A new scheme of clarifying clinical forms of toxocariasis is proposed to include: (i) systemic forms: classical VLM and incomplete VLM; (ii) compartmentalized forms: ocular and neurological toxocariasis; (iii) covert toxocariasis; and (iv) asymptomatic toxocariasis. The following markers are helpful in defining clinical forms namely, patient characteristics and history, clinical symptoms and signs, positive serology, eosinophilia and increased levels of IgE. Amongst the available drugs albendazole is the most commonly used, although other benzimidazole compounds have a similar efficacy. The recommended dose of albendazole is 15 mg kg-1 body weight daily for 5 days and in some cases with VLM syndrome the treatment needs to be repeated. An evaluation of treatment efficacy can be made by observing a rise in eosinophilia within a week followed by any improvement in clinical symptoms and signs, lower eosinophilia and serological tests taken over a period of at least 4 weeks. In addition to clinical rationales for the specific treatment of VLM and OLM, preventive treatment needs to be considered bearing in mind the increasing risk of larvae localizing in the brain during the course of an infection. To reduce migration of Toxocara larvae a single course of albendazole is suggested in cases where eosinophilia and serology are at least moderately positive.

Metacercarial aggregation of Fasciola hepatica and Paramphistomum daubneyi was studied under experimental conditions to determine if the formation of these aggregates was influenced by environmental factors, or it was a characteristic of trematode species. This process was studied using the confinement of infected snails on the bottom of Petri dishes (diameter, 14 cm) for 3 days. The formation of metacercarial aggregates of F. hepatica was not significantly modified by environmental factors such as intensity and duration of lighting, quality and volume of water. Metacercariae of F. hepatica were more numerous on the Petri dish walls and 63.9% of them constituted aggregates. In contrast, most metacercariae of P. daubneyi were found on the Petri dish bottoms and 78.3% of them were isolated or in groups of two metacercariae each. The mean number of metacercariae per aggregate ranged from 6.7 to 12.2 in the case of F. hepatica, and from 2.7 to 4.5 in the case of P. daubneyi. However, these mean numbers were independent of the site of cercarial attachment. The tendency of cercariae to form metacercarial aggregations was a characteristic of F. hepatica and was species determined.

Parasitic infections were studied for the first time in an urban population of brown rats (Rattus norvegicus) from Doha. Only one species of helminth was found, the cestode Hymenolepis diminuta, and one ectoparasite, the flea Xenopsylla astia, from a sample size of 136 rats (52 males and 84 females). The prevalence of H. diminuta was 17.6%, increasing with host age but not in relation to host sex nor season of capture. Host age was a key factor in influencing abundance of infection, although there was a significant three-way interaction with season and host sex arising through heavy infections in juvenile male rats in the summer. The prevalence of X. astia was 45.6%, although both prevalence and abundance of infestations were season and host age dependent. In the winter prevalence and abundance were similar in both host age and sex groups, but in the summer both parameters of infestation were markedly higher among juveniles compared with adults. We found evidence for some association between these two species: H. diminuta was more prevalent among rats with fleas than among those without, although this association was season-, and independently sex- and age-dependent. There were no quantitative interactions and reasons for this are discussed in relation to the foraging and breeding behaviour of the brown rat in Qatar.

The host–parasite relationship of a 100 metacercarial cyst inoculum of Echinostoma caproni in the ICR mouse was examined. Three groups of mice, A, B and C, each with six mice per group were used and all mice were necropsied at 14 days postinfection (p.i.), at which time the worms were ovigerous. Group A consisted of uninfected controls, whereas group B received 25 cysts per mouse (low dose) and group C received 100 cysts per mouse (high dose). There was no significant difference in food consumption between any of the groups from 0 to 14 days p.i. Control mice increased their body weight by 12%, group B by 5%, and group C showed a less than 1% increase in body weight between 0 and 14 days p.i. Echinostome parasitism caused a significant increase in the diameter of the mouse gut, with the gut of group C being more significantly dilated than that of either group A or B. The average worm recovery from group B was 20 worms per host, compared to 72 worms per host from group C. The mean wet and dry weights per worm from group B were 2.4 and 0.4 mg, respectively as compared to 0.6 and 0.2 mg respectively for group C. The mean number of uterine eggs per worm from group B was 180 compared to 125 for worms from group C. Worms from group C were more widely distributed in the small intestine than those from group B. Crowding effects associated with the high dose infection were clearly demonstrated in E. caproni from ICR mice.

The occurrence of benzimidazole (BZ) and levamisole resistance was investigated in 18 randomly selected dairy goat herds located in southwestern France and characterized by extensive management. On each of the 18 farms, 45 adult goats were randomly allocated into three groups of 15 animals each: an untreated control group, a group that was orally administered fenbendazole (10 mg kg-1 body weight) and a group that received orally a levamisole drench (12 mg kg-1 body weight). Individual faecal egg counts and pooled larval cultures were done 10 days after anthelmintic treatment. Naive lambs were infected with larvae obtained from control and fenbendazole treated groups and were necropsied 35 days after infection for worm recovery. Faecal egg count reductions (FERC) were calculated for fenbendazole and levamisole and, when less than 95 per 100, were considered as indicative of anthelmintic resistance. An in vitro egg hatch test (EHT) was conducted with thiabendazole on eggs isolated from pooled faeces of fenbendazole treated goats in nine farms. Faecal egg count reductions indicated the occurrence of benzimidazole resistance in 15 out of 18 farms. Among these farms, nine had EHT values above 0.1 μg thiabendazole ml-1 confirming the benzimidazole resistance status. Levamisole resistance was detected in two farms through FECR. Based on necropsy results, the prevalence of benzimidazole resistance was higher in Trichostrongylus colubriformis, medium in Haemonchus contortus and lower in Teladorsagia circumcincta. In nine farms the benzimidazole resistance was monospecific whereas multispecific resistance was found in the six remaining farms. A negative relationship was found between FECR for fenbendazole and the average number of anthelmintic treatments given per year on the farm. Despite extensive management including a low number of treatments, the prevalence of benzimidazole resistance was very high suggesting that the repeated and sometimes exclusive use of benzimidazole drugs, even at low frequency, is probably the main cause in developing nematode resistance in dairy goat herds. The importance of other factors such as under-dosing or buying animals already carrying resistant nematodes are discussed.

Species co-occurrences and interspecific associations between intensity of infection were studied in helminth communities of three populations of brown trout, Salmo trutta, from northern Italy. Of the eight helminth species, only four were common enough to be included in the analyses: Pomphorhynchus laevis, Acanthocephalus anguillae, Echinorhynchus truttae and Cyathocephalus truncatus. The observed frequencies of co-occurrences of the different species, based on presence/absence data, did not differ from those predicted by a null model derived from prevalence data. However, the intensity of infection (number of individuals per fish) of different helminth species were generally, but not always significantly, negatively correlated in tests of pairwise associations. Variation in fish sizes and its effect on infection levels, and whether or not two helminth species used the same or different intermediate hosts, had no influence on these findings. Of the few significant negative associations found between pairs of helminth species, none was found in more than one fish population. This suggests that interspecific associations may be condition-dependent: even in apparently similar localities, the same combinations of helminth species show different associations. Without evidence of replicability, it is almost impossible to conclude to the consistent role of competition between any pair of helminth species in the field.

Over the last century in the uplands of Scotland, the extent of heather moorland which supports high densities of mountain hares Lepus timidus has diminished and has gradually been replaced by large-scale commercial forestry plantations or expanding natural woodlands. The potential impact of such a change in land use on host–parasite interactions was investigated by comparing the intensity and prevalence of infection of hares by parasites in two separate habitats: a large hare-fenced young forestry plantation and the adjacent open moorland. Carcasses were collected in November 1990 from within both habitats and after the woodland had been enclosed for nine months. Age, sex, fatness (kidney fat index) and degree of infection of hares were noted. Two parasites were recorded: the nematode Trichostrongylus retortaeformis and the cestode Mosgovoyia pectinata. Clear differences in the intensity of infection of adults occupying the different habitats had occurred in the nine months since woodland enclosure. Adult mountain hares in the woodland had levels of infections approaching four times that observed in hares occupying the open moorland and although not significant, the prevalence of infection was greater in hosts inhabiting the woodland than the open moorland. It is suggested that the parasite–host relationship differs between the two habitats and as heather-dominated moorland landscapes become more fragmented with the increasing establishment of woodlands, the impact of parasites on the life history strategies of mountain hares needs to be reconsidered.

Effects of the anthelmintics, pyrantel and levamisole, on egg development of Angiostrongylus costaricensis were studied in vitro. After 7 days, about 80% of eggs developed to first-stage larvae in Ham's F-12 medium with 10% foetal calf serum under 5% CO2. Significant inhibition of development was caused by pyrantel (10-9–10-8 g ml-1) and levamisole (10-9–10-8 g ml-1) (Mann-Whitney U-test; P<0.05), and none of the eggs developed to first-stage larvae in higher concentrations of these anthelmintics (10-7 g ml-1). Furthermore, incubation with these drugs at 10-8 g ml-1 for at least 3 h or at 10-4 g ml-1 for 1 h caused irreversible effects on egg development.

Rats are known to be relatively resistant to infection with Echinococcus multilocularis. However, when rats are inoculated with the parasite tissues, E. multilocularis proliferates slowly at first but after 6 months the cysts increase in size considerably and contain large numbers of protoscoleces. As rats survive for 18 months or longer, approximately 100 ml of packed protoscoleces can be produced from each rat. A comparison of the antigenicity of the protoscoleces and microvesicles by immunoblot methods showed that both Em18 and Em16 are shared components between both protoscoleces and microvesicles, although the latter have some additional antigenic components. In antigens prepared from protoscoleces, the banding patterns around Em18 were much simpler than those from microvesicles. Therefore, for serodiagnosis of E. multilocularis, antigens should be carefully prepared from protoscoleces rather than microvesicles from the rat.

The prevalence of Spirocerca lupi in 260 privately owned dogs with different life and hunting styles in Greece was based on the examination of randomly taken faecal samples using Teleman's sedimentation technique. The dogs did not demonstrate any clinical signs of spirocerciasis. Although the prevalence was 10%, it was found to be significantly higher in trace hunting dogs (21%), than in scent hunting dogs (5%) and household pets (0%). There was no relationship between prevalence and age/sex of dogs. The impact of life and hunting styles on the prevalence of S. lupi in the dog and that of the faecal examination technique, are discussed.

The abomasal and small intestinal helminth fauna of three species of captive gazelles (Gazella dama mhorr, G. cuvieri and G. dorcas neglecta) kept in captivity in Almería (southeast Spain) have been studied, and the following species were identified: Nematodirus spathiger, N. filicollis, N. helvetianus, Camelostrongylus mentulatus, Trichostrongylus vitrinus, T. probolurus, T. colubriformis, Ostertagia ostertagi, O. harrisi, Teladorsagia (Ostertagia) circumcincta, and T. (Ostertagia) davtiani. Camelostrongylus mentulatus and N. spathiger were the most prevalent and abundant parasites. Ostertagia ostertagi, O. harrisi, N. helvetianus, and T. (Ostertagia) davtiani were identified for the first time in the genus Gazella. In addition, O. harrisi and Trichostrongylus probolurus are new records for Spain.

Successful transmission of macroparasites is dependent on exposure of susceptible hosts to free-living infective stages. When these hosts are herbivores that feed mostly on a single food plant then natural selection should favour those infective larvae that selectively ascend this main food plant. Red grouse feed predominantly on heather, Calluna vulgaris, so we predict that the infective larvae (L3) of the caecal nematode Trichostrongylus tenuis selectively locate and ascend heather plants. To determine whether the presence of heather influences the horizontal dispersal of T. tenuis L3 across soil, the movement of L3 across trays of soil with and without heather was investigated in the laboratory. More T. tenuis L3 were recovered from soil when heather was present, implying that larval migration may be influenced by chemical cues produced by heather plants. This was investigated in a second experiment, in which the horizontal dispersal of T. tenuis larvae was examined in the presence of heather and grass vegetation. This trial was repeated with larvae of a second species, Haemonchus contortus, a nematode whose hosts feed on a wide range of grass and shrub species. Significantly more larvae of both nematode species were recovered in the region of the heather than the grass or controls. This implies that T. tenuis and H. contortus L3 exhibit selective migration towards heather, perhaps reflecting a general response to plant cues which may be stronger for heather than for grass.

Dactylogyrid species (Monogenea) communities were studied in roach, Rutilus rutilus, collected from two localities in the basin of Morava river, Czech Republic, during the period from April to November 1997 and March to September 1998 to determine the effect of water temperature on parasite abundance, species richness and diversity. Dactylogyrid species were found to co-occur on the gills of roach with up to six species found on the same host individual. Nine dactylogyrid species were identified with the abundance of each reaching a very low level. Niche size was considered to increase with species abundance even when water temperature was high. There was a strong effect of water temperature on abundance of the common dactylogyrid species (D. crucifer, D. nanus, D. rutili and D. suecicus) as well as of the rare species D. rarissimus. The temporary occurrence of the rare species was found without any temperature effect. Water temperature did not affect the relationship between abundance and niche size. Niche size increased with abundance, even when the water temperature was high, which suggests that negative interspecific interactions are not important within dactylogyrid communities.