The relationship between the age of infective O.cunictili larvae and the proportion that remained retarded in a subsequent infection was investigated. The proportion of retarded larvae recovered was found to depend on the length of time and the temperature at which infective larvae were stored prior to infection. At 4 °C the level of retardation was found to increase with increase in the length of storage until a maximum was reached. Further storage tended to decrease the proportion of larvae that remained retarded. These effects were found to be less marked when the larvae were stored at a higher temperature. At 17 °C the maximum level of retardation reached was lower and the process of the increase and the decrease in retardation was of shorter duration. An increase in the number of larvae from 200 to 6000/rabbit did not appreciably change the proportion that remained retarded.

We are most thankful for the advice and criticisms of Dr J. D. Dunsmore. The skilled technical assistance of Mr Ted Eaton is gratefully acknowledged. This work was supported by the Ontario Department of Agriculture and Food.

The time-course of low and high intensity primary infections with Heligmosomoides polygyrus was monitored in SJL and SWR mice, both of which usually expel worms within 7 weeks of larval administration. Worm expulsion in these strains was not dependent on the intensity of infection, with low and high intensity worm burdens being lost within the same period of time. The ability to expel worms rapidly was inherited in a dominant manner in F1 offspring of SJL or SWR mice mated with C57Bl10 mice; the latter being a strain in which no loss of worms was evident within 10 weeks of infection. However, neither (SJL × C57Bl10)F1 nor (SWR × C57Bl10)F1 mice expelled worms as rapidly as the parental SJL and SWR strains. (SWR × B10G)F1 [H-2q] mice eliminated worms faster than (SWR × C57Bl10)F1 [H-2bq], suggesting that the b haplotype had a moderating influence on the expulsion process. In fact (SWR × B10G)F1 mice showed a significant reduction in worm burdens by week 4 but by weeks 6–8 the rate of worm loss had slowed considerably. In contrast, SJL and SWR mice, whilst initiating rejection slightly later, (after week 4) expelled all worms within the following 2 weeks. Thus two distinct patterns of response were observed among the fast responder strains as exemplified by SWR and SJL mice on the one hand and (SWR × B10G)F1 on the other. Our results support the hypothesis that the course of a primary infection with H. polygyrus is influenced by multiple host gene loci, some of which are encoded within the MHC. SJL and SWR mice probably have similar if not identical gene combinations at loci which determine a fast responder phenotype, distinguishing them from the other mouse strains which have been studied.

Maintaining the puparial stage of successive generations of a population of tsetse 3 °C lower than normal reduced the numbers of rickettsia-like organisms (RLO) carried by emerging flies. The susceptibility of these flies to midgut infection with Trypanosoma congolense was also significantly reduced compared with control flies held at normal temperature. These results support the view that the relationship between RLO and susceptibility is quantitative – teneral flies with heavier RLO infections being more susceptible to trypanosome infection.

Treatment of cutaneous leishmaniasis by antimonial compounds when administered by various routes to mice infected with Leishmania major or L. mexicana amazonensis is enhanced, relative to the free drug, by entrapment of these compounds within liposomes. The efficacy of the liposome treatment is dependent on the time and route of administration, and upon the phospholipid composition of the liposomes themselves. Drug-loaded liposomes administered intravenously (i.v.) are more effective at reducing the growth of a cutaneous lesion if they are administered after the nodule has begun to develop, rather than at the time of inoculation of the parasites. In contrast to the i.v. route, liposomes administered subcutaneously (s.c.) at the inoculation site are only effective if given at the time of infection.

An analysis of the metrics of Schistocephalus solidus infection of the threespine stickleback, Gasterosteus aculeatus, in Walby Lake, Alaska, showed that an epizootic ended between 1996 and 1998 and another occurred between 1998 and 2003. The end of the first epizootic was associated with a crash in population size of the stickleback, which serves as the second intermediate host. The likely cause of the end of that epizootic is mass mortality of host fish over winter in 1996–1997. The deleterious impact of the parasite on host reproduction and increased host predation associated with parasitic manipulation of host behaviour and morphology to facilitate transmission might also have played a role, along with unknown environmental factors acting on heavily infected fish or fish in poor condition. The second epizootic was linked to relatively high levels of prevalence and mean intensity of infection, but parasite:host mass ratios were quite low at the peak and there were no apparent mass deaths of the host. A number of abiotic and biotic factors are likely to interact to contribute to the occurrence of epizootics in S. solidus, which appear to be unstable and variable. Epizootics appear to depend on particular and, at times, rare sets of circumstances.

The fresh-water crustacean Daphnia magna may acquire an infection with the microsporidium Octosporea bayeri either by ingesting spores from the water (horizontally), or directly from its mother (vertically). Due to differences in the time and mechanisms of transmission, horizontal and vertical infections may lead to differences in the growth of the parasite within the host. This may influence parasite virulence, transmission to new hosts, and, consequently, epidemiology and evolution. Here we describe the within-host dynamics of 3 spore-types of O.bayeri from infections that were acquired either horizontally or vertically. In all treatments the number of spores increased exponentially until spore density reached a plateau, suggesting density-dependent within-host growth. The spore types seen differ in their growth dynamics, suggesting different roles in the parasite life-cycle. Horizontally-infected hosts harboured significantly fewer spores than vertically-infected hosts. Further, host survival was affected by infection route, with mortality being higher in horizontal infections than in vertical infections. Our results suggest that different routes of infection have an immediate effect on within-host parasite growth and thus on parasite fitness and epidemiology.

Interleukin (IL)-13 and alternatively activated macrophages (AAMs) play an important role in liver granuloma and fibrosis of schistosomiasis. Paeoniflorin (PAE, C23H28O11) has been reported to have an anti-hepatic fibrosis effect in schistosomiasis; however, the mechanism has not been fully elucidated. In this study, we measured serum hyaluronic acid (HA) concentrations, liver granuloma diameter and volume density, fibrosis degree and expressions of IL-13, arginase-1 (ARG-1), nitric oxide synthase-2 (NOS-2), and phosphorylated signal transducer and activator of transcription 6 (p-STAT6) in mice liver of schistosomiasis. Then we detected expressions of specific biomarkers of AAMs and activity of Arg-1 in Kupffer cells (KCs) from infected and PAE-treated mice, or in KCs from uninfected mice, but exposed to rIL-13 in vitro. Finally, we observed expression of IL-13 signalling molecules in KCs and secretion of IL-13 from lymphocytes of infected and PAE-treated mice. Our results showed that during schistosomiasis, IL-13 expression and secretion increased with liver macrophages activated alternatively. PAE not only directly inhibited alternative activation of macrophages via reducing the phosphorylations of janus-activated kinase 2 (JAK2) and/or STAT6, leading to reduction of AAMs-related markers and Arg-1 activity, but also indirectly suppressed alternative activation of macrophages through decreasing secretion of IL-13. PAE might be a promising prophylactic agent for hepatic granuloma and fibrosis of schistosomiasis japonica.

The effects of macrocyclic lactone anthelmintics (MLs) on feeding by Trichostrongylus colubriformis nematodes in vitro were examined using inulin uptake as a measure of ingestion and electropharyngeograms as a record of the electrical events associated with pharyngeal pumping. Inulin uptake was inhibited by the 4 MLs tested (EC50s 0.045–4.57 nM), with an order of potency of eprinomectin (most potent), ivermectin, ivermectin monosaccharide, and ivermectin aglycone. The MLs caused both the frequency and amplitude of pharyngeal electrical events to decrease. In individual worms the inhibition of pump frequency preceded the inhibition of pump amplitude. The order of potency of the MLs as inhibitors of frequency was ivermectin aglycone, ivermectin, ivermectin monosaccharide and eprinomectin. The difference compared with the inulin assay results are probably due to the dynamics of drug uptake in the two systems. It was possible that the nematodes in the electrophysiology experiments were effectively orally ligated by enclosure of the worm's head in the recording pipette which contained no drug. Despite this difference in relative potencies, both the ingestion assays and the electrical events indicate that MLs are potent inhibitors of the pharynx in T. colubriformis in vitro. The sequence of effects on pharyngeal electrical activity suggests that ML action involves an initial inhibitory effect on the rate of pharyngeal contractions, followed by a decrease in the amplitude of the potentials associated with pharyngeal pumping events.

In this study, we employed a mutation scanning approach for the direct visual display of genetic variability in mitochondrial DNA (mtDNA) fragments within and among populations of Schistosoma japonicum from the People's Republic of China. Fragments of the NADH dehydrogenase 1 gene (ND1) and the cytochrome c oxidase subunit I (COI) were individually amplified from parasite DNA by polymerase chain reaction (PCR), denatured and subjected to single-strand conformation polymorphism (SSCP) analysis. Using ND1 and COI fragments, individuals representing different genotypes could be readily identified based on characteristic and reproducible SSCP profiles. The results demonstrated the usefulness of SSCP for the direct visual display of low-level sequence variation in mtDNA of S. japonicum prior to DNA sequence analysis. This approach has important implications for studying the genetic structure and biology of S. japonicum populations, and for analysing the inheritance of mitochondrial DNA.

Giardia duodenalis is a ubiquitous flagellated protozoan parasite known to cause giardiasis throughout the world. Potential transmission vehicles for this zoonotic parasite are both water and food sources. As such consumption of water contaminated by feces, or food sources washed in contaminated water containing parasite cysts, may result in outbreaks. This creates local public health risks which can potentially cause widespread infection and long-term post-infection sequelae. This paper provides an up-to-date overview of G. duodenalis assemblages, sub-assemblages, hosts and locations identified. It also summarizes knowledge of potential infection/transmission routes covering water, food, person-to-person infection and zoonotic transmission from livestock and companion animals. Public health implications focused within the UK, based on epidemiological data, are discussed and recommendations for essential Giardia developments are highlighted.

The validity of Gyrodactylus thymalli has been questioned, based on its morphological and genetic resemblance to G. salaris. This taxonomic problem has practical implications regarding correct diagnosis of G. salaris, which has proved to be highly pathogenic to stocks of wild Norwegian Atlantic salmon. The host specificity and pathogenicity of G. salaris and G. thymalli were experimentally tested on salmon and grayling. Both parasite species were able to infect, live and reproduce on both fish species. G. salaris was highly pathogenic for the experimental stock of salmon, while grayling mounted an effective response against this parasite. Both fish species responded to an infection with G. thymalli. The results did not support the hypothesis of conspecificity between G. thymalli and G. salaris. The ribosomal RNA gene intergenic spacer of both species was sequenced. Variation in sequence was lower than expected for different species. Variation in the sequences of tandemly repeated elements was found and may prove useful in distinguishing G. salaris and G. thymalli.

The monogenean ectoparasite, Gyrodactylus salaris Malmberg, 1957, has had a devastating effect on wild Atlantic salmon (Salmo salar) since its introduction to Norway in the mid-1970s. In Lake Pålsbufjorden, southern Norway, upstream of the stretches of the River Numedalslågen with anadromous Atlantic salmon, a resident Arctic charr (Salvelinus alpinus) population has been reported to be infected with G. salaris which is viable in the absence of its normal host, the Atlantic salmon. Currently, there is no record of G. salaris infecting Atlantic salmon in the downstream sections of the River Numedalslågen. We studied experimentally the infectivity and reproductive capacity of G. salaris from Lake Pålsbufjorden on wild and hatchery-reared Atlantic salmon as well as on Arctic charr and rainbow trout (Oncorhynchus mykiss). Arctic charr and rainbow trout were moderately susceptible, whereas the Atlantic salmon stocks from River Numedalslågen and River Drammenselva were innately resistant to only slightly susceptible. Thus, the G. salaris from Arctic charr in Lake Pålsbufjorden is considered non-pathogenic to Atlantic salmon. This is the first observation of variation in host preference among Norwegian G. salaris populations. The observed differences in virulence between G. salaris populations could have important consequences for the international legislation and management of Atlantic salmon.

To comprehend natural host–parasite systems, ecological knowledge of both hosts and parasites is critical. Here I present a view of marine systems based on the snail Ilyanassa obsoleta and its trematodes. This system is reviewed and two others, those of the snails Cerithidea californica and Littorina littorea, are then summarized and compared. Trematodes can profoundly affect the physiology, behaviour and spatial distribution of hosts. Studying these systems is challenging because trematodes are often embedded in host populations in unappreciated ways. Trematode prevalence is variable, but can be high in populations of all three hosts. Conditions under which single- and multiple-species infections can accumulate are considered. Adaptive relations between species are likely the most important and potentials for adaptation of parasites to hosts, hosts to parasites, and parasites to other parasites are also considered. Even if colonization rate is low, a snail population can develop high trematode prevalence, if infections persist long and the host is long-lived and abundant. Trematodes must be adapted to use their snail hosts. However, both I. obsoleta and L. littorea possess highly dispersed planktonic larvae and trematode prevalence is variable among snail populations. Host adaptation to specific infections, or even to trematodes in general, is unlikely because routine exposure to trematodes is improbable. Crawl-away juveniles of C. californica make adaptation to trematodes in that system a possibility. Trematode species in all three systems are not likely adapted to each other. Multiple-species infections are rare and definitive hosts scatter parasite eggs among snail populations with variable prevalences. Routine co-occurrence of trematodes in snails is thus unlikely. Adaptations of these larval trematodes to inhabit the snail host must, then, be the basis for what happens when they do co-occur.

Leishmania protozoa are obligate intracellular parasites that reside in the phagolysosome of host macrophages and cause a large spectrum of pathologies to humans known as leishmaniases. The outcome of the disease is highly dependent on the parasite species and on its ascribed virulence factors and the immune status of the host. Characterization of the genome composition of non-pathogenic species could ultimately open new horizons in Leishmania developmental biology and also the disease monitoring. Here, we provide evidence that the lizard non-pathogenic to humans Leishmania tarentolae species expresses an Amastin-like gene, cysteine protease B (CPB), lipophosphoglycan LPG3 and the leishmanolysin GP63, genes well-known for their potential role in the parasite virulence. These genes were expressed at levels comparable to those in L. major and L. infantum both at the level of mRNA and protein. Alignment of the L. tarentolae proteins with their counterparts in the pathogenic species demonstrated that the degree of similarity varied from 59% and 60% for Amastin, 89% for LPG3 and 71% and 68% for CPB, in L. major and L. infantum, respectively. Interestingly, the A2 gene, expressed specifically by the L. donovani complex which promotes visceralization, was absent in L. tarentolae. These findings suggest that the lack of pathogenicity in L. tarentolae is not associated with known virulence genes such as LPG3, CPB, GP63 and Amastin, and that other factors either unique to L. tarentolae or missing from this species may be responsible for the non-pathogenic potential of this lizard parasite.

ES62, an immunomodulatory phosphorylcholine-containing glycoprotein secreted by the rodent filarial nematode Acanthocheilonema viteae, has previously been shown to be produced by L4 larvae and adult worms only. However, homologous sequences to ES62 have recently been found in L1 and L3 cDNA libraries of certain human filarial nematodes. Therefore, the various stages of A. viteae were re-examined and it was again found that only the post-L3 stages secreted ES62. Synthesis but not secretion by earlier stages was ruled out by examination of the protein content of whole worm extracts and by immunoelectron microscopy. However, examination by PCR of the mRNA for ES62 revealed that it was found in the L1 and L3 larvae. This may explain why homologous sequences to ES62 have been found in Brugia malayi and Onchocerca volvulus larval cDNA libraries. It also suggests that filarial nematodes, in general, may secrete ES62. To obtain evidence for this, we investigated production by Brugia pahangi, a close relation of B. malayi. We found that ES62 was indeed secreted but, as with A. viteae, only by the post-L3 stages, although again the mRNA for ES62 could be detected in the earlier stages. Overall our results suggest that production of ES62 is not species specific, that it is indeed stage specific, and that this may be due to post-transcriptional control of expression.

Trypanosome infection of mammalian hosts leads, within days, to a strong early response against a small, distinct number of parasite proteins. One of these proteins is the variable surface glycoprotein (VSG). Most of the others are apparently non-variable, intracellular trypanosome proteins. Two of these antigens I2 and I17 are now characterized at the molecular level. Both exhibit a highly repetitive amino acid sequence organization, but they show no sequence similarity either to each other or to any other proteins known to date. Preliminary serological analyses indicate that both allow the early, sensitive and specific detection of infections with different species of trypanosomatids, making them interesting candidates for the development of diagnostic tools for trypanosomiasis detection.

A surface agglutination/immobilization antigen was purified from the novel agglutination/immobilization serotype (serotype G37) of the ciliated protozoan Cryptocaryon irritans, a parasite of seawater fishes. Serum from fish immunized with C. irritans theronts had agglutination/immobilization activity against theronts in vitro. However, fish and rabbit antisera raised against serotype G32 (reported previously) caused little agglutination/immobilization of serotype G37 theronts. Immunological analysis indicated that the 37 kDa theront surface membrane protein may be the agglutination/immobilization antigen of this serotype. The full-length 37 kDa antigen cDNA contained 1171 base pairs, encoding a 331–amino acid protein with hydrophobic N- and C-termini, which are characteristically found in proteins containing a C-terminal glycosylphosphatidylinositol anchor. In addition, the genetically characterized nucleotide sequences of the first internal transcribed spacer region of ribosomal DNA of these 2 serotypes were compared. The internal transcribed spacer rDNA sequence of serotype G32 was identical to that of isolates from Pingtung, Taiwan, and from the USA. On the other hand, the sequences of serotype G37 were not identical to those of any C. irritans isolate.

The number of facilities in which customers make contact with cats before eating and drinking, called ‘cat cafés’, has recently increased in Tokyo, Japan. In a survey to clarify the possibility of zoonotic transmission in Giardia duodenalis, the infection rates of G. duodenalis in 321 stool samples of cats from 16 cat cafés, 31 pet shops, and the Animal Care and Consultation Center of Tokyo were 19·1% (22/115), 1·2% (1/85), and 2·5% (3/121), respectively. In the molecular analysis of 26 G. duodenalis isolates, 6 samples from 2 cat cafés belonged to the zoonotic genotype assemblage A I, and 20 other samples were of assemblage F. Moreover, phylogenetic analysis of glutamate dehydrogenase (GDH) and triosephosphate isomerase (TPI) genes of the 20 assemblage F isolates revealed 2 major lineages. The 6 assemblage A isolates belonged to the same cluster with regard to the GDH gene; however, 2 of the 6 isolates belonged to a different cluster from the other 4 isolates with regard to the TPI gene. Therefore, a risk of transmission from cats to humans is suggested because of the detection of zoonotic Giardia genotypes in cat cafés.

The ultrastrcuture and development of the protozoan Histomonas meleagridis in the reproductive system of the female nematode, Heterakis gallinarum, have been described. It has been shown that there is a distinct cycle of events in the reproductive system. The stage of Histomonas in the germinal zone of the ovary is extracellular; the protozoan feeds and multiplies here. The histomonads move down the ovary with the oogonia and become intracellular when they penetrate the developing oocytes in the growth zone of the ovary. This is apparently an active penetration of the oocyte by the parasite. Feeding and division of the histomonad occurs in the oocyte and also in the newly formed egg; apparently a gradual reduction in size occurs along the reproductive system. These stages in the parasite are similar to the tissue-inhabiting stages in the bird but are much smaller. There are no mitochondria present.

There is strong circumstantial evidence that the nematode is able to repair damage to the wall of the reproductive system and to the oolemma caused by the protozoan.

I wish to thank Dr E. E. Lund of Beltsville Parasitological Laboratory, Maryland, U.S.A., who very kindly sent me some of his Histomonas-free strain of Heterakis and Dr L. P. Joyner and Mr C. C. Norton of the Central Veterinary Laboratory, Weybridge, for the strain of Heterakis which was found to transmit Histomonas wenrichii. I also wish to thank Mrs B. Fisher, Mr B. Millard and Mr M. Shirley for technical assistance and Mr P. Rogers for assistance with the photography.

The life cycle and pathogenicity are described of a pure strain of Eimeria isolated from turkey poults in Great Britain and identified as E. meleagrimitis.

There were three schizogony cycles followed by a sexual generation.

The coccidium produced a high mortality and loss of weight in young poults.

An age resistance developed by the time the poults were 8–10 weeks of age.

The pathology of the infection is described.