The occurrence of Protostrongylus stilesi in a population of introduced muskoxen, Ovibos moschatus wardi, on the Arctic Coastal Plain, Yukon Territory (YT) and Northwest Territories (NT), Canada, is consistent with a contemporary colonization event from Dall's sheep, Ovis dalli dalli, which indicates that host specificity may be ecologically based and contextual for this parasite. Colonization of muskoxen by P. stilesi may be a predictable event in zones of sympatry with Dall's sheep; exposure to infection may coincide with occupation of winter ranges of Dall's sheep by muskoxen during the summer season. Disruption of contemporary ecological isolating barriers can result from anthropogenically or climatologically driven habitat perturbation, and result from management practices that influence the distribution of ungulate hosts. Thus, if zones of contact become more extensive or the temporal limits on allopatry are relaxed, we may observe increasing instances of host switching by parasites or pathogens at the interface of newly emerging ecotones. Impacts to northern systems linked to climatologically and anthropogenically driven global change and the effects of management must be tracked within the context of biodiversity survey and inventory and archival collections, as foundations for monitoring ecosystem-level perturbations. A developing interface for muskoxen, wild sheep, and parasites along the Mackenzie River ecotone represents a natural model or field laboratory to examine these processes. Additonally, lungworms, Protostrongylus spp., had not been reported in muskoxen, and a new geographic record for this nematode was established in Dall's sheep from the northern Richardson Mountains, NT.

The helminth fauna of Mexican ictalurids was investigated through original surveys and published literature in order to evaluate the biogeography of host-parasite associations of a primarily nearctic host group in a major faunal transition area. In total, 84 specimens of 4 species of ictalurids (Ictalurus balsanus, Ictalurus dugesi, Ictalurus furcatus, and Ictalurus punctatus) were sampled from 7 localities in 5 hydrological drainages. Ten species of adult endohelminths were recovered from this survey, including 4 species of digeneans (Phyllodistomum lacustri, Genarchella tropica, Alloglossidium corti, and Campechetrema sp.), 3 cestodes (Corallobothrium fimbriatum, Megathylacoides giganteum, and Choanoscolex lamothei), and 3 nematodes (Dichelyne mexicanus, Goezia sp., and Rhabdochona sp.). The adult helminth fauna of ictalurids reported in this study is composed of taxa that are typical of ictalurids in other parts of North America, north of Mexico. This core fauna (in a historical biogeographic sense) includes the corallobothriines C. fimbriatum and M. giganteum and the digeneans P. lacustri and A. corti. Two other helminths, C. lamothei and D. mexicanus, may be added to this group in the future. Other helminths occurred sporadically and provide evidence for host-sharing (ecological host extensions), but we were unable to identify any valid cases of host-switching from more distantly related hosts. The helminth fauna provides evidence that the ictalurids developed their characteristic helminth fauna without neotropical influences and that the phylogenetic affinities of the ictalurids do not appear to be with any neotropical siluriform.

A molecular phylogeny was inferred from newly obtained partial (D1 domain) 28S rDNA gene sequences of Bothitrema bothi (Bothitrematidae), Neocalceostoma sp. (Neocalceostomatidae), Bravohollisia sp. (Ancyrocephalidae), and other already available sequences of Ancyrocephalidae, Anoplodiscidae, Pseudodactylogyridae, and Sundanonchidae, with the Diplectanidae as outgroup. Bothitrema, Anoplodiscus, and Sundanonchus formed a very robust clade that was the sister group to a group that included all other species examined. In this latter group, Neocalceostoma and Thaparocleidus were basal to a clade in which the Ancyrocephalidae and Pseudodactylogyridae were sister groups. Molecular results that suggest inclusion of the families Bothitrematidae, Anoplodiscidae, and Sundanonchidae in the same group partially contradict a previous morphological analysis of Boeger and Kritsky in which the first 2 were placed in the Gyrodactylidea and the third in the Dactylogyridea.

Seven species of helminths (6 nematodes and 1 cestode) were recovered from 38 plains vizcachas, Lagostomus maximus (Desmarest, 1817). Collections were made at 2 ranches, Los Valles Ranch (LVR) and El Estribo Ranch (EER), that are ∼300 km apart in La Pampa Province, Argentina. Prevalence and intensity of helminths from both LVR and EER were analyzed with respect to host gender, location, weight, season, and, where possible, colony. Between males and females there were no statistical differences in prevalence or intensity for the 7 helminths at each location. There was no difference in prevalence of Lagostonema ecasience between LVS and EER; however, the intensity was significantly higher at LVS (x̄ = 636) than at EER (x̄ = 6) (P = 0.003). Graphidioides affinis, Heteroxynema viscaciae, and Monoecocestus sp. are reported from the plains vizcacha for the first time. The most prevalent parasites were the nematodes L. ecasience (97%) and Viannella viscaciae (97%). An anterior shift in the distribution of V. viscaciae within the small intestine occurred with concurrent infections of Monoecocestus sp.

Helminth parasites collected at postmortem from the alimentary tracts of 5 Japanese giant salamanders, Andrias japonicus (Temminck, 1837), are reported. One trematode, Liolope copulans (Cohn, 1902); and 5 nematodes, Amphibiocapillaria tritonispunctati (Diesing, 1851), Dioctophyme renale (Goeze, 1782) (larva), Spiroxys hanzaki Hasegawa, Miyata et Doi, 1998, Kathlaniidae sp. (larva), and Physalopteroidea sp. (larva) were found. Examination of premolt and molting larvae of S. hanzaki showed that the advanced third-stage larvae molt directly to the adult stage. Strict host specificity of some helminths is surmised to be linked to the piscivorous nature of the giant salamander. This is the first report of A. tritonispunctati and D. renale from A. japonicus. The chromosome number of L. copulans is recorded for the first time.

During a survey of endohelminths from willets Catoptrophorus semipalmatus from the Texas Gulf coast, U.S.A., 22 species were found, including 1 acanthocephalan, 3 cestodes, 3 nematodes, and 15 trematodes. Two new species of cestodes, Kowalewskiella catoptrophori sp. n. and Kowalewskiella macrospina sp. n. (Dilepididae Railliet and Henry, 1909), are described. Willets represent new host records for 3 nematodes (Capillaria sp., Skrjabinoclava sp., and Skrjabinocara sp.) and 6 trematodes (Levinseniella hunteri, Lyperosomum sp., Probolocorpha glandulosa, Prosthogonimus ovatus, Renicola glandoloboides, and Stephanoprora sp.). A key to species of Kowalewskiella is included.

A new species and genus of digenetic trematode of the family Dicrocoeliidae is described from 2 species of grass mice, Akodon fumeus and Akodon mimus, both collected from an isolated area in the eastern part of the Andes mountains or Yungas of Bolivia. This species differs from all known dicrocoeliids in the unique disposition of the vitelline fields, the much less extensive uterus through the body of the worm (extending posteriad only just past the midline), and cecal branches that are generally conspicuous and lined with a thick layer of glandular epithelial tissue.

Galactosomum stelleri sp. n. (Trematoda: Heterophyidae), a new trematode from the small intestine of the Steller's or northern sea-lion Eumetopias jubatus is described. An adult female specimen of E. jubatus collected from Indian Beach, Oregon, U.S.A., harbored over 100 specimens of these trematodes. The new species most closely resembles Galactosomum ubelakeri (Dailey, 1969) Pearson, 1977, and Galactosomum humbargari Park, 1936 but differs in body shape and size, lack of tegumental spines, length of esophagus, and ventral genital complex configuration. This is the third report of a species of Galactosomum from a marine mammal.

Enterobius (Colobenterobius) pygatrichus sp. n. (Nematoda: Oxyuridae) is described on the basis of females expelled spontaneously from an adult male golden monkey Pygathrix roxellana (Milne-Edwards, 1870) (Primates: Cercopithecidae: Colobinae) that was being kept temporarily in a Japanese zoo. This species is distinguished from the previously known members of the subgenus by the cephalic morphology and a short tail.

The nematode Ascarophis ayalai Caballero, 1975, originally inadequately described from Arius liropus (Bristol in Gilbert, 1897) in Nayarit and Sonora, Mexico, is redescribed on the basis of examination of types and new material obtained from the stomach of the Mayan sea catfish Ariopsis assimilis (Günther, 1864) from the Bay of Chetumal, Quintana Roo, Mexico. Ascarophis ayalai differs markedly from its congeners in possessing a left spicule of unusual shape and structure. Ariopsis assimilis represents a new host record for A. ayalai.

The clinical courses of 6 canine hookworm infections were examined in 19–20-wk-old dogs infected with 400, 600, or 800 third-stage infective larvae (L₃) of Ancylostoma caninum. Dogs infected with 600 L₃ exhibited the greatest adult hookworm burden (289 ± 44), fecal quantitative egg counts, leukocyte counts, and eosinophilia, as well as the lowest overall hematocrit and hemoglobin concentrations. Dogs infected with 800 L₃ harbored fewer adult hookworms in their intestines (226 ± 20) than dogs infected with 600 L₃ (289 ± 44). Dogs infected with 400 L₃ exhibited the lowest hookworm burden (133.5 ± 12.5). All of the dogs developed anti-A. caninum antibody responses. The adult hookworm recovery data were used to calculate a sample size for future canine vaccine trials that will employ recombinant hookworm antigens formulated with adjuvant.

Deformed amphibians have been reported from several locations in North America, with the prevalences of these deformities varying from region to region. These deformities have been attributed to both anthropogenic and natural changes in the abiotic and biotic factors in the environment. Suggested causes for these deformities include toxins, ultraviolet B irradiance, larval trematodes, or synergistic interactions of some or all of these factors. Several studies, beginning in 1990, have investigated the helminths infecting amphibians from southern Michigan, U.S.A., with emphasis on locating populations of deformed amphibians. Although high numbers of many species of larval and juvenile helminths (Fibricola sp., Clinostomum sp., gorgoderid, strigeid, or unknown metacercariae, Mesocestoides sp., Spiroxys sp.) were found infecting the hind limbs, these helminths did not cause deformities in southern Michigan.

The occurrence of a large digenean, Otodistomum plunketi, in 8 rajid host species from the Falkland Islands was investigated. All infected hosts are new host records for O. plunketi. The parasites were in the abdominal cavity except in 1 individual host, which harbored some trematodes within the pericardium. The prevalence and mean intensity of O. plunketi in all hosts examined were 31% and 1.95, respectively. Bathyraja multispinis had the greatest infection rate, with a prevalence of 100%, a mean intensity of 50.4, and a range of 8–136 parasites. Bathyraja scaphiops and Raja doellojuradoi were not infected. For Bathyraja albomaculata, a significant positive correlation (P < 0.05) was found between mean abundance and total length. For the remaining hosts, no relationship was found between intrinsic host factors and infection. Thirty small crabs, Peltarion spinosulum, a major prey item for B. multispinis and B. albomaculata, were examined for O. plunketi metacercariae but were not infected.

Three species of Belostoma Latreille, 1807 (Insecta, Heteroptera) were found to be intermediate hosts of digenetic trematodes of the genus Stomylotrema Looss, 1900, parasitic in birds. Several infected specimens of Belostoma elegans (Mayr, 1871) and Belostoma oxyurum (Dufour, 1863) were collected in the Arroyo Zapata, Province of Buenos Aires, Argentina; one infected specimen of Belostoma foveolatum (Mayr, 1863) was found in the Arroyo Cuña-Pirú, in the Province of Misiones. Encysted metacercariae were found mainly in the abdominal cavity of adult male and female belostomatids, with low prevalences and variable intensities of infection. Species of Belostoma are reported for the first time as intermediate hosts of digenetic trematodes and as new intermediate hosts for representatives of the genus Stomylotrema. Natural infections of adult Stomylotrema spp. were found in several insectivorous birds present in the Buenos Aires study area. The role of other aquatic organisms as intermediate hosts of Stomylotrema spp. is discussed.

Blood films from 46 fish crows (Corvus ossifragus Wilson) and 42 American crows (Corvus brachyrhynchos Brehm) from Florida, U.S.A., were examined for blood parasites. Haemoproteus picae Coatney and Roudabush, Haemoproteus danilewskii Kruse, Trypanosoma avium (Danilewsky), and microfilariae of an unidentified filarioid were identified from both species of crows. An unidentified species of Haemoproteus and Trypanosoma ontarioensis Woo and Bartlett were observed in American crow blood films. Fish crow blood films contained Plasmodium relictum Celli and Sanfelice. Prior to this study, T. avium and P. relictum had not been reported from fish crows.

Fourteen species of endohelminths, including 1 acanthocephalan, 3 cestodes, 1 nematode, and 9 trematodes, were collected from 13 little blue herons Egretta caerulea from the area of Galveston, Texas, U.S.A. A mean of 4.3 (3–6) species of endohelminths per host was found. Five species (3 cestodes and 2 trematodes) represent new host records. Comparison of results from this study with a similar survey by Sepúlveda et al. (1996) from Florida, U.S.A., suggests some hypotheses concerning possible roles of composition and complexity of trophic structures of these 2 regions in establishment of their respective endohelminth communities in little blue herons.

The endohelminth parasite fauna of the teleost fish Labrisomus philippii, the “trambollo” (Labrisomidae), from the central Peruvian coast is quantitatively described. The assemblage was composed of 7 species: the adult digeneans Helicometra fasciata (Rudolphi, 1819), Zoogonus rubellus (Olsson, 1868), Prosorhynchus Odhner, 1905 sp., and Bucephalopsis (Diesing, 1855) sp.; metacercariae of Bucephalus Baer, 1826, sp.; and the larval Lacistorhynchus tenuis (van Beneden, 1858) (Eucestoda) and Corynosoma australe Johnston, 1937 (Acanthocephala). Up to 98% of the fish were parasitized. The highest prevalence was shown by Z. rubellus (74%) and the highest mean intensity by Bucephalopsis sp. (103.7). No common pattern of infection as a function of host body size or sex was noted. The major characteristic of the endohelminth community of L. philippii was the richness of digeneans compared with those of other marine fishes in this geographical area. This richness may be a consequence of abiotic factors particular to the Peruvian Faunistic Province.

Larval stages (metacestodes) of 2 dilepidid tapeworms (Eucestoda: Cyclophyllidea) are reported from the mesenteries and liver of the mummichog Fundulus heteroclitus and striped killifish Fundulus majalis from South Carolina, U.S.A. Cyclustera ibisae (Schmidt and Bush, 1972) is reported for the first time from a fish intermediate host, whereas metacestodes of Glossocercus caribaensis (Rysavy and Macko, 1973) (syn. Parvitaenia heardi Schmidt and Courtney, 1973) have only recently been found in fish from southeastern Mexico (Yucatan).

Trematode larvae of the family Accacoeliidae were obtained from Flaccisagitta enflata collected in the Mexican Caribbean Sea during February, March, May, and August 1991. Two parasites were found in the coeloms of 2 chaetognaths of 14,583 examined (prevalence = 0.014%; intensity = 1). The parasites have 5 or 6 branches on each side of the anterior intestinal ceca and 2 deeply stained zones, 1 internal on the posterior edge of the acetabulum and the other a glandular structure around the cloacal pore in the posterior part of the body. Two tegumental folds are present on the anterior and posterior parts of the parasite. These trematode larvae, their host, and their occurrence in the Mexican Caribbean Sea are reported for the first time.