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Zoonoses

Zoonoses are diseases of humans acquired from an animal source. Although there are many recognised zoonoses in Australia, only five zoonotic infections were reported at the national level in 2000. These were brucellosis, hydatid infection, leptospirosis, ornithosis and Q fever. All notifiable zoonoses have epidemic potential and are often associated with particular occupations. Zoonotic infection may present with non-specific clinical symptoms and a definitive diagnosis depends on appropriate laboratory investigations. The trend in the number and rates of zoonoses disease notifications reported to the NNDSS between 1991 and 2000 are shown in Tables 24 and 25.

A total of 969 notifiable zoonotic infection cases were received by the NNDSS in 2000, which accounted for 1.1 per cent of all notifications. The number of notifications remained at almost the same level as in previous years.

Table 24. Trends in notifications of zoonotic disease, Australia, 1991 to 2000*

Disease	1991	1992	1993	1994	1995	1996	1997	1998	1999	2000
Brucellosis	25	32	13	38	24	39	39	45	52	27
Hydatid infection†	25	34	25	33	31	28	56	37	26	26
Leptospirosis	163	170	174	122	164	214	114	202	323	243
Ornithosis‡	136	110	83	87	185	86	35	64	84	100
Q fever	544	561	870	656	456	544	545	560	515	573

*All jurisdictions reported for all years with the following exceptions:
† Hydatid infection not reported from New South Wales (1991-2000).
‡ Ornithosis not reported from New South Wales (1991 to 2000) and only reported from Queensland during the period of 1992 to 1996.

Table 25. Trends in notification rates of zoonotic disease, Australia, 1991 to 2000* (rate per 100,000 population)

Disease	1991	1992	1993	1994	1995	1996	1997	1998	1999	2000
Brucellosis	0.1	0.2	0.1	0.2	0.1	0.2	0.2	0.2	0.3	0.1
Hydatid infection†	0.2	0.3	0.2	0.3	0.3	0.2	0.5	0.3	0.2	0.2
Leptospirosis	0.9	1.0	1.0	0.7	0.9	1.2	0.6	1.1	1.7	1.3
Ornithosis‡	1.6	1.0	0.7	0.7	1.5	0.7	0.4	0.7	0.9	1.1
Q fever	3.1	3.2	4.9	3.7	2.5	3.0	2.9	3.0	2.7	3.0

*All jurisdictions reported for all years with the following exceptions:
† Hydatid infection not reported from New South Wales (1991-2000).
‡ Ornithosis not reported from New South Wales (1991 to 2000) and only reported from Queensland during the period of 1992 to 1996.

All States and Territories reported brucellosis, leptospirosis and Q fever to the NNDSS in 2000. In New South Wales neither hydatid infection nor ornithosis were notifiable diseases in 2000 and ornithosis was not notifiable in Queensland. Zoonotic diseases are not found in all jurisdictions in Australia. The Northern Territory has not reported any cases of brucellosis or Q fever and only a single case of hydatid disease between 1991 and 2000, and Tasmania has not reported any cases of brucellosis during the same period. The majority of zoonotic infections were reported from Queensland (558, 58%), followed by New South Wales (184, 19%). Queensland had the highest notification rate of Q fever (10.9 cases per 100,000 population), the Northern Territory had the highest notification rate of leptospirosis (4.1 cases per 100,000 population) while Victoria had the highest notification rate of ornithosis (1.8 cases per 100,000 population) (Table 25).

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Brucellosis

Brucella are small aerobic gram-negative bacilli. Human brucellosis is caused by any of four species: Brucella melitensis (primarily from goats, sheep, and camels), Brucella abortus (from cattle), and Brucella suis (from pigs) and Brucella canis (from dogs). B. melitensis and B. abortus are exotic to Australia and cases of B. melitensis are usually imported into Australia from overseas travellers who have consumed unpasteurised dairy products. B. suis is restricted to localised populations of feral pigs in Queensland.

Brucella remains one of the world's major zoonotic pathogens, and is responsible for enormous economic losses as well as considerable human morbidity in endemic areas, especially in developing areas of the Mediterranean Region, Middle East, western Asia and parts of Africa and Latin America. The Brucella organism 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. Airborne transmission from animal to humans is also possible. The organism may also be transmitted from human to human via blood transfusion and bone marrow or organ transplantation, through the placenta, during breast-feeding, and during sexual activity.^68,69,70 The disease usually presents within weeks of exposure, but in some exceptional cases, the incubation period may be as long as several years.⁷¹ The pathogen could also be a potential agent of biological terrorism, particularly B. melitensis and B. suis. The bacteria are highly infectious by aerosol and could be delivered as a slurry in bomblets which may survive for 6 weeks in dust and 10 weeks in soil or water.^72,73,74

There were 27 notifications of brucellosis in 2000, a rate of 0.1 cases per 100,000 population, a signification decrease from 1999 (52 cases; 0.3 cases per 100,000 population). This is the lowest national notification rate on record since 1994.

The majority of notifications (20, 74%) occurred between August and December. The age-specific rate was highest in the age 40-44 year age group at 0.5 cases per 100,000 population. Men were more affected than women with the overall male to female ratio being 8:1.

Almost all the cases of brucellosis were reported from Queensland, except for one case which was reported from New South Wales. The highest rates of disease were reported in the Central West (24.7 cases per 100,000 population) and the South West (15.6 cases per 100,000 population) Statistical Divisions of Queensland. A previous study has suggested that there is a high frequency of B. suis infections in Queensland among men who hunt and slaughter feral pigs.⁷⁵

Hydatid infection

Hydatid infection, caused by the larval stage of the tapeworm Echinococcus granulosus, is generally found in rural Australia. Disease typically occurs where humans become infected by the ingestion of eggs passed in the faeces of dogs, dingoes or foxes.⁷⁶ 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.⁷⁷

Symptoms of hydatid disease usually occur only in the advanced stages of disease, and the infection may remain asymptomatic for many years. In the past, hydatid disease has been shown to be under-reported in Australia.⁷⁸

In 2000, hydatid infection was notifiable in all States and Territories in Australia, except New South Wales. Following a successful elimination program in the period 1965 to 1996, Tasmania was declared free from hydatid disease in 1996 and has remained this status since. A total of 26 cases were notified during 2000. This is the same number as reported in 1999. The annual notification rate was 0.2 cases per 100,000 population. The highest number of cases (n=13) was reported in Victoria, followed by Queensland (8) and Western Australia (5). The highest rate of hydatid infection as reported in the Kimberley region of Western Australia (3.3 cases per 100,000 population).

Of the 26 hydatid cases notified, 10 were men, 13 were women and three were of unknown gender. The male to female ratio was 0.8:1. The highest age-specific rates were in women aged 65-74 years (0.9 cases per 100,000 population) and in men aged 75-79 years (1.4 cases per 100,000 population).

Information on the country of birth was obtained for 13 of 26 hydatid notifications. There were 6 cases among Australian born people (including an Indigenous Australian case) and 7 cases among overseas born persons (4 cases from Greece; 1 case each from Bosnia, China and England).

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Leptospirosis

Leptospirosis is a zoonotic disease transmitted by wild and domestic animals. The causative organisms are the spirochetes of the Leptospira genus. The source of infection is often soil or water contaminated with the urine of domestic or wild animals. Farmers, veterinarians, abattoir workers and some recreational sporting athletes are recognised to be at high risk of infection.²⁷

Leptospirosis was first recognised in Australia in 1934,⁷⁹ and occurs in all parts of Australia today. The disease may be asymptomatic, mild or severe and can cause death. The clinical manifestations of the disease include a variety of symptoms, but the most common presentations include fever, myalgia, meningitis, rash, haemolytic anaemia and jaundice.²⁷

Leptospirosis is a notifiable disease in all States and Territories of Australia. There were 243 notifications of leptospirosis reported to the NNDSS in 2000, with an annual notification rate of 1.3 cases per 100,000 population (Figure 46). This represents a decrease in the number of notifications relative to 1999 (323 cases, 1.7 per 100,000 population). The majority of notifications (55%) were reported in Queensland, followed by New South Wales (22%) and Victoria (14%). The highest rates of disease were localised to the Far North Statistical Division of Queensland (43.9 cases per 100,000 population) and the Western District of Victoria (13.2 cases per 100,000 population) (Map 9).

Figure 46. Trends in notification rates of leptospirosis, Australia, 1991 to 2000, by month of onset



Map 9. Notification rates of leptospirosis, Australia, 2000, by Statistical Division of residence



The seasonal trends show two distinct peaks of leptospirosis in 2000. The first peak of 38 notifications occurred in May and the second peak of 33 notifications was in November (Figure 46). The majority of notifications were male, with a male to female ratio of 8.3:1. The highest age-specific rate for men was in those in the 35-39 year age group (5.2 cases per 100,000 population) (Figure 47).

Top of pageFigure 47. Notification rates of leptospirosis, Australia, 2000, by age and sex



In early September, the Centers for Disease Control and Prevention (CDC) in United States of America alerted the DoHA to an outbreak of leptospirosis among participants of the Eco Challenge Race that was held in Sabah, Malaysia from 20 August to 3 September 2000. The event attracted a total of 304 athletes from 27 countries, which included 12 Australian athletes from New South Wales, Queensland, Tasmania and Victoria. The Surveillance and Epidemiology Section, DoHA, cooperated with the directors and epidemiologists of the health authorities in these jurisdictions to conduct the outbreak investigation. All of the athletes (except one who resided in the USA at the time of the investigation) were contacted by jurisdictional health authorities. Public health officers conducted interviews using a structured questionnaire collecting information on symptoms and possible exposures. The questionnaire was sent to the CDC via the Surveillance and Epidemiology Section. Blood samples were collected from some of athletes and sent to the Collaborating Centre for Reference and Research on Leptospirosis, WHO/FAO Western Pacific Region in Queensland.

There was no case of leptospirosis identified among the Australian participants in the overall investigation. During the international investigation, 158 (52%) the participating athletes were contacted by the CDC. Of the 158 respondents, 109 reported illness, including chills, myalgias, headache, diarrhoea, dark urine and arthralgias; 68 (44%) had illness that met the case definition of leptospirosis of the CDC.⁸⁰ The age of cases ranged from 22 to 50 years (median: 34 years) and 73 per cent were male. The median duration of illness was 6 days (range: 1-19 days) and 25 (34%) case-patients were hospitalised for the illness.⁸⁰

An outbreak of leptospirosis was reported in the Northern Territory in November and December 2000.⁸¹ Six cases of leptospirosis were notified to the NT Department of Health and Community Services. Two men and 3 women were involved in hunting during the time they acquired the disease. The third male case lived on a rural block where there are many animals and reported regularly going barefoot. In response to the outbreak a media release was issued by the Northern Territory health department, to highlight the risk for contracting this potentially fatal infection.

Other leptospirosis surveillance

The Collaborating Centre for Reference and Research on Leptospirosis, WHO/FAO Western Pacific Region report for 2000

This report summarises the leptospirosis notification data for 2000. The information has been collated from questionnaires distributed to all human cases in Australia and collected by the collaborating centre. In total, 204 cases of leptospirosis were investigated in 2000.

There was an elevated number of cases during the first 6 months of the year but not at the level reported in 1999. The increased number of notifications in the early part of the year reflects an increasing level of awareness of the disease among clinicians and a higher than average rainfall. The latter resulted in optimal conditions for the survival of the organism in the environment and favourable conditions for an increase in rodent populations.

Of the 204 cases, 179 reported illness, and the most frequently reported symptoms included headache (68.7%), followed by myalgia (60.9%), severe fever (57.0%), sweats (56.4%), chills (53.1%) and arthralgia (49.7%). The hospitalisation rate for leptospirosis remained high (56.3%) in 2000, and the average hospital stay for the patients was 5 days.

Data on occupation were available for 169 of the 204 leptospirosis cases. Animal associated occupations (63/169; 37%) and agricultural based occupations (61/169; 36%) accounted for the majority of the notifications nationally. The most frequently reported animal contacts were cattle (44.4%) and rats (38%). In Queensland however, agricultural related occupations were reported more commonly among the 115 leptospirosis cases (45.2%), specifically, banana farms accounted for 35.7 per cent of the total leptospirosis cases in Queensland.

Serovar information was recorded for 203 of 204 leptospirosis cases in 2000. Commonly identified serovars were L. hardjo (67/203; 33.0%), followed by L. zanoni (44 cases; 21.6%) and L. australis (37 cases; 18%).

The full report Leptospirosis: surveillance report for 2000 can be found on the Queensland Health Website at: http://www.health.qld.gov.au/qhpss/pdf/Leptospirosis/reports/lepto_jandec_2000.pdf

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Ornithosis

Ornithosis, also known as psittacosis, is an acute generalised infection with Chlamydia psittaci. The disease in humans is commonly associated with exposure to birds, particularly parrots, although some studies showed an association with lawn mowing and gardening in areas with high numbers of native birds.⁸² In 2000, ornithosis was notifiable in all States and Territories in Australia, except New South Wales and Queensland.

The NNDSS received 100 notifications of ornithosis in 2000, representing the third consecutive annual increase in the number of notifications since 1998 (Figure 48). The national notification rate was 1.1 cases per 100,000 population, and the majority of cases occurred in Victoria (85%).

Figure 48. Trends in notification rates of ornithosis, Australia, 1991 to 2000, by year of onset



All but one case of ornithosis was linked to exposure to birds. The male to female ratio of disease was 2.6:1. The highest age-specific rates were reported in the 60-64 year age group for both men (7.0 cases per 100,000 population) and women (2.7 cases 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.⁸² Shedding of C. psittaci into the environment by sick birds and subsequent inhalation of aerosolised dust and bird excreta may also lead to human infection.

Q fever

Q fever is the most common zoonotic disease reported to the NNDSS in Australia. 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.⁸³ Risk occupations include stockyard workers, meat packing and rendering workers, abattoir and dairy workers, and medical and veterinary research facility workers.⁸⁴ An effective vaccine is available for Q fever in Australia⁸⁵ to protect the populations which are high at risk of this disease.

Transmission is usually through airborne dissemination of the organism in dust particles, through 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. These cases, however, have resided downwind from contaminated areas.²⁷

In 2000, 573 notifications of Q fever were reported to the NNDSS with an annual notification rate of 3.0 cases per 100,000 population, a slight increase from 2.7 cases per 100,000 population reported in 1999 (Figure 49). The majority of Q fever cases occurred in Queensland (68.1%), followed by New South Wales (22.7%). High notification rates were localised to the South West (250.0 cases per 100,000 population) and the Central West (164.8 cases per 100,000 population) of Queensland.

Top of pageFigure 49. Trends in notification rates of Q fever, Australia, 1991 to 2000, by year of onset



The majority (92.8%) of the cases were adults in the 15-64 age range. The highest age-specific notification rates were in the 40-44 year age group for men (8.6 cases per 100,000 population) and in the 35-44 year age range for women (1.9 cases per 100,000 population) (Figure 50). The male to female ratio was 4.8:1. The true prevalence of the disease is likely to be under-estimated as the disease may be asymptomatic or self-limited.⁸⁶ Among 1,417 Australian abattoir staff tested for Q fever, 394 (27.8%) had serological evidence of exposure to Q fever.⁸⁷

Figure 50. Notification rates of Q fever, Australia, 2000, by age and sex



This article was published in Communicable Diseases Intelligence Volume 26, No 2, June 2002