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Vectorborne diseases

Notifications

During 2006, there were 8,606 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, accounting for 88% of the total mosquito-borne disease notifications for 2006. 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).²⁸

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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 2,120 notifications of Barmah Forest virus (BFV) infections notified to NNDSS in 2006, which accounted for 39% of total mosquito-borne disease notifications for the year. Forty-five per cent of BFV infection notifications were reported from Queensland (n=957) and 30% from New South Wales (644 cases). BFV infection notifications during 2006 were 1.8 times the mean for the previous 5 years.

The highest rates of BFV infection notifications were reported by the Northern Territory (62.9 cases per 100,000 population compared with 25.1 cases per 100,000 population in 2005), Queensland (23.6 cases per 100,000 compared with 17.2 cases per 100,000 in 2005), and South Australia (12 cases per 100,000 population compared with 2.6 cases per 100,000 in 2005), (Figure 60). The national BFV infection notification rate in 2006 was 10.3 cases per 100,000 population, compared with 6.5 cases per 100,000 population in 2005.

Figure 60. Notification rate of Barmah Forest virus infections, Northern Territory, Queensland, and South Australia, 2001 to 2006, by month and year of onset

In the Northern Territory, the lowest BFV infection notification rate was 17.4 cases per 100,000 population during December and the peak occurred during March (127.7 cases per 100,000 population). Notification rates for the Northern Territory were significantly higher than the other states and territories from February through to November.

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For 2006, the highest regional BFV infection notification rate was reported in South Australia's Murray Lands Statistical Division (86.8 cases per 100,000 population).

Figure 61 shows the age and sex distribution of BFV infection notifications. The BFV infection notification rate was highest amongst the 40–44 years age range (16.5 cases per 100,000 population), and the male to female ratio was 0.8:1. Males in the 35–39, 40–44 and 45–49 years age groups had the highest age-specific rate (13.8 cases per 100,000 population). The highest age specific BFV infection notification rate in females was in the 40–44 years age group (19.1 cases per 100,000 population). The notification rate in females for the 15–19 years age group was 2.5 times higher than males. The major contributing jurisdictions were the Northern Territory (154.3 cases per 100,000 population) and South Australia (40 cases per 100,000 population).

Figure 61. Notification rate of Barmah Forest virus infections, Australia, 2006, 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 5,487 notifications of Ross River virus (RRV) infections reported to NNDSS in 2006, which accounted for 63% of the total of mosquito-borne disease notifications received during this year.

The majority of RRV infection notifications in 2006 were from Queensland (48%, 2,615 cases) and New South Wales (22%, 1,225 cases). The highest rate of notifications was reported in the Kimberly Statistical Division of Western Australia (236.9 cases per 100,000 population). The national RRV infection notification rate for 2006 was 26.6 cases per 100,000 population.

RRV infection notifications in the Northern Territory peaked in January at 441.2 cases per 100,000 population (Figure 62). This was a 28% increase from the peak notification rate in 2005 (February, 319.5 cases per 100,000 population). Queensland reported a peak notification rate for RRV infection in March at 200.4 cases per 100,000 population, which was a 51% increase from the peak notification rate in 2005 (March, 99.6 cases per 100,000 population).

Figure 62. Notification rate of Ross River virus infections, Northern Territory, Queensland and Western Australia, 2001 to 2006, by month and season of onset

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The age and sex distribution of RRV infection notifications is shown in Figure 63. The national notification rate was highest in the 45–49 years age group (46.1 cases per 100,000 population). The highest RRV infection notification rate in males (43.3 cases per 100,000 population) was observed in the 50–54 years age group and the highest notification rate in females was recorded in the 45–49 years age group (49.4 cases per 100,000 population).

Figure 63. Notification rate of Ross River virus infections, Australia, 2006, 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 (MVEV), Kunjin (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 infection, JEV infection and KUNV infection. This program is designed to provide early warning of flavivirus activity (excluding dengue).²⁹ Sentinel chicken surveillance reports from previous seasons have been published,^30,31,32 and the latest report has been published as part of the National Arbovirus and Malaria Advisory Committee annual report 2006–07.³³

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Murray Valley encephalitis virus infection

Case definition – Murray Valley encephalitis virus infection 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.

In 2006, Western Australia reported to NNDSS 1 case of Murray Valley encephalitis virus infection in an 8-year-old female, the case fully recovered.

Kunjin virus infection

Case definition – Kunjin virus infection Top of page 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.

During 2006 there were 3 notifications of KUNV reported to NNDSS, of which Queensland reported 1 notification (male, 44 years) and Western Australia reported 2 notifications (both females 20 and 27 years).

Dengue virus infection

Case definition – Dengue virus infection 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.

There were 187 notifications of dengue virus infection reported to NNDSS in 2006 (Figure 64), of which Queensland reported 78 notifications (42%). Of the 78 notifications, Queensland reported 28 notifications that were acquired locally.

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Figure 64. Notifications of dengue virus infection (locally-acquired and imported cases), New South Wales, Northern Territory, Queensland and Western Australia, 2001 to 2006, by month and year of onset

The age and sex distribution of DENV notifications is shown in Figure 65. The highest rates occurred in the 20–24 years age group (13 cases) for males, and in females in the 40–44 years age group (10 cases). The notification rate in males from the 20–24 years age group was 1.25 times higher than females, 8 of the 13 notifications in this group of males reported overseas acquisition.

Figure 65. Number of notifications of dengue virus infection (locally-acquired and imported cases), Australia, 2006, by age group and sex

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Japanese encephalitis virus infections

Case definition – Japanese encephalitis virus infection 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 infection notified in 2006. The last JEV infection notification was reported by Queensland in February 2004 when a 66-year-old male acquired JEV infection in Papua New Guinea. There have been 9 other cases of JEV infection reported to NNDSS since 1995, although JEV infection 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 infection case was reported in a resident from the Cape York Peninsula, Queensland. The remaining 4 cases were reported as acquired from overseas countries.

Flavivirus infection (NEC)

Case definition – Flavivirus infection (NEC) 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 33 flavivirus infection (NEC) notifications during 2006; notified by Queensland (23 cases) and Victoria (10 cases).

There were 6 Kokobera virus and 1 Stratford virus infection notifications from Queensland in this category.

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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 775 notifications of malaria in Australia in 2006. The majority of cases were reported by Queensland (35%, 268 cases), New South Wales (18%, 140 cases), Victoria (15%, 115 cases) and Western Australia (15%, 115 cases). Queensland reported that 135 of 268 notifications were acquired in Papua New Guinea.

The largest number (99 cases) of malaria notifications was in the 20–24 years age group (Figure 66). The male to female ratio was 1:0.5.

Figure 66. Number of notifications of malaria, Australia, 2006, by age group and sex

The infecting Plasmodium species was reported for 94% for malaria notifications in 2006 (Table 17). Of these 775 notifications, P. falciparum (46%, 354 cases) and P. vivax (42%, 324 cases) were the predominant species while untyped Plasmodium species accounted for 6% (48 cases). The remaining cases were P. ovale (2%, 17 cases), P. malariae (1%, 11 cases) and mixed Plasmodium species infections (3% 21 cases).

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Table 17. Malaria notifications in Australia, 2006, by parasite type and jurisdiction

Parasite type	Type (%)	State or territory
		ACT	NSW	NT	Qld	SA	Tas.	Vic.	WA	Aust.
Plasmodium falciparum	46	4	47	46	115	21	18	37	68	354
Plasmodium malariae	1	0	5	0	6	0	0	0	0	11
Plasmodium ovale	2	0	2	0	4	1	1	8	1	17
Plasmodium vivax	42	7	78	19	126	8	6	62	18	324
Plasmodium species	6	0	5	0	16	1	1	0	23	48
Mixed P. falciparum and P. vivax*	1	0	2	0	0	2	0	0	0	4
Mixed P. falciparum and other species*	2	0	0	1	0	1	0	8	4	14
Mixed P. vivax and other species*	0	0	1	0	1	0	0	0	1	3
Total	100	11	140	66	268	34	26	115	115	775

* 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.

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