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.

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.

Leishmania braziliensis strain M2903 was adapted for growth and serially maintained as amastigotes at 34°C in modified UM-54 medium, with growth curves exhibiting typical log and stationary phases. In late passages, amastigote growth took place in the absence of supplementary haemin and was unaffected when the initial medium pH was adjusted between 5·4 and 6·3. In contrast to promastigotes, which were elongated and exhibited very long free flagella endowed with the paraflagellar rod (PFR), axenic amastigotes were rounded to ovoid and displayed a short flagellum restricted to the pocket area. The absence of PFR in axenic amastigotes was confirmed in Western blots and confocal immunofluorescence microscopy, by lack of reactivity with mAb 1B10. The antibody, which specifically labelled the paraflagellar structure, recognized a 70/72 kDa doublet in Trypanosoma cruzi epimastigotes and two 70/74 kDa related proteins in L. braziliensis promastigotes. Surface 125I-labelling experiments identified promastigote-specific components (>100, 74, 45/47 and 28 kDa) and at least 1, a 76 kDa polypeptide was specific for the amastigote stage. While axenic amastigotes were agglutinated by both peanut (PNA) and Lens culinaris (LCA) agglutinins, respectively at 50 and 12·5 μg/ml, promastigotes were not agglutinated by PNA and agglutinated in the presence of LCA at concentrations of 100 μg/ml and higher. Axenic amastigotes infected rat bone marrow-derived macrophages and were avidly taken up by J774 cells, from which numerous organisms, able to proliferate at 34°C in UM-54 medium, could be recovered 48 h later.

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.

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.

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.

Schistosoma haematobium and S. intercalatum readily hybridize with each other producing generations of viable hybrid offspring. Experiments were designed to investigate the infectivity and viability of the S. haematobium×S. intercalatum F1 and F2 hybrid larvae in their two intermediate snail hosts compared with the parental species. Analysis of the data obtained suggested that the S. haematobium [male ]×S. intercalatum [female] F1 hybrid miracidia were more infective to Bulinus truncatus than to B. forskalii, and also more infective to B. truncatus compared with the parental S. haematobium miracidia. This hybrid was also observed to have a greater cercarial productivity from both intermediate hosts and these cercariae were shown to be more infectious and to have a longer longevity compared with the cercariae of S. haematobium, S. intercalatum and the S. haematobium [female]×S. intercalatum [male ] F1 hybrid cercariae. The S. haematobium [female]×S. intercalatum [male ] F1 hybrid was shown not to be very successful in all stages of the investigations. The results indicate that the S. haematobium [male ]×S. intercalatum [female] F1 hybrid may have many reproductive advantages over the reciprocal hybrid and the parental schistosome species. The significance of the results is discussed in relation to the epidemiological consequences occurring in Loum, Cameroon, and other areas where S. haematobium and S. intercalatum are sympatric and able to hybridize.

Objective: Numerous studies have revealed the presence of oxidative stress in parasitic infections. However, such studies were lacking in the Malaysian population. Previously, we have provided evidence that oxidative stress is elevated in Malaysians infected with intestinal parasites. Stool examinations revealed that about 47·5% of them were infected with the polymorphic protozoa, Blastocystis hominis. However, they were found to have mixed infection with other intestinal parasites. Methodology: Therefore, in order to investigate the role of B. hominis alone in affecting oxidative stress status, here we compared the levels of oxidative stress biomarkers in urine and blood samples between uninfected and B. hominis-infected rats. Results: Infected rats exhibited elevated levels of oxidative indices namely advanced oxidative protein products (AOPP), hydrogen peroxide (H2O2) and lipid hydroperoxide (LHP) indicating that their overall oxidative damage level was higher. Ferric reducing antioxidant power (FRAP) was elevated at the initial stage of infection but decreased significantly during the last week of study duration suggesting that the antioxidant status of the host may be overwhelmed by oxidative damage. Conclusion: To date, this is the first comprehensive in vivo study to provide evidence for Blastocystis infection to correlate with significant oxidative burst leading to oxidative stress.

Atlantic salmon (Salmo salar) parr (age 0+), infected by the ectoparasite Gyrodactylus salaris, were exposed to aqueous aluminium (Al), copper (Cu), zinc (Zn), iron (Fe) and manganese (Mn), at 4 different concentrations. There was a negative correlation between G. salaris infections and metal concentrations in both Zn- and Al-exposed salmon. In the Zn-experiment, all 4 concentrations tested caused a decrease in the G. salaris infections, while in the Al-experiment the G. salaris infection did not decline at the lowest concentration. The number of G. salaris increased continuously during the experiments in all control groups, and in all groups exposed to Cu, Fe and Mn. At the highest concentration, however, copper seemed to impair the growth of G. salaris infection. The results show that aqueous Al and Zn are environmental factors of importance controlling the distribution and abundance of the pathogen G. salaris. Other pollutants might also have an influence on the occurrence of G. salaris. Finally, the results demonstrate that aqueous Al and Zn have a stronger effect on the parasite than on the salmonid host, suggesting that both metals may be used as a pesticide to control ectoparasites such as G. salaris.

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.

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. Theskilled technical assistance of Mr Ted Eaton is gratefully acknowledged. This workwas supported by the Ontario Department of Agriculture and Food.

The present study addresses the effect of varying temperature and host species on the size and shape of the opisthaptoral hard-parts in isogenic strains of Gyrodactylus salaris and G. thymalli. Variation in shape was examined using geometric morphometrics. Since the opisthaptoral hard-parts of Gyrodactylus have few specific landmarks, their shape information mostly being represented by outlines and surfaces, a method based on sliding semi-landmarks was applied. The ventral bars of G. salaris did not follow the previously postulated negative correlation between size and temperature, and the largest hamuli and marginal hooks from G. salaris and the smallest from G. thymalli clearly overlapped in size. Consistent shape differences with temperature were detected for the hard-parts from G. thymalli but not from G. salaris. The hard-parts of G. salaris were similar in size but significantly different in shape when grown on secondary hosts rather than the primary host.

Before the discovery of Toxoplasma gondii as a coccidium of the cat in 1970, cat and dog coccidia were classified in the genus Isospora and considered of little clinical or zoonotic significance. Since 1970, several new (Hammondia sp., Neospora sp.) and previously described species, including Sarcocystis, Besnoitia, and Cryptosporidium have been found as coccidians of cats and dogs with clinical and zoonotic significance. In the present paper I review salient features of the evolution of cat and dog coccidia.

We examined for the presence of trypanosomes in blood samples from 259 anurans (47 species from 8 families), the majority of which were from the Brazilian Amazonia, Atlantic Forest and Pantanal biomes. Trypanosomes were detected by a combination of microhaematocrit and haemoculture methods in 45% of the anurans, and 87 cultures were obtained: 44 from Hylidae, 22 from Leptodactylidae, 15 from Bufonidae, 5 from Leiuperidae and 1 from an unidentified anuran. High morphological diversity (11 morphotypes) was observed among blood trypanosomes from anurans of different species and of the same species as well as among trypanosomes from the same individual. Conversely, morphologically similar trypanosomes were found in anurans from distinct species and biomes. ITS and SSU rDNA polymorphisms revealed high diversity among the 82 isolates examined.† Twenty-nine genotypes could be distinguished, the majority distributed in 11 groups. Phylogenetic relationships based on rDNA sequences indicated that isolates from more phylogenetically related anurans are more closely related. Comparison of anuran trypanosomes from Brazil and other countries revealed several new species among the isolates examined in this study. Phylogenetic relationships suggest that host restriction, host switching and overall ecogeographical structure may have played a role in the evolution of the anuran trypanosomes.

Experiments on the larval development of Fasciola gigantica carried out under natural conditions have shown that at temperatures of 16° C. or less the rediae did not produce cercariae. The first-generation rediae, developed from the sporocyst, and all the rediae of subsequent generations produced only daughter rediae and did not change over to the production of cercariae as long as the low temperatures of the cold season lasted.

As soon as the cold season ended and the temperature of the water in the aquaria containing the infected snails rose to a mean maximum of 20° C. all the rediae switched from redial to cercarial production.

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.

Recent work on the inheritance of susceptibility to malaria suggests that, over what may have been a relatively short evolutionary period, a remarkably diverse series of gene families have been modified in response to the selective drive of this single infection. The phenotype consequences are not confined to the red cell, but involve the immune system, cytokines and many other systems. It seems likely that the mechanisms of variation in genetic susceptibility to other infective agents will reflect at least a similar degree of complexity and, if the selective pressures have been present for longer periods of our evolutionary history, may be even more diverse. This may have important implications for work directed at trying to define susceptibility loci for current infectious and non-infectious diseases.

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.

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.

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.