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This article was published in 1957
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INSTITUTE OF INSPECTORS OF STOCK OF N.S.W. YEAR BOOK.
Definitive Hosts of Echinococcus granulosus (Rudolphi, 1805) (Batsch, 1786) in Australia
M. A. GEMMELL. B.V.Sc. Department of Veterinary Pathology and Bacteriology, University of Sydney
INTRODUCTION
No species of animal is susceptible to all parasites and the converse is true that no parasite is capable of existing in all hosts. The majority of parasites infest only a few hosts and these are in most instances closely related. That the larval stage of the hydatid tapeworm can infest such a large range of unrelated hosts is therefore exceptional amongst metazoan parasites; but is the adult Echinococcus granulosus also adapted to live and reproduce in the intestinal tract of a variety of hosts? These might include, not only the natural and well-recognised, closely-related hosts, such as the Dog (Canis familiaris) and the Dingo (Canis dingo), but also the Red Fox (Vulpes vulpes) and the Cat (Felis domesticus). From an analysis of the data obtained in a survey of this cestode in 561 station and farm dogs, 41 foxes and 21 dingoes and experimental infestations of foxes and cats, it is possible to indicate the role each of these carnivora plays in the persistence of hydatid disease in Australia.
GEOGRAPHICAL DISTRIBUTION OF HYDATID DISEASE IN NEW SOUTH WALES
As hydatid disease has a limited distribution in New South Wales, and the dingo, unlike the fox, dog and cat, is prevalent only in certain districts, it is necessary to define the extent of the areas where this parasite occurs so that the responsibility of each species in spreading the disease may be determined.
Both the dog and the fox are well distributed throughout the State. It is estimated that there are at least 120,000 station and farm dogs in the Southern and Central Tablelands and South-western Slopes alone (Gemmell, 1956). Unfortunately, no records are available on the prevalence of the fox, but since its introduction it has spread throughout New South Wales and it is stated by some graziers to be more common than dogs in some districts. The dingo, unlike these two former animals, is extremely shy, and is found when the country is sparsely populated. Although a few dingoes are caught annually in regions adjacent to closely-populated rural districts in the Southern and Central Tabelands, the main dingo area is in parts of the Northern Tablelands and North Coast,
As judged by the incidence of hydatid disease in sheep. the parasite is found most frequently in the Northern and Southern Tablelands and decreases gradually from these regions into the central division, slopes and plains. There are many districts in the plains and Western Division where the incidence in sheep is extremely low, except in some drafts of animals (sheep) which originally come from districts in the Tablelands. It appears probable that the incidence is largely dependent on the length of time climatic conditions are favourable for the ova of the parasite, and not on the animal populations.
RESULTS OF THE SURVEY
Of the 561 station and farm dogs examined, 138 (24%) were infested with E. granulosus, and of 21 dingoes examined, 10 (47.6%) carried the parasite. In one only of the 41 foxes there was found a single segment which appeared similar to E. granulosus.
INCIDENCE OF E. GRANULOSUS IN THE DOG, DINGO AND FOX IN NEW SOUTH WALES
| Animal | Number examined | Number infested | Percentage |
|---|---|---|---|
| Station and farm dogs | 561 | 138 | 24.6% |
| Dingo | 21 | 10 | 47.6% |
| Fox | 41 | 0 or 1
|
O or 2% |
*
1 segment only.
These results suggest that the two main definite hosts of E. granulosus are the closely-related species, the dog and the dingo. It also appears unlikely that the fox is a normal host of this parasite in New South Wales.
THE ROLE OF THE DOG IN THE PERSISTENCE OF HYDATID DISEASE
Although the dog is a natural host of this cestode, not all animals would have the same chance of becoming infested or be responsible for the continuity of the hydatid cycle. This would depend largely on the place of residence and occupation of the dog.
Station and farm dogs were more often infested with E. granulosus than dogs living in cities or country towns (Gemmell, 1957). However, not all dogs on properties appear to have the same chance of harbouring the parasite. Although living under similar conditions, a higher incidence occurs amongst sheepdogs (27%) than rabbit dogs (20%); but in those districts where rabbits are scarce and no longer form the main diet of the rabbiting pack, the incidence in both sheep dogs and rabbit dogs is similar.
Although a high incidence of E. granulosus is found in abattoir dogs (21.3%) (Gemmell, 1957), these animals live for most of the year in cities or towns and have little contact with sheep (other than those for slaughter), and would consequently have little responsibility for the persistence of the disease. It is also of interest that stray dogs in country towns appear to have little chance of picking up infective offal, living for the most part on rats, rabbits or garbage, as judged by the stomach contents and the high incidence of Taenia pisiformis and Taenia serialis in these animals
It is apparent, therefore, that the station and farm dog, and, in particular, the sheep dog by the nature of its environment and contact with sheep, is responsible for the high incidence of hydatid disease in most districts of New South Wales.
THE ROLE OF THE DINGO IN THE PERSISTENCE OF HYDATID DISEASE
Durie and Riek (1952) enquiring into the high incidence of hydatid disease in cattle (31%) in Southern and Coastal Queensland where sheep numbers are low, found that the dingo was responsible for this high incidence in bovines. They examined 11 dingoes and found nine (81.8%) infested with E. granulosus. Furthermore (as most cattle cysts are sterile), they established that the wallaby and kangaroo were the main hosts for the cystic stage.
In Northern New South Wales, ten of the 21 dingoes examined carried this parasite (see Table). As the contact between dingo and sheep is usually low (except in certain instances), because the dingo is either contained within a dog-proof fence or sheep properties are fenced against this carnivore, it is necessary to suggest another intermediate host for the cystic stage. It has not been possible to examine wallabies or kangaroos in these districts, but as they form a considerable part of the diet of the dingo as judged by stomach contents, it is reasonable to assume that a "dingo-wallaby cycle" exists here as in Queensland.
As there is a high incidence of cysts in the sheep in these northern districts and the contact between dingo and sheep is restricted, it is evident that the "dog-sheep cycle" is continued here at the same time and at approximately the same level as that of the sylvatic cycle.
THE ROLE OF THE FOX IN THE PERSISTENCE OF HYDATID DISEASE
The results of this survey and that undertaken by Murray Pullar (1946), who examined 61 foxes in Victoria and found none infested, suggest that the fox plays no part in the spread of hydatid disease.
Unlike the dingo, the fox does not normally attack or eat sheep carcases except the soft, easily accessible parts such as the tongue and the crutch. By the time the internal organs (lungs and livers) become accessible to this animal, as the result of the initial opening by other animals or natural disintegration, putrefaction would probably have killed the scolices. This might explain the findings in Murray Pullar's survey and our own. However, in certain parts of Europe, Asia, Alaska and Siberia, the fox has been found to carry a species of Echinococcus. The question arises, therefore, is the fox capable of acting as a natural host of the particular species of Echinococcus found in Australia if it had access to infested offal containing scolices?
Twelve foxes were experimentally drenched with fertile scolices from cysts in sheep. In nine of these killed after varying periods, a very small number of Echinococci were found, but none had developed to sexual maturity. Dogs drenched with a similar dose of the same batch of scolices and examined post-mortem after the same period, showed large numbers of E. granulosus. These all exhibited the various stages of development up to full maturity with ripe segments, containing ova, by seven weeks after drenching. This indicates that the fox, even it it can gain access to infested material (which may not occur frequently) may harbour a few tapeworms for a period; but as these cestodes cannot develop to sexual maturity, the fox is not a natural host of the species of E. granulosus as found in Australia, and consequently plays no role in the persistence of hydatid disease in this country.
THE ROLE OF THE CAT IN THE SPREAD OF HYDATID DISEASE
Arecoline hydrobromide is not a satisfactory drug for use in cats, and as no cats could be secured on stations or farms for post-mortem, during this survey. However, 12 cats were drenched experimentally at the same time as the foxes referred to above with the same material and the results were similar to those found in the fox. Although some cats harboured a few specimens for a period, these did not mature sexually and the cat therefore cannot be regarded as a natural host of E. granulosus; consequently, chance infestation with this cestode would not add to the incidence of hydatid disease in man or domestic animals.
It is of interest to note that, although the cat is not a natural host of the species of Echinococcus occurring in Australia, felines have been found to be infested by two species of this genus-E. oligarthrus and E felidis. The former has been found in a puma (Felis concolor) and a Jaguar (Felis yaguarondi) and its intermediate stage occurs in a large South American rodent (Myocastor). E. felldis has been found in a lion (Felis leo), but the host for its intermediate stage is not known. However, Rausch (1953) suggests that it may occur in one or more species of artiodactyl or perrisodactyl. Neither species has been found in Australia.
THE ROLE OF OTHER PREDATORES IN THE PERSISTENCE OF HYDATID DISEASE
Certain marsupials are predatory (Seddon, 1950), notably the Thalacine or Tasmanian Wolf (Thalacinus cynocephalus) and the Tasmanian Devil (Sarcophilus harrisii), both of which attack sheep. Although no evidence is available to indicate whether these animals are natural hosts, as it appears that the E. granulosus occurring in Australia in its sexual stage may be host specific, it is unlikely that these animals would be dennite hosts. Furthermore, as they are almost extinct they obviously play no role in the spread of the parasite.
Other predatores of livestock are the tiger cat (Dasyurops maculatus) and a few species of small native marsupial "cats"; as these are too small to attack sheep, it is evident, even if they were natural hosts, that they would play no part in the hydatid cycle.
Feral pigs occasionally eat sheep carcases, but there is no evidence to suggest that these animals can harbour the adult stage of E. granulosus.
Full details of these experiments related to the fox and other possible hosts will be published elsewhere.
DISCUSSION, CONCLUSIONS AND SUMMARY
One in every three station and farm dogs was found to harbour E. granulosus in the Southern Tablelands, one in every four in the South-western slopes and one in every five or six in the Central Tablelands. These findings, and also the fact that foxes and cats are not natural hosts and that very few dingoes are present in these districts, all indicate that it is the station and farm dog which is responsible for the high incidence of hydatid disease in domestic food animals in these regions. Furthermore, as the dingo does not occur in the Slopes, Plains and Western Division, the domestic dog is responsible for the disease in these districts also.
The high incidence of hydatid disease in food animals in the Northern Tabelands and North Coast is of interest, as two natural hosts of E. granulosus exist in these regions. As the contact between sheep and the dingo is limited, the dog is responsible for most of the high incidence of hydatid cysts in sheep; but as there may be a relatively close contact between dogs, dingoes and cattle. both these animals must be responsible for hydatid cysts in bovines in the northern regions.
ACKNOWLEDGEMENTS
My grateful thanks are due to Professor H. R. Carne, Department of Veterinary Pathology and Bacteriology, University of Sydney, and H. McL. Gordon, B.V.Sc., Senior Principal Research Officer, McMaster Laboratory, C.S.I.R.O., for their help and advice.
Many thanks are also due to C. C. Blumer, B.V.Sc., Chief, New South Wales Department of Agriculture and his veterinary officers, to G. Edgar, B.V.Sc., Director, Glenfield Veterinary Research Station, to Dr. D. F. Stewart. Officer-in-charge, McMaster Laboratory, C.S.I.R.O. and J. M. Keep, B.V.Sc., Superintendent, Veterinary Clinic and Hospital, University of Sydney, for placing facilities at my disposal.
This study was made possible by the generous help received from many Veterinary Inspectors and District Veterinary Officers. In this regard, my special thanks are due to D. J. Walker, B.V.Sc., Veterinary Inspector, Armidale, whose help and advice on dingoes were much appreciated. My thanks are also due to J. C. Beardwood, B.V.Sc.; D. W. Duncan, B.V.Sc.; P. T. Diplock, B.V.Sc.; P. D. Carter, B.V.Sc.; M. Barry, B.V.Sc.; D. Rennell, B.V.Sc.; C. D. Gee, B.V.Sc.; and N. L. C. Jones, Veterinary Inspectors or former Inspectors, at Camden, Gundagai, Mudgee, Coonabarabran, Albury, Tenterfeld, Condobolin and Lismore respectively, and to R. Falk, B.V.Sc., District Veterinary Officer at Cootamundra; H. R. Peisley, B.V.Sc., and N. Bolas, B.V.Sc., Veterinary Officers at Canberra, and R. B. Ramsay, B.V.Sc., of Drake, for collection of the material used in this survey.
Many thanks are also due to Mr. J. Stone, Technical Assistant, C.S.I.R.O., for his help in looking after the experimental animals, and to the many property owners who sent information and specimens at their own expense.
This research work on hydatid disease was done by the author whilst holding the George Aitken Pastoral Research Scholarship, and grants in aid were received by the Rural Bank of New South Wales and the Rural Credits Development Fund of the Commonwealth Bank.
References:
Durie. P. H. and Riek, R. F. (1952), Aust. vet. J., 28 : 249.
Gemmell, M, A. (1956), Aust. vet. J., 32 : 252.
Pullar, E. Murray (1946), Aust. vet. J., 22 : 12.
Seddon, H. R. (1950), Aust. Dept. Hlth. Serv. Publ, No. 5.
Gemmell, M. A. (1957), Aust. vet. J., 33 : 8.
Rausch, R. (1963), Thapar Commemoration Volume, Department of Zoology, University of Lucknow, India, pp. 233-246.