Australasian contributions to an understanding of the epidemiology and control of hydatid disease caused by Echinococcus granulosus—past, present and future

Abstract

For several years after Echinococcus granulosus was introduced into Australasia from Europe, its life cycle was unknown. Before the end of the 19th century, however. Cystic Hydatid Disease (CHD) was recognized in humans as an important cause of death, although its magnitude was not quantified. During the first 50 years of the 20th century, the urban component declined, but CHD remained a serious source of ill-health. During the second half of the 20th century major research contributions have included: (i) differentiation of pastoral from wildlife Echinococcus and (ii) breaking the ‘epidemiological code’ of the family Taeniidae, thereby denning the conditions under which transmission occurs. Based on this research and concurrent surveys, it is concluded that the present geographical distribution of E. granulosus in domestic animals and CHD in the rural population is determined by climate; being uncommon where hot dry seasons continue beyond a few months. The parasite's range may be extended in its wildlife cycle through a highly susceptible definitive host—the dingo. The ease with which blowflies transfer taeniid eggs from dog faeces to animal and human foodstuffs implies that in Australasia, CHD can sometimes be regarded as foodborne. A perceived decline in autochthonus cases in the rural community during the second half of the 20th century may be accounted for by increased standards of living generated by economic advancement. Where a decline has not occurred or incidence is unusually high, CHD may be acting as an indicator of social disadvantage. Field trials and control programmes demonstrated that pastoral echinococcosis readily responded to intervention. Indeed, in both New Zealand and Tasmania, using different administrative structures and methods of funding, E. granulosus was driven from endemic towards extinction status. The really convincing result was the rapid decline in CHD in all age groups. The problem still to be solved is to identify methods for eliminating foci where high levels of CHD still exist but, continent- or even state-wide intervention may not be considered to be cost-effective using current tools. Here, mathematical modelling and cost-benefit analysis can be regarded as powerful methods to assist the decision-making process.