Zoonoses

Zoonoses are diseases and infections which are naturally spread between vertebrate animals and humans. Although there are more than 60 recognised zoonoses in Australia,⁴¹ only a subset of these with increased epidemic potential and occupational risk are reported to the NNDSS. All notifiable zoonoses can produce non-specific clinical signs and symptoms and therefore a definitive diagnosis depends on appropriate laboratory investigation.

Brucellosis

There were 41 notifications of brucellosis in 1997 and rates were 0.2 per 100,000 nationally. This is unchanged for all years dating back to 1994. Thirty-five (85%) notifications were in males, and age-specific rates were highest in the 25 to 29 year age group at 0.62 per 100,000. Two reports were in children less than 10 years of age.

Of the 41 notifications, 34 (83%) were from Queensland, 4 (10%) from New South Wales, and 3 (7%) from Victoria. The highest rates of disease were reported in Southern Queensland. Brucella species was not indicated in any of the notifications.

Hydatid infection

Sixty-one cases of hydatid disease were reported for 1997. Thirty-one (51%) were reported from Victoria, where 14 cases were reported in 1996. The National rate was 0.3 per 100,000, which is similar to previous years.

The highest age-specific rates were in the 55 to 59 year age group at 0.82 per 100,000.

Male to female ratio of disease was 1.14:1

Highest rates of disease were reported in the South West statistical Division of Queensland.

Leptospirosis

A total of 126 cases of leptospirosis were reported for 1997 with a corresponding rate of 0.7 per 100,000. The Australian Capital Territory was the only jurisdiction to have had no reported cases for the year. The peak onset was in May and December (Figure 27). This bimodal distribution was most marked in Queensland which accounted for 56 (44%) of all notifications. Thirty-three cases were notified from New South Wales and 27 cases from Victoria.

The highest age specific rates were in the 20 to 24 year age group, at 1.89 per 100,000.

Males accounted for 108 (86%) of cases.

The highest rates of disease were localised to the Far North Statistical Division of Queensland and the Western District of Victoria, where 19 and 8 cases were reported for the year respectively.

Figure 27. Notifications of leptospirosis, 1997, by month of onset

Ornithosis

Ornithosis, or Chlamydia psittaci infection, is notifiable in all states except New South Wales and has not been notifiable in Queensland since 1996. Forty-six cases were notified for the year and 39 (85%) of these were from the state of Victoria. The only other states to have notified cases were South Australia (4 notifications) and Western Australia (3 notifications).

The highest age-specific rates of 0.69 per 100,000 were reported in the 60 to 64 year age group. Females accounted for 54 per cent of cases.

The rate of 0.4 per 100,000 was lower than has been reported in previous years.

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Q fever

Notifications of Q fever, or Coxiella burnetii, for 1997 numbered 593. Rates of disease were consistent with those reported in 1996. Australian rates were 3.2 per 100,000. Queensland and New South Wales each accounted for 275 notifications. The highest rates of disease were reported in Queensland at 8.1 per 100,000 and New South Wales at 4.4 per 100,000 (Map 12).

The highest age-specific notification rate of 5.7 per 100,000 was reported in the 20 to 24 year age group.

The male to female ratio was 5.7:1.

Map 12. Notification rate of Q fever, 1997, by Statistical Division of residence

Discussion

The highest rates of notifiable zoonotic infections reported for 1997 occurred in the eastern states. Whereas Q fever and brucellosis rates were highest in the state of Queensland, Victoria accounted for the highest notification rates for ornithosis and hydatid disease. Leptospirosis was more widely distributed, with peak rates being reported in the Far North of Queensland and the South West Division of Victoria.

Q fever is the most important of all zoonotic diseases in terms of reported numbers of cases, and is the only disease for which an effective vaccine is available. It has long been associated with outbreaks in abattoirs and among animal handlers who predominantly work with sheep, cattle and feral goats.⁴² The disease tends to be quiescent in animal hosts.

Brucellosis due to B. abortus is an uncommon disease in Australia due to effective eradication programs in cattle.⁴³ The reporting of brucella species to the NNDSS is poor. Earlier case series have confirmed the dominance of B. suis as a human pathogen in Queensland, especially among occupational groups who hunt and slaughter feral pigs.⁴⁴

Reported rates of ornithosis are 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 or 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.⁴⁵ Shedding of C. psittaci into the environment by sick birds and subsequent inhalation of aerosolised dust and bird excreta was postulated as the mechanism of human infection.

Hydatid disease is under-reported in Australia.⁴⁶ Symptoms occur in the advanced stages of disease, and infection may remain quiescent for many years. Infection acquired in childhood will usually manifest in adulthood. The disease is distributed widely in rural Australia and disease occurring in urban dwellers is more common in the overseas born. Disease in the Australian born occurs typically in rural settings where humans become infected by the ingestion of eggs passed in the faeces of dogs, dingoes or foxes. Wallabies, wombats, feral pigs, sheep and kangaroos are all intermediate hosts that act as reservoirs of the disease. Dogs and foxes, feeding off the offal or other remains of these animals become infected, and can carry the disease into rural communities, or to the periphery of urban settlements.⁴⁷

This article {extract} was published in Communicable Diseases Intelligence Vol 23 Number , 21 January 1999 and may be downloaded as a full version PDF from the Table of contents page. Volume 23 1999.