Behavioural patterns involved in avoiding, repelling, or removing parasites allow mammalian hosts to defend themselves from an array of parasites that threaten the host's fitness in the natural world. Some examples of behavioural defenses and the presumed target parasites are: grooming to remove ticks, grouping to reduce attack rate of biting flies, fly repelling movements to reduce parasitic flies, and selective grazing to reduce intake of faecal-borne parasites. These behavioural defenses are discussed with regard to effectiveness in controlling the target parasites. Parasites have sometimes evolved behavioural strategies of evading, penetrating or disabling these behavioural defenses. These parasite behavioural strategies, though less studied, are discussed. Also discussed is the possibility that host behavioural patterns that may defend against one parasite may be exploited by a different type of parasite to facilitate its own transmission. The interplay between host defensive strategies, the cost versus the effectiveness of such strategies, and a parasite's evasion or exploitation of such strategies, may be useful in understanding some aspects of host-parasite dynamics in nature.

Toxoplasma gondii, the coccidian parasite, is known to induce changes in the behaviour of its intermediate hosts. The high prevalence of this parasite in the human population (20–80%) offers the opportunity of studying the influence of the parasite on human behaviour by screening of a normal population. A total of 224 men and 170 women were tested for toxoplasmosis and their personality profiles were measured by Cattell's questionnaire. Highly significant differences between Toxoplasma-infected and uninfected subjects were observed (P < 0·01). For men the factors G (low superego strength), L (protension), O (guilt proneness), and Q2 (group dependency) were positively influenced in infected subjects. For women the prevailing factors were A (affectothymia, P < 0·01), L (alaxia), O (untroubled adequacy) and Q2 (self-sufficiency). To reveal whether toxoplasmosis induces personality factor-shifts or whether certain combinations of personality factors influence the probability of acquiring Toxoplasma infection, we examined the personality profiles of 164 male patients diagnosed with acute toxoplasmosis during the past 13 years. The existence of a positive correlation between the duration of latent toxoplasmosis and the intensity of superego strength decrease (P < 0·02) suggested that the decrease of superego strength (the willingness to accept group moral standards) was induced by T. gondii infection.

The protozoan parasites Eimeria spp. Toxoplasma gondii and Neospora caninum are significant causes of disease in livestock worldwide and T. gondii is also an important human pathogen. Drugs have been used with varying success to help control aspects of these diseases and commercial vaccines are available for all three groups of parasites. However, there are issues with increasing development of resistance to many of the anti-coccidial drugs used to help control avian eimeriosis and public concerns about the use of drugs in food animals. In addition there are no drugs available that can act against the tissue cyst stage of either T. gondii or N. caninum and thus cure animals or people of infection. All three groups of parasites multiply within the cells of their host species and therefore cell mediated immune mechanisms are thought to be an important component of host protective immunity. Successful vaccination strategies for both Eimeria and Toxoplasma have relied on using a live vaccination approach using attenuated parasites which allows correct processing and presentation of antigen to the host immune system to stimulate appropriate cell mediated immune responses. However, live vaccines can have problems with safety, short shelf-life and large-scale production; therefore there is continued interest in devising new vaccines using defined recombinant antigens. The major challenges in devising novel vaccines are to select relevant antigens and then present them to the immune system in an appropriate manner to enable the induction of protective immune responses. With all three groups of parasites, vaccine preparations comprising antigens from the different life cycle stages may also be advantageous. In the case of Eimeria parasites there are also problems with strain-specific immunity therefore a cocktail of antigens from different parasite strains may be required. Improving our knowledge of the different parasite transmission routes, host-parasite relationships, disease pathogenesis and determining the various roles of the host immune response being at times host-protective, parasite protective and in causing immunopathology will help to tailor a vaccination strategy against a particular disease target. This paper discusses current vaccination strategies to help combat infections with Eimeria, Toxoplasma and Neospora and recent research looking towards developing new vaccine targets and approaches.

Three species of lung nematodes have been found in Felidae in Palestine: Aelurostrongylus abstrusus, Troglostrongylus brevior n.sp. and Anafilaroides rostratus n.g., n.sp. The life histories of all these species have been studied. Their larvae develop in terrestrial molluscs. Some new observations on the factors influencing the development of the larvae of Aelurostrongylus abstrusus are described. The whole developmental cycle of Troglostrongylus brevior has been experimentally reproduced. Initial stages of the development of the larva of Anafilaroides rostratus in molluscs have been observed. The taxonomic position of the genera Aelurostrongylus and Troglostrongylus is discussed and their protostrongyline character is demonstrated.

High prevalences of Echinococcus multilocularis have been reported from foxes of the city of Zurich, Switzerland. In order to characterize transmission in urban areas, a coproantigen ELISA was evaluated for diagnosing the infection in fox faecal samples collected in the environment. In addition, trapped rodents were investigated for the presence of metacestodes. Faecal samples could reliably be classified as being of fox origin by assessing physical properties as shown by the different parasite spectra of putative fox and dog faecal specimens. From the total of 604 tested putative fox faecal samples 156 (25·8%) were positive in the ELISA with a distinct increase in the proportion of positive samples from the urban to the periurban zone. Furthermore, samples collected in the border zone had significantly more coproantigen-positive results during winter. Prevalence of E. multilocularis in rodents was 9·1% (81/889) for Arvicola terrestris (with 3·5% of the animals harbouring between 14 and 244400 protoscoleces) and 2·4% (2/83) for Clethrionomys glareolus. E. multilocularis-infected A. terrestris were found in 9 of 10 trapping sites in the border zone. The high infection pressure in the periphery of urban areas might pose a risk for infection with E. multilocularis for both domestic carnivores as well as for urban inhabitants. Interventions into the cycle aiming at reducing the infection pressure should therefore focus on these areas.

In young (6- to 8-week-old) NTH strain inbred mice expulsion of a primary infection of Trichinella spiralis began on day 8 and was virtually complete by day 11·5. In older mice expulsion occurred 1 or 2 days earlier. Experience of a primary infection elicited strong immunity to challenge, whether the challenge was given immediately after worm expulsion (day 14) or delayed (day 42). Challenge infections were expelled rapidly, the majority of worms being lost during the first day. Immunity to challenge was elicited by low-level primary infections and was effective against large challenge infections. These results are discussed in relation to conventionally accepted parameters of immunity to T. spiralis in mice which, it is considered, are applicable only to mice with a genetically-determined low-level of responsiveness to the parasite.

Lepeophtheirus salmonis is a specific parasite of salmonids that occurs in the Atlantic and Pacific Oceans. When infestations are heavy fish mortality can occur although the factors that are responsible for causing epizootics, especially in wild salmonid populations are still largely unknown. Over the past 20 years this parasite has caused significant economic losses in farmed salmon production and possibly in wild salmonid populations locally. Understanding the connectivity between populations is crucial to an understanding of the epidemiology of infections and for management of infections in aquaculture. Data from genetics, pesticide resistance, larval dispersal models and spatial and temporal patterns of infestation in wild and farmed hosts suggests a spatially highly structured metapopulation the components of which have different levels of connectivity, probabilities of extinction and influence on the development of local infestations. The population structure is defined mainly by the dispersal dynamics of the planktonic stages and the behaviour of the host.

Until recently virtually nothing was known about the relationship between the parasite and the host, or how the host may influence lice at local or population level. Typically, impacts on the host have usually been reported in terms of pathological lesions caused by attachment and feeding of the adult stages, as well as localised mild epithelial responses to juvenile attachment. However many studies report pathology associated with severe infestation. Recent new studies on the host–parasite interactions of L. salmonis have shown that this parasite induces stress-related responses systemically in the host skin and gills and that the stress response and immune systems are modulated. In the second part of this review, these new studies are presented, together with results from other host–parasite model systems where data for caligid sea lice are missing. One of the most revealing methods reported recently is the application of a net confinement stressor to examine modulation of the stress response and immune system of the host fish. This approach has shown that although until now, infective stages of L. salmonis were not thought to affect the host, they do induce systematic effects in the host that result in a stress response and modulated immune system. Host–parasite interactions affecting these stress responses and the immune system may be key factors in facilitating epizootics by reducing the host's ability to reject the parasites, as well as reducing disease resistance under some environmental conditions. The host–parasite interaction therefore needs to be incorporated into any model of population structure and dynamics.

Samples of DNA from a panel of Giardia isolated from humans and animals in Europe and shown previously to consist of 2 major genotypes–‘Polish’ and ‘Belgian’–have been compared with human-derived Australian isolates chosen to represent distinct genotypes (genetic groups I–IV) defined previously by allozymic analysis. Homologous 0·52 kilobase (kb) segments of 2 trophozoite surface protein genes (tsa417 and tsp11, both present in isolates belonging to genetic groups I and II) and a 1·2 kb segment of the glutamate dehydrogenase (gdh) gene were amplified by the polymerase chain reaction (PCR) and examined for restriction fragment length polymorphisms (RFLPs). Of 21 ‘Polish’ isolates that were tested, all yielded tsa417-like and tsp11-like PCR products that are characteristic of genetic groups I or II (15 and 6 isolates respectively) in a distinct assemblage of G. intestinalis from Australia (Assemblage A). Conversely, most of the 19 ‘Belgian’ isolates resembled a second assemblage of genotypes defined in Australia (Assemblage B) which contains genetic groups III and IV. RFLP analysis of gdh amplification products showed also that ‘Polish’ isolates-were equivalent to Australian Assemblage A isolates (this analysis does not distinguish between genetic groups I and II) and that ‘Belgian’ isolates were equivalent to Australian Assemblage B isolates. Comparison of nucleotide sequences determined for a 690 base-pair portion of the gdh PCR products revealed ≥ 99·0% identity between group I and group II (Assemblage A/‘Polish’) genotypes, 88·3–89·7% identity between Assemblage A and Assemblage B genotypes, and ≥ 98·4% identity between various Assemblage B/‘Belgian’ genotypes. The results confirm that the G. duodenalis isolates examined in this study (inclusive of G. intestinalis from humans) can be divided into 2 major genetic clusters: Assemblage A (= ‘Polish’ genotype) containing allozymically defined groups I and II, and Assemblage B (= ‘Belgian’ genotype) containing allozymically defined groups III and IV and other related genotypes.

The potential of biological invasions to threaten native ecosystems is well recognized. Here we describe how an introduced species impacts on native host-parasite dynamics by acting as an alternative host. By sampling sites across an invasion front in Ireland, we quantified the influence of the introduced bank vole (Clethrionomys glareolus) on the epidemiology of infections caused by flea-transmitted haemoparasites of the genus Bartonella in native wood mice (Apodemus sylvaticus). Bartonella infections were detected on either side of the front but occurred exclusively in wood mice, despite being highly prevalent in both rodent species elsewhere in Europe. Bank vole introduction has, however, affected the wood mouse-Bartonella interaction, with the infection prevalence of both Bartonella birtlesii and Bartonella taylorii declining significantly with increasing bank vole density. Whilst flea prevalence in wood mice increases with wood mouse density in areas without bank voles, no such relationship is detected in invaded areas. The results are consistent with the dilution effect hypothesis. This predicts that for vector-transmitted parasites, the presence of less competent host species may reduce infection prevalence in the principal host. In addition we found a negative relationship between B. birtlesii and B. taylorii prevalences, indicating that these two microparasites may compete within hosts.

The regulation of helminth populations tends to occur primarily as a result of limitations imposed on the build up of parasite subpopulations within individual hosts (Anderson & May, 1979; May & Anderson, 1979). Considering the relevance of these factors to the success or otherwise of intestinal helminth control programmes, it is perhaps surprising that more information is not yet available concerning the particular mechanisms which may be responsible, and in particular, the population consequences of the immune responses which such parasites may precipitate. Density-dependence in a single rate parameter, if operative over the naturally observed numerical range, is sufficient to regulate parasite population flow throughout the life-cycle, whether direct or indirect (Anderson, 1976). For the genera given in Table 1, this could be provided by the observed pattern of parasite mortality and/or fecundity. It is of interest to note, however, that circumstantial evidence cited in the Table suggests that each of the 6 genera is also potentially able to induce host mortality under certain conditions. Whether this acts in a density-dependent manner in natural infections is almost entirely unknown. Rapid reproduction may be of great selective advantage to intestinal helminths, even if it is necessarily accompanied by pathogenicity (see Anderson, 1981). If the manner in which this pathogenicity acts in any way enhances the stability of the host-parasite interaction, then perhaps it may have contributed to the selection pressures which have led so many genera to continue to break the rules of the ‘well-adapted’ parasite (see, for example, Noble & Noble, 1971).

The paper draws together a large and scattered body of empirical evidence concerning the prevalence of snail infection with schistosome parasites in field situations, the duration of the latent period of infection in snails (and its dependence on temperature), and the mortality rates of infected and uninfected snails in field and laboratory conditions. A review and synthesis of quantitative data on the population biology of schistosome infections within the molluscan host is attempted and observed patterns of infection are compared with predictions of a schistosomiasis model developed by May (1977) which incorporates differential snail mortality (between infected and uninfected snails) and latent periods of infection. It is suggested that the low levels of prevalence within snail populations in endemic areas of schistosomiasis are closely associated with high rates of infected snail mortality and the duration of the latent period of infection within the mollusc. In certain instances, the expected life-span of an infected snail may be less than the duration of the latent period of infection. Such patterns generate very low levels of parasite prevalence. A new age prevalence model for schistosome infections within snail populations is developed and its predictions compared with observed patterns.

The implications of this study of observed and predicted patterns of snail infection within molluscan populations are discussed in relation to the overall transmission dynamics of schistosomiasis.

Genetic polymorphism was determined among 13 isolates of Taenia solium from various regions using PCR-amplified sequences of 2 mitochondrial genes: cytochrome c oxidase subunit 1 and cytochrome b. The 2 phylogenies obtained were similar to each other regardless of the genes examined. The isolates from Asia (China, Thailand, Irian Jaya and India) formed a single cluster, whereas the isolates from Latin America (Mexico, Peru, Ecuador, Bolivia and Brazil) combined with those from Africa (Tanzania, Mozambique and Cameroon) to form an additional cluster. These results and historical data of swine domestication, distribution of pigs and colonization suggest that T. solium was introduced recently into Latin America and Africa from different regions of Europe during the colonial age, which started 500 years ago, and that the tapeworm of another origin independently spread in Asian countries.

Currently available methods for the diagnosis of human schistosomiasis often lack enough sensitivity and specificity. Recently, several authors have developed more specific and sensitive diagnostic methods, mainly based on the polymerase chain reaction (PCR) technique. Nevertheless, these have been only applied for the diagnosis of 1 out of 4 Schistosoma species affecting man (S. mansoni). Additionally, application of specific PCR has been exclusively used for blood or faecal patients' samples. Here, we develop a new, high sensitive PCR approach that allows the genus- and species-specific amplification of the main 4 Schistosoma species causing disease in man plus S. bovis. We further successfully apply this technique for the detection of parasite DNA in easy-to-handle urine samples from patients with schistosomiasis. With these samples, we have found 94·4% sensitivity and 99·9% specificity when applying a genus-specific (Schistosoma spp.) primer pair, and 100% sensitivity and 98·9% specificity in a species-specific (S. mansoni) PCR.

Hybridization of parasites is an emerging public health concern in our changing world. Hybridization and introgression in parasites and pathogens can have major impacts on the host and the epidemiology and evolution of disease. Schistosomiasis is a Neglected Tropical Disease of profound medical and veterinary importance across many parts of the world, with the greatest human burden within sub-Saharan Africa. Here we review how early phenotypic identification and recent confirmation through molecular studies on naturally occurring infections, combined with experimental manipulations, have revealed evidence of viable hybridization and introgressions within and between human and animal schistosome species. Environmental and anthropogenic changes in selective pressures following, for instance, new dam constructions, altered agricultural practices, together with mass drug administration programmes, may all be predicted to further impact the availability of suitable definitive and intermediate hosts for schistosomes. It is therefore imperative to understand the distribution and role of such novel zoonotic hybrid schistosomes on host range, drug efficacy, and hence ultimately transmission potential, if we are to achieve and maintain sustainable control.

There are many species of fungi attacking terrestrial and aquatic insects of agricultural and medical importance. Of these, few species have received much attention with a view to their use as biological control agents. The mechanisms of infection have been comparatively well studied, although many questions remain to be answered. The knowledge so far obtained has shed some light on the reasons for host specificity. Temperature, above all relative humidity, and their interactions are the most important physical factors influencing infection of terrestrial insects by entomopathogenic fungi and these are discussed in relation to epizootiological events. In aquatic environments, temperature, salinity and organic pollution are the important factors. In addition to these physical factors, numerous biotic factors at the level of the insect and the fungal pathogen influence both infection and spread of disease in insect populations. The complexity of the interactions of the biotic and abiotic factors makes it extremely difficult to study the influence of any one of these. Virulence of fungal pathogens and its measurement are discussed, together with the shortcomings of present bioassay systems; virtually no laboratory bioassay system exists which has been designed to yield data meaningful in the field. Mass-production techniques are described as are their inherent problems and those of formulation and storage. Finally, the achievements of fungal control of insects in the field are reviewed. Thus far, several species are mass-produced and are in widespread use, two of which, Verticillium lecanii and Hirsutella thompsonii, have been commercialized. More studies, ecological, fundamental and developmental are required in this field to realize fully the potential of other candidate fungi.

This review begins with a description of the parasitoid life-style and the ecological and evolutionary factors which generate the remarkable diversity of insect parasitoids. We then describe the various ways that parasitoids have been used in the biological control of insect pests, and survey their success to date. The use of parasitoids remains largely an art, aided by past experience of success and failure. A more fundamental approach, involving basic research and theory, has not as yet contributed significantly to practical biological control. We explore the potential for such a science of parasitoid use and review basic research on parasitoid ecology and evolution which is of particular relevance to biological control. Mathematical models are used to identify and examine those parasitoid and host attributes which lead to successful biological control. Factors such as parasitoid foraging behaviour, fecundity, larval survival and sex ratio are shown to be important in influencing the depression of host populations and/or the stability of host–parasitoid interactions after depression. Multiple release is discussed and a model for inundative release of parasitoids is explored.

A 298 bp region of the Cryptosporidium parvum 18S rDNA and a 390 bp region of the acetyl-CoA synthetase gene were sequenced for a range of human and animal isolates of Cryptosporidium from different geographical areas. A distinct genotype is common to isolates from cattle, sheep and goats and also an alpaca from Peru and is referred to here as the ‘calf’-derived Cryptosporidium genotype. Another genotype of ‘human’-derived isolates also appears to be conserved amongst human isolates although humans are also susceptible to infection with the ‘calf’ Cryptosporidium genotype. Mice and pigs carry genetically distinct genotypes of Cryptosporidium. Three snake isolates were also analysed, 2 of which exhibited C. muris genotypes and the third snake isolate carried a distinct ‘mouse’ genotype.

The role of the peritrophic matrix (PM) in the development of Leishmania major infections in a natural vector, Phlebotomus papatasi, was investigated by addition of exogenous chitinase to the bloodmeal, which completely blocked PM formation. Surprisingly, the absence of the PM was associated with the loss of midgut infections. The chitinase was not directly toxic to the parasite, nor were midgut infections lost due to premature expulsion of the bloodmeal. Most parasites were killed in chitinase-treated flies within the first 4 h after feeding. Substantial early killing was also observed in control flies, suggesting that the lack of PM exacerbates lethal conditions which normally exist in the blood-fed midgut. Early parasite mortality was reversed by soybean trypsin inhibitor. Allosamadin, a specific inhibitor of chitinase, led to a thickening of the PM, and also prevented the early parasite mortality seen in infected flies. Susceptibility to gut proteases was extremely high in transitional-stage parasites, while amastigotes and fully transformed promastigotes were relatively resistant. A novel role for the PM in promoting parasite survival is suggested, in which the PM creates a barrier to the rapid diffusion of digestive enzymes, and limits the exposure of parasites to these enzymes during the time when they are especially vulnerable to proteolytic damage.

We have used nuclear (ribosomal ITS1) and mitochondrial (ND1) sequences to characterize human and pig isolates of Echinococcus granulosus collected by fine needle aspiration biopsy (FNAB) in Poland. The data indicate clearly that the Polish patients were not infected with the common sheep strain (G1 genotype) of E. granulosus, normally associated with human cystic hydatid infection. Instead, the hydatid parasite infecting the Polish patients shares very similar ND1 sequence with the previously characterized pig (G7) genotype but it also exhibits some clear differences. In particular, E. granulosus DNA from the Polish patients amplified a single ITS1 fragment in PCR and distinct ITS1–RFLP patterns were obtained after restriction digestion. The form of hydatid isolated from the Polish patients appears, therefore, to represent a distinct, previously undescribed genotype (designated G9) of E. granulosus.

We investigated the influence of infection by the trematode Curtuteria australis on the burrowing behaviour of its intermediate host, the bivalve Austrovenus stutchburyi. Laboratory experiments and field observations revealed that cockles, unable to bury completely or even partially under the sediment, have a reduced foot length compared with buried individuals. The ability to bury proved to be highly repeatable in field experiments: cockles found at the surface and transplanted to an experimental area did not bury themselves, and cockles found buried stayed buried when relocated. All metacercariae of C. australis were found strictly in the foot and for each of 3 samples collected in different sites, there was a negative and significant relationship between the relative length of the foot and the parasite load. A predation test conducted under natural conditions indicated that cockles with the stunted foot and the altered behaviour are significantly more susceptible to predation by aquatic birds than other cockles. Given that the definitive host of C. australis is an oystercatcher, we first discuss our results in the context of transmission strategy. Comparisons with other studies on more or less related trematode species parasitic in bivalves and evolving under similar constraints for their transmission, shed light on the origin of this adaptation in C. australis.