L.M. Kumaratilake

Observations on Echinococcus granulosus of cattle origin in Switzerland

Switzerland is one of the few countries where high fertility rates have been reported in cattle hydatid cysts and where the cattle/dog cycle is the most important for the maintenance of Echinococcus granulosus. The developmental and morphological characteristics of E. granulosus of Swiss cattle origin were studied and compared with that of E. granulosus of domestic animal origin from Great Britain and Australia, countries where bovine hydatid cysts are usually sterile and cattle play little role in the life-cycle of the parasite. Adult E. granulosus of Swiss cattle origin differed markedly in its developmental characteristics compared to other isolates, particularly in its rate of maturation in dogs, producing eggs as early as 35 days post-infection. The morphology of E. granulosus of Swiss cattle origin was characteristic and it could be easily distinguished from other isolates of the parasite. Further, E. granulosus of Swiss cattle origin was found to closely resemble that occurring in cattle in South Africa where high fertility rates have also been reported in bovine hydatid cysts. It is concluded that a strain of E. granulosus exists which is adapted to cattle and that further studies are required to determine whether this strain warrants formal taxonomic status as the species E. ortleppi which was originally described for the parasite of South African cattle origin.

A review of the taxonomy and speciation of the genus Echinococcus Rudolphi 1801.

The taxonomy ofEchinococcus is reviewed and consideration given to speciation within the genus. The morphological and other biological characteristics of all species and subspecies so far described are given, and evidence for the existence of other intraspecific variants is presented. A total of 16 species have been described but only four have well-defined characteristics and are generally accepted as being taxonomically valid;E. granulosus, E. multilocularis, E. oligarthrus andE. vogeli. The taxonomic status of intraspecific variants is uncertain. Some authorities consider that the majority of described subspecies are invalid taxonomically. However, concern is expressed that previous taxonomic considerations ofEchinococcus have not taken into account the nature of its reproductive mechanism which, like that of most cestodes, defies the application of traditional taxonomic concepts and definitions derived from dioecious cross-fertilising organisms. At the present time intraspecific variants ofEchinococcus are referred to as strains. The existence of such strains, particularly ofE. granulosus, in different parts of the world is firmly established. Their importance in the epidemiology of hydatidosis has high-lighted the needed to establish criteria for their differentiation and characterisation. The limitations of morphology as a sole differential criterion are emphasised. Attention is given to recent studies on strain variation which have demonstrated the value of applying several different criteria in which the developmental, physiological and biochemical characteristics of different strains are compared in conjunction with morphological investigations.

Echinococcus granulosus of equine origin from different countries possess uniform morphological characteristics

Echinococcus granulosus of equine origin from different countries possess uniform morphological characteristics. International Journal for Parasitology16: 529–540. Detailed comparative studies on isolates of larval and adult Echinococcus granulosus of equine origin from England, Scotland, Ireland, Belgium, Switzerland, South Africa and New Zealand demonstrated the morphological uniformity of the equine parasite. The morphological features of the equine strain of E. granulosus were fully characterized and it was found that on the basis of morphology alone, this strain could be differentiated from all other inter- and intraspecific variants of Echinococcus that have been described. The most important differential morphological characters are the dimensions of both larval and adult rostellar hooks, shape of ovary, testes distribution and details of the cirrus. As a result of the present study, it is apparent that the equine strain of E. granulosus has a widespread geographical distribution and there is evidence that the parasite may extend its range in the future. The question of whether consideration should be given to recognizing the equine strain as a formal taxonomic entity is discussed.

Comparative strobilar development of Echinococcus granulosus of sheep origin from different geographical areas of Australia in vivo and in vitro

Consistent differences in the growth, segmentation and maturation of Echinococcus granulosus in dogs were demonstrated between the parasite of Tasmanian sheep origin and that of Eastern and Western Australian sheep origin. These results were complemented by in vitro studies which found that Tasmanian E. granulosus produced eggs approx. 7 days earlier than the parasite of Eastern and Western Australian origin. These results support the suggestion that at least two distinct strains of E. granulosus of domestic animal origin exist in Australia. The significance of the differences in development demonstrated in this study is discussed.

Morphological characterisation of Australian strains of Echinococcus granulosus

Previous studies utilising biochemical and developmental criteria demonstrated the occurrence of three distinct strains of E. granulosus in Australia. In order to further characterise these strains, we studied metacestode and adult morphology of E. granulosus of various domestic and wild animal origin from different geographical areas of Australia. Morphological comparisons included specimens from natural infections as well as experimentally-derived adult worms of known age. Three morphologically distinct populations of E. granulosus were recognised in domestic and wild animals. These populations corresponded to the three strains described previously on the basis of biochemical and developmental criteria. One strain is common to all domestic intermediate hosts on the Australian mainland, the second is confined to macropods on the mainland and the third to sheep in Tasmania. No evidence was found that domestic animals on the mainland are susceptible to the sylvatic macropod strain, whereas 15% of macropods examined were infected with the mainland domestic strain. Natural infections with both mainland strains were found in dogs and dingoes. The practical value of morphology as a criterion in taxonomic and speciation studies is discussed. Suggestions as to the probable origin of the three Australian strains of E. granulosus are given.

Intraspecific variation in Echinococcus granulosus: the Australian situation and perspectives for the future

The current status of knowledge of speciation and strain differentiation in Echinococcus is discussed, with particular reference to the Australian scene. A new approach to the problem using morphological, developmental and biochemical differences is described and the importance of correct identification for the practical aspects of controlling the disease is stressed.

Biochemical characterisation of Australian strains of Echinococcus granulosus by isoelectric focusing of soluble proteins

The existence of three distinct strains of E. granulosus in Australia has been previously demonstrated on the basis of several criteria. In the present study, numerous isolates of E. granulosus from domestic and wild animal populations in different geographical areas of Australia were subjected to detailed biochemical analysis using isoelectric focusing of soluble proteins. Three different populations were recognised which corresponded to the three strains described previously, thus confirming their genetic distinction. One strain is common to all domestic intermediate hosts on the Australian mainland. Evidence is presented that humans and macropod marsupials are also susceptible to infection with this strain and that it is similar to E. granulosus occurring in sheep in New Zealand and the United Kingdom. The other two strains are confined to macropod marsupials on the Australian mainland and sheep in Tasmania respectively.

A comparison of Echinococcus granulosus from different geographical areas of Australia using secondary cyst development in mice

Significant differences in the rate of development of secondary hydatid cysts of Echinococcus granulosus in the same strains of mice were demonstrated between the parasite of Tasmanian sheep origin and that from sheep in Eastern and Western Australia. Similar differences were also found between E. granulosus of macropod and sheep origin, from Eastern Australia. These results complement previous comparative studies on strobilar development and support the suggestion that at least three distinct strains of E. granulosus exist in Australia. Two are found in sheep, one on the mainland and the other in Tasmania and the third is perpetuated amongst macropods on the mainland. The value of secondary hydatidosis as a criterion for strain differentiation of Echinococcus is emphasised.

Comparative development of Australian strains of Echinococcus granulosus in dingoes (Canis familiaris dingo) and domestic dogs (C.f. familiaris), with further evidence for the origin of the Australian syl vatic strain

The growth and development of Australian strains of E. granulosus were compared in domestic dogs and pure-bred dingoes. The sylvatic strain, which is maintained in a cycle between dingoes and wallabies on the Australian mainland, was found to develop far more rapidly in dingoes than in dogs. Development of this strain in dogs was markedly retarded. However, domestic strains of E. granulosus originating from sheep in Tasmania and the Australian mainland developed at a comparable rate in dingoes and dogs. Dingoes were also found to be more susceptible to infection with the sylvatic strain than dogs, as evidenced by considerable differences in worm burdens. No such differences in susceptibility were seen with the domestic strains. These results not only emphasise the inherent differences between the sylvatic and domestic strains of E. granulosus, but also support previous suggestions that the strains were introduced into Australia independently. The fact that the sylvatic strain appears to be physiologically adapted to the dingo indicates that it was brought into Australia many thousands of years before the original domestic strain.