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Zoonoses

A zoonosis is 'an infection or infectious disease transmissible under natural conditions from vertebrate animals to humans'.³⁴ Animal hosts play an essential role in maintaining the infection in nature, and humans are only incidental hosts.³⁵ Animals are thought to be the origin of approximately 75% of emerging human infectious diseases and wildlife contribute significantly to this threat.³ The Australian Government, through the animal and human health agencies, is proactively addressing this threat by strengthening the link between animal and human health systems.

In 2006, zoonotic diseases notifiable to the NNDSS were anthrax, Australian bat lyssaviral or lyssaviral (unspecified) infection, brucellosis, leptospirosis, ornithosis and Q fever. During 2006, a total of 767 notifications of zoonotic disease (0.5% of total notifications) were made to the NNDSS.

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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.

Anthrax is primarily a disease of herbivores; humans and carnivores are incidental hosts.³ Anthrax has a low decreasing prevalence, and occurs only sporadically in Australia.³⁶ It can be an occupational hazard for veterinarians, agriculture and wildlife workers who handle infected animals.

One case of cutaneous anthrax in a 48-year-old man was reported to NNDSS in 2006. The case was from the western part of New South Wales and was associated with exposure to infected cattle in an area where anthrax was endemic.³⁷ Before this 2006 case, a human case of cutaneous anthrax had not been reported in Australia since 1998.

In 2006, 10 outbreaks of anthrax were reported in livestock. All cases occurred in central New South Wales, where cases have been known to occur in the past. In all cases, properties were subject to the recommended protocol of quarantine, carcass incineration, site disinfection and vaccination of in-contact animals. All movements from affected properties were traced to ensure that relevant product did not enter the export and domestic chains.³⁶

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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 notified 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 cases of either Australian bat lyssaviral or lyssaviral (unspecified) infections were notified during 2006. Previously, 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. One case was associated with a sub-order Megachiroptera (from a frugivorous bat) and the other was associated with sub-order Microchiroptera (found in smaller, mainly insectivorous bats).

Surveillance indicates Australian bat lyssavirus infection is and may have been present in Australian bats 15 years prior to its first detection. Sick and injured bats (opportunistic specimens) and change in seasonality and bat ecology pose an increased public health risk.

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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.

Brucellosis is mainly an occupational disease for farm workers, veterinarians, and abattoir workers who work with infected animals or their tissue.³

In 2006, 49 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 (40 cases), New South Wales (8 cases) and Western Australia (1 case). The highest notification rate (74 cases per 100,000 population) was from the Central West region of Queensland. There is little evidence of change in the trend in the national or Queensland notification rates of brucellosis over the last 13 years (Figure 67). Most cases were male (43 cases, male to female ratio 7:1), and of these, 80% were aged between 20 and 64 years.

Figure 67. Trends in notifications rate for brucellosis, Australia and Queensland, 1991 to 2006

Species data was available for 31% of notifications (12 cases). Of these 6 were Brucella suis, 4 cases were B. melitensis (3 reported from New South Wales and 1 reported from Western Australia) and 2 cases were B. abortus (reported from New South Wales). All of these cases were acquired overseas.

Except for B. suis, cases are assumed to have had overseas exposure. Bovine brucellosis (B. abortus) was eradicated from the Australian cattle herd in 1989 and is presently considered an exotic animal disease in Australia.³⁸ Caprine and ovine brucellosis (caused by B. 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, with human cases predominantly seen in recreational feral pig hunters.

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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 2 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, which is found in the renal tubules of wild and domestic animals. In affected areas, where there is exposure to infected urine of domestic and wild animals, this disease can be an occupational and recreational hazard.³

Nationally, 147 notifications of leptospirosis were received during 2006 (0.7 cases per 100,000 population). During the last 13 years, notification rates peaked in 1999 and from 2000 onwards continued to decline (Figure 68).

Figure 68. Trends in notifications for leptospirosis, Australia and Queensland, 1991 to 2006

In 2006, the highest notification rate was in Queensland (117 notifications, 2.9 cases per 100,000 population). There were also notifications received from the Northern Territory (2 notifications, 1 case per 100,000 population), New South Wales (17 notifications, 0.2 cases per 100,000 population), Tasmania (1 notification, 0.2 cases per 100,000 population), Victoria (6 notifications, 0.1 cases per 100,000) and South Australia (1 notification 0.06 cases per 100,000 population). Sixty-six per cent of all notifications were from Far North Queensland; the notification rate in this region was 31 cases per 100,000 population.

Most leptospirosis cases were male (131 cases, male to female ratio 8.2:1), and the 20–24 years age group had the highest notification rate (1.7 cases per 100,000 population).

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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 2 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, rigours, 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 2 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, rigours, dry cough or dyspnoea, AND exposure to birds or bird products, or proximity to an outbreak of ornithosis.

Ornithosis is caused by Chlamydophila psittaci and is transmitted to humans by exposure to waterfowl, seabirds, shore birds, pigeons and doves and many psittacine birds. Birds can become carriers of the disease without becoming infected. The mode of transmission to humans is by inhaling bacteria usually from contaminated dried faeces, nasal or eye secretions and dust from infected birds.3 Human-to-human transmission is rare.

In 2006, there were 168 ornithosis infections notified to NNDSS, giving a national rate of 0.8 cases per 100,000 population. The national rate of notifications has steadily increased from 1997 to 2004, but in 2005 and 2006 decreased to 2001 levels (Figure 69).

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Figure 69. Trends in notification rates for ornithosis, Australia, 1991 to 2006

New South Wales had the highest number of notifications (94 notifications, 1.4 cases per 100,000 population). Notifications were also received from Victoria (65 cases), Western Australia (4 cases), the Australian Capital Territory (2 cases), Queensland (2 cases), and Tasmania (1 case). The majority of cases were male (97 cases, male to female ratio 1.3:1). Eighty-one per cent of cases were aged 40 years or over, with the highest notification rate in males in the 70–74 years age group (12 notifications, 3.9 cases per 100,000 population) and in females in the 75–79 years age group (6 notifications, 2.0 cases per 100,000 population) (Figure 70).

Figure 70. Notification rate for ornithosis, Australia, 2006, by age group and sex

At risk groups of people contracting ornithosis include bird owners, pet shop employees, veterinarians, poultry processing workers, zoo workers and taxidermists. Older adults and pregnant women may have a more severe illness.39 An outbreak in the Blue Mountains in June 2002 reinforced that infections in humans can be associated with wild birds, rather than with pet birds and aviaries.⁴⁰

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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.

Q fever is caused by Coxiella burnetii. Primary reservoirs of these bacteria are cattle, sheep and goats. The organisms are resistant to heat, drying and many common disinfectants, this enables the bacteria to survive for long periods in the environment. The mode of transmission to humans is commonly through the airborne route in dust, but it can also occur though direct contact with infected animals and other contaminated material. Humans are often very susceptible to the disease, and very few organisms may be required to cause infection. Person-to-person transmission is rare.³

In 2006, 402 cases of Q fever were notified to the NNDSS. The highest rates of notifications were from Queensland (164 notifications, 4 cases per 100,000 population) and New South Wales (174 notifications, 2 cases per 100,000 population) (Figure 71). The highest rates were in the 45–49 years age group for males (5.4 cases per 100,000 population), and in the 60–64 years age groups for females (1.8 cases per 100,000 population). There were 14 cases reported in people aged less than 14 years and 6 cases reported in adults aged over 75 years. The male to female ratio was 3.8:1.

Figure 71. Notification rate for Q fever, Queensland and New South Wales, 1999 to 2006, by month of onset

Production of the Q fever vaccine ceased at the end of 2005 because of the manufacturers' inability to meet new regulations and other product pressures.⁴¹ At the end of 2006, the Australian Ministers for Health and Agriculture announced funding for CSL Limited to recommence production of the Q fever vaccine.⁴¹ Adults at risk, including abattoir workers, farmers, veterinarians, stockyard workers, shearers, animal transporters and many others exposed to cattle, sheep or goats or their products should be considered for vaccination.

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