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Abstract - Authors' details - Introduction - Methods - Results - Discussion - Acknowledgement -
References -
Box 1 -
Box 2 -
Figure 1 -
Figure 2 -
Figure 3 -
©MJA1996 -
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The tapeworm genus Echinococcus is an important zoonosis which is endemic in many parts of the world. The only species occurring in Australia is Echinococcus granulosus. It was probably introduced with infected domestic livestock during European settlement and is now widespread in domestic livestock and wildlife, with wildlife acting as an important reservoir.1 Dogs (domestic and wild) and foxes are the definitive hosts (Figure 1).
Humans become infected by the ingestion of eggs passed in faeces of dogs. Oncospheres released from the eggs penetrate the intestinal mucosa and, via the portal system, lodge in the liver, lungs, muscle or other organs, where the hydatid cysts form.
Because of inadequate reporting, the prevalence of human hydatid infection in Australia is unknown. From the earliest published studies human hydatidosis in New South Wales has occurred mainly in people living in rural areas in the eastern half of the State associated with the Great Dividing Range.2-4 Dew, in 1928, reported a relatively even distribution of patients with hydatidosis in eastern New South Wales, but subsequent reports showed an increasing trend for patients to be concentrated in the north-eastern and south-eastern Tablelands.3-5
To assess the health risk associated with E. granulosus, a retrospective survey of hydatid infection was conducted between 1987 and 1992 by examining records of patients with hydatidosis from hospitals and health services in New South Wales (NSW) and the Australian Capital Territory (ACT).
- Sex;
- Date of admission;
- Date and country of birth;
- Place of residence at admission;
- Cyst location; and
- Whether the infection was new or recurrent.
We maintained patient confidentiality by using initials only for individual identification. Multiple admissions for the same patient were identified from admission dates, initials, age, sex and general location of residence at the time of admission. We calculated mean annual prevalences of infection using 1991 Census data.6
Two hundred and eighty-two patients (172 new cases and 110 recurrent cases [including those not classified as new or recurrent]) were treated in NSW and 39 patients (23 new cases and 16 recurrent and unclassified cases) were treated in the ACT (16 and 14, respectively, of those treated in the ACT lived in NSW).
The mean annual prevalence of human hydatidosis in rural NSW was 2.6 cases per 100 000 rural population. Cases occurred in 15 shires [counties] in the north-east and 24 shires in the south-east. On a shire-to-shire basis, the mean annual prevalence of infection ranged from 0.3 to 17.7 and 0.5 to 23.5 (cases per 100 000 population), respectively, in these two areas (Box 1).
Four of the cases (three new and one recurrent) were in Aboriginal people. These four cases represented a mean annual prevalence of hydatid infection of 1.1 cases per 100 000 in the Aboriginal population of NSW.
Of the patients born overseas, all were living in NSW, except one ACT resident. The mean annual prevalence of infection was calculated for 25 ethnic groups (each with a population of over 1000) resident in NSW (Box 2). The highest mean annual prevalence occurred in the Iranian population (6.6 cases/100 000) and the lowest in the German population (0.5 cases/100 000). Most cases came from the Greek and Lebanese communities and communities of people from the former Yugoslavia (13, 10 and 8, respectively), but because of their relatively large populations in NSW, these cases represented only a mean annual prevalence of 4.8, 3.2 and 2.2, respectively.
Our study confirmed the concentration of hydatidosis in the north-eastern and south-eastern Tablelands reported previously.3-5 The narrow corridor parallel to the coast in the central part of the State is an area where there have been few cases reported previously, but where considerable urban development has occurred over the last decade, and previously undiagnosed patients may have moved to this region.
Population movement from country areas to cities may also account for many of the Australian-born patients diagnosed in urban areas. However, it is also possible for urban residents to be exposed to eggs of E. granulosus. Recent studies have identified infection with E. granulosus in dogs of a recreational pig hunter living in suburban Perth,7 and in dogs of Perth residents living in uncleared areas on the outskirts of the city.8 Foxes infected with E. granulosus have been found in the suburbs of Canberra.9
The older age of the Australian-born compared with the immigrant patients largely reflects the different age-group structures of the two groups. In 1990, 88.3% of immigrants were aged less than 45 years when they arrived in Australia and 27.4% were less than 14 years of age.10 Migrants may be already infected when they arrive as children, but the long latent period of hydatid disease means it is first detected in adulthood. It is difficult to explain why most Australian-born patients were detected in the age group 31 to 40 years whereas most immigrants were not detected until 41 to 50 years. Infections in immigrants may be caused by a different strain type of E. granulosus with a slower cystic growth rate. Alternatively, there may be a reluctance among newer immigrants to consult local doctors.
The migrants infected with hydatid disease origin(Box 2)ated in countries where E. granulosus is endemic. The order of ranking of countries according to the mean annual prevalence of hydatid infection in their migrant populations in NSW closely reflected the relative importance of human hydatidosis in their countries of origin. The range of prevalences in the migrant populations were no higher than those recorded in shire populations in north-eastern and south-eastern NSW. In at least three of these shires the prevalence of human hydatidosis was two to three times higher than the highest level recorded in a migrant population.
Three of the urban patients and one of the rural patients born in Australia were Aboriginals. The three urban Aboriginal patients are likely to be from a rural background, but as their place of birth was unknown it was not possible to calculate a prevalence of hydatid infection for rural Aboriginal people. The mean annual prevalence of 1.1 cases per 100 000 for the total Aboriginal population of NSW is about a third of the prevalence in the rural non-Aboriginal population. Few cases of hydatid disease in Aboriginal people have been reported. All the reports are from studies in Western Australia during the 1970s, where Aboriginals were always highly represented: 15/57 cases11 and 13/31 cases.12 Our data represent the first report of hydatid infection in Aboriginal people in NSW; a previous study reported E. granulosus infection in a dog from a NSW Aboriginal community.13
The reason for human hydatidosis not being perceived as a problem in Australia can be attributed largely to under-reporting of this notifiable disease;5 this has been a problem for many years,,5,12,14,15 with no signs of improvement. Only 17 of the 321 new and recurrent cases identified in this study had been notified, and in a retrospective study in Victoria for the 12 months up to July 199116 only two of the 50 new or recurrent cases had been notified.
Disease recurrence after operative treatment is an important aspect of human hydatid infection. A carefully conducted follow-up study of 39 patients treated surgically in Australia first drew attention to this problem;17 22% had had recurrent infection by 30 months, mainly caused by cyst rupture before surgery. In our study, 37.5% of patients (for whom information on new or recurrent infection status was supplied) were treated for recurrent infection.
Effective chemotherapy of patients with hydatid infection would substantially reduce the cost of treatment. This topic has been reviewed,18 and the most promising drug studied was albendazole. Data from studies on 253 patients indicated that albendazole was an effective cure in 28%, 51% showed improvement, 18% were unchanged and in 2% the cysts continued to grow.19 The most appropriate use of albendazole may be as an adjunct to surgery. Rupture of cysts and spilling of protoscoleces (which can form new cysts) into the body cavity during surgery is a constant risk, but an immediate postoperative course of albendazole will greatly reduce the chance of new cysts developing.20
Hydatid disease is preventable, and education is one of the most effective tools to achieve this. It is important that State and Federal governments take a responsible attitude towards increasing community awareness, and implement control strategies through education, either by themselves or by funding organisations such as the Australian Hydatid Control and Epidemiology Program. Control of this parasite in Australia requires a long term commitment; the alternative is that hydatid disease will continue to incapacitate individuals and be an additional financial drain on an already overstretched health service.
(©MJA 1996; 164: 14-17)
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