Historical Aspects of Echinococcosis

Echinococcosis is a zoonosis whose history dates back to antiquity. This article provides an overview on the general history of echinococcosis, including the elucidation of Echinococcus life cycles and the long controversy on the aetiology of the cystic and alveolar forms of echinococcosis (CE and AE), lasting about 100years since the middle of the 19th century. Furthermore, selected historical aspects of some fields of echinococcosis research are discussed and compared with our current knowledge, such as geographic distribution and epidemiology of CE (Echinococcus granulosus) and AE (Echinococcus multilocularis), clinical aspects and pathology, diagnosis in humans and animals, treatment (with focus on chemotherapy), control and basic research. A short paragraph is devoted to the neotropical forms of echinococcosis, caused by Echinococcus vogeli and Echinococcus oligarthrus. In this context the achievements of some ancestral pioneers of echinococcosis research are particularly highlighted and appreciated. Finally, the role of associations, international organizations (World Health Organization and others) and international working groups in echinococcosis research and control is briefly outlined. The retrospective reveals both the admirable achievements of our ancestors and the scientific progress of more recent times. But, it also shows the gaps in our knowledge, skills and resources that we need to control or even eradicate echinococcosis.

Observations on the Genus Echinococcus Rudolphi, 1801

Tænia echinococcus has always been recognised as one of the most important tapeworms of carnivores, both from the human and the economic point of view. Its intermediate stage, or Hydatid, assumes many forms, but most modern workers believe that all these forms—with one possible exception, the alveolar form from Central Europe—are merely the manifestations of a single species.

Comparative studies on the biology and morphology ofEchinococcus granulosusfrom domestic livestock, moose and reindeer

1. As an intermediate host of the hydatid tapeworm in boreal North America, the moose is of relatively greater importance than other indigenous cervids (white-tailed deer, wapiti, barren-ground caribou) primarily because of a higher rate of infection in different individuals and the fertility of the hydatid cysts.

2. The European reindeer introduced into north-western Canada is of considerable importance as an intermediate host where it occurs locally.

3. Timber wolves are the important definitive hosts; no infections occurred naturally or were produced experimentally in the bobcat, Canada lynx, raccoon, fisher, marten, striped skunk or European ferret.

4. A description using biological and morphological criteria is presented forEchinococcus granulosus granulosusin dogs, sheep and other domestic animals,E. g. borealissubsp.nov. in timber wolves, moose and other cervids indigenous to North America, andE. g. canadensisWebster and Cameron, 1961, in dogs and reindeer introduced into north-western Canada from Laplandic Norway.

5. The rate of cystic growth, scolex production, infectability of timber wolves and dogs and prepatent period are similar for all three subspecies.

6.E. g. borealisreached a gravid state in experimental red foxes (Vulpes fulva).

7. Hydatid cysts developed only rarely in sheep fed eggs ofE. g. borealisorE. g. canadensis.

8. Eggs ofE. g. granulosusproduced only one viable hydatid cyst in a series of experimental red deer (Cervus elaphus) and fallow deer (Dama dama).

9.E. g. granulosus, E. g. borealisandE. g. canadensisare morphologically distinct, the most distinctive characters occur inE. g. canadensis.

10. Besides the above andE. multilocularis, other species inEchinococcusare little known. Those recognized as being currently valid areE. lycaontis, E. ortleppi, E. felidis, E. cameroni, E. oligarthrus, E. cruziand possiblyE. patagonicus.

The writers wish to thank Sir Charles Hercus and the other members of the Hydatid Research Committee for their interest and encouragement in the present study. Valuable discussion in the early stages of this work was had with Prof. A. M. Fallis, Director, Department of Parasitology, Ontario Research Foundation. Much of the field work was done with various members of the Ontario Research Foundation; Institute of Parasitology, McGill University; Canada Department of Agriculture; and Canada Department of Northern Affairs and Natural Resources, to whom we extend our thanks. Norwegian material was kindly provided by Dr Sven Skjenneberg, Statens Veterinaera Laboratorium for Nord-Norge. Technical assistance was provided by Messrs G. D. Page, D. V. Weston, Miss L. A. Duncan and Mrs B. R. Clarke.

New aspects of neotropical polycystic (Echinococcus vogeli) and unicystic (Echinococcus oligarthrus) echinococcosis

Of the four species of the genus Echinococcus (Cestoda) distinguished by biological and morphological characteristics, two species, E. vogeli and E. oligarthrus, occur widely in the Neotropics. Approximately 200 cases of polycystic echinococcosis (PE) have been recorded from 12 countries in South America. Following early proliferation of E. vogeli in the human host, typically in the liver, the metacestode usually spreads in the peritoneal and pleural cavities, and numerous organs may be invaded. The clinical characteristics of PE in 81 patients with sufficient information are reviewed. Type I disease consists of polycysts in the liver and abdominal cavity (37% of the patients had this characteristic); type II is similar to type I but also includes hepatic insufficiency (26%); type III consists of cysts in liver and chest (14%); type IV consists of cysts only in the mesenteries (16%); and type V consists of cysts calcified in liver and lung (4%). The percentage of patients with polycysts in the liver was 81%, and the percentage of patients with polycysts in the chest was 14%. PE is most ready diagnosed by geographic origin of the patient and by means of ultrasound or computerized tomography scanning showing cysts and calcifications. The highest mortality was for patients with type II disease, due to hepatic failure and its complications. There were five patients who died due to surgical accidents, whereas 35 cases had uncomplicated surgery. Twenty-three patients died of PE, making the total mortality 29% (23 of 78 cases). None of the 13 patients treated only with albendazole, the most efficacious treatment, was completely cured. PE represents a severe medical problem in South America. A reevaluation of the characteristics of the metacestode of E. oligarthrus indicated that it is unicystic. Only three human cases are known (two with infection in the orbit and one with infection in the heart). The metacestode of E. oligarthrus, in contrast with that of E. vogeli, consists of a spherical, fluid-filled vesicle that enlarges concentrically and is not known to undergo exogenous proliferation.

Emergence of polycystic neotropical echinococcosis

The discovery of an unusual parasitic disease and its causative agents is recounted.

Echinococcosis is a parasitic zoonosis of increasing concern. In 1903, the first cases of human polycystic echinococcosis, a disease resembling alveolar echinococcosis, emerged in Argentina. One of the parasites responsible, Echinococcus oligarthrus, had been discovered in its adult strobilar stage before 1850. However, >100 years passed from the first description of the adult parasite to the recognition that this species is responsible for some cases of human neotropical polycystic echinococcosis and the elucidation of the parasite’s life cycle. A second South American species, E. vogeli, was described in 1972. Obtaining recognition of the 2 species and establishing their connection to human disease were complicated because the life cycle of tapeworms is complex and comprises different developmental stages in diverse host species. To date, at least 106 human cases have been reported from 12 South and Central American countries.

Polycystic hydatid disease in Brazil. Report of five new human cases and a short review of other published observations

This paper describes five additional Brazilian human cases of polycystic hydatid disease due to Echinococcus vogeli, reviews the previous cases reported in Brazil, including one report of E. oligarthus (20 in total), and some epidemiological aspects of this disease which is no longer a curiosity but rather a problem that is not medically easy to handle. Its presence should be expected in any rural area of the New World where humans have not eliminated wild felids/canids, bush dogs, pacas, agoutis and other wild rodents.

Polycystic hydatid disease (Echinococcus vogeli). Clinical, laboratory and morphological findings in nine Brazilian patients

Polycystic hydatid disease occurs in neotropical zones and is caused by Echinococcus vogeli. The paca, a wild rodent, is the intermediate host and the final host is the dog. Seven cases of polycystic hydatid disease autochthonous to the Brazilian Amazon region are described. The disease was polycystic in all cases and diagnosis was based on anatomopathological findings. E. vogeli was identified by the shape and dimensions of the rostellar hooks. The liver was the organ most often involved (6/7), followed by the lungs (2/7) and mesentery (2/7), spleen (1/7) and pancreas (1/7). The main clinical manifestations were abdominal pain, hepatomegaly, jaundice, weight loss, anemia, fever, hemoptysis, palpable abdominal masses and signs of portal hypertension. Hepatic calcifications were detected in four cases. Two cases from the hinterland of the State of São Paulo are also reported. Both had calcified round structures in the liver, highly suggestive of calcified polycystic hydatids. The aim of the present report was to report on this relatively unknown hydatid disorder of Tropical America and to disseminate its clinical, ultrasound and radiological features.

[Echinococcus vogeli cysts in paca liver (Cuniculus paca) native from the Acre State, Brazil]

Four of the patients with polycystic hydatid disease observed by us reported that they were aware of the presence of liver disease in the pacas hunted for food. The viscera of these animals were usually given to domestic dogs. All of our 7 patients reported contact with dogs that had previously ingested viscera of pacas. Examination of the liver considered to be diseased by one of the patients and removed from a paca killed in the same region (State of Acre, Brazil) from which the human cases originated showed the presence of hydatid cysts. The characteristics of the rostellar hooks of the protoscolex indicated that this was the larval form of Echinococcus vogeli. These observations confirm the participation of pacas in the biological cycle of E. vogeli and the pathway through which man may become an alternative intermediate host of this echinococcus.

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

The taxonomy of Echinococcus 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 and E. 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 of Echinococcus 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 of Echinococcus are referred to as strains. The existence of such strains, particularly of E. 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.