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Zoonoses

The list of zoonoses (diseases transmitted to humans from animals that are the primary host) which are notified to NNDSS was modified in 2001. Hydatid disease was no longer notifiable and three new diseases (anthrax, Australian bat lyssavirus and other lyssaviruses) were made notifiable. Anthrax has been added to the list because of its potential for use as an agent of bioterrorism. The Australian bat lyssavirus came to attention after a human became infected and died after handling a fruit bat in 1996. The other notifiable zoonotic diseases are brucellosis, leptospirosis, ornithosis and Q fever.

Altogether, 1,091 notifications of zoonoses were received. This number accounted for one per cent of the total of all notifications for all diseases during 2001.

Brucellosis

Brucellosis in humans is caused by four species of Brucella bacteria, found in four different hosts - B. melitensis (sheep/goats), B. abortus (cattle), B. suis (pigs) and B. canis (dogs). Infection occurs principally from exposure through breaks in the skin to the fluid or tissues of infected animals, or from the ingestion of unpasteurised goat or sheep's milk and cheese (most often in visitors from overseas). The disease is characterised by fever, headache, arthralgia, depression and weight-loss.

In Australia during 2001, 19 cases (0.1 cases per 100,000 population) of human brucellosis were notified to the NNDSS. Most of these (n=17) were from Queensland (0.5 cases per 100,000 population), with one each from South Australian and Victoria. The 19 notifications for brucellosis in 2001 are the second lowest since 1991 (Figure 57).

Figure 57. Trends in notifications of brucellosis, Australia, 1991 to 2001, by year of onset



Of the 19 notifications of brucellosis, 17 were in adult males (age range 17-79 years) and the highest notification rates were observed in the 20-25 year age-group(n=4, 0.6 cases per 100,000 population). The two female cases were aged 40 and over 70 years. The male to female ratio was 8.5:1.

Bovine brucellosis was eradicated from Australia in 1989,⁹⁴ and the notifications of human disease occurring now are due to infections from the other species. The feral pig population in northern Queensland, estimated to be more than several million (McGaw and Mitchell, referred to in Williams et. al.),⁹⁵ has been identified as a primary reservoir of brucellosis.⁹⁵ Of the 17 notifications from Queensland, only two were typed to species level, both B. suis.

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Leptospirosis

Leptospirosis is caused by infection with the Leptospira spirochaete. Infection in humans occurs from exposure, through mucosal surfaces or breaks in the skin, to soils or fluids (bodies of water and animal urine) contaminated with the organism. Rats are a common reservoir of infection, and their presence in the cane fields in Australia is a source of exposure to cane growers. Fever, headache, lower limb myalgia and conjunctival suffusion are typical symptoms. There is a wide range of disease severity, from sub-clinical to death from hepatorenal failure. Increased disease severity is associated with increased age and with certain leptospiral serovars. Clinical disease is more likely to be milder in areas of endemic infection.¹⁶

There were 245 notifications of leptospirosis in Australia during 2001 (1.3 cases per 100,000 population). Notifications were received from all states and territories except the Australian Capital Territory. Most cases occurred in Queensland (n=129) and New South Wales (n=65). The highest rate was observed in Queensland (3.5 cases per 100,000 population). By Statistical Division, the areas with the highest rates were the Central West of Queensland (32.0 cases per 100,000 population) and Far North Queensland (31.4 cases per 100,000 population) (Map 11).

Map 11. Notification rates of leptospirosis, Australia, 2001, by Statistical Division of residence



Reflective of a strong occupational association with the stock and horticultural (bananas, sugarcane) industries, males aged 15-64 years accounted for 87 per cent of all notifications. The peak rate of 4.0 notifications per 100,000 population occurred in males in the 30-34 year age group (Figure 58).The male to female ratio was 6.7:1.

Figure 58. Notification rates of leptospirosis, Australia, 2001, by age group and sex



Trends in the notification rate for leptospirosis are shown in Figure 59. A peak in notification rates was observed in 1999, when 184 cases were notified. This has been attributed to prolonged rainfall in northern Queensland, with a concomitant increase in rodent populations.⁹⁶ It is possible, however, that reporting artefacts, such as increased awareness, underlie these changes.

Figure 59. Trends in notification rates of leptospirosis, Australia, 1991 to 2001, by year of onset



The 2001 annual report of the WHO Leptospirosis Reference Laboratory further describes the laboratory characteristics of leptospirosis isolates in Australia (www.health.qld.gov.au/qhpss/qhss/lepto_jandec_2001.pdf). Seventeen serovars were identified in human infections in 2001, and the Leptospira interogans serovar hardjo was the most commonly identified, in 38 per cent of infections. This serovar is most associated with the cattle and dairy industry, whereas Leptospira interogans serovar australis, identified in 12 per cent of cases, occurs more in horticultural settings. Since 1992, the number of notifications of Leptospira interogans serovar hardjo has increased tenfold.

Infection with leptospirosis is a public health concern in the tropical WPR. New Caledonia for example, reported 180 cases per 100,000 population - a rate over 100 times greater than that observed in Australia.⁹⁷ Leptospirosis has also been identified as an emerging infectious disease, because of changes in animal husbandry, climate and human behaviour.⁹⁸

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Ornithosis

Ornithosis is an infection caused by the intracellular organism Chlamydia psittaci. Symptoms of infection include fever, headache, rash and respiratory tract infections and, especially among older people, atypical pneumonia. C. psittaci often infects birds but because of its more particular association with parrots the human disease is also known as psittacosis. As well as directly from birds, the disease can be transmitted to humans through bird detritus (e.g. feathers and dust) and droppings. As infections in birds are commonly asymptomatic, it is prudent to avoid these materials.

During 2001, 131 notifications of ornithosis were reported in Australia. The largest number were from Victoria (n=68) and New South Wales (n=37). The highest rate occurred in Victoria with 1.4 cases per 100,000 population. Notification in Queensland commenced from July 2001. Nationally the rate was 0.7 cases per 100,000 population. The trends in the annual national notification rate between 1991 and 2001 ranged from approximately 0.5 to 1.5 cases per 100,000 population. The peaks in notification rates may reflect particular outbreaks (Figure 60).

Figure 60. Trends in notification rates of ornithosis, Australia, 1991 to 2001, by year of onset



In 2001, males and females were equally affected by ornithosis (male: female ratio 1.1:1). The highest notification rates of ornithosis were in males in the 75-79 years age group and in females in the 55-59 years age group (4.4 and 3.0 cases per 100,000 population respectively, Figure 61).

Figure 61. Notification rates of ornithosis, Australia, 2001, by age group and sex



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Q fever

Q fever is caused by infection with the rickettsia Coxiella burnetii. The disease is particularly associated with workers in the livestock industry. The organism is extremely infectious, and the tissues and fluids of infected animals are sources of infection. The dusts around stock facilities are also sources of infection because the organism is resistant to desiccation.

In 2001, 698 cases of Q fever were notified to NNDSS, a rate of 3.6 cases per 100,000 population. Most cases were from Queensland (n=454, 12.5 cases per 100,000 population). In Victoria, an outbreak of 18 cases occurred in Wodonga between early April and July.

The groups with the highest notification rates were 50-54 year old males (9.6 cases per 100,000 male population) and 45-49 year old females (3.0 cases per 100,000 female population) (Figure 62). The overall male to female ratio was 4.1:1.

Figure 62. Notification rates of Q fever, Australia, 2001, by age group and sex



Sixteen cases of Q fever in children (aged less than 15 years) were notified from New South Wales (n=4) and Queensland (n=12). Information on exposure was available for 10 cases, all of who lived on or visited farms. Seven cases were linked to other cases of Q fever in family members, neighbours or other contacts.

The rate of Q fever notifications in Australia in recent years has remained relatively consistent since 1995 (Figure 63). Recent increases may be due to increased testing as a result of the Q fever vaccination program.

Figure 63. Trends in notification rates of Q fever, Australia, 1991 to 2000, by year of onset



A Commonwealth program to reduce the occurrence of Q fever commenced in October 2000. In the first phase abattoir workers and shearers were provided with free skin testing and Q fever vaccination. Under this program, Q fever-related medical costs were underwritten by the Commonwealth. The Q fever register has been established to provide a record of the vaccination status of abattoir workers (www.qfever.org). The second phase commenced in October 2001, and is directed at beef, sheep and dairy workers.

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Australian bat lyssavirus and lyssavirus (unspecified)

The death of two Queensland women after handling fruit bats in 1996 and 1998 led to the discovery of the Australian bat lyssavirus (ABL). ABL and lyssavirus (unspecified) are closely related to the rabies virus. During 2001 there were no notifications of Australian bat lyssavirus or lyssavirus (unspecified) in Australia. African and European lyssaviruses may infect travellers and thus are included in lyssavirus (unspecified) on the list of notifiable diseases.

The symptoms of lyssavirus infection are similar to those of rabies, and are sometimes indistinguishable. Onset of symptoms occurs weeks after infection (this can be longer again in pre-pubertal individuals). Early symptoms are headache, fever and malaise, and, indicative of neural involvement, a sense of apprehension, and indefinite sensory changes. Following this, excitability, paresis or paralysis, a fear of water, delirium and convulsions then occur. By this stage the disease is inevitably fatal.^16,89

Between 1996 and 1999, 205 people reported being bitten or scratched by bats in Queensland.⁹⁹ The rate of ABL seropositivity in bats involved in human exposures or in sick, injured or orphaned bats was approximately 5.5 per cent.

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Anthrax

The bacterium causing anthrax, Bacillus anthracis, occurs in many parts of the world, most commonly as spores in the soil. When soil becomes moist and warm, spores enter a reproductive stage and quickly multiply. Animal hosts such as herbivores (sheep, goats, cows) can then become infected, and if not treated, die. Following the animal's death spores are released, which can lie dormant in the soil for decades. Vaccination protects livestock from becoming infected, and also provides protection from infection in humans.

There were no cases of human anthrax infection in Australia in 2001. Human anthrax occurs in three forms (cutaneous, gastrointestinal and pulmonary), depending on the route of infection.⁸⁹ Cutaneous anthrax occurs in handlers of animals or animal hides (tannery workers were once a high risk occupational group). The skin lesion is quite characteristic. With treatment the mortality rate is usually less than one per cent. Gastrointestinal anthrax results from the consumption of infected meat. The primary site of infection may be the lower gut or throat. This form has been effectively eliminated in countries where the butchering of livestock is regulated. The non-specific nature of the early symptoms (nausea, vomiting and fever) prevents early diagnosis, and the mortality rates can be substantial.

Pulmonary anthrax results from inhalation of the anthrax spores into the lungs. A two-phase illness results. The first phase produces only mild symptoms, which again are non-specific (e.g. fatigue, myalgia, mild fever), and last for 2-4 days. The second phase of illness is characterised by severe respiratory distress with a sudden onset. The highest rate of mortality from anthrax infection occurs with pulmonary anthrax. In the past, workers in textile mills inhaling fine dusts were often affected by anthrax (wool-sorters disease). Improvements in industrial hygiene and the use of synthetic fabrics have since resulted in fewer cases of pulmonary anthrax being recorded.⁸⁹

In October 2001, 22 people in the United States of America became infected with anthrax. The source of infection was believed to be letters containing anthrax spores. Eleven cases were of the cutaneous form, and the other 11 were inhalational anthrax. Five deaths resulted.¹ Shortly afterwards in Australia and other countries there were many white powder incidents. Over 400 samples were tested for the presence of anthrax in New South Wales. None contained anthrax spores.¹⁰⁰

Human anthrax infections arising from natural (i.e. soil-borne) sources in Australia have been reported between 1917 and 1990. Infections occurred at very low rates of about 0.8 to 1.0 cases per 100,000 population, and were associated with occupational exposure.¹⁰¹

Some areas in Australia are well known for sporadic anthrax infection in livestock. Most cases in livestock in Australia occur in a band running north-south in central New South Wales and into northern Victoria. The occurrence of cases has been correlated with drier periods in summer following wet or humid weather (www.brs.gov.au/usr-bin/aphb/ahsq?Disease=ATX).


This article was published in Communicable Diseases Intelligence Volume 27, No 1, March 2003.