A print friendly PDF version is available from this Communicable Diseases Intelligence issue's table of contents.

Zoonoses

Zoonoses are diseases of humans acquired from an animal source. Although there are many recognised zoonoses in Australia, only 5 zoonotic infections are reported at the national level. All notifiable zoonoses have epidemic potential and are associated with certain occupations. Zoonotic infection may present with non-specific clinical symptoms and a definitive diagnosis depends on appropriate laboratory investigations.

Brucellosis, leptospirosis and Q fever infections were nationally notifiable in 1999. In New South Wales neither hydatid infection nor ornithosis were notifiable diseases and ornithosis was not notifiable in Queensland. Zoonotic diseases in Australia are not found in all jurisdictions; the Northern Territory has never reported a case of Q fever and has only reported a single case of hydatid (in 1994).

A total of 1,001 notifiable zoonotic infection cases were received by NNDSS in 1999, which accounted for 1.1 per cent of all the notifications. Most notifiable zoonotic infections were reported from Queensland (569, 57%) and New South Wales (222, 22%). Queensland had the highest notification rates for Q fever (8.5 per 100,000 population), leptospirosis (6.2 per 100,000 population) and brucellosis (1.4 per 100,000 population), and Victoria had for the highest notification rates for ornithosis (1.4 per 100,000 population) and hydatid infection (0.4 per 100,000 population).

Brucellosis

Brucella are small aerobic gram-negative bacilli. Human brucellosis is caused by any of 4 species: Brucella melitensis (primarily from goats, sheep, and camels), Brucella abortus (from cattle), Brucella suis (from pigs) and Brucella canis (from dogs).

Brucellosis is transmitted from Brucella-infected animals to humans by direct contact with blood, tissues and urine of infected animals. Infection is through breaks in the skin or through consumption of contaminated animal products, such as milk and meat. Airborne transmission from animal to humans is also possible. Zoonotic organisms may be transmitted from human to human via blood transfusion and bone marrow transplantation, through the placenta, during breast-feeding, and during sexual activity.

Brucellosis is still a significant public health problem in some geographical areas in Australia. There were 52 notifications of brucellosis in 1999, giving a notification rate of 0.3 per 100,000 population which was an increase from 1998 (43 cases; 0.2 per 100,000 population). The national notification rate has been stable since 1991.

Most notifications (33, 63.4%) occurred between August and November. The majority of the brucellosis cases were males (48/52, 92.3%), with the overall male to female ratio of 12:1 reflecting occupational risk. The age-specific rates peaked in the 25-29 years male age group at 1.3 per 100,000 population.

Queensland reported 94.2 per cent (49/52) of all cases, with the other 3 cases from Victoria. The highest rates of disease were reported in the Central West (97.9 per 100,000 population) and the South West (31.1 per 100,000 population) Statistical Divisions of Queensland. A study has shown a high frequency of B. suis infections in Queensland, especially among men who hunt and slaughter feral pigs.⁶⁰

Hydatid disease

Hydatid disease is caused by the larval stage of the tapeworm Echinococcus granulosus. Hydatid cysts are prevalent in areas where livestock is raised in association with dogs. In 1999, hydatid infection was notifiable for all States and Territories in Australia, except New South Wales.

There were a total of 29 hydatid disease notifications in 1999, the lowest since 1991; giving an annual notification rate of 0.2 per 100,000 population (Table 2). Notifications of hydatid infection were from Victoria (17 cases, 59% of the national total), Queensland (5 cases), Western Australia (3 cases), South Australia (3 cases) and Tasmania (1 case). The highest rates of disease were reported in the South West Statistical Division of Queensland (3./100,000 population), followed by the Midland Statistical Division of Western Australia (1.9 per 100,000 population).

Of the 29 notifications, 13 were in men, 14 were in women and two were in persons of unknown gender. The male to female ratio of disease was 0.9:1. Hydatid infections commonly occurred in the 45-64 year age range. The highest age-specific rates were in women aged 60-64 years (1.1 per 100,000 population) and in men aged 45-49 years (0.6 per 100,000 population).

Hydatid disease is distributed widely in rural Australia. In urban dwellers it is more common among the overseas born who would probably have acquired the infection overseas.⁶¹ 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, infected by feeding off the offal or other remains of these animals, can carry the disease into rural communities, or to the periphery of urban settlements.⁶² Because the symptoms of hydatid disease usually occur only in the advanced stages of disease, and the infection may remain quiescent for many years, hydatid disease is thought to be under-reported in Australia.⁶¹

Top of page

Leptospirosis

Leptospirosis is a zoonotic disease transmitted by wild and domestic animals caused by spirochetes of the Leptospira genus. The source of infection is soil or water contaminated with the urine of domestic or wild animals. Farmers, veterinarians and abattoir workers are at an increased risk of infection. Infections may be asymptomatic and the clinical manifestations of the disease are highly variable including fever, myalgia, meningitis, rash, haemolytic anaemia, and jaundice.²⁹ Leptospirosis occurs in all parts of Australia with the highest incidence in Queensland, where a laboratory based notification system has been in place since 1988.

There were 318 notifications of leptospirosis in Australia in 1999, a 68 per cent increase in notifications compared with 1998. The notification rate rose from 1.1 per 100,000 population in 1998 to 1.7 per 100,000 population in 1999 (Figure 40). The increased notification was mainly caused by an outbreak in January in Queensland, which consisted of 184 cases, half of whom required hospitalisation. This followed a period of heavy rainfall and flooding, and an increase in rodent population. At least 14 different serovars causing disease were isolated in this outbreak.⁶³

Figure 40. Trends in national notification rate for leptospirosis, Australia, 1991 to 1999



In 1999, Queensland reported 69 per cent of all notifications (218 cases), 57 (18%) cases were from New South Wales and 29 (9%) cases were from Victoria. The highest rates of disease were localised to the Far North (19.2 per 100,000 population) and the South West (11.6 per 100,000 population) of Queensland, and the Western District (10.1 per 100,000 population) of Victoria.

The seasonal trend showed notifications were higher in summer months and reached a peak in March and April (Figure 41). Ninety-one per cent of all notifications were male with a male to female ratio of 10:1. The most frequent age for disease onset was from 20-59 years.

Figure 41. Notifications of leptospirosis, Australia, 1991 to 1999, by month of onset



Top of page

Ornithosis

Ornithosis, also known as psittacosis, is an acute generalised infection with Chlamydia psittaci and is commonly associated with exposure to pet birds, particularly parrots.

Eighty-four notifications of ornithosis were reported in 1999, an increase compared with 1998 (64 cases). The national notification rate was 0.9 per 100,000 population. In 1999 ornithosis was not a notifiable diseases in New South Wales or Queensland. Of the 84 cases reported in this year, 66 (79%) were from Victoria, 49 (58.3%) were male and 35 (41.7%) female, and the male to female ratio of disease was 1.4:1. The highest age-specific rates were reported in the 45-49 years age group for women (1.2 per 100,000 population) and in the 50-54 years age group for men (1.8 per 100,000 population).

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.⁶⁴ 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.

Q fever

Q fever is a rickettsial illness caused by Coxiella burnetii. Livestock, such as sheep, cattle, goats, cats, dogs, some wild animals (bandicoots and many species of feral rodents), birds and ticks are natural reservoirs. Outbreaks have occurred in occupational groups working with animals, including stockyard workers, meat packing and rendering workers, abattoir and dairy workers, and medical and veterinary research facility workers.

Transmission is usually through airborne dissemination of the organism in dust particles but also via direct contact with contaminated material, ingestion of contaminated placentas or ingestion of milk. Ticks may also be involved in transmission of the organism. Cases have occurred in individuals with no direct contact with contaminated animals and their bodily fluids, but such cases have resided downwind from areas that are contaminated.

In 1999, 518 notifications of Q fever were reported with an annual notification rate of 2.7 per 100,000 population, a slight decrease from 3.0 per 100,000 population reported in 1998. Queensland and New South Wales each accounted for 57 per cent and 32 per cent of all the cases for the year, respectively. The highest notification rates for Statistical Divisions were localised to the South West (155.6 per 100,000 population) and the Central West (130.6 per 100,000 population) of Queensland (Map 11).

Map 11. Q fever notification rate by Statistical Division of residence, 1999



The highest age-specific notification rates were in the 35-39 year age groups for males (9.5 per 100,000 population) and in the 40-44 year age groups for women (2.8 per 100,000 population, Figure 42). Males accounted for 79 per cent of all the notifications, and male to female ratio was 3.8:1.

Figure 42. Notifications of Q fever, Australia, 1999, by age and sex



Q fever is still the most important of all zoonotic diseases in terms of reported numbers of cases in Australia. The true prevalence of the disease is likely to be under-estimated. A recent study found that 27 per cent of Australian abattoir staff tested positive for Q fever infection.⁶⁵ An effective vaccine is available in Australia for people who are at high-risk.⁶⁶


This article was published in Communicable Diseases Intelligence Volume 25, No 4, November 2001.