This article {extract} was published in Communicable Diseases Intelligence Vol 30 No 1 March 2006 and may be downloaded as a full version PDF from the Table of contents page.

Results, continued

Vectorborne diseases

During 2004, there were 6,000 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.

Alphavirues

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, which facilitate the transmission of these viruses in diverse environments (freshwater habitats, coastal regions, salt marshes, floodwaters, established wetlands and urban areas).²⁰

Top of page

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 1,052 notifications of Barmah Forest virus (BFV) infection notified to NNDSS in 2004, which accounts for 18 per cent of the total mosquito-borne disease notifications for the reporting period. Eighty-nine per cent of BFV notifications were reported from Queensland (n=535) and New South Wales (n=402).

The highest rates of BFV notifications were reported by Queensland (13.8 cases per 100,000 population), the Northern Territory (11 cases per 100,000 population) and New South Wales (6 cases per 100,000 population). The national BFV notification rate was 5.2 cases per 100,000 population which was the third highest since 1999. Figure 49 shows that there was a peak in the BFV notification rate in Queensland in March 2004 (26.6 cases per 100,000 population). The Northern Territory reported a peak BFV notification rate in May 2004 (24.4 cases per 100,000 population), whereas New South Wales reported a peak BFV notification rate in April 2004 (9.8 cases per 100,000 population). The peak BFV notification rates in 2004 for Queensland and New South Wales represent a 60–66% reduction from the previous peak notification rates in 2003.

Figure 49. Notification rates for Barmah Forest virus infection, select jurisdictions, January 1999 to December 2004, by month and year of onset

The highest rate of BFV infection in 2004, was in the mid-North Coast area of New South Wales (67.5 cases per 100,000 population, Map 7).

Map 7. Notification rates for Barmah Forest virus infection, Australia, 2004, by Statistical Division of residence

Figure 50 shows the age and sex distribution of BFV notifications. The national rate of notifications for BFV was highest amongst the 50–54 year age group (10.4 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 rates (12.4 cases per 100,000 population). The highest age-specific BFV notification rate in females was recorded in the 45–49 year age group (9 cases per 100,000 population).

Figure 50. Notification rates for Barmah Forest virus infections, Australia, 2004, by age group and sex

Top of page

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 4,000 notifications of Ross River virus (RRV) infection reported to NNDSS in 2004, which accounts for two-thirds (67%) of the total mosquito-borne disease notifications received in 2004.

The highest contributors to RRV notifications in 2004 were Queensland (45%, n=1,795), Western Australia (27%, n=1,099), and New South Wales (18%, n=700). The highest rates of infection were reported by the Northern Territory (117.6 cases per 100,000 population), Western Australia (55.4 cases per 100,000), and Queensland (46.2 cases per 100,000 population). The 2004 national RRV notification rate (19.9 cases per 100,000) was the third highest RRV notification rate reported to NNDSS since 1999.

Map 8 shows that the highest rate of RRV infection in 2004, was in the Kimberley region area of Western Australia (202.8 cases per 100,000 population).

Map 8. Notification rates for Ross River virus infections, Australia, 2004, by Statistical Division of residence

RRV infection notifications in the Northern Territory peaked in January 2004 at 606.3 cases per 100,000 population (Figure 51). This was the highest rate since 1999, closely resembling the RRV peak notification rate and profile in the Northern Territory in January 2001. Queensland reported the peak notification rate for RRV in March 2004 at 216.7 cases per 100,000 population, and this was a 24 per cent reduction from the peak notification rate for April 2003 (286.3 cases per 100,000 population).

In Western Australia, a state-wide outbreak of RRV peaked in January 2004 at 263.9 cases per 100,000 population which was the largest recorded outbreak of RRV in Western Australia^21,22 despite early warning through media and publicity channels. The predisposing environmental, entomological and virological aspects of the outbreak have been described elsewhere.^22,23

Figure 51. Notification rates for Ross River virus infection, select jurisdictions, 1999 to 2004, by month and season of onset

The age and sex distribution of RRV notifications are shown in Figure 52. The notification rates were highest in the 40–44 age group (38.9 cases per 100,000) and the female to male ratio was 1:0.9.

Figure 52. Notification rates for Ross River virus infection, Australia, 2004, by age group and sex

Top of page

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 and dengue viruses.

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.²⁴ 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,^25–27 and the latest report was published in CDI in 2005 as part of the National Arbovirus and Malaria Advisory Committee annual report, 2004–05.²⁸

Top of page

Murray Valley encephalitis virus

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.

In April 2004, there was one notification of MVEV from Central Australia, when an 11-month-old infant with an onset of symptoms in March 2004 was hospitalised in Alice Springs for one week, and then transferred to South Australia. The infant developed serious neurological sequelae and after a long and debilitating illness, died from complications from MVEV. The Health Department of the Northern Territory government issued a general seasonal warning for MVEV and KUNV for the Alice Springs region and other regions in January 2004, and for the Top End in March 2004 after sentinel chicken seroconversions in the Leanyer swamp area near Darwin, and in April for the whole of the Northern Territory after notification of the MVEV case.

Top of page

Kunjin virus

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 were 12 notifications of KUNV during 2004, with 11 of the cases reported from Queensland. These 11 cases were symptomatic with a mild febrile illness but without encephalitis. Of the 11 cases, nine were reported in January and February 2004 and it is likely that these cases were identified because of increased testing undertaken in north Queensland due to the major dengue outbreak (Jeffrey Hanna, personal communication). There is nothing to indicate any genuine increase in human health risk from Kunjin virus activity during that time.

The other jurisdiction to report a KUNV notification in 2004 was Victoria. In October 2004, a 35-year-old female was notified as having acquired KUNV infection. The person lived in metropolitan Melbourne, but a detailed investigation did not reveal any likely exposure within Victoria, nor was there any other evidence of KUNV activity. She had travelled extensively overseas and it is assumed that she acquired KUNV or a closely-related virus while overseas.

Top of page

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 2004, there were 326 notifications of dengue (DENV) reported to NNDSS, of which Queensland reported 249 notifications (76%). The only locally acquired notifications were reported by Queensland (n=181), while other jurisdictions reported imported cases from overseas (n=70), or from unknown sources (n=74). Queensland reported a peak in DENV notifications in November 2003 and February 2004 (95–97 cases). These were much lower than the previous peak of 252 notifications in March 2003 (Figure 53).

Figure 53. Notifications of dengue (locally acquired and imported cases), select jurisdictions, January 1998 to June 2005, by month and year of onset

The Queensland notifications resulted from outbreaks that began in late 2003 in Cairns, Townsville and the Torres Strait islands. A summary of identified outbreaks of locally acquired cases is shown in Table 21.

Table 21. Outbreaks of locally acquired cases of dengue, Queensland, 2003 to 2004

Year	Location	Reported cases	Duration (weeks)	Type
2003–04	Cairns, Townsville, Torres	536	69	Dengue 2
2003–04	Torres, Cairns	356	41	Dengue 2
2004	Torres	1	1	Dengue 2

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

Dengue serotype 2 was the major serogroup circulating in Queensland during these outbreaks. A 40-year-old Torres Strait Islander woman and 70-year-old man died from dengue shock syndrome (DSS) in February and March 2004, respectively, and it has been suggested that the primary infection for these two cases occurred in 1981,²⁹ when there was a dengue serotype 1 epidemic. The deaths from DSS were the first from locally acquired dengue in Australia for 100 years.

An incursion of the mosquito vector for DENV, Aedes aegypti, occurred in Tennant Creek in the Northern Territory in February 2004.^30,31 This species of mosquito has not been endemic in the Northern Territory since 1955.³² Mosquito control activities including fogging in residential and public places, distribution of surface sprays, removal of water-filled receptacles and residual insecticide spraying were initiated along with public awareness campaigns.³³ No human cases of dengue were reported in Tennant Creek.

The age and sex distribution of DENV notifications is shown in Figure 54. Most cases in males occurred in the 30–34 year age group (25 cases), and in females in the 25–29 year age group (24 cases).

Figure 54. Notifications of dengue (locally acquired and imported cases), Australia, 2004, by age group and sex

Top of page

Japanese encephalitis virus

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 was one case of Japanese encephalitis virus (JEV) notified in February 2004, when Queensland reported that a 66-year-old male acquired JEV from Papua New Guinea. There have been nine other cases of JEV reported to NNDSS since 1995, although JEV was not nationally notifiable until 2001. Four of these nine 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 four cases were reported as acquired from overseas countries.

The Australian Quarantine and Inspection Service, through the Northern Australia Quarantine Strategy (NAQS) program, conducted monitoring for JEV for the 2004 wet season using sentinel pigs at sites on Badu Island in Torres Strait and its northern peninsula area (NPA) site at Injinoo airport in Cape York Peninsula. The five sentinel pigs on Badu Island all seroconverted (based on results of testing at Queensland Health Scientific Services and the CSIRO Australian Animal Health Laboratory). JEV was also identified through the detection of RNA by TaqMan polymerase chain reaction in a pool of culicine mosquitoes collected in a Banks trap on Badu Island. This was collaborative mosquito trapping performed by NAQS for Queensland Health.

The five NPA sentinel pigs located at Injinoo Airport, all seroconverted to JEV (based on results of testing at Queensland Health Scientific Services and the CSIRO Australian Animal Health Laboratory). This is the second time that JEV has been detected on the mainland; the first detection was in 1998. As a follow up to this mainland detection, the Queensland Health Tropical Public Health Unit conducted mosquito trapping at various sites in the NPA. A total of 147 pools, comprising 23,144 mosquitoes, were processed using the JEV-specific TaqMan RT-PCR. Pools were comprised of up to 200 mosquitoes. There was one positive pool of 200 mosquitoes obtained from a trap set at Bamaga rubbish tip. There was inconclusive serological evidence of exposure to JEV in feral pigs sampled by NAQS on the west coast of Cape York Peninsula in July 2004. The time of exposure could not be determined, but it is unlikely to be linked to the 1998 incursion.

Top of page

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 49 flavivirus (NEC) notifications during 2004. These include flavivirus infections (e.g. MVEV and KUNV) where serology was unable to differentiate between the different viruses.

Queensland reported 46 of the 49 flavivirus (NEC) notifications, of which there were six each of Kokobera and Stratford viruses, one KUNV notification and the remaining 33 notifications were of unknown flavivirus type.

Top of page

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 559 notifications of malaria in Australia in 2004. The majority of cases were reported by Queensland (47%, n=263), New South Wales (18%, n=101), and Victoria (12%, n=67). There were no reports of locally acquired malaria during the reporting period.

The largest number of malaria notifications was reported amongst males in the 20–24 year age group, and in females in the 25–29 year age group (Figure 55). The male to female ratio was 2:1.

Figure 55. Notifications of malaria, Australia, 2004, by age group and sex

Table 22 shows that the infecting Plasmodium species were reported for 91 per cent of malaria notifications in 2004. Of these 559 notifications, P. falciparum (48%, n=270) and P. vivax (44%, n=248) were the predominant species while untyped Plasmodium species accounted for 2 per cent (n=9). The remaining cases were P. ovale (4%, n=20) and P. malariae (1%, n=7). It should be noted that mixed infections (<1%, n=5) are underestimated due to the variation in reporting practice in different states and territories.

Table 22. Malaria notifications in Australia, 2004, by parasite type and jurisdiction

Parasite type	Type (%)	State or territory
		ACT	NSW	NT	Qld	SA	Tas	Vic	WA	Australia
Plasmodium species	2	0	0	0	1	0	1	0	7	9
Plasmodium falciparum	48	2	44	31	137	14	9	13	20	270
Plasmodium malariae	1	1	0	2	3	0	0	0	1	7
Plasmodium ovale	4	1	5	0	4	1	0	4	5	20
Plasmodium vivax	44	12	50	8	118	3	5	50	2	248
Mixed infection (unspecified)*	0.2	–	0	–	–	0	0	0	1	1
Mixed P. falciparum and P. vivax*	0.7	–	2	–	–	2	0	0	0	4
Mixed P. falciparum and P. ovale*	0	–	0	–	–	0	0	0	0	0
Mixed P. falciparum and P. malariae*	0.0	–	0	–	–	0	0	0	0	0
Total	100	16	101	41	263	20	15	67	36	559

* New South Wales, South Australia, Tasmania, Victoria, 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.