J.W. Lewis

Gill Damage in the Freshwater Fish Gnathonemus Petersii (Family: Mormyridae) Exposed to Selected Pollutants: An Ultrastructural Study

The histopathological effects of three heavy metals, cyanide and atrazine on the gill tissues of the mormyrid fish, Gnathonemus petersii, were determined primarily by electron microscopy. Replicate samples of fish were exposed for 6 hours to two concentrations of each toxicant in a continuous flow system comprising aerated, dechlorinated and heated water. Specific alterations to gill ultrastructure were found to be associated with each toxicant. Cadmium damage at 1.0 mg l−1 was associated with the formation of large subepithelial spaces within the secondary lamellae and at 10.0 mg l−1 with lamellar aneurism. Chromium caused epithelial hyperplasia at 1.0 mg l−1 and extensive fusion of secondary lamellae at 10.0 mg l−1. Copper exposure stimulated hyperactivity of mucous cells at 0.1 mg l−1 which resulted in the accumulation of a thick layer of mucus on the gills at 0.5 mg l−1. Cyanide caused desquamation of filamental epithelium at 0.05 mg l−1 and stripping of the epithelium and underlying tissue down to th...

Song as an indicator of parasitism in the sedge warbler

We studied female choice and reproductive success in a marked population of sedge warblers Acrocephalus schoenobaenus, from 1995 to 1996. Three genera of parasitic blood protozoans, namely Haemoproteus sp. Trypanosoma sp. Plasmodium sp., were identified from blood samples taken from all breeding adults. Relatively high prevalence values of 19.5% in 1995 and 37.5% in 1996 were associated with increased levels of white blood cells relative to the number of red blood cells. Compared with nonparasitized males, parasitized males had significantly lower repertoire sizes in both years of the study; in one year, they also spent less time in song flights and weighed less. They also provisioned their broods at a lower rate. Parasitized females produced the same clutch size as nonparasitized females, although their broods were smaller at 7 days old. We suggest that haematozoan infections may reduce the expression of sexually selected song traits. Furthermore, such infections may influence the standard of parental care provided by males, although further research is needed to determine whether this is mediated through genetic resistance to parasitism or the effects of parasitism upon immediate body condition. Copyright 1999 The Association for the Study of Animal Behaviour.

Helminth infections in Apodemus sylvaticus in southern England: interactive effects of host age, sex and year on the prevalence and abundance of infections

Helminth parasites were studied in the wood mouse, Apodemus sylvaticus, in southern England in September of each of four successive years (1994-1997). Nine species of helminths were recorded: five nematodes (Heligmosomoides polygyrus, Syphacia stroma, Pelodera strongyloides, Trichuris muris, Capillaria murissylvatici), two cestodes (Microsomacanthus crenata, Taenia taeniaeformis) and two trematodes (Corrigia vitta, Brachylaemus recurvum). In total, 134 mice were examined and 91.8% carried at least one species of helminth. The majority of mice carried two to three species (60.5%) and the highest combination was six of the nine species recorded in the study. The patterns of between-year variations in the prevalence and abundance of infection were different for each of the six species for which sufficient quantitative data were available to enable statistical analysis. For H. polygyrus, the most important source of variation arose from between-year differences, host age and the interaction of these factors: abundance increased with host age but in 1995 the age pattern was markedly different from that in the remaining years. The abundance of C. vitta also varied significantly between years but additionally there was a strong independent age effect. For M. crenata, the year x age interaction was significant, indicating that abundance among different age cohorts varied from year to year but there was also a weak significant main effect of age arising from the youngest age cohort carrying no parasites and the oldest age cohort the heaviest infections. For P. strongyloides the only significant factor was between-year variation with 1995 being a year of exceptionally low prevalence and abundance of infection. No significant between-year variation was detected for S. stroma but there was a strong sex effect (males carrying heavier infections) and an age effect (older mice of both sexes carrying heavier infections). The abundance of Trichuris muris varied only in relation to host age, worm burdens growing in intensity with increasing age, but there was also a significant interaction between year and host sex with respect to prevalence. For the remaining three species, the prevalence of infections was too low (< 8.2%) to enable any meaningful interpretation. This analysis emphasizes the need for carefully controlled statistical procedures in aiding the interpretation and the prioritization of the factors affecting worm burdens in wild rodents.

Pollution toxicity to the transmission of larval digeneans through their molluscan hosts

The increased occurrence of pollutants in ecosystems is a continuing area of concern. It is known that numerous diseases of wild aquatic animals can occur with decreased or increased prevalences in areas associated with high or chronic levels of pollution. This may have serious implications for environmental health. There has consequently been an increasing number of laboratory and field studies on disease transmission under polluted conditions, especially focusing on digeneans of medical or economic importance. The effect of pollutants to the transmission of larval digeneans (miracidia, cercariae, metacercariae) and snail-digenean interactions is therefore considered. An overview and interpretation of the published literature on laboratory and field studies is provided. It is apparent from these studies that the influence of pollutants on digenean transmission is highly complex with much of the observed effects in the laboratory often masked by a complexity of other factors in the field. Future studies would benefit from a standardisation of experimental procedures, increasing the number of combined laboratory and field studies, and increasing the complexity of the experiments undertaken.

Epidemiological studies on intestinal helminth parasites of rural and urban red foxes (Vulpes vulpes) in the United Kingdom

An epidemiological study of intestinal helminths in 843 foxes (Vulpes vulpes) from southern England revealed the presence of 13 parasite species: five nematodes--Toxocara canis (prevalence 55.9%), Toxascaris leonina (1.5%), Uncinaria stenocephala (68.0%), Trichuris vulpis (0.5%) and Capillaria aerophila (0.2%); four cestodes--Taenia pisiformis (13.8%), Taenia hydatigena (2.5%), Echinococcus granulosus (0.1%) and Dipylidium caninum (3.8%); two trematodes--Brachylaima recurva (2.9%) and Cryptocotyle lingua (2.3%); two acanthocephalans--Prosthorhynchus transversus (0.7%) and Macracanthorhynchus catulinus (0.1%). Trichuris vulpis, Brachylaima recurva, Macracanthorhynchus catulinus and Prosthorhynchus transversus are new host records for the UK. Results are discussed with reference to variations in the diets of urban and rural foxes and to their potential as reservoir hosts for helminths of medical and veterinary importance.

Seasonal and site specific variation in the component community structure of intestinal helminths in Apodemus sylvaticus from three contrasting habitats in south-east England

Seasonal fluctuations in the prevalence and abundance of infection with intestinal helminths were studied in Apodemus sylvaticus (wood mouse, n = 399), from three contrasting habitats in southern England, to test the hypothesis that both intrinsic (host sex, age) and extrinsic (season, site) factors influence parasite species richness and abundance. Five species of helminths were recovered but only one of these (Capillaria murissylvatici) was site-specific (Dungeness). Total species richness was therefore 5 at Dungeness and 4 at the other two sites. Mean species richness was 1.4, but in adult mice there was a pronounced difference between the sites, and an independent highly significant effect of season. Syphacia stroma and Corrigia vitta both showed marked differences between sites in respect of prevalence and abundance of infection. Capillaria murissylvatici was encountered at Dungeness mostly in the spring whereas seasonal changes in abundance of S. stroma were consistent across all three sites. Seasonal fluctuations in the abundance of Catenotaenia pusilla were compounded by differences between sites. Host sex was not a significant factor in any species, although a posteriori analysis of S. stroma worm burdens for the Isle of Wight site revealed a moderate local sex effect. Overall the principal determinants of variation in helminth burdens were the extrinsic factors, site and season.

Molecular evidence that Heligmosomoides polygyrus from laboratory mice and wood mice are separate species

The gastro-intestinal (GI) nematode Heligmosomoides polygyrus is an important experimental model in laboratory mice and a well-studied parasite of wood mice in the field. Despite an extensive literature, the taxonomy of this parasite in different hosts is confused, and it is unclear whether laboratory and field systems represent the same or different Operational Taxonomic Units (OTUs). Molecular analyses reveal high sequence divergence between H. p. bakeri (laboratory) and H. p. polygyrus (field); 3% difference in the ribosomal DNA Internal Transcribed Spacers (ITS) and 8.6% variation in the more rapidly evolving mitochondrial cytochrome c oxidase I (COI) gene. The COI sequence of U.K. H. p. polygyrus is more similar to H. glareoli from voles than to H. p. bakeri, while a single isolate of H. p. polygyrus from Guernsey confirms the extent of genetic variation between H. p. polygyrus populations. Analysis of molecular variance demonstrated that mtCOI sequence variation is associated primarily with groups with distinct ITS2 sequences, and with host identity, but is not partitioned significantly with a single combined taxon H. polygyrus incorporating European and North American isolates. We conclude therefore that the laboratory OTU should be raised to the level of a distinct species, as H. bakeri from the laboratory mouse Mus musculus, and we reject the hypothesis that H. bakeri has diverged from H. polygyrus in the recent past following introduction into America. However, we are unable to reject the hypothesis that H. polygyrus and H. bakeri are sister taxa, and it may be that H. polygyrus is polyphyletic or paraphyletic.

Fish macroparasites as indicators of heavy metal pollution in river sites in Austria

This paper describes two approaches to evaluate the use of fish macroparasites as bioindicators of heavy metal pollution at selected river stretches in Austria. Firstly changes in the diversity and richness of endoparasites of the cyprinid barbel, Barbrus barbuls (L.), were tested in relation to heavy metal contents in the aquatic system. Secondly, the bioaccumulation potential of cadmium, lead and zinc was assessed in the acanthocephalan, Pomphorhynchus laevis (Miller, 1776), and compared with that in the muscle, liver and intestine of its barbel host. The present results indicated that in order to validate the role of parasite community patterns related to heavy metal pollution, more investigations on food web dynamics, interelationships between parasites and the presence/absence of intermediate hosts will be essential. Heavy metal concentrations differed significantly between the organs of barbel and P. laevis (P=0.001) with levels up to 2860 fold in the parasite. The high level of heavy metal accumulation in P. laevis compared with that in its barbel host, suggests that despite variability in the parasite infrapopulation, host mobility and feeding behaviour, P. laevis is a most sensitive indicator of heavy metals in aquatic ecosystems.

Pollutant-induced effects on immunological and physiological interactions in aquatic host–trematode systems: implications for parasite transmission

Under conditions of pollution both host and parasite are susceptible to the pathogenic effects of toxicants, which in turn may result in detrimental changes to their immunological and physiological processes. Digenetic trematodes, which encompass species of both medical and economic importance, possess complex life cycles and are common parasites of both vertebrates and molluscs. The combined stress induced by pollution and parasitism influences the physiology of the host which can have implications not only on host survival but also on the functional biology of resident parasite populations. The present paper reviews the effects of pollutants on the immunology and physiology in both vertebrate and molluscan host-trematode systems and the implications for parasite transmission.

An evaluation of pollutant induced changes in the gills of rainbow trout using scanning electron microscopy

Abstract The effects of phenol, copper and ammonia on the surface ultrastructure of the gills of rainbow trout were determined by scanning electron microscopy (SEM). Although the gills exhibited some common pollutant‐induced changes, certain types of pathological response were pollutant‐specific. Phenol caused destruction of epithelial layers down to supporting cartilage. Copper damage was characterized by lamellar fusion, swelling in the tips of the filaments and formation of epithelial swellings and ridges. Ammonia caused the development of distinctive circular depressions and pits in the epithelium. These results suggest that SEM of fish gills should be evaluated further as a diagnostic tool in water pollution investigations.