Intestinal pathology and site specificity of the acanthocephalan Neoechinorhynchus carpiodi Dechtiar, 1968, in quillback, Carpiodes cyprinus (Lesueur)

Intestinal pathology and site specificity of Neoechinorhynchus carpiodi Dechtiar, 1968, in quillback, Carpiodes cyprinus (Lesueur), from Dauphin Lake, Manitoba, was investigated. Neoechinorhynchus carpiodi elicits the formation of a nodule at the point of proboscis attachment. Over 98% of the worms were attached in sections 6-8 of the intestine. Fish had clusters of 1-8 nodules, cluster size increased with worm burden, and the volume of nodules increased with worm numbers. Nodule number, size, and pathology was related to intensity of infection and to depth of proboscis penetration. Three types of pathology were noted. Type I nodules had few worms and the proboscides were attached in the lamina propria; Type II nodules harbored more worms and the proboscides penetrated to, but not through, the stratum compactum; and Type III nodules had the greatest numbers of N. carpiodi and proboscides penetrated through the stratum compactum. Hyperplasia, vascularization, and collagen deposition were extensive, especially in Type III nodules. An epithelium-lined channel was present in most nodules. Type III nodules were most anterior (75% of the time), harbored the greatest proportion of immature worms regardless of cluster size, and had more gravid females. The largest nodules (Type III pathology) were well vascularized, long-lasting, and appeared to be the preferred microhabitat for the parasite.     

Gastrointestinal parasites of cougars (Felis concolor) in Washington and the first report of Ollulanus tricuspis in a sylvatic felid from North America.

Gastrointestinal helminths including two species of cestodes (Taenia omissa and T. ovis krabbei) and three species of nematodes (Toxocara cati, Cylicospirura subequalis and Ollulanus tricuspis) are reported from two free-ranging cougars (Felis concolor) in Washington (USA). Ollulanus tricuspis is reported for the first time from cougars and represents the first occurrence of this parasite in a sylvatic felid from North America.     

Lack of interferon-gamma confers impaired neutrophil granulocyte function and imparts prolonged survival of adult filarial worms in murine filariasis

We investigated the role of IFN-gamma in host defense during murine filariasis. Using the fully permissive infection of BALB/c mice with the rodent filaria Litomosoides sigmodontis, we show that interferon (IFN)-gamma is essential for encapsulation of adult filarial worms in inflammatory nodules and for normal worm clearance. IFN-gamma knockout (KO) mice had only one third of the nodules of wild-type mice but displayed a more than twofold increase in worm burden and increased microfilaremia. Neutrophil granulocytes, but not macrophages or eosinophils, appear to directly control worm load and nodule formation. Neutrophils, which we showed earlier to be essential for the encapsulation process in the thoracic cavity, where the worms reside, were diminished at this location in IFN-gamma KO compared to wild-type mice; they also displayed strongly reduced chemotactic and phagocytic activity compared to neutrophils of controls. This argues for a distinct defect in neutrophil activation accounting for the low formation of inflammatory nodules. Tumor necrosis factor-alpha, a major neutrophil-activating cytokine expressed by macrophages in the thoracic cavity around the worms, was highly induced in wild-type but absent in KO mice. Diminished activation of neutrophils seems to be a general hallmark of IFN-gamma KO mice, since neutrophils from uninfected KO mice also showed a reduction in chemotactic and phagocytic activity when induced by casein. In conclusion, these data are the first to define an IFN-gamma-dependent immune effector mechanism in murine filarial infection, i.e. neutrophil-mediated control of the adult worm load.     

Seasonal population dynamics of Pallisentis (Neosentis) celatus (Acanthocephala: Quadrigyridae) in the intestine of the rice-field eel Monopterus albus in China

Studies on the seasonal population dynamics of Pallisentis (Neosentis) celatus (Acanthocephala: Quadrigyridae) in the intestine of the rice-field eel Monopterus albus from the paddies and ditches in the Dong-ting Lake basin of China, were carried out with samples taken from June 2002 to May 2003. Prevalences were above 21% in all seasons sampled and with a distinct seasonal trend, which was highest (45.81%) in the spring and decreased by degrees. The mean intensity of infection was above 4.0 worms per fish. The maximum intensity of worms recovered from a single fish was 86 in the autumn of 2002. No significant seasonal differences were found in mean intensities, and differences in the mean abundance between winter and spring, winter and autumn were significant. Over-dispersed distributions of P. (N.) celatus in the host population, due to heterogeneity and feeding habits, were observed in all seasons. The size composition of both sexes of P. (N.) celatus showed males between 2.0 mm and 14.0 mm and females between 2.2 mm and 22.2 mm, with the main recruitment phase in the worm populations occurring in the summer and autumn, especially in the autumn, with the lowest recruitment occurring in the winter. The maturation and copulation of worms were mainly focused in the spring season. The sex ratio of female to male was both high in summer (1.09:1) and autumn (1.08:1). The higher proportion of females and the change in the worm sex ratio in summer can be attributed to the reduced longevity of male worms. As immature male worms exhibit a higher proportion of the worm population than females in all seasons, further studies are needed to determine if such a situation compensates for the shorter life span of males.     

Characteristics of natural infections of the stomach worm, Obeliscoides cuniculi (Graybill), in lagomorphs and woodchucks in Canada

Wild lagomorphs and woodchucks collected predominantly in southern Ontario, Canada were examined for subspecies of Obeliscoides cuniculi (Graybill). Obeliscoides cuniculi multistriatus was found in snowshoe hares (Lepus americanus). Obeliscoides cuniculi cuniculi was found in cottontail rabbits (Sylvilagus floridanus), European hares (Lepus capensis) and woodchucks (Marmota monax). Prevalence of Obeliscoides cuniculi multistriatus in snowshoe hares was 100% and mean intensity (and range of intensity) was 760 (9-4, 198) in Lindsay, Ontario in 1980. Mean intensity in hares varied trimonthly. The highest mean intensity of worms occurred in spring when most worms were adult. Transmission occurred mainly in spring. Most worms present in fall (70%) and winter (54%) were fourth stage. Immature fifth-stage and gravid females were present in hares during fall and winter. Prevalence and mean intensity of O. c. cuniculi in cottontails was 15% and 29 (1-118). Prevalence and mean intensity of O. c. cuniculi in woodchucks was 6% and 56 (16-118). European hares were infected with O. c. cuniculi, prevalence was 10% and mean intensity was 60 (36-83). In Ontario woodchucks and European hares were common in areas frequented by cottontail rabbits and probably acquired sporadic infections of O. c. cuniculi from infected cottontails.     

In vitro and in vivo studies on the bioactivity of a ginger (Zingiber officinale) extract towards adult schistosomes and their egg production

The bioactivity of an ethyl acetate extract of ginger (Zingiber officinale) towards Schistosoma mansoni adult pairs, both cultured in vitro and in vivo in laboratory mice, was investigated by monitoring worm mortality and fecundity. In vitro, a concentration of 200 mg l(-1) of extract killed almost all worms within 24 h. Male worms seemed more susceptible than female under these conditions. Cumulative egg output of surviving worm pairs in vitro was considerably reduced when exposed to the extract. For example, after 4 days of exposure to 50 mg l(-1), cumulative egg output was only 0.38 eggs per worm pair compared with 36.35 for untreated worms. In vivo efficacy of the extract was tested by oral and subcutaneous delivery of 150 mg kg(-1) followed by assessment of worm survival and fecundity. Neither delivery route produced any significant reduction in worm numbers compared with untreated controls. Worm fecundity was assessed in vivo by cumulative egg counts per liver at 55 days post infection with mice treated subcutaneously. Such infections showed egg levels in the liver of about 2000 eggs per worm pair in 55 days, in both treated and control mice, with no significant difference between the two groups. To ensure that density-dependent effects did not confound this analysis, a separate experiment demonstrated no such influence on egg output per worm pair, at intensities between 1 and 23 worms per mouse.     

Population dynamics and epidemiology of Toxocara canis in Danish red foxes

Toxocara canis, an intestinal helminth of canids with zoonotic potential, was found in 618 (59%) of 1,040 red foxes (Vulpes vulpes) collected from all Danish provinces (1997-2002). The prevalence and average worm burden were significantly higher for cubs than older foxes and in males than in females. A multiple logistic regression demonstrated that the prevalence was influenced significantly by sex and age of foxes in addition to location, season, and year of collection. The highest prevalence and worm burden were found in rural areas. The size and number of female worms was positively correlated to the fecal egg excretion. The length and fecundity of the worms was significantly higher in male foxes, and a general intensity dependence was suggested from a negative correlation between worm numbers and worm lengths. As compared to intestinal recovery of worms, somatic larvae were recovered from 20% of muscle samples and fecal eggs in 41% of fecal samples. The consistent finding of T. canis larvae in somatic tissues of naturally infected foxes is new.     

Single and multiple worm infections of Echinostoma caproni (Trematoda) in the golden hamster

Six of 10 hamsters fed a single metacercarial cyst of Echinostoma caproni (single-worm infections) and 13 of 19 hamsters fed either 2 or 5 cysts (multiple-worm infections) were infected with adult echinostomes at necropsy 22 days post-infection. Considerable histopathological changes to the small intestine occurred in hamsters carrying single-worm infections. There were no differences in either mean length, width or wet weight of echinostomes in single- versus multiple-worm infections. The mean number of eggs/worm from single-worm infections (525) was significantly greater than that from multiple-worm infections (288). The average percentage of fully developed miracidia/worm from single worms (94%) was similar to that from worms in multiple infections (92-95%). Single worms of E. caproni were capable of self-fertilization and production of viable eggs. Miracidia derived from single worms were as capable of infecting laboratory-reared Biomphalaria glabrata and producing patent rediae as were those from multiple infections.     

Nematospiroides dubius: arrested development of larvae in immune mice.

When immune NIH mice were killed 10 days after a challenge infection with Nematospiroides dubius, approximately 10% of the inoculated larvae were recovered from the intestinal lumen, irrespective of the dose administered. When such mice were treated with cortisone from Day 10 for a period of 8 to 14 days and were subsequently killed for worm counts, it was found that they had significantly more worms than the immune control mice killed on Day 10. During the week following the beginning of treatment with cortisone there was little change in the low worm burdens in immune mice. However, 9 to 11 days after this treatment worm counts indicated that worms were accumulating in the intestinal lumen, and concurrently eggs were recorded in the feces of the mice. These observations indicated that a period of 9 to 11 days was required after the initiation of cortisone treatment on Day 10 for the worms in immune mice to complete their development to the adult lumen-dwelling stage. It is suggested that the larvae in the challenge infection became arrested early in their development in the intestinal wall and that growth resumed only after cortisone treatment. When treatment with cortisone was initiated later after challenge, it was still effective in reactivating arrested worms, but the lower worm recoveries in these mice indicated that the arrested larvae were being slowly rejected by the host. In subsequent experiments it was established that the arrested larvae of N. dubius were insusceptible to the activity of pyrantel embonate, an anthelmintic which is 99% effective against adult worms in the intestinal lumen. The mechanism whereby the larvae of N. dubius became arrested in immune mice and subsequently resumed their development after cortisone treatment is discussed.     

Seasonal variation in the prevalence and intensity of canine Gnathostoma spinigerum infection in northeastern Thailand.

Gnathostoma spinigerum was found in gastric nodules in 4.1% of 2940 dogs surveyed in northeastern Thailand. The prevalence and worm burden of G. spinigerum exhibited a seasonal fluctuation. The parasites were more abundant in the rainy season and the early winter (August-December) than in the summer (April-March). Most parasites were sexually mature between August and December while immature worms were observed during March and April. The distribution of gnathostomes within the sampled dogs was highly dispersed and few animals were found to harbour more than five worms.     

Competition and coexistence in sympatric bobcats and pumas

Space use and diets of sympatric bobcats Lynx rufus and pumas Puma concolor were compared using sign surveys and scat analysis during 1997–2002 in south-eastern Arizona, USA. Bobcats appeared to use grassland, scrub, riparian and woodland habitats equally, but pumas had higher activity in riparian and woodland habitats. There was little evidence that bobcats avoided pumas in space use. Bobcats ate primarily rodents (33% of items in scats), lagomorphs (32%) and ungulates (16%), whereas pumas ate primarily ungulates (69%) and carnivores (21%). Pumas had a narrower dietary niche breadth than bobcats, and puma diet overlapped bobcat diet by 56%, suggesting that pumas may be more vulnerable to changes in prey density than bobcats. Pumas also killed and consumed bobcats, indicating that interference competition may be manifesting through intraguild predation.     

Effect of host sex and litter on the population dynamics of Echinococcus granulosus in dogs.

Twenty-one Beagle dogs consisting of 10 males and 11 females and belonging to 3 litters were infected with 60,000 E. granulosus protoscolices each. They were killed on day 40, the parasites from their intestines recovered, and the number of worms, average number of proglottides per worm, average length per worm, percentage of worms with a uterine cavity, and percentage of egg-bearing worms were determined for each dog and analyzed per sex and litter. On average, the dogs had 1,253 +/- 339 worms (means +/- standard error) with 2.42 +/- 0.1 proglottides, were 1.59 +/- 0.07 mm long, and 25.6 +/- 4.8% of the worms presented a uterine cavity and 1.2 +/- 0.6% bore eggs. The number of worms exhibited a bimodal distribution with 19 dogs having less than or equal to 2,565 worms and 2 greater than or equal to 5,520 worms. Average number of proglottides also showed a bimodal distribution with 7 dogs having less than or equal to 2.1 proglottides per worm and 14 dogs having greater than or equal to 2.4 proglottides per worm. The parasites were significantly more numerous in females than in the males (1,964 +/- 573 vs. 681 +/- 202), had more proglottides (2.67 +/- 0.08 vs. 2.15 +/- 0.16), and were longer (1.72 +/- 0.07 vs. 1.44 +/- 0.11 mm). The percentages of parasites with a uterine cavity (27.8 +/- 5.9 vs. 23.2 +/- 8.1) or bearing eggs (1.0 +/- 0.5 vs. 1.5 +/- 1.8) were comparable in females and males.(ABSTRACT TRUNCATED AT 250 WORDS)     

Helminth species diversity and biology in the bobcat, Lynx rufus (Schreber), from Nebraska

Cestodes of 4 species and nematodes of 9 species were collected from 75 bobcats, Lynx rufus (Schreber), in Nebraska from 1977 to 1979. Of these 75, 11 were trapped from 6 border counties in 3 border states: South Dakota, 7 carcasses/3 counties; Kansas, 3/2; and Wyoming, 1/1. Helminths recovered included: Mesocestoides corti Hoeppli, 1925 (15% prevalence), Taenia rileyi Loewen, 1929 (67%), Taenia pisiformis (Bloch, 1780) Gmelin, 1790 (27%), Taenia macrocystis (Diesing, 1850) Lühe, 1910 (19%), Physaloptera praeputialis von Linstow, 1889 (55%), Physaloptera rara Hall and Wigdor, 1918 (32%), Toxascaris leonina (von Linstow, 1902) Leiper, 1907 (31%), Toxocara cati (Schrank, 1780) (39%), Ancylostoma tubaeforme (Zeder, 1800) von Linstow, 1885 (5%), Pterygodermatites (Multipectines) cahirensis (J?gerski?ld, 1909) Quentin, 1969 (1%), Vogeloides felis (Vogel, 1928) Davtian, 1933 (7%), Cylicospirura felineus (Chandler, 1925) Sandground, 1932 (12%), and Capillaria aerophila (Creplin, 1839) (4%). One bobcat was not infected; 74 had 1 to 7 species (means = 3). Simpson's index for helminth species was moderately low (0.12), indicating a relatively diverse helminth fauna. Mean levels of infection between prominent species pairs and within each species were compared with bobcat sex and age differences using Student's t-test. Mean intensity of Physaloptera praeputialis was significantly (P less than 0.01) greater than that of Toxocara cati; mean intensity of Mesocestoides corti was significantly (P less than 0.01) greater than that of all other prominent species. No significant intensity differences were indicated among bobcat sex and age categories. G-tests computed for prevalence of prominent species with bobcat age indicated no significance.(ABSTRACT TRUNCATED AT 250 WORDS)     

Distribution and prevalence of Echinococcus multilocularis in wild predators in Nebraska,Kansas, and Wyoming

To further determine the distribution and prevalence of Echinococcus multilocularis in the central United States, 245 wild canids (125 red foxes, 120 coyotes) and 33 bobcats were collected from Nebraska, Kansas, and Wyoming and examined for this parasite. Animals examined included 11 red foxes from the western panhandle of Nebraska; 5 red foxes and 30 coyotes from southern Nebraska; 56 red foxes and 1 coyote from northeastern Nebraska; 20 red foxes, 63 coyotes, and 13 bobcats from northern Kansas; 2 red foxes, 26 coyotes, and 20 bobcats from southern Kansas; and 31 red foxes from east-central Wyoming. Of these, 27 of 72 (37.5%) red foxes from Nebraska were positive, including 2 of 11 (18.2%) from the western panhandle and 25 of 56 (44.6%) from the northeastern part of the state. Mean intensity of infection was 282 worms (range, 1-5,150). New distribution records were established for E. multilocularis in western Nebraska as well as for several northeastern counties. These findings support previous estimates that the southernmost front of the parasite's range extends along the southern border of Wyoming, eastward through central Nebraska and central Illinois into Indiana and Ohio.     

Prevalence and intensity ofCapillaria catostomi (Nematoda: Trichuroidea) in white sucker (Catostomus commersoni) in southern Lake Huron,Canada

Synopsis A total of 314 white suckers (Catostomus commersoni) taken monthly during May to December 1975 and in April and May 1976 from southern Lake Huron, Ontario, Canada, were examined forCapillaria catostomi.Prevalence determined from fresh white suckers (66%) was significantly lower than from frozen white suckers (81%). However, there was no significant difference in prevalence ofC. catostomi in samples taken at monthly intervals; in male and female white suckers; or in the age categories.Mean intensity of infection was not significantly different in fresh (9.6 [± 13.41]) or frozen (10.4 [± 13.11]) white suckers. There was no significant difference in intensities between monthly samples in male and female white suckers or in the age categories. Suckers were infected with 1–172 worms. The percentage of male, female and immature worms did not change with sex or age of host or by month. The frequency distribution showed the parasites were overdispersed.A possible life cycle forC. catostomi involving an oligochaete intermediate host is discussed and an attempt made to explain the almost constant levels of prevalence and intensity.     

Canine heartworms in coyotes in Illinois

Canine heartworm (Dirofilaria immitis) disease affects wild canids and may be a factor impacting the health and population dynamics of coyotes (Canis latrans). Coyotes may serve also as a potential reservoir for transmission of these parasites to domestic dogs. We investigated 920 coyotes harvested by hunters and trappers throughout Illinois (USA) from 1995-1997. The objectives of the study were to: 1) survey the regional prevalence and intensity of heartworms in coyotes in Illinois, 2) determine whether heartworm intensity correlates with physical condition, particularly body weight and winter fat levels, and 3) evaluate the relationship between heartworm infections and the reproductive success of females. Prevalence of heartworms statewide was 16.0%. Prevalence was significantly higher in males (17.7%) than in females (14.1%; P = 0.04) and was higher in the older age-classes (P < 0.0001). The regional prevalence of heartworms increased from northern to southern Illinois. Intensity ranged from 1 to 111 with a mean of 8.7 (SD = 13.2) worms. Intensities did not differ significantly between sexes (P = 0.53) or among age-classes (P = 0.84). Most infected coyotes had low intensity infections, 78.2% carried < 12 heartworms, 11.6% had 12-24 worms, and 10.2% were infected with > 24 worms. Body weights were not correlated with the presence of heartworms, nor were levels of kidney fat and marrow fat. However, reproductive success was lower in infected females. The percent of yearling females that bred was lower among infected females, as was the number of offspring produced by adults > or = 3.5 yr old. Our study demonstrates that heavy infections adversely affect fur quality and reduce fecundity of some females, but these effects are small and few coyotes (4.1%) had enough worms to trigger them. Coyote populations have increased in Illinois during the past 20 yr, but prevalence and intensity of heartworm disease appears to have changed little in that period. We conclude that heartworm disease is only a minor factor influencing coyote population dynamics in Illinois.     

Secondary infections of Hymenolepis diminuta in mice: effects of varying worm burdens in primary and secondary infections.

In one (1 c) and six (6 c) cysticercoid primary infections of Hymenolepis diminuta in NIH (inbred) and CFLP (outbred) male mice 6 +/- 1 weeks old greater than 85% of the worms established but were rejected (destrobilated or expelled) subsequently. Rejection occurs more quickly in 6 c infections than in 1 c infections. Considerable worm growth occurs in 1 c and 6 c primary infections but worms from 6 c infections weighed less than worms from 1 c infections on all days studied. Expulsion of H. diminuta does not occur more rapidly in secondary infections than in primary infections; loss of 6 c secondary worms occurs at the same rate as 6 c primary worms but 1 c secondary worms survive longer than 1 c primary worms. Although worms are not lost more quickly in secondary than in primary infections, they are affected at an early age by the immune response which stunts their growth. Increasing the intensity of primary and secondary infections increases the severity of stunting of secondary worms. The results are discussed and it is suggested that immune responses to Hymenolepis spp. in rodents are common but that thresholds of worm numbers exist below which appreciable worm loss does not occur. Stunting due to crowding, which generally is attributed to inter-worm competition, may be in part immunologically mediated. For future immunological studies attempting to induce secondary responses to H. diminuta in mice, worm growth, not survival, is the criterion to evaluate.     

Inequalities in size and intensity-dependent growth in a mermithid nematode parasitic in beach hoppers

Inequality in body sizes is a common feature in populations of helminth parasites, with potential consequences for egg production and population genetics. Inequalities in body lengths and the effects of intraspecific competition on worm length were studied in a species of mermithid nematode parasitic in the crustacean Talorchestia quoyana (Amphipoda: Talitridae). The majority of the 753 worms recovered were relatively small, and an analysis using a Lorenz curve and Gini coefficient suggested that there were no marked inequalities in body lengths among the worms. Total worm length in the 356 infected amphipods (i.e. the sum of the lengths of all the worms in a host) increased steadily as a function of the number of worms per amphipod, whereas the length of the longest worm per amphipod peaked in amphipods harbouring intermediate numbers of worms. This last result was not significantly accounted for by the observed increase in host size with increasing intensity of infection, but resulted from a correlation between worm length and host size. As the number of worms per amphipod increased, the relative sizes of the second-, third-, and fourth-longest worms per host increased markedly. This means that relative inequalities in sizes become less pronounced, i.e. subordinate worms get closer in size to the longest worm, as the number of worms per host increases. The main consequence of this phenomenon is that worm sizes in the mermithid population are more homogeneous than they would be if intraspecific competition had stronger effects on worm growth.     

Biochemical effects of thiabendazole and cambendazole on Hymenolepis diminuta (Cestoda) in vivo

An investigation of the chemotherapeutic and biochemical effects of two benzimidazole anthelmintics, thiabendazole (TBZ) and cambendazole (CBZ), on Hymenolepis diminuta in experimentally infected rats is reported. Thiabendazole was active against H. diminuta at a relatively high dosage. A single oral dose of TBZ at 250 mg/kg body weight on day 15 of infection eliminated 100% of the tapeworms as determined at necropsy 5 days after treatment. The chemotherapeutic actions of TBZ on H. diminuta were accompanied by marked changes in worm weight and chemical composition. Tapeworms recovered from rats that had received a therapeutically effective dose of TBZ 24 hr earlier were significantly smaller and contained much less glycogen (as a percent of the wet weight) than worms from unmedicated controls. Protein concentrations increased in TBZ-treated worms and at a rate sufficient to offset the decline in glycogen concentration. Glycogen/protein ratios in TBZ-treated worms were significantly lower than the corresponding control values. Cambendazole proved to be five times more potent than TBZ against H. diminuta and produced the same basic changes in worm weight and chemical composition within 18 hr of treatment of the host. Administration of a single oral dose of TBZ or CBZ to the host produced in H. diminuta another change, the onset of which coincided with, or preceded, the gross alterations in worm weight and chemical composition. That change, observed in in vitro studies carried out 14 hr after treatment, revealed that tapeworms from drug-treated rats absorbed and metabolized much smaller quantities of exogenous glucose than did the controls, and the ability of the worm to accumulate glucose against a concentration difference was significantly depressed.     

Temporal variation in abundance of the egg predator Carcinonemertes epialti (Nemertea) and its effect on egg mortality of its host,the shore crab,Hemigrapsus oregonensis

An outbreak of the nemertean, Carcinonemertes epialti, was observed on Hemigrapsus oregonensis during October, 1982 at Campbell Cove, Bodega Harbor, California. Mean worm intensity (296 worms/crab) was the highest recorded for this nemertean egg predator on H. oregonensis. During the outbreak, male crabs were found to harbor more worms than both non-ovigerous and ovigerous females. Crab egg mortality was substantial; 83% of the ovigerous females experienced 75–100% brood mortality. The seasonal peak in worm abundance coincided with the seasonal low in crab reproduction at this locality. A method for estimating the impact of C. epialti on H. oregonensis natality was developed using crab size and fecundity, and worm prevalence and intensity. For a non-outbreak sampling period, a mean of 5.6% egg mortality was experienced by infested crabs for the period selected. Thus, brood mortality during the outbreak was much greater than that experienced at non-outbreak periods. Heavy fishing pressure on some commercially important crab species has been suggested as a possible factor inducing worm outbreaks and facilitating their continued persistence. These observations suggest that fisheries are not necessarily responsible for the outbreaks of nemerteans on commercially important crab species. However, fishing pressure may still be a sufficient condition to promote nemertean outbreaks.