Erroneous reports of the neotropical Echinococcus oligarthrus as a cause of echinococcosis in India.

Two cases of submandibular echinococcosis have been reported in adult residents of India (Kini et al., 1997; Sahni et al., 2000). It was stated in both publications that the cestode was E. oligarthrus, "a rare variety of E. granulosus", based on morphogical characteristics. It was also mentioned that 3 cases of E. granulosus with similar submandibular metacestode had been previously diagnosed in India. The metacestode is readily distinguishable from that of E. oligarthrus. The final hosts of E. oligarthrus are several neotropical species of wild cats and metacestode occurs in hystricognath, all of them absent in India. The larval stage of all 4 species of Echinococcus can be differentiated on the basis of the form and dimensions of rostellar hooks of protoescoleces. With the information provided in the two papers we concluded that the 2 cases of echinococcosis described in India were due to E. granulosus.

Cystic echinococcosis in the Arctic and Sub-Arctic.

The northern biotype of Echinococcus granulosus occurs throughout the holarctic zones of tundra and taiga, from eastern Fennoscandia to the Bering Strait in Eurasia and in North America from arctic Alaska approximately to the northern border of the United States. The cycle of the cestode is complex in taiga at lower latitudes, because of the greater diversity of potential hosts. In the Arctic and Subarctic, however, four patterns of predator/prey relationships may be discerned. Two natural cycles involve the wolf and wild reindeer and the wolf and elk (moose), respectively. Where deer of the two species coexist, both are prey of the wolf; the interactions of the wolf and elk are here described on the basis of long-term observations made on Isle Royale (in Lake Superior near the southern limit of taiga), where only the wolf and elk serve as hosts for E. granulosus. A synanthropic cycle involving herding-dogs and domesticated reindeer caused hyperendemicity of cystic echinococcosis in arctic Eurasia, mainly in northeastern Siberia. The 4th pattern, a semi-synanthropic cycle, formerly existed in Alaska, wherein sled-dogs of the indigenous hunters became infected by consuming the lungs of wild reindeer. The sequence of changes in life-style inherent in the process of acculturation affected the occurrence of cystic echinococcosis among nomadic Iñupiat in arctic Alaska. When those people became sedentary, the environs of their early villages soon became severely contaminated by faeces of dogs, and cases of cystic echinococcosis occurred. Compared to cystic echinococcosis caused by E. granulosus adapted to synanthropic hosts (dog and domestic ungulates), the infection produced by the northern biotype is relatively benign. Nearly all diagnosed cases of cystic echinococcosis (> 300) in Alaska have occurred in indigenous people; only one fatality has been recorded (in a non-indigenous person). After sled-dogs were replaced by machines, cases have become rare in Alaska. A similar effect has been observed in Fennoscandia, in the Saami and domesticated reindeer. Recent records indicate that the prevalence of cystic echinococcosis is increasing in Russia, suggesting that dogs are used there in herding.

Description of Paranoplocephala etholeni n. sp. (Cestoda: Anoplocephalidae) in the meadow vole Microtus pennsylvanicus, with a synopsis of Paranoplocephala s. l. in holarctic rodents.

Paranoplocephala etholeni n. sp., parasitizing the meadow vole Microtus pennsylvanicus in Alaska and Wisconsin, USA, is described. Paranoplocephala etholeni is morphologically most closely related to the Nearctic Paranoplocephala ondatrae (Rausch, 1948). Available data suggest that P. etholeni is a host-specific, locally rare species that may have a wide but sporadic geographical distribution in North America. The finding of P. ondatrae-like cestodes in Microtus spp. suggests that this poorly known species may actually be a parasite of voles rather than muskrat (type host). A tabular synopsis of all the known species of Paranoplocephala s. l. in the Holarctic region with their main morphological features is presented.

Characterization of the laminated layer of in vitro cultivated Echinococcus vogeli metacestodes.

The metacestode (larval) stages of the cestode parasites Echinococcus vogeli and E. multilocularis were isolated from the peritoneal cavity of experimentally infected C57BL/6 mice and were cultured in vitro for a period of up to 4 mo under conditions normally applied for the in vitro cultivation of E. multilocularis metacestodes. In contrast to E. multilocularis, E. vogeli did not exhibit extensive exogenous budding and proliferation but increased in size with a final diameter of up to 10 mm. Most metacestodes contained protoscoleces, singly or in groups, either associated with brood capsules or growing directly out of the germinal layer. Each individual metacestode was covered by an acellular translucent laminated layer that was considerably thicker than the laminated layer of E. multilocularis metacestodes. The ultrastructural characteristics, protein content, and carbohydrate composition of the laminated layer of in vitro cultivated E. vogeli and E. multilocularis were assessed using transmission electron microscopy, lectin fluorescence labeling, and lectin blotting assays. The laminated layer of E. vogeli is, as previously described for E. multilocularis metacestodes, largely composed of N-acetyl-beta-D-galactosaminyl residues and alpha- and beta-D-galactosyl residues, as well as of the core structure of O-linked carbohydrate chains, N-acetylgalactosamine-beta-1,3-galactose. However, in contrast to E. multilocularis, N-linked glycopeptides and alpha-D-mannosyl and/or glucosyl residues were also associated with the laminated layer of E. vogeli. The laminated layer from both species was isolated from in vitro cultivated metacestodes, and the purified fractions were comparatively analyzed. The protein:carbohydrate ratio (1:1) was similar in both parasites; however, the protein banding pattern obtained by silver staining following sodium dodecyl sulfate polyacrylamide gel electrophoresis suggested intrinsic differences in protein composition. A polyclonal antiserum raised against the E. multilocularis laminated layer and a monoclonal antibody, G11, directed against the major E. multilocularis laminated layer antigen Em2 did not cross-react with E. vogeli, indicating distinct compositional and antigenic differences between these 2 parasites.

Natural transfer of helminths of marine origin to freshwater fishes with observations on the development of Diphyllobothrium alascense.

Infective stages of helminths of 5 species that occur as adults in marine mammals were found in burbot, Lota lota (L.) (Gadidae), from the lower Kuskokwim River (southwestern Alaska): Diphyllobothrium alascense Rausch et Williamson, 1958; Pyramicocephalus phocarum (Fabricius, 1780); Corynosoma strumosum (Rudolphi, 1801); Corynosoma semerme (Forsell, 1904); and Pseudoterranova decipiens (Krabbe, 1878). Some larval stages were obtained also from smelt, Osmerus mordax dentex Steindachner, an anadromous fish important as prey of burbot. Burbot, which are freshwater fish, could become paratenic hosts of those helminths by means of at least 3 interactions: by consuming marine fishes in brackish waters at river mouths, by feeding on marine fishes that enter lower reaches of rivers, or by preying on anadromous fishes as they migrate up rivers. Consumption of burbot by people may result in infection by helminths of marine origin; of those recorded, only P. decipiens may be significantly pathogenic. Attempts to rear P. phocarum in dogs were unsuccessful. Plerocercoids of D. alascense, of very small size and found only in the gastric lumen of burbot, readily infected dogs. For study of their development, strobilae were obtained at intervals of 48 hr to 32 days postinfection. In heavy infections, some strobilae developed slowly, while others underwent rapid development.

A phylogenetic hypothesis for species of the genus Taenia (Eucestoda : Taeniidae).

Cladistic analysis of a numerical data matrix describing 27 characters for species of Taenia resulted in 4 most parsimonious phylogenetic trees (174 steps; consistency index = 0.28; homoplasy index = 0.72; retention index = 0.48). Monophyly for Taenia is diagnosed by the metacestode that is either a cysticercus or a form derived from a bladder-like larva; no other unequivocal synapomorphies are evident. Tree structure provides no support for recognition of a diversity of tribes or genera within the Taeniinae: Fimbriotaeniini and Taeniini have no phylogenetic basis. Hydatigera, Fimbriotaenia, Fossor, Monordotaenia, Multiceps, Taeniarhynchus, Tetratirotaenia must be subsumed within Taenia as synonyms. Taenia saginata and Taenia asiatica are sister species and distantly related to Taenia solium. Cospeciation with respect to carnivorous definitive hosts and Taenia appears to be limited. Although felids are putative ancestral hosts, contemporary associations appear to have resulted from extensive host-switching among felids, canids, hyaenids, and others. In contrast, relationships with herbivorous intermediate hosts are indicative of more pervasive coevolution; rodents as intermediate hosts are postulated as ancestral for the Taeniidae, Taenia + Echinococcus. Patterns appear consistent with rapid shifts between phylogenetically unrelated carnivores but among those that historically exploited a common prey resource within communities in specific biogeographic regions.

Histogenesis in the metacestode of Echinococcus vogeli and mechanism of pathogenesis in polycystic hydatid disease.

Histogenesis of the metacestode of Echinococcus vogeli was traced mainly in rodents inoculated intraperitoneally with finely minced infective vesicles. The fragments aggregated in the peritoneal cavity and coalesced, forming structures (plaques) from which primary vesicles arose. From primordia in their germinal tissue, exogenous vesicles developed, enlarged, and migrated outward to the surface of the laminated membrane, where they remained attached and proliferated. Each unit of vesicles so formed retained discrete identity and, within 6-8 mo, acquired an adventitia; thereafter, exogenous multiplication ceased and endogenous proliferation supervened. Large numbers of daughter cysts arose in the germinal tissue lining chambers within the units; endogenous proliferation also finally ceased, and the daughter cysts produced brood capsules containing protoscoleces. Primordia of exogenous vesicles were not observed in the walls of daughter cysts. Production of protoscoleces involved 3 processes: they developed in typical brood capsules, singly in minute brood capsules, or directly from germinal tissue. Exogenous proliferation is not characteristic in the natural intermediate host of E. vogeli, the paca. Evidently in primates, the initial proliferation in the liver is followed by extension of the metacestode into the peritoneal cavity and eventual invasion of abdominal and thoracic organs. Exogenous proliferation by a process unique to E. vogeli accounts for the clinical course of polycystic hydatid disease.

Limited range of genetic variation in Echinococcus multilocularis.

DNA sequencing of 1.3 kb of rDNA containing both internal transcribed spacers (ITS1, ITS2) and adjoining rRNA coding regions in each of 11 Echinococcus multilocularis isolates from Germany, Japan, and Alaska resulted in identical nucleotide sequences except for a single polymorphic locus 54 bp upstream of the 3' end of the 18S coding region, separating Eurasian isolates from an Alaskan isolate. The same base substitution was found in each of 2 additional isolates from Alaska. The distribution of the resulting genotypes with regard to their origin is highly significant (>99.9%) and corresponds to the traditional subspecies Echinococcus multilocularis multilocularis and Echinococcus multilocularis sibiricensis.

Burhinotaenia colombiana n. sp. (Cestoda, Cyclophyllidea) from the double-striped stone curlew Burhinus bistriatus (Aves, Charadriiformes) in Colombia.

Burhinotaenia colombiana n. sp. (Dilepididae) is described from the small intestine of the double-striped stone curlew Burhinus bistriatus (Burhinidae) captured at Carimagua, Colombia. The new species is distinguished from the most similar Burhinotaenia delachauxi (Baer, 1925), a parasite of the Old World Burhinus spp., by the longer cirrus-sac (375-590, avg. 514 microns vs. 322-393, avg. 354 microns) and longer rostellar hooks (412-451, avg. 440 microns vs. 358-367, avg. 364 microns). The validity of the genus Burhinotaenia Spasskii and Spasskaya, 1965 and its generic diagnosis as proposed by Bona (1994) are confirmed. This is the first record of a species of Burhinotaenia in the New World.

Immunodiagnosis of polycystic hydatid disease/polycystic echinococcosis due to Echinococcus vogeli.

A crude antigenic metacestode extract from Echinococcus vogeli was assessed by enzyme-linked immunosorbent assay (ELISA) and showed strong binding activity with serum antibodies from patients with polycystic echinococcosis. Major cross-reactions occurred with serum antibodies from patients with cystic and alveolar echinococcosis and from patients infected with other species of helminths. An E. vogeli antigen fraction, Ev2, was subsequently purified by immunosorption. The respective Ev2 ELISA demonstrated improved specificity, allowing discrimination of non-Echinococcus infections from polycystic echinococcosis. Based upon the calculation of a comparative (Ev-crude ELISA versus Ev2 ELISA) reactivity index, it became possible to discriminate all cystic echinococcosis cases, but only some alveolar echinococcosis cases, from polycystic echinococcosis. Immunoblot analyses revealed an antibody banding pattern highly conserved among polycystic, cystic, and alveolar echinococcosis. However, immunoblotting reliably distinguished between echinococcosis and all non-Echinococcus infections.

Alveolar hydatid disease. Review of the surgical experience in 42 cases of active disease among Alaskan Eskimos.

OBJECTIVE: The authors reviewed the pathophysiology and clinical management of endemic alveolar hydatid disease in Alaskan Eskimos, incorporating recent developments in diagnosis and treatment. SUMMARY BACKGROUND DATA: Alveolar hydatid disease is a highly lethal zoonotic infection caused by the larval stage of Echinococcus multilocularis. This cestode is restricted geographically to northern climates, where foxes and small rodents represent the natural hosts. Domestic dogs also may serve as definitive hosts, and thus, transmit the parasite to humans. Human infection is characterized by the development of a cancer-like hepatic mass, which may extend to adjacent structures or metastasize to distant sites. If the infection goes untreated, mortality reaches 80%. METHODS: The medical records of all patients with alveolar hydatid disease diagnosed or treated at the Alaska Native Medical Center between 1951 and 1993 were reviewed. Forty-two cases of active disease are presented. RESULTS: Nine patients underwent resection of hepatic lesions with intent to cure, and each had a favorable result. Average post-diagnosis survival of those patients was 22 years; six still are living and free of disease. Partial resections or drainage procedures were performed in ten patients. Chemotherapy was used to augment the surgical treatment of eight patients, and four received chemotherapy alone, resulting in improved outcomes compared with historic controls. Late complications included hepatic abscess, biliary obstruction, and portal venous hypertension. CONCLUSIONS: Whereas alveolar hydatid disease rarely is encountered in other areas of North America, the biologic potential for spread of the disease may be increasing because of illegal importation of infected foxes to the Eastern seaboard. Therefore, the surgical community should maintain an awareness of the diagnosis and management of this potentially devastating parasitic infection.

Transberingian dispersal of cestodes in mammals.

During Pleistocene glaciations, eustatic lowering of sea-level exposed the continental shelf between northeastern Eurasia and northwestern North America. That land in combination with unglaciated areas on the adjacent continents formed a vast region open to the west but bounded on the east by continental ice. Organisms from Eurasia spread into the unglaciated Beringian refugium, which was biotically an eastward extension of the Palaearctic. With rising sea-levels following glacial periods, the Bering Strait was formed and organisms of Eurasian origin were left within the nearctic sector of Beringia. As the continental ice disappeared, plants and animals spread eastward and southward from Beringia, while organisms from beyond the southern margins of the ice extended their ranges northward. The significance of Beringia is discussed with reference to the dispersal of host-specific cestodes in mammals that attained holarctic status during the late Pleistocene.

Choanotaenia atopa n. sp. (Cestoda: Dilepididae) from a domestic cat in Kansas.

Choanotaenia atopa (Cestoda: Dilepididae) is described (host: domestic cat from the vicinity of Manhattan, Kansas); its natural host is presumed to be a rodent. Choanotaenia atopa is morphologically similar to cestodes of 6 species, all from rodents, formerly placed in the genus Rodentotaenia Matevosian, 1953, and subsequently removed to the genera Choanotaenia Railliet, 1986, or Monopylidium Fuhrmann, 1899. The systematic position of those cestodes is discussed; Monopylidium and Rodentotaenia are treated as synonyms of Choanotaenia. Choanotaenia atopa is distinguished by size and form of rostellar hooks, regularly alternating genital pores, and other characters in genital organs.

Establishment and survival of the strobilar stage of Taenia crassiceps in hamsters, gerbils, and mice, with reference to different helminth isolates.

Following the oral administration of metacestodes of two isolates of Taenia crassiceps, the enteral establishment and survival of the strobilar stage were examined in golden hamsters (Mesocricetus auratus), Mongolian gerbils (Meriones unguiculatus) and laboratory mice. The origin of the isolates was Microtus montebelli caught in Japan in 1985 or Clethrionomys rutilus captured on St. Lawrence Island, Bering Sea, in 1988 (abbreviated as JPN and SLI isolates), respectively. The enteral establishment of the SLI isolate was distinctly higher than that of the JPN isolate in golden hamsters and mice, whereas the difference was marginal in Mongolian gerbils. All initially-established parasites survived to become gravid adults in prednisolone-treated golden hamsters and Mongolian gerbils; the average recovery of cestodes of the SLI and JPN isolates were 55.8%-76.7% vs 11.7%-35.0% in the former and 28.0%-52.7% vs 25.8%-32.2% in the latter. The distinctly higher level of enteral establishment of the SLI isolate in golden hamsters makes available a model for quantitative studies on parasite-host relationships in experimental taeniasis.

Parasiticidal effect of chemotherapy in alveolar hydatid disease: review of experience with mebendazole and albendazole in Alaskan Eskimos.

Evidence that the larval stage of Echinococcus multilocularis in humans is killed by chemotherapy is presented in a review of our 17-year experience with treatment of alveolar hydatid disease in Alaska. The efficacy of chemotherapy was assessed with use of an in vivo assay of parasite viability by means of inoculation of voles, immunohistochemical tests, and histopathologic findings. Of 14 tests performed for nine patients, 12 in vivo assays (86%) were negative after chemotherapy, while only two (17%) of 12 vole tests for seven untreated patients were negative. Regression of arrest of growth of metastatic and primary hepatic lesions, together with their partial-to-complete calcification and prolonged survival times has been observed among patients treated with the benzimidazole compounds. For six who received appropriate chemotherapy, treatment has been discontinued for an average of 4.6 years (range, 3-7 years) without an increase lesion size or other evidence of reactivation.

Cysticerci (Cestoda: Taeniidae) from white-tailed deer, Odocoileus virginianus, in southern Florida.

Metacestodes (cysticerci) of Taenia omissa Lühe, 1910, and Taenia hydatigena Pallas, 1776, were found in 9 and 1 of 124 white-tailed deer, respectively, in southern Florida in 1984-1986. Intensities of T. omissa varied from 1 to 15 (mean = 4.6); only 1 cysticercus of T. hydatigena was collected. No significant difference in the prevalences of T. omissa according to sex, age, or locality was observed.

A programme to reduce the risk of infection by Echinococcus multilocularis: the use of praziquantel to control the cestode in a village in the hyperendemic region of Alaska.

This paper reports the results of a 10-year field trial designed to reduce the risk of infection by Echinococcus multilocularis to residents of a village in a hyperendemic area (Savoonga, St. Lawrence Island). The objective was to prevent dispersal of infective eggs of the cestode within the village by means of monthly treatments of dogs with praziquantel. Northern voles, Microtus oeconomus, present in the village as commensals, served as an index of risk, as the incidence of infection in the voles provides information about the availability of eggs within the confines of the inhabited area. Voles were examined annually during early June before the population of overwintering voles was diluted by the first annual litters. The pretreatment infection-rate within the village was 29% (range 22-35%), and in control areas at some distance from the village for the entire study period it averaged 53% (284 infected voles from a sample of 533). Some fluctuation in incidence of infection in village voles occurred, apparently depending on the extent to which the residents kept their dogs chained and thus available for treatment. The success of the programme was demonstrated by the reduction in prevalence of infection to about 1% of voles in 1985, and an average infection rate during the last five years of the study of 5% (29 infected voles in a sample of 582). This 83% average reduction in the prevalence of the larval cestode within the village reflects a corresponding reduction in the risk of acquiring by the residents of the village. The method would be applicable for the control of E. multilocularis in most hyperendemic regions. Success depends, however, on elimination of unrestrained dogs and a precise schedule of treatment.

Cysticerci of Taenia mustelae in the fox squirrel.

The liver of a fox squirrel (Sciurus niger rufiventer) contained many clear, spherical cysts approximately 1 mm in diameter throughout the parenchyma. On dissection, most of these exhibited a dense, white area with four muscular suckers at a single point on the bladder. Based on the size of the organisms, the characteristically tiny hooks on the scolex and the location of the cysts in this host, the parasites were identified as cysticerci of Taenia mustelae. This is the first report in this host. The parasites were surrounded by an intense inflammatory response consisting primarily of lymphocytes mixed with some eosinophils, and early deposition of fibrous connective tissue.