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.     

Pathology and epizootiology of Dirofilaria scapiceps (Leidy, 1886) (Nematoda: Filarioidea) in Sylvilagus floridanus (J.A. Allen) and Lepus americanus erxleben

Dirofilaria scapiceps was found between the synovial sheath and tendons, i.e., within the tendon sheath, in the ankle region of eastern cottontail rabbits (Sylvilagus floridanus) and snowshoe hares (Lepus americanus). In cottontail rabbits, tendons and sheaths appeared normal and all worms were adults. Only one (4%) of 24 infected rabbits contained dead worms. All female worms were gravid in rabbits killed in late winter or early spring. Microfilaremias in rabbits were high (approximately 30-100 microfilariae/60 microliter blood) and of long duration (at least 8-28 mo), and rabbits were considered normal hosts of D. scapiceps. In some snowshoe hares, tendons and sheaths also appeared normal; however, in other hares a chronic proliferative tenosynovitis, characterized by fibrinous exudate, hyperplasia and hypertrophy of the intima and inflammatory cell (predominantly lymphocytes and plasma cells) infiltration of the intimal and fibrous layers of the synovial sheath led to encapsulation of worms. Dead subadult, dead adult, and live adult worms were found in the ankles of hares; 86 (46%) of 186 infected hares contained some or only dead worms. Fibrosis commonly occurred around dead worms. Dead subadults were also found in subcutaneous connective tissues over the trunk of the body. Degenerate embryos and amorphous material were observed in uteri of some female worms in hares killed in late winter or early spring. Few (1-5 microfilariae/60 microliter blood) or no microfilariae were observed in the peripheral blood of hares and microfilaremias were of short duration (less than 8 mo). Microfilariae in hares are probably trapped and destroyed in the chronic inflammatory lesions in the tendon sheaths since normal, degenerate, and calcified microfilariae were observed in the capsules around adult worms. Some microfilariae might also be destroyed in lymph nodes. Although D. scapiceps can be maintained within snowshoe hare populations, hares are considered abnormal hosts of D. scapiceps. Dirofilaria scapiceps may have spread from cottontail rabbits to snowshoe hares relatively recently.     

Prevalence of helminths in a cyclic snowshoe hare population

Five species of helminths were monitored in a population of snowshoe hares (Lepus americanus) near Rochester, Alberta, during 1961-1977. Prevalence of both Obeliscoides cuniculi and Protostrongylus boughtoni among young hares averaged about 50% by age 2 mo, then tended to level off. Prevalence of Taenia pisiformis (cysticerci) and Dirofilaria scapiceps rose more slowly, but continued to increase steadily beyond their mean levels of 8% and 1% at age 2 mo. There were well defined seasonal (within-year) cycles in prevalence of O. cuniculi and P. boughtoni that were generated evidently to a major degree by arrested development of larvae in fall and renewed development in late winter. It was hypothesized that renewed larval development was triggered (in February) in O. cuniculi by the seasonal rise of circulating pituitary gonadotrophins, and (in April) in P. boughtoni by the seasonal rise of gonadal androgens and estrogens. Indices to gonadal hormone levels in hares indicated that these increased most rapidly among males, and may have accounted for the higher prevalences of P. boughtoni in males during April-May. Neither T. pisiformis nor D. scapiceps exhibited conspicuous seasonal changes in prevalence. Maximum prevalence of T. pisiformis was attained at about 1 yr of age, whereas D. scapiceps increased among adult snowshoes through age 2 yr before stabilizing. Long-term (between-year) changes in prevalence of O. cuniculi, T. pisiformis, and D. scapiceps were correlated significantly with the cyclic hare population which declined from a peak in fall 1961 to a low in 1965-1966, rose to another peak by fall 1970, and declined again to a low in 1975. There was no detectable time lage between this "10-yr" cycle in hare density and the cycles of parasite prevalence among juveniles (less than 1 yr of age). Among adult hares, the cycle of O. cuniculi prevalence was likewise synchronous with that of the hare population, but the cycles of D. scapiceps and T. pisiformis lagged by approximately 1 and 2 yr, respectively. This lag in T. pisiformis prevalence was largely inexplicable to us. Our data on P. boughtoni were not suitable for analyses of between-year trends; nor were those for the fifth helminth, Taenia serialis (coenuri), because mean prevalence was less than 1% among both juveniles and adults. An apparent decline in T. serialis after the early 1950's, and its continued scarcity thereafter, paralleled a major change in numbers of one important definitive host--the red fox (Vulpes vulpes).(ABSTRACT TRUNCATED AT 400 WORDS)     

Modulated immune responsiveness associated with experimental Encephalitozoon cuniculi infection in BALB/c mice

Spleen cell blastogenesis to mitogens and antibody responses to sheep erythrocytes (sRBC) were tested in BALB/c mice with experimental E. cuniculi infections. Blastogenesis responses of spleen cells 1 week post-infection were significantly lower than normal to T-cell mitogens (Con A and PHA) and were unchanged in response to B-cell mitogens (LPS and PWM). After 2 weeks post-infection, the responses to T cell mitogens returned to normal. Mixing spleen cells from 1-week infected mice with cells from uninfected mice failed to reveal the presence of suppressor cells. Antibody responses to sRBC were significantly slower to develop in 1 week-infected mice compared with uninfected mice or mice infected 2 weeks earlier or at the same time as sRBC challenge. Infected mice displayed splenomegaly which was most pronounced 1 week post-infection and the differential spleen cell counts revealed the presence of lymphoblasts. Lymphohyperplasia appeared to cause the splenomegaly. No shifts in the proportion of Thy 1.2+ T cells, Ig+ B cells, or esterase-positive macrophages were detected. These results indicate that the immune system in BALB/c mice is depressed early during E. cuniculi infections.     

Sarcocystis and related organisms in Australian Wildlife: IV. Studies on Sarcocystis cuniculi in European rabbits (Oryctolagus cuniculus)

The role of the cat (Felis domestica) as a definitive host for Sarcocystis cuniculi of European rabbits (Oryctolagus cuniculus) was confirmed. It was shown that after dosing with sporocysts from cats, rabbits developed sarcocysts and these became infective for cats at not less than 93 days post-infection (p.i.). The earliest infection detected was at 142 days p.i. Infected muscle from an experimental rabbit did not transmit Sarcocystis when fed to other rabbits. Microscopically, sarcocysts in European rabbits (O. cuniculus) were morphologically indistinguishable from those in cottontail rabbits (Sylvilagus floridanus).     

Parasitism in a declining population of snowshoe hares

Prevalence and intensity of six endoparasites were determined in 346 snowshoe hares (Lepus americanus) obtained at Rochester, Alberta, during December-April 1981-1982, the second winter of a cyclic population decline. The data were analyzed for (1) differences among host sex and age classes, and among months and sample sources, and (2) evidence that parasitism was of demographic significance to the hare population. Prevalence and intensity of Obeliscoides cuniculi were consistently highest among adult hares, but rose most sharply from February to March among juveniles. In contrast, prevalence and intensity of Nematodirus triangularis were highest among juveniles; prevalence reached 90-100% by January, whereas intensity continued to rise through April. Prevalence and intensity of both Trichuris leporis and Protostrongylus boughtoni were highest also among juvenile hares; neither parameter exhibited a definite trend over time. Prevalences of Taenia pisiformis (cysticerci) and Eimeria spp. were unrelated to sex, age or month; but Taenia intensity was highest among juveniles, and Eimeria intensity tended to decrease from December to April. Intensities of Nematodirus, Protostrongylus and Eimeria were higher in male hares than in females. Prevalence and intensity were correlated directly in Obeliscoides, Nematodirus, Trichuris and Eimeria. Hares that died during trapping and handling, or from natural predation, had greater intensities of Obeliscoides than did animals killed on purpose. There was no indication, however, that risk of death was increased by the other parasitic infections. Age-related immune responses to parasitism (except Obeliscoides) were evidenced by reduced or stabilized prevalence and/or intensity among older hares. A multiple-regression model predicted depressed body weight with increasing intensities of Nematodirus, Trichuris or Protostrongylus. Other body-condition and reproductive indices were unassociated with parasite intensities. Within the hare population, Obeliscoides, Trichuris, Protostrongylus and Taenia had overdispersed distributions (typical of many endoparasites) that did not differ from a negative binomial. The frequency with which each possible combination of helminth species occurred within individual hares was consistent with the assumption that such infections occurred independently. There was no compelling reason to believe parasitism was a significant factor in the overwinter decline of this population of snowshoe hares.     

Multiscale habitat relationships of snowshoe hares (Lepus americanus) in the mixed conifer landscape of the Northern Rockies,USA: Cross‐scale effects of horizontal cover with implications for forest management

Snowshoe hares (Lepus americanus) are an ecologically important herbivore because they modify vegetation through browsing and serve as a prey resource for multiple predators. We implemented a multiscale approach to characterize habitat relationships for snowshoe hares across the mixed conifer landscape of the northern Rocky Mountains, USA. Our objectives were to (1) assess the relationship between horizontal cover and snowshoe hares, (2) estimate how forest metrics vary across the gradient of snowshoe hare use and horizontal cover, and (3) model and map snowshoe hare occupancy and intensity of use. Results indicated that both occupancy and intensity of use by snowshoe hares increased with horizontal cover and that the effect became stronger as intensity of use increased. This underscores the importance of dense horizontal cover to achieve high use, and likely density, of snowshoe hares. Forest structure in areas with high snowshoe hare use and horizontal cover was characterized as multistoried with dense canopy cover and medium‐sized trees (e.g., 12.7–24.4 cm). The abundance of lodgepole pine (Pinus contorta) was associated with snowshoe hare use within a mixed conifer context, and the only species to increase in abundance with horizontal cover was Engelmann spruce (Picea engelmannii) and subalpine fir (Abies lasiocarpa). Our landscape‐level modeling produced similar patterns in that we observed a positive effect of lodgepole pine and horizontal cover on both occupancy and use by snowshoe hares, but we also observed a positive yet parabolic effect of snow depth on snowshoe hare occupancy. This work is among the first to characterize the multiscale habitat relationships of snowshoe hares across a mixed conifer landscape as well as to map their occupancy and intensity of use. Moreover, our results provide stand‐ and landscape‐level insights that directly relate to management agencies, which aids in conservation efforts of snowshoe hares and their associated predators.     

Life history and pathogenesis of Gallegostrongylus australis (Nematoda: Angiostrongylidae) in muridae

Gallegostrongylus australis Spratt, Haycock & Walter, 2001 (Nematoda: Angiostrongylidae) developed in Deroceras panormitanum, Lehmannia nyctelia, L. flava and Milax gigates (Gastropoda). The first moult occurred at 18-19 days after infection (DAI) and the second moult at 28 DAI. Larvae were infective to experimental murid definitive hosts at 35 DAI. In experimentally infected Rattus fuscipes larvae moulted L3-4 at 3 DAI and L4-5 at 6-7 DAI. Patency in R.fuscipes, R. lutreolus, R. norvegicus and R. rattus occurred 27-64 DAI and duration varied from 7-392 days. Histopathological changes in the lungs of R. lutreolus and development of debilitating clinical signs, in contrast to R. fuscipes, suggests that the former host-parasite relationship may be the more recent one but other traits suggest the opposite. Patent infections were established in some wild R. rattus and some laboratory R. norvegicus but not in wild M. domesticus, laboratory M. musculus, rabbit, Oryctolagus cuniculus, and marsupial bandicoot, Isoodon macrourus.     

Diagnosis of encephalitozoonosis in experimentally infected rabbits by intradermal and immunofluorescence tests.

The indirect immunofluorescence antibody test was performed on serial blood samples from eight young New Zealand White rabbits with experimental encephalitozoonosis. The test showed seroconversion in six of the eight infected rabbits by the 8th day after inoculation and in all rabbits by the 15th day. Antibody titers reached a peak by about the 36th day after inoculation and remained significantly elevated until the termination of the experiment at 84 days after inoculation. None of four sham-inoculated rabbits showed an immunofluorescence response by the 60th day after inoculation. Immunofluorescence and intradermal test responses were compared before infection and at the 60th day after inoculation in a total of 32 experimentally infected rabbits. Both tests were equally effective (100%) in detecting infected animals. Six of eight (first group) and 22 of 24 (second group) experimentally infected rabbits were confirmed histologically to have lesions compatible with encephalitozoonosis. No cross reactions were observed between Encephalitozoon cuniculi and Toxoplasma gondii, Eimeria perforans, or Eimeria stiedai by intradermal test or immunofluorescence test.     

In utero transmission of Encephalitozoon cuniculi strain type I in rabbits

Pregnant rabbits were serologically diagnosed as having been infected with Encephalitozoon cuniculi. At necropsy at 28 days of gestation, does, placentas and fetuses were found to be infected with E. cuniculi strain type I as evidenced by using the nested-polymerase chain reaction (PCR) technique, thereby confirming vertical transplacental transmission.     

Winter Habitat Selection by Canada Lynx in Maine: Prey Abundance or Accessibility?

Abstract: We related winter habitat selection by Canada lynx (Lynx canadensis), relative abundance of snowshoe hares (Lepus americanus), and understory stem densities to evaluate whether lynx select stands with the greatest snowshoe hare densities or the greatest prey accessibility. Lynx (3 F, 3 M) selected tall (4.4-7.3 m) regenerating clear-cuts (11-26 yr postharvest) and established partially harvested stands (11-21 yr postharvest) and selected against short (3.4-4.3 m) regenerating clear-cuts, recent partially harvested stands (1-10 yr), mature second-growth stands (>40 yr), and roads and their edges (30 m on either side of roads). Lynx selected stands that provided intermediate to high hare density and intermediate cover for hares (i.e., prey access) but exhibited lower relative preference for stand types with highest hare densities where coniferous saplings exceeded 14,000 stems/ha.     

Biological control of Dutch elm disease: Bacillus thuringiensis as a potential control agent for Scolytus scolytus and S. multistriatus

J assim , H.K., F oster , H.A. & F airhurst , C.P. 1990. Biological control of Dutch elm disease: Bacillus thuringiensis as a potential control agent for Scolytus scolytus and S. multistriatus. Journal of Applied Bacteriology 69 , 563–568.
The effects of exposing fifth instar larvae of Scolytus scolytus and S. multistriatus to spore suspensions of Bacillus spp. were investigated. Bacillus thuringiensis ser 3a, 3b increased the mortality of larvae cultured on an artificial medium from approximately 20% in control cultures to over 80% in cultures exposed to the bacteria. The mortality was dose-dependent for S. multistriatus and the approximate LC₅₀ value was 2.2 times 10³ spores/ml. Different serotypes of B. thuringiensis caused different levels of mortality: H6 produced the highest mortality and H1 the lowest. Bacillus alvei and B. cereus were also pathogenic but B. megaterium was not. The results are discussed in relation to the mechanism of pathogenicity and the potential for the use of B. thuringiensis for the control of the vectors of Dutch elm disease.     

Efficacy of an essentifal oil of Cinnamomum zeylanicum against Psoroptes cuniculi

The aim of the present study was to investigate the in vitro and in vivo acaricidal effects of an essential oil of Cinnamomum zeylanicun leaves on Psoroptes cuniculi, a mange mite. In vitro, 2.5 ml of the essential oil diluted at different concentrations, from 10% to 0.03%, in paraffin oil were added to Petri dishes containing all motile stages of P. cuniculi. Mites mortality observed in these dishes was compared with that observed in untreated and treated (AcaCerulen R) control plates. In vivo, one group of six P. cuniculi infected rabbits was topically treated two times at seven days interval with two ml of the essential oil at the concentration of 2.5% in paraffin oil and compared with untreated and treated (AcaCerulen R) control groups of six rabbits each. After 24 h of contact, all concentrations of essential oil between 0.10 and 10% showed a good in vitro acaricidal efficacy if compared with the untreated controls (p<0.01), but only the concentrations between 0.16 and 10% turned out as active as the drug. In vivo, the treatment with the essential oil cured all infested rabbits and no statistical differences were observed with the treated control group.     

Serum IgG, IgM, and C3 levels in Schistosoma japonicum infected rabbits

New Zealand white rabbits were infected with 250 or 500 Schistosoma japonicum cercariae of Philippine-Leyte strain. Following the initial pre-infection bleed, blood was collected 2, 4, 6, 8, 11, 14, 17, 20, 23, 26, 29, and 32 weeks post-infection, and IgG, IgM, and C3 levels were assayed in the serum samples by single radial immunodiffusion. IgG and IgM achieved peak levels at 14 weeks post-infection and began to decrease in concentration by 26 weeks. At 32 weeks, some of the infected rabbits exhibited significantly reduced IgG and IgM levels which approached the concentrations assayed in the control animals. The infected animals demonstrated significantly elevated C3 levels (p less than or equal to 0.001) during the 6th to 26th weeks post-infection, with the exception of the 20th week.     

The immunoperoxidase test diagnosis of Encephalitozoon cuniculi in rabbits.

Sera collected from both naturally and artificially infected rabbits were found to show excellent correlation when examined for the presence of Encephalitozoon cuniculi antibodies using the immunoperoxidase and immunofluorescence tests. Out of 85 randomly selected rabbits, 21 were found to be serologically positive using both the tests. However, lesions which could be attributed to E. cuniculi infection were only demonstrated in 16.     

Overwinter mass loss of snowshoe hares in the Yukon: starvation, stress, adaptation or artefact?

1. Overwinter mass loss can reduce energetic requirements in mammals (Dehnel's phenomenon). Alternatively, mass loss can result from food limitation or high predation risk. 2. We use data from fertilizer, food-supplementation and predator-exclusion experiments in the Yukon during a population cycle from 1986 to 1996 to test the causes of overwinter mass loss by snowshoe hares (Lepus americanus). In all years, some hares on control sites gained mass overwinter. During the increase phase the majority gained mass, but in all other phases the majority lost mass. 3. Snowshoe hares weighing <1000 g in autumn always gained mass overwinter, as did the majority that weighed 1000-1400 g. Hares weighing >1800 g in autumn usually lost mass. 4. Snowshoe hares on the predator-exclosure + food site gained mass overwinter in all years. Hares on the food-supplementation sites lost mass during the decline but gained mass in all other phases. Fertilization had little effect on mass dynamics. 5. Snowshoe hares were more likely to lose mass during winters with low survival rates. Snowshoe hares on the predator-exclosure treatments were more likely to gain mass than were hares on control sites. 6. Overwinter mass loss was correlated with maximum snow depth. At equivalent snow depths, hares on food-supplemented areas lost 98 g (+/- 14.6 SE) less on average than hares on the controls and predator-exclosure treatment. 7. Bone-marrow fat was related to body mass and cause of death. Small hares had the lowest marrow fat. Hares killed by humans had higher marrow fat than those killed by predators; hares that simply died had the lowest marrow fat. Hares on food-supplemented sites had the highest kidney and marrow fat. 8. Overwinter-mass loss for snowshoe hares is explained interactively by winter conditions, food supply, predation risk and autumn mass. Some snowshoe hares lost mass overwinter in all years and on all treatments, suggesting that reducing body mass may facilitate survival, especially in cases where foraging costs are high energetically or increase predation risk.     

Roles of host species, geographic separation, and isolation in the seroprevalence of jamestown canyon and snowshoe hare viruses in newfoundland

California serogroup viruses, including Jamestown Canyon virus (JCV) and snowshoe hare virus (SSHV), are mosquito-borne members of the Bunyaviridae family and are endemic across North America. These arboviruses are potential pathogens which occasionally cause neuroinvasive disease in humans and livestock. A neutralization assay was used to document JCV and SSHV seroprevalence using blood collected from a variety of domestic and wildlife host species. These species were sampled in an island setting, Newfoundland, which contains diverse ecoregions, ecological landscapes, and habitats. Seroprevalence rates for each virus differed significantly among host species and within certain species across different geographic areas. JCV was significantly associated with large mammals, and SSHV was significantly associated with snowshoe hares. Seroprevalence rates in the 5 species of animals tested for prior exposure to JCV ranged from 0% in snowshoe hares to 64% in horses. Seroprevalence rates for SSHV ranged from less than 1% in bovines to 55% in all snowshoe hares. The seroprevalence of SSHV differed significantly (P < 0.05) among hares occupying the discrete habitats of watersheds separated by 14 to 35 km. Cattle on farms in boreal forest landscapes displayed significantly higher JCV seroprevalence (P < 0.001) than those on farms located in seacoast landscapes. Lifelong geographic isolation of cattle to insular Newfoundland was associated with significantly lower JCV seroprevalence (P < 0.01) than that for cattle which had lived off-island.     

Powassan virus infection in snowshoe hares (Lepus americanus)

Sera from snowshoe hares (Lepus americanus) trapped near Rochester, Alberta, Canada were tested for Powassan virus antibody by the constant virus/serum dilution neutralization test. Of 1264 serum samples tested, 137 had an antibody titer of at least 1:4 for Powassan virus. Ten hares were inoculated with Powassan virus in the laboratory. Viremia lasted 4-5 days and ceased with the appearance of Powassan antibody in the serum. Neutralizing antibody reached a peak titer of 1:119 on day 15 post-inoculation and was still detectable 13 months post-inoculation.     

Population genetic structure of the cyclic snowshoe hare (Lepus americanus) in southwestern Yukon,Canada

Spatial population structure has important ecological and evolutionary consequences. Little is known about the population structure of snowshoe hares (Lepus americanus), despite their ecological importance in North American boreal forests. We used seven variable microsatellite DNA loci to determine the spatial genetic structure of snowshoe hares near Kluane Lake, Yukon during a cyclic population peak. We sampled 317 hares at 12 sites separated by distances ranging from 3 to 140 km, and used 46 additional samples from Alaska and Montana. The level of genetic variation was high (13.4 alleles/locus, 0.67 expected heterozygosity) and the distribution of alleles and genotypes was not homogeneous across the sites. The degree of differentiation was low among Yukon sites (FST = 0.015) and between Yukon and Alaska (FST = 0.012), but the Montana site was highly differentiated (FST = 0.20). A weak pattern of isolation by distance was found over the Yukon study area, with an indication that local genetic drift may be important in shaping the regional genetic structure. Landscape barriers expected to influence gene flow did not consistently affect genetic structure, although there was evidence for a partial barrier effect of Kluane Lake. The high level of inferred gene flow confirms that snowshoe hare dispersal is widespread, successful and equal between the sexes. A stepping-stone model of gene flow, potentially influenced by the synchronous density cycle, appears to best explain the observed genetic structure. Our results suggest that despite their dramatic fluctuations in density, snowshoe hares in the northern boreal forest have a large evolutionary effective population size and are not strongly subdivided by either physical or social barriers to gene flow.     

Inhibition phenomena mechanisms in experimental obeliscoidosis in rabbits. II. Local and systemic antibody responses

A series of experiments was carried out using adult outbred Polish race rabbits of both sexes infected, during spring or autumn, with 10,000 larvae of Obeliscoides cuniculi, either fresh or stored at 4 degrees C. Extracts of mucosal proteins and bile were collected at postmortem 6 or 12 weeks after infection. Antibody levels were determined in antisera, bile and stomach mucosa by haemagglutination and precipitation tests. Local antibody responses were demonstrated in the stomach and bile, and reactions were obtained with the tissue fluids by haemagglutination and precipitation tests with worm antigens and ES products. Additionally, some specific immunological response was observed in the circulation during the primary infection. These results suggest a clear-cut relationship between increased levels of these antibodies and either larval inhibition or worm expulsion during O. cuniculi infections.