Australia's notifiable diseases status, 2004: Annual report of the National Notifiable Diseases Surveillance System - Zoonoses

The Australia’s notifiable diseases status, 2004 report provides data and an analysis of communicable disease incidence in Australia during 2004. The full report is available in 20 HTML documents. This document contains the section on Zoonoses. The full report is also available in PDF format from the Table of contents page.

Page last updated: 30 March 2006

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

Zoonoses

Zoonoses are diseases and infections naturally transmitted between non-human vertebrate animals and humans.34 Animal hosts play an essential role in maintaining the infection in nature, and humans are only accidental hosts.35 Strikingly, 75 per cent of emerging infectious diseases have been identified as zoonotic in origin.36 In 2004, zoonotic diseases notifiable to the NNDSS were anthrax, Australian bat lyssaviral or lyssaviral (unspecified) infection, brucellosis, leptospirosis, ornithosis and Q fever. During 2004, a total of 877 notifications of zoonotic disease (0.8% 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.

Following the deliberate release of anthrax spores in the United States of America in 2001, anthrax became a nationally notifiable disease in Australia. In 2004, no cases of anthrax were notified. 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. Cases only occur sporadically, mostly in partially vaccinated animals.

In 2004, 15 outbreaks of anthrax were reported in livestock (13 from New South Wales and 2 from Victoria). Only one of these outbreaks was from outside the known anthrax endemic areas, on a farm that was part of an old stock route leading to the endemic zone in New South Wales. In all instances the usual protocols of quarantine, disinfection of contaminated ground, carcass incineration, and vaccination of the herd and neighbouring herds were implemented. All animal movements from affected properties were traced and there was no risk of further spread of disease.

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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 2004. Two cases of human infection with Australian bat lyssavirus, in 1996 and 1998, occurred following close contact between bat-handlers and infected bats. Both resulted in the death of the infected person.

There are two 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.37 Research into the genetic sequences of lyssaviruses isolated from different groups of bats using molecular methods suggests that the virus has been associated with bats in Australia for more than 1,500 years.38 That is, the virus was well established before European colonisation, and its recent 'emergence' is in all likelihood due to changes in human behaviour and encroachment on bat habitats.

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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 2004, 36 cases of brucellosis were reported to the NNDSS, giving a national notification rate of 0.2 cases per 100,000 population. This number of notifications lies in the middle of the range observed over the previous 13 years (13–54 notifications). Most cases were reported from Queensland (26 cases; 72 per cent; Map 9), with a further 19 per cent of cases reported from New South Wales (7 cases), and 8 per cent of cases reported from Victoria (3 cases). There is little evidence of a trend in the national or Queensland notification rates of brucellosis over the last 13 years (Figure 56). Most cases were male (n=32, male to female ratio 6.4:1), and of these, 22 were aged between 20 and 39 years.

Figure 56. Trends in notification rates of brucellosis, Australia and Queensland, 1991 to 2004

Figure 56. Trends in notification rates of brucellosis, Australia and Queensland, 1991 to 2004

Map 9. Notification rates of brucellosis, Australia 2004, by Statistical Division of residence

Map 9. Notification rates of brucellosis, Australia 2004, by Statistical Division of residence

Among the nine reported cases for whom species data were available, four cases (all from Queensland) were identified as Br. suis which is endemic in feral pigs in Australia. Four cases were identified as Br. Melitensis (all overseas acquired). Ovine and caprine brucellosis ( Brucella melitensis) has never been reported in Australian sheep or goats.39 One case was identified as Br. abortus ('undulant fever'); which was presumably acquired overseas. Bovine brucellosis ( Brucella abortus) was eradicated from the Australian cattle herd in 198939 and is presently considered an exotic animal disease in Australia.

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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 the spirochaete, Leptospira. Nationally, 166 notifications of leptospirosis were received during 2004 (0.9 cases per 100,000 population). This rate is relatively low compared to the previous years but is 31 per cent higher than the national rate in 2003 (Figure 57).

Figure 57. Trends in notification rates of leptospirosis, Australia and Queensland, 1991 to 2004

Figure 57. Trends in notification rates of leptospirosis, Australia and Queensland, 1991 to 2004

In 2004, the notification rate was highest in Queensland (110 notifications, 2.8 cases per 100,000 population), the Northern Territory (1 notification, 1.0 cases per 100,000 population) and New South Wales (40 notifications, 0.6 cases per 100,000 population). Forty per cent of all notifications were from Far North Queensland (Map 10); the notification rate in this Statistical Division of residence was 28.8 cases per 100,000 population.

Map 10. Notification rates of leptospirosis, Australia, 2004, by Statistical Division of residence

Map 10. Notification rates of leptospirosis, Australia, 2004, by Statistical Division of residence

Most cases were male (n=151, male to female ratio 10.1:1). There was little evidence that rates of notification varied between age groups.

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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 2004, there were 235 ornithosis infections notified to NNDSS, giving a national rate of 1.2 cases per 100,000 population. This represents the highest number of notifications in a 12 month period since NNDSS records began in 1991. The national rate of notifications has steadily increased since 1997 (Figure 58).

Figure 58. Trends in notification rates of ornithosis, Australia, 1991 to 2004

Figure 58. Trends in notification rates of ornithosis, Australia, 1991 to 2004

Victoria had the highest number of notifications (146 notifications, 2.9 cases per 100,000 population). Notifications also occurred in New South Wales (81 notifications), South Australia (5 notifications) and Queensland (3 notifications). The majority of cases were male (n=138, male to female ratio 1.4:1). The highest reporting rates were in the 80–84 year age group for males (7 notifications, 4.5 cases per 100,000 population) and in the 60–64 year age group for females (13 notifications, 2.9 cases per 100,000 population) (Figure 59).

Figure 59. Notification rates of ornithosis, Australia, 2004, by age group and sex

Figure 59. Notification rates of ornithosis, Australia, 2004, by age group and sex

During 2004, three outbreaks of ornithosis and one death were reported. The first outbreak occurred at a Victorian poultry farm in February. There were 26 cases (14 confirmed and 12 probable) notified, nearly all of whom had worked in the onsite abattoir. In this outbreak, the ratio of males to females was 2:1, and the median age was 43 years (range 17 to 69 years). The second outbreak involving four poultry processing workers occurred at a game processing plant. The three males and one female were aged from 37 to 56 years (median 53 years), two were hospitalised. The other identified outbreak was in New South Wales where eight cases were linked to a pet shop. The one death was reported from South Australia in a female in the 45–49 year age group.

Infection of parrots with Chlamydia psittaci has been traditionally known as psittacosis, whereas infection in domestic poultry, waterfowl, pigeons and finches has been called ornithosis. In the past human cases of C. psittaci infection have been described as psittacosis, which has led to the common misconception that this disease is associated only with exposure to diseased psittacine birds (i.e. parrots). Subclinical infection with C. psittaci is common in numerous wild and domesticated bird species in Australia.40 Epizootics of clinical disease in commercial flocks and domestic bird collections can be initiated through stresses such as poor animal husbandry. 40 Furthermore, poor biosecurity of commercial poultry flocks can lead to contact with infected native birds (or their excretions) leading to establishment of latent infection within the flock. The two reported outbreaks involving poultry production workers emphasise the need for increased awareness within animal production industries of appropriate animal husbandry and occupational health and safety. Spill-overs of a commonly subclinical avian disease from poultry into human populations, possibly emanating from wild bird reservoirs, is concerning given the present highly pathogenic avian influenza (HPAI) epidemic in South East Asia.

Reported rates of ornithosis have repeatedly been 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, although an outbreak investigation in rural Victoria in 1995 showed no association with direct bird handling but rather lawn mowing and gardening in areas with high numbers of native birds.41 Shedding of C. psittaci into the environment by native birds and subsequent inhalation of aerosolised dust and bird excreta was postulated as the mechanism of human infection.

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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 2004, 440 cases of Q fever were notified to the NNDSS, a decrease of 24.5 per cent on 2003. This number of cases is relatively low compared to the count of previous years and the national rate (2.2 cases per 100,000 population) is the lowest recorded since 1991 ( Figure 60). The highest rates of notifications were from Queensland (137 notifications, 3.5 cases per 100,000 population), New South Wales (223 notifications, 3.3 cases per 100,000 population) and South Australia (38 notifications, 2.5 cases per 100,000 population). The highest reporting rates were in the 40–44 year age group for males (6.8 cases per 100,000 population), and in the 55–59 year age group for females (2.3 cases per 100,000 population). Few cases were reported from children or the elderly. The male to female ratio was 3.3:1.

Figure 60. Trends in notification rates of Q fever, Australia, 1991 to 2004

Figure 60. Trends in notification rates of Q fever, Australia, 1991 to 2004

An outbreak of Q fever occurred among persons attending sheep saleyards in rural South Australia during October and November 2004. In total, 25 persons were linked to this outbreak. A case-control study identified a statistically significant association between human illness and attendance at the saleyard. Intervention strategies including vaccination and dust control were implemented. Many of the cases were unvaccinated sheep and grain farmers.

Q fever has long been associated with work in the Australian stock industry and abattoir workers are an occupational group 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 due for completion on 30 June 2004. Several jurisdictions have completed the Program, however, Victoria and South Australia have extended the Program until 30 June 2006 and Queensland has extended it until 30 June 2007.

Figure 61. Notification rates of Q fever, Queensland and New South Wales, January 1999 to December 2004, by month of onset*

Figure 61. Notification rates of Q fever, Queensland and New South Wales, January 1999 to December 2004, by month of onset

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Other emerging zoonotic disease in 2004

Bat-associated emerging zoonoses (Hendra and Nipah virus activity 2004)

Surveillance of flying foxes ( Pteropus spp.) and associated research continued to focus on henipaviruses in 2004. Hendra virus is a viral infection associated with flying foxes. Sporadic infections may occur in horses that come in close contact with infected flying foxes or their body fluids. A horse from Cairns examined by a veterinarian in early December 2004 and subsequently euthanised, tested positive to Hendra virus.39 The veterinary doctor involved in autopsy of the horse developed a Hendra-related illness soon after and recovered. This was an isolated case. Hendra was also suspected in a horse that died south of Cairns in October 2004. These cases are consistent with previous findings and do not reflect a change in the known distribution or epidemiology of Hendra virus in Australia.39 The timing of incidents suggests a seasonal pattern of outbreaks possibly related to the seasonality of fruit bat birthing, as Hendra virus has been isolated from foetal tissues and fluids.42

This report of the re-emergence of Hendra virus, and repeated outbreaks of Nipah virus-associated encephalitis in humans in Bangladesh underline our still-limited understanding of the ecology of these agents, and the need to maintain surveillance and research efforts.39



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