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

Zoonoses

Zoonoses are diseases and infections naturally transmitted between non-human vertebrate animals and humans.²⁶ Animal hosts play an essential role in maintaining the infection in nature, and humans are only accidental hosts.²⁷ Animals are thought to be the origin of approximately 75% of emerging human infectious diseases²⁸ and wildlife contribute significantly to this threat. In Australia, the Federal Government, through the animal and human agencies, is proactively addressing this threat by strengthening the link between animal and human health systems. In 2005, zoonotic diseases notifiable to the NNDSS were anthrax, Australian bat lyssaviral or lyssaviral (unspecified) infection, brucellosis, leptospirosis, ornithosis and Q fever. During 2005, a total of 687 notifications of zoonotic disease (0.5% of total notifications) were made to the NNDSS.

Anthrax

Case definition – Anthrax Only confirmed cases are reported. Confirmed case: Requires isolation of Bacillus anthracis-like organisms or spores confirmed by a reference laboratory OR Detection of Bacillus anthracis by microscopic examination of stained smears, OR detection of Bacillus anthracis by nucleic acid testing AND Cutaneous: skin lesion evolving over 1–6 days from a papular through a vesicular stage, to a depressed black eschar invariably accompanied by oedema that may be mild to extensive, OR gastrointestinal: abdominal distress characterised by nausea, vomiting, anorexia and followed by fever, OR rapid onset of hypoxia, dyspnoea and high temperature, with radiological evidence of mediastinal widening, OR meningeal: acute onset of high fever, convulsions, loss of consciousness and meningeal signs and symptoms.

No cases of anthrax were notified to NNDSS in 2005. The last reported human cases of anthrax in Australia (both cutaneous anthrax) occurred in July 1998 and February 1997.

Anthrax is a notifiable animal disease subject to compulsory government control strategies including: vaccination of susceptible livestock located on sites with a known history of anthrax; epidemiological investigation of outbreaks; quarantine and decontamination of affected premises; and safe disposal of carcases. Certain rural areas in central New South Wales and northern and north-eastern Victoria are associated with recurring cases of anthrax in cattle and sheep. In these endemic areas, anthrax has a low and decreasing prevalence and cases only occur sporadically.

In 2005, 9 confirmed anthrax incidents occurred. All except one occurred in the known anthrax endemic areas; the exception was in an area where anthrax had been reported in a neighbouring district in 1973. Cases involved sheep, cattle or both. In all cases, properties were subject to the recommended protocol of quarantine, carcass incineration or burial, site disinfection and vaccination of in-contact animals. All movements from affected properties were traced, and there was no risk of further spread of disease.³¹

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Australian bat lyssaviral and lyssaviral (unspecified) infections

Case definition – Australian bat lyssavirus Only confirmed cases are reported. Confirmed case: Requires isolation of Australian bat lyssavirus confirmed by sequence analysis, OR detection of Australian bat lyssavirus by nucleic acid testing.

 

Case definition – Lyssavirus (unspecified) Only confirmed cases are reported AND only where there is insufficient evidence to meet a case definition for Australian bat lyssavirus or rabies. Confirmed case: Requires positive fluorescent antibody test result for lyssaviral antigen on fresh brain smears, OR specific immunostaining for lyssaviral antigen on formalin fixed paraffin sections of central nervous system tissue, OR presence of antibody to serotype 1 lyssavirus in the cerebrospinal fluid, OR detection of lyssavirus-specific RNA (other than to Australian bat lyssavirus or rabies). AND Acute encephalomyelitis with or without altered sensorium or focal neurological signs.

No new cases of either Australian bat lyssaviral or lyssaviral (unspecified) infections were notified during 2005. The 2 known cases of human infection with Australian bat lyssavirus were fatal and occurred in 1996 and 1998 following close contact between bat-handlers and infected bats.

There are 2 strains of Australian bat lyssavirus known: one circulates in frugivorous bats, sub-order Megachiroptera, and the other circulates in the smaller, mainly insectivorous bats, sub-order Microchiroptera. Each strain has been associated with one human fatality. Surveillance indicates infected bats are widespread at a low frequency on the Australian mainland.²⁹ Research suggests that the virus has been associated with bats in Australia for more than 1,500 years³⁰ and that its recent ‘emergence’ is in all likelihood due to changes in human behaviour and in bat ecology due to habitat loss and changes in feed availability.

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Brucellosis

Case definition – Brucellosis Only confirmed cases are reported. Confirmed case: Requires isolation of Brucella species, OR IgG seroconversion or a significant increase in antibody level or a fourfold or greater rise in titre in Brucella agglutination titres or complement fixation titres between acute and convalescent phase serum samples. (Where possible both tests should be conducted at the same laboratory), OR a single high Brucella agglutination titre.

In 2005, 41 cases of brucellosis were reported to the NNDSS, giving a national notification rate of 0.2 cases per 100,000 population. Cases were from Queensland (37 cases), New South Wales (3 cases) and Victoria (1 case). The highest notification rate (90 cases per 100,000 population) was from the Central West region of Queensland (Map 9). There is little evidence of change in the national or Queensland notification rates of brucellosis over the last 13 years (Figure 56). Most cases were male (n=35, male to female ratio 6:1), and of these, 80% were aged between 15 and 39 years.

Map 9. Notification rate for brucellosis, Australia 2005, by Statistical Division of residence

Figure 56. Trends in notification rate for brucellosis, Australia and Queensland, 1991 to 2005

Species data was available for 31% of notifications (n= 13). Of these 10 were Brucella suis, (all acquired in Queensland) and 2 cases from New South Wales and a case from Victoria were Br. melitensis (all overseas acquired).

Bovine brucellosis (Brucella abortus) was eradicated from the Australian cattle herd in 1989 31 and is presently considered an exotic animal disease in Australia. Caprine and ovine brucellosis (caused by Brucella melitensis) has never been reported in Australian sheep or goats. Swine brucellosis (caused by B. suis) is confined to small areas of northern Australia where it occurs in feral pigs and occasionally spills over into domestic pigs. B. suis was not detected in domestic piggeries during 2005.³¹

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Leptospirosis

Case definition – Leptospirosis Only confirmed cases are reported. Confirmed case: Requires isolation of pathogenic Leptospira species, OR a fourfold or greater rise in Leptospira agglutination titre between acute and convalescent phase sera obtained at least two weeks apart and preferably conducted at the same laboratory, OR a single Leptospira micro agglutination titre greater than or equal to 400 supported by a positive enzyme-linked immunosorbent assay IgM result.

Leptospirosis is caused by spirochaetes of the genus, Leptospira. Nationally, 130 notifications of leptospirosis were received during 2005 (0.6 cases per 100,000 population). This rate is lower than in 2004. During the last 13 years, notification rates peaked in 1999 and declined from 2000 onwards (Figure 57).

In 2005, the highest notification rates were in Northern Territory (5 notifications, 2.5 cases per 100,000 population), Queensland (72 notifications, 1.8 cases per 100,000 population), and New South Wales (35 notifications, 0.5 cases per 100,000 population). Thirty-two per cent of all notifications were from Far North Queensland (Map 10); the notification rate in this region was 18 cases per 100,000 population.

Most leptospirosis cases were male (n=109, male to female ratio 5:1), and the 30–34 year age group had the highest notification rate (2.8 cases per 100,000 population).

Figure 57. Trends in notification rate for leptospirosis, Australia and Queensland, 1991 to 2005

Map 10. Notification rate for leptospirosis, Australia 2005, by Statistical Division of residence

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Ornithosis

Case definition – Ornithosis Both confirmed cases AND probable cases are reported. Confirmed case: Requires A fourfold rise or greater in antibody titre against Chlamydia psittaci as demonstrated by micro-immunofluorescence (MIF) on acute and convalescent sera (collected at least two weeks later) tested in parallel, OR detection of C. psittaci by nucleic acid testing or culture. AND Pneumonia, OR AT LEAST TWO of the following: fever, headache, myalgia, rigors, dry cough or dyspnoea. AND Exposure to birds or bird products, or proximity to an outbreak of ornithosis. Probable case: Requires a single high total antibody level or detection of IgM antibody to C. psittaci by MIF, OR a single high total antibody titre to Chlamydia species demonstrated by complement fixation (CF) in at least one sample obtained at least two weeks after onset of symptoms, OR a fourfold or greater rise in antibody titre against Chlamydia species as demonstrated by CF. AND Pneumonia, OR AT LEAST TWO of the following: fever, headache, myalgia, rigors, dry cough or dyspnoea. AND Exposure to birds or bird products, or proximity to an outbreak of ornithosis.

In 2005, there were 161 ornithosis infections notified to NNDSS, giving a national rate of 0.8 cases per 100,000 population; representing a decrease on the 1.2 cases per 100,000 population reported in 2004. The national notification rate increased from 1997 to 2004, but in 2005 slightly decreased to equal that reported in 2001 (Figure 58).

New South Wales had the highest number of notifications (121 notifications, 1.8 cases per 100,000 population). Notifications were also received from Victoria (34 cases), Queensland (2 cases), Western Australia (3 cases) and South Australia (1 case). The majority of cases were male (n=89, male to female ratio 1.2:1). Eighty per cent of cases were aged 40 years and over, with the highest notification rate in males in the 80–84 year age group (6 notifications, 3.5 cases per 100,000 population) and in females in the 55–59 year age group (12 notifications, 1.9 cases per 100,000 population) (Figure 59).

Notification rates of ornithosis continued to be highest in the older age groups, which may reflect increased investigation and laboratory testing for atypical community-acquired pneumonia in this group. Previously reported outbreaks have been associated with aviaries, pet shops and poultry processing plants. An outbreak investigation in rural Victoria in 1995 showed an association with lawn mowing and gardening in areas with high numbers of native birds.³² Shedding of Chlamydia psittaci into the environment by native birds and subsequent inhalation of aerosolised dust and bird excreta was postulated as the mechanism of human infection. Sub-clinical infection with C. psittaci is common in numerous wild and domesticated bird species in Australia.^33,34

Figure 58. Trends in notification rate for ornithosis, Australia, 1991 to 2005

Figure 59. Notification rate for ornithosis, Australia, 2005, by age group and sex

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Q fever

Case definition – Q fever Only confirmed cases are reported. Confirmed case: Requires detection of Coxiella burnetii by nucleic acid testing, OR seroconversion or significant increase in antibody level to Phase II antigen in paired sera tested in parallel in absence of recent Q fever vaccination, OR detection of C. burnetii by culture (note this practice should be strongly discouraged except where appropriate facilities and training exist). OR Detection of specific IgM in the absence of recent Q fever vaccination. AND A clinically compatible disease.

In 2005, 355 cases of Q fever were notified to the NNDSS, a decrease of 23% on 2004. At 1.7 cases per 100,000 population, the Q fever notification rate in 2005 was lowest since 1991 (Figure 60). The highest rates of notifications were from Queensland (157 notifications, 4 cases per 100,000 population) and New South Wales (142 notifications, 2 cases per 100,000 population). The highest age-specific rates were in the 40–44 and 50–54 year age groups for males (5.7 cases per 100,000 population), and in the 45–49 and 50–54 year age groups for females (1.6 cases per 100,000 population). Few cases were reported from children or the elderly. The male to female ratio was 4:1.

Q fever has long been associated with work in the Australian livestock industry and abattoir workers are at high risk of infection. Since October 2000, abattoir workers and shearers have been eligible for free vaccination under the National Q Fever Management Program (Figure 61). The second phase of the Q fever vaccination program began in October 2001 to include workers in the beef, sheep and dairy industries and was completed on 30 June 2004. However, Victoria and South Australia have extended the Program until 30 June 2006 and Queensland has extended it until 30 June 2007.

Figure 60. Trends in notification rate for Q fever, Australia, 1991 to 2005

Figure 61. Notification rate for Q fever, Queensland and New South Wales, 1999 to 2005, by month of onset*