Humoral immune responses of the Indian leaf monkey (Presbytis entellus) experimentally infected with Brugia malayi and exhibiting disease manifestations were studied. Microfilaraemia, filaria-specific IgG and circulating immune complexes (CICs) were determined in the monkeys at different time-points after inoculation of B. malayi 3rd-stage larvae. Sera were analysed for recognition pattern of adult parasite antigen molecules by immunoblotting. More than 60% of the infected monkeys developed episodic or persistent limb oedema with or without fever and with low or no microfilaraemia. While both CIC and filaria specific IgG levels were comparable in animals showing no disease symptoms (asymptomatics) and some animals showing symptoms (symptomatics), IgG levels peaked during pre-patent stage in symptomatics and during latent stage in asymptomatic animals. However, some of the symptomatic animals showed a low level of filaria-specific IgG as compared to asymptomatic and other symptomatic animals. The immunoblot analysis showed non-reactivity of 17 and 55 kDa antigens with sera of symptomatic animals. The results thus suggest that humoral immune responses as measured in the present study do not precede the development of the manifestations. However, 2 non-reactive antigen molecules identified by symptomatic sera need further study to establish their possible involvement, if any, in the development of acute disease manifestations in this model.

Salmo salar and Salmo trutta co-exist in coastal river systems in Europe and produce hybrids with little loss of viability or growth. This report describes the susceptibility of pure full-sibs of S. salar and S. trutta and their reciprocal half-sib hybrids to their respective gyrodactylids, Gyrodactylus salaris and Gyrodactylus derjavini. The pure-bred salmon and trout, and half-sib hybrids, were produced using eggs and sperm from wild anadromous S. salar (River Alta stock, North Norway) and wild anadromous S. trutta (River Fossbekk stock, Southwest Norway). Infections were initiated by exposing experimental fishes (0+) to S. salar naturally infected with G. salaris (River Lierelva strain) or S. trutta naturally infected with G. derjavini (River Sandvikselva strain). Fishes were then kept individually isolated under standardized conditions at 12 °C. Pure-bred S. salar were susceptible but frequently mounted a response to G. salaris without eliminating the infection, whereas pure-bred S. trutta were innately resistant to this species. Pure-bred S. trutta ranged from innately resistant to susceptible to G. derjavini but later most of the susceptible trout mounted a host response to G. derjavini. Pure-bred S. salar were also susceptible to this species, although parasite population growth rates were reduced and a host response frequently appeared eliminating G. derjavini. The abundance of both gyrodactylids was lower on the hybrids than on their respective pure-bred natural hosts, and a parental sire- and dam-influence on the resistance of hybrids was observed. When the sire was S. salar, the susceptibility of hybrids to G. salaris was similar to that of pure S. trutta; when the dam was S. salar both innately resistant, intermediately susceptible and responding individuals were present. In the case of G. derjavini, when the sire was S. trutta, infections on hybrids were similar to those on pure S. salar; when the dam was S. trutta, an increased level of susceptibility was observed. The present results provide evidence that: (1) Norwegian salmon stocks are variable in their susceptibility/resistance, with some fish able to control S. salaris infections; (2) trout stocks are innately resistant to G. salaris; (3) individual trout show a spectrum in susceptibility/resistance to G. derjavini, ranging from innate resistance through slightly susceptible to highly susceptible but with acquired resistance controlling infection; (4) although G. derjavini infections grow poorly on salmon, this host stock is susceptible to the parasite, but can limit infection by a host reaction; (5) susceptibility/resistance traits to gyrodactylids are genetically controlled and resistance can be transferred as a dominant trait through interspecific crosses between different salmonids; (6) interspecific hybrids between susceptible and resistant salmonids have a pattern of susceptibility to gyrodactylids intermediate to that of the parents; (7) resistance to gyrodactylids may be controlled by relatively few genes in salmonids; (8) epidemiologically, hybrids may act as a reservoir for gyrodactylids, may support a wider diversity of species than either parent and may disseminate gyrodactylids of both host species.

A cDNA encoding a β-galactoside-binding lectin (galectin) was identified by immunoscreening a Haemonchus contortus cDNA library with antisera from lambs vaccinated with a membrane protein complex (H-gal-GP) derived from the parasites' gut. The cDNA sequence, exhibiting a tandem repeat structure and designated Hco-gal-2, showed significant levels of similarity with galectins from several species of nematode as well as mammalian galectin type 4. Native galectin was preferentially extracted from the H-gal-GP complex and also from an insoluble membrane fraction prepared from adult worms using lactose–agarose affinity chromatography. The affinity-purified material had apparent molecular mass of around 35 kDa with 3 distinct bands visible on SDS–PAGE. All 3 bands were identified as galectins by reaction with antiserum raised to recombinant Hco-GAL-2 on Western blot. To determine whether H. contortus galectins have any protective capacity against infection lambs were vaccinated with affinity-purified galectin and subsequently given a single challenge infection. Vaccination did not confer any protection against infection with H. contortus as judged by faecal egg output or worm counts.

We develop the hypothesis that parasites do not invade extreme environments, i.e. hostile hosts, but rather ‘create’ them. We argue that parasites may have driven the evolution of the constitutive and adaptive immune system. This leads to several implications. First, parasites respond to ‘genes to kill’ by ‘genes to survive’ and this triggers an indefinite selection of measures and counter-measures. Second, these revolutionary arms races may lead to local adaptation, in which parasite populations perform better on local hosts. Third, the evolution of the immune system, whose responses are predictable, may allow parasites to specialize, to evade and even to manipulate. Finally we show that the correlations between the increase in the antibody repertoire, the expansion of MHC loci and parasite pressures support our hypothesis that both host complexity and parasite pressures can be invoked to explain the diversity of antibodies, T-receptors and MHC molecules.

The biodiversity of Trypanosoma cruzi is one of the main factors complicating the understanding of its molecular epidemiology. As an alternative to classical genetic methods, investigators have used DNA-mediated transformation techniques to study this diversity. Recently, transient expression data were shown to correlate with the genetic data. This led investigators to speculate on a potential speciation within clonal populations of Trypanosoma cruzi. To further test the phylogenetic significance of transient expression analysis in Trypanosoma cruzi, multiple plasmids were used to drive the expression of a reporter gene in different parasite populations. In our study, population specific expression of the reporter gene was observed but the variability revealed by these transient expression assays was very large and did not follow the grouping of Trypanosoma cruzi populations in 2 lineages. In this report, we discuss some of the limitations of transient assays on such a diverse parasite.

Secretions were induced from second (invasive) stage juveniles (J2s) of the potato cyst nematode Globodera rostochiensis by exposing them to 5-methoxy-N,N-dimethyl tryptamine oxalate (DMT). Secretions were collected from J2s in sufficient quantity to allow direct analysis. Gel electrophoresis followed by monochromatic silver staining demonstrated the presence of at least 10 proteins. The presence of several enzymes, including superoxide dismutase and proteases, was demonstrated using Western blots and activity assays. Antisera raised against the secretions recognized bands on Western blots consistent in molecular mass with those identified on silver stained gels. The antisera recognized structures implicated in the production of secretions including the subventral gland cells and surface of J2s.

The geographical distance between conspecific host populations is no doubt a key determinant of the likelihood that exchanges of parasite species occur between these populations. This variable must therefore be taken into account in studies that compare parasite species richness or similarity among host populations. This paper presents a multivariate approach, based on the permutation of matrices, that allows all pairwise geographical distances between host populations to be included as independent variables. The method is illustrated with 3 separate data sets on parasite communities of conspecific fish from different lakes. In 2 of 3 cases, geographical distances among lakes had a significant influence on the similarity of their parasite communities. The effect of geographical distance on species richness of parasite communities also proved important in 2 of the 3 case studies. These examples demonstrate the pervasive influence of distances among host populations on their parasite communities, and the need to properly control for them in statistical analyses.

Monthly data collected during 1993 in the Vaccarès lagoon (Rhône Delta, France) were used to investigate the influence of the trematode Aphalloïdes cœlomicola on the survival of the common goby Pomatoschistus microps, which acts both as second intermediate and definitive host. Prevalence of the parasite did not increase with fish size in either sex. Mean abundance and variance to mean abundance ratio gave evidence that the trematode could have an impact on host mortality. Gonad weight of parasitized females was reduced and the parasite seemed to provoke a gonadal regression above a certain parasitic biomass. Fecundity and egg diameters did not differ between parasitized and unparasitized females, we thus hypothesize that the energy content of eggs (composition in lipids and proteins) was probably modified as an adaptation to energy losses. Prevalence of infection in males compared to females and influence of the parasite on host survival and reproductive effort are discussed.

The genetic population structures of the freshwater snail Bulinus globosus and its trematode parasite Schistosoma haematobium from 8 river sites in the Zimbabwean highveld were compared using randomly amplified DNA(RAPD) markers. There was significant variability between snail populations collected at different sites, but schistosome populations only showed differentiation at a wider geographical scale (between 2 non-connected river systems). For snails, genetic distance was better correlated with proximity along rivers than absolute geographical separation. In contrast, schistosome genetic distance was better correlated with absolute geographical separation than proximity along rivers. These results are consistent with different dispersal mechanisms for snails and schistosomes and the implications for host–parasite coevolution are discussed.

Two clones, totalling 8068 bp and spanning over half of the coding region of the mitochondrial genome of Schistosoma mansoni, have been sequenced. Complete sequences are presented of the large and small ribosomal RNA subunits, CO2, ND3, ND4, ND6 and ATPase 6 genes. Incomplete sequences were found for the CO1, ND2 and CytB genes. At least 10 tRNAs were also detected and alternative structures for some of these discussed. The gene order of S. mansoni is unique and differs from that of Fasciola hepatica, the only other trematode for which any information is available.

Schistosoma japonicum from the People's Republic of China is considered to represent a single species comprising either 1 or 4 ‘strains’. We conducted an allozyme electrophoretic study to examine the extent of genetic variation in S. japonicum from mainland China. The allelic profiles of S. japonicum from 7 provinces were established at 16 enzyme loci. S. japonicum from Sichuan had 3–5 (19–31%) fixed differences compared with those from Zhejiang, Anhui, Jiangxi, Hunan, Hubei and Yunnan, suggesting that S. japonicum in mainland China represents a species complex. In addition, genetic markers were also established for different laboratory-maintained populations of S. japonicum which has significant implications for studying the biology of these organisms in human and animal hosts, and for the control and surveillance of human schistosomiasis in China.

Living and fixed specimen of Oesophagostomum dentatum were labelled in situ with serum antibodies or a panel of biotin- labelled lectins. Specific binding of antibodies was observed in all parasitic stages – freshly exsheathed 3rd-stage larvae (L3), 3rd- and 4th-stage (L4) larvae cultured in vitro and L3 and L4 and adults isolated from pig intestines. The shedding of the stained layer by motile larvae was inhibited by levamisole-induced paralysis. Larvae cultured in vitro exposed serum-derived proteins on their surface which could be labelled with secondary antibody directed against the respective serum donor species. While freshly exsheathed larvae were recognized by O. dentatum-positive serum only, older larvae and adults cross-reacted with serum from pigs infected with O. quadrispinulatum, a closely related species. Lectin binding varied considerably between stages. While binding was not observed in pre-parasitic stages, Concanavalin A, Soybean Agglutinin, Wheat Germ Agglutinin, Ricinus communis Agglutinin and Peanut Agglutinin bound to developing larvae in varying degrees. Dolichos biflorus Agglutinin only bound to advanced (luminal) larval stages, while adults generally displayed only weak or partial lectin binding (except with Concanavalin A and Wheat Germ Agglutinin). Ulex europaeus Agglutinin only labelled larvae derived from cultures containing 10% pig serum. Cleavage of the carbohydrate residues by sodium periodate treatment resulted in reduction of antibody binding to cultured larvae, but not to freshly exsheathed L3. Concanavalin A, Soybean Agglutinin, and Peanut Agglutinin binding was also reduced by periodate treatment, while binding of Wheat Germ Agglutinin and Ricinus communis Agglutinin was inhibited only in early L3, but not in older stages. The different lectin labelling patterns are related to the different stages of the nematode – infective, invasive, histotropic, and luminal – and may serve as a mode of adaptation for the parasite against the host's immune attack by surface glycoprotein variation, together with antigen shedding (as demonstrated by labelling of motile larvae) and a possible acquisition of host molecules at the parasite's surface. Furthermore, a possible role of this developmental variation in surface carbohydrates in parasite–parasite interactions is discussed.

Haemoflagellates of the genus Trypanosoma are prevalent in freshwater fishes and are transmitted by leeches as vectors. As demonstrated by sequence comparisons of nuclear small subunit rRNA genes, trypanosomes isolated from several fish species at different localities can be divided into at least 2 closely related types, designated Type A and Type B. A clone derived from a Type A isolate from carp (Cyprinus carpio) was used to study the anti-parasite immune response in specified pathogen-free outbred carp. Infection leads to an initial rise in parasitaemia in the blood followed by a sharp decline in all fish (acute phase). Thereafter, in some carp, parasites become undetectable both in the blood and in internal organs while, in others, low numbers can be found in the blood for up to 1 year (chronic phase). Fish that have controlled an acute infection with the clone are not only protected against an homologous challenge infection, but also against the infection with parasite lines derived from carp in the chronic phase of infection. Passive immunization experiments with IgM purified from serum of recovered carp indicate that the infection is controlled by antibodies. The anti-parasite antibody level in recovered carp remains high for many months although the parasitaemia is controlled at very low levels and the half life of IgM, t1/2=22·5 days, is comparatively short. The effective control of trypanosomes in laboratory infections is in contrast to the high prevalence in natural and farmed freshwater fish populations.

Even the most generalist parasites usually occur in only a subset of potential host species, a tendency which reflects overriding environmental constraints on their distributions in nature. The periodic shifting of these limitations represented by host-switches may have been an important process in the evolution of many host-parasite assemblages. To study such events, however, it must first be established where and when they have occurred. Past host-switches within a group of parasites are usually inferred from a comparison of the parasite phylogeny with that of the hosts. Congruence between the phylogenies is often attributed to a history of association by descent with cospeciation, and incongruence to host-switching or extinction in ‘duplicated’ parasite lineages (which diverged without a corresponding branching of the host tree). The inference of host-switching from incongrucnt patterns is discussed. Difficulties arise because incongruence can frequently be explained by different combinations of biologically distinct events whose relative probabilities are uncertain. Also, the models of host parasite relationships implicit in historical reconstructions may often not allow for plausible sources of incongruence other than host-switching or duplication/extinction, or for the possibility that colonization could, in some circumstances, be disguised by ‘false’ congruence.

The Monogenea fauna was studied from the gills of the catfish Pimelodus maculatus. Fish were caught from Río de la Plata, in Buenos Aires harbour (Argentina). Five species of Monogenea were found. The structure of the monogenean community was analysed at the component and infracommunity level. The nature of the monogenean community, its possible interactivity, seasonal variation and predictability are also discussed.

The first and second internal transcribed spacer sequences of 28 morphologically-defined species of horse strongyle were characterized, and specific oligonucleotide primers were designed for some species based on the nucleotide differences. Utilizing these primers, a PCR approach was developed for the specific amplification of ribosomal DNA of Strongylus vulgaris, Cyathostomum catinatum, Cylicocyclus nassatus, Cylicostephanus longibursatus or Cylicostephanus goldi. The method allowed the species-specific amplification of parasite DNA derived from faecal samples and/or copro-cultures, demonstrating the potential of the approach for the diagnosis of equine strongyloidosis. The establishment of this PCR assay also has implications for studying the biology and epidemiology of equine strongyles and anthelmintic resistance using faecal egg count reduction tests.

The normal tissue migration of Ascaris suum in the pig host involves larval development in the liver accompanied by considerable pathological changes. The vast majority of larvae that reach the small intestine are later expelled by unknown mechanisms. We show that when migration through the liver is bypassed by inoculation of pigs with an intravenous dose of larvae hatched in vitro, the larvae not only complete migration and return to the small intestine, but they also seem to have a greater chance of survival to adulthood. This technique offers new possibilities for studies on specific lung involvement in protective immunity, provides valuable information for the understanding of self cure by larval expulsion, and adds to our understanding of the evolution of migration of Ascaris larvae in tissues.

Studies on the digenean parasites of deep-sea (> 200 m depth) teleosts are reviewed and two case study generic phylogenies are presented based on LSU rDNA and ND1 mtDNA sequences. The phylogeny of the lepocreadiid genus Lepidapedon, the most common deep-sea digenean genus, is not clearly resolved as the two gene trees are not compatible. It can be inferred, however, that the genus has radiated in the deeper waters off the continental shelf, mainly in fishes of the gadiform family Macrouridae. Steringophorus, a fellodistomid genus, is better resolved. In this case a deep-sea radiation is also indicated, but the pattern of host-specificity is not clear, with evidence of much host-switching. Results of studies of the parasites of the macrourid fish Coryphaenoides (Nematomirus) armatus from various depths have reinforced recent views on the lack of zoned depth-related communities in the deep-sea. The diversity of deep-sea digeneans is relatively low with only 18 families (of about 60) reported. Little, or nothing, is known from most deep-sea areas and nothing from trenches and mid-ocean ridge systems.

Five Monogenea species were found on the gills of the catfish Pimelodus maculatus in Río de la Plata (Argentina). These were used for studying the preference of species on different gill-hemibranches, niche breadth and niche overlap between species. It was found that congeneric species had a generic-specific preference for certain gill-hemibranches. Niche breadth appeared to be related to the number of individuals of each species. Niche overlap between the species is discussed.

The antibody responses of 8 cattle experimentally infected with Onchocerca ochengi to 18 recombinant O. volvulus antigens were measured by ELISA. In addition to establishing antigenic cross-reactivity between the species, the dynamics of antigen-specific responses were examined to assess how the recognition of the antigens compared to the known stage-specificity of expression. Six cattle responded to all of the antigens and 2 animals responded to all but 1. The dynamics of the recognition of 4 antigens (B20, MOv-2, MOv-14 and OvNHR2 02E1) were characterized by rapid seroconversion following infection. Antibody levels to 2 antigens (Ov7 and OvALT-1) increased gradually over the course of infection. Antibody levels to 4 antigens (OvTPX-2, OvL3Chitinase, Ov103 and Ov9m) reached maximum levels coincident with the onset of patency. The levels to 3 antigens (OvProalf C50, OvAldolase, Ov39) varied little over the course of infection. Responses to antigens with functional similarities (OvSOD1, OvSOD2 and OvSOD3 or OvGST1 and OvGST2) showed comparable temporal profiles. This study demonstrates the high degree of immunological cross-reactivity between the antigens of O. volvulus and O. ochengi. The immunogenicity of antigens varied over the course of infection in an antigen-specific manner, which not always reflected developmentally regulated expression of the corresponding gene, possibly owing to cross-reactive epitopes on distinct parasite products.