Batracholandros salamandrae (Oxyuroidea: Pharyngodonidae) in Endemic Salamanders (Amphibia: Plethodontidae) of the Trans-Mexican Volcanic Belt: Host Range Wide Distribution or Cryptic Species Complex?

Salamanders of the tribe Bolitoglossini Hallowell are a highly diversified group of amphibians, and their helminth parasite fauna has been scarcely studied. Some species of plethodontid salamanders distributed along the Trans-Mexican Volcanic Belt, in central Mexico, were sampled, and their helminth parasites were recovered for taxonomic identification. Specimens of a pharyngodonid nematode from 2 species of bolitoglossines of the genus Pseudoeurycea Taylor were morphologically identified as Batracholandros salamandrae (Schad, 1960) Petter and Quentin, 1976. These specimens were studied in further detail through light and scanning electron microscopy and were sequenced for 2 ribosomal genes and 1 mitochondrial gene to test the hypothesis of whether B. salamandrae is a species widely distributed in salamanders across the Nearctic biogeographic region, or if it represents a cryptic species complex. Our molecular results revealed that these specimens consisted of 2 genetic lineages in concordance with host species, although with slight morphological differences among specimens in each of them. A thorough study, including the generation of molecular data from individuals from other areas of North America, and the examination of type specimens, is required to test the reliability of these morphological differences and to corroborate the species identity of the 2 genetic lineages.

Immunomodulatory effect of Syphacia obvelata in treatment of experimental DSS-induced colitis in mouse model.

The ability of helminth parasite infections to manipulate the immune system of their host towards T regulatory responses has been proposed to suppress the inflammatory response. The aim of this study was to investigate the protective and therapeutic effect of Syphacia obvelata in the treatment of experimental DSS -induced colitis. 50 male C57BL/6 mice were divided into 5 groups: healthy uninfected controls, DSS colitis, receiving only S. obv, preventive (S. obv + DSS) and therapeutic group (DSS + S.obv). Colitis intensity was investigated by measuring body weight changes, stool consistency/bleeding and colon length. To evaluate the immune responses induced by this nematode, TNF-α, IL-10, IL-17, IFN-γ and expressing of FoxP3+ T cells were measured in mesenteric lymph nodes and Peyer's patches cells. Mice in preventive and therapeutic groups treated with S. obv egg significantly ameliorated the severity of the DSS colitis, indicated by the reduced disease manifestations, improved histopathological scores correlated with the up regulation of Treg responses and down regulation of proinflammatory cytokines. S. obv can prevention and reverse on-going murine DSS colitis. The data suggest that induction of Tregs and change in cytokine profiles during helminthic therapies were responsible for reversed inflammatory events in IBD.

Syphacia muris infection in rats attenuates colorectal carcinogenesis through oxidative stress and gene expression alterations. Implications for modulatory effects by Bryostatin-1.

Accumulating evidence suggest that some infectious agents may interfere in the natural progression of neoplasia. This study examined the association between chronic infection with adult Syphacia muris parasites and 1,2-dimethylhydrazine (DMH)-induced colorectal carcinogenesis in rats. In addition, the conceivable therapeutic effect of Bryostatin-1, a potent extract of the marine Bryozoan, Bugulane ritina, was investigated against this combined effect.DMH administration has induced aberrant crypt foci (ACF), surrogate biomarkers for colorectal carcinogenesis, while the S. muris infection combined with DMH has significantly increased the total numbers of ACF. Nonetheless, treatment with Bryostatin-1 after infection has significantly reduced the ACF numbers particularly larger ones. This inhibition was concomitant with significant inhibition in the immunohistochemical levels of the ki67, Caspase-3 and IgM levels in colorectal epithelium, as well as serum levels of IgM and IgG. Additionally, treatment with Bryostatin-1 after S. muris + DMH has modulated enzymatic antioxidative markers levels of superoxide dismutase and catalase as well as the non-enzymatic antioxidant markers levels of reduced glutathione, lipid peroxidation, nitric oxide and total antioxidant capacity. Further, treatment with Bryostatin-1 has down-regulated the mRNA expression levels of COX-2 and APC genes in colorectal mucosa. In conclusion, infection with S. muris during colorectal carcinogenesis has significantly modulated the oxidative stress markers in the colorectum, while treatment with Bryostatin-1 has exerted significant curative potential. A mechanism could be explained that Bryostatin-1 treatment has reduced oxidative stress markers activities along with affecting host to parasite immunity possibly leading to changes in the COX-2 and APC expression, retarding cellular proliferation and subsequently reducing the colorectal carcinogenesis events.

Syphacia obvelata (Nematode, Oxyuridae) infecting laboratory mice Mus musculus (Rodentia, Muridae): phylogeny and host-parasite relationship.

Syphacia obvelata is a pinworm nematode parasite infecting man and laboratory animals in high abundance. This parasitological study was carried out during the period of March 2014-February 2015 to investigate the helminth parasites infecting the laboratory mice Mus musculus in the Animal House at Cairo University, Egypt. The prevalence of S. obvelata in M. musculus was 75.0 %. The extent of infection with S. obvelata is analyzed according to the sex of the host mice. It was shown that the prevalence of male infection was greater than female worms. Morphological characterization revealed that the present Oxyurid species possesses a rounded cephalic end with less developed lips, esophagus divided into cylindrical corpus, and globular bulb supported internally with valvular apparatus; three mamelons are located at the ventral surface with a single chitinized spicule and a gubernaculum provided with an accessory hook in males, and ovijector apparatus opens ventrally by the vulva surrounded by protruded lips in female worms. Body of the male was 0.623-1.130 (0.830 ± 0.11) mm long and 0.092-0.130 (0.110 ± 0.01) mm wide; the esophagus was 0.164-0.280 (0.210 ± 0.01) mm long; the nerve ring and excretory pore are located at 0.035-0.132 (0.073 ± 0.01) and 0.087-0.191 (0.145 ± 0.01) mm from the anterior end, respectively, while the female measured 2.930-4.650 (3.540 ± 0.1) mm long and 0.120-0.232 (0.156 ± 0.001) mm wide; the esophagus was 0.213-0.410 (0.342 ± 0.01) mm long; the nerve ring, excretory pore, and vulval opening are located at 0.026-0.157 (0.121 ± 0.01), 0.134-0.243 (0.195 ± 0.01), and 0.323-0.632 (0.546 ± 0.11) mm from the anterior end, respectively; eggs measured 0.120-0.139 (0.129 ± 0.001) mm long and 0.030-0.052 (0.045 ± 0.001) mm wide. It compared morphometrically with other Syphacia species described previously and showed little differences in measurements. Molecular characterization based on small subunit ribosomal DNA (rDNA) was done to confirm the obtained morphological and morphometric results. A preliminary genetic comparison between SSU rDNA of the present parasite and other species of Oxyuridae places it as a putative sister taxon to other S. obvelata.

Diagnosis of the pinworm Syphacia muris in the Wistar rat Rattus norvegicus.

This study aimed to compare three qualitative parasitological methods for the diagnosis of Syphacia muris infection in 30 Wistar rats (Rattus norvegicus) infected naturally. Methods of spontaneous sedimentation (Hoffman, Pons and Janer, or HPJ) and spontaneous flotation (Willis) for faecal samples and a method of taping (Graham) were performed and compared. The Graham and Willis methods were more sensitive than the HPJ method (P< 0.05). The Graham method was able to detect S. muris eggs in 100% of the samples. Eggs were detected in 83% and 60% of the samples using the Willis and HPJ methods, respectively. Method choice is important for screening for parasites of rats kept under laboratory conditions, as accurate diagnosis helps prevent future environmental contamination and infection. We concluded that the Graham method was the most efficient of those tested in this study for detection of S. muris infection in rats. This method is also rapid, inexpensive and practical, and should be implemented as a necessary measure for infection control.

The effect of Syphacia muris on nutrient digestibility in laboratory rats.

This study was carried out to investigate how pinworm infection in rats affects nutrient digestibility in the hosts. Twenty-four male outbred Wistar rats were randomly divided into two groups of 12 rats each. The rats from the first group (GI) were kept in cages with bedding containing pinworm eggs, and the second (control) group (GII) were kept in a separate room in clean, uncontaminated filter-top cages. The animals were put into individual metabolic cages later. Metabolic trials lasted five days and records of animal weight, food ingestion, and faecal weight were taken daily. Based on laboratory analysis of the feed and faecal nutrient content, digestibility values were determined. On day 15 of the experiment, the animals were euthanized. Although Syphacia muris were found in all rats from the GI group, animals exhibited no clinical signs. In our experiment, S. muris infection reduced the overall digestibility of all measured nutrients (P < 0.01). The most significant differences in digestibility were observed in the case of crude fibre and mineral matter (P < 0.01).

Characterization of rat pinworm (Syphacia muris) epidemiology as a means to increase detection and elimination.

Rodent pinworms persist in many institutions, suggesting deficiencies in eradication and diagnostic processes. When pinworms are detected, treatment success is common, but false-negative test results during health surveillance or after treatment likely contribute to the continued presence of this parasite. PCR testing is not always practical, and increased information regarding the life cycle and general epidemiology of pinworm infestations could improve the sensitivity of traditional nonPCR detection methods and improve eradication efforts. We therefore investigated a pinworm (Syphacia muris) infestation in Sprague-Dawley rats (Rattus norvegicus) to develop a more accurate testing strategy. In addition, we sought to determine the duration of egg viability by using an in vitro hatching protocol to assess environmental persistence. Finally, we tested the ovicidal efficacy of a disinfectant used at our institution. Eggs were shed in higher numbers in the midafternoon as compared with other times of the day, and the sex of the host had no consistent effect on egg shedding. Egg shedding showed periodicity over time, with shedding decreasing to 0 at 2- to 3-wk intervals. Neither cecal examination nor tape tests alone reliably predicted pinworm infestation, and results of the 2 tests did not necessarily coincide. Eggs aged for as long as 7 mo remained viable, indicating a potential for recontamination from the environment. Finally, gaseous chlorine dioxide was an effective ovicidal agent, with a kill rate of 99.7%. These results suggest that strategies for S. muris eradication can be optimized to increase detection and elimination.

Nematodes from the caecum and colon of Pogonomys (Muridae: Anisomyini) from Papua New Guinea with the descriptions of a new genus of Oxyuridae (Nematoda: Oxyurida) and a new species of Trichuridae (Nematoda: Enoplida).

Nematodes, comprising 2 species, a new genus from the family Syphaciidae and a new species from the family Trichuridae were collected from the lower digestive tracts of 4 species of Pogonomys; P. championi, Flannery (12 individuals), P. loriae, Thomas (14 individuals), P. macrourus, (Milne Edwards) (19 individuals) and P. sylvestris, Thomas (27 individuals) from Papua, Indonesia and Papua New Guinea. Pogonomicola rugala n. gen., n. sp. differs from all other genera in the Sypaciidae in having cervical alae with numerous folds and a single weakly defined mamelon. Trichuris germani n. sp. differs from all congeners, including the cosmopolitan T. muris, the only other trichurid reported from the region, by the lengths of the spicules and vagina, the ratio of anterior to posterior body length and the number of convolutions of the testis. The genus Pogonomys, with four species from four nematode families had a relatively rich helminth fauna in the lower digestive tract compared to other ansomyins studied. The Oxyuridae, with three genera comprising 5 species was the dominant group found in the lower digestive tract of the Anisomyini, indicating the possibility that the isolation of the old endemic rodents in New Guinea has been associated with a period of coevolution between anisomyin hosts and their syphaciine parasites.

Total IgE as a serodiagnostic marker to aid murine fur mite detection.

Mites of 3 genera-Myobia, Myocoptes, and Radfordia -continue to plague laboratory mouse facilities, even with use of stringent biosecurity measures. Mites often spread before diagnosis, predominantly because of detection difficulty. Current detection methods have suboptimal sensitivity, are time-consuming, and are costly. A sensitive serodiagnostic technique would facilitate detection and ease workload. We evaluated whether total IgE increases could serve as a serodiagnostic marker to identify mite infestations. Variables affecting total IgE levels including infestation duration, sex, age, mite species, soiled-bedding exposure, and ivermectin treatment were investigated in Swiss Webster mice. Strain- and pinworm-associated effects were examined by using C57BL/6 mice and Swiss Webster mice dually infested with Syphacia obvelata and Aspiculuris tetraptera, respectively. Mite infestations led to significant increases in IgE levels within 2 to 4 wk. Total IgE threshold levels and corresponding sensitivity and specificity values were determined along the continuum of a receiver-operating characteristic curve. A threshold of 81 ng/mL was chosen for Swiss Webster mice; values above this point should trigger screening by a secondary, more specific method. Sex-associated differences were not significant. Age, strain, and infecting parasite caused variability in IgE responses. Mice exposed to soiled bedding showed a delayed yet significant increase in total IgE. Treatment with ivermectin reduced total IgE levels within 2 wk. Our data suggest that increases in total IgE in Swiss Webster and C57BL/6 mice warrant investigation, especially because mite infestations can rapidly elevate total IgE levels. We propose that using total IgE levels routinely in serologic panels will enhance biosecurity.

Using social networks to deduce whether residents or dispersers spread parasites in a lizard population.

1. Heterogeneity of host behaviour can play an important role in the spread of parasites and pathogens around wildlife populations. Social networks have previously been suggested to represent transmission pathways within a population, but where the dynamics of host-parasite interactions are difficult to observe, networks may also be used to provide insights into transmission processes. 2. Pygmy bluetongue lizards, Tiliqua adelaidensis, occupy individual territories, live exclusively in burrows constructed by spiders in Australian native grasslands and are hosts to a tick, Bothriocroton hydrosauri, and a nematode, Pharyngodon wandillahensis. 3. On five monthly occasions, the locations of all individual lizards in three study plots were used to construct weighted, undirected networks based on proximity of adjacent burrows. 4. The networks were used to explore alternative hypotheses about the spread of each parasite through the population: that stable population members that remained in the same burrow over the study period played a major role in influencing the pattern of infection or that dispersing individuals played a more significant role. 5. For ticks, host individuals that were infected were more connected in the network than uninfected hosts and this relationship remained significant for connections to residents in the population, but not for connections to dispersers. 6. For nematodes, infected and uninfected hosts did not differ in their overall strength of connection in the network, but infected hosts were more connected to dispersers than were uninfected hosts, suggesting that lizards moving across the population are the major agents for the transmission of nematodes. 7. This study shows how network analyses can provide new insights into alternative pathways of parasite spread in wildlife populations, where it is difficult to make direct observations of transmission-related behaviours.

Does home range use explain the relationship between group size and parasitism? A test with two sympatric species of howler monkeys.

Group size is related to parasite infections in primates. This relationship probably reflects the fact that group size is associated with body contact between group members and with contact with contaminated items in the environment. The latter is highly associated with range use. In the present study we hypothesized that if infection by directly transmitted parasites (DTP) is mainly determined by the exposure of individuals to parasites that accumulate in the environment, and group size correlates negatively with the intensity of home range use, then smaller groups should be more infected by DTP. Additionally, groups that share a higher proportion of their home range with other groups should be more infected. To test our hypothesis we observed and collected fecal samples of two groups of Alouatta palliata (large group size) and two groups of A. pigra (small group size) that live sympatrically in a forest fragment located in Macuspana (Mexico). Group size was positively correlated with range area size and negatively correlated with the intensity of home range use. Range use variables were not related to either DTP prevalence or load. However, there were significant differences in DTP loads between groups, which were positively correlated with group size. Our results suggest that the intensity of home range use is a poor predictor of DTP infection parameters in groups with marked differences in size. Therefore, it is possible that the individual or combined effects of other ecological (e.g., microclimate), social (e.g., contact rate), or physiological (e.g., immune function) factors are more important in the dynamics of DTP in free-ranging primates.

Distribution and reproductive strategies of Gyrinicola batrachiensis (Oxyuroidea: Pharyngodonidae) in larvae of eight species of amphibians from Nebraska.

In total, 462 tadpoles and salamander larvae of 8 species were examined for the presence of Gyrinicola batrachiensis from 5 locations in Nebraska. Infection by G. batrachiensis occurred in tadpoles of Rana blairi , Rana catesbeiana, Rana pipiens, and Bufo woodhousii. Tadpoles of Hyla chrysoscelis , Spea bombifrons, and Pseudacris maculata and larvae of Ambystoma mavortium were not infected with G. batrachiensis. Population structure, defined as prevalence, mean abundance, and mean intensity of G. batrachiensis, varied among tadpoles of different amphibian species and was determined by collection locality, developmental period of tadpole hosts, amphibian species co-occurrence, and different reproductive strategies of G. batrachiensis , or a combination. Gyrinicola batrachiensis observed in all ranid tadpoles and B. woodhousii tadpoles from where bufonids were the only anuran species present, confirmed to the didelphic haplodiploidy and monodelphic parthenogenetic reproductive strategies, respectively. However, tadpoles of B. woodhousii that co-occurred with tadpoles of R. pipiens at Cedar Creek were inconsistent with these predictions and contained both male and didelphic female nematodes, but at a low mean intensity (1.61 ± 0.70). Didelphic female nematodes from B. woodhousii tadpoles at Cedar Creek only produced thick-shelled eggs, whereas nematodes in R. pipiens tadpoles had a high mean intensity (14.88 ± 23.83) from this location and contained both thick-shelled and thin-shelled eggs in their respective uteri. More importantly, adult female nematodes from tadpoles of R. pipiens and B. woodhousii from Cedar Creek were morphologically more similar to each other than to female nematodes recovered from tadpoles of other anuran species, other locations, or both. These data suggest that when strains of G. batrachiensis are shared by tadpoles of different amphibian species that differ in developmental period, the nematodes have an intermediate reproductive strategy in amphibian species, with tadpoles having short development.

Pinworm infection in laboratory mice in southern China.

The present investigation examined the prevalence and intensity of pinworm infection in laboratory mice from three laboratory animal centres in China's southern Guangdong Province between August 2008 and April 2009. A total of 301 laboratory mice representing BALB/c, Kunming (KM) and C57BL/6J breeds were examined and the worms were counted and identified according to existing keys and descriptions, and their specific identity was ascertained by polymerase chain reaction (PCR) amplification of the second internal transcribed spacer (ITS-2) of ribosomal DNA. While the BALB/c and C57BL/6J mice were not found to be infected with pinworms, postmortem examination of the KM mice revealed a prevalence of 46.7%. PCR amplification of ITS-2 rDNA and subsequent sequencing confirmed that the mice were infected with Syphacia obvelata. The results of the present investigation demonstrated that the prevalence of pinworm infection in laboratory mice was high in the Guangdong province, and integrated control strategies and measures should be implemented to prevent and control pinworm infection in laboratory mice.

Syphacia obvelata modifies mitogen-activated protein kinases and nitric oxide synthases expression in murine bone marrow cells.

Syphacia obvelata is a rodent nematode parasite with high prevalence in laboratory mice. In our previous work we have demonstrated that this gut-dwelling helminth induces significant hematopoietic changes, characterized by increased myelopoiesis and erythropoiesis in infected animals, and accompanied with altered reactivity of bone marrow hematopoietic progenitors to interleukin (IL)-17. In this study we extended these investigations by demonstrating that naturally acquired S. obvelata infection induces significant alterations in murine bone marrow cells manifested at the molecular level. Namely, S. obvelata infection induced sustained phosphorylation of the members of three major groups of distinctly regulated mitogen-activated protein kinases (MAPKs), the p38, the c-Jun amino-terminal kinase (JNK) and the extracellular signal-regulated kinase (ERK), as well as enhanced expression of mRNA for the inducible nitric oxide synthase (iNOS) in the bone marrow cells of infected animals. Furthermore, the infection interfered with the IL-17-mediated effects in bone marrow cells, since in normal mice IL-17 significantly enhanced phosphorylation of p38 MAPK and upregulated the expression of iNOS and the constitutive, endothelial (e)NOS mRNA, while in S. obvelata-infected animals IL-17 did not influence the MAPKs activation, but markedly down-regulated the expression of both NOS isoforms. The data obtained demonstrating that S. obvelata is able to manipulate signal transduction pathways in the hosts' bone marrow cells, pointed to the multiple layers of immunomodulatory ability of this pinworm parasite and highlighted the importance of working under pinworm-free conditions when using experimental murine models for immunohematopoietic investigations.

Eradication of Syphacia muris from food-restricted rats without environmental decontamination.

Rodent pinworms rarely cause clinical disease, but infestation can affect experimental results. Our facility maintained a colony of Wistar rats for behavioral pharmacology studies that had been infested with Syphacia muris for > 15 years. The laboratory in which the animals were housed encompassed several rooms and contained a variety of complex behavioral equipment, including > 60 operant chambers. Several prior attempts to eliminate the pinworms were unsuccessful because of inadequate duration of treatment and incomplete environmental decontamination. Many of the rats in this colony were food-restricted as part of behavioral studies. Pinworms were eliminated from these animals by treating them with 450 ppm fenbendazole-containing feed for 3 consecutive weeks followed by 6 weeks of alternating every other week with standard rodent diet. Rats not on food restriction protocols were treated on the same schedule with 150 ppm fenbendazole-containing feed. Environmental decontamination of eggs from the behavioral equipment was not attempted. One year after treatment, the colony has remained free of S. muris. We adapted previously published protocols to our situation, including the problem of food-restricted rats and unfeasible environmental decontamination, to eradicate S. muris from our colony.

Expanded geographical range, new host accounts, and observations of the nematode Gyrinicola batrachiensis (Oxyuroidea: Pharyngodonidae) in tadpoles.

We describe the first account of the nematode Gyrinicola batrachiensis in the gastrointestinal tracts of tadpoles of Bufo terrestris, Gastrophryne carolinensis, Hyla femoralis, H. squirella, Rana heckscheri, and R. utricularia. Infection by G. batrachiensis was also noted in tadpoles of R. catesbeiana and R. clamitans, species previously described as harboring these nematodes. These observations represent a major expansion of the known geographical range of G. batrachiensis to include the southeastern United States. In our study, female G. batrachiensis nematodes in ranid host species were didelphic, but females in B. terrestris tadpoles were monodelphic. Furthermore, only female nematodes were found in the latter host species. Such variations in nematode uterine morphology and sex ratios among these tadpole host species are in accordance with the apomictic and haplodiploid reproductive strategies previously reported for G. batrachiensis. These observations also support a generalized pattern relating G. batrachiensis reproductive modes and the life cycles of their tadpole hosts.

Correlated evolution between host immunity and parasite life histories in primates and oxyurid parasites.

Maturation time is a pivotal life-history trait of parasitic nematodes, determining adult body size, as well as daily and total fecundity. Recent theoretical work has emphasized the influence of prematurational mortality on the optimal values of age and size at maturity in nematodes. Eosinophils are a family of white blood cells often associated with infections by parasitic nematodes. Although the role of eosinophils in nematode resistance is controversial, recent work has suggested that the action of these immune effectors might be limited to the larval stages of the parasite. If eosinophils act on larval survival, one might predict, in line with theoretical models, that nematode species living in hosts with large eosinophil numbers should show reduced age and size at maturity. We tested this prediction using the association between the pinworms (Oxyuridae, Nematoda) and their primate hosts. Pinworms are highly host specific and are expected to be involved in a coevolutionary process with their hosts. We found that the body size of female parasites was negatively correlated with eosinophil concentration, whereas the concentration of two other leucocyte families-neutrophils and lymphocytes-was unrelated to female body size. Egg size of parasites also decreased with host eosinophil concentration, independently of female size. Male body size was unrelated to host immune parameters. Primates with the highest immune defence, therefore, harbour small female pinworms laying small eggs. These results are in agreement with theoretical expectations and suggest that life histories of oxyurid parasites covary with the immune defence of their hosts. Our findings illustrate the potential for host immune defence as a factor driving parasite life-history evolution.

Evaluation of coinfection with pinworms (Aspiculuris tetraptera, Dentostomella translucida, and Syphacia obvelata) in gerbils and mice.

Mongolian gerbils (Meriones unguiculatus) naturally infected with the nematode Dentostomella translucida and mice (Mus musculus) that were either pinworm-free or harboring either or both Aspiculuris tetraptera and Syphacia abvelata were crossinfected experimentally with these nematode species. Gerbils were susceptible to infections by S. obvelata and A. tetraptera from mice, whereas mice were resistant to infection by D. translucida from gerbils. The data presented are the first regarding coinfections with these three pinworms in gerbils.

Epizootiology of Syphacia obvelata from a domestic mouse population on the subantarctic Kerguelen Archipelago.

The effects of abundance, age, and sex of feral domestic mice Mus musculus domesticus on infections with the nematode parasite Syphacia obvelata were analyzed during a long-term study of the mouse population on Guillou Island (1.45 km2), a part of the subantarctic Kerguelen Archipelago. The population dynamics of the nematode did not follow the variation in host abundance. However, depending on the year, differences in pinworm abundance were found between the age classes and sex. Such patterns suggest that parasitic infections may have been modulated by host-intrinsic factors, e.g., either by the way of innate or adaptive immunity, rather than extrinsic factors, e.g., host abundance.

Worm burdens in outbred and inbred laboratory rats with morphometric data on Syphacia muris (Yamaguti, 1935) Yamaguti, 1941 (Nematoda, Oxyuroidea).

Syphacia muris worm burdens were evaluated in the rat Rattus norvegicus of the strains Wistar (outbred), Low/M and AM/2/Torr (inbred), maintained conventionally in institutional animal houses in Brazil. Morphometrics and illustration data for S. muris recovered from Brazilian laboratory rats are provided for the first time since its proposition in 1935.