Sheep infected with adult Fasciola hepatica were drenched with rafoxanide. At 4, 8, 16 and 24 h after drenching the sheep were killed and the flukes removed, washed and rapidly frozen in liquid nitrogen. The content of key metabolites in the fermentation pathway were determined and compared with those in control F. hepatica, whose hosts were not treated with rafoxanide.

Rafoxanide decreased glycogen, malate, NADH and ATP levels. The level of other metabolites in the pathway increased for the first 8–16 h after rafoxanide treatment. The marked decrease in ATP and glycogen, and the increase in total [NAD+]/[NADH] and [oxaloacetate]/[malate], together with the changed content of other metabolites, led to the conclusion that the mode of action of rafoxanide against F. hepatica in vivo is by uncoupling oxidative phosphorylation.

The reaction of Balb/c mice to primary and secondary subcutaneous infection with chinoeoccu.s granulosus protoscoleces (PSC) is described. From 3 to 14 days following primary exposure to PSC, draining lymph nodes increase in weight and there is expansion of T and B lymphocyte populations, enhancement of in vitro lymphocyte transformational responses and production of PSC-specific 1gM and IgE antibodies. Despite the persistence of viable PSC in host tissues, lymphocyte responses decline to pre-infection values over the period 3–8 weeks post-infection. Secondary exposure to PSC immediately induces lympho proliferation, enhancement of transformational responses, production of IgE antibody and encapsulation of PSC by inflammatory cells. Although specific antibody levels remain high until at least 8 weeks after challenge infection, lymphocyte activity begins to decline after 4 days and is profoundly suppressed by 10 days. Parasite viability appears to be significantly reduced in secondary, as opposed to primary, infection and is associated with the accumulation of large numbers of eosinophils, mast cells and macrophages in infected tissues.

The intraerythrocytic multiplication of two strains of Theileria annulata was studied with parasites maintained in stationary cultures and in the blood of infected cattle. In cultures established with blood from infected cattle 20–60% of single T. annulata piroplasms divided into quadruplet forms by day 6 in vitro. Transmission electron microscopic studies of T. annulata in culture showed that piroplasms possess intracytoplasmic food vacuoles and cytostomes during a pre-division trophozoite stage. The onset of intraerythrocytic multi plication was marked by the appearance of rhoptries and electron-dense plaques beneath the parasite's plasmalemmal membrane. The plaques developed into short segments of subplasmalemmal double membranes which were closely associated with the rhoptries. It was concluded that multiplication of T. annulata in erythrocytes occurred by schizogony, as nuclear division preceded cytoplasmic division and the final separation of merozoites. The four merozoites produced by intraerythrocytic schizogony had the same ultrastructural features as the T. annulata merozoites produced by intralymphocytic schizogony. Clusters of four merozoites, identical to those observed in stationary cultures, were also seen in the erythrocytes of persistently infected cattle and appeared to represent the most significant dividing forms of T. annulata in vivo.

We have previously described the major yolk protein, vitellin, in the British blackfly Simulium ornatum Meigen. Here we demonstrate that vitellogenin, synthesized in the fat body and secreted into the haemolymph, is composed of subunits with the same approximate molecular weight as vitellin, namely 200 and 68 kDa. Simulium ornatum is the natural vector for the cattle filarial nematode Onchocerca lienalis Stiles, which induces host fecundity depletion. A significant reduction in ovarian vitellin content was associated with infection by intrathoracic injection of 20 O. lienalis microfilariae immediately after blood-feeding. Fat body synthesis of vitellogenin was significantly reduced as early as 8 h post-infection in comparison with sham-injected flies. When total haemolymph protein from infected and sham injected flies was compared, titres were significantly depressed 6 h post-infection. However, later in the infection, titres were elevated by 30%, the major component being vitellogenin. The injection of dead microfilariae had no effect. An infection burden of a single parasite caused a significant reduction in ovarian protein content in comparison with shams, but no further significant decrease was observed as the parasite burden was increased from 5 to 20. Possible mechanisms underlying the disturbance of Simulium reproductive physiology are proposed.

1. Trypanosomes were found in the blood of thirty-five of seventy-two fish of five genera (chiefly Tilapia spp.) from Lakes Victoria and George, Uganda.

2. The trypanosomes, which were never numerous in the blood, showed two morphological forms—small (22–44μ. long) and large (45–65μ). No significant differences were observed between the trypanosomes from the different species of fish, and all the trypanosomes seen are provisionally identified as Trypanosoma mukasai Hoare, 1932.

3. Crithidia were found in the gut of a glossosiphoniid leech which had been removed from a fish; although suggestive, this cannot be taken as conclusive evidence that leeches of this family are vectors of T. mukasai.

4. The taxonomy of the trypanosomes of African fresh-water fish is reviewed, and it is concluded that only the following species should be regarded as valid at present: T. toddi Bouet, 1909, T. mukasai Hoare, 1932, and T. tobeyi Dias, 1952.

5. Dactylosoma mariae Hoare, 1930, was found in the blood of thirty-six of the seventy-two fish examined. Merozoites, schizonts and gametocytes of this small unpigmented parasite were observed within erythrocytes. No developmental stages were found in certain viscera of two infected fish.

The life-cycles of the two species of Crepidostomum occurring in a stream in North Wales are investigated. Both species share the same arthropod and definitive hosts, viz. Gammarus pulex and Salmo trutta, respectively, but have different molluscan hosts, viz.: Lymnaea peregra for C. metoecus and Pisidium casertanum for C. farionis.

C. metoecus and C. farionis have annual cycles, hence periodicity of occurrence in their hosts. In C. metoecus the dynamics of occurrence in the three hosts are correlated. The inverse relationship in G. pulex and S. trutta as well as the existence of a time-lag of 3–4 months between the establishment of this worm in G. pulex and in S. trutta are discussed.

Neither premunition nor age-resistance occurs in the parasitization of S. trutta and G. pulex by C. metoecus. The increase in the rate and degree of infestation with the age and length of fish, except in the oldest and longest group, is shown to be due to trophic factors.

C. metoecus is more abundant and widely distributed in the stream than C. farionis. This fact is associated with the occurrence of their molluscan hosts.

Experimental observations were made on the stages in the life-history of C. metoecus, including the mode of emergence of the cercaria, invasion of shrimps and encystment, as well as development of the metacercariae in G. pulex.

More cercariae are shed by day and at higher temperatures, and they live for about 5 days at 8 °C. The metacercaria undergoes considerable development before becoming infective. C. metoecus does extensive damage to L. peregra, has no observed ill-effect on trout, and apparently affects the life-span of shrimps adversely only in cases of very heavy infestations.

The non-parasitization of Cottus gobio by the two flukes is probably due to the prevailing ecological factors.

My thanks are due to Professor H. B. N. Hynes and Dr J. C. Chubb for many helpful criticisms at all stages of this study; to Miss Joan Venn for helping with the sampling programme; and the Commonwealth Scholarship Commission in the United Kingdom for financial support.

Numerous studies have demonstrated that parasites with complex life-cycles can cause phenotypic modifications in their hosts that lead to an increased rate of transmission, and suggest that these modifications are the result of parasitic adaptations to manipulate the host. Little attention is paid, however, to separating the possibility of adaptive host manipulation from incidental (if fortuitous) side-effects of infection. In this study we combine statistical and analytical tools to interpret the impact of the macroparasite Ligula intestinalis L. (Cestoda, Pseudophyllidea) on the behaviour of its intermediate fish host (the roach, Rutilus rutilus L.), using field data on a natural system. Two distinct sets of generalized linear models agree that both the presence and the intensity of infection contribute to a modified behavioural response in the host. This was illustrated by a preference for the lake-edge in infected fish during autumn. Furthermore, the effect of parasites upon their host is heterogeneous with respect to parasite size, with larger parasite individuals having a disproportionate impact. A series of game-theoretic models of adaptive host manipulation illustrate a potential rationale for a size-dependent manipulation strategy in parasites. These findings illustrate the potential complexity and functionality of the impact of L. intestinalis upon its fish host, which together reduce the parsimony of the alternative ‘incidental effect’ hypothesis.

In an immunocytochemical study, using an antiserum and a monoclonal antibody specific for the amino acid, γ-aminobutyric acid (GABA), GABA-like immunoreactivity (GLIR) has been demonstrated for the first time in parasitic flatworms. In Moniezia expansa (Cestoda), GLIR was seen in nerve nets which were closely associated with the body wall musculature and in the longitudinal nerve cords. In the liver fluke Fasciola hepatica (Trematoda), the GLIR occurred in the longitudinal nerve cords and lateral nerves in the posterior half of the worm. GLIR was also detected in subtegumental fibres in F. hepatica. The presence of GABA was verified, using high-pressure liquid chromatography coupled with fluorescence detection. The concentration of GABA (mean ± S.D.) in M. expansa anterior region was 124·8 ± 15·3 picomole/mg wet weight, while in F. hepatica it was 16·8 ± 4·9 picomole/mg. Since several insecticides and anti-nematodal drugs are thought to interfere with GABA-receptors, the findings indicate that GABAergic neurotransmission may be a potential target for chemotherapy in flatworms too.

The outcome of Plasmodium yoelii 17XL-infected BALB/c and DBA/2 mice, ranging from death to spontaneous cure, respectively, depends largely on the establishment of effective pro-inflammatory type 1 responses during the early stages of infection and associates with CD4+CD25+Foxp3+regulatory T cells (Tregs). Here, effects of Tregs were analysed on early P. yoelii 17XL infection in BALB/c and DBA/2 mice. In vivo depletion of Tregs significantly reversed the inhibited establishment of effective pro-inflammatory type 1 responses in BALB/c mice, indicating that this cell population contributed to the suppression of T-cell function in malaria. Moreover, the proportion and absolute numbers of IL-10-secreting Tregs in BALB/c mice were significantly higher than that found in DBA/2 mice by intracytoplasmic staining, and IL-10 production was correlated with the Tregs population. In addition, in vivo Tregs depletion decreased the production of IL-10 and the apoptosis of CD4+ T cells. Consistently, IL-10R blockade also had the same effect as that of Tregs depletion in P. yoelii 17XL-infected BALB/c mice. Our data demonstrate that Tregs perhaps have an important role in regulating pro-inflammatory type 1 responses in an IL-10-dependent manner and induce CD4+ T cell apoptosis during the early stage of P. yoelii 17XL infection.

Randolph and Dobson (2012) criticize the dilution effect, which describes the negative relationship between biodiversity and infectious disease risk. Unfortunately, their commentary includes distortions, errors of omission, and errors of commission, which are rebutted herein. Contrary to their claims, the dilution effect is not a ‘mantra’ that asserts that reduced disease risk is a ‘universal’ outcome of high diversity. Although universality of the dilution effect has not been claimed, and conditions under which diversity can amplify disease risk have been described, the growing literature indicates that the dilution effect is indeed a widespread phenomenon.

Muscle cells from adult male Schistosoma mansoni have been isolated using a combination of papain digestions and mechanical dissociation procedures. The muscle fibres isolated in this way lacked nuclei but they did contract and relax in response to high [K+], a response which was blocked in the presence of Co2+. From this we conclude that the isolation procedure yields viable muscle fibres useful for physiological studies. Patch-clamp recordings taken from the isolated fibres show a variety of discrete ionic conductances. In inside-out patches one prominent channel was a Ca2+-activated K+ channel with a conductance of 195 pS and a selectivity greater than 10:1 for K+ over Na+, Cs+ or NH4+. Percentage open time was dependent on [Ca2+] at the intracellular face. With [Ca2+] at 1 μM or greater percentage open time was > 95%; at 0.1 μM it was < 2%. No voltage sensitivity could be detected in the voltage range from –50 to –10 mV membrane potential. Ba2+ (10 mM), but neither tetraethylammonium nor 3,4-diaminopyridine blocked the channel from the intracellular face. This Ca2+-activated K+ channel in the muscle membrane of this acoelomate animal is similar in most respects to the maxi-K+ channels which have been described in a variety of cells from more highly evolved animals.

An automated flow cytometric (FCM) detection method has been developed and validated with a simple diagnostic procedure in parasitized erythrocytes of Plasmodium berghei-infected rats using the nucleic acid-binding fluorescent dye YOYO-1. High levels of reticulocytes were detected during the course of the infection, ranging from 1·2–51·2%, but any RNA potentially confounding the assay could be removed by digestion with RNAse. The cell counts of uninfected, infected, and nucleated cells occurred with high precision. The cells were divided into different populations according to their physical or chemical properties but various factors within the assay such as cell fixation, RNA digestion, and compensation required optimization. In this study, FCM greatly simplified and accelerated parasite detection, with a mean precision of 4·4%, specificity of 98·9% and accuracy of 101·3%. The detection and quantitation limits in the assay were 0·024% and 0·074% parasitaemia, respectively. Overall, the parasite counts by FCM measurement correlated highly (r2=0·954–0·988) with the parasitaemia measured by light microscopical analysis when animals treated with suppressive, clearance, and curative doses of novel antimalarial drugs were examined. The lower levels of parasitaemia (30%) detected by microscopy compared to FCM may be related to a number of schizonts externally attached to the erythrocyte membranes that normally would not be included in microscopy counting. Lower sampling error and reliable identification of rodent erythrocyte parasites based on the principles of FCM have replaced the traditional blood smear in our laboratory.

A comparison was made of the development, survival and reproduction of 5 isolates of Trichinella spiralis in inbred mice. Low responder C57BL/10 mice allowed worms of all isolates to survive longer and reproduce more successfully than did high responder NIH mice, suggesting that host immunity exerted a dominant influence upon infectivity. One isolate (Is-5 (W) — an arctic isolate) had a markedly lower infectivity than all other isolates, and was selected for more detailed study, together with isolate Is-1 (S) (a temperate isolate) which showed high infectivity. The lower infectivity of Is-5 (W) reflected a more rapid onset of immunity in mice infected with this parasite, immunity reducing the reproductive potential of female worms and causing an early expulsion from the intestine. No evidence of a dose-dependent suppression of immunity was found to explain the higher infectivity of Is-1 (S). Is-5 (W) provided a very rapid mucosal mastocytosis in infected mice, whereas Is-1 (S) caused no measurable response. In contrast, Is-1 (S) elicited higher levels of circulating parasite-specific antibodies than did Is-5 (W). These results are discussed in relation to the interplay of parasite immunogenicity and host immune responsiveness in determining infectivity, and point to the importance of identifying those immunodominant parasite molecules which control the balance of the host—parasite relationship.

A simple technique is described for preparation of Giardia cysts from faecal samples, the growth of trophozoites in suckling mice and the isolation of trophozoites for genetic analysis by allozyme electrophoresis. In total, 125 new isolates of Giardia have been collected from human and animal sources over a wide geographical area of South Australia and the Northern Territory of Australia. A number of long-established axenized isolates of G. intestinalis belonging to Groups I and II also adapted to grow in suckling mice. These findings indicate that suckling mice are permissive hosts for a variety of genetically dissimilar but morphologically similar organisms of the G. duodenalis type and that this in vivo technique may be less selective than isolation by in vitro culture. The use of suckling mice has revealed that infections can be composed of mixed genotypes and that isolation and purification techniques can be selective. Allozymic interpretation is essential to reveal the genetic complexity of such mixtures

The Brachylaimoidea are digenean parasites of vertebrates, including humans, domestic animals, poultry and wild game. Numerous Brachylaimoidea, particularly adults of Brachylaima and Leucochloridium, are difficult to identify to species. We provide and analyse sequences of two nuclear (18S rDNA, ITS2) and two mitochondrial (CO1, ND1) DNA loci of central European species of the Brachylaimoidea, namely Leucochloridium holostomum, Leucochloridium paradoxum, Leucochloridium perturbatum, Leucochloridium subtilis, Leucochloridium vogtianum, Urotocus rossitensis, Urogonimus macrostomus, Michajlovia migrata, Leucochloridiomorpha lutea, Brachylaima arcuatus, Brachylaima fuscata and Brachylaima mesostoma. We identified three clades in the genus Leucochloridium, which do not correspond to the previously suggested subgenera Neoleucochloridium, Papilloleucochloridium and Leucochloridium. We reject classification of Urotocus and Urogonimus in Leucochloridiinae, and, instead, re-establish the subfamilies Urotocinae and Urogoniminae. We synonymize the genus Renylaima with the genus Brachylaima. We reject M. migrata as a member of Leucochloridiinae sensu stricto or Brachylaimidae suggested by some previous authors. We found that the previously sequenced Glaphyrostomum sp. does not cluster with any hitherto sequenced Brachylaimidae. We also provide comparative measurements of the examined central European Brachylaimoidea, address the the specificity of their localization in the host and discuss their host-specific prevalence and intensity of infections based on the extensive dataset of birds examined in 1962–2015.

Different parasite taxa exploit different host resources and are often unlikely to interact directly. It is unclear, however, whether the diversity of any given parasite taxon is indirectly influenced by that of other parasite taxa on the same host. Some components of host immune defences may operate simultaneously against all kinds of parasites, whereas investment by the host in specific defences against one type of parasite may come at the expense of defence against other parasites. We investigated the relationships between the species diversity of 4 higher taxa of ectoparasites (fleas, sucking lice, mesostigmatid mites, and ixodid ticks), and between the species richness of ectoparasites and endoparasitic helminths, across different species of rodent hosts. Our analyses used 2 measures of species diversity, species richness and taxonomic distinctness, and controlled for the potentially confounding effects of sampling effort and phylogenetic relationships among host species. We found positive pairwise correlations between the species richness of fleas, mites and ticks; however, there was no association between species richness of any of these 3 groups and that of lice. We also found a strong positive relationship between the taxonomic distinctness of ecto- and endoparasite assemblages across host species. These results suggest the existence of a process of apparent facilitation among unrelated taxa in the organization of parasite communities. We propose explanations based on host immune responses, involving acquired cross-resistance to infection and interspecific variation in immunocompetence among hosts, to account for these patterns.

Utilization of chemical pesticide to control monogenean diseases is often restricted in many countries due to the development of pesticide resistance and concerns of chemical residues and environmental contamination. Thus, the use of antiparasitic agents from plants has been explored as a possible way for controlling monogenean infections. Extracts from Cinnamomum cassia were investigated under in vivo conditions against Dactylogyrus intermedius in goldfish. The two bioactive compounds, cinnamaldehyde and cinnamic acid, were identified using nuclear magnetic resonance and electrospray ionization mass spectrometry. The 48 h median effective concentrations (EC50) for these compounds against D. intermedius were 0·57 and 6·32 mg L−1, respectively. The LD50 of cinnamaldehyde and cinnamic acid were 13·34 and 59·66 mg L−1 to goldfish in 48 h acute toxicity tests, respectively. These data confirm that cinnamaldehyde is effective against D. intermedius, and the cinnamaldehyde exhibits potential for the development of a candidate antiparasitic agent.

The influence of a chronic subclinicael infection of Trichostrongylus colubriformis, 2500 larvae/day for 12 weeks, on gastrointestinal motility and digesta flow was studied in 12 sheep supplied ad libitum with food and water. Motility was recorded by X-radiography and electromyography from chronically implanted electrodes;abomasal volume and outflow were estimated by dilution of CrEDTA; small intestinal transit time was estimated by passage of Phenol Red. The findings were compared with measurements made prior to infection at restricted food intake and reported separately. The first effects of infection were seen after 3–4 weeks. No animal developed diarrhoea, but food intake was progressively reduced. Small intestinal transit time, abomasal volume and half-time of marker dilution increased while abomasal outflow decreased during infection. These changes occurred both in absolute terms and when compared with values predicted from the observed level of food intake. As the animals became resistant to the parasites abomasal volume and digesta flow returned towards control values (weeks 10–12). The migrating myoelectric complex (MMC) was disrupted in only one sheep, and only transiently. In all sheep the frequency of the MMC was increased during infection and there was a progressive inhibition of abomasal, duodenal and jejunal motility. X-radiography showed there was prolonged pooling of digesta in the proximal small intestine which was cleared only at the phase of regular spiking activity. Two sheep given an anthelmintic drench recovered normal motility and clearance of digesta. It is concluded that subclinical infection of sheep with T. colubriformis alters the normal pattern of gastrointestinal motility in the absence of any diarrhoea, and causes inhibition of abomasal and proximal small intestinal motility and digesta flow. The increased frequency of MMCs helps to maintain digesta flow through the proximal small intestine.

Between August 1978 and July 1979, freshwater gastropods were collected at monthly intervals from 9 different non-lacustrine habitats in the Mwanza region of Tanzania. Of a total of 11708 gastropods representing 14 species, 1748 (14–9%) were infected with trematode sporocysts and/or rediae. Altogether 38 morphologically distinguishable ‘species’ of cercariae were recovered (13 furcocercous, 10 xiphidiocercaria, 6 echin-ostome, 4 cystophorous, 3 gymnocephalous and 2 amphistome species), 22 of which did not conform to previously described African species. The majority (63–8%) of all mature infections were xiphidiocercariae. Biomphalaria pfeifferi, B. sudanica and Ceratophallus natalensis each yielded 11 species of cercariae. Lymnaea natalensis had the highest overall prevalence of infection (36–9%). Cercaria guttera from L. natalensis accounted for 20–4% of all recovered trematode infections and C. blukwa from Biomphalaria accounted for 18–4% of all infections; the high prevalence of these two xiphidiocercariae may alter the transmission patterns of Fasciola gigantica and Schistosoma mansoni, respectively. S. mansoni was recovered from both B. sudanica (22 of 2393 infected) and B. pfeifferi (79 of 1913 infected); S. haematobium (or related species) was recovered from Bulinus (Physopsis) nasutus (50 of 1503 infected) and to a lesser extent from B. (P.) africanus (6 of 186 infected). The findings are discussed in relation to the biological control of trematode diseases in Tanzania.

A growth curve of the parasitic stage of Cooperia curticei was drawn from measurements of worms collected from sheep between 2 and 22 days after infection. Exsheathed third-stage larvae did not grow during the first 48 hr. in the host. However, growth commenced between 48 and 72 hr. after infection, immediately prior to the third ecdysis. Following this ecdysis, the young fourth-stage larvae increased in length until the sixth day after infection, when growth ceased with the onset of the fourth lethargus. In most worms, this lethargus was terminated by the fourth ecdysis 8 days after infection. However, even in the oldest infections, late fourth-stage larvae were found which had been unable to enter the fifth stage. The first worms to reach the fifth stage ceased growth between 12 and 14 days after infection.