The family Ascarididae, as defined by Hartwich (1957) and emended by Osche (1958), comprises species in the genera Ascaris, Toxascaris, Parascaris and Lagochilascaris, all occurring in terrestrial mammals. Other ascaridoids of terrestrial mammals occur in Crossophoridae and Toxocaridae, the latter including Toxocara and Neoascaris (see Hartwich, 1957; Sprent, 1957; Osche, 1958).

Cleaning behaviour has generally been viewed from the cleaner or client's point of view. Few studies, however, have examined cleaning behaviour from the parasites' perspective, yet they are the equally-important third players in such associations. All three players are likely to have had their evolution affected by the association. As cleaner organisms are important predators of parasites, cleaners are likely to have an important effect on their prey. Little, however, is known of how parasites are affected by cleaning associations and the strategies that parasites use in response to cleaners. I examine here what parasites are involved in cleaning interactions, the effect cleaners have on parasites, the potential counter-adaptations that parasites have evolved against the predatory activities of cleaner organisms, the potential influence of cleaners on the life history traits of parasites, and other factors affected by cleaners. I have found that a wide range of ectoparasites from diverse habitats have been reported to interact with a wide range of cleaner organisms. Some of the life history traits of parasites are consistent with the idea that they are in response to cleaner predation. It is clear, however, that although many cleaning systems exist their ecological role is largely unexplored. This has likely been hindered by our lack of information on the parasites involved in cleaning interactions.

Faecal specimens from 287 diarrhoeic calves younger than 21 days, collected over a 2-year period (2006–2007) from 82 dairy cattle farms in 14 provinces across the north of Spain, were examined for the presence of Cryptosporidium oocysts. Overall, 63 farms (76·8%) and 166 calves (57·8%) tested positive by microscopy. In order to elucidate the genetic diversity, selected positive specimens from 149 calves originating from 61 farms in the 14 provinces were examined by genotyping and subtyping techniques. Cryptosporidium parvum was the only species identified by PCR-RFLP of SSU rDNA from all 149 isolates and sequencing of a subset of 50 isolates, except for 2 specimens that were identified as C. bovis. Sequence analyses of the glycoprotein (GP60) gene revealed that most C. parvum isolates (98%) belonged to the subtype family IIa and 2 isolates were identified as the novel subtype IIdA23G1. Subtype IIaA15G2R1 was the most common and widely distributed (80·3% of the 61 farms), followed by subtype IIaA16G3R1 (14·7%), whereas the remaining IIa subtypes (IIaA16G2R1, IIaA17G2R1, IIaA18G3R1, IIaA19G3R1) were restricted to 1–3 farms. All these C. parvum IIa subtypes have previously been described in human patients, indicating that most isolates from diarrhoeic calves in northern Spain have zoonotic potential.

Isoenzyme patterns of normal adult Nippostrongylus brasiliensis were compared with those of damaged worms permanently affected by immunity and adapted worms which show increased resistance to immunity.

Isoenzymes of acetylcholinesterase, found in glands of the head end of the worms, showed changes in damaged and adapted worms which can be related to the effects of immunity.

Aminopeptidases and non-specific esterases from the same glands were unchanged in worms affected by immunity.

Isoenzymes of acid phosphatase found in the gut of the worms were altered in damaged and adapted worms; these changes are probably secondary to the changes in acetylcholinesterases.

Of the enzymes studied, acetylcholinesterase is the enzyme most likely to be the antigen which stimulates host immunity, but final proof of this is required.

We are most grateful to Dr Valerie E. Jones for many helpful suggestions.

The objective of this review was to outline an epidemiological profile of Strongyloides stercoralis by parasitological and serological diagnosis in inhabitants, and to associate this profile with different immunosupression situations, in Brazil, over 20 years (1990–2009). The occurrence of S. stercoralis using parasitological methods was 5·5%, being 4·8% in rural and 5·0% in urban areas, characterizing the country as hyperendemic. There was a diversity of techniques used as a diagnostic tool and only 39·1% of the studies presented results based on at least 1 specific method. The occurrence increased with age, being 12·1%, for those over 60 that suggests an epidemiological condition of concern for the elderly population. Of the seroepidemiological studies in the general population the mean positivity in serum samples was 21·7% and 29·2%, using an immunofluorescence antibody test and enzyme-linked immunosorbent assay (ELISA), respectively. The occurrence of strongyloidiasis in immunosuppressed individuals was 11·8% by parasitological methods and 19·5% using immunological methods. Considering that Brazil is a tropical country and that the character of chronicity and autoinfection of the parasite that can result in severe forms of hyperinfection or dissemination makes strongyloidiasis an important medically and socially neglected problem.

DNA contents of individual stages of Isospora (Toxoplasma) gondii and other Eucoccida were measured after Feulgen-pararosaniline (SO2) staining either by direct microfluorometry or by scanning of microphotographic negatives. Frequency distributions were analysed using a computer program based on a mathematical model describing cell division. All stages of I. (T.) gondii, except fertilized macrogametes (2c), contained a haploid amount of DNA (1c), indicating that meiosis in I. (T.) gondii occurs during sporogony. Microgametes possessed 3·3% DNA in excess, presumably mitochondrial DNA. Nuclei of M2-and M3-merozoites differed in two characteristics: a small but distinct nucleolus was observed in almost 50% of the M2-merozoites but in none of the M3-merozoites; all M2 merozoites were strictly haploid, while all M3-merozoites were synthesizing DNA (17% above the haploid value). It may be concluded that all M2- and M3-merozoites are already sexually differentiated, i.e. are macro- and microgamontoblasts, respectively. DNA synthesis necessary for the development of the microgamont starts already in the microgamontoblast stage (M3-merozoite). M2-merozoites macrogametes, synthesize 11% extra DNA before fertilization, (after fertilization an extra amount of 12% of the diploid value was found), probably by amplification of genes for proteins which are needed for rapid maturation and later sporogony. Essentially parallel results have been found in Eimeria tenella and in crescent cystozoites of Sarcocystis cruzi. Absolute DNA values in representatives of the Eucoccida have been estimated as follows (10−15 g): I. (T.) gondii, 96; E. tenella and E. acervulina, both 75; S. cruzi, 216; Plasmodium berghei, 27. The value of the estimation of total haploid amounts as a tool in taxonomy of Eucoccida is discussed.

Systematics involves resolving both the taxonomy and phylogenetic placement of organisms. We review the advantages and disadvantages of the two kinds of information commonly used for such inferences – morphological and molecular data – as applied to the systematics of metazoan parasites generally, with special attention to the malaria parasites. The problems that potentially confound the use of morphology in parasites include challenges to consistent specimen preservation, plasticity of features depending on hosts or other environmental factors, and morphological convergence. Molecular characters such as DNA sequences present an alternative data source and are particularly useful when not all the parasite's life stages are present or when parasitaemia is low. Nonetheless, molecular data can bring challenges that include troublesome DNA isolation, paralogous gene copies, difficulty in developing molecular markers, and preferential amplification in mixed species infections. Given the differential benefits and shortcomings of both molecular and morphological characters, both should be implemented in parasite taxonomy and phylogenetics.

The effect of digestion in trypsin and acid pepsin on Toxoplasma gondii tachyzoites and bradyzoites was re-evaluated because of recent use of this method to distinguish tachyzoites from bradyzoites. Toxoplasma gondii tachyzoites survived better in 0·5% trypsin solution for 1 h than in 1·0% solution, and occasionally survived for 2 h in acid pepsin solution. Extracellular tachyzoites ([ges ]1000) were also infectious orally to mice and cats. Bradyzoites survived equally in trypsin and acid pepsin solutions but the digestion of brain tissue in 0·5% trypsin solution was better than in acid pepsin solution. The resistance to digestion in acid pepsin solution is not a reliable method to distinguish tachyzoites from bradyzoites.

Delimiting species of malaria parasites (Haemosporida) has become increasingly problematic as new lineages of parasites are identified solely by molecular information, particularly mitochondrial cytochrome b sequence data. In this review, we highlight some of the issues, both historical and contemporary, that have hindered the development of objective criteria to diagnose, delimit and define species of haemosporidians. Defining species is not the focal interest of most researchers, most of whom merely wish to determine whether lineages identified in their samples match those of other researchers, and if so, where and in which host species. Rather than revisiting all the issues with respect to delimiting and naming species, we instead focus on finding a practical near-term resolution to the ‘species problem’ that utilizes the community's largest resource: mitochondrial cytochrome b DNA sequences. We recommend a standardized procedure to ‘tag’ these sequences, based on per cent sequence similarity, that will allow researchers to directly assess the novelty, known hosts and geographic distribution of avian malaria parasite lineages.

If parasitic infection is a driving force in female mate choice, then females should preferentially select parasite-free males. The role of infection on female mate choice in mammals was assessed using a 3-chambered apparatus. A female CD-1 mouse was allowed to choose between 2 tethered male mice, 1 uninfected and 1 infected with 200 larvae (L3) of the intestinal nematode Heligmosomoides polygyrus. Both uninfected and infected males were equally receptive to the oestrous females, and females did not differ in the number of visits and time spent exploring the 2 males. Female time preference was not a useful predictor of ultimate mate choice, whereas first mount preference of the female was a reliable indicator. Results indicate that female mice preferentially mated with uninfected males as evidenced by first ejaculation choice, but that male infection status did not significantly affect female reproductive success. Interestingly, litters sired by infected males contained a significantly higher percentage of females suggesting that parasite-induced hormonal changes may alter the sex ratio of the offspring. This study provides the first direct evidence of the impact of parasitic infection on mammalian mate choice.

In a sleeping sickness focus of Côte d'Ivoire, trypanosomes were characterized in humans, pigs and tsetse using various techniques. Out of 74 patients, all the 43 stocks isolated by KIVI (Kit for In Vitro Isolation) appeared to belong to only one zymodeme of Trypanosoma brucei gambiense group 1 (the major zymodeme Z3). The only stock isolated on rodents belonged to a different, new, zymodeme (Z50), of T. b. gambiense group 1. From 18 pigs sampled in the same locations as the patients, PCR showed a high proportion of mixed infections of T. brucei s. l. and T. congolense riverine-forest. Zymodemes of T. brucei s. l. from these pigs were different from those found in humans. From a total of 16260 captured tsetse (Glossina palpalis palpalis), 1701 were dissected and 28% were found to be infected by trypanosomes. The most prevalent trypanosome was T. congolense riverine-forest type, followed by T. vivax, T. brucei s. l. and T. congolense savannah type, this latter being associated to the forest type of T. congolense in most cases. Mixed infections by 2 or 3 of these trypanosomes were also found. Use of a microsatellite marker allowed us to distinguish T. b. gambiense group 1 in some of the mature infections in tsetse. Differences in infection rates and in trypanosome genotypes according to the host might indicate that the pig may not be an active animal reservoir for humans in this focus.

Recent studies on the motility of coccidian sporozoites have demonstrated a membrane-associated contractile system capable of moving certain intramembraneous components down the parasite surface propelling it forwards. The properties of this system resemble recorded observations on host cell invasion. In this study the invasive behaviour of Eimeria tenella and E. acervulina has been examined, with reference to the above findings, by light microscope and scanning and transmission electron microscopes. Known inhibitors of motility prevent invasion, though attachment appears unaffected. Invasion itself consists of 3 phases; attachment and orientation, induction of a parasitophorous vacuole and translocation of the parasite into the vacuole. Ultrastructural examination reveals a close membrane/membrane association maintained throughout invasion. From these results it is suggested that the parasite enters the parasitophorous vacuole by ‘capping’ the host/parasite junction down its body, so locomoting into the host cell. Such a model has two main advantages; it requires no additional modifications to either cell, and the specificity of membrane receptors would enable the one membrane-associated contractile system to be responsible for locomotion, antibody capping and host cell invasion.

The hypothesis that the parasite Toxoplasma gondii manipulates the behaviour of its intermediate rat host in order to increase its chance of being predated specifically by its feline definitive host, rather than a non-definitive host predator species, was tested. The impact of a range of therapeutic drugs, previously demonstrated to be effective in preventing the development of T. gondii-associated behavioural and cognitive alterations in rats, on definitive-host predator specificity was also tested. Using a Y-shaped maze design, we demonstrated that T. gondii-associated behavioural changes, apparently aimed to increase predation rate, do appear to be specific to that of the feline definitive host – there were significant and consistent differences between the (untreated) infected and uninfected rats groups where T. gondii-infected rats tended to choose the definitive host feline-predator-associated maze arm and nest-box significantly more often than a maze arm or nest-box treated with non-definitive host predator (mink) odour. Drug treatment of infected rats prevented any such host-specificity from being displayed. We discuss our results in terms of their potential implications both for T. gondii epidemiology and the evolution of parasite-altered behaviour.

The effects of parasitism by five species of larval Digenea on the digestive gland cells of Littorina saxatilis (Olivi) subsp. tenebrosa (Montagu) were investigated by comparing histochemically stained cells in healthy, starved and parasitized animals.

Two distinct effects were apparent: (a) The germinal sacs compress the walls of the digestive gland tubules and block the lumen. Since food cannot pass this block, digestive gland cells behind undergo starvation autolysis. (b) In digestive gland tubules not cut off from their food supply, glucose, glycogen, glycoproteins and lipid food storage globules are reduced and there is a compensatory increase in the number of food vacuoles in the digestive cells; an increase in glucose but a decrease in glycogen in the visceral haemocoel; and an increase in the number of secretory cells, perhaps in order to eliminate the parasite's excretory products from the visceral haemocoel.

Many issues concerning the taxonomy of Echinococcus have been resolved in recent years with the application of molecular tools. However, the status of Echinococcus maintained in transmission cycles involving cervid intermediate hosts remains to be determined. The recent characterization of the parasite from cervids in Finland has highlighted the paucity of data available, particularly that from North America. In this study, we have characterized a large number of Echinococcus isolates from cervids from Western Canada on the basis of morphology and molecular genetic techniques. Our results support earlier studies suggesting that Echinococcus of cervid origin is phenotypically and genetically distinct to Echinococcus maintained in domestic host assemblages, and also confirms that Echinococcus of cervid origin does not constitute a genetically homogeneous group. However, our data do not support the existence of 2 distinct genotypes (strains/subspecies) with separate geographical distributions. Our data appear to support the existence of only 1 species in cervids, but additional isolates from cervids and wolves in other endemic regions should be characterized before a final decision is made on the taxonomic status of Echinococcus in cervids.

Two clones of the human malaria parasite Plasmodium falciparum, denoted 3D7 and HB3, were grown in vitro under conditions permitting the development of gametocytes. The two clones differ in their allelic forms of two antigen genes MSP1 and MSP2. The alleles can be distinguished as size differences of polymerase chain reaction (PCR) amplified fragments of repetitive regions of each gene. Mosquitoes (Anopheles stephensi) were fed on a mixture of these gametocytes. A total of 128 oocysts was isolated from the midguts of infected mosquitoes from 9 crossing experiments between the clones. DNA extracted from these oocysts was amplified by PCR. Oocysts which contained both alleles of each gene (MSP1 and MSP2) had developed from heterozygotes produced by cross-fertilization events between 3D7 and HB3 gametes. The remaining oocysts contained single alleles of each gene, in parent clone combinations, and these had developed from homozygotes formed by self-fertilizations. The results suggest that gametes in the original mixture fed to mosquitoes had undergone random mating.

The protozoa Leishmania spp. are obligate intracellular parasites that inhabit the macrophages of their host. Since macrophages are specialized for the identification and destruction of invading pathogens, both directly and by triggering an innate immune response, Leishmania have evolved a number of mechanisms for suppressing some critical macrophage activities. In this review, we discuss how various species of Leishmania distort the host macrophage's own signalling pathways to repress the expression of various cytokines and microbicidal molecules (nitric oxide and reactive oxygen species), and antigen presentation. In particular, we describe how MAP Kinase and JAK/STAT cascades are repressed, and intracellular Ca2+ and the activities of protein tyrosine phosphatases, in particular SHP-1, are elevated.

Nematode infections are subject to density-dependent effects on their establishment, survivorship and fecundity within a host. These effects act to regulate and stabilize the size of nematode populations. Understanding how these density-dependent effects occur is important to guide the development of control strategies against parasitic nematodes and the diseases that they cause. These density-dependent effects have been hypothesized to result from intraspecific competition between parasites for limited resources or from the action of host immune responses. However, no specific evidence exists to distinguish between these two hypotheses. We find that in nematode (Strongyloides ratti) infections, density-dependent effects on parasite establishment, survivorship and fecundity are mediated by the host immune response. These density-dependent effects are only observed late in primary infections and no density-dependent effects are observed in infections in immuno-compromised animals. We find no evidence for intraspecific competition between parasites in experimental infections over a range of doses that encompasses all that is observed in natural infections. We conclude that density-dependent effects due to the immune response will act to regulate S. ratti infections before competition for space or nutrients within the host gut ever occurs.

Oral administration of mebendazole at a rate of 1 g/kg ieed (approximately 50 mg/kg body weight/day) for 14 days killed mature and immature cysticerci of Taenia pisiformis in rabbits, and multiplying tetrathyridia of Mesocestoides corti in mice. Progressive degrees of parasite damage caused by mebendazole treatment could be assessed by histological examination of calcareous corpuscles. A single subcutaneous injection of 10% mebendazole in carrier, at a rate of 100 mg/kg body weight, resulted in the death of all M. corti tetrathyridia in mice within 4 weeks, but the drug in saline was slowly mobilized and was relatively ineffective. Neither subcutaneous injections of mebendazole in saline or in carrier could kill cysticerci of T. pisiformis within 5 weeks, but the drug in carrier was effective after several months. Mebendazole in saline was effective when injected intraperitoneally, but adhesions often resulted from this route of administration. Echinococcus granulosus protoscoleces administered to mice by intraperitoneal injection were rapidly encapsulated by host lymphoid cells. The vesiculating protoscoleces were all contained within a fibrous capsule for more than 2 months after infection, but by 4 months almost all had grown free of the host reaction. Treatment of the encapsulated protoscoleces with mebendazole in feed for 14–21 days caused collapse of the outer cysts and death of the germinal membrane of all but the innermost protoscoleces. Six weeks later, however, cysts had regrown from surviving germinal tissue and a further treatment with mebendazole in feed for 14–21 days again did not destroy all germinal cells. Treatment of the 4-month-old scoleces with mebendazole in feed for 14 days caused all cysts to collapse and destroyed practically all E. granulosus germinal tissue. Three subcutaneous injections of mebendazole at fortnightly intervals, of drug in saline at 500 mg/kg body weight, or in carrier at 100 mg/kg body weight, were required in order apparently to kill all secondary cysts of E. granulosus. Host lymphoid cells were not able to traverse the laminated membrane of either untreated or collapsed cysts, and it has been shown that only a small amount of living germinative tissue is required to produce a new E. granulosus cyst. These factors could contribute to the relative ability of E. granulosus cysts to recover from mebendazole treatment, compared with cysticerci or tetrathyridia. The effectiveness of mebendazole thus seemed to depend on the formulation of the drug and its route of administration. Mebendazole is probably the first anthelmintic to have a lethal effect on larval cestodes. When applied orally there do not appear to be any adverse effects due to treatment.

1. The distribution of non-specific esterase and of cholinesterase in Ascaris lumbricoides has been determined using histochemical methods.

2. Non-specific esterase has been shown to be present in the cuticle, in the walls of the excretory canals, in the innervation processes of the muscles, in the coelomocytes, in the oesophageal glands, in the intestine, in the rectal glands, in the male and female reproductive systems, in parts of the nervous system and as 'caps' of enzyme on fat globules in the hypodermis and muscles.

3. Cholinesterase has been detected in the innervation processes and sheath of the muscles, in the sphincter muscles, in the intestine, in the sensory papillae and amphids, and in parts of the nervous system, including a nerve in the spicules.

4. Parts of the nervous system and the innervation processes of the muscles contain an esterase which is not inhibited by cholinesterase inhibitors and it is suggested that there may be esterase, distinct from cholinesterase, involved in nerve transmission.

5. Merocrine secretion of esterase has been observed in the intestine.