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.

We have investigated the influence of heteroxenous coccidia (Apicomplexa: Eimeriorina) on the predation risk of intermediate hosts. Voles infected with Frenkelia spp. were found more frequently in buzzards' (Buteo buteo) prey than among snap-trapped rodents. To eliminate the possibility of traps selecting for uninfected rodents, a laboratory experiment was performed. Mice experimentally infected with Sarcocystis dispersa seemed to be more likely caught by the final host, the long-eared owl (Asio otus); this result was confirmed by a mathematical model. Field data confirmed the adaptive value of parasite-induced changes. The increase of predation is directed towards the specific final host only or is non-specific. In the populations studied the probability of predation of parasitized individuals by the specific predator was increased.

There is no published account which allows the morphological discrimination of microfilariae of Onchocerca volvulus and M. ozzardi from each other. However, they occur together in parts of Brazil and Venezuela, and presumably there is always the possibility that migration could establish new sympatric populations in the future. The objective of this study was to evaluate simple morphological characters that might be used for species-diagnosis of microfilariae. The conclusions were that the location of microfilariae in the blood or skin, the body size and the nucleation of the nerve ring are expected to be useful first indications of species identity, but cannot be used for confident diagnosis. The structure of the cephalic armature (stained with alcian blue) seems to be species specific, but is of limited application because it is often difficult to see. However, the pattern of nucleation of the tail (as expressed by the ratio of the length of the terminal nucleus compared with the length of the tail space) is distinctive and is expected to be diagnostic.

The intermediate hosts for Taenia saginata and T. solium are cattle and pigs (and humans for the latter), respectively. In vitro-hatched (but not activated) oncospheres of both Asian Taenia (T. saginata asiatica, a new subspecies of T. saginata or T. asiatica, a new species) and T. solium injected subcutaneously into the backs of mice with severe combined immunodeficiency (scid) developed into fully matured cysticerci. Five-month-old metacestodes of Asian Taenia had no hooklets and were bigger in size than those previously reported and similar to those of T. saginata. Their morphology suggested that the cysticerci were more advanced than those in the intermediate host animals. It is suggested that scid mice are valuable experimental animal models for studying human taeniid cestode infections.

Leishmania are obligatory intracellular parasitic protozoa that cycle between sand fly mid-gut and phagolysosomes of mammalian macrophages. They have developed genetically programmed changes in gene and protein expression that enable rapid optimization of cell function according to vector and host environments. During the last two decades, host-free systems that mimic intra-lysosomal environments have been devised in which promastigotes differentiate into amastigotes axenically. These cultures have facilitated detailed investigation of the molecular mechanisms underlying Leishmania development inside its host. Axenic promastigotes and amastigotes have been subjected to transcriptome and proteomic analyses. Development had appeared somewhat variable but was revealed by proteomics to be strictly coordinated and regulated. Here we summarize the current understanding of Leishmania promastigote to amastigote differentiation, highlighting the data generated by proteomics.

The tegumental membrane complex of Schistosoma mansoni is the site of interaction between the parasite and the host. The tegument is involved in uptake of many nutrients, but also plays a crucial role in the evasion of the actions of the host immune system. Essential for the success of this evasion is maintaining the integrity of the tegumental membranes. The rate of turnover of phospholipids was investigated by pulse-labelling worms cultured in vitro, followed by additional incubation in the presence of unlabelled substrates. Tegumental membranes were isolated, characterized using antibodies against specific tegumental proteins, and analysed. It was demonstrated that the most prominent fatty acid found in tegumental phospholipids, palmitate, incorporated rapidly into the phospholipid fraction during a 30 min pulse labelling. In a subsequent 20 h chase with unlabelled substrates, the incorporated radioactivity was lost again from the tegumental membrane complex. This high turnover of palmitate was found to be limited to phosphatidylcholine (PC) only. The turnover was due to deacylation/reacylation, and not to the sloughing of membranes as is the case in schistosomula. It is speculated that this rapid turnover of PC in the tegument of adult schistosomes plays a new and important role in the immune evasion by the parasite.

Animals are common hosts of mutualistic, commensal and pathogenic microorganisms. Blood-feeding parasites feed on a diet that is nutritionally unbalanced and thus often rely on symbionts to supplement essential nutrients. However, they are also of medical importance as they can be infected by pathogens such as bacteria, protists or viruses that take advantage of the blood-feeding nutritional strategy for own transmission. Since blood-feeding evolved multiple times independently in diverse animals, it showcases a gradient of host–microbe interactions. While some parasitic lineages are possibly asymbiotic and manage to supplement their diet from other food sources, other lineages are either loosely associated with extracellular gut symbionts or harbour intracellular obligate symbionts that are essential for the host development and reproduction. What is perhaps even more diverse are the pathogenic lineages that infect blood-feeding parasites. This microbial diversity not only puts the host into a complicated situation – distinguishing between microorganisms that can greatly decrease or increase its fitness – but also increases opportunity for horizontal gene transfer to occur in this environment. In this review, I first introduce this diversity of mutualistic and pathogenic microorganisms associated with blood-feeding animals and then focus on patterns in their interactions, particularly nutrition, immune cross-talk and gene exchange.

Oxidative stress has been implicated as an important pathogenic factor in the pathophysiology of various life-threatening diseases such as cancer, cardiovascular diseases and diabetes. It occurs when the production of free radicals (generated during aerobic metabolism, inflammation, and infections) overcome the antioxidant defences in the body. Although previous studies have implied that oxidative stress is present in serum of patients with parasitic infection there have been no studies confirming oxidative stress levels in the Malaysian population infected with intestinal parasites. Three biochemical assays namely hydrogen peroxide (H2O2), lipid peroxidation (LP) and advanced oxidative protein product (AOPP) assays were carried out to measure oxidative stress levels in the urine of human subjects whose stools were infected with parasites such as Blastocystis hominis, Ascaris, Trichuris, hookworm and microsporidia. The levels of H2O2, AOPP and LP were significantly higher (P<0·001, P<0·05 and P<0·05 respectively) in the parasite-infected subjects (n=75) compared to the controls (n=95). In conclusion, the study provides evidence that oxidative stress is elevated in humans infected by intestinal parasites. This study may influence future researchers to consider free radical-related pathways to be a target in the interventions of new drugs against parasitic infection and related diseases.

Strongyloidiasis is frequently asymptomatic and diagnosis of latent infection is difficult due to limitations of current parasitological and serological methods. This study aimed to verify the use of conventional polymerase chain reaction (PCR) assay for molecular diagnosis of Strongyloides stercoralis infection. Fresh stool samples were obtained from 103 individuals: 33 S. stercoralis positive, 30 positive for other parasites and 40 negative for parasitological methods. These samples were examined by the Lutz, Rugai and agar plate culture methods and conventional PCR assay. Two sets of primers (S. stercoralis species-specific and genus-specific sets), located in the 18S ribosomal RNA gene, were used for PCR. Of the 33 samples positive for S. stercoralis by parasitological methods, 28 (84·8%) were also detected by PCR assay using species-specific primers and 26 (78·8%) using genus-specific primers. Among the stool samples negative by parasitological methods, seven (17·5%) were positive by PCR using species-specific primers and two (5·0%) using genus-specific primers. In conclusion, the conventional PCR assay described in this study using a species-specific primer pair provided a molecular method for S. stercoralis diagnosis in human stool samples.

1.Cases of accelerated development of insects due to parasitism are reviewed.

2.Two new cases are recorded.

3.The phenomenon is discussed in the light of Roubaud's study of the diapause.

1. An account is given of the seasonal occurrence and maturation of Triaenophorus nodulosus, based on the examination of the worms from 104 pike taken in Llyn Tegid from December 1957 to October 1959.

2. The plerocercoids of T. nodulosus were found in the livers of the perch of Llyn Tegid. Infective plerocercoids were found throughout the year, and it is considered that invasion of the pike, also, occurred throughout the year.

3. The annual cycle of maturation of T. nodulosus described by other workers is confirmed. Currently, five arbitrary stages of maturity were recognized, and the incidence of each of these stages during each month of the investigation is given. During June to September the worms were of plerocercoid-form, from October to December genital development occurred and the first eggs were observed in the uteri in December. Egg liberation was at a peak from April to May, and by June the population of matured worms was lost.

4. A non-linear relationship was found between the length of the pike and the numbers of worms occurring in the intestines of these fish. This phenomenon was related to the feeding habits of the pike; the medium-sized most heavily infected pike were eating the largest number of the perch containing the plerocercoids.

5. It was found that although invasion of the pike by plerocercoids of T. nodulosus occurred throughout the year, there was no increase in the numbers of worms in the pike intestines, to a maximum, at any time of the year, rather there was a more or less constant number of worms in pike of given length at all times of the year. It is suggested, therefore, that a dynamic equilibrium exists between gain of plerocercoids and loss of worms from the pike intestines at all times.

6. Factors affecting the change from plerocercoid to a mature worm are discussed. It is suggested that an experimental approach is needed.

I am grateful to the Welsh Land and Agricultural Sub-Commission for permission to net Llyn Tegid, and to Captain G. H. A. Boyle of the Sub-Commission for his help in the capture of the pike. I also wish to thank Professor R. J. Pumphrey in whose Department this work was carried out, Dr P. M. Sheppard for statistical analyses, Dr J. W. Jones and Mr S. Prudhoe (British Museum, Natural History) for discussion of the manuscript. The work was carried out during the tenure of a Department of Scientific and Industrial Research studentship.

Plasmodium falciparum, P. knowlesi and P. chabaudi showed a significant activity of methylenetetrahydrofolate reductase (MTHFR). The presence of this enzyme completes the methionine synthesis cycle, in which the one-carbon fragment from serine side-chain can be transferred to methionine. However, while metabolic labelling of methionine from l-3 [14C]serine could not be demonstrated in P. falciparum, the significance of MTHFR was implicated by a novel pathway for salvage of exogenous 5-methyltetrahydrofolate from the host cell. The methyl group of the cofactor was incorporated into methionine, and the folate cofactor was found in the same pool as that derived from de novo synthesis with paminobenzoic acid as the precursor, shown previously as polyglutamylated 5-methyltetrahydrofolate. It is proposed from these results that the function of MTHFR and the methionine synthesis cycle is not the supply of methionine, but the generation of active folate cofactors from more stable precursors salvaged by the parasites

Rats harbouring a 35-day-old primary infection of Moniliformis dubius were inoculated with constant doses of Nippostrongylus brasiliensis and 10 days later, after post mortem examination, rats with concurrent infections harboured significantly fewer Nippostrongylus than rats with single infections. Similar infections of Moniliformis were carried out, but with post mortem taking place on days 8,9, 12 and 14 of the Nippostrongylus infections. On days 8 and 9 of infection, rats with concurrent infections did not harbour significantly fewer Nippostrongylus compared with single infections. Both single and concurrent infections of 12-and 14-day-old Nippostrongylus were found to harbour lower numbers of worms. In the single infection this corresponds to the timing of the typical immune expulsion of a primary single infection which takes place on approximately day 12 of infection. The Moniliformis population was not significantly affected, in terms of numbers, dry weight and length, although each parasite population did show a slight shift in site in the presence of the other. A significant reduction in egg production by Nippostrongylus was detected throughout concurrent infection. The possible role of non-reciprocal cross-immunity is discussed as an explanation for the apparent early expulsion of the Nippostrongylus population in the presence of Moniliformis.

Worm counts, faecal egg counts and erythrocyte losses are recorded for lambs which were exposed on a naturally infected pasture for different periods in different years. After each exposure period the lambs were kept under conditions in which no further infection could occur; at varying times, usually after the infections had had time to maturo, the lambs were killed and examined. A detailed analysis of the results is given. It is concluded that the negative binomial distribution of worms among sheep within a flock is not a reflexion of the pasture distribution of infective stages but is the result of a combination of Poisson distributions, these distributions being generated by genetic subsets within the flock. There is a remarkable correlation between the numbers of Haemonchus present and the numbers of worms of the other genera. It is suggested that there are host-mediated common elements in the biomass regulating parameters of mixed trichostrongyle infections and that there is a resource-allocating device. Three main hypotheses are proposed. The hypotheses are: (1) The dimensional constraints on the host-parasite system are the results of various kinds of pace-setters or biological clocks. In each annual cycle the parent worms programme the rate of development through each generation. (2) The rate of development of the worms is tied stochastically or deterministically to the rate of senescence and death. (3) The rate of development and death for each trichostrongyle is set at the start of each season by a host factor which acts on a comparable area of the genome in each trichostrongyle. Methods of testing these hypotheses are discussed and the work related to other systems.

Trypanosomes were isolated before and after the formation of infected detectable antibody from various brain sites and the blood of Microtus montanus. All isolates were serotyped by the agglutination reaction, and the isolates obtained prior to antibody formation were serologically identical to the original inoculum. Later isolates obtained from separate sites of an infected animal were serologically different from the original inoculum and also from each other. It was therefore concluded that in a single chronically infected animal there are numerous different antigenic populations of trypanosomes each occupying separate brain sites. A hypothesis to account for this antigenic diversity is given.

1. A fungus disease of epidemic proportions was found in the common sea herring (Clupea harengus) throughout the Gulf of Maine.

2. The fungus was also found to infect the common winter flounder (Pseudopleuronectes americanus) and the alewife (Pomobolus pseudoharengus).

3. The causative agent was found to be a species of fungus belonging to the genus Ichthyosporidium Caullery and Mesnil (1905). The specific name is tentatively accepted as hoferi Plehn and Muslow (1911).

4. The organism is believed to be a normal parasite to the herring and reaches epidemic proportions only when certain unknown factors are operative.

5. The causative organism was found in herring preserved in 1926, and it is believed that the epidemic has been increasing in severity since that time.

6. It is believed that such an epidermic, once initiated, increases in severity, reaches a peak, and subsides to a subpatent level. The peak is believed to have been reached in 1931.

7. The life history and effects of the organism in the herring and flounder are described.

8. The herring is believed to acquire the infection by the ingestion of parasites liberated from fish in the same school.

9. The flounder is believed to acquire the infection by the consumption of infected herring.

10. The alewife is beleived to acquire the infection by ingestion of the parasite during its infrequent association with the herring.

11. Infection is believed to be established by way of the alimentary canal and, once established, to spread throughout the host by way of the blood stream or the lymphatics.

12. Direct cross infection from the herring to the flounder establishes the theory that the parasites in these two hosts are one and the same organism.

13. Direct cross infection experiments from the herring to the flounder eliminate the necessity of an intermediate host.

14. There is no reason to believe that this parasite is capable of infecting warm-blooded animals.

Subadult and adult specimens of the pond snail Lymnaea stagnalis were infected with the schistosome Trichobilharzia ocellata. Egg production and growth of the snails were monitored over an 8-week period post-infection (p.i.). Snail haemolymph was collected and analysed for the presence of schistosomin, a neuropeptide which antagonizes the action of the snails' female gonadotropic hormones. Snails infected as subadults showed an increase in fecundity during the first 4 weeks p.i. compared with non-infected controls. The possibility is discussed that this increase is caused by an accelerated maturation of the female sex organs due to elevated levels of Dorsal Body Hormone, a female gonadotropic hormone. No difference in fecundity was found between snails infected as adults and control snails during the first 4 weeks p.i. Snails infected as subadults and as adults showed a decrease in fecundity from week 5 p.i. and onwards. This decrease coincided with the appearance of schistosomin in the haemolymph of the snails and with that of differentiating cercariae in the daughter sporocysts. Cercariae are probably involved in the induction of schistosomin release from the snails' CNS into the haemolymph. Snails infected as subadults or as adults grew at approximately the same rate as uninfected snails.

Egg production by Reighardia sternae, implanted at various stages of maturity into the interclavicular air sacs of captive gulls, is described.

Females produce only 2900 eggs per lifetime over a short patent period of 1–3 days. The problem of a direct life-cycle in relation to this unusually low fecundity is discussed, and speculation is advanced concerning a possible parasitic behavioural trait which could facilitate direct transmission. The hazards of the latter are also offset by auto-reinfection.

Incorporation of labelled amino acid into tegumental proteins and acquisition of protection by schistosomula against antibody-mediated killing in vitro were simultaneously stimulated by serum factors and inhibited by puromycin. Comparison of polyacrylamide gel electrophoresis patterns with fluorographic autoradiography indicates that the majority of proteins in the parasite tegument were labelled with the isotope after incubation for 3 h. No new, clearly defined band was observed in the autoradiography pattern. During this period a decreasing susceptibility of the schistosomula to antibody plus complement was observed. Quantitative fluorescence assay shows that schistosomula insensitive to antibody plus complement were still able to bind the same amount of antibody as the unprotected parasites. Pre-culture of schistosomula in the presence of inactivated normal rabbit serum also decreased the susceptibility of the parasites to the in vivo killing mechanism.

Isometric tension recordings and the single sucrose-gap technique were used to record mechanical and electrical activity from Grillotia erinaceus metacestodes in vitro. Both complete preparations and those cut longitudinally (to allow access of the bathing medium to the region of the somatic muscle) showed spontaneous contractions of frequency ≃ 1/min in Hanks’ Balanced Salt Solution (HBSS) at 13 °C. Changing the pH, temperature or osmolarity of the HBSS did not improve the activity but rather abolished it at extremes of these variables, so confirming the adequacy of the experimental environment for further work. The neurotoxin tetrodotoxin (TTX; 3 × 10−6 M) failed to abolish or modify these spontaneous contractions although excitatory and inhibitory responses to 5-hydroxytryptamine (5-HT) and acetylcholine (ACh) respectively were demonstrated. Electrical recordings showed that spontaneous contractions were mediated by slow membrane depolarizations upon which spike-like potentials were often superimposed. 5-HT was shown to mediate its excitatory effect via membrane depolarization and an increase in the frequency of both slow depolarization and spikes. In contrast, inhibition by ACh was accompanied by membrane hyperpolarization and loss of all regenerative electrical activity. Electric field stimulation of the preparation using a range of stimulus parameters failed to demonstrate a functional motor innervation to the somatic muscle.