A. W. Pike

Strategies for the avoidance of faeces by grazing sheep

Experiments were conducted to investigate which environmental cues were used by sheep when discriminating against patches of pasture contaminated with faeces. The influence of the spatial distribution of contaminated patches and the parasite infection status of sheep on avoidance of contaminated patches and ingestion of parasite larvae was also investigated. In experiment 1, sheep infected with the parasite Ostertagia circumcincta were given the opportunity to graze in uncontaminated or aggregated contaminated patches. Patch contamination comprised of either faeces from sheep infected with O. circumcincta larvae, faeces from uninfected sheep, or O. circumcincta larvae only. Infected sheep discriminated against faeces from parasite-infected animals and faeces from uninfected animals equally. Sheep did not discriminate against patches contaminated with parasite larvae only. In experiment 2, sheep infected with O. circumcincta and uninfected sheep grazed experimental plots with differing spatial patterns of faecal-contaminated patches, allowing animals the opportunity to forage in contaminated or uncontaminated patches of herbage. Plots were also grazed by infected and uninfected animals that were fistulated at the oesophagus to enable the collection of ingested herbage. Sheep spent a greater proportion of their time foraging in uncontaminated patches than in contaminated patches. Where patches were highly aggregated, infected animals spent a greater proportion of total grazing time in uncontaminated patches than did uninfected animals, and grazed uncontaminated patches for longer on each sampling occasion. On grazing plots where all patches were contaminated, the difference between the numbers of larvae isolated from pasture herbage and ingested herbage was greatest for infected animals. In this situation, infected animals avoided parasites most. On grazing plots consisting of both contaminated and uncontaminated patches, the difference between the numbers of larvae isolated from pasture herbage and ingested herbage was greatest for uninfected animals. In this situation, uninfected animals were most effective at parasite avoidance as they consumed fewer parasite larvae relative to what was available on pasture.

Leucocyte migration in rainbow trout (Oncorhynchus mykiss [Walbaum]): Optimization of migration conditions and responses to host and pathogen (Diphyllobothrium dendriticum [Nitzsch]) derived chemoattractants

A rainbow trout leucocyte-derived chemoattractant(s) was prepared and tested as a stimulant of leucocyte migration. It was used to optimize an in vitro leucocyte migration assay using a 48-well micro chemotaxis chamber. This assay has subsequently been used to test the chemoattractant activity of antigen extracts from the tegument of Diphyllobothrium dendriticum plerocercoids and conditioned medium obtained after in vitro maintenance of live plerocercoids. Leucocytes were found to have an increased directional motility (chemotactic response) to the host-derived chemoattractant(s) but a random increased motility (chemokinetic response) following stimulation/contact with parasite-derived antigens.

Development and survival of the free-living stages of Trichostrongylus tenuis , a caecal parasite of red grouse Lagopus lagopus scoticus

In the laboratory, yields of infective 3rd-stage larvae of Trichostrongylus tenuis were determined by temperature when moisture was adequate. On the moor, eggs in caecal faeces did not develop to infective larvae during the winter. In summer, development did occur and yields of infective larvae were related to temperature: greatest yields were obtained when mean monthly soil surface temperatures ranged between 7.6 and 10.3 degrees C. Rainfall was unimportant, as was desiccation. During summer the mean monthly mortality of infective larvae was 44% but over winter survival was negligible.

Sequential development of the immune response in rainbow trout [Oncorhynchus mykiss (Walbaum, 1792)] to experimental plerocercoid infections of Diphyllobothrium dendriticum (Nitzsch, 1824).

Development of the inflammatory response of rainbow trout to experimental infections with Diphyllobothrium dendriticum plerocercoids is described using light and electron microscopy. The cellular response to plerocercoids occurred within 2 weeks post-infection (p.i.). This was followed by an increase in leucocyte numbers during weeks 3-6 p.i., with full encapsulation of plerocercoids by week 6 p.i. Neutrophils were the first leucocytes to engage the developing plerocercoid, followed by large influxes of macrophages which transformed into epithelioid cells. With longer times p.i. the accumulation of different leucocyte types increased, and a blood vascular network developed. Full development of the composite cyst was characterized by fibroplasia, particularly at the periphery of the cyst, and the subsequent deposition of a collagenous tissue matrix. Enzyme-linked immunosorbent assay (ELISA) examination of serum samples taken over the 20 week period showed that specific anti-D. dendriticum antibody titres were first detected at 5 weeks p.i. and increased to a maximum by 11 weeks p.i.

Rainbow trout [Oncorhynchus mykiss (Walbaum, 1792)] leucocyte interactions with metacestode stages of Diphyllobothrium dendriticum (Nitzsch, 1824), (Cestoda, Pseudophyllidea)

Procercoids of Diphyllobothrium dendriticum were incubated for 5 or 24 h with rainbow trout head kidney leucocyte suspension in vitro , in the absence or presence of complete and/or incomplete (heat inactivated) normal or specific immune serum. Neutrophils and macrophages were the predominant leucocytes that were found to adhere to the procercoid tegument, although a third unidentified leucocyte type was also seen. Leucocyte adherence was considerably increased by the presence of immune serum, indicating a possible interaction between the non-specific and specific immune response in the host inflammatory reaction to this parasite. Indeed, it was only in the presence of immune serum that damage to the procercoid tegument occurred. Production of both hydrogen peroxide and superoxide anion from macrophages was induced by antigen extracts from plerocercoids of D. dendriticum , prepared either by freezing and thawing specimens or by culturing live plerocercoids in vitro to obtain a conditioned medium. The possibility that reactive oxygen species contribute to the damage observed in the adherence assays is discussed.

Parasites of the Patagonian toothfish, Dissostichus eleginoides Smitt 1898, in different parts of the Subantarctic

The parasite faunas of the Patagonian toothfish Dissostichus eleginoides from six locations around the Southern Ocean were studied and compared. Thirty-two parasite taxa were found. Ten parasite species are reported from D. eleginoides for the first time and some other previously reported species were new locality records. Sample size at Shag Rocks was sufficient to examine the effect of intrinsic host factors, including sex and length, on the parasite fauna and these results are discussed here. Some parasite species were found only in certain areas. Sørensen’s similarity index indicated that the parasite faunas at Heard, Maquarie and Prince Edward Islands were the most similar, while those from the Ross Sea was the most dissimilar. There may be a gradual decrease in parasite diversity the further east the samples were collected around the Southern Ocean.

Ultrastructure of the epidermis of adult and embryonic Paravortex species (Turbellaria, Eulecithophora)

The epidermis and associated structures of adult and embryonic Paravortex cardii and Paravortex karlingi, internal parasites of Cerastoderma edule, have been examined using scanning and transmission electron microscopy. The cellular epidermis of adult Paravortex bears cilia and microvilli which differ in number and distribution between P. karlingi and P. cardii. Cellular organelles include mitochondria, lipid bodies, Golgi bodies, and ultrarhabdites. Epidermal nuclei are located in the proximal portion of the cells. The development of the tegument of embryo Paravortex has been described and a possible origin for the embryo capsule is suggested. These findings are discussed in relation to the phylogenetic status of the Turbellaria in relation to other Platyhelminthes and in the functional adaptation of the epidermis for a parasitic mode of life.

VARIATIONS IN THE PARASITE FAUNA OF THE PATAGONIAN TOOTHFISH (DISSOSTICHUS ELEGINOIDES SMITT, 1898), WITH LENGTH, SEASON, AND DEPTH OF HABITAT AROUND THE FALKLAND ISLANDS

The parasite fauna of Dissostichus eleginoides was examined from locations around the Falkland Islands. In total, of 11,362 individual parasites of 27 taxa were recovered from 105 fish. Two species, Ceratomyxa dissostichi and Sphaerospora dissostichi, represent new host records. The nematode Ascarophis nototheniae and the larval acanothocephalan Corynosoma bullosum were found to be new locality records and add to the knowledge of the biogeography and host specificity of parasites on the Patagonian Shelf. There were no significant differences in the mean abundance and prevalence of parasites recovered between sexes. Therefore, sex was not considered in further analysis and the data were pooled. Cysts of unknown etiology (CUE), the monogenean Neopavlovskioides georgianus, the larval acanthocephalan Corynosoma bullosum, and the digenean Neolepidapedon magnatestis had significant positive correlations with increasing host length. The larval Trypanorhynch cestode Grillotia erinaceus and the digenean Elytrophalloides oatesi showed significant negative correlations with increasing host length. CUEs, N. georgianus, the digenean Gonocerca physidis and E. oatesi showed statistically significant prevalence between summer, winter, and spring. The effect of depth on parasite communities was also examined, initially using a linear discriminant function analysis. The prevalence of individual parasites was then compared between depth strata using the chi-square test. The parasite communities on the shelf and deep water (>1,000 m) were found to be different, whereas those caught at intermediate depths on the shelf slope were found to have parasite communities that were intermediate, containing a mixture of shelf and deeper-water parasites. The causes of the variations in parasite faunas in association with these intrinsic and extrinsic factors are discussed.

Structure and development of Sphaerospora elegans Thélohan 1892 (Myxozoa : Myxosporea) in the sticklebacks Gasterosteus aculeatus L. and Pungitius pungitius L. (Gasterosteidae)

The structure and development of Sphaerospora elegans Thélohan 1892 was studied by light and electron microscopy. Specimens of Gasterosteus aculeatus and Pungitius pungitius were examined from localities in England, Scotland and France. The kidney was found to be the main site of infection in both species, with a frequent co-infection with Myxobilatus gasterostei (Parisi, 1912) Davis, 1944 present in several populations of G. aculeatus. Possible extrasporogonic stages were located in the interstitial haematopoietic tissue of the kidney and in the choroidal rete of the eye. Within renal tubules sporogonic events could be followed and were seen to result in the formation of mature sub-spherical spores 10.2 × 10.1 μm in size, containing 2 almost spherical polar capsules of equal size. Only minor pathological changes were found, even in heavy infections. Relationships with other Sphaerospora spp. and PKX cells are discussed.

Variation in the morphology of adult Apatemon gracilis Rudolphi, 1819 (Digenea: Strigeidae) reared in different avian hosts

Adult Apatemon gracilis (Rudolphi, 1819) were reared experimentally in three different avian hosts: herring gulls Larus argentatus Gmelin, domestic chicks Gallus gallus (L.) and eider ducklings Somateria mollissima (L.). Comparisons of size, body proportions and fecundity were made between these and specimens obtained from a naturally infected goosander Mergus merganser L. The eider duck proved to be a suitable experimental host, rearing adults of comparable size and fecundity to those from the natural host. The growth and development of the parasite in domestic chicks and herring gulls were significantly reduced. Similar conditions are likely to exist in the natural environment and this should be taken into consideration when choosing experimental hosts for use in the laboratory or when identifying species.