The aim of this work was to study the structure of the parasite communities of Digeneans of 2 families of Teleost fishes (Sparidae and Labridae) of the Mediterranean sea. We tried to quantify the importance of both the microhabitat requirements of the parasite species and the effect of host biological factors on the parasite communities. We applied, for the first time in parasite community studies, the Canonical Correspondence Analysis (CCA) to analyse (i) the spatial distribution of parasite species within the digestive tract of the hosts; (ii) the host's biological factors (such as diet, host length, gregariousness and abundance) that may influence this spatial distribution of parasite species. Our results showed that potential microhabitats were vacant in the 2 host families studied revealing a lack of niche saturation because either there was little inter- and/or intraspecific competition or there were enough available space and resources within the host. Our results also indicated that the position of the parasite in the digestive tract is much more important than host biological factors for the structure of parasite community. Finally, we highlight the potential use of the CCA method for controlling for phylogenetic constraints in multi-species analyses.

Psoroptic sheep scab and psoroptic otoacariasis of domestic rabbits occur in the same geographical regions of Switzerland. To address the question as to whether Psoroptes mites are naturally transmitted between sheep and rabbits, we determined the sequences of the rDNA second internal transcribed spacer (ITS-2) from psoroptic mites from sheep (5 field isolates from Switzerland and 2 laboratory isolates from Ireland and the UK) and from rabbits (8 field isolates from Switzerland). The ITS-2 sequences for all Psoroptes mites originating from sheep were identical and differed at 1 nucleotide position from all the sequences of the rabbit-derived isolates. A statistically significant difference between a rabbit-derived isolate and isolates originating from sheep was also obtained by morphometric analysis of the lengths of the outer opisthosomal setae. For comparative purposes, the ITS-2 sequences from Chorioptes and Sarcoptes collected in Switzerland were also determined. No intraspecies variation was found in 6 sarcoptic isolates from red foxes, with a sequence identity of 41% as compared to Psoroptes. The ITS-2 sequences of 3 chorioptic isolates differed by 24–29% from the Psoroptes sequence. Identical sequences were found for the Chorioptes isolates from sheep and a camel, which differed by 18% from the sequence of an isolate from a cow. These genetic data of psoroptic mites originating from sheep and rabbits from the same geographical area suggest the existence of epidemiologically separated populations.

The distribution of helminth parasites within their host population is usually overdispersed and can be described by the negative binomial distribution. The causes of this overdispersion are poorly understood, but heterogeneity in the distribution of infective stages within the environment has been implicated as a possible factor. Here we describe the distribution of infective stages of the rat intestinal nematode parasite Strongyloides ratti among the faecal pellets of its host. The distribution of infective stages between faecal pellets is overdispersed and well described by the negative binomial distribution. This overdispersion increases during the course of infection and occurs over a range of infection intensities. Overdispersion of nematode infective stages among faecal pellets may result in increased spatial heterogeneity of the infective stages in the environment and thus may contribute to the generation of overdispersion of adult parasitic stages. In addition, these findings raise important issues regarding the accurate quantification of helminth egg counts from faecal samples.

Cement gland protein in male and inseminated female individuals of an acanthocephalan parasite of fish, Pomphorhynchus laevis (Müller, 1776), was localized by immunohistochemistry using an antibody specific for cement protein. Male P. laevis possess 3 pairs of round to oval cement glands ranging from 0·5 to 0·9 mm in length and from 0·3 to 0·7 mm in width. Each gland has an outer portion containing nuclear fragments and other cellular organelles surrounding a space for storage of gland products. Very little work has been carried out on the nature of the cement gland secretions. We have previously reported that the major component of cement is a protein with molecular weight of 23 kDa; in fresh glands it is white in colour. Immunohistochemical studies herein reported were carried out using a polyclonal antibody raised against purified P. laevis p23 cement protein (anti-p23PL). Localization of p23 cement protein at the light microscope level, by means of the anti-p23PL antibody, shows that p23 is present within the cytoplasmic layer of the gland as well as in the gland duct lumen. Interestingly, the p23 cement protein was also identifiable at the posterior ends of females retaining the cap. Positivity to anti-p23PL antibody was obtained not only in the external part of the copulatory cap, but also within the vaginal tract and at the base of the uterine duct. Thus, we report herein the first photographic evidence that the copulatory cap is not a simple gonopore lid but it is really an intravaginal plug.

The somatic muscle of Ascaris suum is principally under the excitatory control of neuromuscular junction transmitter, acetylcholine (ACh). However, it has recently been shown that neuropeptides also play an important role in the motor-nervous system and one of these, AF3 (AVPGVLRFamide), also contracts muscle. The events which trigger contraction to ACh and AF3 would appear to be different, with ACh activating a nicotinic acetylcholine receptor whilst the response to AF3 is most likely to involve a G-protein coupled receptor negatively coupled to adenylate cyclase. In order to further elucidate differences in the cellular signalling pathways through which ACh and AF3 elicit muscle contraction, we investigated the actions of protein kinase C inhibitors, tamoxifen and chelerythrine, on the dorsal somatic muscle strip of A. suum. Contractions in response to 1 μM AF3 were potentiated by 17% in the presence of 10 μM tamoxifen (P<0·05; n=8); however, contractions in response to 10 μM ACh were markedly inhibited (tamoxifen IC50 44±18 μM; n=6). Tamoxifen also blocked muscle cell depolarizations to 5 μM ACh (IC50 4±1 μM; n=6) and 1 μM levamisole (IC50 14±6 μM; n=4). This was unlikely to be a non-specific effect on the membrane as hyperpolarizations to 10 μM GABA were unaffected (93% of control with 10 μM tamoxifen; n=6; P>0·05). However, another inhibitor of mammalian protein kinase C, chelerythrine, did not affect the response either to ACh or AF3 (n=6).

Authors' correction

In the recently published paper by J. Leiro et al. Parasitology119, 267–272, the legend to Fig. 4 should have read as follows:

Fig. 4. Dot–blot hybridization analyses to evaluate sensitivity of the probes C38-DIG (for Microgemma caulleryi) and F9-DIG (for Tetramicra brevifilum). Lanes 1 and 3, genomic DNA of M. caulleryi and T. brevifilum respectively; lanes 2 and 4, C38 and F9 fragments in pBluescript II SK(+). Visualization was with the aid of alkaline-phosphatase-coupled anti-DIG antibody (see text).