The method of attachment of the cattle tick Boophilus microplus (Canestrini) has been investigated on cattle of different breeds and susceptibility to infestation.

Despite their differing sizes, the larval, nymphal and adult mouthparts penetrate to a similar depth towards the base of the Malpighian layer. Penetration may occur within 5 min of the arrival of the tick on the host.

Attachment is accomplished by the secretion of a cement substance in which the mouthparts are embedded and which adheres firmly to the hosts skin.

The cement consists of two main components: a cortex of carbohydrate-containing protein, stabilized by quinone tanning and disulphide linkages, and an internum which is lipoprotein in nature.

The start of the secretion of cement and the initial cutting of the host tissues by the chelicerae occur simultaneously. Final rapid engorgement of each stage is preceded by a secondary secretion of cement into a fluid-filled cavity which forms directly beneath the mouthparts and provides additional support.

It is concluded that attachment is an entirely mechanical process by an inert cement which does not provoke the development of host-parasite factors inimical to the tick.

It is with much pleasure that we acknowledge generous financial support by the Australian Cattle and Beef Research Committee which has made possible this project.

The enzyme-linked immunosorbent assay (ELISA) was used to survey human sera for antibodies to Encephalitozoon cuniculi using spores obtained from in vitro cultures as antigen. Sera were obtained from patients with tropical diseases, neurological and renal disorders, patients who were HIV positive and those who had been tested for HIV but found to be negative. Sera from inhabitants of the village of Jali, The Gambia and from healthy blood donors were also examined. Numerous sera from all groups except the blood donors gave positive ELISA reactions at dilutions of 1:400. On titration, those with titres of 1:400 were reclassified as negative. Antibody titres of 1:800 and above were considered to be indicative of past or present infections with E. cuniculi. Many of these ELISA seropositives were also positive by IFAT or PAP. When examined by Western blotting of SDS–PAGE protein profiles of E. cuniculi spores, sera from many patients who had a tropical association reacted with the characteristic profiles shown by known positive mouse and rabbit sera. Others in the tropical group showed antibody binding to some but not all of the immunodominant polypeptides and yet others were negative in spite of their reactivity in the ELISA, IFAT or PAP test. Less agreement between ELISA and Western blotting results was obtained with the other groups of patients, although reactivity with one or more of the major polypeptide bands was sometimes seen. Serum from one blood donor, examined by ELISA and Western blotting, was positive. Differences in the methods of antigen preparation and of epitopes recognized by individuals may account for different reactivities in the tests. It is concluded that infections of E. cuniculi are common in the tropics and that reactivations of these infections might be a hazard to AIDS patients.

The effects of the novel benzimidazole, triclabendazole (TCBZ) (‘Fasinex’, Ciba-Geigy), in its active sulphoxide metabolite form (TCBZ-SX), on the tegumental ultrastructure of Fasciola hepatica were determined in vitro by transmission electron microscopy (TEM), using both intact flukes and tissue-slice material. At a concentration of 15 µ/ml, the tegument of the whole adult fluke showed ultrastructural changes only after prolonged time-periods, with vacuolation at the base of the syncytium and accumulation of T2 secretory bodies in the tegumental cells. At a concentration of 50 µ/ml, with both whole flukes and tissue-slices, the tegument appeared extremely abnormal with accumulation of secretory bodies towards the base of the syncytium. With longer incubation times, the tegument was completely sloughed away and the tegumental cells became synthetically inactive. The tegument of the 3-week-old juvenile became progressively convoluted at the apex, while in the basal regions there was severe vacuolation. In the tegumental cells, there were accumulations of T1 secretory bodies. These results confirm TCBZ as a potent fasciolicide, being very effective in disrupting the fluke tegument. They may go some way to explain the mode of action of this important fasciolicide.

Gastrointestinal infection with the nematode Trichinella spiralis is accompanied by a rapid and reversible expansion of the mucosal mast cell and goblet cell populations in the intestinal epithelium, which is associated with the release of their mediators into the gut lumen. Both goblet cell and mast cell hyperplasia are highly dependent on mucosal T-cells and augmented by the cytokines IL-4 and IL-13. However, the contribution of both mast and goblet cells, and the mediators they produce, to the expulsion of the adults of T. spiralis is only beginning to be elucidated through studies predominantly employing T. spiralis-mouse models. In the present article, we review the factors proposed to control T. spiralis-induced mucosal mast cell (MMC) and goblet cell differentiation in the small intestine, and focus on some key MMC and goblet cell effector molecules which may contribute to the expulsion of adult worms and/or inhibition of larval development.

The mechanism of action of praziquantel (PZQ), the drug of choice against schistosomiasis, is still unclear. Since exposure of schistosomes to the drug is associated with calcium influx and muscular contraction, calcium channels have been suggested as the target, although direct combination of PZQ with their subunits was never demonstrated. We report a hitherto unknown effect of PZQ, namely the inhibition of nucleoside uptake, as observed in living worms using radio-isotope labelled adenosine and uridine. This effect is clearly seen in schistosomes but is absent in mammalian cells in culture. Moreover it is a specific pharmacological effect seen exclusively with the active levo-R(−)stereo isomer of the drug, and is shared by at least one benzodiazepine having antischistosomal activity. This novel effect acquires significance given that schistosomes cannot synthesize purine nucleosides de novo. A possible relationship between this novel effect and the known action of PZQ on calcium channels is discussed, since adenosine is known to bind to specific receptors and to behave as an indirect antagonist of calcium release in mammalian cells. If calcium channels were correlated with adenosine receptors also in schistosomes, as they are in mammals, this would support the hypothesis that PZQ-induced calcium influx may be correlated to adenosine receptor blockade.

This paper contains an account of four new Coccidia from Uganda: Caryospora legeri sp.n., from a snake, Psammophis sibilans; Isospora dirumpens sp.n., from a snake, Bitis arietans; Wenyonella africana gen.n., sp.n., from a snake, Boaedon lineatus; and Eimeria urnula sp.n., from a bird, Phalacrocorax carbo lugubris. Eimeria dukei. Lavier 1927, is recorded from a new host, Chaerephon (= Nyctinomus) limbatus (bat).

The characters of the new Coccidia are summarised in the diagnoses (pp. 364, 369, 373, 378). There is a list of all the known species of Isospora found in snakes and lizards. It is noted that I. coelopeltis Galli-Valerio 1926, is actually an Eimeria, and its name is amended to E. coelopeltis. The diagnostic characters of the three species of Caryospora are given in tabular form.

The discovery of a new type of Coccidia, with oocysts containing sixteen sporozoites, divided between two sporocysts in Dorisiella Kay 1930, and between four in Wenyonella gen.n., necessitated a revision of the systematics of the Eimeriidea.

When the genera comprising this suborder (with a few exceptions) are arranged in the ascending order of the number of structural elements (sporocysts and sporozoites) contained in their oocysts, they form parallel series or groups in the horizontal and vertical directions, which consist of homologous members, as represented graphically in Fig. VI (p. 383). The oocyst characters of each genus are determined by those of its four neighbours in the horizontal and vertical groups.

This scheme serves as the basis for the new classification proposed, which is represented in Table III (p. 385). The higher systematic units (subfamilies) are distinguished from each other by the number of sporocysts within the oocyst, while the genera of each subfamily differ from each other in the number of sporozoites within each sporocyst, thus forming a homologous series.

Schistosomes infect the mammalian host by direct penetration of the skin and must then undergo a protracted migration to the site of parasitization, for Schistosoma mansoni the hepatic portal vasculature. This article reviews the work published roughly between 1976 and 1986 that clarified our understanding of the process in the laboratory mouse. A combination of histopathology, larval injection experiments and autoradiographic tracking revealed that migration involved one to several circuits of the pulmonary-systemic vasculature before chance delivery in cardiac output to splanchnic arteries that lead indirectly to the portal tract. The kinetics of migration through different capillary beds was established, with the lungs of naïve mice not the skin proving the greatest obstacle; a proportion of schistosomula entered the alveoli from where they did not recover. The ‘immunity’ displayed by mice with a chronic infection was shown to be an artefact of a ‘leaky’ hepatic portal system, generated as a result of egg-induced hepatic pathology. The blockade of pulmonary migration was exacerbated in mice vaccinated with irradiated cercariae by immune-mediated inflammatory foci that developed around lung schistosomula thus decreasing the proportion that matured, but parasite elimination was a prolonged process, not an acute cytolytic ‘hit.’

In order to investigate the phenomenon of age-related immunity to visceral leishmaniasis, a 1 year prospective survey was carried out on 5671 people in a Leishmania infantum focus in north-west Iran. The average incidence rate of infection since 1985 was 2·8%/year with all ages equally at risk. One in 13 infections in children led to visceral leishmaniasis (VL), and this ratio decreased significantly with age. Seroprevalence also dropped rapidly with age, suggesting that the same process may affect both clinical outcome and the humoral immune responses. Cell-mediated immunity was associated with a reduction in the seroconversion rate and an increase in the serorecovery rate. Even amongst people with no detectable cell-mediated immunity to Leishmania, the seroconversion rate decreased and the serorecovery rate increased with age. All current VL patients had a negative leishmanin skin test response. Hence, adults may develop protection against L. infantum through 2 processes, 1 dependent and 1 independent of acquired cell-mediated immunity.

Leishmania are intracellular protozoan parasites which reside primarily, if not exclusively, in host mononuclear phagocytes. Several studies have demonstrated that infectious promastigotes rapidly and efficiently fix complement when they encounter serum components during their transmission to the mammalian host. Activation of the complement system by a microorganism can have 3 distinct biological effects. First, fixation of the terminal complement components can result in complement-mediated lysis. Second, fixation of the 3rd component of complement can lead to opsonization of the organism for uptake by phagocytic cells. Finally, the elaboration of the complement anaphylotoxins, C3a and C5a, can lead to inflammation. In the present chapter, we discuss the interaction of leishmania promastigotes with the complement system. We show that infectious promastigotes avoid the lytic effects of complement and resist fixation of the terminal complement components. At the same time, however, these organisms depend on fixation of opsonic complement to invade host mononuclear phagocytes efficiently. We discuss the mechanisms which allow metacyclic leishmania promastigotes to exploit the opsonic properties of complement and the receptors on macrophages involved in leishmania recognition. The role of complement mediated inflammatory processes in the host response to leishmania infection is an area which requires additional study.

A flagellate isolated from the intestinal tract of a reduviid bug Ricolla simillima (Heteroptera) in Costa Rica was found to represent a new trypanosomatid species by the phylogenetic analysis of small subunit ribosomal RNA (SSU rRNA), glyceraldehyde phosphate dehydrogenase (GAPDH) and large subunit of RNA polymerase II (RPOIILS) genes. The phylogenetic position of this trypanosomatid, together with its typical promastigote morphology and the host identity, allowed its classification as a species that belongs to the polyphyletic genus Leptomonas. Interestingly, the new species was revealed as a member of the novel phylogenetic clade representing the closest known relative of Leishmania. With the new species used as an outgroup to root the Leishmania RPOIILS phylogenetic tree, the lineage of the Neotropical species L. enriettii was found to branch off early, and was followed by a deep split between the Old World and the remaining New World species. This tree topology supports the hypothesis that the initial transition to dixenous parasitism in this group pre-dated the continental split and that afterwards the Neotropical and the Old World groups evolved largely independently.

Development of cercariae within intramolluscan germinal sacs is recognized to be in seven stages; in brief, these stages are: 1, germinal cell; 2, naked cell aggregate; 3, germ ball prior to elongation; 4, elongating germ ball; 5, tail bud stage; 6, tail elongation stage; and 7, fully developed cercaria.

Schistosoma mansoni cercariae at each of the developmental stages is described.

The dimensions of both germinal and somatic cells comprising the bodies of developing S. mansoni cercariae decrease with maturation.

The surfacial membrane of Stage 3 cercarial embryos is formed by a number of small somatic cells which migrate to the surface and coalesce.

The chronologic and partially synchronized development of S. mansoni cercariae is presented.

The body-tail ratio during S. mansoni cercarial development is presented.

The degradation of several protein substrates, including the blood proteins haemoglobin, albumin and fibrinogen, by proteinases present in extracts of adult Haemonchus contortus was examined over a broad pH range. These proteinases were further characterized on the basis of substrate specificity, inhibitor sensitivity and molecular size by spectrophotometric and substrate gel analysis. The majority of the proteinases capable of degrading the blood proteins tested were active at acidic pH and could be ascribed to the cysteine proteinase class. In addition, evidence is presented that these proteinases are differentially recognized and inhibited by immune sera and that parasites capable of withstanding protective host immune responses exhibit modified expression of proteinases.

Regular samples made on the 1978 cohort of brook sticklebacks (Culaea inconstans) from a swamp in Ile Perrot, Quebec, Canada were examined for Apatemon gracilis metacercariae. The prevalence of the parasite rapidly reached 100% in the fish population. The mean parasite burden increased from zero to a plateau of about 44 parasites/fish. Over-dispersion of the frequency distribution of parasites in the fish host, as measured by variance to mean ratios, increased to a peak and then decreased significantly while the mean parasite burden remained constant. The effects of parasite burden on the survival of the stickleback host are discussed, as well as the validity of the use of changes in over-dispersion for demonstrating parasite-induced mortality.

Echinococcus multilocularis, a vulpine intestinal tapeworm, is the causative agent of alveolar echinococosis in humans, one of the most severe and lethal parasitic infections in man. To date, there is very little knowledge about the genetical polymorphism of this parasite. To assess sequence polymorphism, we analysed a sample of 33 E. multilocularis isolates from Europe, North America and Asia by PCR-SSCP followed by nucleotide sequencing. This assessment was performed comparatively to sheep, cattle and pig E. granulosus strains. Coding (nuclear antigen B and mitochondrial NADH dehydrogenase genes) and non-coding (introns of actin and homeobox-containing genes) regions of the parasite genome were chosen as targets. Since the estimated nucleotide diversity among genotypes of E. multilocularis were, in general, 10 times lower than among the recognized different strains of E. granulosus, we suggest that the conventional classification of the former species in 2 separated strains (European and North American) should be reviewed.

Understanding the temporal and spatial distribution of entomopathogenic nematodes is essential for determining the role of these insect parasites in soil communities and ultimately for their use in suppression of pest insect populations. We measured the vertical and horizontal distribution of endemic populations of entomopathogenic nematodes (Steinernema carpocapsae and Heterorhabditis bacteriophord) in turfgrass. Vertical distribution was determined by taking soil cores every 3 h from 05.00 to 23.00 h, over 4 days, and dividing the cores into 8, 1 cm deep sections. Steinernema carpocapsae was recovered primarily near the soil surface: 50% of positive sections were recovered in the thatch or first 1 cm of soil. S. carpocapsae recovery was lower during the middle of the day and none were recovered in the upper section. H. bacteriophora was recovered uniformly throughout the top 8 cm of soil and its vertical distribution did not change over the course of the day. Horizontal distribution was measured as the number of nematodes recovered from cores taken from 12 randomly selected 0·3 × 0·8 m sections from within four 15·3 × 15·3 m plots. Samples were collected biweekly over a 9-month period. H. bacteriophora had a patchier distribution than S. carpocapsae and both nematode species had more patchy distributions then their potential hosts. Our results support the hypothesis that these two species of nematode utilize different foraging strategies; S. carpocapsae primarily a surface adapted ambusher and H. bacteriophora as a cruise forager.

Cryptosporidium parvum is a zoonotic protozoan parasite that mainly affects the ileum of humans and livestock, with the potential to cause severe enteric disease. We describe the complete life cycle of C. parvum in an in vitro system. Infected cultures of the human ileocecal epithelial cell line (HCT-8) were observed over time using electron microscopy. Additional data are presented on the morphology, development and behavioural characteristics of the different life-cycle stages as well as determining their time of occurrence after inoculation. Numerous stages of C. parvum and their behaviour have been visualized and morphologically characterized for the first time using scanning electron microscopy. Further, parasite-host interactions and the effect of C. parvum on host cells were also visualized. An improved understanding of the parasite's biology, proliferation and interactions with host cells will aid in the development of treatments for the disease.

The epidemiology of pregnancy malaria infection and disease is complex but reflects underlying interactions between the Plasmodium falciparum parasite, the mother, and the foetus. Parasites sequester in the human placenta by binding to chondroitin sulfate A (CSA), a novel receptor that does not commonly support binding of other parasites. Women become resistant to P. falciparum malaria over successive pregnancies as they acquire antibodies against the CSA-binding placental parasite forms. Due to acquired immunity, placental malaria is briefer and less inflammatory in multigravid women than primigravid women, and these parity differences may account for the different outcomes these women and their offspring experience. Commonly recognized sequelae of malaria-like maternal anaemia and low birth weight primarily occur in first and second pregnancies. Hypertension may result from maternal-foetal conflict over the inflammatory response to placental malaria, and occurs in young, first-time mothers. Placental malaria can either increase or decrease parasitaemia risk in the offspring, depending on the mother's parity. The burden of disease due to pregnancy malaria, and the benefits of an effective vaccine, may be much greater than is currently appreciated.

Oocysts from Anopheles stephensi mosquitoes fed on murine blood infected with Plasmodium berghei berghei, were fixed for electron microscopy 6–12 days post-feeding. Ultrastructural analysis focused on Golgi-related trafficking pathways for rhoptry and microneme formation during sporogony. A small Golgi complex of 1–3 cisternae is formed close to the spindle pole body from coated vesicles budded from the nuclear envelope which is confluent with the endoplasmic reticulum. Rhoptries begin as small spheroidal bodies apparently formed by fusion of Golgi-derived vesicles, lengthening to 3–4 μm, and increasing in number to 4 per sporozoite. Ultrastructural data indicate the presence of a novel mechanism for vesicle transport between the Golgi complex and rhoptries along a longitudinal 30 nm – thick fibre (rootlet fibre or tigelle). Filamentous links between vesicles and rootlet indicate that this is a previously undescribed vesicle transport organelle. Genesis of micronemes occurs late in bud maturation and starts as spheroidal dense-cored vesicles (pro-micronemes), transforming to their mature bottle-like shape as they move apically. Filamentous links also occur between micronemes and subpellicular microtubules, indicating that as in merozoites, micronemes are trafficked actively along these structures.

Cryptosporidium parvum is composed of multiple subtypes, which appear to be zoonotic or anthroponotic. Therefore, in order to understand the molecular epidemiology of this species and to control the zoonotic transmission, it is essential to identify the isolates at the subtype level. In the present study, 60·2% of 103 examined dairy calves from 10 farms in the Belgrade area were positive for Cryptosporidium infection by PCR, and all of them were identified as C. parvum by PCR-RFLP of SSUrRNA and COWP genes. Eighteen C. parvum isolates selected randomly from 9 positive farms were classified by molecular phylogenetic analysis of the 60 kDa glycoprotein gene sequences into 3 subtype allele families, IIa and IId, which are known to be zoonotic, and a new family IIj. Furthermore 10 isolates in IIa were classified into 3 subtypes IIaA16G1R1b, IIaA18G1R1, IIaA20G1R1, 2 in IId into IIdA18G1b, and 6 in IIj into IIjA16R2 and IIjA17R2. The last 2 subtypes in IIa and 2 subtypes in IIj were new subtypes. These results suggest that C. parvum isolates harboured in calves in the Belgrade area have zoonotic potential and C. parvum is genetically diverse only in a limited area. This is the first molecular epidemiological report about Cryptosporidium infection in Serbia and Montenegro.

Twenty-eight isolates of E. granulosus, collected from humans at surgery, and a range of intermediate hosts, including sheep, cattle and camels from abattoirs in North and South Xinjiang Uygur Autonomous Region, People's Republic of China, were analysed for DNA sequence variation within regions of the mitochondrial cytochrome c oxidase I (COI) and NADH dehydrogenase subunit I (NDI) genes. The isolates were categorized into 2 distinct and uniform genotypic groupings, based on the sequences obtained, and the data clearly indicated that the camel/dog strain (G6 genotype) of E. granulosus as well as the cosmopolitan, common sheep strain (G1 genotype) occur in north Xinjiang. The presence of the camel strain has thus been confirmed in Xinjiang but it is evident from this and a previous molecular genetic survey of E. granulosus isolates from north-western China that the common sheep strain is the most predominant in the region. From the public health perspective, the majority of infected livestock will act as reservoirs of human infection there. During the course of the study, a polymerase chain reaction (PCR)-restriction fragment length polymorphism (RFLP) assay, based on the NDI sequence variation, was developed that allows rapid discrimination of the G1 and G6 genotypes.