Sex steroids play a significant role in regulating the parasite load in experimental intraperitoneal Taenia crassiceps cysticercosis of male and female Balbc/anN mice. Briefly, oestrogens increase parasite loads and androgens decrease them (1) by acting directly on the parasite, favouring or hindering its reproduction, respectively, and (2) by biasing the hosts' immune response towards a parasite-permissive Th2 or a parasite-restrictive Th1 response. The infected male host also undergoes drastic endocrinological and behavioural changes that may impinge upon the course of infection, and the host's mating behaviour and its exposure to predators. In addition, at different times of infection, significant changes occur in the expression of c-fos in the host's hyppocampus, hypothalamus and preoptic area. Thus, the host's brain seems to sense and/or react to intraperitoneal infection. The physiological domains of the network affected by the infection, which classically included the hypothalamus-pituitary-axis and the immune system, must now incorporate the host's sexual hormones and other areas of the brain. The network's complex circuitry and functions may help understand some basic questions of parasitology (i.e. the hosts' sexual dimorphism in parasite infections, host-parasite specificity, heterogeneity in the course and outcome of infections at different stages of parasite and host development). The plurality of elements and the complexity of the network that regulates the host-parasite relationship also point to additional strategies for the treatment and control of infections.

Many different drug-resistant lines of rodent malaria are available as screening models. It is obligatory to screen new compounds for antimalarial activity against a series of resistant lines in order to identify a compound with potential for the treatment of multi-drug resistant (MDR) malaria infections. Instead of using a battery of resistant lines, a single MDR Plasmodium yoelii nigeriensis strain that shows a wide spectrum of drug resistance to high doses of chloroquine, mepacrine, amodiaquine, mefloquine, quinine, quinidine, halofantrine as well as tetracyclines, fluoroquinolines and erythromycin, was used to assess the blood schizontocidal efficacy of a new macrolide azithromycin and other antibiotics. The present study shows that only azithromycin has the potential to control an MDR P. y. nigeriensis infection in Swiss mice, provided the treatment with a dose of 50–100 mg/kg/day by oral route is continued for a period of 7 days. Tetracycline, oxytetracycline, doxycyline, erythromycin, ciprofloxacin and norfloxacin, although active in vitro, failed to protect the mice. Tetracycline, ciprofloxacin and norfloxacin combinations with chloroquine did not control the infection. Additionally, the antimalarial efficacy of azithromycin can be potentiated with the addition of arteether, which is an ethyl ether derivative of artemisinin. A total (100%) curative effect has been obtained with a shorter regimen of 4 days only.

This paper aims to test the influence of route of infection (intravitreal and instillation) on the course of ocular toxoplasmosis in mice, using the Toxoplasma gondii Me-49 strain. All mice inoculated intravitreally or by instillation presented the same pattern of infection. Using either route, parasites were observed in the retinal vessel with the formation of a glial reaction in the inner plexiforme layer and discontinuity of the pigmented epithelium of the retina 7 days after infection. However, when the intravitreal route was used a more intense inflammatory infiltrate was observed in the retina. The results suggest that inoculation route remarkably influences the inflammatory pattern in ocular toxoplasmosis and that the instillation route should be preferentially used in experimental infections in the murine ocular model of infection by T. gondii, specially with small animals where there is extensive needle damage, which is not observed in the instillation route.

To clarify the taxonomy of trichomonads associated with human respiratory diseases, we examined a collection of axenic trichomonad strains isolated from the oral cavity and bronchi of patients from pulmonary diseases clinics in Tallin, Estonia. The oral and bronchial strains were compared mutually as well as with a reference strain of Trichomonas tenax, a common inhabitant of the human oral cavity, and other trichomonad species from humans and animals. Unexpectedly, the morphological studies, as well as DNA sequencing of ITS1-5.8S rRNA-ITS2 regions revealed that the Estonian strains belong to the genus Tetratrichomonas, with a high similarity to the avian species Tetratrichomonas gallinarum. None of the strains belonged to Trichomonas tenax. DNA fingerprinting using the RAPD method separated Estonian strains into 2 distinct groups: ‘bronchial’ consisting of 5 and 2 strains isolated from bronchi and ‘oral’ cavity, respectively, and oral consisting of 3 oral strains. Consistent differences between ‘bronchial’ and ‘oral’ groups were confirmed by analysis of ITS1-5.8S rRNA-ITS2 sequences. Our results have revealed novel trichomonad species of the human oral cavity and bronchi.

The protozoan parasite Leishmania belongs to the most ancient eukaryotic lineages and this is reflected in several distinctive biological features, such as eukaryotic polycistronic transcription and RNA trans-splicing. The disclosure of this organism's unusual characteristics leads to a better understanding of the origin and nature of fundamental biological processes in eukaryotes. Here we report another unusual phenomenon as we demonstrate that precursor ribosomal RNA can be extensively polyadenylated during post-transcriptional processing[dagger]. Furthermore, we demonstrate that the degree of precursor rRNA polyadenylation is variable in different strains and in the different life-stages of a strain.

The microsporidian parasite, Pleistophora mulleri, infects the abdominal muscle of the freshwater amphipod Gammarus duebeni celticus. We recently showed that P. mulleri infection was associated with G. d. celticus hosts being more vulnerable to predation by the invasive amphipod Gammarus pulex. Parasitized G. d. celticus also had a reduced ability to prey upon other co-occurring amphipods. We suggested the parasite may have pervasive influences on host ecology and behaviour. Here, we examine the association between P. mulleri parasitism and parameters influencing individual host fitness, behaviour and interspecific interactions. We also investigate the relationship between parasite prevalence and host population structure in the field. In our G. d. celticus study population, P. mulleri prevalence was strongly seasonal, ranging from 8·5% in summer to 44·9% in winter. The relative abundance of hosts with the heaviest parasite burden increased during summer, which coincided with high host mortality, suggesting that parasitism may regulate host abundance to some degree. Females were more likely to be parasitized than males and parasitized males were paired with smaller females than unparasitized males. Parasitism was associated with reduction in the host's activity level and reduced both its predation on the isopod Asellus aquaticus and aggression towards precopula pairs of the invasive G. pulex. We discuss the pervasive influence of this parasite on the ecology of its host.

Patterns of parasite site selection, variation in infection parameters and interspecific associations are examined in the light of new field data on larval microphallids in Gammarus insensibilis from a Black Sea lagoon. These patterns are discussed in relation to the predictions for the manipulative effect of Microphallus papillorobustus and its relationships with the other microphallid species based on studies on the French Mediterranean coast. Four species were recovered: Maritrema subdolum, Microphallus hoffmanni, M. papillorobustus and Levinseniella propinqua. The latter two were located in both corporal and cephalic segments, but the selection of brain appeared stronger for L. propinqua. M. subdolum was the first colonizer of amphipod population recruits, and unequivocally the dominant species in the lagoon. There was a significant positive relationship between the parasite load of all 4 species. Concurrent infections were exceedingly frequent, and no departures from random association were detected. We found no evidence that the cerebral metacercariae of M. papillorobustus consistently predict the parasite load of any of the other species in the system and identify sources for heterogeneity that may account for the differences between the Black Sea and the Mediterranean system: habitat heterogeneity, bird diversity and host-parasite systems used to infer relationships between microphallids.

We examined the patterns of parasite melanization in Gammarus insensibilis using data on microphallids from Pomorie Lagoon (Black Sea) in the light of 3 predictions associated with host survival: (i) hosts invest more in defence in an environment where the likelihood for infection is higher; (ii) multiple immune challenges exhaust host reserves and result in decreased melanization rates in older hosts; (iii) host immune response is directed against the cerebral metacercariae of Microphallus papillorobustus that alter amphipod behaviour and are most detrimental to the host. G. insensibilis was capable of melanizing the metacercariae of all four species of trematodes found to be hosted by the amphipods. The frequency of melanization and mean abundance of melanized metacercariae were substantially higher than those observed in the same amphipod-gammarid system on the French Mediterranean coast. However, the rate of melanization was low and showed a significant decrease with amphipod size. Although the 4 species were differentially melanized, the host response was largely directed against Microphallus hoffmanni and M. subdolum. We suggest that (i) the lower melanization efficiency with age is due to the mode of infection, probably leading to loss of haemolymph and monopolization of the defence resources for wound healing and (ii) in the French system, host response focuses on the most prevalent and abundant species.

To investigate the prevalence of a flea-borne protozoan (Trypanosoma (Herpetosoma) microti) in its field vole (Microtus agrestis) host, we monitored over a 2-year period a range of intrinsic and extrinsic parameters pertaining to host demographics, infection status and vector (flea) prevalence. Generalized Linear Mixed Modelling was used to analyse patterns of both flea and trypanosome occurrence. Overall, males of all sizes and ages were more likely to be infested with fleas than their female counterparts. Flea prevalence also showed direct density dependence during the winter, but patterns of density dependence varied amongst body mass (age) classes during the summer. Trypanosome prevalence did not vary between the sexes but was positively related to past flea prevalence with a lag of 3 months, with the highest levels occurring during the autumn season. A convex age-prevalence distribution was observed, suggesting that individuals develop a degree of immunity to trypanosome infection with age and exposure. An interaction between age and whether the individual was new or recaptured suggested that infected animals are less likely to become territory holders than their uninfected counterparts.

Aggregation is one of the distinctive features in parasite-host relationships, which has generally been studied at the level of host communities. Parasite aggregation at the infracommunity level may nevertheless be important for intraspecific interactions such as parasite mating success and opportunities for cross-fertilization. In the present paper, we studied the infracommunity aggregation of 3 highly abundant Dactylogyrus (Monogenea) species occurring on the gills of crucian carp (Carassius carassius). In line with the previous work on monogenean communities, we observed no competition between the species. At the species level, parasites were distributed unevenly on the gills showing aggregation in the majority of infracommunities. However, aggregation decreased with increasing parasite abundance, which supports the hypothesis that less aggregation may be needed to ensure successful mating when the distance to a potential mate decreases with increasing number of conspecifics. Lack of interspecific interactions, species specific site selection and the importance of study scale for aggregation patterns in dactylogyrids are discussed.

In order to reveal the mechanisms underlying nurse cell formation during Trichinella spiralis infection, the expression of the factors of tumor necrosis factor-alpha (TNF-α)/TNF receptor 1 (TNFR-1) signalling pathway mediating apoptosis was investigated. The analysed factors included TNF-α, TNFR-1, TNF receptor-associated death-domain (TRADD), caspase 3, caspase 8, TNF receptor associated factor-2 (TRAF2) and receptor interactive protein (RIP), all of which are involved in the TNF-α/TNFR-1 signalling pathway-mediated apoptosis. The quantitative RT-PCR indicated that the infected muscle tissues up-regulate the expression of pro-apoptosis genes (TNF-α, TNFR-1 and TRADD, caspase 3 and caspase 8), and anti-apoptosis genes (TRAF2 and RIP) at the beginning of cyst formation. The expression returned to the normal level after cyst formation. The quantitative RT-PCR analysis of mRNA from tissue samples isolated by laser capture micro-dissection confirmed that the up-regulation of these genes was restricted in infected muscle cells, was not in the inflammation cells around infected muscle cells nor in normal muscle cells. The in situ localization study of pro-apoptosis (TRADD, caspase 3) and anti-apoptosis gene products (TRAF2) indicated that these were expressed in the basophilic cytoplasm (infected muscle cell origin) of the nurse cells. Thus the present study suggests that the TNF-α/TNFR-1 signalling pathway is involved in nurse cell formation.

Strongyloides ratti is a parasitic nematode of rats. The host immune response against S. ratti affects the development of its free-living generation, favouring the development of free-living adult males and females at the expense of directly developing, infective 3rd-stage larvae. However, how the host immune response brings about these developmental effects is not clear. To begin to investigate this, we have determined the effect of non-immune stresses on the development of S. ratti. These non-immune stresses were subcurative doses of the anthelmintic drugs Ivermectin, Dithiazanine iodide and Thiabendazole, and infection of a non-natural host, the mouse. These treatments produced the opposite developmental outcome to that of the host immune response. Thus, in infections treated with subcurative doses of Ivermectin, Dithiazanine iodide and in infections of a non-natural host, the sex ratio of developing larvae became more female-biased and the proportion of female larvae that developed into free-living adult females decreased. This suggests that the mechanism by which the host immune response and these non-immune stresses affect S. ratti development differs.

Macroparasites are almost always aggregated across their host populations, hence the Negative Binomial Distribution (NBD) with its exponent parameter k is widely used for modelling, quantifying or analysing parasite distributions. However, many studies have pointed out some drawbacks in the use of the NBD, with respect to the sensitivity of k to the mean number of parasites per host or the under-representation of the heavily infected hosts in the estimate of k. In this study, we compare the fit of the NBD with 4 other widely used distributions on observed parasitic gastrointestinal nematode distributions in their sheep host populations (11 datasets). Distributions were fitted to observed data using maximum likelihood estimator and the best fits were selected using the Akaike's Information Criterion (AIC). A simulation study was also conducted in order to assess the possible bias in parameter estimations especially in the case of small sample sizes. We found that the NBD is seldom the best fit for gastrointestinal nematode distributions. The Weibull distribution was clearly more appropriate over a very wide range of degrees of aggregation, mainly because it was more flexible in fitting the heavily infected hosts. Moreover, the Weibull distribution estimates are less sensitive to sample size. Thus, when possible, we suggest to carefully check on observed data if the NBD is appropriate before conducting any further analysis on parasite distributions.

A potential control strategy for nematode infection in sheep is the implementation of a breeding programme to select for genes associated with resistance. The Texel breed is more resistant to gastrointestinal nematode infection than the Suffolk breed, based on faecal egg count, and this difference should enable the identification of some of the genes responsible for resistance. The objective of this study was to determine if variation at the ovine MHC-DRB1 locus was associated with variation in faecal egg count in Suffolk and Texel sheep. Ovar-DRB1 alleles and faecal egg count were determined for Texel (n=105) and Suffolk (n=71) lambs. Eight Ovar-DRB1 alleles, including 1 previously unknown allele, were identified in the Texel breed by sequence-base-typing. Seven Ovar-DRB1 alleles were identified in the Suffolk breed. Two Ovar-DRB1 alleles were common to both breeds, but were among the least frequent in the Suffolk population. In the Suffolk breed 1 Ovar-DRB1 allele was associated with a decrease in faecal egg count and 2 alleles with an increase in faecal egg count. This locus accounted for 14% of the natural variation in faecal egg count in Suffolks. There was no evidence for an association between Ovar-DRB1 alleles and faecal egg count in the Texel breed and the Ovar-DRB1 locus accounted for only 3% of the phenotypic variation in faecal egg count. These results suggest that the Ovar-DRB1 gene plays an important role in resistance to nematode infection in the Suffolk breed. The difference in faecal egg counts between these breeds may be attributable in part to the different allele profile at the Ovar-DRB1 locus.

Infection of the central nervous system by Taenia solium cysticerci is the cause of human neurocysticercosis, a major neurological infection in the Third World and an emerging infectious disease in the United States. We previously isolated a cysteine proteinase from cysticerci of Taenia crassiceps and demonstrated that it degrades human IgG in vitro. We have now isolated a 48 kDa thiol-dependent proteinase from T. solium. The T. solium enzyme also degrades human IgG, but does not significantly degrade albumin. IgG degradation was inhibited by cysteine proteinase inhibitors, but not significantly by inhibitors of aspartic, serine, or metalloproteinases. The peptide substrate specificity and pH optimum resemble cathepsin L. The Km for the peptide substrate Z-Phe-Arg-AFC was calculated to be 7·0×10−6M, the Kcat was 1·98×105 s−1, and the Kcat/Km 2·84×109M−1 s−1, a value which is within the diffusion control limit for highly catalytic enzymes. We propose that immunoglobulin degradation by the T. solium cysteine proteinase may play a key role in the host-parasite interface and could be employed as a target for chemotherapy.

Despite evidence for the existence of interspecific interactions between helminth species, there has been no theoretical exploration of their effect on the distribution of the parasite species in a host population. We use a deterministic model for the accumulation and loss of adult worms of 2 interacting helminth species to motivate an individual-based stochastic model. The mean worm burden and variance[ratio ]mean ratio (VMR) of each species, and the correlation between the two species are used to describe the distribution within different host age classes. We find that interspecific interactions can produce convex age-intensity profiles and will impact the level of aggregation (as measured by the VMR). In the absence of correlated exposure, the correlation in older age classes may be close to zero when either intra- or interspecific synergistic effects are strong. We therefore suggest examining the correlation between species in young hosts as a possible means of identifying interspecific interaction. The presence of correlation between the rates of exposure makes the interpretation of correlations between species more difficult. Finally we show that in the absence of interaction, strong positive correlations are generated by averaging across most age classes.

As a zoologist, I have never really understood why those of us who study nematodes continue to partition ourselves into at least two distinct camps, one of which works on the plant-parasitic and free-living species, and the other primarily on animal-parasitic species. And I suspect that nematodes themselves are equally puzzled by this segregation of their ardent scholars. Historically, of course, plant nematologists aggregated in crop research and botany departments, whereas the animal nematologists were stationed in livestock, veterinary, medical and zoological departments of research institutes and universities. I found much of interest in NematologyVol. 1, but I was left with the impression that, whilst the ‘iron curtain’ was beginning to tumble, it still had a long way to fall. We have not yet reached a stage where nematodes as distinct organisms, whatever their niche, take priority in our thinking. But I race ahead. Let us retrace and begin with the details of this volume.

Four years on from the 2nd Edition of this useful introductory text this book remains good value at a modest price rise of only £5.00. In twenty chapters Professor Service follows his well-worked and consistent pattern in each chapter by describing the morphology of each group of vectors, followed by life-cycle, medical importance and control. The further reading information provided at the end of each chapter has been updated wherever relevant. In addition, as an aide-mémoire to revising, certain key words now appear in bold. In many groups, new information is provided on the numbers of species now described. In the case of mosquitoes this is now 3300, an increase of 100 and there are now 4 further genera including Ochlerotatus, a previous subgenus of Aedes. Outstanding developments in control include the innovative development of manufactured bed nets that are impregnated with synthetic pyrethroids, which are designed to release the active molecule over periods as long as four years. Mike Service is, however, cautious, and warns that despite our great hopes for this new development, the incidence of resistance to pyrethroids is a realistic potential threat to its success. In similar vein it is noted that mosquitoes in the laboratory have been observed to develop resistance to the bacterial insecticides Bacillus thuringiensis and B. sphaericus. This has not as yet proved to be a problem in the field with mosquitoes, but experience with agricultural pests, such as the diamondback moth, indicates the need for vigilance.

Back in the early 1960s, when the curtain was falling on British colonial administration in Africa, the newly-created Ministry of Overseas Development decided to gather together for posterity the expertise and experience of authorities on tsetse and trypanosomiasis control. Weighing in at three and a half pounds, the resulting publication, ‘The African Trypanosomiases’ edited by Colonel Hugh Mulligan and published in 1969, has since been a baseline not only for investigators in the field but also for pure scientists working on related problems at the laboratory bench. The editors of the present volume were inspired by the enormous progress made in trypanosomiasis research over the last thirty years to produce ‘an update of Mulligan’ – so, how do the two books compare? Well, amazingly, their weights are exactly the same – but content and coverage are, as might be expected, very different.