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.

Alveolar hydatid disease. A review of clinical features of 33 indigenous cases of Echinococcus multilocularis infection in Alaskan Eskimos.

The clinical features of 33 cases of alveolar hydatid disease (AHD) in Alaskan Eskimos and a review of the surgical experience with this disease are presented. Among untreated patients, progression of the disease to a fatal outcome was observed in 70%. The primary hepatic lesion resembles cancer, and errors in diagnosis by both the surgeon and pathologist are common. Although surgical resection of the entire primary hepatic lesion offers the only proven curative treatment, only 26% of those explored were resectable. All seven patients resected for cure are alive 6-27 years post-operatively (average survival, 14.7 years). A 5-year experience with continuous mebendazole therapy in the management of five nonresectable cases of AHD indicates that a favorable effect of this drug is being observed. It now appears that Echinococcus infections are no longer the sole province of the surgeon. Although the role of medical therapy is not yet clearly defined, it must be considered in the management of all cases of AHD. The first reported locally-acquired case of AHD in the conterminous United States, and the widespread occurrence and expanding range of E. multilocularis in the north-central United States and south-central Canada, point to the increasing public health importance of alveolar hydatid disease.

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.

Discrimination of the larval stages of Echinococcus oligarthrus (Diesing, 1863) and E. vogeli Rausch and Bernstein, 1972 (Cestoda: Taeniidae).

Rostellar hooks of protoscolices from known larval stages of Echinococcus oligarthrus (Diesing, 1863) and E. vogeli Rausch and Bernstein, 1972 were compared to determine whether morphologic differences could be defined. The large and small hooks, respectively, of the two species were found to differ significantly in length (P = less than 0.0001) as well as in relative proportions. Host-related variation in lengths of hooks was not observed. Dimensions of the rostellar hooks were found to provide means for the discrimination of the larval stages of E. oligarthrus and E. vogeli, of which the latter is the cause of polycystic hydatid disease in man in South and Central America. The defined criteria were used in the identification of larvae from wild rodents and man.

Characteristics of the larval Echinococcus vogeli Rausch and Bernstein, 1972 in the natural intermediate host, the paca, Cuniculus paca L. (Rodentia: Dasyproctidae).

In Colombia, the natural intermediate host of Echinococcus vogeli Rausch and Bernstein, 1972 is the paca, Cuniculus paca L. (Rodentia: Dasyproctidae). The larval cestode develops in the liver of the host, where it usually is situated superficially, partly exposed beneath Glisson's capsule. The infective larva consists of a subspherical to asymmetrical, fluid-filled vesicle, up to 30 mm in diameter, enclosed by a thick laminated membrane. It typically contains numerous chambers, often interconnected, produced by endogenous proliferation of germinal and laminated tissue, within which brood capsules arise in an irregular pattern from the germinal layer. Invasive growth by means of exogenous proliferation, typical of infections in man, was not observed in the natural intermediate host. The development of the larval cestode is described on the basis of material from pacas, supplemented by observations on early-stage lesions in experimentally infected nutrias, Myocastor coypus (Molina) (Rodentia: Capromyidae). The tissue response is characterized for early-stage, mature (infective), and degenerating larvae in the comparatively long-lived intermediate host. In addition to previously reported differences in size and form of rostellar hooks, other morphologic characteristics are defined by which the larval stage of E. vogeli is distinguished from that of E. oligarthrus (Diesing, 1863). Pathogenesis by the larval E. vogeli in man, like that by the larval E. multilocularis Leuckart, 1863, is the consequence of atypical proliferation of vesicles attributable to parasite-host incompatibility.

Echinococcus vogeli in man, with a review of polycystic hydatid disease in Colombia and neighboring countries.

Three cases of polycystic hydatid disease (PHD) from Colombia are reported and 11 others from the region are reviewed. When cysts from two patients were fed to a dog and an ocelot about 250 mature and gravid specimens of Echinococcus vogeli and two poorly developed strobilae, respectively, were recovered. These human cases constitute the first record of the larval stage of E. vogeli, previously known only from the strobilar stage in the type host, the bush dog (Speothos venaticus). Based on the morphological characteristics of the protoscolex rostellar hooks from other PHD cases (6 Colombian, 1 Ecuadorian, and 1 Panamanian), it was concluded that all were also due to E. vogeli, rather than to E. oligarthrus as had been previously suggested. Although E. oligarthrus is or may be present in the same areas, so far no human infection due to this parasite has been confirmed. Of the 14 cases reported, 13 were pathologically proven to be PHD. Clinically, eight had an undiagnosed tumor-like mass in or near the liver, one had a subcutaneous mass in the anterior sixth intercostal space, and in two the cysts were in the chest. Two were autopsy findings. In contrast to E. multilocularis, the cysts produced by E. vogeli were found to be relatively large and filled with fluid; brood capsules and protoscolices were numerous. Focal necrosis was commonly observed but large necrotic cavities were not seen. The main natural intermediate host is the paca (Cuniculus paca); man probably obtains the infection by contamination from feces of infected hunting dogs.

Spontaneous death of Echinococcus multilocularis: cases diagnosed serologically (by Em2 ELISA) and clinical significance.

Nine cases of asymptomatic alveolar hydatid disease (AHD) of the liver were diagnosed in 1985 among Eskimos from the endemic region of western Alaska. The patients were identified by screening with the enzyme-linked immunosorbent assay, using purified Echinococcus multilocularis antigen (Em2 ELISA). Five patients, and one diagnosed earlier (1979), were found to have lesions in which the larval E. multilocularis had died spontaneously at an early stage of infection. Viability was assessed histologically; by the avidin-biotin immunohistochemical method; and in vivo through intraperitoneal inoculation of membranes of the larval cestode into red-backed voles, Clethrionomys rutilus. The results were in agreement with the clinical impression, based on findings by computerized tomography and ultrasound scanning, and on the macroscopic appearance of the lesions, that the cestode was dead. Spontaneous death of E. multilocularis in humans has not been previously reported. The findings show that the Em2 ELISA may be positive in patients having lesions of AHD in which the etiologic agent is no longer viable.

Echinococcus infections in Colombian animals.

The results of a survey involving more than 4,000 Colombian mammals, carried out to detect Echinococcus infections, are presented. Adult worms were found in 5 of 121 carnivores: E. oligarthrus in 1 of 11 ocelots, 2 of 9 jaguarundi cats and single puma; and E. vogeli in 1 of 15 domestic dogs. Although bush dogs were present, none could be examined. Polycystic larvae were found in 96 of 325 pacas (29.5%) and in 6 of 1,168 (0.5%) spiny rats, Proechimys spp. None of the 118 agouti showed hydatids but an infected heart was provided by hunters. The paca's infection rate increased with age but was not related to sex or geographic region. In 73 of 96 pacas the infection was due to E. vogeli, and the cysts were located in the liver. In 3 it was due to E. oligarthrus and the hydatids were extrahepatic, mainly attached to muscles. In the remaining 20, the species involved could not be determined. The parasites in two of the spiny rats, and in the agouti heart were E. oligarthrus. Although most of the infected animals were collected in the eastern plains, other records and verbal information indicate that, at least in Colombia where man has not exterminated pacas, agoutis, wild canids and felids, one still can find enzootic neotropical Echinococcus infection. The cycle of E. vogeli involves the bush dog and paca as hosts, and that of E. oligarthrus, the paca, agouti, spiny rat, and several species of wild felids.

Serologic tests for diagnosis and post-treatment evaluation of patients with alveolar hydatid disease (Echinococcus multilocularis).

The indirect hemagglutination (IHA) and immunoelectrophoresis (IEP) tests were used for diagnosis and follow-up evaluation of 17 patients with alveolar hydatid disease caused by Echinococcus multilocularis. Follow-up periods ranged from 2 to 22 years. At the time of diagnosis 16 (94%) patients' sera gave IHA titers greater than or equal to 1:128. Serum specimens from 13 patients were examined by IEP; nine (69%) revealed the arc 5, and three of the four arc 5-negative sera revealed one or more non-characterized bands. Titers declined markedly during the first year following radical surgical resection of the larval lesions; in three cases clinical evidence of recurrence was preceded by rising serologic titers. Antibody has persisted at high levels in non-resected patients treated continuously with high doses of mebendazole.

Albendazole therapy in alveolar hydatid disease: a report of favorable results in two patients after short-term therapy.

Albendazole was administered preoperatively to two patients with active alveolar hydatid disease for 58 and 84 days. Vesicles of larval Echinococcus multilocularis obtained from surgical tissues were inoculated into red-backed voles for in vivo testing viability. No proliferation of the larval cestode had occurred when the animals were dissected three months post-inoculation. These findings suggest that short-term therapy with albendazole was effective in killing the larval cestode in these two cases. Albendazole was found to be hepatotoxic but resulting transaminase abnormalities have been reversible. Close monitoring of liver function and hematology is essential in patients under albendazole therapy.

Application of the avidin-biotin immunohistochemical method for the diagnosis of alveolar hydatid disease from tissue sections.

The avidin-biotin immunohistochemical (ABC) method was applied to the diagnosis of alveolar hydatid disease in patients from the hyperendemic region of western Alaska. The test was specific for larval cestodes of the genus Echinococcus, and exhibited high sensitivity. A negative reaction was obtained in all cases in which spontaneous death of the larval cestode had occurred. Results were inconsistent in sections of lesions from patients who had received long-term therapy with mebendazole, because of the persistence of antigens for a considerable time following the death of the parasite.

Cysts resembling hydatids in a chicken.

Two large cysts recovered from the abdominal cavity of a domestic chicken superficially resembled hydatid cysts of Echinococcus spp. No protoscolices were present. Microscopic examination of the internal lining of one of the cysts revealed a single cuboidal to columnar, ciliated epithelium, leading to a diagnosis of oviduct cysts. Earlier records of hydatids of fowl are reviewed.

Aploparaksis borealis sp. n. (Cestoda: Hymenolepididae) from passeriform and charadriiform birds in Chukotka and Alaska.

Aploparaksis borealis sp. n. (Cestoda: Hymenolepididae), from the long-tailed jaeger, Stercorarisu longicaudus Vieillot, on the Seward Peninsula, Alaska, and from the red-throated pipit, Anthus cervinus (Pallas), and the Lapland longspur, Calcarius lapponicus (Linnaeus), in Chukotka, northestern Siberia, is described. This cestode is distinguished by the structure of the cirrus and other morphologic characters from other species of Aploparaksis Clerc 1903 in which there are 10 rostellar hooks and the vitelline gland is aporal to the ovary. A. borealis is the first species of Aploparaksis to be reported from birds representing 2 orders (Passeriformes and Charadriiformes).

Monoecocestus thomasi sp. n. (Cestoda: Anoplocephalidae) from the northern flying squirrel, Glaucomys sabrinus (Shaw), in Oregon.

Monoecocestus thomasi sp. n. (Cestoda: Anoplocephalidae), from the northern flying squirrel, Glaucomys sabrinus (Shaw), in Oregon, is described and distinguished from its congeners. Monoecocestus thomasi is the sixth species of Monoecocestus to be described from nearctic rodents, and the first from a member of the family Sciuridae. Our comparisons of taxonomic characters of the nominal species of Monoecocestus in North American rodents have shown that M. giganticus Buhler 1970 is a synonym of M. americanus (Stiles 1895), both from the porcupine, Erethizon dorsatum (Linnaeus). Insemination in Monoecocestus ssp. is discussed, with the conclusion that it takes place only by way of the vagina in early immature segments.

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.

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.

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.

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.

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.

The taxonomic status of Echinococcus cruzi Brumpt and Joyeux, 1924 (Cestoda: Taeniidae) from an agouti (Rodentia: Dasyproctidae) in Brazil.

Paratype material of Echinococcus cruzi Brumpt and Joyeux, 1924, described from an agouti, Dasyprocta leporina (L.), in Brazil, was compared with Echinococcus oligarthrus (Diesing, 1863), of which the larval stage occurs also in agoutis and other rodents in South America and Central America. Comparisons of the larval cestodes (metacestodes) showed that the rostellar hooks from protoscolices of the two taxa corresponded in form, and their slightly greater lengths in E. cruzi were considered to be of no taxonomic significance. They agreed as well in other morphological characteristics. Echinococcus cruzi was compared also with the other neotropical species, E. vogeli Rausch and Bernstein, 1972, Based on these comparisons and in agreement with the earlier conclusion of Cameron (1926), E. cruzi Brumpt and Joyeux, 1924 is placed in synonymy with E. oligarthrus (Diesing, 1863).