Virulent strains of Entamoeba histolytica have been reported to produce a mixture of phosphoglycoconjugates that share some structural features with the lipophosphoglycans (LPGs) of Leishmania. Purification of these glycoconjugates is essential to their precise structural characterization. In this study we have extracted ‘LPG-like’ molecules from various virulent E. histolytica strains and purified on the basis of charge differences, 2 apparently related glycoconjugates a ‘LPG’ and a ‘lipophosphopeptidoglycan (LPPG)’. In marked contrast to the abundance of these ‘LPG’ and ‘LPPG’ molecules in the virulent strains, avirulent E. histolytica and E. dispar strains produce either very low, or no detectable levels of LPG, and either low levels or modified forms of ‘LPPG’. Monospecific polyclonal antibodies prepared against that ‘LPG’ of the virulent strain HM-1: IMSS cl6 identified epitopes shared between both the ‘LPG’ and the ‘LPPG’ of this and other virulent strains, using Western blot analysis. Flow cytometric analysis of a range of strains using these antibodies identified a surface distribution of these molecules and confirmed a correlation between surface exposure of epitopes bound by these antibodies and parasite virulence.

Based on substrate preferences, cercariae of Schistosoma mansoni were seen to express both cathepsin L and cathepsin B cysteine proteinases, although the former activity was many-fold greater. Two cathepsin L activities identified in cercarial extracts by zymography co-migrated with activities in extracts of 3 h and 24 h schisotosomula and in extracts of adult worms. Since these enzymes have been implicated in haemoglobin digestion by adult worms, they may perform a similar function in schistosomula. Immunolocalization using scanning electron micrographs showed that cathepsin L and cathepsin B proteinases were present in the cercarial post-acetabular glands. In addition, cercarial serine proteinase activities considered to facilitate skin penetration efficiently cleaved the substrates Z-Gly-Pro-Arg-NHMec and Z-Gly-Pro-Lys-NHMec. Cercariae release most of this serine proteinase activity when induced to secrete the contents of their acetabular glands. In contrast, newly transformed 3 h and 24 h schistosomula did not express this activity.

Schistosoma mansoni egg counts by faecal examination vary considerably and are not very sensitive, so prevalences are underestimated. The distribution of egg counts can adequately be described by a stochastic model which distinguishes variation in counts between persons and variation in repeated counts within a person. Based on this model a pocket chart has been developed which predicts the proportion of individuals harbouring at least 1 S. mansoni worm pair – the ‘true prevalence’ – from a simple single survey prevalence and geometric mean egg count (using common duplicate 25 mg Kato–Katz smears). The current paper describes the validation of this chart by comparing predicted true prevalences with prevalences observed after 5–7 repeated Kato–Katz faecal examinations (Burundi), by examination of a large quantity of stool using the Visser filter (Brazil) or a selective sedimentation–filtration method (Surinam). Because 5–7 repeated examinations do not suffice to measure all infections, predictions have been made of the cumulative proportion positives over 5–7 surveys – the ‘approximate true prevalence’ – as well. After dividing the data into age groups, 12 different subsets were considered for validation. In all 12 cases, predicted true prevalences (or approximate true prevalences for the Burundi data) agree well with those observed. The overall agreement depends only slightly on the assumed relationship between worm numbers and mean egg counts, with a good fit for a productivity between 0·8 and 4·4 eggs per gramme faeces (EPG) per worm pair (WP). This interval includes the most plausible value from the literature, i.e. 1·0 EPG/WP, which has been applied in the initial pocket chart. These findings support the validity of the chart to predict true prevalences for a wide range of productivity assumptions, and reinforces the applicability of its underlying stochastic model to describe egg count variation. However, as predictions appear to vary importantly when using only part of the data, it is also concluded that the pocket chart never compensates for limited validity of initial single survey prevalences and geometric means in consequence of small sample sizes.

Developmental rates for Wuchereria bancrofti larvae maturing in the vector Aedes polynesiensis were estimated by analysing stage-frequency data consisting of counts of larval stages in mosquitoes reared at 20, 22·5, 25, 27·5, 30 and 32 °C. Base temperatures (i.e. low temperature thresholds) for W. bancrofti development were estimated by the x-intercept method and the model of Lactin et al. (1995). Resulting values were similar with both methods and were ≈12·5 °C for microfilariae (mf) in thorax, ≈17 °C for L1, 15·5 °C for L2 and 16·5 °C for L3. Upper thresholds estimated by the Lactin et al. model were 29·3 °C for mf, 29·1 °C for L1, 32·2 °C for L2 and 31·5 °C for L3. In addition, an original method was devised for computing the L3 upper threshold, by modelling L3 length shrinkage with temperature. It gave a value of 31·4 °C. At 32 °C, L2 and L3 stages exhibited altered morphology, larvae being shorter and wider than expected. The model of Lactin et al. described adequately the non-linear relationship between developmental rate and temperature, but a linear degree-day approach may be applied for temperatures below 27–28 °C.

Excretory–secretory (E–S) products, released by Trichobilharzia ocellata cultured in vitro, were assessed for their modulatory effects on the internal defence system of the freshwater snail, Lymnaea stagnalis. E–S products were concentrated and fractionated using high-pressure liquid chromatography (HPLC) and bacterial clearance activity of haemocytes was taken as a parameter for the internal defence system. Two main fractions of E–S products were produced by T. ocellata, a low molecular fraction (low MW) and a high molecular fraction (high MW), weighing approximately 2 kDa and 40 kDa, respectively. Stage-dependent release of E–S products by transforming miracidia and mother sporocysts was indicated by the difference in proportions of these two fractions, which varied over time. After a culture time of 0–33 h, the smaller fraction was prominent whilst E–S products released between 33 and 72 h consisted of a higher proportion of the high MW fraction. After a culture of 72–96 h, lower and comparable quantities of both fractions were produced by the same batch of cultured parasites. Assaying the 2 fractions released during 0–33 h revealed that the high MW fraction had a suppressing effect on the bacterial clearance activity of haemocytes from juvenile snails and the low MW fraction activated haemocyte activity. Combined fractions obtained during 0–33 h had an activating effect on haemocyte activity but fractions separated from media collected at 33–72 h culture had a suppressing effect on the bacterial clearance activity of the haemocytes. The combined E–S fractions from the 72–96 h incubation had no effect on haemocyte activity. The present study shows that T. ocellata modulates the internal defence system of L. stagnalis by actively interfering with haemocyte function. MALDI-MS analysis of the low MW fraction revealed several components ranging from 450 to 1600 Da. Although it is as yet not clear which factor is responsible for the activating effect it is supposedly a peptide as it is pronase-sensitive and resistant to TFA and acetonitrile.

To study the infection dynamics of metacercariae of the digenean Cryptocotyle lingua, wild living Atlantic cod, Gadus morhua, were caged for 18 months close to the shore. Here they were exposed to naturally occurring transmission stages of the parasite. First, both the abundance and the variance to mean ratio of metacercariae increased, but during the second half of the study the abundance levelled out, and the variance to mean ratio showed a significant decrease. Host mortality was negligible throughout the study. Based on the relationship between pigment spots and metacercariae observed by skin digestion, there was no indication of density-dependent parasite mortality. We conclude that the infrapopulations of metacercariae on the caged cod probably were regulated by density-dependent host responses acting against the cercariae.

The distribution of Varroa jacobsoni on clustered, overwintering workers of Apis mellifera was investigated. The majority of mites were found between the 3rd and 4th ventro-lateral tergites of the abdomen with a significant preference for the left side of the host. This position would enable the mites to place their mouthparts in close proximity to the central portion of the bees' ventriculus. This may allow the mites access to nutrients at higher concentrations than would occur elsewhere in the haemolymph. At the start of winter, most infested bees carried only a single mite but towards the end increasing numbers of bees carried 2 or more mites. There was also an increase in the mite : bee ratio and more mobile mites (i.e. those moving about on the bees) were recorded. These results suggest that the mites suffer a lower overwinter mortality than the bees and are capable of transferring to a new host either before the original host dies or before it falls to the floor of the hive. This will have consequences for the transfer of diseases by Varroa within the hive.

We studied flea assemblages on rodents in different habitats of the Ramon erosion cirque in the Negev Desert to examine whether host–habitat relations influence flea spatial distribution. Eleven flea species parasitizing 12 rodent species were recorded. There was significant positive relationship between flea species richness and body mass of the host species; no relationships were found between relative richness of flea assemblage and either the number of habitats occupied by the host species or the size of host geographical range. The differences in pattern of flea parasitism among habitat types within host species were determined by both environmental features of a habitat and the specific pattern of habitat use by rodents. There was replacement of Xenopsylla conformis by Xenopsylla ramesis on Meriones crassus and Gerbillus dasyurus among different habitats. The results of ordination of the flea collections from each individual host demonstrated that the flea assemblages were segregated mainly along 4 axes, which explained 86% of total variance. Each of the ordination axes corresponded with a change in flea species composition. The directions of these changes were (1) among-hosts within a habitat and (2) among-habitats within a host.

Infection with developing metacestodes of the rat tapeworm, Hymenolepis diminuta, is known to retard the accumulation of the yolk protein, vitellin, in the terminal ovarian follicles of the intermediate host, Tenebrio molitor. It is probable that this is the result of competitive inhibition of juvenile hormone binding at a microsomal binding site in the beetle follicular epithelium. Experiments were designed to test the hypothesis that inhibitor molecules were circulating in the haemolymph of infected beetles. Whole haemolymph, collected from male or female beetles at various stages post-infection, was injected into non-infected female recipients 2 days post-emergence. Ovaries were removed 3 days later and the vitellin content of the same sized follicles measured using an ELISA. The vitellin content of follicles from recipients of haemolymph from females infected with metacestodes at stage 1 and stage 3–4 was significantly reduced (24 and 27·9%) compared to sham-infected females. However, haemolymph from females infected with mature metacestodes did not affect the vitellin content. Results were thus comparable to those obtained by monitoring ovarian vitellin levels in female T. molitor with bona fide infections. Haemolymph from infected males did not affect ovarian vitellin content. These results indicate that molecules that can modulate vitellogenesis may be present in the haemolymph of females infected with developing metacestodes but that these factors disappear later in infection.

The time-course of differentiation/proliferation of mast cells in gut epithelium was investigated in mice infected with the nematode Strongyloides venezuelensis. After infection, expression of proliferating cell nuclear antigen increased in gut intraepithelial mast cells on days 7 to 11, followed by an increase in the number of intraepithelial mast cells from days 11 to 14. Mast cell precursors were defined as cells that formed mast cell colonies in methylcellulose culture. After infection, the numbers of mast cell precursors in the population of gut intraepithelial mononuclear cells (IEMNC) increased significantly on day 3 and returned to the pre-infection level by day 7. Mast cell precursors in Peyer's patches, mesenteric lymph nodes (MLN), and spleen also increased from day 7 p.i. Production of IL-3 and IL-4 in MLN and spleen were increased between 7 and 11 days p.i. These results show that murine intestinal mastocytosis is initiated by an early increase in mast cell precursor number in the gut epithelium followed by proliferation/differentiation of mast cells. Mast cell precursor numbers increased even before the production of IL-3 and IL-4 in MLN and spleen, suggesting that some local factors might be involved in this phenomenon.

Helminthologically naive 8-week-old lambs were administered 50000 infective-stage larvae of the trichostrongyle nematode Nematodirus battus. Initial mean adult worm burdens were significantly reduced (P < 0·01) at day 21 post-infection (p.i.). Peripheral blood eosinophil counts showed a significant increase (P < 0·001) by day 25 p.i. when compared with uninfected control animals. Sections of small intestine taken at post-mortem from the area of adult worm establishment over the course of infection showed a significant increase in mucosal eosinophil and mast cell numbers during the period of adult worm rejection, when compared with uninfected control animals. These results show that young lambs develop significant increases in the numbers of cells associated with an inflammatory reaction in the intestine during the development of a partially protective immune response to this parasitic nematode.

Parasite life-history traits should reflect past environmental and host-related selective pressures acting to produce strategies that maximize transmission success. The evolution of adult body size and egg production in 804 species of trematode parasites was investigated using independent contrasts derived from a phylogeny of trematodes. Contrasts in trematode body size were positively correlated with contrasts in egg size, and almost significantly correlated with contrasts in numbers of uterine eggs. After controlling for body size, no relationship existed between egg size and egg numbers, suggesting that there is no trade-off between the two components of egg production. Average host body mass and latitude of the sampling site did not correlate with either trematode body size or egg size. Contrasts between trematode taxa exploiting ectotherm hosts and their sister taxa exploiting endotherms showed no consistent difference in either body size or egg size. The effect of other variables on trematode life-histories, such as the nature of the habitat in which eggs are released, the site of attachment within the host's body, or the number of hosts involved in the life-cycle, could not be evaluated statistically. The similarity in life-history traits among members of given clades suggests that phylogenetic constraints may have acted to limit or mask any adaptive changes expected from changes in host-related or environmental conditions.