Here we examined the impact of host immunity on relationships between parasite virulence, transmission rate, intrinsic growth rate and host recovery rate in the rodent malaria parasite, Plasmodium chabaudi. Groups of naïve and immunized mice were infected with 1 of 10 cloned lines of parasites and their infection dynamics were monitored for 19 days. We found that (1) host immunity reduced the growth rate, virulence, transmission rate and infection length, with a consequent 3-fold reduction in life-time transmission potential, (2) clone means for these traits ranked similarly across naïve and immunized mice, (3) regression slopes of transmission potential on growth rate, virulence and infection length were similar in naïve and immunized mice, (4) virulence and infection length were positively correlated in immunized but not naïve mice, and (5) for a similar level of parasite growth rate and virulence, transmission potential and infection length were lower in immunized than naïve mice. Thus host immunity reduced all these fitness traits in a manner consistent with direct parasite-driven biological links among them. These results support the basic assumption underlying our theory that predicts that anti-disease vaccines will select for higher virulence in those microparasites for which virulence is integrally linked to transmission.

Studies of population genetic structure of parasites can be used to infer which parasite genes are under selection. Here, the population structure of 4 genes associated with drug resistance of Plasmodium falciparum (the chloroquine resistance transporter, pfcrt, dihydrofolate reductase, dhfr, dihydropteroate synthase, dhps, and multi-drug resistance, pfmdr-1) were examined in parasite populations in 3 villages in eastern Sudan and in an urban area of Khartoum, the capital. In order to differentiate the effects of drug selection from neutral influences on population structure, parasites were also genotyped for 3 putatively neutral microsatellite loci (polyα, TA81 and pfg377), and for 2 antigenic loci that are either under balancing selection or neutral, merozoite surface protein 1 and 2, (MSP-1 and MSP-2). Cross-sectional surveys were carried out during the peak transmission (wet) season and in the ensuing dry season. No significant variation in frequencies of MSP-1 and MSP-2 alleles was seen among villages in the eastern region and between the villages and Khartoum, nor between the wet and dry season. However, the drug resistance genes, pfmdr-1, pfcrt and dhfr and to a lesser extent the microsatellite loci showed high FST values when comparing villages with Khartoum, indicating strong geographical differentiation at these loci. Moreover, variation in frequencies of the drug resistance genes, pfmdr-1, pfcrt and dhfr, was observed between the wet and dry season. These differences most probably reflect the variation in drug pressure between each region, and in drug usage between the wet and dry season in a given region.

Intracellular bacteria of the genus Wolbachia are found in most filarial nematodes, but are lacking in some species like Acanthocheilonema viteae. Due to their symbiotic nature and their role in the pathology of filarial infections they are considered to be potential targets for intervention against filarial infections in man. Infection of A. viteae (a species which does not naturally carry Wolbachia) with Wolbachia bacteria could allow comparative studies on the effect of the endobacterium on the parasite and on the host's immune systems. As a step towards such studies we microinjected adult female A. viteae with Wolbachia obtained from Litomosoides sigmodontis. The bacteria were isolated from L. sigmodontis by density-gradient centrifugation, microinjected into A. viteae worms and bacterial DNA detected by PCR with Wolbachia specific primers (ftsZ gene). Microinjected worms were cultured in vitro, and 81% survived for 10 days. Implantation of microinjected worms into Meriones unguiculatus, the rodent host of A. viteae resulted in 38% survival. The DNA of the microinjected worms recovered from jirds 8 weeks after implantation contained Wolbachia DNA as shown by PCR, suggesting that Wolbachia of L. sigmodontis can be horizontally transmitted to A. viteae.

This paper reports the comparative antimalarial efficacy of intravenous artelinate and artesunate in rats. Prior to efficacy experiments, a Plasmodium berghei–Sprague-Dawley rat model of malaria was developed, in which the clearance effects of intravenous drugs could be readily compared. In efficacy experiments, groups of P. berghei-infected rats were given 3 daily intravenous treatments of artelinate or artesunate at molar equivalent dose rates (total of 0–191·2 μmoles/kg). Artelinate was superior to artesunate in terms of clearance (100% clearance dose of 95·6 μmoles/kg (40 mg/kg) versus 191·2 μmoles/kg for AS (73·4 mg/kg)) and parasite clearance time (1·7±0·5 days for AL versus 2·7±0·5 days for AS at a dose rate of 191·2 μmoles/kg, P<0·01). No frank clinical toxicity was observed, though both artesunate and artelinate induced dose-related vascular necrosis at the site of injection. The necrosis was less severe and reversible when the drugs were administered via femoral, rather than tail/foot veins. The data suggest that the P. berghei–7-week-old Sprague-Dawley rat model of malaria is reproducible and useful for assessing the efficacy of antimalarials and that artelinate is at least as potent, and safe, as artesunate, the leading clinical treatment for severe malaria.

Genes encoding small subunit ribosomal RNA (SSUrRNA) of 16 Blastocystis isolates from humans and other animals were amplified by the polymerase chain reaction, and the corresponding fragments were cloned and sequenced. Alignment of these sequences with the previously reported ones indicated the presence of 7 different sequence patterns in the highly variable regions of the small subunit ribosomal RNA. Phylogenetic reconstruction analysis using Proteromonas lacertae as the outgroup clearly demonstrated that the 7 groups with the different sequence patterns are separated to form independent clades, 5 of which consisted of the Blastocystis isolates from both humans (B. hominis) and other animals. The presence of 3 higher order clades was also clearly supported in the phylogenetic tree. However, a relationship among the 4 groups including these 3 higher order clades was not settled with statistical confidence. The remarkable heterogeneity of small subunit ribosomal RNAs among different Blastocystis isolates found in this study confirmed, with sequence-based evidence, that these organisms are genetically highly divergent in spite of their morphological identity. The highly variable small subunit ribosomal RNA regions among the distinct groups will provide useful information for the development of group-specific diagnostic primers.

Cytokine responses to Leishmania infection begin very early in infection, and differ between susceptible and resistant mice. Susceptibility to chronic Leishmania infection has been associated with increased haematopoiesis. To analyse the effect that acute infection with L. major has on bone-marrow haematopoiesis in susceptible (BALB/c) and resistant (CBA) mice, we enumerated erythroid progenitors and granulocyte-monocyte progenitors 3 days after infection. We found that haematopoiesis was stimulated in BALB/c mice infected with L. major, while haematopoiesis was inhibited in CBA mice. We found that this effect could be partially explained by cytokine production: interleukin-4 was involved in stimulation of BALB/c haematopoiesis and tumour necrosis factor-α was involved in inhibition of CBA haematopoiesis. Our conclusions are that haematopoietic changes occur shortly after L. major infection, and may be related to disease outcome.

Perkinsus marinus is responsible for a chronic disease (Dermo) of the Eastern oyster, Crassostrea virginica. In order to simulate the in vivo environment more closely, a chemically defined medium (JL-ODRP-3) was supplemented with tissue homogenate extracts or plasma from oysters possessing varying degrees of susceptibility to P. marinus infection. In media supplemented with extracts from highly susceptible oysters (C. virginica), P. marinus cells secreted elevated amounts of a set of low molecular weight serine proteases (LMP: 30–45 kDa) as assessed by enhanced digestion within gelatin-substrate SDS–PAGE gels. Oyster species of low susceptibility (C. gigas and C. ariakensis) did not exhibit this ability to upregulate P. marinus LMP expression. Oyster extract supplementation also led to pronounced changes in P. marinus cellular morphology, such that the cells were comparable to those observed within naturally infected oysters.

The increased occurrence of pollutants in ecosystems is a continuing area of concern. It is known that numerous diseases of wild aquatic animals can occur with decreased or increased prevalences in areas associated with high or chronic levels of pollution. This may have serious implications for environmental health. There has consequently been an increasing number of laboratory and field studies on disease transmission under polluted conditions, especially focusing on digeneans of medical or economic importance. The effect of pollutants to the transmission of larval digeneans (miracidia, cercariae, metacercariae) and snail-digenean interactions is therefore considered. An overview and interpretation of the published literature on laboratory and field studies is provided. It is apparent from these studies that the influence of pollutants on digenean transmission is highly complex with much of the observed effects in the laboratory often masked by a complexity of other factors in the field. Future studies would benefit from a standardisation of experimental procedures, increasing the number of combined laboratory and field studies, and increasing the complexity of the experiments undertaken.

Borrelia burgdorferi sensu lato (s.l.) is maintained in nature by complex zoonotic transmission cycles, involving a large variety of vertebrates as hosts and hard ticks of the genus Ixodes as vectors. Recent studies suggest that the genospecies of B. burgdorferi s.l. and sometimes their subtypes are propagated by different spectra of hosts, mainly birds and rodents. In order to test the concept of host-association, we analysed the relationships between Borrelia genospecies, rodent hosts and I. ricinus ticks in an endemic focus of Lyme borreliosis in western Slovakia. Rodents and questing ticks were collected at a forested lowland locality near Bratislava. Tick infestation levels on rodents were determined, and spirochaete infections in ticks and in ear punch biopsies were analysed by PCR followed by genotyping. Mice were more heavily infested with ticks than bank voles, and a higher proportion of mice was infected with spirochaetes than voles. However, the infectivity of voles was much higher than that of mice. The vast majority of infections detected in the skin and in ticks feeding on the rodents represented B. afzelii. In contrast, more than half of all infections in questing ticks collected in the same region of Slovakia were identified as B. valaisiana and B. garinii. In conclusion, whilst the study reveals that mice and voles play different quantitative roles in the ecology of Lyme borreliosis, it demonstrates that B. afzelii is specifically maintained by European rodents, validating the concept of host-association of B. burgdorferi s.l.

The objectives of this study were (a) to evaluate the sensitivity and specificity of fœtal Doppler indices for the prediction of abnormal fœtal heart rate (aFHR) at delivery after malaria crisis and (b) to test Doppler parameters against crisis duration for predicting aFHR. Every day during the malaria crisis, the umbilical and cerebral vascular resistance indices were measured by Doppler. These indices allowed evaluation of the amplitude of the fœtal flow redistribution induced by malaria (C/U=cerebral resistance/umbilical resistance ratio), the duration of the flow redistribution period and the hypoxic index (mean %C/U change×crisis duration). It was found that the mean duration of the flow redistribution period was: 7±2 days, mean C/U change −7%±4, hypoxic index −56±37, prematures 35%, and aFHR 17%. An hypoxic index >150 predicted occurrence of aFHR with high sensitivity and specificity (100%/91%). The highest fœtal flow disturbance (max %C/U) and the duration of the period with flow disturbance (>7 days) predicted aFHR at delivery with a sensitivity of 10% and 40% and a specificity of 77% and 78%. It was concluded that the hypoxic index was more predictive of aFHR at delivery than the amplitude or the duration (i.e. crisis duration) of the fœtal flow redistribution.

In Europe, the zoonotic cycle of Babesia microti has not been determined so far. Recently, B. microti was detected in Ixodes ricinus ticks in Slovenia by using molecular methods. In order to investigate the mammalian hosts of B. microti in Slovenia we collected 261 small mammals representing 11 species. They were tested for the presence of babesial parasites with a PCR assay based on the nuclear small subunit rRNA gene (nss-rDNA). The bank vole (Clethrionomys glareolus) and yellow-necked mouse (Apodemus flavicollis) were infected with B. microti. The prevalence rate was 15·9% for C. glareolus and 11·8% for A. flavicollis. Nucleotide sequences of amplified portions of B. microti nss-rDNA from C. glareolus and A. flavicollis were indistinguishable from each other and identical with those previously described in I. ricinus ticks collected in Slovenia. The results of this study represent molecular evidence of B. microti in small mammals in Europe.

Mutations in pfcrt K76T are associated with chloroquine resistance in Plasmodium falciparum. Previous studies of K76T mutations in Senegal reported the association of T76 with in vitro-resistant isolates, but this mutation was also prevalent in chloroquine-sensitive isolates. This suggests involvement of additional genetic loci in modulating chloroquine resistance. Additional pfcrt polymorphisms at codons A220S, Q271E, N326S and R371I have been found in chloroquine-resistant isolates. We wanted to test if sequential acquisition of mutations at these codons leads to in vitro chloroquine resistance. Stepwise accumulation of mutations was not detected, rather there was almost complete linkage between the pfcrt K76T mutation and polymorphisms in these codons. Therefore these additional polymorphisms do not enhance the correlation between pfcrt T76 and chloroquine resistance in Senegal. These data suggest that in vitro chloroquine resistance requires the genetic background of the pfcrt K76T mutation and additional mutations in genetic loci outside the pfcrt gene.

Protein tyrosine phosphatases (PTPases) have been described as virulence factors in different pathogenic microorganisms. The pathogenic process by Entamoeba histolytica is a multifactorial phenomenon that occurs in 3 steps: adhesion, cytolytic and cytotoxic effect, and phagocytosis. Lytic enzymes may participate during the second part of this process. In this work, we determined that purified membrane-bound acid phosphatase (MAP) from E. histolytica trophozoites has PTPase activity. The enzyme specifically dephosphorylated O-phospho-L-tyrosine at optimum pH of 5·0, with little activity towards O-phospho-L-serine, O-phospho-L-threonine, and ATP. It was inhibited by ammonium molybdate and sodium tungstate, and trifluoperazine did not show any effect. A monoclonal antibody against the catalytic domain of the human placental PTPase 1B, cross-reacted with a 55 kDa molecule present in the solubilized fraction. The interaction of the amoebic PTPase with HeLa cells resulted in the alteration of the cell actin cytoskeleton by disruption of the actin stress fibres.

A species of Besnoitia from naturally infected rabbits from Argentina was propagated experimentally in mice, gerbils, rabbits, cats, and cell cultures. Cats fed tissue cysts from rabbits shed oocysts with a prepatent period of nine to 13 days. Sporulated oocysts were infective to gerbils, rabbits, outbred Swiss Webster and interferon gamma gene knockout mice. Bradyzoites were infective orally to gerbils and cats. Tachyzoites were successfully cultivated and maintained in vitro in bovine monocytes and African green monkey kidney cells. Schizonts were seen in the lamina propria of the small intestine of cats fed tissue cysts; the largest ones measured 52×45 μm. Schizonts were also present in mesenteric lymph nodes, livers, and other extra-intestinal organs of cats fed tissue cysts. Oocysts were 10–14×10–13 μm in size. This rabbit-derived species of Besnoitia resembled B. darlingi of the North American opossum, Didelphis virginiana with an opossum-cat cycle, but it was not transmissible to D. virginiana, and B. darlingi of opossums was not transmissible to rabbits. Based on biological, serological, antigenic, and molecular differences between the rabbit and the opossum Besnoitia, a new name, B. oryctofelisi is proposed for the parasite from domestic rabbits from Argentina.

Eight major reviews are cited to indicate a recent knowledge explosion on the use of marine parasites as potential indicators of pollution. A literature update is given for the period 1995–2001. An analysis of the publications cited is used to provide 10 refined criteria for selecting parasites as indicator/monitor species. Previously unpublished data on Diclidophora merlangi and Dictyocotyle coeliaca confirm their value as potential indicators of hydrocarbon pollution in the North Sea. An extensive knowledge of D. merlangi is summarised to emphasize its potential value as an indicator species and also to encourage studies on the health status and immune responses of its host when subjected to pollutant stressors and infection with this monogenean. A discussion focuses on publications which have reported significant recent advances in this area of research and also on accompanying issues, problems and controversies. These selected publications are used to suggest species, stages in the development of species and assemblages of species worthy of further more detailed investigations into their value as indicators/monitors of pollution. It is predicted that further good progress will be made when contaminants can be accurately identified, their precise effects on both host and parasite can be measured by histochemical and biological methods and the roles of contaminants and parasites in causing disease can be assessed separately. About 100 references are cited.

Although purely vertically transmitted parasites are predicted to cause low pathogenicity in their hosts, the effects of such parasites on host fitness under stressful environmental conditions have not previously been assessed. Here, we investigate the effects of Nosema granulosis, a vertically transmitted, microsporidian parasite of the brackish water amphipod Gammarus duebeni, on host growth and survival under conditions of host–host competition and limited food. The parasite had no effect on host survival, but caused a reduction in juvenile growth. Stressful environmental conditions also led to a reduction in G. duebeni growth. However, we found no evidence to support the prediction that parasitized hosts would suffer a greater reduction in fitness than uninfected hosts under adverse environmental conditions. We interpret our results in the context of selection for successful vertical parasite transmission.

NcSAG1 and NcSRS2, the two major immunodominant tachyzoite surface antigens of the apicomplexan parasite Neospora caninum, were investigated for their potential as vaccine candidates in mice. Recombinant recNcSRS2 and recNcSAG1 were expressed in Escherichia coli as poly-histidine-tagged fusion proteins. Separate groups of mice were immunized with purified recNcSAG1, recNcSRS2, or a combination of both, and were then challenged with N. caninum tachyzoites. Subsequent experiments included intramuscular vaccination of mice with the eukaryotic expression plasmid pcDNA3 containing either NcSRS2 or NcSAG1 cDNA inserts, followed by a single booster with the corresponding recombinant antigens. Immunization with a crude somatic antigen (NC1-extract) was included in the experiments. Following challenge, the presence of the parasite in the different organs was assessed by a N. caninum-specific PCR, while the parasite burden in infected brain tissue was assessed by quantitative real-time PCR. Immunization of mice employing individual recombinant antigens, or combined recNcSAG1/recNcSRS2, resulted in a lower degree of protection against cerebral infection, when compared to combined DNA/recombinant antigen vaccination. Serological analysis showed that this protective effect was associated with the occurrence of antibodies directed against native parasite antigens in those animals receiving combined DNA/recombinant antigen vaccination. Conversely, mice immunized with recombinant antigens alone generated antibodies recognizing only the recombinant antigens. Mice experiencing clinical signs such as walking disorders, rounded back, apathy and paralysis were observed only in the untreated positive control groups, but never in the vaccinated groups. Our results suggest that a combined DNA/recombinant antigen-vaccine, based on NcSAG1 and NcSRS2, respectively, exhibited a highly significant protective effect against experimentally induced cerebral neosporosis in mice.

This study reports that inhibition of Leishmania Topo-I with the minor groove-binding ligands (MGBLs) Hoechst 33342 (Ho342) blocks parasite growth in culture by mechanisms involving DNA breakage. While Ho342 inhibited the replication of several species of Leishmania in a dose- and time-dependent manner, Ho258 was not effective. Cytofluorometric analysis suggested that superior effectiveness of Ho342 over Ho258 was attributed to Leishmania parasites being more permeable toward Ho342. This observation was supported by the ability of both Ho342 and Ho258 to block the relaxation of supercoiled pBR322 DNA by Leishmania Topo-I. The Ho342 specificity toward L. donovani Topo-I was reinforced by the observation that increased Topo-I gene expression and Topo-I activity in Leishmania was paralleled by augmented resistance for this compound. Furthermore, the capacity of NaCl treatment to reverse MGBL-mediated DNA break suggests that Ho342 targetted Topo-I. Moreover, we observed that Ho342-inducible arrest of Leishmania growth was accompanied by G1 arrest and induction of cell death that closely resembles apoptosis. Taken together, our results suggest that MGBL compounds show promise as Topo-I inhibitors against Leishmania infection.

Schistosomes are digenean flukes, parasitic of birds, mammals and crocodiles. The family Schistosomatidae contains species of considerable medical and veterinary importance, which cause the disease schistosomiasis. Previous studies, both morphological and molecular, which have provided a good deal of information on the phylogenetics of this group, have been limited in the number of species investigated or the type or extent of molecular data used. This paper presents the most comprehensive phylogeny to date, based on the sequences of 3 genes, complete ribosomal small subunit rRNA and large ribosomal subunit rRNA, and mitochondrial cytochrome oxidase 1, sequenced from 30 taxa including at least 1 representative from 10 of the 13 known genera of the Schistosomatidae and 17 of the 20 recognized Schistosoma species. The phylogeny is examined using morphological characters, intermediate and definitive host associations and biogeography. Theories as to the origins and spread of Schistosoma are also explored. The principal findings are that Ornithobilharzia and Austrobilharzia form a sister group to the Schistosoma; mammalian schistosomes appear paraphyletic and 2 Trichobilharzia species, T. ocellata and T. szidati, seem to be synonymous. The position of Orientobilharzia within the Schistosoma is confirmed, as is an Asian origin for the Schistosoma, followed by subsequent dispersal through India and Africa.