To compare the structures of natural and re-established populations of Ascaris in humans, universal (mass) chemotherapy was carried out at the beginning and the end of the study year using pyrantel pamoate. Worms expelled within 48 h of treatment were collected, their sex determined, and measurements made of length, width and weight. Length was used as the criterion for estimating the developmental stage of the worms. In comparison with the natural population, the re-established population displayed similar sex ratio as well as distribution patterns among individuals and age groups of the host. However, the mean worm burden of the re-established population was significantly decreased, with a reduction of burdens in children aged 5–9 years. Also, the re-established population showed significant changes in population structure and worm measurements in that it comprised more immature and less fertile males, less fertile and more senile females, smaller and lighter males, larger (but not heavier) females than the natural population. The results suggested that the re-established Ascaris population did not restore to its original status in relation to mean density, composition and fecundity. Therefore, universal treatment once a year should decrease the transmission of Ascaris in humans. Combined with previous results for the same study sites, the present findings also indicated that caution is warranted to avoid misleading conclusions when using prevalence and faecal egg counts as parameters for evaluating the success of control programmes.

The frequency distribution of an ectoparasitic mite, Gammaridacarus orchestoideae, on its amphipod host, Orchestoidea corniculata, was found to differ significantly from random for all monthly samples taken between October 1977 and October 1978. The negative binomial distribution provided a good fit to these aggregated distributions. The degree of aggregation was negatively correlated with the prevalence of infestation. Prevalence and intensity were highest in the winter, when the degree of aggregation was lowest, and vice-versa in the late summer. This seasonal pattern can be explained through changes in size and density of the host population, which are associated with changes in the size of the habitat of the hosts. Within each sample the host population was highly heterogeneous with regard to infestation by mites. Females carried heavier loads of mites than did males. Both prevalence and intensity were low in the post-moult stages of the moult cycle. Reproductive females showed lower prevalence and intensity of infestation than did either non-reproductive females or males. Analysis of the regression analysis of ‘mean crowding’ on mean density also indicated that aggregation stemmed from a non-random distribution of individual parasites, rather than from clumping of the infective stages of the parasite. Heterogeneity of the host population is suggested as an important cause of the aggregated distribution of the parasite population.

Infection with Hymenolepis microstoma significantly affected the lipid metabolism of young male Balb/C mice. Infection increased the rates of hepatic fatty acid and cholesterol synthesis and cholesterol synthesis by the gut. Decreases were recorded in testicular fatty acid synthesis and in the weights of testes and white epididymal adipose tissue. Plasma glucose decreased rapidly during infection. The observed changes in lipogenesis could not be attributed to changes in food intake or body temperature. The changes are discussed in relation to nutritional interactions between host and parasite and the possible effects on host hormone levels. The presence of newly synthesized fatty acid in H. microstoma is also reported.

Alaria arisaemoides, n.sp., is described from the red fox, Vulpes fulva. The attachment of this parasite to its host and the host reaction are discussed in detail.

A description of Zalophotrema hepaticum is presented. Study of this species and review of the literature show that the genera assigned to the two families, Fasciolopsidae and Campulidae, may be included in a single family. Furthermore, since Fasciola is the nomenclatorial type of the family to which it belongs, the rules of nomenclature do not permit the substitution of the name Fasciolopsidae for Fasciolidae. Consequently the family Fasciolidae is restored with three sub-families, Fasciolinae, Fasciolopsinae, and Campulinae. A new genus, Synthesium, is erected to contain Distomum tursionis Marchi.

The external structure of the capitulum of all stages of Dermacentor parumapertus is described in detail. The capitulum is divisible into an extra-basis and basis regions. The former consists of a dorsally grooved hypostome or food channel overlapped by a labral membrane, along its whole length. The salivary channel lies above the labral membrane, being bordered laterally by the meso-ventral margins of the outer cheliceral sheaths. Within the basis a vertical wall separates the base of the palpal cavity from the rest of the basis. This wall is produced backwards to form a wing or ala on either side of the pharynx and to it are attached dilator and constrictor muscles. Opening of the fore-part of the pharynx, i.e. where it is in the form of a V-shaped depression overlapped by a wedge, is effected by ventral and ventro-lateral dilator muscles, and closure by the elasticity of the pharyngeal walls.

The pharynx, oesophagus and salivary glands are described.

Trypanosoma brucei variable surface glycoproteins (VSGs), isolated from some antigenic types of trypanosomes, degraded during isolation. We show that this degradation occurred immediately after breakage of the organism, presumably because of liberation of internal enzymes, and resulted in heterogeneity of isolated VSGs with respect to charge and/or molecular weight. Degradation and consequent heterogeneity of these VSGs could be abolished by releasing VSG from the trypanosome surface without breakage of the organism. The method was a modification of an incubation and shaking procedure initially described for Trypanosoma congolense (Reinwald, Rautenberg & Risse, 1979). WaTat 1.11 VSG released by this method and isolated, had a molecular weight (mol. wt) of 63000 and bound to a heterologous anti-VSG serum. VSG isolated from the same trypanosomes following breakage of organisms was of lower molecular weight. One such WaTat 1.11 VSG fragment of 42000 mol. wt, did not bind to the heterologous anti-VSG serum and therefore lacked cross-reacting antigenic determinants present in the 63000 mol. wt VSG

Many parasites survive harsh periods together with their hosts. Without the possibility of horizontal transmission during host diapause, parasite persistence depends entirely on host survival. We therefore hypothesize that a parasite should be avirulent during its host's diapausing stage. In contrast, the parasite may express higher virulence, i.e. parasite-induced fitness reduction of the host, during host life stages with good opportunities for horizontal transmission. Here we study the effects of a vertically and horizontally transmitted microsporidium parasite, Hamiltosporidium tvaerminnensis, on the quantity and survival of resting eggs of its host Daphnia magna. We find that the parasite did not affect egg volume, hatching success and time to hatching of the Daphnia's resting eggs, although it did strongly reduce the number of resting eggs produced by infected females, revealing high virulence during the non-diapause phase of the host's life cycle. These results also explain another aspect of this system – namely the strong decline in natural population prevalence across diapause. This decline is not caused by mortality in infected resting stages, as was previously hypothesized, but because infected female hosts produce lower rates of resting eggs. Together, these results help explain the epidemiological dynamics of a microsporidian disease and highlight the adaptive nature of life stage-dependent parasite virulence.

Sarcocystis neurona is a terrestrial parasite that can cause fatal encephalitis in the endangered Southern sea otter (Enhydra lutris nereis). To date, neither risk factors associated with marine contamination nor the route of S. neurona infection to marine mammals has been described. This study evaluated coastal S. neurona contamination using California mussels (Mytilus californianus) as sentinels for pathogen pollution. A field investigation was designed to test the hypotheses that (1) mussels can serve as sentinels for S. neurona contamination, and (2) S. neurona contamination in mussels would be highest during the rainy season and in mussels collected near freshwater. Initial validation of molecular assays through sporocyst spiking experiments revealed the ITS-1500 assay to be most sensitive for detection of S. neurona, consistently yielding parasite amplification at concentrations ⩾5 sporocysts/1 mL mussel haemolymph. Assays were then applied on 959 wild-caught mussels, with detection of S. neurona confirmed using sequence analysis in three mussels. Validated molecular assays for S. neurona detection in mussels provide a novel toolset for investigating marine contamination with this parasite, while confirmation of S. neurona in wild mussels suggests that uptake by invertebrates may serve as a route of transmission to susceptible marine animals.

The object of this communication is to focus attention on certain interesting facts concerning the mid-gut of the larva of Anopheles subpictus previously reported in outline by us (Dasgupta & Ray, 1954,1955). In the course of our routine examination on Anopheles larvae collected from different parts of the city and its outskirts, we directed our inquiry on certain histochemical problems. Our observation was mainly concentrated on detecting the sites of alkaline phosphatase activity in the mid-gut. Our interest, however, was quickly aroused by the occurrence in the secretory cells of the mid-gut of Feulgen-positive intra-nuclear inclusions. So far as we are aware, inclusion bodies of this nature have never been reported from Diptera.

1. Between November 1936 and February 1937, ninety-six rabbits were examined, whilst between August 1937 and July 1938, 446 rabbits were examined for cestode parasites. The rabbits were obtained from the same area.

2. The rabbits were infected with the following cestodes to the extent given, for the two periods respectively:

3. Two species of the genus Hymenolepis are recorded for the first time from the rabbit, and they are briefly described.

4. The seasonal fluctuations in the incidence of the above cestodes are discussed.

5. The span of life of both Cittotaenia pectinata and C. denticulata is seen to be not greater than 10 months, and evidence is given to show that the intermediate host of C. denticulata is available between April and December, and that of C. pectinata from August to April.

6. Evidence of host and age resistance is demonstrated in Cysticercus pisiformis.

The host-specificity of monocystids was investigated experimentally by infesting infection-free Dendrobaena subrubicunda f. typica with sporocysts of Apolocystis megagranulata and A. lavernensis normally found in Dendrobaena subrubicunda and Allolobophora longa respectively. An attempt to infect worms raised free from infection with sporocysts of Monocystis agilis normally harboured by Lumbricus spp. was unsuccessful. Eighteen of the thirty identified monocystids were found to be monobiotic (species-specific), eleven were oligobiotic (genus-specific) and only one was polybiotic (family-specific).

The writer wishes to express his sincere appreciation to Dr Anne Terry for her advice and useful suggestions, and to Mr D. Etherington, the head of department, for his encouragements throughout the research period.

Hymenolepis diminuta migrates up the small intestine in response to feeding the host 1 g of glucose. Locomotion during migration may result from fixed patterns of retrograde peristaltic-like waves in the strobila of the tapeworm which propel the organism against the normal expulsive forces in the small intestine. The peristaltic-like locomotory waves occur in a gradient along the strobila with a frequency of 24·9±0·9 cycles/min in the anterior segments of the worm, decreasing linearly to 6·6±1·4 cycles/min in the posterior segments of the worm. Chemical signals, isolated from the small intestine of fed hosts, which stimulate migration behaviour in vivo do not alter the behaviour of the scolex or strobila in vitro. Removal of the scolex containing the cerebral ganglia does not alter the frequency or pattern of locomotory activity in the strobila. After the worm is cut into pieces, each region generates the pattern of locomotory activity that is appropriate for that region. These data suggest that the peripheral nervous system, and not the central nervous system, is responsible for the coordination of the fixed patterns of locomotory activity in these tapeworms.

The plerocercoid of Callitetrarhynchus gracilis was found in the body cavity of 14 species of fishes from Bermuda. The scolex, having completed its development, continues to grow within the blastocyst. The two mobile bothridia possess lateral grooves containing backwardly directed spines. Rapid evagination of the proboscides is effected by two layers of contra-rotating spiral muscles in the walls of the proboscis bulbs. The proboscis retractor is protected from constriction, during contraction of the bulbs, by a rigid ring at the junction of bulb and sheath. Nine series of extrinsic muscles anchor the proboscis sheaths to the body wall and a ladder-like series of dorsal, ventral and lateral muscles anchors the bulbs to one another. The bulbar nerves arise from the lateral nerve cords and are joined by a series of central ring commissures along the length of the bulbs. Uniciliate sensilla occur on the scolex and glandular cells in the peduncle.

Oogenesis in Brugia pahangi has been studied by means of the aceto-orcein chromosomal squash technique and light-microscope autoradiography. The use of colchicine has demonstrated a 2–3 mm terminal germinative zone within the ovary, in which continuous and rapid mitotic division of germ cells occurs. In 80% of the gonads, oocytes within a 1–2 mm length of the ovary proximal to the germinative zone were at the prophase of meiosis I. Primary oocytes with markedly less condensed chromatin, apparently interphase cells, were observed in the corresponding region of the ovary in the remaining 20% of material examined. A cyclical or phased development of primary oocytes is suggested. Autoradiographic studies, concerned with the incorporation of [5-3H]uridine into germ cells of B. pahangi in vitro, further suggest that the onset of meiotic prophase is associated with the initiation of high RNA synthetic activity. Following meiotic prophase, oocytes complete meiosis I before entering a period of growth during which the chromatin material is decondensed. Recondensation of chromosomes prior to meiosis II is only observed after fertilization within the seminal receptacle. On completion of meiosis II, with the extrusion of a polar body, the haploid chromosome complement of the female unites with that of the male, re-establishing the diploid number of the zygote (2n = 10).

Eukaryotic 5S rRNA, synthesized by RNA polymerase III (Pol III), is an essential component of the large ribosomal subunit. Most organisms contain hundreds of 5S rRNA genes organized into tandem arrays. However, the genome of the protozoan parasite Leishmania major contains only 11 copies of the 5S rRNA gene, which are interspersed and associated with other Pol III-transcribed genes. Here we report that, in general, the number and order of the 5S rRNA genes is conserved between different species of Leishmania. While in most organisms 5S rRNA genes are normally associated with the nucleolus, combined fluorescent in situ hybridization and indirect immunofluorescence experiments showed that 5S rRNA genes are mainly located at the nuclear periphery in L. major. Similarly, the tandemly repeated 5S rRNA genes in Trypanosoma cruzi are dispersed throughout the nucleus. In contrast, 5S rRNA transcripts in L. major were localized within the nucleolus, and scattered throughout the cytoplasm, where mature ribosomes are located. Unlike other rRNA species, stable antisense RNA complementary to 5S rRNA is not detected in L. major.

Sarcocystis neurona is an apicomplexan parasite that causes severe neurological disease in horses and marine mammals. The Apicomplexa are all obligate intracellular parasites that lack purine biosynthesis pathways and rely on the host cell for their purine requirements. Hypoxanthine-xanthine-guanine phosphoribosyltransferase (HXGPRT) and adenosine kinase (AK) are key enzymes that function in two complementary purine salvage pathways in apicomplexans. Bioinformatic searches of the S. neurona genome revealed genes encoding HXGPRT, AK and all of the major purine salvage enzymes except purine nucleoside phosphorylase. Wild-type S. neurona were able to grow in the presence of mycophenolic acid (MPA) but were inhibited by 6-thioxanthine (6-TX), suggesting that the pathways involving either HXGPRT or AK are functional in this parasite. Prior work with Toxoplasma gondii demonstrated the utility of HXGPRT as a positive-negative selection marker. To enable the use of HXGPRT in S. neurona, the SnHXGPRT gene sequence was determined and a gene-targeting plasmid was transfected into S. neurona. SnHXGPRT-deficient mutants were selected with 6-TX, and single-cell clones were obtained. These Sn∆HXG parasites were susceptible to MPA and could be complemented using the heterologous T. gondii HXGPRT gene. In summary, S. neurona possesses both purine salvage pathways described in apicomplexans, thus allowing the use of HXGPRT as a positive-negative drug selection marker in this parasite.

Nosema leptinotarsae Lipa, 1968 is a microsporidian pathogen of the Colorado potato beetle, Leptinotarsa decemlineata Say. (Coleoptera: Chrysomelidae). To determine the phylogenetic status of N. leptinotarsae, the 16S SSU rRNA gene was sequenced (GenBank Accession No. MN841279) and compared phylogenetically against 21 microsporidian 16S SSU rRNA sequences using neighbour-joining and maximum-parsimony methods. The per cent identities of the N. leptinotarsae and other members of the Nosema–Vairimorpha clade ranged from 78.1 to 98.5%. Pairwise phylogenetic distances between the N. leptinotarsae and other species ranged from 0.009 to 0.320. Phylogenetic analysis shows clearly that N. leptinotarsae is a member of the Vairimorpha clade rather than the Nosema clade. The sequence divergence and morphological traits separated the N. leptinotarsae from other species in the Vairimorpha complex. As a result, a new assignment of Vairimorpha leptinotarsae comb. nov. has been implemented for N. leptinotarsae according to the phylogenetical positioning in the present study.

This paper records the presence of a new species of trypanosome in the lizard Uranoscodon superciliosa L. (family Iguanidae), caught near Codajaz, Amazonas, Brazil, in August 1964 during the Guy's Hospital Expedition to the Lower Amazon.

Examination of a methanol-fixed and Giemsa-stained smear of blood taken from the heart of the lizard showed a heavy infection of trypanosomes. Camera lucida drawings of twenty were made, measurements being determined with dividers and a map-measuring wheel. The animal was preserved in 10% formalin, portions of liver, spleen, brain, heart, and lung being later extracted. Sections 5 μ in thickness were cut and stained in Ehrlich's haematoxylin and eosin, and in Giemsa's stain.

The chief distinguishing feature of the trypanosomes was their comparatively enormous size, up to 124 μ in total length, including the free flagellum, and 19 μ in width. The cytoplasm stained deep blue in Giemsa's stain, there being little indication of any vacuoles or inclusions. The posterior end was generally less intensely stained, and in certain cases pale, narrow, channel-like extensions from this region forward into the main body of the organism could be detected (Fig. 1). The nucleus, elongated and rather variable in shape, was distinguished by being less deeply coloured than the surrounding cytoplasm; it lay slightly posterior to the mid-point of the body, its longest diameter being parallel to the longitudinal axis of the animal. The kinetoplast, situated slightly posterior to the nucleus, was usually of circular shape, staining deep red; from it arose the flagellum, which passed forward along the margin of an undulating membrane and terminated in a free portion at the anterior end. Measurements of the organisms are given in Table 1.

Protective immunity against larval Taenia crassiceps has been shown to rely on T cells; however, the roles of the specific subsets of T cells during infection are not known. To investigate a possible role for γδT cells, this study investigated larval infection in δ-chain knock-out C57BL/6 (deltaKO) and wild-type C57BL/6 mice. It was found that deltaKO mice and C57BL/6 mice were equally susceptible to infection suggesting γδT cells do not play a major role in protective immunity. Cytokine production by concanavalin A (ConA)-stimulated spleen cells from infected deltaKO mice and C57BL/6 mice were determined. All infected mice demonstrated an increased IL-10 production suggesting a Th1-inhibitory function. Cells from infected deltaKO mice and C57BL/6 mice did not show increases in IL-4 production. Heavily-infected C57BL/6 mice showed a decrease in IFN-γ production compared to deltaKO mice. These observations suggest that an increase in IL-10 production best correlates with a non-protective immune response. To make comparisons between in vitro cytokine production and systemic immune responses, cytokine levels in serum were determined. C57BL/6 mice and deltaKO mice showed increases in serum levels of IL-4 and IFN-γ at 52 days post-infection. The systemic immune response of these mice, therefore, is a mixed Th1/Th2-type response and γδT cells are apparently not responsible for the systemic increases in these cytokines.