Hydatid disease: medical problems, veterinary solutions, political obstacles

Editorial

Hydatid disease: medical problems, veterinary solutions, political obstacles

It is to be hoped that in the near future Australia will cease to have the unenviable reputation of being the home of perhaps the most important parasitic disease common to man and domesticated animals, which carries with it the added stigma that it is preventable.¹

Notorious under-reporting of cases of hydatid disease has made it easier for authorities to remain inactive to the need for control. In this issue of the Journal, Jenkins and Power (page 18) have effectively documented the failure of the New South Wales (NSW) and Australian Capital Territory (ACT) health care systems to take the problem seriously. Their survey of medical records from hospitals and health care services identified 195 new cases of hydatidosis (172 in NSW, and 23 in the ACT) during the six-year period 1987-1992. This compares with official notifications of 37 and three cases, respectively, during the (partially overlapping) five-year period 1990-1994.² New cases presented predominantly in the north-eastern and south-eastern Tablelands and in metropolitan areas. Whereas the latter could have included some patients from rural areas, 60% of the urban cases were migrants who had most probably contracted hydatidosis outside Australia. Their presentation to city practitioners may present diagnostic difficulties if medical awareness of hydatidosis is less acute than in endemic rural areas.

Would complete notification of all cases (assuming that it could be achieved) alleviate the problem? Apart from causing transient embarrassment, I believe it would have little impact. Certainly, accurate incidence figures are essential for assessing any pattern of change in a disease, but there are other major obstacles interfering with successful hydatid control in mainland Australia. In Tasmania, a concerted campaign involving collaboration between government and community organisations over several decades eliminated transmission of hydatid disease to humans,³ but in the larger mainland areas problems stem from the disease failing to conform to a pattern to which health care systems are designed to respond.

Firstly, hydatidosis occurs in a limited number of regions, and centrally directed health programs operate on a state-wide basis (with a strong urban bias). Secondly, hydatidosis, although a human disease, requires veterinary, agricultural and educational expertise for effective prevention. Thirdly, the treatment of hydatidosis is exclusively surgical (and undertaken at a high standard in Australia) but its prevention is not ( in a way, surgery is as relevant to hydatid control as panel beating is to the prevention of road accidents. Fourthly, because successful prevention requires diverse skills, hydatidosis is not accepted as the responsibility of any one bureaucracy. Health, agriculture, education and conservation all have a role, but collaboration across such a range of portfolios to solve a regional problem is apparently unthinkable. And finally, the coup de grace ( there are no votes in hydatids. The largest and longest operating control campaign on the mainland (under the auspices of which the research of Jenkins and Power was undertaken) succumbed after a decade in which it received no State funding whatsoever: the Government eliminated the campaign and left the parasite!

To what extent would complete prevention of human hydatidosis be attainable if political support and collaboration between government departments were coupled with the enthusiasm of many in rural communities who have attempted the task in the past?

Ongoing investigations of hydatidosis epidemiology in Australia indicate that the textbook description of the life cycle of Echinococcus granulosus is no longer comprehensive.⁴ Surveys of parasite prevalence in regions with a high incidence of human hydatidosis consistently reveal a high prevalence of infection in wild dogs (including dingoes) as definitive hosts, and in macropods (kangaroos and wallabies) and feral pigs as intermediate hosts.⁵ In the light of these findings, the practice of baiting pigs in national parks, and thus providing an appetising source of echinococcal infection for wild dogs, may require re-examination. Contrary to earlier beliefs, foxes have been found to carry the parasite,⁶ and they frequent urban locations such as barbecue areas where their habit of demarcating territories by depositing faeces may introduce a significant human hazard.⁷ Dogs living in Perth suburbs but used for recreational pig hunting have been found to carry the parasite.⁸

It is not clear whether these new patterns of hydatidosis represent changes in the parasite, in its ecosystem, or in both. The extent to which human activity has contributed to the changes is also unclear. Increasingly, there are indications that the concept of separate wildlife and domestic animal strains of the parasite is breaking down and that a single strain, albeit manifesting host-determined phenotype variation, may have the capacity to infect both types of host in each of the traditional wildlife and domestic cycles. The domestic and wildlife strains of E. granulosus do not appear to be genetically distinguishable.⁹ Consequently, the wildlife cycle is likely to be of considerable human health importance. A case of hydatidosis in a child from the Southern Tablelands was the first documented instance of human disease produced by the wildlife strain.¹⁰

When a serious decision to combat hydatidosis is taken, it is clear that new strategies will be required.

Peter J McCullagh
Senior Fellow, Division of Clinical Sciences
John Curtin School of Medical Research
Australian National University, Canberra, ACT

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10. 10. Thompson RCA, Nott DB, Squire J, Rennell D. Evidence that the Australian sylvatic strain of Echinococcus granulosus is infective to humans [letter]. Med J Aust 1987; 146: 396-397.