The cercaria of Acanthostomum brauni penetrates the skin of its fish host in response to a combination of two chemical signals from the fish skin surface: free fatty acids and a macro-molecular mucus component. The latter seems to be a protein, as the penetration-stimulating activity of fish skin surface mucus is eliminated by digestion with proteinase, but not by digestion with glycosidases, nor by a removal of glycosaminoglycans. These penetration-stimulating host signals differ from the glycoproteins that stimulate the attachment of A. brauni cercariae to the host and also from the macro-molecular fish host signals which have been found to stimulate the attachment and penetration by Opisthorchis viverrini cercariae.

Trichomonas sp. from a corais snake

Description. Body usually pear-shaped. Average size 12 × 8μ, Three anterior flagella of unequal length. Basal fibre absent. Feebly developed undulating membrane.

Habitat. Intestine of Dymarchon corais, from North America.

Locality. London.

The patients we are concerned about in tropical medicine are unfortunately affected by a wide range of conditions, not only those seen and studied extensively in the West, such as cancer, cardiovascular diseases and viral or bacterial infections, but also the major protozoan and metazoan conditions – the parasitic diseases. It is with this spectrum of pathophysiological changes that occurs in this last group that we are presently concerned and this communication is intended to present an overview of the subject.

Figs and their pollinating wasps are a classic example of an obligate mutualism. In addition, figs are parasitized by a suite of non-mutualistic wasps whose basic ecology is largely undescribed. Sycophilomorpha (subfamily Epichrysomallinae) fig wasps are ovule gallers and the genus contains only 1 described species. An undescribed Sycophilomorpha species parasitized Ficus altissima at Xishuangbana, Southwestern China. The wasp was observed ovipositing on the tiny immature figs that were still concealed beneath the involucral bracts. A Sycophilomorpha wasp oviposited on more than 1 fig and spent long time-periods to lay large clutches on a single fig. The wasps naturally occurred on all 7 sampled trees, but the occurrence of wasps was significantly different among trees, crops and months. These wasps were able to prevent unpollinated figs from being aborted, and their offspring were able to develop in the figs that otherwise had no pollinator wasps or seeds. The Sycophilomorpha wasp had a detrimental effect on the fig–fig wasp mutualism. Figs in which Sycophilomorpha wasps were present, produced significantly fewer seeds, pollinators and cheaters. However, the abundance of Sycophilomorpha in a fig was only significantly negatively correlated with pollinator production and not seed or cheater production. Our study illustrates a previously unknown fig wasp niche and expands our understanding of factors that can affect the fig–fig wasp interaction.

A prominent filamentous and granular cell coat is associated with the plasma membraneof haptomonads of Crithidia fasciculata attached to the cuticular lining of the hindgut of Anopheles gambiae. This surface material is completely absent from morphologically identical haptomonads from the mosquito foregut and from rosettes in culture. On the basis of these observations, it is suggested that cell coat formation is dependent on suitable environmental conditions.A cytochemical staining technique indicates the presence of carbohydrates in (a) the cell coat, (b) the outer leaflet of the plasma membrane of haptomonads from all locations and (c) small cytoplasmic vesicles and multivesicular bodies in all haptomonads. It is suggested that these cytoplasmic organelles represent stages in the intracellular pathway for material ingested by pinocytosis rather than elements involved in surface coat formation.

The precise biology of the body louse under experimental conditions is a subject not sufficiently explored. At present we need quantitative information about the possible rate of increase of the insect: we must also know about the normal biology in studying insecticides. The present moment is therefore an appropriate one for publishing certain experiments which have occupied a part of my time for the last 4 years.

The size and shape of the trophozoite of Nyctotherus ovalis in different species of cockroaches was found to vary considerably, and this was attributed chiefly to the presence or absence of large paraglycogen granules within the ciliate.

The size and shape of the cysts of N. ovalis which were passed in the faeces of the host on successive days were found to fluctuate around means which were more or less constant over a long period. The constants varied according to the species of the host: the largest and fattest cysts were found in the faeces from Blatta, the smallest and most slender from Blattella. Those from Blaberus were of the Blattella-type, but Periplaneta harboured populations which gave rise either to the Blatta-type of cysts or to the Blattella-type.

The constant size and shape of the cysts was not altered when the host moulted, but there was always a decrease in size and sometimes a change of shape when an infection was established in a new host. The cause of these changes is unknown. An increase in size was induced by an increase in environmental temperature, but the size declined during a subsequent period at lower temperatures. The work of other authors on changes in the sizes of protozoan cysts is discussed.

The cyst wall of N. ovalis consists of four separate layers plus an outer membrane. They all seemed to be proteinaceous in nature. Treatment with various inorganic reagents and proteolytic enzymes revealed that the knob is the most easily destroyed part of the wall. A histochemical test for keratin showed that this is the chief constituent of the wall. The keratin appeared to be least organized in the knob, and hence the knob is the least impermeable part of the wall.

This work was done during the tenure of a Research Studentship awarded by the Agricultural Research Council. I am deeply indebted to Dr P. Tate for his encouragement and counsel at all stages of the work.

Dujardin (1835) was the first to describe an adult gregarine occurring in an earthworm. This description contains illustrations of a typical Nematocystis species (Dujardin's Text-figs. B1-B7 and C1 and C2). Subsequent workers made many other observations, but it was Hesse (1909) who first carried out a comprehensive study of these parasites. It was Hesse's excellent work which laid the foundation for succeeding students of the group, the more important of whom are Cognetti de Martiis (1911, 1918, 1920, 1921, 1923, 1925, 1926, 1927), Berlin (1923, 1924), Bhatia (1924, 1924b, 1929, 1930), Bhatia & Setna (1926), Setna (1927), Bhatia & Chatterjee (1925), Troisi (1933, 1940), Tuzet & Loubatières (1946, 1948) and Loubatières (1947, 1948, 1949). Hesse gave a good historical resumé of the work carried out until 1909, while Loubatières (1949) has given a complete and very useful resumé of the work since.

Intraerythrocytic parasites (Apicomplexa: Sarcocystidae) of the South American mouse opossum (Thylamys elegans) from Chile, South America, and of the yellow-bellied glider (Petaurus australis) from Australia were found to be monophyletic using SSU rDNA and partial LSU rDNA sequences. Phylogenetic reconstruction placed both species within the family Sarcocystidae. These intraerythrocytic parasites of marsupials represent an as yet unnamed genus predicted to have bisporocystic oocysts and tetrazoic sporocysts, which is a characteristic feature of all members of the family Sarcocystidae. These results show that erythrocytic parasites share a common ancestor and suggest co-evolution with their vertebrate host.

At field rates (ca 0·1–10 μg active ingredient/ml), non-fumigant nematicides such as oxamyl do not kill plant-parasitic nematodes directly but act by impairing neuromuscular activity. The present study has shown that neutral lipid levels in 2nd-stage (infective) juveniles of Globodera rostochiensis, which had been incubated with the oximecarbamate nematicide oxamyl (1 μg a.i./ml) for between 8 and 35 days, were significantly (P < 0·05) greater when compared with controls maintained in water alone. The difference between treatments was found to be due principally to changes in the lipid content in the posterior half of the body which appears to act as the major long-term lipid store. When nematodes were allowed to recover for 72 h following incubation for 35 days with oxamyl, their infectivity was not significantly (P > 0·05) different from that of controls. This work is discussed in relation to the action of oxamyl and similar nematicides and to the use of controlled-release formulations as a means of increasing their efficacy.

1. The different lipid fractions in Gastrothylax crumenifer after starvation for 8–10 hr. have been estimated.

2. The percentages of different fractions in the total ether extract were found to be: acetone-insoluble material 16, unsaponifiable matter 25, saturated fatty acids 5, unsaturated fatty acids 20, glycerol 2 and unidentified lipids 32.

3. The above percentages of lipid fractions have been compared with the corresponding data for different parasites obtained by other workers.

In the present study fibrogenic gene expression was determined in murine Schistosoma japonicum infection during the progression of immune modulation of infection and following chemotherapy during the course of immune modulation. Histomorphometric analysis of granuloma size and collagen deposition revealed peak granuloma size in acute infection (5 weeks) and peak hepatic collagen content at 16 weeks of infection. Peak Type I collagen gene expression was concomitant with TGF-β1 gene expression at 8–11 weeks. Chemotherapy during either acute (9 weeks) or chronic (24, 28 weeks) infection resulted in increased collagen deposition and increased gene expression of Type I collagen and TGF-β1. However, chemotherapy at 14–16 weeks resulted in decreased levels of TGF-β1 gene expression and essentially minimal change in Type I collagen deposition and gene expression. These data indicate that chemotherapy of schistosomiasis japonica does not reverse hepatic fibrogenesis when administered in acute infection – when granuloma size is maximal – or in chronic infection. However, a beneficial effect on hepatic fibrogenesis is seen when chemotherapy is administered at 14–16 weeks post-infection, a time of decreasing granuloma size and maximal hepatic collagen content. Thus the ability to reverse schistosomal-induced hepatic fibrogenesis by chemotherapy may depend on disease stage.

Proteomes are complex and dynamic entities that are still poorly understood, but the application of proteomic technologies has become invaluable in many areas of biology, including parasitology. These technologies can be exploited to identify proteins in both complex or relatively simple samples, that formerly could only be characterized by targeted approaches such as Western blotting. Quantitative proteomic approaches can reveal modulations in protein expression that accompany phenotypes of interest. Proteomic approaches have been exploited to understand some of the molecular basis for host:parasite interactions and to elucidate phenotypes such as virulence, antigenicity and drug resistance. Many of the same technologies can also be more easily applied to targeted sub-proteomes.

Examples from several studies on pathogen proteomes and sub-proteomes, from bacteria to helminths, are presented to illustrate the potential and limitations of proteomic technologies.

Complete development of Ancylostoma ceylanicum (Hamster strain) is reported for the first time in mice. A patent infection (viz. ova in faeces) could be established only under the influence of hydrocortisone acetate. Cultures made from the faeces containing eggs produced viable larvae which were infective to mice.

To improve both safety and stability of the vaccines used in the field to vaccinate foxes against rabies by the oral route, a recombinant vaccinia virus, expressing the glycoprotein of rabies virus (VVTGgRAB) has been developed. VVTGgRAB innocuity was verified in target species and in domestic animals as well as in numerous wild animal species that could compete with the red fox in consuming vaccine baits in Europe. Oral immunization of foxes, by distributing VVTGgRAB vaccine-baits, was undertaken for the whole infected area in Belgium (10000 km2). Five campaigns of fox vaccination, were carried out from autumn 1989 until 1991. Each time, 150000 vaccine-baits were dropped by air at a mean density of 15 per km2. These campaigns induced a drastic decrease in the incidence of rabies and the elimination of the disease from 80% of the initially infected area. Regarding the geographical evolution of rabies in Belgium and in adjacent regions in neighbouring countries, new spatial strategies for bait dispersal were planned for 1992, 1993 and 1994: successive confined campaigns were carried out along political borders only. These campaigns induced a new decrease of incidence; no rabid fox could be detected in 1993 in spite of an improved epidemiological surveillance. In 1994, rabies was again confirmed in 13 foxes collected in an area close to the French border. These cases demonstrate the persistence of a border rabies focus and justify further restricted vaccination campaigns.

A PCR strategy using degenerate oligonucleotide primers based upon consensus sequences of the active site of serine proteases yielded a 467 bp fragment from genomic DNA from Schistosoma mansoni cercariae. The sequence presented a continuous open reading frame and the deduced amino acid sequence (156 aa) presented homologies with various serine proteases, in particular the highest percentage identity was observed with a mammalian plasma kallikrein. The expression of this serine protease was studied first at the mRNA level and it was only detected by RT-PCR in cercariae and in adult worms. At the protein level we were able to detect it by Western blotting and by using antigen extracts from metabolically radio-isotope labelled worms. The absence of any positive signal in Northern blot and the detection of the protein suggest that the mRNA has a very short half-life, however the protein may be accumulated in the parasite. The significance of identity with mammalian kallikrein was confirmed by cross-immunoreactivity with a native porcine pancreatic kallikrein. However, no cross-reactivity was observed with S. mansoni elastase, another serine protease. Thus, we suggest that the serine protease described in this paper is a kallikrein-like protease.

In snails maintained at 20 °C rediae of Fasciola hepatica emerge from sporocysts from 11 days after infection onwards. The number of mother rediae rises steadily thereafter until at least 40 days after infection. Daughter rediae are seldom observed in mother rediae dissected from snails maintained at 20 °C. Their production can, however, be stimulated by subjecting the snail host to starvation, to low, and to high temperature shocks. The parasite is susceptible to stress from immediately after infection for about 16 days, when maintained at 20 °C. In general, the more extreme the shock, the greater is daughter redial production. Increasing the length of the period of stress from 12 h up to 9 days does not increase the production of daughter rediae, nor does repeated on/off cold shocks or continuous maintenance at 10 °C. Daughter rediae develop more rapidly than cercariae and leave the mother rediae several days earlier. There is no evidence that presence of daughter rediae coincides with the suppression of cercarial production. The findings are discussed with reference to possible mechanisms by which parasite development might be controlled.

The co-infection between visceral leishmaniasis (VL) and human immunodeficiency virus (HIV) has increased in several countries in the world. The current serological tests are not suitable since they present low sensitivity to detect the most of VL/HIV cases, and a more precise diagnosis should be performed. In this context, in the present study, an immunoproteomics approach was performed using Leishmania infantum antigenic extracts and VL, HIV and VL/HIV patients sera, besides healthy subjects samples; aiming to identify antigenic markers for these clinical conditions. Results showed that 43 spots were recognized by antibodies in VL and VL/HIV sera, and 26 proteins were identified by mass spectrometry. Between them, β-tubulin was expressed, purified and tested in ELISA experiments as a proof of concept for validation of our immunoproteomics findings and results showed high sensitivity and specificity values to detect VL and VL/HIV patients. In conclusion, the identified proteins in the present work could be considered as candidates for future studies aiming to improvement of the diagnosis of VL and VL/HIV co-infection.

Chagas’ disease is a neglected tropical disease caused by Trypanosoma cruzi and constitutes a serious public health problem for Latin America. Its unsatisfactory chemotherapy stimulates the search for novel antiparasitic compounds. Amidines and related compounds exhibit well-known activity towards different microbes including T. cruzi. In this vein, our present aim was to evaluate the biological effect of 10 novel structurally related amidines in vitro against bloodstream and intracellular forms of the parasite as well as their potential toxicity on cardiac cell cultures. Our results show that although active against the extracellular forms, with some of them like DB2247 being 6-fold more effective than benznidazole and displaying very low toxicity (>96 μ m), none presented superior trypanocidal effect against intracellular forms as compared with the reference drug. These results may be due to differences in susceptibility profiles related to distinct uptake/extrusion mechanisms and cellular targets between bloodstream and amastigote forms. The present study adds to the knowledge base for the future design of novel amidines that may provide promising activity against T. cruzi.

We studied the monogenean communities of 34 species of butterflyfish from the tropical Indo-West Pacific, identifying 13 dactylogyrid species (including two species that are presently undescribed). Monogenean assemblages differed significantly between host species in terms of taxonomic structure, intensity and prevalence. Parasite richness ranged from 0 (Chaetodon lunulatus) to 11 (C. auriga, C. citrinellus and C. lunula). Host specificity varied between the dactylogyrids species, being found on 2–29 of the 34 chaetodontid species examined. Sympatric butterflyfish species were typically parasitized by different combinations of dactylogyrid species, suggesting the existence of complex host–parasite interactions. We identified six clusters of butterflyfish species based on the similarities of their dactylogyrid communities. Dactylogyrid richness and diversity were not related to host size, diet specialization, depth range or phylogeny of butterflyfish species. However, there was a weak positive correlation between monogenean richness and diversity and host geographical range. Most communities of dactylogyrids were dominated by Haliotrema aurigae and H. angelopterum, indicating the importance of the genus Haliotrema in shaping monogenean communities of butterflyfishes. This study casts light on the structure of the monogenean communities of butterflyfishes, suggesting that the diversity and complexity of community structures arises from a combination of host species-specific parameters.