Cleaning behaviour has generally been viewed from the cleaner or client's point of view. Few studies, however, have examined cleaning behaviour from the parasites' perspective, yet they are the equally-important third players in such associations. All three players are likely to have had their evolution affected by the association. As cleaner organisms are important predators of parasites, cleaners are likely to have an important effect on their prey. Little, however, is known of how parasites are affected by cleaning associations and the strategies that parasites use in response to cleaners. I examine here what parasites are involved in cleaning interactions, the effect cleaners have on parasites, the potential counter-adaptations that parasites have evolved against the predatory activities of cleaner organisms, the potential influence of cleaners on the life history traits of parasites, and other factors affected by cleaners. I have found that a wide range of ectoparasites from diverse habitats have been reported to interact with a wide range of cleaner organisms. Some of the life history traits of parasites are consistent with the idea that they are in response to cleaner predation. It is clear, however, that although many cleaning systems exist their ecological role is largely unexplored. This has likely been hindered by our lack of information on the parasites involved in cleaning interactions.

The anisakid nematodes morphologically corresponding with Pseudoterranova decipiens sensu lato (s.l.) (Krabbe, 1878) from different seal or sea lion hosts and geographical origins, previously identified as Pseudoterranova krabbei, P. decipiens (s.s.), P. bulbosa, P. azarasi and P. cattani by multilocus enzyme electrophoresis, were characterized using a DNA approach. Also a population of P. decipiens (s.l.) from Chaenocephalus aceratus, the blackfin icefish, from Antarctica and another from Osmerus eperlanus, the European smelt, from Germany were included in the study. The first (ITS-1) and second (ITS-2) internal transcribed spacers (ITS) of ribosomal DNA (rDNA) were amplified by PCR from individual nematodes and analysed by single-strand conformation polymorphism (SSCP), followed by selective sequencing. While no variation in single-stranded ITS-1 and ITS-2 profiles was detected among samples representing each of the species or populations (with the exception of slight microheterogeneity), SSCP analysis of the ITS-2 amplicons allowed the unequivocal differentiation of all of the 5 sibling species of P. decipiens (s.l.) examined, which was supported by sequence differences in ITS rDNA. Samples representing the P. decipiens (s.l.) population from O. eperlanus had the same SSCP profile as those of P. decipiens (s.s.), which was supported by a lack of nucleotide difference in the ITS between them, suggesting that the former represented P. decipiens (s.s.). Based on SSCP results and ITS sequence data, P. decipiens (s.l.) from C. aceratus was genetically most distinct with respect to all other members of Pseudoterranova examined, which indicated that it may represent P. decipiens E (based on geographical origin) or a distinct species. These findings and the molecular approach taken should have important implications for studying the life-cycles, transmission patterns, epidemiology and population genetics of these anisakid nematodes, and the diagnosis of their infections.

A DNA-construct coding for the elastase of the parasite Schistosoma mansoni was prepared from adult S. mansoni worm RNA which was reverse transcribed into cDNA. The gene coding for the elastase was amplified using primers specific for the sequence of cercarial elastase and was cloned into a mammalian expression vector. Expression of the elastase gene at the transcriptional level was achieved for the first time in transfected mammalian cells (COS-7) and was also successful in muscle tissue of mice injected with the DNA-construct. These mice developed antibodies recognizing in Western blots the elastase from cercarial secretions. Also, these antibodies reacted in immunofluorescence tests with the preacetabular glands of cercariae, i.e. the site of origin for elastase. Thus, the DNA-construct induced the expression of elastase in mice and formation of antibodies that recognized the native antigen.

The action of intra- and interspecific competition, mediated by density-dependent effects on growth, was investigated among the 3 helminth species found in the alimentary tract of 104 cormorants, Phalacrocorax carbo sinensis. Intraspecific density-dependent effects on worm sizes were observed in the abundant nematode Contracaecum rudolphii, as shown by a negative correlation between mean worm size and intensity of infection. Higher intensities of infection by C. rudolphii were also associated with more variable worm sizes in the nematode Syncuaria squamata, suggesting a one-sided and density-dependent interspecific effect. There was also clear evidence of some form of negative interaction between the nematode S. squamata and the acanthocephalan Southwellina hispida from two fronts. First, there was a strong negative correlation between the intensities of infection of the 2 species across hosts. Second, sizes of worms of 1 species became more variable as the number of worms of the other species per host increased, and vice versa. This interspecific density-dependent effect on growth was thus apparently symmetrical. We also found evidence that worm size is a predictor of egg output in the 3 helminth species, indicating that intra- and interspecific density-dependent effects on growth can affect population dynamics in these worms. These results illustrate the complex nature of density dependence in helminth growth, and how its effects can act both within and among species.

Helminth parasites of fish in marine systems are often considered to be generalists, lacking host specificity for both intermediate and definitive hosts. In addition, many parasites in marine waters possess life cycles consisting of long-lived larval stages residing in intermediate and paratenic hosts. These properties are believed to be adaptations to the long food chains and the low densities of organisms distributed over broad spatial scales that are characteristic of open marine systems. Moreover, such properties are predicted to lead to the homogenization of parasite communities among fish species. Yet, these communities can be relatively distinct among marine fishes. For benthos, the heterogeneous horizontal distribution of invertebrates and fish with respect to sediment quality and water depth contributes to the formation of distinct parasite communities. Similarly, for the pelagic realm, vertical partitioning of animals with depth will lead to the segregation of parasites among fish hosts. Within each habitat, resource partitioning in terms of dietary preferences of fish further contributes to the establishment of distinct parasite assemblages. Parasite distributions are predicted to be superimposed on distributional patterns of free-living animals that participate as hosts in parasite life cycles. The purpose of this review is first, to summarize distribution patterns of invertebrates and fish in the marine environment and relate these patterns to helminth transmission. Second, patterns of transmission in marine systems are interpreted in the context of food web structure. Consideration of the structure and dynamics of food webs permits predictions about the distribution and abundance of parasites. Lastly, parasites that influence food web structure by regulating the abundance of dominant host species are briefly considered in addition to the effects of pollution and exploitation on food webs and parasite transmission.

The effect of platyhelminth FaRPs and selected classical neurotransmitters on the motility of intact Mesocestoides corti (syn. M. vogae) tetrathyridial larvae was studied in vitro using a micromotility meter. The effects of the test substances were temperature dependent and these were examined at 4, 23, 30 and 36 °C. At 36 °C all test substances had concentration-dependent excitatory effects, with thresholds for activity of: 100 nM (GNFFRFamide), 10 μM (YIRFamide), 30 μM (GYIRFamide), 100 nM (serotonin) and 100 μM (acetylcholine). At this temperature significant elevation of motility indices (MI) was recorded within 5 min of the addition of peptide or serotonin. The effect of acetylcholine was slower in onset and appeared 15–20 min post-addition. At 30 °C larval motility diminished more rapidly than that recorded at 36 °C, following the addition of 1 mM of each test substance. At 23 °C only serotonin (1 mM) significantly increased the MI, all other test substances having no apparent effect. Larval movement was completely arrested at 4 °C. The results demonstrate for the first time excitatory effects of platyhelminth neuropeptides and acetylcholine on muscle systems in cestode larvae. The fact that the only known cestode FaRP, GNFFRFamide, was more potent than any of the turbellarian FaRPs tested, suggests structural conservation of FaRPs and FaRP receptors within the cestodes.

Trypanosoma cruzi is currently classified into 2 major phylogenetic lineages, T. cruzi I and II, that correlate with the formerly described zymodeme 1 and 2, respectively. Another isoenzymic group (zymodeme 3–Z3) was also described. In this study, we analysed the genetic diversity among Z3 isolates of the Brazilian Amazon by restriction fragment length polymorphism of the intergenic transcribed spacers (ITSs) of the ribosomal RNA cistron and the size of the divergent domain D7 of the 24Sα rRNA gene. DNAs from 12 T. cruzi Z3 isolates obtained from humans (2), Panstrongylus geniculatus (1), and Rhodnius brethesi (9) were submitted to PCR amplification of the ITSs plus the 5·8S rDNA. The PCR products were digested with 4 distinct endonucleases and the profiles analysed by a numerical methodology. The phenetic dendrogram revealed a clear dichotomy in the Z3 group, defining 2 groups that were named Z3-A and Z3-B. Dimorphism was also found in the band sizes of the amplified D7 divergent domain of the 24Sα rDNA, which showed a perfect correlation with the ITSs clustering. The organization of the ribosomal cistron was investigated by Southern blotting and shown to be conserved in the genome of the 2 Z3 groups. This study shows that the rDNA cistron allows the definition of 2 distinct subclusters in Z3 isolates.

This paper describes the ability of the Asian fish nematode Camallanuscotti to carry out both heteroxeny, i.e. an indirect life-cycle using copepods as intermediate host, and monoxeny, i.e. direct infection and development in the definitive fish host. C. cotti occurs naturally in various freshwater teleosts in Asia. During the past decades it has been disseminated into closed or semi-closed aquaculture systems and aquaria around the world, mainly due to the ornamental fish trade. Under such conditions the species may frequently face a bottleneck situation with regard to the availability of copepods. It is known that C. cotti may reproduce and persist in copepod-free aquaria for several months. In order to investigate whether C. cotti has selected towards monoxeny in water systems lacking copepods, in contrast to the opposite selection pressure when copepods are present, 2 separate infection trials were run. It was shown that the parasite can infect the fish host both indirectly via copepods, and directly. However, C. cotti has significantly higher fitness, expressed as survival to maturity, when transmitted indirectly compared to the direct transmission mode. We suggest that the ability of aquarium populations of C. cotti to carry out a direct life-cycle is favoured by selection in order to avoid extinction whenever copepods are absent. It still remains unknown, however, whether the parasite shows the same characteristics in the wild.

Viviparous gyrodactylid monogeneans which are detached from their host may form an important source of infection in fish communities. This is particularly significant for these ectoparasites which have no specific free-living stage and where transmission usually occurs through transfer of adult parasites when fish come into close contact. In this study, in vitro survival of Gyrodactylus gasterostei was correlated with changes in tissue ultrastructure of parents and their embryos during detachment and following return to a host. At 10 °C, detached worms survived for up to 89 h (50% survival = 20 h) with mortality influenced by both age-independent and age-dependent factors. The gastrodermis of attached, fed parasites is syncytial and contains a variety of vesicles and feeding vacuoles. However, following detachment and starvation, degenerative changes occur within the gastrodermis, eventually leading to marked damage to the embryo/s. When starved worms reattached to a fish, they began browsing on host epithelial cells within 1 min and ultrastructural evidence for phagocytic activity in the gastrodermis was detected after 5 min. Putative waste vacuoles increased in abundance after 5–30 min on the new host, coinciding with the reappearance of electron-dense vesicles and possibly indicating completion of the first intracellular cycle of digestion. Parental feeding directly influenced the normal cyclical maturation and regression of the uterine lining between births. In extreme cases, starvation led to detached parasites (6·1%) aborting their embryos. However, even short periods off the host influenced development and survival of embryos, suggesting that temporary interruption of nutrient flow to the embryo can significantly affect gyrodactylid reproductive rates.

Life-history attributes of the capsalid monogenean Benedenia lutjani, a parasite of Lutjanus carponotatus from the Great Barrier Reef, Queensland, Australia, were investigated from experimental infections. Oncomiracidia of B. lutjani invaded and attached at any site on the fish, but more commonly invaded body surfaces. Immature specimens then migrated to the pelvic fins. Development of the reproductive organs of B. lutjani corresponded with migratory movements on the host. Parasite aggregation on the pelvic fins coincided with the development of functional male reproductive organs and some protandrous worms that possessed a vagina appeared to be inseminated. Migration to, and aggregation on, the branchiostegal membranes (membranous folds posterior to the opercula) coincided with the onset of sexual maturity and commencement of egg production by parasites. The rate of parasite development and the timing of migratory events on the host were influenced by water temperature. All specimens of B. lutjani reached sexual maturity between 12 and 14 days p.i. at 24 °C and between 8 and 10 days p.i. at 27 °C. Anterior hamuli grew continually during a 16-day experiment at 27 °C and 25-day experiment at 23 °C and their length appeared to provide a suitable index to estimate parasite age. The possible adaptive significance of the migratory behaviour, site-specificity and its link with changes in parasite development are discussed.

High prevalences of Echinococcus multilocularis have been reported from foxes of the city of Zurich, Switzerland. In order to characterize transmission in urban areas, a coproantigen ELISA was evaluated for diagnosing the infection in fox faecal samples collected in the environment. In addition, trapped rodents were investigated for the presence of metacestodes. Faecal samples could reliably be classified as being of fox origin by assessing physical properties as shown by the different parasite spectra of putative fox and dog faecal specimens. From the total of 604 tested putative fox faecal samples 156 (25·8%) were positive in the ELISA with a distinct increase in the proportion of positive samples from the urban to the periurban zone. Furthermore, samples collected in the border zone had significantly more coproantigen-positive results during winter. Prevalence of E. multilocularis in rodents was 9·1% (81/889) for Arvicola terrestris (with 3·5% of the animals harbouring between 14 and 244400 protoscoleces) and 2·4% (2/83) for Clethrionomys glareolus. E. multilocularis-infected A. terrestris were found in 9 of 10 trapping sites in the border zone. The high infection pressure in the periphery of urban areas might pose a risk for infection with E. multilocularis for both domestic carnivores as well as for urban inhabitants. Interventions into the cycle aiming at reducing the infection pressure should therefore focus on these areas.

The strongest evidence for host specificity of mammalian trypanosomes comes from parasites of the subgenus Trypanosoma (Herpetosoma). Laboratory studies have shown that T. (Herpetosoma) species will not infect an alternative host. However, this has not been demonstrated in wild populations. We screened 560 bank voles (Clethrionomys glareolus) and 148 wood mice (Apodemus sylvaticus) for trypanosomes by PCR amplification of the 18S rRNA gene. In total, 109 (19%) bank voles and 12 (8%) wood mice were infected. A HaeIII restriction site was discovered that could be used to discriminate between T. (H.) evotomys of the bank vole and T. (H.) grosi of the wood mouse. All the parasites in the bank voles were identified as T. (Herpetosoma) evotomys by RFLP-PCR. Out of the 12 wood mouse infections 10 were due to T. grosi. Two of the wood mice were infected with parasites with a novel genotype that was most similar to those of T. evotomys and T. microti of voles. Fifty-six fleas collected from the rodents were also screened for trypanosomes; 9 were infected with T. evotomys and 1 with T. grosi. One of the fleas infected with T. evotomys was collected from a wood mouse.

Previous studies in deliberately infected sheep have shown an association between IgA activity against 4th-stage larvae of Teladorsagia circumcincta and parasite growth, development and fecundity. The purpose of this research was to determine if these results could be confirmed in naturally infected sheep and to explore the hypothesis that plasma IgA activity could help to identify resistant lambs with shorter adult nematodes. Plasma IgA activity was skewed with most animals having relatively low levels of IgA activity. Plasma IgA activity was repeatable and highly heritable. Animals with increased IgA activity had lower egg counts and shorter adult female T. circumcincta. Therefore, under conditions of natural parasite challenge, plasma IgA activity may help to identify lambs resistant to T. circumcincta.

There is mounting evidence that parasites can influence the composition and structure of natural animal communities. In spite of this, it is difficult to assess just how important parasitism is for community structure because very few studies have been designed specifically to address the role of parasites at the community level, no doubt because it is difficult to manipulate the abundance of parasites in field experiments. Here, we bring together a large amount of published information on parasitism in intertidal communities to highlight the potential influence of parasites on the structure and biodiversity of these communities. We first review the impact of metazoan parasites on the survival, reproduction, growth and behaviour of intertidal invertebrates, from both rocky shores and soft-sediment flats. Published evidence suggests that the impact of parasites on individuals is often severe, though their effects at the population level are dependent on prevalence and intensity of infection. We then put this information together in a discussion of the impact of parasitism at the community level. We emphasize two ways in which parasites can modify the structure of intertidal communities. First, the direct impact of parasites on the abundance of key host species can decrease the importance of these hosts in competition or predator-prey interactions with other species. Second, the indirect effects of parasites on the behaviour of their hosts, e.g. burrowing ability or spatial distribution within the intertidal zone, can cause changes to various features of the habitat for other intertidal species, leading to their greater settlement success or to their local disappearance. Our synthesis allows specific predictions to be made regarding the potential impact of parasites in certain intertidal systems, and suggests that parasites must be included in future community studies and food web models of intertidal ecosystems.

Schistosomes are parasites of considerable medical and veterinary importance and, therefore, all aspects of their biology have been intensively studied. In contrast, our knowledge of species of the largest genus, Trichobilharzia, is insufficient. Because morphological characterization of Trichobilharzia species provides a limited number of criteria for species determination, molecular data are required. In the present paper, we sequenced internal transcribed spacers ITS1 and ITS2, and 5·8S ribosomal RNA (rRNA) genes of 3 European Trichobilharzia species (T. regenti, T. szidati and T. franki). We showed that ITS1 and ITS2 sequences can be used in species identification. Repetitive elements were found in ITS1 of all 3 Trichobilharzia species; their number and length varied depending on the species. Phylogenetic analysis showed that the visceral T. franki is more related to the nasal T. regenti, than to the visceral T. szidati. The newly designed primer, which is specific for T. regenti, might be used as a tool for diagnosis of this potential pathogen.

Variation in host susceptibility causes significant differences in infection rates between hosts living in a semi-natural situation. Such knowledge has implications for population dynamics and evolutionary models of host–parasite interactions as well as for estimations of parasite abundance. Infection rates by Lernaeocera branchialis (L.) were measured through time and space on caged Atlantic cod (Gadus morhua L.). One group of hosts, identified by their infection history, developed significantly higher infection rates than the others. These were fish which had been infected previously, but had lost their infection. Differences between groups were consistent through both time and space. Two types of cod seem to have been present in the caged population; a small group of inherently susceptible fish, which were infected, and reinfected if the parasite was lost, and another group of resistant hosts with a small chance of becoming infected.

Marteilia refringens is a major pathogen of the European flat oyster, Ostrea edulis Linnaeus. Since its description, the life-cycle of this protozoan parasite has eluded discovery. Attempts to infect oysters experimentally have been unsuccessful and led to the hypothesis of a complex life-cycle involving several hosts. Knowledge of this life-cycle is of central importance in order to manage oyster disease. However, the exploration of M. refringens life-cycle has been previously limited by the detection tools available and the tremendous number of species to be screened in enzootic areas. In this study, these two restrictions were circumvented by the use of both molecular detection tools and a mesocosm with low biodiversity. Screening of the entire fauna of the pond for M. refringens DNA was systematically undertaken using PCR. Here, we show that the copepod Paracartia(Acartia) grani is a host of M. refringens. Not only was DNA of M. refringens consistently detected in P. grani but also the presence of the parasite in the ovarian tissues was demonstrated using in situ hybridization. Finally, successful experimental transmissions provided evidence that P. grani can be infected from infected flat oysters.

The Baltic Sea is characterized by organisms that can tolerate brackish water. Because of the Sea's history during glacial times, its flora and fauna (and also their parasites) can be traced to marine, freshwater and genuine brackish elements beside glacial relics. Snails, planktonic copepods, benthic amphipods and isopods are important intermediate hosts of diverse helminths; in addition polychaetes, bivalves and fishes may also act as final hosts. The most important final hosts, beside fishes, were seals and birds; these were able to disperse the parasites over the whole of the Baltic. Decreasing salinity from west to east limits the distribution of many parasites. Several marine and genuine brackish water species have almost spread over the whole Baltic. Freshwater species, however, have a lower tolerance than marine species and are only rarely found in the western part. A serious problem in the Baltic is eutrophication which can lead to massive abundances of generalist parasites, in host populations as well as host individuals. The final stage of this influence can cause a general decrease of host abundance and, as a consequence, of all kinds of parasites, due to oxygen deficiency. In comparison with the species spectrum of other brackish waters in Europe, the Baltic presents some endemic parasites as well as sharing parasite species with the Mediterranean and even the Black Sea.

Faecal egg counts and peripheral blood eosinophil counts were taken from Scottish Blackface lambs following natural, predominantly Teladorsagia circumcincta infection. Peripheral eosinophil concentrations were higher in animals with lower egg counts but only in lambs that were at least 3 months of age. The reduced egg counts were due to reduced fecundity of T. circumcincta; there was no association with the number of adult T. circumcincta. Associations with the number of parasites from other species of gastrointestinal nematodes appeared to be neutral or favourable. Estimated heritabilities for eosinophil concentrations in 4- and 5-month-old lambs were 0·48±0·16 and 0·43±0·17, respectively. Therefore, under defined circumstances, eosinophil concentrations may be a useful indicator of resistance to predominantly T. circumcincta infection.

The natural history of human filarial infections leading to development of disease has been a subject of intense debate. The models proposed so far have largely been based on cross-sectional data on microfilariae (Mf) and disease prevalence in filariasis endemic areas. In an attempt to study the parasitological and clinical consequences of filarial infection in Beldal (Orissa, India), an area endemic for Bancroftian filariasis, cohorts of 59 asymptomatic Mf carriers (AS) and 187 asymptomatic and amicrofilaraemic subjects or ‘endemic normals’ (‘EN’), were followed-up and a fraction (73% and 46% respectively) re-examined after 13 years to monitor (a) Mf prevalence, (b) Mf density, (c) circulating filarial antigen (CFA) and (d) chronic disease manifestations. The Mf prevalence and density were also monitored in Mf carriers after 1 and 4 years. Both Mf prevalence and density decreased progressively in the cohort of Mf carriers over a period of 13 years in Beldal. Only 37% of them continued to be microfilaraemic and the Mf density in these subjects was only 10% of the original level. However, loss of circulating Mf in this cohort did not result in loss of CFA and 95% remained CFA positive regardless of Mf status. About 23% of males in the ‘EN’ cohort developed hydrocoele while only 5·7% of male Mf carriers, who were not treated with DEC, had developed hydrocoele after 13 years. A cohort of Mf carriers in another area, Jatni, was also examined after 10 years to study the parasitological and clinical outcome. In this area, about 59% of the Mf carriers continued to be microfilaraemic after 10 years. These results reveal that in Mf carriers adult filarial worms persist for several years and that loss of circulating Mf with or without chemotherapy with DEC (single 12-day course) does not influence adult worm survival. The findings have been discussed in the context of ‘static’ and ‘dynamic’ models describing the relationship between infection and disease in human filariasis.