of locally acquired cases of dengue, Queensland, 2005

Location	Reported cases	Duration	Type
Torres	56	10 weeks	Dengue 4
Townsville	18	16 weeks	Dengue 4

Data provided by Dr Jeffrey Hanna, Tropical Public Health Unit, Cairns, 2005.

The age and sex distribution of DENV notifications is shown in Figure 54. The highest rates occurred in the 45–49 year age group (19 cases) in males, and in females in the 25–29 year age range (14 cases).

Figure 54. Notifications of dengue (locally-acquired and imported cases), Australia, 2005, by age group and sex

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Japanese encephalitis virus infections (JEV)

Case definition – Japanese encephalitis virus Only confirmed cases are reported. Confirmed case: Requires isolation of Japanese encephalitis virus, OR detection of Japanese encephalitis virus by nucleic acid testing, OR IgG seroconversion or a significant increase in antibody level or a fourfold or greater rise in titre of Japanese encephalitis virus-specific IgG proven by neutralisation or another specific test, with no history of recent Japanese encephalitis or yellow fever vaccination, OR detection of Japanese encephalitis virus-specific IgM in cerebrospinal fluid, in the absence of IgM to Murray Valley encephalitis, Kunjin and dengue viruses, OR detection of Japanese encephalitis virus-specific IgM in serum in the absence of IgM to Murray Valley encephalitis, Kunjin and dengue viruses, with no history of recent Japanese encephalitis or yellow fever vaccination. AND A clinically compatible febrile illness of variable severity associated with neurological symptoms ranging from headache to meningitis or encephalitis. Symptoms may include headache, fever, meningeal signs, stupor, disorientation, coma, tremors, generalised paresis, hypertonia, and loss of coordination. The encephalitis cannot be distinguished clinically from other central nervous system infections. Confirmation of laboratory result by a second arbovirus reference laboratory is required if the case appears to have been acquired in Australia.

There were no human cases of JEV notified in 2005. The last JEV notification was reported by Queensland in February 2004 when a 66-year-old male acquired JEV from Papua New Guinea. There have been 9 other cases of JEV reported to NNDSS since 1995, although JEV was not nationally notifiable until 2001. Four of these 9 notifications were reported in Torres Strait Islanders from the Badu Island community. The other locally acquired JEV case was reported in a resident from the Cape York Peninsula, Queensland. The remaining 4 cases were reported as acquired overseas.

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Flavivirus infections (NEC)

Case definition – Flavivirus infection (not elsewhere specified) Only confirmed cases are reported. Confirmed case: Requires isolation of a flavivirus that cannot be identified in Australian reference laboratories or which is identified as one of the flaviviruses not otherwise classified, OR detection of a flavivirus, by nucleic acid testing, that cannot be identified in Australian reference laboratories or which is identified as one of the flaviviruses not otherwise classified, OR IgG seroconversion or a significant increase in antibody level or a fourfold or greater rise in titre of flavivirus specific IgG that cannot be identified or which is identified as being specific for one of the flaviviruses not otherwise classified. There must be no history of recent Japanese encephalitis or yellow fever vaccination, OR detection of flavivirus IgM in cerebrospinal fluid, with reactivity to more than one flavivirus antigen (Murray Valley encephalitis, Kunjin, Japanese encephalitis and/or dengue) or with reactivity only to one or more of the flaviviruses not otherwise classified, OR detection of flavivirus IgM in the serum, with reactivity to more than one flavivirus antigen (Murray Valley encephalitis, Kunjin, Japanese Encephalitis and/or dengue) or with reactivity only to one or more of the flaviviruses not otherwise classified. This is only accepted as laboratory evidence for encephalitic illnesses. There must be no history of recent Japanese encephalitis or yellow fever vaccination. AND non-encephalitic disease: acute febrile illness with headache, myalgia and/or rash, OR encephalitic disease: acute febrile meningoencephalitis characterised by one or more of the following: 1. focal neurological disease or clearly impaired level of consciousness, 2. an abnormal computerised tomograph or magnetic resonance image or electrocardiograph, 3. presence of pleocytosis in cerebrospinal fluid. Confirmation by a second arbovirus reference laboratory is required if the case cannot be attributed to known flaviviruses.

There were 29 flavivirus infection (not elsewhere classified or NEC) notifications during 2005; notified by Queensland (n=20), New South Wales (n=6) and Victoria (n=9).

There were 5 Kokobera notifications and 1 KUNV from Queensland in this category. Eight notifications of the alphavirus Sindbis were included under flavivirus infections (NEC).

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Malaria

Case definition – Malaria Only confirmed cases are reported. Confirmed case: Requires detection and specific identification of malaria parasites by microscopy on blood films with confirmation of species in a laboratory with appropriate expertise, OR detection of Plasmodium species by nucleic acid testing.

There were 822 notifications of malaria in Australia in 2005. The majority of cases were reported by Queensland (36%, n=297), New South Wales (25%, n=204), Victoria (13%, n=110) and Western Australia (10%, n=85). There were no reports of locally-acquired malaria during the reporting period.

The largest number (n=113) of malaria notifications was reported in refugee children,²⁵ in the 5–9 year age group (Figure 55). The male to female ratio was 1:0.7.

Figure 55. Notifications of malaria, Australia, 2005, by age group and sex

The infecting Plasmodium species was reported for 97% of malaria notifications in 2005 (Table 14). Of these 822 notifications, P. falciparum (56%, n=460) and P. vivax (35%, n=285) were the predominant species while untyped Plasmodium species accounted for 2% (n=13). The remaining cases were P. ovale (3%, n=24), P. malariae (1%, n=10) and mixed Plasmodium species infections (4%, n=30).

Table 14. Malaria notifications in Australia, 2005 by parasite type and jurisdiction

Parasite type	Type (%)	State or territory
		ACT	NSW	NT	Qld	SA	Tas	Vic	WA	Australia
Plasmodium falciparum	56	6	119	29	149	33	18	39	67	460
Plasmodium malariae	1	0	2	0	4	0	0	2	2	10
Plasmodium ovale	3	0	6	2	8	0	0	6	2	24
Plasmodium vivax	35	6	64	16	133	5	6	50	5	285
Plasmodium species	2	0	2	0	3	3	0	2	3	13
Mixed P. falciparum and P. vivax*	0.2	–	1	–	–	1	0	0	0	2
Mixed P. falciparum and other species*	3	–	9	–	–	1	0	11	0	21
Mixed P. vivax and other species*	0.1	–	1	–	–	0	0	0	0	1
Mixed infection (unspecified)*	0.7	–	0	–	–	0	0	0	6	6
Total	100	12	204	47	297	43	24	110	85	822

* 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 one notification for each species in a mixed infection.

† Unknown.