We have studied the genomic organization and transcription of the histone H2A genes in the protozoan parasite Leishmania infantum. In the parasite genome 2 gene clusters exist, each containing 3 H2A gene copies. Sequence analysesNucleotide sequence data reported in this paper are available in the GenBank™, EMBL and DDBJ databases under the accession numbers AJ419625, AJ419626 and AJ419627. showed the existence of significant sequence divergence among the H2A genes, mainly in their 5′- and 3′-untranslated regions (UTRs). Also, the existence of allelic alternatives has been evidenced. Based on the divergence in the 3′UTR regions, we have defined 3 classes of H2A transcripts, which are present at different levels in L. infantum promastigotes. However, transcription of the 3 classes of H2A genes occurs at similar levels, as measured by nuclear run-on assays, indicating that their abundance is regulated post-transcriptionally. Also, differences in regulation were observed among the H2A transcripts: the levels of transcripts with 3′-UTR type I and type III are affected by growth phase whereas transcripts with 3′-UTR type II, that are barely detected, remain constant. It is likely that the complexity, in both gene organization and differential expression exhibited by the L. infantum H2A genes, is imposed by the nature of the post-transcriptional mechanisms of regulation operating in this parasite.

The prophylactic efficacy of autoclaved Leishmania donovani (ALD) and autoclaved L. major (ALM) – a heterologous vaccine developed against cutaneous leishmaniasis (used as a reference vaccine), along with BCG – was evaluated against L. donovani in hamsters (Mesocricetus auratus). Animals were immunized with triple doses (21 days apart) of either ALD or ALM (1·0 mg) with or without BCG (0·1 mg) and challenged 21 days later with 1×106L. donovani amastigotes intracardially. Animals immunized with ALM+BCG and ALD+BCG yielded 94·3% and 86·1% parasite inhibition respectively in comparison to the BCG only and unvaccinated controls. Fifty and 33·3% of the vaccinated animals (ALM+BCG and ALD+BCG respectively) were completely devoid of parasites when tested on day 45 post-challenge (p.c.) and survived till the experiment was terminated. The mean survival of ALM+BCG and ALD+BCG groups (animals harbouring parasites) was longest (168 and 139 days respectively). No significant increase in anti-leishmanial antibody level (ELISA) was noticed in ALD+BCG and ALM+BCG groups whereas it increased progressively in the rest of the experimental groups. The lymphoproliferative responses to PHA and Con A, of the 2 vaccinated groups were comparable to that of normal controls on day 45 p.c. The study suggests that ALD along with BCG can offer substantial protection against visceral leishmaniasis in hamsters.

Numbers of leucocytes in squirrels with gametocytes of Hepatozoon in their blood (infected) were compared with animals without gametocytes (uninfected). Typical values for leucocytes/mm3 blood in uninfected squirrels were: leucocytes 5·7×103, granulocytes 3·4×103, lymphocytes 2·0×103 and monocytes 0·3×103 cells. Infection caused an increase in monocytes, lymphocytes and granulocytes, and there was a significant positive association between parasitaemia level and numbers of both total leucocytes and monocytes. Infected animals had more uninfected monocytes/mm3 blood than did uninfected animals. The proportions of monocytes were more variable over time in infected animals, but no shift between infected and uninfected status was detected. Transfer of serum from infected squirrels to mice resulted in elevated counts of total blood leucocytes, monocytes and granulocytes, but not of lymphocytes, as compared with controls. Serum from squirrels with high parasitaemias had a more marked effect than serum from squirrels with low parasitaemias. Results indicate an infection-related monocytosis, possibly controlled by cytokines, that increases the number of cells available for invasion by gametocytes, thus enhancing the chances of parasite transmission.

The aim of the study was to investigate the effect of a low-level primary infection of Schistosoma japonicum on a challenge infection in pigs. Groups of pigs were given either light or heavy primary infections and heavy challenge infections 14 weeks later. One group of pigs served as a challenge control group. Challenge infection superimposed on the heavily infected pigs did not result in increased worm burden, faecal and tissue egg counts or IgG levels. In contrast, the challenge infection established fully when superimposed on the light primary infections. However, neither faecal egg counts nor the IgG levels increased, and the amount of liver pathology, as judged by septal fibrosis, did not increase either, as compared to the challenge control group. These results suggest that pigs are not able to mount an effective anti-worm response to reinfection when the primary infection is low. However, some modulation of the infection takes place, possibly as a result of an anti-embryonation effect. Collagen content in the liver was found to be relatively insensitive as a marker for liver pathology, as judged using portal and septal fibrosis as a criteria.

Two recognized strains of Schistosoma intercalatum, one from the Democratic Republic of Congo (DRC), formerly Zaire, and the other from Cameroon, have been investigated using DNA sequences from 3 mitochondrial genes, cytochrome oxidase subunit 1 (cox1), NADH dehydrogenase subunit 6 (nad6) and the small ribosomal RNA gene (rrnS). In addition, partial DNA sequences from the nuclear large subunit ribosomal RNA gene (lsrDNA) were included within the study. Although partial lsrDNA alone reveals little taxonomic information, phylogenetic analysis of the mitochondrial data demonstrates a clear dichotomy between the 2 purported strains and it is proposed that they should be treated as distinct taxa. The ‘original’ S. intercalatum now falls relatively basal in the S. haematobium group, while the proposed new species is more derived and sister taxon to S. bovis and S. curassoni.

Sarcoptes scabiei is an important parasitic mite in both man and animals. Little is known about the molecular interactions between this pathogen and its host. This is in part explained by the paucity of mite-derived material, including antigens. To extend the knowledge of the molecular repertoire in S. scabiei, we have performed a gene survey by an expressed sequence tag (EST) analysis. A total of 1020 ESTs were generated from an S. scabiei cDNA library. The average sequence read was 510 bp after editing and the overall sequencing success was 89%. Clustering of the sequences resulted in 76 clusters, comprising 36% of the ESTs. Sequence similarity searches showed that almost half of the S. scabiei ESTs could be assigned a putative identity. Many of these transcripts shared similarity with genes involved in basic metabolism and cellular organization. In the data set we also identified several proteases and other types of potential allergens implicated in various disease mechanisms. A relatively large fraction of the ESTs coded for different proteins carrying protease inhibitor-like domains. The clones with no similarity to previously identified genes constituted 11% of our transcripts. The EST data generated in this study will be a valuable resource in further studies of the biology of S. scabiei and in the identification of genes that can serve as potential targets in the control of the parasite.

Laboratory reared Culex quinquefasciatus Say, 1823 originating from the vicinity of Belem, in northern Brazil, were allowed to engorge on caimans (Caiman c. crocodilus) infected with Hepatozoon caimani (Carini, 1909) and boas (Boa constrictor) infected with H. cf. terzii (Sambon and Seligmann, 1907) both from Para State. Engorged mosquitoes killed on successive days post-feeding (p.f.) were studied by transmission electron microscopy. Images of oocysts from 13 days p.f., caiman-fed mosquitoes were also examined by scanning electron microscopy. The Hepatozoon spp. from the respective hosts differed in their ability to develop in C. quinquefasciatus. Most female mosquitoes fed on caimans, became fully engorged, and survived beyond 22 days p.f., whereas those engorged on boa became debilitated and did not survive beyond 9 days p.f. In boa-fed mosquitoes oocysts were found on the 6th day p.f. The few mosquitoes surviving to the 9th day p.f. contained either undivided oocysts or those that had already commenced sporogenic division. By 8–10 days p.f. caiman-fed mosquitoes contained uninucleate oocysts. Sporogonic divisions were observed from day 12 p.f. onwards. Although sporogenic development conformed in general with the previously reported accounts, the study allowed a more detailed examination of the plasmalemmal endocytotic system, and the consolidation of the crystalline body in specialized ‘factories’ of cystalline material. Sporozoite differentiation occasionally started on the 18th day p.f., but otherwise was observed only on day 22 p.f.

As a potential ultimate cause of microhabitat restriction for ectoparasites of fish, it has been postulated that selection has favoured narrow microhabitats to facilitate mating. The evidence for this hypothesis is evaluated with males and females of the parasitic copepod Lernanthropus cynoscicola, by using methods commonly used in community ecology, and considering the influence of host ontogeny on site selection. No evidence supporting the mating hypothesis was found after comparison of niche measurements between both sexes. Furthermore, aggregation among individuals of the same sex was stronger than among males and females, and the co-occurrence of both sexes did not depart from that expected by chance; also, negative correlations between the intensity of infection of both sexes were observed. Restriction of the microhabitats cannot therefore be due to facilitation of mating. Moreover, both sexes displayed a sequential displacement over the gill arches and differential preferences by specific gill sections in response to an increasing host size, probably as a consequence of a host-size related cline of optimal conditions where fitness is improved. Thus, reproductive benefits other than increased chances of mating may have played a role in the evolution of restricted niches in parasites, and selection may have favoured a narrowing of the niche around sites where fitness is maximized.

A laboratory population of a Danish Gyrodactylus salaris variant founded by 1 single specimen was established and infection studies performed. Rainbow trout as well as Atlantic salmon of 3 different stocks were infected both in cohabitation systems and as single-parasite infections on isolated hosts. Both infection systems revealed that this particular morphotype exhibits low virulence towards Atlantic salmon. Thus, in isolated hosts, the parasites could either not establish or only reproduce to a limited degree on salmon. Rainbow trout, in contrast, proved to be rather susceptible to infection with this G. salaris variant and abundances on this host species always attained significantly higher values in cohabitation systems compared to salmon. Detailed morphological examination confirmed the very high resemblance to G. salaris (sensu stricto), as the range of variation in sclerite characters of the morphotype is almost fully covered by the total range of variation reported for reference G. salaris. Morphological similarities to the closely related congeneric species G. bohemicus were noted. Molecular studies, however, showed that the morphotype most likely represents a G. salaris variant, as it differed only slightly from G. salaris sensu Malmberg, 1957, which is also known to inhabit Danish watercourses. The genomic target region investigated does not allow us to rule out the possibility that it represents a variant form of G. thymalli. Sequences of the ribosomal RNA internal transcribed spacer (ITS) revealed that single individuals contained 2 different ITS sequences, one identical to reference sequence of G. salaris while the other differed at 3 positions. This can be interpreted as an example of a hybrid or, more likely, as intra-individual variation of ITS within single individuals. As one of the nucleotide changes in the variant ITS affects an Hae III restriction site, the current G. salaris variant can be distinguished from G. salaris sensu Malmberg by RFLP diagnosis.

In this study, we conducted phylogenetic analyses of nematode parasites within the genus Dictyocaulus (superfamily Trichostrongyloidea). Lungworms from cattle (Bos taurus), domestic sheep (Ovis aries), European fallow deer (Dama dama), moose (Alces alces), musk ox (Ovibos moschatus), red deer (Cervus elaphus), reindeer (Rangifer tarandus) and roe deer (Capreolus capreolus) were obtained and their small subunit ribosomal RNA (SSU) and internal transcribed spacer 2 (ITS2) sequences analysed. In the hosts examined we identified D. capreolus, D. eckerti, D. filaria and D. viviparus. However, in fallow deer we detected a taxon with unique SSU and ITS2 sequences. The phylogenetic position of this taxon based on the SSU sequences shows that it is a separate evolutionary lineage from the other recognized species of Dictyocaulus. Furthermore, the analysis of the ITS2 sequence data indicates that it is as genetically distinct as are the named species of Dictyocaulus. Therefore, either this taxon needs to be recognized as a new species, or D. capreolus, D. eckerti and D. viviparus need to be combined into a single species. Traditionally, the genus Dictyocaulus has been placed as a separate family within the superfamily Trichostrongyloidea. The present molecular phylogenetic analyses support the placement as a separate family, but the current data do not support the placement of the Dictyocaulidae within the Trichostrongyloidea without a reassessment of the placement of the superfamily Strongyloidea. While D. eckerti has been regarded as the one and only lungworm species of cervids, this study showed that 4 host species including 3 members of Cervidae (moose, reindeer, red deer) and 1 Bovidae (musk ox) were infected with this parasite. Host ranges of D. viviparus (cattle), D. filaria (sheep) and D. capreolus (moose and roe deer) were more restricted. No clear pattern of co-evolution between the dictyocaulid taxa and their bovid and cervid hosts could be determined.

Chemotactic responses of Strongyloides stercoralis infective larvae (L3) to sodium chloride (NaCl) were investigated by recording larval tracks on a saline gradient in agarose. On agarose, larvae migrated randomly, whereas when placed at 0·01 M NaCl larvae moved to approximately 1·1 M NaCl where they turned, headed down the gradient and eventually remained circling at a favoured salinity (0·03–0·07 M). Conversely, when placed at 2·85 M NaCl, the L3 larvae moved unidirectionally to lower, more favoured salt concentrations. Here they circled, changing directions frequently while making ‘loop-like’ tracks. Larvae were immobilized within 5 min at salt concentrations exceeding 3 M NaCl. When placed at 0·01 M NaCl, 51·1%±26·9 migrated to 1·1 M NaCl after 2 min, and 80%±18·7 did so after 8 min, at an average velocity of 4·1±1·4 mm/min. Larvae (53·6%±21·6) were repelled from 2·85 M NaCl to lower concentrations after 2 min. After 8 min, 95%±11·1 were repelled, moving at an average velocity of 6·2±1·1 mm/min. Using this bioassay, the influence of neuronal control over chemotactic behaviour of S. stercoralis and other parasitic nematodes can be elucidated.