The immunoprotective potential of Babesia divergens antigens released in supernatants of in vitro cultures of the parasite is generally known. Among a number of parasite molecules, a 37 kDa protein has been found in the supernatants of Babesia divergens cultures. In this report the cloning and biochemical characterization of this protein, called Bd37, are describedThe sequence data reported herein have been deposited in EMBL under Accession No. AJ422214. . In addition, the processing of the protein was studied in vitro. Results suggest that Bd37 is encoded by a single copy gene. Bd37 appears to be a merozoite-associated molecule attached to the surface by a glycosylphosphatidylinositol moiety containing a palmitate residue attached to the inositol ring. In addition, it is demonstrated that both extremities of the protein are linked by a disulphide bond. Results further indicate that a soluble, hydrophilic form of Bd37 can be released from the merozoite surface by GPI-specific phospholipase D. The potential role the Bd37 protein and the GPI anchor are discussed.

The epidemiology of the sucking lice Echinophthirius horridus was studied over a 4 year period in which their harbour seal hosts experienced marked inter-annual changes in food availability. Prevalence and intensity of infection varied in relation to host age but not sex. Burdens were highest on immature seals, but both prevalence and intensity of infection were significantly higher in years when food availability was low. Observed intra-population variations in ectoparasite dynamics suggested that reported geographical differences in the prevalence of E. horridus may have resulted from methodological differences. In contrast to previous studies of other pinnipeds, lice were also absent on weaned pups, suggesting that E. horridus is transferred horizontally. No significant differences were found in the haematological parameters of infected and uninfected hosts. Nevertheless, there was a significant negative correlation between intensity of infection and several erythrocyte parameters, suggesting that high burdens of lice may compromise diving ability.

Cyclical transmission of different variable antigen types of Trypanosoma congolense STIB 228 resulted in the development of metacyclic trypanosome populations which were similar in their variable antigen composition as judged by immunofluorescence and neutralization assays. The variable antigen types present in the ingested bloodstream populations were not found in the metacyclic populations. The bloodstream populations which were obtained from cyclically infected, irradiated (900 rad.) mice contained variable antigen types which were not present in the corresponding metacyclic populations. When derivatives of 2 other stocks of T. congolense, isolated in a different area of Tanzania, underwent cyclical development in the tsetse fly, the metacyclic populations of each stock also had a characteristic variable antigen composition. The metacyclic populations of the 3 stocks were, however, completely dissimilar in variable antigen composition. Simultaneous infection of tsetse flies with a mixture of different stocks resulted in the concurrent production of metacyclic trypanosomes which contained the characteristic variable antigen types of each stock. The effect of cyclical transmission on the process of antigenic variation in T. congolense infections is therefore similar to that in T. brucei infections.

The Schistosoma mansoni protein, SPRM1lc, is a light chain member of a new family of heterodimeric amino acid permeases. These proteins require covalent association with a type II glycoprotein (like h4F2hc) for functional surface localization when expressed in Xenopus oocytes. We previously reported that, when co-expressed with h4F2hc, the transport properties of SPRM1lc resemble system y and y+ while its human homologue, E16, functions as an L-type permease. Here we extend the functional characterization of SPRM1lc in oocytes and show by competitor studies that its amino acid transport capacity is similar to that of whole adult schistosomes. We demonstrate by Northern and Western analysis that SPRM1lc is expressed within both larval and adult schistosomes. In all stages, SPRM1lc is associated into a high molecular weight complex that can be disrupted by reducing agents, consistent with the hypothesis that a significant fraction of the endogenous SPRM1lc is linked by a disulphide bond to an uncharacterized schistosome amino acid transporter heavy chain. Immunofluorescence localization detects SPRM1lc in miracidia, daughter sporocysts and adult worms. Confocal microscopy demonstrates that SPRM1lc is found in the apical membrane of the syncytial, double-lipid bilayer tegument which surrounds adult worms. Aqueous biotinylation studies on living worms show that SPRM1lc is exposed on the host-interactive surface of this tegumental membrane. Host exposed, functionally important surface proteins such as SPRM1lc could form the basis of an effective schistosomiasis vaccine. These studies are the first to describe a helminth amino acid transporter, and the first to characterize an invertebrate heterodimeric amino acid transporter.

Heat shock is believed to be a developmental inductor of differentiation in Leishmania. Furthermore, heat shock genes are extensively studied as gene models to decipher mechanisms of gene regulation in kinetoplastids. Here, we describe the organization and expression of the HSP70 loci in representative Leishmania species (L. infantum, L. major, L. tropica, L. mexicana, L. amazonensis and L. braziliensis). With the exception of L. braziliensis, the organization of the HSP70 loci was found to be well conserved among the other Leishmania species. Two types of genes, HSP70-I and HSP70-II, were found to be present in these Leishmania species except for L. braziliensis that lacks HSP70-II gene. Polymorphisms in the HSP70 locus allow the differentiation of the Old and New World species within the subgenus Leishmania. A notable discrepancy between our data and those of the L. major genome database in relation to the gene copy number composing the L. major HSP70 locus was revealed. The temperature-dependent accumulation of the HSP70-I mRNAs is also conserved among the different Leishmania species with the exception of L. braziliensis. In spite of these differences, analysis of the HSP70 synthesis indicated that the HSP70 mRNAs are also preferentially translated during heat shock in L. braziliensis.

Vaccination of lambs with the membrane-bound (S3) thiol-Sepharose binding protein (TSBP) fraction derived from the gut of Haemonchus contortus confers significant protection against homologous challenge. The S3 TSBP peptide profile is dominated by a major protein of ca. 60 kDa which is strongly recognized by antisera from sheep demonstrably protected following immunization with S3 TSBP. In an attempt to identify this protein, sera from protected lambs were employed to screen a λgt11 cDNA library of the adult parasite and resulted in the isolation of numerous clones encoding a homologue of the mitochondrial enzyme, glutamate dehydrogenase (GDH). GDH enzyme activity was readily demonstrable in S3 TSBP material and immunolocalization studies showed that the enzyme was localized to the cytoplasm of the parasite's gut. Furthermore, the enzyme appeared to be developmentally regulated, with both GDH mRNA and protein expressed almost exclusively during the blood-feeding parasitic stages.

Plasmodium knowlesi has risen in importance as a zoonotic parasite that has been causing regular episodes of malaria throughout South East Asia. The P. knowlesi genome sequence generated in 2008 highlighted and confirmed many similarities and differences in Plasmodium species, including a global view of several multigene families, such as the large SICAvar multigene family encoding the variant antigens known as the schizont-infected cell agglutination proteins. However, repetitive DNA sequences are the bane of any genome project, and this and other Plasmodium genome projects have not been immune to the gaps, rearrangements and other pitfalls created by these genomic features. Today, long-read PacBio and chromatin conformation technologies are overcoming such obstacles. Here, based on the use of these technologies, we present a highly refined de novo P. knowlesi genome sequence of the Pk1(A+) clone. This sequence and annotation, referred to as the ‘MaHPIC Pk genome sequence’, includes manual annotation of the SICAvar gene family with 136 full-length members categorized as type I or II. This sequence provides a framework that will permit a better understanding of the SICAvar repertoire, selective pressures acting on this gene family and mechanisms of antigenic variation in this species and other pathogens.

Site specificity and distribution of 5 species offreshwater acanthocephalans Acanthocephalus clavula, A. lucii, A. anguillae, Pomphorhynchus laevis and Echinorhynchus trultae and I marine species, E. gadi, were studied in the intestines of several species of fish, especially Anguilla anguilla. When data are presented in the conventional manner with results from all fish and all parasites in a sample combined, each species exhibited a preference for a particular region of the intestine which altered in some species in relation to host identity and sex and abundance of parasite. Each species could nevertheless inhabit most of the length of the intestine and there was a considerable degree of overlap in most cases between the distributions of species in the same host, but the mean position of each species differed significantly from that of any other and the species appeared to exhibit site segregation and resource partitioning along the length of the intestine. In individual fish, fidelity of site location and distribution is poor and may bear little or no relationship to the position and distribution of the parasites in the population as a whole, and it is concluded that the concepts of site specificity and segregation are most applicable at the population level. Mixed species infections are very rarely encountered in Britain since most freshwater localities contain, or are almost completely dominated by, only a single species of acanthocephalan. The results are discussed in relation to current ideas on the role of interspecific competition in determining site segregation and community structure of parasites. It appears that site specificity in fish acanthocephala is not related to the probability of mating, or site segregation to interspecific competition past or present. Acanthocephalan communities do not exist as such; the normal situation is chance assemblages, with vacant niches, little organization, few or no interactions and little fidelity between habitats.

Previously, we described the protective action of the immunomodulatory extract of Kalanchoe pinnata (Kp) in murine and human cutaneous leishmaniasis. In the present study, we investigated the effectiveness of Kp against visceral leishmaniasis, using the BALB/c mouse model of infection with Leishmania chagasi. Mice receiving oral daily doses of Kp (400 mg/kg) for 30 days displayed significantly reduced hepatic and splenic parasite burden, when compared with untreated animals. Protectiveness was accompanied by a reduction in parasite-specific IgG serum levels, and impaired capacity of spleen cells to produce IL-4, but not IFN-γ and nitric oxide upon antigen recall in vitro. The reference drug Pentostam (72 mg/kg) given by the intra-peritoneal route on alternate days produced an anti-leishmanial effect similar to oral Kp. Our findings show that the oral efficacy of Kp, seen previously in murine cutaneous leishmaniasis, extends also to visceral leishmaniasis caused by L. chagasi, a difficult to treat and lethal disease of man.

HIV-1 and parasitic infections co-circulate in many populations, and in a few well-studied examples HIV-1 co-infection is known to amplify parasite transmission. There are indications that HIV-1 interacts significantly with many other parasitic infections within individual hosts, but the population-level impacts of co-infection are not well-characterized. Here we consider how alteration of host immune status due to HIV-1 infection may influence the emergence of novel parasite strains. We review clinical and epidemiological evidence from five parasitic diseases (malaria, leishmaniasis, schistosomiasis, trypanosomiasis and strongyloidiasis) with emphasis on how HIV-1 co-infection alters individual susceptibility and infectiousness for the parasites. We then introduce a simple modelling framework that allows us to project how these individual-level properties might influence population-level dynamics. We find that HIV-1 can facilitate invasion by parasite strains in many circumstances and we identify threshold values of HIV-1 prevalence that allow otherwise unsustainable parasite strains to invade successfully. Definitive evidence to test these predicted effects is largely lacking, and we conclude by discussing challenges in interpreting available data and priorities for future studies.

New drugs against Trypanosoma brucei, the causative agent of Human African Trypanosomiasis, are urgently needed to replace the highly toxic and largely ineffective therapies currently used. The trypanosome alternative oxidase (TAO) is an essential and unique mitochondrial protein in these parasites and is absent from mammalian mitochondria, making it an attractive drug target. The structure and function of the protein are now well characterized, with several inhibitors reported in the literature, which show potential as clinical drug candidates. In this review, we provide an update on the functional activity and structural aspects of TAO. We then discuss TAO inhibitors reported to date, problems encountered with in vivo testing of these compounds, and discuss the future of TAO as a therapeutic target.

Ichthyophthirius multifiliis is a widespread, ciliated protozoan ectoparasite of fish. In the present study, we investigated the effects of metal nanoparticles on the reproduction and infectivity of free-living stages of I. multifiliis. We determined that ~50% of theronts could be killed within 30 min of exposure to either 20 ng mL−1 gold, 10 ng mL−1 silver or 5 ng mL−1 zinc oxide nanoparticles. Silver and zinc oxide nanoparticles at concentration of 10 and 5 ng mL−1 killed 100 and 97% of theronts, respectively and inhibited reproduction of tomonts after 2 h exposure. Gold nanoparticles at 20 ng mL killed 80 and 78% of tomonts and theronts 2 h post exposure, respectively. In vivo exposure studies using rainbow trout (Oncoryhnchus mykiss) demonstrated that theronts, which survived zinc oxide nanoparticles exposure, showed reduced infectivity compared with control theronts. No mortalities were recorded in the fish groups cohabited with theronts exposed to either nanoparticles compared with 100% mortality in the control group. On the basis of the results obtained from this study, metal nanoparticles particularly silver nanoparticles hold the best promise for the development of effective antiprotozoal agents useful in the management of ichthyophthiriosis in aquaculture.

In PVG rats a single immunizing infection with Schistosoma mansoni cercariae exposed to 0, 5, 10 or 20 krad. gamma radiation failed to induce more than minimal resistance (17–29%) to challenge 4 weeks later, whereas 4 immunizations with 20 krad.-irradiated cercariae, over several months, induced substantial resistance (75%). In contrast, significant protection was induced in Fischer rats by a single immunization with unirradiated cercariae or cercariae irradiated with up to 80 krad. Comparable resistance was induced by unirradiated and by 2, 5 and 20 krad.-irradiated cercariae (67–74%) and lower levels by 10, 40 and 80 krad.-irradiated infections (57, 48 and 33%, respectively). Although the resistance induced by a single dose of 1000 20 krad.-irradiated cercariae could be boosted by a second (88%), further immunizations failed to enhance this resistance. Also, increasing the number of immunizing cercariae in single or multiple vaccinations from 1000 to 3000 failed to increase the resistance. While the resistance induced by 20 krad.-irradiated cercariae persisted undiminished for at least 25 weeks (67%), the resistance induced by normal cercariae declined to insignificant levels by 25 weeks (21%). Comparison of the migration and survival of unirradiated and of 20 and 40 krad.-irradiated cercariae revealed dramatic differences in their fate: parasites exposed to 40 krad. remained in the skin, while the majority of 20 krad.-irradiated parasites died in the lungs after a sojourn of at least 14 days. Thus, although skin schistosomula alone could induce significant protection, optimal resistance was induced only by parasites which migrated to the lungs or beyond. The immunizing potential of these older parasites was investigated by exposing rats to lung-and liver-stage larvae injected into the tail and mesenteric veins, respectively. Irradiated 4-day lung schistosomula induced comparable resistance (79%) to that induced by a complete unattenuated cercarial infection (78%), whereas less resistance was induced by irradiated and unirradiated 11-day-old liver worms (30 and 27%) and by 25-day-old pre-adult worms (48%).

1. The distribution of acid and alkaline phosphatases in the hepatopancreatic cells of the molluscan host of Echinoparyphium sp. and in the redia and cercaria of this trematode has been studied.

2. There is a heavier concentration of acid phosphatase in the hepatopancreas of infected snails than in uninfected snails.

3. No acid phosphatase is present in the bodies of the rediae or cercariae but this enzyme is present in the contents of the redial caeca.

4. Alkaline phosphatase activity is greater in the hepatopancreas of infected snails than in uninfected snails.

5. Alkaline phosphatase is present in the tissues of the rediae and the cercariae, especially in the fully developed cercariae.

6. It is suspected that the increase in acid and alkaline phosphatases in Helisoma trivolvis infected with Echinoparyphium redia is correlated with the breakdown of glycogen by the parasite.

This research was made possible by Grants E-3443, E-3443C1, and AI 3443–03 from the Institute of Allergy and Infectious Diseases, National Institutes of Health, U.S. Public Health Service. The author is grateful to Mr Randall W. Snyder, Jr., School of Medicine, The University of Virginia, for technical assistance.

In this review we have given an account of the various methods which are available to determine the size of virus particles. In § IV we have endeavoured to bring the ultrafiltration method into agreement with other methods by suggesting a different factor for converting pore size to virus size from the factors commonly used. Throughout we have recognized the probability that most viruses are hydrated in solution and have distinguished between the size and molecular weight in solution and the size and molecular weight when dried.

In § VII we have given formulae suitable for interpreting centrifugation and diffusion data when the possibility of hydration is contemplated.

It is evident that this complication, added to that of shape, makes it necessary for several measurements by different methods to be made before one can claim to know the size of a virus. For this reason, only in the cases of three viruses have we thought the data sufficiently adequate to enable the size and shape and molecular weight of the Virus, both dry and hydrated, to be stated. These three viruses, tobacco mosaic, tomato bushy stunt and vaccinia respectively, are separately discussed in § X.

It will be clear from the preceding sections that, while the position regarding our knowledge of the absolute sizes of viruses is far from satisfactory, there has been amassed a large amount of data bearing on this subject. We should, however, point out that we have found it necessary to select what we consider to be the best experimental data in some cases and that there may be conflicting ideas expressed by various authorities. Frampton (1942) has studied the electron microscope photographs published by Stanley & Anderson (1941) and Anderson & Stanley (1941) and arrives at an entirely different estimate of the length of tobacco mosaic virus. Kausche, Pfankuch & Ruska (1939) reported one value for the length of this virus which is approximately half that given by Stanley & Anderson. Electron photomicrographs published by von Ardenne (1940) and Holmes (1941) for what are probably strains of the same virus, also suggest that the values given should not be taken as absolute. Frampton (1939 a, b), on the basis of diffusion and viscosity experiments and the stream birefringence of this virus, has suggested previously that it forms a gel at any concentration and therefore cannot be said to have a size. Lauffer (1940) has given reasons for supposing this argument to be incorrect. Bernal & Fankuchen (1941a) have discussed the possibility of tobacco mosaic virus particles being shorter than the value taken from Kausche et al. (1939) and conclude that in the plant itself the particle may be as short as 100 mμ.

In obtaining values of size arid shape from electron microscope data we have made the assumptions, which may not be correct, that long, thin viruses shrink in width rather than in length on drying and that almost spherical viruses contract approximately evenly in all directions. At the moment there would seem to be no method of proving or disproving the truth of these assumptions, but we believe it unlikely that drying will result in such a gross change in shape that it would invalidate our calculations. For instance, in the case of haemocyanin from Helix pomatia, it seems improbable that, on drying, an already anhydrous ellipsoidal molecule of 66 × 15·32 mμ would contract in length and expand in-width to form a sphere of some 24 mμ diameter.

In our treatment of hydration we have found it necessary to regard the density and volume of ‘bound’ water as being the same as that of water in bulk, which may not be entirely true. However, we regard the total volume occupied by water in cases of great hydration, as shown by tomato bushy stunt virus, as being not markedly smaller than that of the same mass of free water. It is, nevertheless, a well-established fact that in certain cases, gelatin for example (Svedberg, 1924), a small contraction in volume does take place when dry protein is added to water. This phenomenon does not, however, necessitate the assumption that the water of hydration, is denser than ordinary water, and can be explained in other ways.

The viscosity of solutions of viruses, especially the rod-shaped plant viruses, has attracted much attention as a method of finding frictional and axial ratios of viruses (Frampton, 1939 a, b; Lauffer, 1938; Loring, 1938; Neurath, Cooper, Sharp, Taylor, Beard & Beard, 1941; Kobinson, 1939 a, b; Stanley, 1939), but, in addition to the lack of experimental verification of the formulae used, in many cases (Robinson, 1939 a, b; Frampton, 1939 a, b) the formulae have been applied to experimental results obtained in circumstances which exclude the fundamental postulates on which the formulae are based. For this reason we have omitted a detailed discussion of such methods.

It would appear that in order to obtain evidence as to the size of a virus it is desirable to study the virus in as purified a form as possible and also to show that when ‘homo-geneous’ preparations are obtained, they do not consist merely of macromolecular substances contaminated with a small quantity of virus. Furthermore it is desirable to obtain at least sufficient data to enable one to assess both size and shape of the particles rather than to assume some shape or some density value which may be incorrect.

As mice recover from infection with Babesia microti, abnormal forms of the parasite are present in some red cells. These forms are non-infective, indistinguishable by light microscopy from those present after treatment with amicarbalide, a babesicidal drug, and persist in splenectomized mice.

Electron microscopy confirmed that these abnormal forms are degenerating intra-erythrocytic parasites. In the absence of evidence for death of B. microti elsewhere in the body, it appears that infections of mice with this parasite are normally terminated by their death within circulating red cells. This has important implications for the mechanism of immunity to both this parasite and those Plasmodium spp. with which it cross-protects in this host.

The action of pyrimethamine, sulphadiazine, proguanil and its active metabolite CPT, and 2:4-diaminopteridines against infections of Plasmodium berghei in mice was antagonized by P–aminobenzoic acid and by pteroylglutamic acid. Antagonism was in some instances detected only when P–aminobenzoic acid was given in solution in the drinking water as well as being injected subcutaneously. No antagonism was detected with a number of amino acids and nucleic acid derivatives.

As all of the above group of drugs can be antagonized by P–aminobenzoic acid and by pteroylglutamic acid, it would seem that they are alike in their mode of action. There must, however, be some differences between the mode of action or absorption of these drugs because species of Plasmodium that are very sensitive to the action of one of these drugs are frequently not very sensitive to the action of others.

As P. berghei is dependent on p–aminobenzoic acid, it is suggested that it can utilize this compound in the synthesis of pteroylglutamic acid to a greater extent than can P. gallinaceum, and that it resembles P. knowlesi more than other species of Plasmodium.

The genomic organization of gp63 genes in 4 and 7 isolates of Leishmania braziliensis and L. peruviana, respectively was studied by RFLP analysis with 3 restriction enzymes (Bgl I, Sal I and Apa I). Our results showed a marked polymorphism among isolates. Some characters were specific to L. braziliensis or to L. peruviana, and others specific to the respective biogeographical populations of L. peruviana. The average minimum copy number of gp63 genes was found to be higher in L. braziliensis (71) than in L. peruviana (46), suggesting that deletion of gp63 genes might be partially involved in the size decrease of the chromosome bearing gp63 genes, observed between those 2 species (from 700 to 610 kb). Our results may suggest the existence of at least 2 arrays of heterologous gp63 repeats, varying in relative copy number between L. braziliensis and L. peruviana, and among isolates of the latter species. Rearrangement of the gp63 genes was observed during long-term in vitro maintenance of a reference strain of L. braziliensis. These observations document the existence of a dynamic gp63 gene organization in Leishmania of the braziliensis complex.

The data needed to develop analytical models of trypanosomiasis transmission have become available only recently. By making some simplifying assumptions, models of the dynamics of the disease in vector, cattle and wild mammal populations can be constructed in order to determine criteria for successful disease control by mass and targetted chemotherapy, and by vector control. The heterogeneity in transmission due to tsetse fly feeding preferences and the variability of immunological characteristics among the vertebrate hosts account for differences in prevalence of Trypanosoma vivax and T. congolense, and also lead to an increase in the basic reproductive rates of the parasites and a corresponding decrease in the vector population density threshold for disease eradication or persistence. The long life-span of the vectors relative to the duration of the parasites' developmental period lead to high infection rates in the vector and high values of R0. The efficacy of chemotherapeutic regimes depends on the relationship between treatment rate and the duration of prophylaxis conferred by the drugs used. The model's predictions of the effects of vector control are shown to be in broad agreement with published field data for Mkwaja Ranch, Tanzania. Vector control programmes are frequently blighted by reinvasion, and the implications of this are discussed in terms of a model for fly immigration. With immigration of vectors, the disease is always endemic, though the infection rate in the fly population is modified by the effect of differential mortalities inside and outside the controlled area on cohorts of incubating flies. Sensitivity analysis of the model, using Monte-Carlo methods, enables an assessment of the relative importance of the parameters to be made. The results emphasize the need for studies of the wild animal reservoir to be carried out alongside entomological surveys. The relative accuracy with which field measurements need to be made in order to minimize the uncertainty in predictions of trypanosomiasis prevalence is discussed.

Controlled human malaria infections (CHMIs) are a powerful tool to assess the efficacy of drugs and/or vaccine candidates, but also to study anti-malarial immune responses at well-defined time points after infection. In this review, we discuss the insights that CHMI trials have provided into early immune activation and regulation during acute infection, and the capacity to induce and maintain immunological memory. Importantly, these studies show that a single infection is sufficient to induce long-lasting parasite-specific T- and B-cell memory responses, and suggest that blood-stage induced regulatory responses can limit inflammation both in ongoing and potentially future infections. As future perspective of investigation in CHMIs, we discuss the role of innate cell subsets, the interplay between innate and adaptive immune activation and the potential modulation of these responses after natural pre-exposure.