Virulent strains of Entamoeba histolytica have been reported to produce a mixture of phosphoglycoconjugates that share some structural features with the lipophosphoglycans (LPGs) of Leishmania. Purification of these glycoconjugates is essential to their precise structural characterization. In this study we have extracted ‘LPG-like’ molecules from various virulent E. histolytica strains and purified on the basis of charge differences, 2 apparently related glycoconjugates a ‘LPG’ and a ‘lipophosphopeptidoglycan (LPPG)’. In marked contrast to the abundance of these ‘LPG’ and ‘LPPG’ molecules in the virulent strains, avirulent E. histolytica and E. dispar strains produce either very low, or no detectable levels of LPG, and either low levels or modified forms of ‘LPPG’. Monospecific polyclonal antibodies prepared against that ‘LPG’ of the virulent strain HM-1: IMSS cl6 identified epitopes shared between both the ‘LPG’ and the ‘LPPG’ of this and other virulent strains, using Western blot analysis. Flow cytometric analysis of a range of strains using these antibodies identified a surface distribution of these molecules and confirmed a correlation between surface exposure of epitopes bound by these antibodies and parasite virulence.

The adhesive organs of diplectanid, tetraonchid and dactylogyrid monogeneans develop in very similar ways indicating that all these gill parasites are closely related to each other. The oncomiracidia make initial contact with the general body skin or the lining of the buccal cavity to which they attach themselves by 14 or 16 ventrally orientated marginal hooklets. The growing parasites then find their way to the gills which call for a different kind of adhesive apparatus. In order to anchor itself between two of the host's secondary gill lamellae, two pairs of the parasite's marginal hooklets migrate to the dorsal surface of the haptor and two of the four developing hamuli rotate so that they also point dorsally.

In diplectanids the hamuli are assisted by accessory friction pads (squamodiscs) which develop on the surface of the body anterior to the hooks.

In dactylogyrids the ventral hamuli do not develop and are represented in the adult only by small spicules. In contrast the marginal hooklets grow during larval development and become important adult attachment organs, together with the dorsal hamuli.

Adults of Tetraonchus monenteron feed on the epidermis covering the gills.

I am most grateful to the Director and Staff of the Laboratory of the Marine Biological Association at Plymouth and particularly to Mr J. E. Green for help and hospitality. I would also like to express my thanks to the East Suffolk and Norfolk River Authority and particularly to the Fishery Superintendent, Mr E. Q. Bitton, and to Mr D. Leary, for supplying me with freshwater fishes.

Deer are important blood hosts for feeding Ixodes ricinus ticks but they do not support transmission of many tick-borne pathogens, so acting as dead-end transmission hosts. Mathematical models show their role as tick amplifiers, but also suggest that they dilute pathogen transmission, thus reducing infection prevalence. Empirical evidence for this is conflicting: experimental plots with deer removal (i.e. deer exclosures) show that the effect depends on the size of the exclosure. Here we present simulations of dynamic models that take into account different tick stages, and several host species (e.g. rodents) that may move to and from deer exclosures; models were calibrated with respect to Ixodes ricinus ticks and tick-borne encephalitis (TBE) in Trentino (northern Italy). Results show that in small exclosures, the density of rodent-feeding ticks may be higher inside than outside, whereas in large exclosures, a reduction of such tick density may be reached. Similarly, TBE prevalence in rodents decreases in large exclosures and may be slightly higher in small exclosures than outside them. The density of infected questing nymphs inside small exclosures can be much higher, in our numerical example almost twice as large as that outside, leading to potential TBE infection risk hotspots.

Stability of trichostrogylid populations indicates that some form of density-dependent regulation occurs which could act through fecundity. We present evidence for intraspecific density-dependent effects in 1 of 2, dominant, abomasal nematodes species (Ostertagia gruehneri) of Svalbard reindeer (Rangifer tarandus platyrhynchus). We found evidence in O. gruehneri, for density-dependent regulation of female worm length in April, July and October 1999. However, it is only in July that female worm length explains the variation in the number of eggs in utero which is also related to egg production per female worm only in this month and not at other times of the year. The seasonal pattern in faecal egg output in this species focuses egg production in the summer months when conditions are favourable to transmission. In contrast, we found no evidence in the other common species (Marshallagia marshalli) for density-dependent regulation of female worm length during or the number of eggs in utero. Faecal egg output in M. marshalli was positively related to worm burden but not to the mean number of eggs in utero. Neither inter-specific interactions nor host body condition appeared to influence worm fecundity. The contrasting patterns of density-dependent regulation of fecundity provides further evidence for divergent life-histories in this nematode community.

Human African trypanosomiasis (HAT) is caused by Trypanosoma brucei gambiense and Trypanosoma brucei rhodesiense and caused devastating epidemics during the 20th century. Due to effective control programs implemented in the last two decades, the number of reported cases has fallen to a historically low level. Although fewer than 977 cases were reported in 2018 in endemic countries, HAT is still a public health problem in endemic regions until it is completely eliminated. In addition, almost 150 confirmed HAT cases were reported in non-endemic countries in the last three decades. The majority of non-endemic HAT cases were reported in Europe, USA and South Africa, due to historical alliances, economic links or geographic proximity to disease-endemic countries. Furthermore, with the implementation of the ‘Belt and Road’ project, sporadic imported HAT cases have been reported in China as a warning sign of tropical diseases prevention. In this paper, we explore and interpret the data on HAT incidence and find no positive correlation between the number of HAT cases from endemic and non-endemic countries. This data will provide useful information for better understanding the imported cases of HAT globally in the post-elimination phase.

The public health threat posed by zoonotic Plasmodium knowlesi appears to be growing: it is increasingly reported across South East Asia, and is the leading cause of malaria in Malaysian Borneo. Plasmodium knowlesi threatens progress towards malaria elimination as aspects of its transmission, such as spillover from wildlife reservoirs and reliance on outdoor-biting vectors, may limit the effectiveness of conventional methods of malaria control. The development of new quantitative approaches that address the ecological complexity of P. knowlesi, particularly through a focus on its primary reservoir hosts, will be required to control it. Here, we review what is known about P. knowlesi transmission, identify key knowledge gaps in the context of current approaches to transmission modelling, and discuss the integration of these approaches with clinical parasitology and geostatistical analysis. We highlight the need to incorporate the influences of fine-scale spatial variation, rapid changes to the landscape, and reservoir population and transmission dynamics. The proposed integrated approach would address the unique challenges posed by malaria as a zoonosis, aid the identification of transmission hotspots, provide insight into the mechanistic links between incidence and land use change and support the design of appropriate interventions.

Some Trypanosoma and Leishmania species are multi-host parasites whose distribution overlaps in several parts of the Brazilian Amazon basin. Despite being a common trait among wild mammals, mixed infections and their consequences for the host's health and parasite transmission are still a poorly known phenomenon. Here we describe a triple mixed infection – Trypanosoma cruzi, T. rangeli and Leishmania infantum – in a bone marrow sample from an anteater Tamandua tetradactyla captured in a house backyard from the endemic Abaetetuba municipality in the Amazon basin. T. cruzi was also isolated from blood samples. The mini-exon multiplex PCR characterization detected the infection by T. rangeli and T. cruzi (TcI genotype), while L. infantum infection was confirmed by an ITS-PCR followed by amplicon sequencing. This is the first description of T. rangeli isolation from bone marrow and the first report of L. infantum infection in xenarthrans. The implications of this finding are discussed considering the influence of mixed infections in the role of this mammal species as a putative reservoir host of these 3 trypanosomatid species.

The effect of different relative humidities on the survival of individual larvae and adults of Ditylenchus dispasci and D. myceliophagus has been examined; experiments were carried out at 5 and 18°C with D. myceliophagusand at 18°C with D. dipsaci. Survival of both species was enhanced when they were dried at high humidities and, for D. myceliophagus, by the lower temperature. The survival of all stages of D. myceliophagus was poor. Generally it was expressed in minutes only; 4th-and 3rd-stage larvae, however, were marginally better at surviving drying than adults and much better than 2nd-stage larvae.

Although the 4th-stage larva of D. dipsaci was overwhelmingly superior to all other stages, the 3rd stage, and to a lesser extent, the adult of this species also showed remarkable powers of survival to desiccation. In general, survival of 4th-, 3rd- and 2nd-stage larvae could be expressed in weeks, days and minutes respectively; for adults, survival was expressed in hours at relative humidites under 50% but in days at higher relative humidites.

The results are discussed in relation to the survival value of the aggregations formed by these species; the validity of the term ‘resistantstage’ as applied to the 4th-stage larva of D. dipsaci is assessed.

It has been shown that mating involving mutual exchange of spermatophores takes place in the skin-parasitic monogenean Entobdella soleae from Solea solea. The spermatophores are attached to the ventral surface of the body in the region of the vaginal opening and they are sucked into the vagina after mating by muscular contractions of the vaginal region.

Mating takes place between young individuals with no vitellaria and between fully mature egg-laying adults but there is no evidence that self-fertilization takes place.

The apparatus which manufactures the spermatophores is described and the evidence indicates that spermatozoa are injected into the jelly-like matrix of the spermatophore as the matrix is being extruded into the surrounding sea-water.

I would like to thank the Director and Staff of the Laboratory of the Marine Biological Association at Plymouth for providing excellent facilities for this work and I am particularly grateful to Mr J. E. Green, who kindly fed and maintained infected soles at the Laboratory.

A Strain ofHaemonchus contortusshowing moderate levels of resistance to thiabendazole (TBZ) (egg hatch assay LC50 2.1 μM) was subjected, in alternating sequence, to 5 in vitro and 4 in vivo selections with TBZ. This resulted in a significant increase in resistance (egg hatch assay LC50 2.8 μM). The isolates obtained after each combined in vitro and in vivo selection were compared in terms of egg hatch assay, establishment, net egg output, per capita egg output and degree of pathology caused in infected hosts. The increase in resistance was accompanied by a significant increase in larval establishment sheep (22 %) and was associated with more severe pathology, higher egg count and worm recovery 3 months post- infection.

Recent studies of Echinococcus granulosus molecular strain typing have enabled a better understanding of the transmission cycle of cystic echinococcosis. There have been many publications in this area but there is a need for the evaluation of these tools. We have attempted to respond to this need in our study, which assessed 8 DNA fragments of 40 E. granulosus cysts from North Africa. Parasitological material was collected from 5 types of intermediate hosts, in 5 different countries. The primers chosen to amplify DNA targets were defined either in nuclear DNA, or in mitochondrial DNA. After amplification, PCR products were sequenced. The sequences obtained were aligned and comparisons were made within the group and with GenBank sequences. Whether the target was nuclear or mitochondrial, the same 2 main groups of genotypes were found. The first one, the ‘sheep’ strain, was found in the human, sheep and cattle samples collected in North Africa. The second one, the ‘camel’ strain, was found in the camel cysts and cattle and human cysts from Mauritania. These findings further confirm the congruence of the data given by the nuclear and the mitochondrial genome.

Partial sequences of the DNA polymerase delta (pold) gene from Taenia saginata-like adult worms were sequenced. Phylogenetic analysis revealed that pold gene sequences were clearly divided into two clades, differing from each other in five to seven nucleotides. There is little doubt that T. saginata and Taenia asiatica were once separated into two distinct taxa as has been concluded in previous studies. On the other hand, most of the adult worms, which were identified as T. asiatica using mitochondrial DNA, were homozygous for an allele that originated from the allele of T. saginata via single nucleotide substitution. These results indicate that most of the adult worms, which had been called T. asiatica, are not actually ‘pure T. asiatica’ but instead originated from the hybridization of ‘pure T. saginata’ and ‘pure T. asiatica’.

Phenotypic alterations induced by parasites in their intermediate hosts often result in enhanced trophic transmission to appropriate final hosts. However, such alterations may also increase the vulnerability of intermediate hosts to predation by non-host species. We studied the influence of both infection with 3 different acanthocephalan parasites (Pomphorhynchus laevis, P. tereticollis, and Polymorphus minutus) and the availability of refuges on the susceptibility of the amphipod Gammarus pulex to predation by 2 non-host predators in microcosms. Only infection with P. laevis increased the vulnerability of amphipods to predation by crayfish, Orconectes limosus. In contrast, in the absence of refuges, the selectivity of water scorpions, Nepa cinerea, for infected prey was significant and did not differ according to parasite species. When a refuge was available for infected prey, however, water scorpion selectivity for infected prey differed between parasite species. Both P. tereticollis- and P. laevis-infected gammarids were more vulnerable than uninfected ones, whereas the reverse was true of P. minutus-infected gammarids. These results suggest that the true consequences of phenotypic changes associated with parasitic infection in terms of increased trophic transmission of parasites deserve further assessment.

It is well established that pregnant women are at an increased risk of Plasmodium falciparum infection when compared to non-pregnant individuals and limited epidemiological data suggest Plasmodium vivax risk also increases with pregnancy. The risk of P. falciparum declines with successive pregnancies due to the acquisition of immunity to pregnancy-specific P. falciparum variants. However, despite similar declines in P. vivax risk with successive pregnancies, there is a paucity of evidence P. vivax-specific immunity. Cross-species immunity, as well as immunological and physiological changes that occur during pregnancy may influence the susceptibility to both P. vivax and P. falciparum. The period following delivery, the postpartum period, is relatively understudied and available epidemiological data suggests that it may also be a period of increased risk of infection to Plasmodium spp. Here we review the literature and directly compare and contrast the epidemiology, clinical pathogenesis and immunological features of P. vivax and P. falciparum in pregnancy, with a particular focus on studies performed in areas co-endemic for both species. Furthermore, we review the intriguing epidemiology literature of both P. falciparum and P. vivax postpartum and relate observations to the growing literature pertaining to malaria immunology in the postpartum period.

A study of neutralization reaction of trypanosomes with immune sera made against them is recorded, together with a description of the technique.

Neutralizing antibody appears in rabbits infected with T. brucei 5 days after infection and reaches its peak (1/320) within 28 days.

The same titre of neutralizing antibody can be produced in rabbits by a series of injections of dead formalized trypanosomes.

Antibody titres persist at high levels for a longer period in animals infected and subsequently treated than in animals immunized with dead trypanosomes.

Neutralizing antibody can be demonstrated in infected guinea-pigs but on a much lower level than in rabbits. Mice and rats infected with T. brucei and not treated failed to show demonstrable neutralizing antibody.

Mice infected with T. brucei can be protected from infection by inoculation at the same time, or even 1 hr. later, with 0·5 ml. of antiserum showing a high level of neutralizing antibody.

Mice inoculated with the same antiserum showed passive immunity lasting for 10 days.

The evidence that T. brucei ‘O‘ after passages through rabbits failed to be neutralized by homologous or heterologous sera which, on the other hand, were able to neutralize the parent strain, suggests that strains after passage through rabbits were not genetic variants, but developed a protective mechanism against immune bodies.

Introduction. Palaeozoic calcareous sponges (stromatoporoids) are common bio-constructing fossils; they are sometimes found in association with helicoidal structures of unknown biological affinities. The interaction between the tube-forming organisms has usually been classified as commensalism. Methods. About 260 stromatoporoid skeletons from the Middle Devonian (Givetian) of the Mont d'Haurs section near Givet (Champagne-Ardenne, France) were thin-sectioned and analysed under transmitted light. Results. Approximately 10% of the examined stromatoporoids (mainly belonging to the genera Actinostroma, Stromatopora and Stromatoporella) contain tubes classified as Torquaysalpinx sp. The Torquaysalpinx organisms penetrated the skeletons of stromatoporoids in vivo (as evidenced by skeletal overgrowths); around the infesting organisms, growth bands are bent down. Conclusion. Diminished growth rates around the infesting organism demonstrate a negative influence on the host, similar to that seen in the modern demosponge–polychaete association of Verongia–Haplosyllis. This is demonstrated by changes in growth bands. As in the above-mentioned association, the endosymbiont might have been feeding directly upon the tissues of the host. The Torquaysalpinx organisms were gaining habitat and possibly also food resources – for them this interaction was clearly positive. This long-term association can therefore be classified as parasitism. This is the first evidence for parasitism in Palaeozoic sponges.

Twenty-seven stocks of Nannomonas trypanosomes isolated from livestock in 1982 on a ranch at Kilifi on the Kenyan coast were characterized by isoenzyme electrophoresis and by the abilities of the parasite's DNA to hybridize to two repetitive sequence DNA probes. Allthe Kilifi stocks which were examined had isoenzyme patterns which were markedly different from the 75 patterns previously described from 78 stocks of Trypanosoma congolense. On average only 15% of the enzyme bands present in the Kilifi stocks were present in those stocks of T. congolense which had previously been surveyed for isoenzymes. The DNA from all the Kilifi stocks which had been examined for isoenzymes hybridized with only the repetitive sequence probe isolated from a clone of a Kilifi stock. In contrast, the DNA from all 27 Kilifi stocks failed to hybridize with a repetitive sequence probe isolated from a clone from a different stock of T. congolense. Thus, the trypanosomes in all the Kilifi stocks examined were both phenotypically and genotypically discrete. These genetically discrete trypanosomes have also been detected in 2 stocks isolated from livestock from another location on the Kenyan coast. The results show that there is a wide range of genetic heterogeneity within the trypanosomes currently classified as T. congolense. We suggest that the limits of this genetic heterogeneity could represent incipient speciation.

In non-permanent parasites the separation from the host should take place in suitable habitats that allow the continuation of their life cycle. Furthermore, detachment strategies determine the parasites' dispersal capability, a characteristic on which epidemiological dynamics and the evolution of host specificity centre. In this study we experimentally investigate in the laboratory how 2 congeneric tick species, with contrasting habitat requirements, time detachment from one of their current songbird hosts (Parus major). Ixodes arboricola is a nidicolous tick, infesting bats and birds breeding or roosting in tree holes. Ixodes ricinus is a non-nidicolous generalist that parasitizes mammals, birds and even reptiles. We experimentally infested full-grown great tits, P. major, and found that I. arboricola detaches during the night, the moment when P. major sleeps in tree holes. In contrast, I. ricinus detaches during the day, the moment when birds are most active. In addition we found that all I. ricinus immatures left the birds within 5.5 days, while in I. arboricola the detachment time was long (up to 20 days) and highly variable. We discuss these findings with respect to their implications on the ticks' dispersal capability and host specificity.

Trichinella spiralis is a parasitic helminth that can infect almost all mammals, including humans. Trichinella spiralis infection elicits a typical type 2 immune responses, while suppresses type 1 immune responses, which is in favour of their parasitism. DNA vaccines have been shown to be capable of eliciting balanced CD4+ and CD8+ T cell responses as well as humoral immune responses in small-animal models, which will be advantage to induce protective immune response against helminth infection. In this study, serine protease (Ts-NBLsp) was encoded by a cDNA fragment of new-born T. spiralis larvae, and was inserted after CMV promoter to construct a DNA vaccine [pcDNA3·1(+)-Ts-NBLsp]. Ts-NBLsp expression was demonstrated by immunofluorescence. Sera samples were obtained from vaccinated mice, and they showed strong anti-Ts-NBLsp-specific IgG response. Mice immunized with the pcDNA3·1(+)-Ts-NBLsp DNA vaccine showed a 77·93% reduction in muscle larvae (ML) following challenge with T. spiralis ML. Our results demonstrate that the vaccination with pcDNA3·1(+)-Ts-NBLsp plasmid promoted the balance of type 1 and 2 immune responses and produced a significant protection against T. spiralis infection in mice.