Seasonal fluctuations in the prevalence and intensity of infection with Heligmosomoides polygyrus (Nematoda) were studied in Apodemus sylvaticus (wood mouse, n = 399), sampled from three contrasting habitats in southern England, to test the hypothesis that both intrinsic (host sex, age) and extrinsic (season, site) factors influence parasite burdens. Maximum likelihood techniques based on log linear analysis of contingency tables were employed to generate a minimum sufficient model for prevalence of infection and 3-way ANOVA with negative binomial errors was used to evaluate the relative contribution of the principal factors and their interactions in explaining variation in worm burdens. Host age could not be entered into either statistical model because of some incomplete subsets of data. However, it was evident that in general juvenile mice carried lower worm burdens compared with adults, although these increased towards the winter season. Host sex was not a significant factor, other than in making a contribution to a weak significant interaction between sex and site, arising from male bias in one site and female bias in the remaining two. The principal determinants of variation in worm burden were the extrinsic factors, site and season, with an approximately equal weighting, and their interaction. These effects arose because worm burdens were lower at Dungeness and showed quite different seasonal patterns to the Egham and Isle of Wight sites. We propose that the unique character of the Dungeness habitat was not conducive to optimal transmission of H. polygyrus throughout most of the year (excepting spring) and we suggest possible explanations for these observations.

T cell populations and IL-3 mRNA expression were analysed in mesenteric lymph node cells and intestinal intraepithelial lymphocytes (IEL) in Strongyloides ratti- infected mice. On days 7 and 12 post-infection, 2.6 times as many mesenteric lymph node cells were present in S. ratti- infected mice compared with uninfected mice. Although the percentages of CD3+, CD4+ and CD8+ cells decreased during infection, the absolute numbers of these cell types increased on day 7 due to an overall increase in the mesenteric lymph node cell number. The CD4/CD8 ratio in IEL was increased on day 5, whereas no significant change in the CD4/CD8 ratio was observed in the mesenteric lymph node cells. Expression of IL-3 mRNA, which is an important cytokine for the induction of murine mucosal mastocytosis and S. ratti- expulsion, was examined in mesenteric lymph nodes and IEL of uninfected and infected mice. IL-3 mRNA was detected in mesenteric lymph nodes of S. ratti-infected mice but not detected in the lymph nodes of uninfected mice. IL-3 mRNA was detected in IEL from both infected and uninfected mice with an 20-fold increase in expression in IEL of infected mice. Overall, IL-3 mRNA levels were higher in IEL than in mesenteric lymph nodes following S. ratti- infection. Expression of IL-4, IL-10, stem cell factor (SCF or c-kit ligand) and IFN-γ mRNA was also examined in these two tissues. IL-10 mRNA was not detected in any tissue examined and IFN-γ mRNA levels were unaltered as a result of an S. ratti- infection. Elevated expression of mRNA for SCF (5-fold) and IL-4 (20-fold) was observed in the mesenteric lymph nodes of infected mice. In contrast, SCF mRNA levels were similar in IEL of uninfected and infected animals and only a modest increase in IL-4 mRNA was observed in IEL of infected mice.

Population genetics seeks to understand the genetic relationships within and between populations of a species and the processes that generate these patterns. Little is known about the population genetics of parasitic nematodes. This is a notable gap in our knowledge since understanding the population genetic patterns and processes of parasitic nematodes has profound implications for our ability to fully understand this important group of pathogens. For example, it is only possible to begin to understand how a parasite population will respond to an imposed selection pressure (such as an anthelmintic drug, a vaccine, or resistant hosts) when the population genetic structure and patterns of gene flow of that population is known. Equally, the epidemiology of many nematode parasites is well known empirically and theoretically, yet this epidemiological information is of limited use without a good understanding of the genetic structure of those populations (Anderson & May, 1992).

Skin mucous cells and mucus from four salmonids (rainbow trout, brown trout, Conon salmon, Iijoki salmon) with different susceptibilities to infection with Gyrodactylus derjavini and G. salaris were partly characterized by cytochemistry, immunoblotting and immunocytochemistry. Mucous cell densities in various fin types were partly correlated with resistance to infection with G. derjavini but not with G. salaris. Lectin binding assays indicated slight differences in carbohydrate composition of mucus from the four salmonids but serum antigens specific for salmonids were found in mucus from all of them. Antisera against salmon immunoglobulin and rainbow trout complement factor C3 reacted with mucus from all of the salmonids but not with mucus from phylogenetically unrelated fish. Antisera raised against ACTH reacted with mucus components from rainbow trout, brown trout and Conon salmon but not with mucus from Iijoki salmon. These findings are discussed in relation to the host specificity of ectoparasites and susceptibility to infection.

IgG and IgM antibody responses to fluke cysteine proteinases in Paragonimus ohirai- and Fasciola sp.-infected rats were followed by means of cystatin capture ELISA using fluke excretory-secretory products for 10 weeks after infection. The specific IgG antibodies were detectable at week 2 postinfection in all P. ohirai-infected and some Fasciola-infected rats. Levels of specific IgG antibodies increased rapidly between week 2 and 6, and slightly thereafter, in both infected groups. From week 3, specific IgG antibody levels were higher in Fasciola-infected than P. ohirai-infected rats. Sera from infected rats did not react with heterologous cysteine proteinases throughout the infection periods. In both infected groups, the kinetic patterns of specific IgM antibody responses were similar to those of specific IgG antibody responses although the ELISA levels of the IgM antibody responses were much lower. In abnormal infections with P. ohirai metacercariae x-irradiated at 2 krad, the specific IgG antibodies were detectable at week 2 postinfection with similar ELISA values to normal P. ohirai infection, but thereafter increased little. In infections with P. westermani, for which the rat is not a suitable host, even stunted worms induced a comparable specific IgG antibody response, although the response was lower than in normal infections with P. ohirai. These results indicate that cystatin capture ELISA can distinguish clearly between Paragonimus and Fasciola infections which show immunodiagnostic cross-reactivity and is useful even in the early stages of the infection and in the infection of unsuitable hosts.

Rainbow trout were experimentally infected with the ectoparasitic monogenean Gyrodactylus derjavini at three temperatures, 5.5°C, 11.6°C and 18.7°C. Subsequently, the infection level was monitored during the following 6 weeks. The population growth was positively correlated with temperature in the initial part of the investigation. At 18.7°C growth of the parasite population was fast reaching a peak abundance within 3 weeks, whereafter the infection level decreased significantly. Peak abundance was recorded in week 5 at 11.6°C. A very slow but steady parasite reproduction was noted at 5.5°C, but no peak abundance was reached within 6 weeks. The decline in parasite population after reaching peak levels is likely to be caused by a host response. The host response is also indicated by the parasites' active selection of particular microhabitats. This anti-monogenean response developed fastest at 18.7°C, more slowly at 11.6°C and was not recorded within 6 weeks at 5.5°C.

Morphometric and chaetotactic studies were carried out on the body and cephalic regions of the rediae of Fasciola hepatica (Trematoda: Fasciolidae) in order to precisely identify the different redial generations of this trematode in Lymnaea truncatula under experimental infection. At day 49 post-exposure at 20°C, the length of the redia was significantly higher in the first group of the first generation (R1a) compared with successive generations, R1b, R2a and R2b/R3a. The width of the body was similar in the R1a, R1b, and R2a rediae, but was significantly lower in the R2b/R3a groups. The intrapharyngeal cavity of R1a rediae was significantly wider compared with the R1b, R2a, and R2b/R3a groups, whereas the pharyngeal wall was significantly thicker in the R2b/R3a rediae compared with the R1b and R2a groups. Four other measurements, namely the maximum length and width of the pharynx, diameter of the mouth, and width of intestine, also showed significant variations in relation to pharyngeal morphology and age of infection. Discriminant analysis based on these measurements demonstrated that 98% of the rediae were readily categorized into the four groups identified. The number of perioral sensillae ranged from 126 to 160 but a significant difference was only noted between the mean values of the first generation and those of the group R2b/R3a. From these parameters, the maximum width of the pharyngeal lumen was found to be the best characteristic in the identification of the redial generations.

The relatively small literature on mitochondrial DNA (mtDNA) diversity in nematode species is summarized here. Nematodes show a wide range of overall genetic diversities and population genetic structures. Species-wide levels of diversity correlate strongly with the breeding system and other life cycle features that control effective population size. Obligate outcrossers that parasitize mobile vertebrate hosts are the most diverse, species having hermaphroditic stages are less so, and species having asexual reproductive stages appear even less diverse. Nevertheless, these conclusions are preliminary because there exist so few data on DNA diversity in nematodes. What is needed are more comparative studies using similar sampling designs and the same DNA markers, including nuclear loci and further work with mtDNA

Water soluble extracts of 3131 adult specimens of Dicrocoelium dendriticum from cattle, sheep and goats, mainly from León province, were analysed by isoelectric focusing in thin-layer polyacrylamide gels. Activity of the following enzymes was studied: lactate dehydrogenase (LDH, EC 1.1.1.27), glucose phosphate isomerase (GPI, EC 5.3.1.9), phosphoglucomutase (PGM, EC 2.7.5.1), acid phosphatase (AcP, EC 3.1.3.2), α-glycerophosphate dehydrogenase (α-GPDH, EC 1.1.1.8), hydroxybutyrate dehydrogenase (HBDH, EC 1.1.1.30) and malate dehydrogenase (MDH, 1.1.1.37). Five distinct enzyme types were recognized for LDH (pH range 6.30–7.13), GPI (pH 6.13–6.80) and PGM (pH 6.20–6.60) whereas AcP showed three different patterns (pH 5.70–5.92). Weak and diffuse activity was detected for MDH (pH 4.8–6.2) and no activity was observed for α-GPDH and HBDH. In general, little phenotypic variation was observed between worms recovered from a single host, between those from hosts of the same species and between those from hosts of different species, although some enzyme types were found in some animals but not others. Nevertheless, it must be taken into account that most parasites came from sheep and also from a relatively small area in north-west Spain.

A herd of goats naturally infected with lungworm and gastrointestinal nematodes was divided into three groups and treated with either morantel tartrate or fenbendazole at strategic periods, i.e. in June (at pre-mating), in November (at pre-kidding) and in January (at early lactation) or left untreated. Morantel tartrate treatment (8mg kg−1) was efficient in reducing the gastrointestinal nematode egg output and fenbendazole treatment (15 mg kg−1) was efficient in reducing the gastrointestinal nematode egg and small lungworm larvae faecal output. Reductions in mortality of adult goats and their progeny and improvement of rearing percentages were recorded in both treated groups, with fenbendazole showing a greater response than morantel tartrate. A relative risk analysis showed that mortality in goats and kids was significantly reduced in treated kids and goats. Reduction of 6.6% in kidding rates, 0.21 in prolificacy, and an increase of 1.3 in abortion rates, 8.3% in kid and 2.2% in goat mortalities, could be attributable to the small lungworm infection. Small lungworm infections seem therefore to be one of the main causes of indirect kid mortality and inadequate breeding performance of goats in the semi-arid Middle Atlas region of Morocco.

Infection levels of Polystoma marmorati (Polystomatidae: Monogenea) in the painted reed frog, Hyperolius marmoratus, and P. umthakathi in the kloof frog, Natalobatrachus bonebergi, were studied under natural conditions. The recorded prevalence for P. marmorati was generally high in adult frogs and low in tadpoles. In the case of P. umthakathi, the opposite was found with a low prevalence in adult frogs and a very high prevalence in tadpoles. Based on these findings, the hypothesis is presented that for P. marmorati the neotenic stage does not play a determining role and the population is maintained by bladder parasites. For P. umthakathi the neotenic stage appears to be more important than the bladder parasite and the population can probably survive without any significant contribution from bladder parasites.

Polymorphic molecular markers are being identified to characterize the genomes of parasitic nematodes. The aim is to construct a map with markers evenly spread over the six chromosomes. With such a map, regions can be identified that are under selection pressure when attempts are being made to eradicate worms, be it by drugs, vaccines or genetic resistance in the sheep. Several types of markers have been developed, microsatellites, transposon-associated markers, amplified fragment length polymorphism (AFLP) and expressed sequence tag (EST) markers. Linkage groups can be constructed using several generic crosses between inbred and drug resistant strains. EST markers will be especially important for comparative mapping with the genome of Caenorhabditis elegans, and therefore localization of the linkage group on a chromosome. It will then be possible to identify functional genes close to markers that have changed allele frequencies under selection pressure and identify the mechanisms of resistance to parasite control.

Two sets of dung-derived organisms from soil routinely fertilized with manure (MA) and soil chemically fertilized (CH) were cultured separately in the laboratory. Baermannized organisms from these cultures were added to 20 g of faeces from strongyle-infected horses to form three treatment groups: (i) no soil organisms; (ii) low inoculum of soil organisms containing all organisms present in a suspension of approximately 100 adult female free-living nematodes; and (iii) high inoculum containing those soil organisms present with approximately 1000 adult female free-living nematodes. Three studies were conducted using MA cultures and faeces containing 50 strongyle epg, CH cultures and faeces containing 1500 strongyle epg, and a mixture of soil organisms from the two cultures (MC) and faeces containing 600 strongyle epg. Within each study, five control cultures and 15 each of low and high inoculum cultures were prepared and incubated at 24°C and 95% humidity in a climate chamber for 15 days. Parasitic and free-living nematodes were then recovered by the Baermann technique and counted. The numbers of third stage larvae were significantly lower in the high inoculum group compared to controls. The percent reductions in the number of third stage larvae for the low and high inoculum groups were 63.6% and 90.9%, 85.1% and 97.1%, 84.5% and 98.4% for MA, CH, and MC studies, respectively, indicating that mortality increased with the number of soil organisms added to cultures. Examination of the source cultures detected the presence of two species of nematophagous fungi and three genera of free-living nematodes reported to be predacious.

The structuring process of the macroparasite community of caged Cichlasoma urophthalmus was studied over time using sentinel fish. Three thousand uninfected cichlids were stocked in floating cages introduced into a quarry in which a wild population of the same species was present. Caged and wild cichlids were sampled monthly over 6 and 7 months, respectively. Seventeen macroparasite species were found in the wild C. urophthalmus population, ten of which were detected in the caged population after 6 months. Early infections were by those species that were more frequent and abundant in the wild population, while helminths with a low prevalence and abundance in the wild appeared later in the caged fish population. The results suggested that the structuring process of the macroparasite community of caged C. urophthalmus followed a predictable pattern, in which those species that were most frequent and abundant in the wild were the first to establish in sentinel fish.

In an abattoir study, 514 camels, slaughtered for meat production in different areas of northern Libya were examined for the presence of cystic echinococcosis (CE). In addition, 367 sheep and 184 goats were examined. The overall prevalence of infection with CE was 48% in camels, 15.8% in sheep and 3.8% in goats. The infection rate, number and size of cysts were significantly higher in older camels. In six city abattoirs across northern Libya, i.e. Zawia, Tripoli, ElKhumes, Mesurata, Sirt and Benghazi, the prevalence rate of infection in camels ranged from 38.7% to 55.2%, in comparison with sheep and goat rates which were between 0% and 37.9% and 0% and 8.2%, respectively. In camels, the lungs were the most frequently infected organs (85.4%) with liver cysts occurring at a significantly lower rate (33%). In contrast, the liver was the predominant infected site with prevalence values of 86% and 100% in sheep and goats, respectively. More than 90% of camel hydatid cysts were fertile. The possible role of camels in the transmission of CE in Libya is discussed.

Incorporation of radiolabelled tyrosine was examined in males of Schistosoma mansoni maintained in vitro. Adult worms were recovered from mice and only those that were paired were used. Males and females were separated and placed in 4°C RPMI 1640 containing 10% fetal calf serum (FCS). Individual males were incubated for 1 h either alone or with a female. Other males were incubated in a medium containing 40 ng ml−1 recombinant tumour necrosis factor α (rTNFα). Subsequently, males were incubated with or without females for 1 h in a medium containing 20 μCi ml−1 [14C]-tyrosine. All incubations were carried out in RPMI 1640 containing 10% FCS at 37°C under 5% CO2. Untreated single males incorporated small amounts of labelled tyrosine. Pretreatment of single males with rTNFα did not affect their tyrosine incorporation (P = 0.693). However, males maintained in vitro with females incorporated 221% more tyrosine than the controls (P = 0.00008), suggesting that a chemical stimulus from the female affects tyrosine incorporation in males.

In an in vitro trial, the trapping ability of Arthrobotrys robusta and Monacrosporium gephyropagum against Strongyloides papillosus infective larvae on corn meal agar plates, was evaluated after seven days of interaction at 25°C. Monacrosporium gephyropagum trapped 93.1% of the larvae whereas A. robusta trapped only 32.3%. Variability in the capture of S. papillosus infective larvae by both trapping fungi is discussed.

We review how constraints on the mating probability of female worms by segregation within individual host guts form a critical element in the parasite population structure of nematodes. We consider the effects of these constraints on the population genetics of nematodes under various assumptions regarding worm competition as reflected in the relationship between the abundance of a certain genotype within the gut and the probability of reproductive success. The consequences for the emergence of resistance to drugs and immunotherapy and implications for host-parasite coevolution are discussed. We also review evidence for genetic heterogeneity in parasite populations as a necessary prerequisite for the applicability of mating probability models designed to assess the population genetics of nematodes.