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.

We tested the chemotactic responses of dauer juvenile stages (DJs) of the insect parasitic nematode Heterorhabditis bacteriophora to a variety of compounds that are known to be highly attractive or highly repellent to Caenorhabditis elegans. While H. bacteriophora DJs respond to alcohols and some aromatic compounds as well as to host metabolites such as uric acid and CO2, the most notable difference in the responses of these two nematodes is that H. bacteriophora DJs are unresponsive to a large number of compounds which C. elegans finds highly attractive. The latter compounds are typical by-products of bacterial metabolism and include aldehydes, esters, ketones and short-chain alcohols. While C. elegans finds long-chain alcohols (e.g. 1-heptanol and 1-octanol) repellent and short-chain alcohols highly attractive, H. bacteriophora DJs are strongly attracted to 1-heptanol, 1-octanol and 1-nonanol and find short-chain alcohols to be only slightly attractive. Parasitic-stage H. bacteriophora nematodes show a very weak chemotactic response to volatile molecules that DJs find highly attractive. Our results suggest that, associated with the adoption of a parasitic mode of life by Heterorhabditis, there was an adaptive change in chemotactic behaviour of the infective stages, resulting in a decreased sensitivity to volatile by-products of bacterial metabolism and an increased sensitivity towards long-chain alcohols and other insect-specific volatiles and possibly also to herbivore-induced plant volatiles.

Mosquitoes’ importance as vectors of pathogens that drive disease underscores the importance of precise and comparable methods of taxa identification among their species. While several molecular targets have been used to study mosquitoes since the initiation of PCR in the 1980s, its application to mosquito identification took off in the early 1990s. This review follows the research's recent journey into the use of mitochondrial DNA (mtDNA) cytochrome oxidase 1 (COI or COX1) as a DNA barcode target for mosquito species identification – a target whose utility for discriminating mosquitoes is now escalating. The pros and cons of using a mitochondrial genome target are discussed with a broad sweep of the mosquito literature suggesting that nuclear introgressions of mtDNA sequences appear to be uncommon and that the COI works well for distantly related taxa and shows encouraging utility in discriminating more closely related species such as cryptic/sibling species groups. However, the utility of COI in discriminating some closely related groups can be problematic and investigators are advised to proceed with caution as problems with incomplete lineage sorting and introgression events can result in indistinguishable COI sequences appearing in reproductively independent populations. In these – if not all – cases, it is advisable to run a nuclear marker alongside the mtDNA and thus the utility of the ribosomal DNA – and in particular the internal transcribed spacer 2 – is also briefly discussed as a useful counterpoint to the COI.

A non-polymorphic antigen associated with the rhoptry organelles of Plasmodium falciparum has been purified by immuno-affinity chromatography. The antigen, RAP-1 (rhoptry associated protein-1). which is defined by monoclonal antibodies which inhibit parasite growth in vitro, is a multi-component antigen consisting of four major proteins of 80, 65, 42 and 40 kDa and two minor proteins of 77 and 70 kDa. These proteins were electro-eluted from preparative sodium dodecyl sulphate polyacrylamide gels and protected Saimiri sciureus monkeys from a lethal blood-stage infection of P. falciparum malaria. Sera from the protected animals recognized only proteins of the RAP-1 antigen when used to probe a Western blot of total parasite protein extract, confirming that RAP-1 is responsible for eliciting the protective immune response.

The term severe falciparum malaria implies an infection with manifestations and complications which are potentially fatal in man, the natural host for this parasite. Much that has been written on the pathophysiology of animal malarias is of doubtful relevance to the understanding of the mechanism of Plasmodium falciparum infection in man. The clinical picture of severe P. falciparum infection differs in several respects from severe animal malarias, even those of non-human primates. Cerebral dysfunction is the most common severe manifestation of falciparum malaria in man. Coma develops suddenly after a generalized convulsion or gradually towards the end of the first week of illness. There are signs of a symmetrical upper motor neurone lesion and brain-stem dysfunction, but only about 5% of survivors show persisting neurological deficit after 2 or 3 days of unconsciousness. The mortality of cerebral malaria depends on how it is defined and on the predominant age group and other factors. In patients with proved acute P. falciparum infection with unrousable coma, in whom other causes of encephalopathy have been excluded, the mortality is between 15 and 50% despite treatment with antimalarial drugs (Warrell, Looareesuwan, Warrell, Kasemsarn, Intaraprasert, Bunnag & Harinasuta, 1982).

Host nutrition plays an important role in determining the development and success of parasitic infections. While studies of vertebrate hosts are accumulating, little is known about how host nutrition affects parasites of invertebrate hosts. Crithidia bombi is a gut trypanosome parasite of the bumble bee, Bombus terrestris and here we use it as a model system to determine the impact of host nutrition on the population dynamics and development of micro-parasites in invertebrates. Pollen-starved bees supported significantly smaller populations of the parasite. In pollen-fed bees the parasite showed a temporal pattern in development, with promastigote transmission stages appearing at the start of the infection and gradually being replaced by choanomastigote and amastigote forms. In pollen-starved bees this developmental process was disrupted, and there was no pattern in the appearance of these three forms. We discuss the implications of these results for parasite transmission, and speculate about the mechanisms behind these changes.

The transmission dynamics of the cercariae of Diplostomum spathaceum were investigated under laboratory conditions using cercariae collected from naturally infected Lymnaea stagnalis. Cercariae were kept in a constant temperature of 20 °C and the survival and infectivity to naïve young rainbow trout recorded at 3-h intervals until few cercariae were alive. Mortality initially remained constant but increased rapidly after 20 h. While a model of constant mortality fitted the survival data, an age-dependent model provided a better fit and implied that cercariae tended to carry similar quantities of resources and once these were exhausted the cercariae died. Cercarial infectivity also showed an age-dependent pattern although infectivity tended (P=0·09) to increase with age over the first 6 h of life and then fall. The per capita transmission rate of cercariae was investigated by experimentally infecting rainbow trout under standardized conditions, first with an increasing cercarial density and second, by keeping density constant but increasing numbers of cercariae. The per capita transmission rate was frequency dependent and averaged 0·341/h (±0·036).

The microsporidian Encephalitozoon cuniculi can infect a wide variety of mammals including man. In this study, E. cuniculi isolates of animal origin were compared with 6 isolates obtained from HIV-infected patients. Based on results of Western blot analysis, random amplified polymorphic DNA (RAPD) and the sequence of the rDNA internal transcribed spacer (ITS) the isolates were classified into 3 groups with the repeated element 5′GTTT-3′ in the ITS being a reliable genetic marker. Five isolates from Swiss patients were found to be homologous to isolates from Swiss rabbits (strain I). The sixth isolate from a patient from Mexico differed by all methods and could be attributed to E. cuniculi strain III that has been described from 2 dogs from the USA. All of these isolates were distinguished from isolates from blue foxes from Norway (strain II). Intraspecific nucleotide divergence of the SSU rRNA gene of E. cuniculi belonging to the 3 strains was in the same low range (0·00–0·15%) as was found for the corresponding sequence of 2 E. hellem isolates. Groups of 2 rabbits were infected by oral inoculation of 107E. cuniculi spores (2 isolates from strain I of human and rabbit origin, 1 from strain III) as shown by antibody responses and the re-isolation of the parasites from brain material. The results provide further evidence that per oral transmission of the parasite between various hosts is feasible.

Promastigotes of Leishmania braziliensis, L. donovani, L. major and L. mexicana recently derived from tissue amastigotes were cultured in Schneider's Drosophila medium supplemented with 20% (v/v) heat-inactivated foetal calf serum and 25 μg gentamicin sulfate/ml at pH 5·5. These cultures produced more metacyclic promastigotes in their stationary-phase populations than others cultured at pH 7·0. Metacyclic promastigotes possessed a short ([les ]8 μm) and narrow ([les ]1·5 μm) cell body with a flagellum twice or more the length of the cell body. Promastigotes from acidic cultures were more resistant to complement-mediated lysis and more infective in vivo than those grown at neutral pH. These results demonstrate that induction of metacyclogenesis by acidic pH is a response conserved across a variety of species of Leishmania.

Sections of salivary glands from the tick R. appendiculatus have been studied to obtain data on the incidence and development of Theileria parva during feeding. Adult ticks previously fed as nymphs on infected cattle were allowed to attach to rabbits after different periods following moulting and removed for dissection after different periods of attachment.

The maximum number of parasites was present from the 3rd to the 5th days of attachment when 30·5–42 % of salivary glands were infected. A small number of undeveloped parasites was observed in the salivary glands of unfed ticks.

The parasites were classified by their appearance into young, intermediate and mature forms and it was shown that the greatest numbers of mature forms were present on the 4th and 5th days of attachment.

It was concluded that with this strain of ticks, reared and infected under the described conditions, the most suitable time for the recovery of the infective forms of T. parva would be the 4th day of feeding.

Acknowledgements are due to the technical staff who contributed to this work, but especially to Mrs D. Backhurst who supervised the processing of the many sections, to Mr B. Wood who prepared the photomicrographs and to Mr K. P. Bailey who maintained the colony of infected R. appendiculatus.

This work was carried out during the assignment of one of us (L.P.J.) by the Food and Agricultural Organization of the United Nations to the East African Veterinary Research Organization.

Parasites reside inside or outside their hosts and get host nutrition and blood. Here, we have emphasized economic losses in cattle caused by parasitic diseases due to ecto- and endo- parasites (flies, ticks, mites and helminths). We have outlined different methods/models including economic evaluation techniques and dynamic analysis as a major class, used for the calculation of economic losses caused by parasites in cattle. According to already conducted studies, a decrease in production is mentioned in quantity and percentage while financial losses are expressed in the form of account with respect to per head, herd or for the specific study area. The parasites cause the reduced production and financial losses due to control, treatment and mortality costs. We calculated the average decrease in milk production and organ condemnation as 1.16 L animal−1 day−1 and 12.95%, respectively, from overall cattle parasitic infections. Moreover, the average calculated financial and percentage losses were US$ 50.67 animal−1 year−1 and 17.94%, respectively. Economically important parasitic diseases mentioned here are caused by specific spp. of protozoans and helminths according to data collected from the literature. Protozoan diseases include tick-borne diseases, coccidiosis, neosporosis, trypanosomiasis and cryptosporidiosis. Losses due to tick-borne infections were encountered for decreased milk production, mortality, treatment and control. Losses from coccidiosis were due to decreased weight gain, treatment costs and mortality. While abortion losses were encountered in neosporosis. Trypanosomiasis caused losses due to a decrease in milk yield. Moreover, only diagnostic (conventional or molecular techniques) cost was taken into account for cryptosporidiosis. Economically important nematode parasites are Oesophagostomum spp., Cooperia spp., Trichostrongylus spp., Strongyloides spp., Ostertagia spp. and Haemonchus placei. Due to the zoonotic importance of echinococcosis, Echinococcus granulosus is the most economically important cestode parasite. Losses caused by echinococcosis were due to organ condemnation, carcass weight loss and decreases hide value, milk production and fecundity. While, fascioliasis is one of the most economically important trematodal disease, which causes cirrhosis of the liver due to parasite migration, and thus, the organ becomes inedible. So, it would be helpful for farmers and researchers to approach these methods/models for calculation of parasitic losses and should adopt suitable measures to avoid long-term economic losses.

Protozoan cysts and helminth eggs preserved in a coprolite from the Early Cretaceous Bernissart Iguanodon shaft in Belgium demonstrate that representatives of 3 phyla parasitized dinosaurs by that period. These fossil parasite stages are described and their possible effect on dinosaurs discussed. These findings represent the earliest fossil records of protozoan and helminth parasites of terrestrial vertebrates.

Clonal cultures of Histomonas meleagridis, Tetratrichomonas gallinarum and a Blastocystis sp. were established for the first time. Single microbes were successfully isolated from a mixture of micro-organisms obtained from caecal contents of turkeys, using a micromanipulation approach. The cloned parasites were propagated in vitro and maintained through continuous passages multiplying to high numbers. Identification of the protists was done by morphological investigation identifying various forms of each parasite. PCR and partial sequencing of the small subunit rRNA were used to confirm clonality and to determine the relationship of the cloned parasites with known protozoan parasites. The clonal cultures established by this technique will be useful to gain more insight into the biological repertoire of the organisms. In addition, refined infection experiments in different poultry species can now be performed to elucidate the pathological pathways of the respective protozoa.

1. Details are given of worm egg counts carried out on faeces from ewes during 1950–3.

2. Two periods of high egg counts were recorded each year; one during spring and the other in late summer.

3. The first increase appeared to correspond to the spring rise of other workers. It has been shown to be of short duration in each individual ewe, and the time of its occurrence directly related to the time of lambing.

4. Details are given of the seasonal incidence of different species of nematodes.

5. The spring rise is discussed and a theory is advanced to account for the phenomenon. It is emphasized that the fall in egg counts after the rise is as important as the increase.

6. A suggestion that the summer rise is spurious and caused by a reduction in volume of faeces passed during the first week after weaning is accepted.

The taeniid tapeworm Echinococcus multilocularis is here reported for the first time at the Svalbard Archipelago in the Norwegian Arctic. This new finding is interesting because the establishment of E. multilocularis is due to a recent anthropogenic introduction of its intermediate host – the sibling vole Microtus rossiaemeridionalis at Svalbard. The parasite itself has probably become naturally transferred to Svalbard due to migratory movements of its final host – the arctic fox Alopex lagopus between source areas for E. multilocularis in Siberia and Svalbard. We report macroscopically determined prevalence of E. multilocularis from a sample of 224 voles trapped in August in 1999 and 2000. The prevalence was among the highest ever recorded in intermediate hosts and was dependent on age and sex of the hosts approaching 100% in overwintered males. The high prevalence and the simplicity of the vole – arctic fox – E. multilocularis system at Svalbard makes it an eminent model system for further epidemiological studies.

Molecular cloning and immunoelectron microscopy have been used to clone the full-length gene encoding Cryptosporidium parvum oocyst wall protein (COWP) and to analyse at the ultrastructural level the expression and localization of COWP during development in the gut. COWP is 1622 amino acids long, has a typical leader peptide and consists of 2 amino acidic domains each containing distinct repeated elements possibly originating from a common ancestral precursor. Electron microscopy localized COWP in a large cytoplasmic inclusion and in the wall-forming bodies of early and late macrogametes, respectively. Ultrastructural analysis of double-walled sporulating and mature oocysts indicated that COWP is selectively localized in the inner layer of the oocyst wall. This study provides the first localization at the ultrastructural level of a cloned coccidian oocyst wall protein.

A detailed description of the anatomy of the proboscis of the blow-fly, C. erythrocephala, and of the functions of the structures found in it is given. Attention is particularly directed to the fact that the fly can feed in several ways. It can filter the larger particles out of its liquid food, or can scrape chosen surfaces, moistened with vomit or saliva, with its prestomal teeth and subsequently ingest the emulsion produced, or can suck up materials, such as thick sputum or faeces containing helminth ova, without the intervention of its filtering apparatus or the application of its teeth. The relation of these modes of feeding to infection is very briefly indicated.

Malaria is one of the most serious infectious diseases with most of the severe disease caused by Plasmodium falciparum (Pf). Naturally acquired immunity develops over time after repeated infections and the development of antimalarial antibodies is thought to play a crucial role. Neonates and young infants are relatively protected from symptomatic malaria through mechanisms that are poorly understood. The prevailing paradigm is that maternal antimalarial antibodies transferred to the fetus in the last trimester of pregnancy protect the infant from early infections. These antimalarial antibodies wane by approximately 6 months of age leaving the infant vulnerable to malaria, however direct evidence supporting this epidemiologically based paradigm is lacking. As infants are the target population for future malaria vaccines, understanding how they begin to develop immunity to malaria and the gaps in their responses is key. This review summarizes the antimalarial antibody responses detected in infants and how they change over time. We focus primarily on Pf antibody responses and will briefly mention Plasmodium vivax responses in infants.

A method for the biochemical identification of protozoa belonging to the genus Eimeria is described for the first time. Starch gel electrophoresis of the enzymes lactate dehydrogenase, glucose phosphate isomerase, 6-phosphogluconate dehydrogenase and glucose-6-phosphate dehydrogenase from parasite extracts revealed both intra- and inter-species differences when 11 strains representative of 6 species of Eimeria were examined. Oocysts were the most accessible parasite stage for investigation but sporozoites and merozoites of an embryo-adapted strain of E. tenella were also examined for enzyme activity.

Two simple experiments were undertaken using the viviparous ectoparasite, Gyrodactylus bullatarudis, and laboratory-reared guppies, Poecilia reticulata, whereby detailed records of the number and temporal sequence of all births and the age at death were obtained for flukes on isolated guppies. Gyrodactylus bullatarudis has an average fecundity of 1·68 offspring during its expected life-span of 4·20 days. The instantaneous birth rate is independent of generation but dependent on age. The first offspring is born approximately 1 day after the birth of the parent and subsequent offspring are born at 2–2·5 day intervals. The average instantancous birth rate (under given experimental conditions) is 0.43/parasite/day. The death rate increases exponentially with the age of the fluke and has an average value of 0.24/parasite/day. A simple deterministic model incorporating age structure and an age-dependent death rate was found to provide a good fit to the observed exponential increase in G. bullatarudis numbers. The variability observed in this host–parasite system was found to be largely a function of chance, as shown by Monte Carlo simulations of stochastic birth–death processes.