Macroparasites potentially play a significant but often ignored role in the ecology and dynamics of wild ruminant populations. In the Arctic, parasites may impact on host populations by exacerbating the effects of seasonal and limited forage availability on the condition, fecundity and survival of individuals. We studied the effects of abomasal nematode parasites and warble flies, Hypoderma tarandi, on condition and pregnancy of caribou Rangifer tarandus in the Dolphin-Union herd, Nunavut, Canada. By the end of winter, female caribou over 2 years old showed a significant decrease in body weight with increasing nematode burden, and a decrease in back fat depth with increasing warble abundance. These effects were exaggerated in the non-pregnant fraction of the population. High warble larvae burdens were also associated with significantly reduced probability of being pregnant. Our research demonstrates a negative relationship between parasites and caribou condition that may have consequences for their fitness. Additionally, we discuss the possibility that muskox Ovibos moschatus share some parasite species with the caribou and could lead to elevated burdens in the sympatric host. Parasites may have been a contributory factor in a previous winter range-shift of the caribou herd and this may reflect a form of apparent competition between the two ungulate species.

The present paper describes two repetitive proteins representing common antigens of African trypanosomes which are non-variant and which are recognized early in infection by the host immune system. These antigens were identified by their ability to immunoreact with bovine serum taken during the early phase of a cyclic trypanosomal infection. Screening of a cDNA library from T. b. gambiense with such early infection serum identified a protein which contains a repetitive motif consisting of 68 amino acid repeat units (GM6). Immunofluorescence and immunogold electron microscopy revealed that GM6 is located on fibres which connect the microtubules of the membrane skeleton with the flagellum. A second repetitive antigen detected by this serum is MARP1 (microtubule-associated repetitive protein 1), a protein previously characterized in this laboratory as a high-molecular weight component of the membrane skeleton, which consists of more than 50 tandemly repeated, near-identical 38 amino acid repeat units. Beta-galactosidase fusion products of both proteins demonstrated a strong immunoreactivity with sera from T. b. brucei and T. congolense-infected cattle. The result from this preliminary immunological evaluation indicates a high immunodiagnostic sensititivy (90%) of the two recombinant antigens which make them interesting candidates for immunodiagnosis of trypanosomiasis in cattle.

The emergence of Lyme borreliosis as a public health burden within the last two decades has stimulated renewed interest in tick-borne infections. This attention towards ticks, coupled with advances in detection technologies, has promoted the recognition of diverse emergent or potentially emerging infections, such as monocytic and granulocytic ehrlichiosis, local variants of spotted fever group rickettsioses, WA-1 babesiosis, or a Lyme disease mimic (Masters' Disease). The distribution of pathogens associated with well-described tick-borne zoonoses such as human babesiosis due to Babesia microti or B. divergens seems wider than previously thought. Bartonellae, previously known to be maintained by fleas, lice or sandflies, have been detected within ticks. Purported ‘new’ agents, mainly identified by sequencing of PCR products and comparison with those sequences present in GenBank, are being increasingly reported from ticks. We briefly review the diversity of these infectious agents, identify aetiological enigmas that remain to be solved, and provide a reminder about ‘old friends’ that should not be forgotten in our pursuit of novelty. We suggest that newly recognised agents or tick/pathogen associations receive careful scrutiny before being declared as potential public health burdens.

Host-parasite interactions are an integral part of ecosystems that influence both ecological and evolutionary processes. Humans are currently altering environments the world over, often with drastic consequences for host-parasite interactions and the prevalence of parasites. The mechanisms behind the changes are, however, poorly known. Here, we explain how host-parasite interactions depend on two crucial steps – encounter rate and host-parasite compatibility – and how human activities are altering them and thereby host-parasite interactions. By drawing on examples from the literature, we show that changes in the two steps depend on the influence of human activities on a range of factors, such as the density and diversity of hosts and parasites, the search strategy of the parasite, and the avoidance strategy of the host. Thus, to unravel the mechanisms behind human-induced changes in host-parasite interactions, we have to consider the characteristics of all three parts of the interaction: the host, the parasite and the environment. More attention should now be directed to unfold these mechanisms, focusing on effects of environmental change on the factors that determine encounter rate and compatibility. We end with identifying several areas in urgent need of more investigations.

Heavy infections of E. acervulina result in a depression in body weight of the host, but anorexia induced by the disease is not the only factor responsible for this, since normal birds starved to the same extent did not lose as much weight. It was shown that the absorption of l-histidine and glucose from the infected part of the small intestine was depressed and may be a contributory factor to this weight loss; restricted feed intake alone tended to increase, rather than decrease, absorption.

The distribution of larval ticks in relation to vegetation cover was studied on two coastal farms in the Port Alfred district of the Cape Province. The following five species were found: Boophilus decoloratus (Koch), Amblyomma hebraeum Koch, Ixodes pilosus Koch, Haemaphysalis silacea Robinson and Rhipicephalus evertsi Neumann. B. decoloratus predominated in short protected vegetation, I. pilosus and H. silacea in short covered vegetation and A. hebraeum in medium-to-tall protected vegetation. R. evertsi was collected in too small numbers to allow any correlation to be established. Both I. pilosus and H. silacea demonstrated activity peaks during the winter months. Microclimatic measurements indicated that larval ticks were not usually collected in microhabitats which experienced midday saturation deficits in excess of approximately 10 mm Hg. Behavioural studies on larval ticks climbing glass rods demonstrated the possible association of larvae with a definite vegetation height. The optimal vegetation heights were correlated with field data. The water balance of some tick species was studied and it was found that at 26 °C a relative humidity of 70% or more (i.e. above 7·53 mm Hg saturation deficit) was required by these larvae. Larvae lost water to the atmosphere at humidities lower than this value and took up water vapour from the atmosphere at values higher than 70% R.H. They were shown to be able to imbibe water through the mouthparts, and this possibly has survival value.

Acetylcholinesterase activity, measured per unit wet weight, is relatively low in the eggs and infective larvae of N. brasiliensis. It increases rapidly during the parasitic phase, especially in the late 3rd- and early 4th-larval stages. Activity in normal adults is extremely high (× 15 egg activity) and this is doubled again in immune-damaged adults. Possible functions of N. brasiliensis acetylcholinesterase are discussed.

It is a pleasure to acknowledge the technical assistance of Miss Anne Cronin and Miss Beryl Crooks.

Partially purified low molecular weight antigens obtained by gel filtration of whole worm homogenates or total adult excretory–secretory (ES) products were tested in a vaccination experiment to determine their ability to induce protective immunity against Haemonchus contortus in sheep. Sheep were challenged with 20000 infective 3rd-stage larvae. One animal in the low molecular weight vaccinated group showed no protection against H. contortus, whereas the 4 other sheep in this group showed a mean reduction of 99·9% in faecal egg counts and of 97·6% in abomasal worm burden compared to the non-vaccinated controls and the adjuvant controls. The ES-vaccinated sheep showed a 32·2% reduction in parasite egg production and a 63·7% reduction in abomasal worm counts. Analysis of the humoral immune responses revealed no significant differences in antibody recognition of putative protective antigens between the protected and non-protected vaccinated animals. However, a marked lower lymphocyte proliferation response was found in non-protected sheep.

An experimental study of the effects of parasitism by H. diminuta on the intermediate host, Tribolium confusum, is described. No density- dependent constraints on parasite establishment within individual hosts are evident, although a reduction in cysticercoid size at high parasite burdens is demonstrated. The relationship between parasite burden, host mortality and host fecundity is investigated. Host mortality is linearly related to parasite burden, whereas the relationship between parasite burden and host fecundity is non-linear. There is no difference in viability between eggs from infected and uninfected females. The generative causes of these effects are not investigated experimentally, although it is postulated that survival is related to the degree of damage to the midgut wall caused by parasite penetration, and fecundity to the biomass of parasites harboured by the host. The significance of these effects is discussed in relation to the overall dynamics of the host-parasite association.

During a longitudinal study investigating the dynamics of malaria in Ugandan lakeshore communities, a consistently high malaria prevalence was observed in young children despite regular treatment. To explore the short-term performance of artemether-lumefantrine (AL), a pilot investigation into parasite carriage after treatment(s) was conducted in Bukoba village. A total of 163 children (aged 2–7 years) with a positive blood film and rapid antigen test were treated with AL; only 8·7% of these had elevated axillary temperatures. On day 7 and then on day 17, 40 children (26·3%) and 33 (22·3%) were positive by microscopy, respectively. Real-time PCR analysis demonstrated that multi-species Plasmodium infections were common at baseline, with 41·1% of children positive for Plasmodium falciparum/Plasmodium malariae, 9·2% for P. falciparum/ Plasmodium ovale spp. and 8·0% for all three species. Moreover, on day 17, 39·9% of children infected with falciparum malaria at baseline were again positive for the same species, and 9·2% of those infected with P. malariae at baseline were positive for P. malariae. Here, chronic multi-species malaria infections persisted in children after AL treatment(s). Better point-of-care diagnostics for non-falciparum infections are needed, as well as further investigation of AL performance in asymptomatic individuals.

Two cases of skin lesions similar to those caused by Leishmania parasites have been reported from Martinique. Parasites isolated from these lesions were unlike Leishmania reference strains by isoenzyme analysis and electron microscopy and were assumed to be monoxenous trypanosomatids which normally only infect invertebrates. Both strains have now been retyped by isoenzyme analysis and found to be identical to each other and distantly related to all other Leishmania species. The sequence of the 18S ribosomal RNA gene and partial sequences of the DNA polymerase alpha and RNA polymerase II largest subunit genes were obtained. These sequences indicated that the Martinique parasites clustered with L. enriettii and were basal to all other euleishmania. However, support for both the position basal to all euleishmania and the clustering with L. enriettii was low. The Martinique parasites may cluster with L.(Leishmania) or L.(Viannia) or form a novel clade within the euleishmania either with or without L. enriettii.

There is increasing interest in the use of the free-living nematode Caenorhabditis elegans as a tool for parasitic nematode research and there are now a number of compelling examples of its successful application. C. elegans has the potential to become a standard tool for molecular helminthology researchers, just as yeast is routinely used by molecular biologists to study vertebrate biology. However, in order to exploit C. elegans in a meaningful manner, we need a detailed understanding of the extent to which different aspects of C. elegans biology have been conserved with particular groups of parasitic nematodes. This review first considers the current state of knowledge regarding the conservation of genome organisation across the nematode phylum and then discusses some recent evolutionary development studies in free-living nematodes. The aim is to provide some important concepts that are relevant to the extrapolation of information from C. elegans to parasitic nematodes and also to the interpretation of experiments that use C. elegans as a surrogate expression system. In general, examples have been specifically chosen because they highlight the importance of careful experimentation and interpretation of data. Consequently, the focus is on the differences that have been found between nematode species rather than the similarities. Finally, there is a detailed discussion of the current status of C. elegans as a heterologous expression system to study parasite gene function and regulation using successful examples from the literature.

Sequence variation within the 18S SSU rRNA V4 hyper-variable region can affect the accuracy of real-time hybridization probe-based diagnostics for the detection of Theileria spp. infections. This is relevant for assays that use non-specific primers, such as the real-time hybridization assay for T. parva (Sibeko et al. 2008). To assess the effect of sequence variation on this test, the Theileria 18S gene from 62 buffalo and 49 cattle samples was cloned and ∼1000 clones sequenced. Twenty-six genotypes were detected which included known and novel genotypes for the T. buffeli, T. mutans, T. taurotragi and T. velifera clades. A novel genotype related to T. sp. (sable) was also detected in 1 bovine sample. Theileria genotypic diversity was higher in buffalo compared to cattle. Polymorphism within the T. parva hyper-variable region was confirmed by aberrant real-time melting peaks and supported by sequencing of the S5 ribosomal gene. Analysis of the S5 gene suggests that this gene can be a marker for species differentiation. T. parva, T. sp. (buffalo) and T. sp. (bougasvlei) remain the only genotypes amplified by the primer set of the hybridization assay. Therefore, the 18S sequence diversity observed does not seem to affect the current real-time hybridization assay for T. parva.

Cercariae are non-feeding free-living stages in the life cycles of trematodes, highly influenced by temperature. Their life span is brief, limited by the depletion of a non-renewable glycogen store. Warmer temperatures under the influence of climate change may promote the transmission of parasites and therefore understanding their thermobiology forms an important step in discerning the future dynamics of parasite populations. An empirical relationship exists between cercarial mean expected life span and the half-life of the population (t0·5) and therefore t0·5 is a good indicator of glycogen utilization. In this study experimental data on the effects of temperature on cercarial survival is compiled from the scientific literature and evaluated in terms of metabolism using Q10 and Arrhenius activation energy (E* or μ), common measures of temperature-mediated reaction rates. Cercariae have a variable response to temperature, which does not appear to be influenced by their life-history attributes or size. There were little differences in Q10 and E* values between most temperature ranges. In almost half the studies examined (7 of 16) cercariae demonstrated a discrete zone of thermostability over a range equivalent to typical individual mean summer temperatures. Distinct intraspecific differences in temperature responses between 3 laboratory strains of Schistosoma mansoni and 2 natural strains of Echinoparyphium recurvatum sensu stricto were apparent. The importance of these results for cercarial biology under global climate change is discussed.

The swim-bladder nematode Anguillicola crassus originates from the Far East where it is a parasite of the Japanese eel (Anguilla japonica). After A. crassus was introduced to Europe, it became a predominant parasite of the European eel (Anguilla anguilla). A study performed with experimentally infected eels (98 days, 23 °C) revealed significant differences in the susceptibility of the two eel species to this parasite. The recovery rate of 30 administered infective A. crassus larvae (L3) from A. japonica was less than half of that from A. anguilla (33·2% and 13·8%, respectively). Almost 60% of the worms recovered from A. japonica were found as dead, encapsulated and necrotic larvae in the swimbladder wall. In contrast, no dead larvae were found in A. anguilla. Additionally, the development of the worms was shown to be significantly slower in A. japonica compared with A. anguilla. The lower survival rate of the worms, together with their slower development, resulted in a significantly lower adult worm burden (11 and 428 mg wet weight, respectively) and in a decreased reproductive success in A. japonica compared with A. anguilla. These results demonstrate that the original host, A. japonica, possesses more effective defence mechanisms against A. crassus than does the non-adapted host, A. anguilla.

An account is given of some viruses affecting insects of economic importance. Twenty-six viruses are listed affecting twenty-two species of insects. Of these viruses eleven cause cytoplasmic, and eight cause nuclear, polyhedroses. Six are granulosis viruses and one virus has no intracellular inclusions. Most of these viruses are new or recently recorded. The granulosis viruses, affecting Pieris brassicae, P. rapae and Melanchra persicariae, and the diseases they cause, are described in some detail.

We are indebted to Dr L. L. J. Ossowski of the Wattle Research Institute, University of Natal, and to Mr T. H. Coaker of the Cotton Research Station, Namulonge, Uganda, who sent us, respectively, diseased specimens of the wattle bagworm and the American cotton bollworm, from which the viruses were isolated. Miss S. Vernon-Smith took the electron micrographs, and Mr Simon Frey the photographs on the optical microscope.

Reciprocal interactions of parasites transmitted by blood-sucking arthropod vectors have been studied primarily at the parasite–host and parasite–vector interface. The third component of this parasite triangle, the vector–host interface, has been largely ignored. Now there is growing realization that reciprocal interactions between arthropod vectors and their vertebrate hosts play a pivotal role in the survival of arthropod-borne viruses, bacteria, and protozoa. The vector–host interface is the site where the haematophagous arthropod feeds. To obtain a blood meal, the vector must overcome the host's inflammatory, haemostatic, and immune responses. This problem is greatest for ixodid ticks which may imbibe as much as 15 ml blood whilst continuously attached to their host for 10 days or more. To feed successfully, the interface between tick and host becomes a battle between the host's mechanisms for combating the tick and the tick's armoury of bioactive proteins and other chemicals which it secretes, via saliva, into the feeding lesion formed in the host's skin. Parasites entering this battlefield encounter a privileged site in their vertebrate host that has been profoundly modified by the pharmacological activities of their vector's saliva. For example, ticks suppress natural killer cells and interferons, both of which have potent antiviral activities. Not surprisingly, vector-borne parasites exploit the immunomodulated feeding site to promote their transmission and infection. Certain tick-borne viruses are so successful at this that they are transmitted from one infected tick, through the vertebrate host to a co-feeding uninfected tick, without a detectable viraemia (virus circulating in the host's blood), and with no untoward effect on the host. When such viruses do have an adverse effect on the host, they may impede their vectors' feeding. Thus important interactions between ticks and tick-borne parasites are displaced to the interface with their vertebrate host - the skin site of blood-feeding and infection.

The mouse whipworm Trichuris muris has long been used as a tractable model of human Trichuriasis. Here we look back at the history of T. muris research; from the definition of the species and determination of its life cycle, through to the complex immune responses that we study today. We highlight the key research papers that have developed our understanding of immune responses to this parasite, and reflect on how original concepts have been transformed, as our knowledge of immunology has grown. Although we have a good understanding of host–parasite interactions in the context of the underlying cellular immunology, there are still many aspects of the biology of the Trichuris parasite that remain undefined. We predict that advances in parasite biology will be key in the future development of new and improved treatments for Trichuriasis.

Freeze fracture study of Schistosoma mansoni membrane differentiation enabled us to describe the characteristic features of the tegumental membrane complex at various stages of development of this parasite. The observation of a membrane exuviation during the 10–20 day period of infection of the definitive host led us to search for possible hormonal control. The development of an appropriate radioimmunoassay has allowed the detection of significant production of ecdysteroids in a human platyhelminth. This hormonal material undergoes level variation during the development of post-cercarial stages of S. mansoni and its precise chemical characterization is presently being investigated.

Heterogeneity in susceptibility of guppies (Poecilia reticulata) to infection with Gyrodactylus bullatarudis was examined by comparing the establishment, reproduction and survival of the parasite on 4 inbred strains of the fish host following low and high levels of exposure to infection. The 4 strains fell into 2 broad categories of innately ‘resistant’ and ‘susceptible’ fish on the basis of strain differences in (a) the rates of growth and decay of the parasite populations, (b) the proportional occurrence of susceptible and resistant fish within each strain, (c) the average duration of primary infection, and (d) the duration of resistance to reinfection following recovery from a primary exposure. The results suggest genetic control of resistance/susceptibility traits and experiments with hybrids tentatively suggest dominance of resistance over susceptibility. The potential of the guppy – Gyrodactylus laboratory system for the investigation of the role of genetic factors in the study of host–parasite interactions is discussed.