Analysis of the seasonal occurrence of Argulus coregoni on Oncorhynchus masou and Salmo gairdneri indicates that the parasites overwinter as eggs and that there are 1 or 2 generations/year. Larvae which hatch from the overwintered eggs are abundant from May through July. Individuals hatched in May and June attain maturity and lay eggs in August. Larvae of the second generation are abundant in September, and they lay eggs in October–November which overwinter. Hatched larvae from overwintered eggs may mature in July and deposit overwintering eggs in September. The sex ratio of A. coregoni is about 1:1. A. coregoni shows an age-specific site preference on O. masou. Small parasites occur on almost all parts of the skin and fins, with slightly heavier concentrations on and around the pectoral and pelvic fins. Large parasites are found mainly on the skin around these fins.

The behaviour of four species of Eimeria was studied in lambs which were given either monospecific or multispecific infections. In the presence of other species the patency of oocyst production of E. ovina and E. weybridgensis was extended and the total number of oocysts produced by all species except E. ninakohlyakimovae was increased. Clinical symptoms were observed only in lambs which received E. ninakohlyakimovae.

1. Spermatophore production in Rhodnius and Triatoma is a structural adaptation for copulation and sperm delivery.

2. In Rhodnius a certain amount of sperm is stored in the spermathecae while the remainder is ejected with the collapsed spermatophore about 12 hr. after copulation. Hypergamesis never occurs.

3. The secretion in the male accessory glands was found to disappear if males were kept unfed for about 60 days. Such males were unable to copulate.

4. An average of ninety-eight fertilized eggs was produced as a result of one insemination by a young male. Four such inseminations at intervals of 45 days are, therefore, necessary to secure fertilized eggs throughout the entire life of the female. In nature repeated copulation is the rule.

5. The first spermatophore produced by males starved for 21–28 days was found to be as efficient as that produced by recently emerging well-fed males.

6. A male is capable of producing a great number of spermatophores; as many as fifty were obtained. Probably spermatophores produced by old males, although they contain a great number of sperm, lack sufficient of some substance necessary for fertilizing the eggs.

Fifty-two Leishmania strains, obtained from human patients and dogs in a visceral leishmaniasis focus in Sudan, were characterized by isoenzyme electrophoresis (15 enzymes). The phylogenetic analysis showed that the 7 Leishmania zymodemes obtained hold ancestral positions on the phylogenetic tree, supporting the hypothesis of an East African origin of visceral leishmaniasis.

Neurological involvement following trypanosome infection has been recognised for over a century. However, there are still many unanswered questions concerning the mechanisms used by the parasite to gain entry to the CNS and the pathogenesis of the resulting neuroinflammatory reaction. There is a paucity of material from human cases of the disease therefore the majority of current research relies on the use of animal models of trypanosome infection. This review reports contemporary knowledge, from both animal models and human samples, regarding parasite invasion of the CNS and the neuropathological changes that accompany trypanosome infection and disease progression. The effects of trypanosomes on the blood-brain barrier are discussed and possible key molecules in parasite penetration of the barrier highlighted. Changes in the balance of CNS cytokines and chemokines are also described. The article closes by summarising the effects of trypanosome infection on the circadian sleep-wake cycle, and sleep structure, in relation to neuroinflammation and parasite location within the CNS. Although a great deal of progress has been made in recent years, the advent and application of sophisticated analysis techniques, to decipher the complexities of HAT pathogenesis, herald an exciting and rewarding period for advances in trypanosome research.

Trypanosoma irwini was previously described from koalas and we now report the finding of a second novel species, T. gilletti, as well as the extension of the host range of Trypanosoma copemani to include koalas. Phylogenetic analysis at the 18S rDNA and gGAPDH loci demonstrated that T. gilletti was genetically distinct with a genetic distance (±s.e.) at the 18S rDNA locus of 2·7±0·5% from T. copemani (wombat). At the gGAPDH locus, the genetic distance (±s.e.) of T. gilletti was 8·7±1·1% from T. copemani (wombat). Trypanosoma gilletti was detected using a nested trypanosome 18S rDNA PCR in 3/139 (∼2%) blood samples and in 2/29 (∼7%) spleen tissue samples from koalas whilst T. irwini was detected in 72/139 (∼52%) blood samples and T. copemani in 4/139 (∼3%) blood samples from koalas. In addition, naturally occurring mixed infections were noted in 2/139 (∼1·5%) of the koalas tested.

Trophically-transmitted parasites generally need to undergo a period of development in the intermediate host before reaching infectivity. During this vulnerable period, manipulation of the host to reduce susceptibility to predation would be advantageous for parasites, because it increases the probability of surviving until infectivity and thus the probability of transmission. We tested this ‘predation suppression’ hypothesis in 2 parasite species that use copepods as first hosts: the tapeworm Schistocephalus solidus and the nematode Camallanus lacustris. In a series of prey choice experiments, we found that copepods harbouring uninfective, still-developing worm larvae were less frequently consumed by stickleback predators than uninfected copepods. The levels of predation suppression were similar in the two parasite species, suggestive of convergent evolution. Additionally, copepods harbouring 2 worms of a given species were not more susceptible to predation than those with 1 worm, suggesting that excessive larval parasite growth does not increase host susceptibility to predation. Our results support the idea that parasites can suppress intermediate host susceptibility to predation while uninfective, but we also note that the available studies suggest that this effect is weaker than the frequently observed enhancement of host predation by infective helminth larvae.

In 1994 and 2002, respectively, the World Health Organisation proposed that treatment for hookworm and schistosomiasis could be provided during pregnancy. It was hoped that this might have benefits for maternal anaemia, fetal growth and perinatal mortality; a beneficial effect on the infant response to immunisation was also hypothesised. Three trials have now been conducted. Two have examined the effects of benzimidazoles; one (the Entebbe Mother and Baby Study) the effects of albendazole and praziquantel. All three were conducted in settings of high prevalence but low intensity helminth infection. Results suggest that, in such settings and given adequate provision of haematinics, the benefit of routine anthelminthics during pregnancy for maternal anaemia may be small; none of the other expected benefits has yet been demonstrated. The Entebbe Mother and Baby Study found a significant adverse effect of albendazole on the incidence of infantile eczema in the whole study population, and of praziquantel on the incidence of eczema among infants of mothers with Schistosoma mansoni. Further studies are required in settings that differ in helminth species and infection intensities. Further research is required to determine whether increased rates of infantile eczema translate to long-term susceptibility to allergy, and to explore the underlying mechanisms of these effects. The risks and benefits of routine anthelminthic treatment in antenatal clinics may need to be reconsidered.

The parasite community of animals is generally influenced by host physiology, ecology, and phylogeny. Therefore, sympatric and phylogenetically related hosts with similar ecologies should have similar parasite communities. To test this hypothesis we surveyed the endoparasites of 5 closely related cheilinine fishes (Labridae) from the Great Barrier Reef. They were Cheilinus chlorourus, C. trilobatus, C. fasciatus, Epibulus insidiator and Oxycheilinus diagramma. We examined the relationship between parasitological variables (richness, abundance and diversity) and host characteristics (body weight, diet and phylogeny). The 5 fishes had 31 parasite species with 9–18 parasite species per fish species. Cestode larvae (mostly Tetraphyllidea) were the most abundant and prevalent parasites followed by nematodes and digeneans. Parasites, body size and diet of hosts differed between fish species. In general, body weight, diet and host phylogeny each explained some of the variation in richness and composition of parasites among the fishes. The 2 most closely related species, Cheilinus chlorourus and C. trilobatus, had broadly similar parasites but the other fish species differed significantly in all variables. However, there was no all-encompassing pattern. This may be because different lineages of parasites may react differently to ecological variables. We also argue that adult parasites may respond principally to host diet. In contrast, larval parasite composition may respond both to host diet and predator-prey interactions because this is the path by which many parasites complete their life-cycles. Finally, variation in parasite phylogeny and parasite life-cycles among hosts likely increase the complexity of the system making it difficult to find all-encompassing patterns between host characteristics and parasites, particularly when all the species in rich parasite communities are considered.

The glutamate-gated chloride channels (GluCls) are members of the ligand-gated ion channel superfamily that are thought to be involved in the mode of action of ivermectin and mechanism of resistance. Using reverse-transcriptase PCR techniques, 2 full-length GluCl cDNAs, encoding GluClα3 and GluClβ subunits, were cloned from Cooperia oncophora, a nematode parasite of cattle. The two sequences show a high degree of identity to similar subunits from other nematodes. The C. oncophora GluClα3 subunit is most closely related to the Haemonchus contortus GluClα3B subunit, while C. oncophora GluClβ subunit shares high sequence identity with the H. contortus GluClβ subunit. Using single-strand conformation polymorphism, the genetic variability of these two genes was analysed in an ivermectin-susceptible isolate and an ivermectin-resistant field isolate of C. oncophora. Statistical analysis suggested an association between the C. oncophora GluClα3 gene and ivermectin resistance. No such association was seen with the GluClβ gene.

An epidemiological survey was conducted during a 4-month period of intense malaria transmission in Dielmo, a holoendemic Senegalese village. Two thick blood smears per inhabitant were collected weekly. The sex ratio of Plasmodium falciparum gametocytes (gamete precursors) was studied in 50 gametocyte carriers. All age classes were represented (mean 19·7 years; range: 2 months–75 years); 42 (84%) of them did not receive antimalarial treatment. Overall 668 thick smears were examined until 100 gametocytes had been counted or for 40 min. A total of 11 204 gametocytes were observed with a mean sex ratio of 0·346 (95% CI 0·317–0·374), i.e. 2·89 females per 1 male. Among the 284 thick smears in which at least 10 gametocytes were observed, the mean percentage of male gametocytes was 27·8%, with a range of 0–82%. Great variability was observed between gametocyte carriers and also between thick smears from the same gametocyte carrier. A multivariate analysis was performed which highlighted the fact that only 2 variables had a significant effect on the sex ratio. Anaemia was associated with an increased percentage of males (Prevalence Rate Ratio [PPR] of male gametocytes was multiplied by 1·65 if haematocrit rate <32%) and a wave of gametocytes was associated with an increased percentage of female gametocytes (PRR was multiplied by 0·48 during the peak of gametocytaemia and for the 2 weeks following this peak). The variables without significant effect on sex ratio were: age, sex, clinical status and sickle cell trait status of the gametocyte carrier, density of asexual parasites, quinine treatment, and gametocyte density (when taking account of its waves). These results are discussed in regard of possible differential production, mortality or sequestration of one gametocyte sex and selective advantages for the transmission of parasites.

Mice inoculated with microfilariae of the filarial nematode Onchocerca lienalis clear their parasites over a period of 3–4 months and are highly resistant to re-infection. We have investigated the comparative roles of the eosinophil, macrophage and neutrophil in effecting this parasite clearance, employing agents specifically to perturb cell function in vivo. Using the anti-IL-5 monoclonal antibody TRFK-5, we show that eosinophils are of primary importance in effecting resistance to re-infection. Ablation of macrophages (with carbon) and neutrophils (with the monoclonal antibody NIMP-R14) had no effect on parasite clearance following re-infection. Neutralization of these 3 cell types during a primary infection showed that while the removal of both eosinophils and macrophages caused a small but significant delay in parasite clearance, the depletion of neutrophils had no effect. This report describes the first direct evidence for eosinophil-mediated killing of microfilariae in vivo, and is consistent with Th-2 cell responses previously described in this model.

Mice infected with 25 to 35 unsexed Schistosoma mansoni cercariae became resistant to homologous challenge by 8 weeks, and the degree of resistance that was acquired correlated with the size of the worm burden and the tissue egg burden. Mice given 100 male or 100 female cercariae alone failed to become resistant even after 30–40 weeks of infection. When a super-infection of 100 male or 100–300 female cercariae was given to mice with 25 unsexed cercariae, the degree of resistance that was acquired was generally lower than in mice given 25 unsexed cercariae alone. In the super-infected mice there was no correlation between the size of the worm burden (mainly unpaired male or female worms) and the degree of acquired resistance. In mice super-infected with male worms there was an inverse correlation between the number of male worms and the number of eggs deposited in the liver and intestine by each mature worm pair. A positive correlation was, however, still found between the degree of acquired resistance and total tissue egg counts in mice super-infected with single sex cercariae. Mice injected intraperitoneally or subcutaneously with intact S. mansoni eggs failed to become resistant to S. mansoni challenge. Transfer of lymphoid cells or serum, separately or together, from heavily infected and demonstrably resistant donor mice to naive normal or T-cell deprived recipients failed to render the recipients resistant to S. mansoni challenge. The results indicate that resistance to re-infection in mice with recently patent S. mansoni infections is dependent on the number of S. mansoni eggs entrapped in the tissues, and that excessive numbers of unpaired S. mansoni male or female worms can inhibit the fecundity of established worm pairs. The apparent acquired resistance to S. mansoni that has been observed in this model system may be largely a consequence of non-specific factors interfering with normal patterns of challenge worm migration and maturation.

Age-dependent survival and infectivity characteristics are described for the cercariae of Echinoparyphium recurvatum. At 18 °C the maximum life-span of the cercariae was 48 h and 50% survival occurred at 30·5 h. Infectivity of cercariae to the second intermediate host, Lymnaea peregra was maximal approximately 2 h after emission from the first intermediate host and it subsequently declined to zero at 19 h. It is suggested that the period of sub-maximal infectivity at the beginning of the cercarial life-span may represent a phase during which dispersal is an important function of the larvae. The relationship between infective stage density and establishment success was linear up to densities equivalent to 5000 cercariae/1. At higher cercarial densities the proportion of parasites establishing in second intermediate hosts declined progressively with increasing cercarial density. The mean number of parasites establishing/host increased linearly with increasing host size.

Cryostat sections of juvenile and adult female stages of the soybean cyst-nematode, Heterodera glycines, were incubated with 4 different naphthylamide-linked peptide substrates to localize and characterize proteinase activity within the animal. Detected activity was restricted to the intestine and 2 distinct classes of proteinase were identified on the basis of substrate specificity and sensitivity to plant proteinase inhibitors. A cathepsin L-like cysteine proteinase activity capable of hydrolysing the synthetic substrates Z-Ala-Arg-Arg-MNA and Z-Phe-Arg-MNA but not Z-Arg-Arg-MNA or L-Arg-NA was inhibited by an engineered variant of a cysteine proteinase inhibitor from rice (Oc-IδD86). The cleavage of Z-Phe-Arg-MNA was sensitive to inhibition by a combination of Oc-IδD86 and cowpea trypsin inhibitor (CpTI). Degenerate oligonucleotide primers were used to amplify fragments of cysteine proteinase genes from 2 cyst-nematodes, H. glycines and Globodera pallida. Comparison of the H. glycines fragment with known genes established highest homology to cathepsin L-like genes. In contrast, the amplified G. pallida fragment displayed greatest homology to cathepsin B-like genes from Caenorhabditis elegans.

A study was carried out to investigate how common Cryptosporidium infections are in beef calves in Swedish suckler herds and to explore which species and subtypes that occur. We further aimed at identifying factors associated with shedding of Cryptosporidium oocysts in this type of calf management. The study was conducted in two regions in Sweden and included 30 herds. Faecal samples were collected from calves younger than 3 months. A brief clinical examination was done and a questionnaire was used to collect data on management routines. Faeces were cleaned and concentrated and oocysts identified by epifuorescence microscopy. Cryptosporidium positive samples were analyzed at the 18S rRNA and GP60 genes to determine species and Cryptosporidium parvum subtype, respectively. Logistic regression was used to identify factors associated with infection. Oocysts were detected in 122 (36·7%) calves from 29 (97%) herds, at 400 to 2·4 × 107 OPG. The youngest positive calves were only 1 and 2 days old. There was no association between age and Cryptosporidium infection. Cryptosporidium bovis, Cryptosporidium ryanae, C. parvum and Cryptosporidium ubiquitum were identified, with C. bovis being the major species. Two C. parvum subtypes, IIaA16G1R1 and IIdA27G1 were identified. Routines for cleaning calf pens and number of cows in calving pens were associated with infection.

Hybridization between Schistosoma mansoni, with a diurnal cercarial emergence rhythm and S. rodhaini, with a nocturnal cercarial shedding pattern leads to F1 and F2 generations, hybrid schistosomes whose chronobiological phenotype of cercariae is characterized by two unequal emergence peaks, one diurnal and the other nocturnal. The relative importance of diurnal and nocturnal peaks depends upon which S. mansoni strain (early or late) is used for the hybridization with S. rodhaini. The results are compared and discussed with those resulting from crosses between intraspecific sympatric and allopatric chronobiological variants (early and late) of S. mansoni. The genetic determinism of the cercarial emergence of schistosomes and the significant differences observed between cercarial shedding patterns of parental species and their hybrids allow the use of this behavioural marker in biological and genetical studies in schistosome populations.

Twelve populations of bats were examined to determine the extent of interspecific associations in determining the species richness of intestinal helminth infracommunities. The pool of helminth species which was available to individual bats ranged from 2 to 21. The ‘summed binomial’ distribution was determined to underlie the host frequency distribution of the number of helminth species per host. Overall covariation in occurrences of species in replicated communities can be detected by testing for the equality of the observed variance of the host frequency distribution to the variance expected when species are allocated to hosts at random. Where statistically significant the covariance was indicative of a majority of positive rather than negative interspecific associations. As the mean number of species per host in a host population increases not only does the number of positive associations increase but so does the proportion of species pairs which exhibit positive associations. Although there is an increase in the proportion of species pairs which exhibit positive associations as the number of species increases, the magnitude of the associations (as indicated by the mean positive or the mean negative pairwise covariances) does not. Therefore, we concluded that positive interactions are more common than negative interactions in determining the species richness of helminth infracommunities of bats. Further, positive associations become even more important as the community becomes more complex. However, the increased importance is derived from the number rather than the strength of the associations.

A large field study has been performed in the Cochabamba region of Bolivia with the aim of comparing the polymerase chain reaction (PCR) with other diagnostic methods for Chagas' disease. The amplification of Trypanosoma cruzi-specific kinetoplast DNA sequences in blood samples was compared with classical serological methods, specific IgM detection and direct parasite visualization for 268 school children in a single village where Chagas' disease transmission is active. Of 113 children positive by classical serology or buffy coat examination, 106 were detected by PCR (sensitivity: 93·8%). We did not observe any significant difference of PCR sensitivity between initial (IgM and/or buffy coat positive) and indeterminate stage (only IgG positive) patients. Among the remaining 155 children unconfirmed as chagasic (who were either only IgM positive, IgG-, IgM-, and buffy coat-negative) only 1 case was PCR positive. This case may be due to DNA contamination, or to a very recent infection not detected otherwise, or to specific immune depression. These results show that PCR is a very sensitive parasitological test for Chagas' disease in active transmission regions. The future follow-up of the possibly infected patients who were only IgM-positive should clarify the interest of PCR and IgM tests in the detection of starting infections.

The microsporidian Encephalitozoon cuniculi can infect numerous mammals, including man. Three strains of E. cuniculi have been identified so far, the major marker being the number of a tetranucleotide repeats in the rDNA internal transcribed spacer. We investigated diversity at the chromosomal level through the electrophoretic karyotypes obtained from 15 E. cuniculi isolates from 5 different host species. All preparations provided patterns with 9–12 bands within a narrow molecular size range. Six karyotype forms were distinguished, involving subdivision of strain I into 3 types (A, B, C) and strain II into 2 types (D, E). The types A, B and C were mainly associated with isolates from rabbits of different geographical origins. The types D, E and F were characterized by a reduced chromosome size range, 2 of these appearing specific to a carnivorous host species (D in dog and F in blue fox). Hybridization experiments showed that all E. cuniculi isolates possess 11 chromosomes, with a size polymorphism entailing occasional electrophoretic comigration of heterologous chromosomes and differential migration of homologous ones. DNA rearrangements should occur during mitosis and the hypothesis of diploidy for the basic state of E. cuniculi seems likely.