This article {extract} was published in Communicable Diseases Intelligence Volume 23 Number 11 - 28 October 1999 and may be downloaded as a full version PDF from the Table of contents page.

Results continued

Zoonoses

Zoonoses are diseases and infections that are naturally spread between vertebrate animals and humans. Although there are more than 60 recognised zoonoses in Australia,⁴¹ only a subset with 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

In 1998, there were 45 cases of brucellosis, with a rate of 0.2 per 100,000; which is the same rate as the previous 4 years. Ninety-one per cent of notifications were in males, and age-specific rates were highest in the 35-39 years age group; at 1.3 per 100,000. Two reports were in children less than 5 years of age.

The majority of brucellosis cases were reported from Queensland (80%), and 5 (11%) were from Victoria. The highest rates of disease were reported in the Central West (24.3 per 100,000) and the South West (11.6 per 100,000) Statistical Divisions of Queensland. The species of Brucella was not indicated in any of these notifications.

Hydatid infection

A total of 46 cases of hydatid infection was reported in 1998 from all States and Territories with the exception of New South Wales where it is not notifiable. The national rate was 0.4 per 100,000, which has increased slightly from previous years.

The highest age-specific rates were in the 75-79 years age group for females (1.7 per 100,000) and in the 80-84 years age group for males (2.8 per 100,000).

Among these 46 notifications, 26 (56.5%) were male and 18 (39.1%) female, and male to female ratio was 1.4:1.

The highest rates of disease were reported in the Murray Lands Statistical Division of South Australia (2.9 per 100,000).
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Leptospirosis

There were 197 notifications of leptospirosis received by the NNDSS during 1998. The notification rate rose from 0.7 per 100,000 in 1997 to 1.1 per 100,000 in 1998. The highest number of reports was late in 1998 (Figure 34). Notifications were primarily received from Queensland (109, 55.3%), then 48 (24.3%) cases from New South Wales and 25 (12.7%) cases from Victoria.

Males accounted for over 90% of notifications, with the most frequent age for disease onset in the 20-44 years age group; the age specific rates ranged from 3.0 to 3.4 per 100,000 (Figure 35).

The highest rates were localised to the Far North (19.2 per 100,000) and the South West (11.6 per 100,000) Statistical Divisions of Queensland, and the Western District (10.1 per 100,000) Statistical Division in Victoria.

Figure 34. Notifications of leptospirosis, 1991-1998, by month of onset



Figure 35. Notification rate of leptospirosis, 1998, by age group and sex

Ornithosis

A total of 56 cases were notified for 1998 from all States and Territories except New South Wales and Queensland where it is not notifiable. Of these 50 (89.3%) were from Victoria. The national notification rate of 0.6 per 100,000 was slightly higher than the 0.4 per 100,000 reported in 1997.

Of these 56 cases, 38 (67.9%) were male and 18 (32.1%) female, with a male to female ratio of 2.1:1.

The highest age-specific rates were 2.0 per 100,000 reported in the 75-79 years age group for males, and 0.7 per 100,000 in the 55-59 years age group for females.

Q fever

In 1998, 571 notifications of Q fever, or Coxiella burnetii were reported, and the overall rate (3.0 per 100,000) was lower than the 3.2 per 100,000 reported in 1997. Queensland and New South Wales each accounted for 45.2% and 41.3% of all the cases for the year, respectively. The highest notification rates were localised to the Statistical Divisions of South West (100.3 per 100,000) in Queensland and the North Western (62.3 per 100,000) in New South Wales (Map 11).

Map 11. Notification rate of Q fever, 1998, by Statistical Division of residence



The highest age-specific notification rate in males was 9.5 per 100,000 in the 35-39 years age group and in females was 2.8 per 100,000 in the 40-44 years age group (Figure 36). Males accounted for 78.8% of all notifications, and the male to female ratio was 3.8:1.
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Figure 36. Notification rate of Q fever, 1998, by age group and sex

Discussion

All States and Territories reported notifiable zoonotic cases to NNDSS during 1998, except New South Wales which only reported cases of brucellosis, leptospirosis and Q fever. A total of 915 notifiable zoonotic cases was received by NNDSS during 1998, which accounted for 1.1% of all notifications. The most frequent notifiable zoonotic infections were reported from Queensland (45.3%) and New South Wales (31.2%). Queensland reported the highest notification rates for Q fever (7.5 per 100,000), leptospirosis (3.2 per 100,000) and brucellosis (1.0 per 100,000); and Victoria reported the highest notification rates for ornithosis (1.1 per 100,000) and hydatid infection (0.6 per 100,000).

Q fever is a worldwide zoonoses except in New Zealand,⁴² and has long been associated with outbreaks in abattoirs and among animal handlers predominantly working with sheep, cattle and feral goats.⁴³ Q fever still is the most important of all zoonotic diseases in terms of reported numbers of cases in Australia. Q fever outbreaks occurred 1998 in abattoir workers⁴⁴ and contract abattoir workers, who were not immunised before work (CDNANZ, personal communication). In general, Q fever tends to be under-reported with only about 50% of Q fever cases diagnosed by health professionals.^45,46 A recent study found that among 829 staff of the New South Wales Department of Agriculture, 89 (10.7%) tested positive for Q fever infection.⁴⁶ An effective vaccine available in Australia is useful in preventing Q fever in high risk groups.

Brucellosis has remained at a low level since 1994 in Australia due to effective eradication programs in cattle.⁴⁷ An earlier report⁴⁸ suggested that Brucella suis is the dominant human pathogen in Queensland, especially among occupational groups hunting and slaughtering feral pigs.

Although the number of notifications of hydatid infection in 1998 was lower than the previous year, the rate increased compared with 1997. This disease is occurs widely in rural Australia, and amongst urban dwellers it is more common in the overseas born. Hydatid infection 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.⁴⁹ Hydatid disease generally is under-reported in Australia,⁵⁰ because the symptoms usually occur in the advanced stages, and infection may remain quiescent for many years. Infection acquired in childhood will usually manifest in adulthood.