Echinococcus granulosus in northern Queensland. 1. Prevalence in cattle.

OBJECTIVE: To determine the prevalence and geographical distribution of hydatidosis and investigate factors that might be expected to influence the prevalence of hydatids in cattle in Queensland north of the Tropic of Capricorn. To determine the effect of natural levels of infection on carcase weight and subsequent economic loss. PROCEDURE: An abattoir survey conducted in 1981 provided information on the distribution, prevalence and viability of hydatid cysts in cattle from all shires north of the Tropic of Capricorn in Queensland. Livers, lungs and spleens from 10,382 cattle were palpated at abattoirs in Cairns, Townsville and Rockhampton to detect hydatid cysts. Prevalence of infection in cattle in each shire was estimated from results of the abattoir study together with reports of infection in a further 22,185 cattle obtained from abattoir records. Linear modelling was used to define the effect of geographical origin, age, breed and sex on prevalence of infection. Differences in the weights of carcases between infected and non-infected cattle of the same age, sex, breed and property of origin were examined. The economic loss to the beef industry in the region surveyed was estimated. RESULTS: Cattle infected with hydatids originated almost entirely from regions to the east of the Great Dividing Range. The mean prevalence inside this zone was 28% compared with 3% in other areas. Viable protoscoleces were found in 0.7% of cysts. Geographical origin and age of the cattle were the most significant factors influencing prevalence. Infection with hydatids had no effect on carcase weight. Economic loss was limited to that associated with condemnations of organs at meat inspection, estimated to be 0.5 million dollars per annum in 1981 and 6 million dollars in 2004. The distribution of hydatids in Queensland north of the Tropic of Capricorn corresponded most closely with the distribution of small wallabies such as Macropus dorsalis (black-striped wallaby), M parryi (whiptail wallaby) and M rufogriseus (red-necked wallaby). CONCLUSIONS: It was concluded that cattle are not an important part of maintaining the life-cycle of E granulosus in Queensland north of the Tropic of Capricorn. Within the endemic zone, which is almost all to the east of the Great Dividing Range, the local pattern of bovine echinococcosis is most likely to be determined by the presence or absence of small species of wallaby such as M dorsalis, M parryi and M rufogriseus.

Echinococcus granulosus in northern Queensland. 2. Ecological determinants of infection in beef cattle.

OBJECTIVE: To provide information on possible ecological determinants of infection with Echinococcus granulosus in a beef pastoral area of northern Queensland. PROCEDURE: An ecological study was carried out on the prevalence and viability of infection with Echinococcus granulosus in definitive and potential intermediate hosts, and their predator prey relationships. Seven adjacent extensive beef properties 100 km south of Townsville, that included areas of savannah, open woodland and dense closed scrub, were selected for the study. Infection with E granulosus in dingoes was determined at post mortem, and in domestic dogs by examining duodenal mucus after purging with arecoline hydrobromide. Cattle, wild pigs and macropods were examined at post mortem for viable hydatid cysts. The diet of dingoes was investigated by identifying the hair of prey species found in their stomach and colon, and that of domestic dogs by questioning their owners. RESULTS: Prevalence of hydatidosis in adult cattle ranged from 41% in animals from properties with large areas of dense closed scrub, to 3% on properties with little or no scrub. Hydatid cysts were found in 21.8% of black-striped wallabies (Macropus dorsalis), 9.4% of feral pigs, 1.5% of wallaroos (Macropus robustus), and 1.4% of eastern grey kangaroos (Macropus giganteus). No rufous rat kangaroos (Aepyprymnus rufescens) or swamp wallabies (Wallabia bicolor) were infected. Most cysts in macropods were viable, whereas in pigs about half were viable and in cattle only 0.7% contained viable protoscoleces. Infection with E granulosus was detected in 76% of dingoes, whereas no infection was detected in domestic dogs in the study area. CONCLUSIONS: It was concluded that the sylvatic cycle of E granulosus in the study area was maintained mainly through predation of black-striped wallabies by dingoes, and that the verges of dense scrub were the main nidus of infection.