The abundance and diversity of parasites vary among different populations of host species. In some host-parasite associations, much of the variation seems to depend on the identity of the host species, whereas in other cases it is better explained by local environmental conditions. The few parasite taxa investigated to date make it difficult to discern any general pattern governing large-scale variation in abundance or diversity. Here, we test whether the abundance and diversity of gamasid mites parasitic on small mammals across different regions of the Palaearctic are determined mainly by host identity or by parameters of the abiotic environment. Using data from 42 host species from 26 distinct regions, we found that mite abundances on different populations of the same host species were more similar to each other than expected by chance, and varied significantly among host species, with half of the variance among samples explained by differences between host species. A similar but less pronounced pattern was observed for mite diversity, measured both as species richness and as the taxonomic distinctness of mite species within an assemblage. Strong environmental effects were also observed, with local temperature and precipitation correlating with mite abundance and species richness, respectively, across populations of the same host species, for many of the host species examined. These results are compared to those obtained for other groups of parasites, notably fleas, and discussed in light of attempts to find general rules governing the geographical variation in the abundance and diversity of parasite assemblages.

A series of 2277 Leishmania strains from Old World visceral leishmaniasis foci, isolated between 1973 and 2008, were studied by isoenzyme analysis. The strains were obtained from humans, domestic and wild carnivores, rodents and phlebotomine sandflies, and came from 36 countries. In all, 60 different zymodemes were identified and clustered by a phenetic analysis into 3 different groups corresponding to the typically visceralizing species L. donovani (20 zymodemes, 169 strains), L. archibaldi (3 zymodemes, 46 strains) and L. infantum (37 zymodemes, 2,062 strains). The taxonomic position of these isoenzymatic groups is discussed in view of contradictory results obtained from recent molecular studies.

The life-cycle of Plasmodium depends on transmission of the parasite from the vertebrate host into its vector when the insect takes a bloodmeal. Transmission success may depend in part on the parasite's gametocyte density and sex ratio in the blood. P. mexicanum, a parasite of fence lizards in California, USA, exploits the sandfly Lutzomyia vexator as its vector. In experimental transmissions using naturally infected lizards as donors of blood, transmission success (measured as percentage of vectors infected and number of parasite oocysts on the insect's midgut) was positively related to gametocyte density, although density above 20/1000 erythrocytes did not improve transmission. Sex ratio (proportion of microgametocytes in the infection) was positively correlated with gametocyte density. Transmission improved with higher proportion of microgametocytes, but partial correlations revealed that this was a result only of higher gametocyte densities. These results agree with the theory of virulence and sex ratios because single clone infections should produce a more female-biased sex ratio and grow to the minimum parasitaemia that would maximize clonal transmission, whereas multiple clone infections will be closer to a 1[ratio ]1 sex ratio and yield a higher parasitaemia when each clone competes for transmission to the vector.

Eimeria arizonensis, E. albigulae and E. onychomysis, morphologically similar species from closely related murid rodents, were distinguished using nuclear rDNA ITS1 sequences obtained from multiple isolates of each taxon. ITS1 sequences were also obtained from 6 other species parasitizing murid rodents: E. falciformis, E. langebarteli, E. nieschulzi, E. papillata, E. separata and E. sevilletensis, and from E. reedi, a parasite of heteromyid rodents. Under parsimony and maximum likelihood analyses, the isolates of E. arizonensis, E. albigulae and E. onychomysis were differentiated as closely related, monophyletic lineages. Maximum likelihood pairwise distances between the latter species ranged from 7 to 12%, and distances within each species ranged from <1 to 5%; thus it is suggested that ITS1 genetic distances may be used to facilitate taxonomic differentiation of Eimeria spp. Against expectation, phylogenetic procedures placed E. reedi within the phylogeny of the Eimeria of murid rodents. ITS1 sequencing appears to provide data that can be used for taxonomic and phylogenetic studies on the speciose genus Eimeria, and may be especially useful when samples contain insufficient numbers of oocysts for other molecular-based methods, e.g. RAPD–PCR.

When measured 56 days postinfection the length, wet weight and dry-weight of Hymenolepis diminuta were all found to decrease with increasing number of cysticercoids given up to 20. The mean position of the worms in 10, 12 and 20 worm infections is significantly posterior to that of 1, 2 and 5 worm infections and the worms are attached over a wider area of the intestine.

Egg production by the worms was followed up to day 56 postinfection; the number of eggs produced per worm and even per rat decreased with increasing population density. Thus the best way to get most eggs and to maintain the parasite in the laboratory is to have rats infected with only one tapeworm.

Rats given 1–20 cysticercoids showed a mean recovery of 100–65%, while rats given 40–200 cysticercoids showed a mean recovery ranging from 13 to 2%. In addition to ‘normal’ worms, defined as worms > 10 mm, small, most probably destrobilated, worms were found. In the 50 and 100 cysticercoid infections, worm recoveries were, respectively, 8% ‘normal’, 16% small, and 2% ‘normal’, 5% small. From the significantly lower recovery from heavy infections it is concluded that a deleterious factor is operating during the 8 weeks after the infection.

Studies on the nutrition and physiology of Trichomonas vaginalis have been hampered by the lack of a defined synthetic medium in which to grow the organism. New synthetic media free of ill-defined supplements and serum which support good growth of T. vaginalis have been developed in this study. The first successful approach to a defined medium resulted from the modification of the tissue-culture medium CMRL 1066. Essential modifications included (1) lowering the redox potential of the medium by adding high levels of ascorbate and (2) modifying the buffer system. Subsequently, CMRL 1066 was replaced by two new media DL7 and DL8 which have greater flexibility in their formulation and permit improved serum-free growth. Serum was replaced by bovine serum albumin and cholesterol, together with either a glyceryl fatty acid ester or a defined mixture of fatty acids. Preliminary nutritional studies using the new media have indicated a requirement for saturated and unsaturated fatty acids and a sterol.

Since pigs are important in the zoonotic transmission of schistosomiasis japonica in China, a veterinary vaccine might contribute to the control of the disease in humans. Pigs were immunized with three doses each of 10000 cercariae of Schistosoma japonicum attenuated with ultraviolet light (400 μWatt·min/cm2). The experiment was performed with portable irradiation equipment in a rural area of the Hubei Province (P.R. China). A challenge infection of 1000 untreated cercariae was given 2·5 or 6 months after the last immunization, and age-matched naive pigs were challenged as a control. Immunized pigs developed about 90% resistance against the challenge. The liver egg load of these animals was reduced by over 90%. Less than 0·01 % of the immunizing cercariae developed to adult parasites and the vaccination had no apparent adverse influence on the pigs' health.

The well-known pathogens of fasciolosis, Fasciola hepatica (Fh) and Fasciola Gigantica (Fg), possess abundant mature sperms in their seminal vesicles, and thus, they reproduce bisexually. On the other hand, aspermic Fasciola flukes reported from Asian countries, which have no sperm in their seminal vesicles, probably reproduce parthenogenetically. The aim of this study was to reveal the origin of aspermic Fasciola flukes. The nuclear single copy markers, phosphoenolpyruvate carboxykinase and DNA polymerase delta, were employed for analysis of Fasciola species from China. The hybrid origin of aspermic Fasciola flukes was strongly suggested by the presence of the Fh/Fg type, which includes DNA fragments of both F. hepatica and F. gigantica. China can be regarded as the cradle of the interspecific hybridization because F. hepatica and F. gigantica were detected in the northern and southern parts of China, respectively, and hybrids flukes were distributed between the habitats of the two species. The Chinese origin was supported by the fact that a larger number of mitochondrial NADH dehydrogenase subunit 1 (nad1) haplotypes was detected in Chinese aspermic Fasciola populations than in aspermic populations from the neighbouring countries. Hereafter, ‘aspermic’ Fasciola flukes should be termed as ‘hybrid’ Fasciola flukes.

The activity patterns and changes in shape of schistosomula recovered from various locations during migration, are described. There is no significant increase in length during the period which worms remain in the skin. Rhythmic cycles of extension and contraction of the worm body are established soon after penetration. Worms newly arrived at the lungs are identical with skin worms of the same age. Within the lungs their maximum length increases to four times that of skin worms, an adaptation which is believed to facilitate migration through the lumina of blood capillaries. Worms recovered from the lungs and systemic organs on, and subsequent to, day 8 post-infection retain this capacity for elongation. When worms arrive at the hepatic portal system they undergo a process of shortening and there is a transient doubling in the duration of cycles of activity. It is suggested that this shape and activity change terminates migration by preventing escape of worms from the hepatic portal system via the liver sinuses. The stimulus which triggers the response is thought to be the high nutrient levels present in hepatic portal blood, but not in peripheral blood. The stimulus which terminates migration also probably initiates growth. Worms cultured in vitro undergo some increase in length, but have a significantly lower maximum length than lung worms of a corresponding age. Although cultured worms were active, the cycles of extension and contraction were much more erratic than those of in vivo worms. The worms shortened spontaneously after 8–10 days in culture. This shortening occurred marginally later than in the most rapidly migrating worms in vivo.

Neospora caninum is a leading cause of abortion in cattle, and is thus an important veterinary health problem of high economic significance. Vaccination has been considered a viable strategy to prevent bovine neosporosis. Different approaches have been investigated, and to date the most promising results have been achieved with live-attenuated vaccines. Subunit vaccines have also been studied, and most of them represented components that are functionally involved in (i) the physical interaction between the parasite and its host cell during invasion or (ii) tachyzoite-to-bradyzoite stage conversion. Drugs have been considered as an option to limit the effects of vertical transmission of N. caninum. Promising results with a small panel of compounds in small laboratory animal models indicate the potential value of a chemotherapeutical approach for the prevention of neosporosis in ruminants. For both, vaccines and drugs, the key for success in preventing vertical transmission lies in the application of bioactive compounds that limit parasite proliferation and dissemination, without endangering the developing fetus not only during an exogenous acute infection but also during recrudescence of a chronic infection. In this review, the current status of vaccine and drug development is presented and novel strategies against neosporosis are discussed.

When mice were infected with female cercariae of Schistosoma mansoni and male cercariae of Schistosomatium douthitti, many mixed pairs formed. The paired females were approximately the same size as those in unisexual infections, far smaller than females paired with S. mansoni males. Although the Sch. douthitti males possessed well-developed testes, sperm were not found in their female partners, which developed scanty vitelline glands and produced laterally spined eggs typical of S. mansoni. Such eggs yielded swimming miracidia infective to the snail host of S. mansoni, Biomphalaria glabrata, but not to the lymnaeid snail host of Sch. douthitti. Sporocysts arising from these miracidia were haploid and produced cercariae infective to mice. Parthenogenetically derived female cercariae in mice co-infected with either parthenogenetically derived male or normal diploid male S. mansoni developed to large adults of normal appearance, whose eggs yielded diploid miracidia and subsequent generations of normal diploid schistosomes. Parthenogenetically derived females co-infected with Sch. douthitti males also paired and produced some eggs containing viable miracidia, which gave rise once again to haploid sporocysts. These observations confirm previous suggestions that the stimulus for maturation in female S. mansoni is distinct from that for growth, and is independent of insemination and fertilization. It is concluded that both diploid and haploid S. mansoni females are capable either of parthenogenesis or of bisexual reproduction when appropriately stimulated.

1. A spring-rise in faecal strongyloid egg count is described in sheep housed under conditions designed to prevent reinfestation. Large rises were observed in the majority of 3-year-old breeding ewes and primiparous ewe-hoggs, and occasional small rises occurred in nulliparous ewe-hoggs and wether-hoggs.

2. Falls were observed in the packed red-cell volumes of ewes during the period of spring-rise and a close inverse correlation was found between packed-cell volumes and transformed worm egg counts. No evidence was obtained to attribute the falls in packed-cell volume to factors other than worm burden.

3. The fall in packed-cell volume was partially alleviated by feeding of one type of perennial rye-grass, but no direct effect of feeding on the worm-egg output was found.

4. Theories of spring-rise are discussed and the conclusion reached that latent overwintering larvae must play a major part generally in the phenomenon.

Chloride regulation. Following the ingestion of a blood meal the tick excretes about half the ingested water in the coxal fluid. The mean haemolymph chloride concentration before feeding is 1.00% and after feeding 0.96% NaCl; and that of the coxal fluid, 0.80% NaCl. These results confirm the values given by Boné (1943).

Morphology of the coxal glands. These comprise the coxal glands proper, which elaborate the bulk of the coxal fluid, and the smaller accessory glands of unknown function. Each flask-shaped coxal gland consists of two distinct regions, an outer ‘filtration chamber’ and an inner system of tubules. The latter lead to the external opening. The filtration chamber, which communicates with the tubules at only one point, is highly folded into an elaborate series of pockets and fingers which closely invest the tubules; numerous small muscle fibres inserted in these pockets pass outwards from the gland to attachments on the body wall. The histology of the two regions is entirely different: the filtration membrane is only 1–2μ in thickness and its cellular origin is much obscured: the tubule walls are 5–30 μ in thickness, are composed of cells with a dense, deeply staining cytoplasm, and are richly supplied with tracheae. In Ornithodorus delanoei acinus the walls of the sac-like coxal glands are lined both by ‘filtration membrane’ and by large irregular groups of ‘secretory’ cells; there are no true tubules.

Function of the coxal glands. The production of coxal fluid is under muscular control. It is believed that the contraction of the coxal gland muscles enlarges the filtration chamber and sets up a sufficient pressure difference across the membrane to initiate filtration into the gland. In the subsequent passage of the fluid down the tubules threshold substances such as chloride are reabsorbed. That the coxal fluid is primarily an ultrafiltrate of the haemolymph is suggested by (a) the rapid passage of dyes and even haemoglobin into the coxal fluid after injection into the haemolymph and (b) the very high rate of liberation of fluid. Serum albumen sometimes passes into the coxal fluid after injection but casein (and the normal haemolymph proteins) are fully retained.

Cyclospora cayetanensis, a coccidian parasite that causes protracted and relapsing gastroenteritis, has a short recorded history. At least 54 countries have documented C. cayetanensis infections and 13 of them have recorded cyclosporiasis outbreaks. Cyclospora cayetanensis infections are commonly reported in developing countries with low-socioeconomic levels or in endemic areas, although large outbreaks have also been documented in developed countries. The overall C. cayetanensis prevalence in humans worldwide is 3.55%. Among susceptible populations, the highest prevalence has been documented in immunocompetent individuals with diarrhea. Infections are markedly seasonal, occurring in the rainy season or summer. Cyclospora cayetanensis or Cyclospora-like organisms have also been detected in food, water, soil and some other animals. Detection methods based on oocyst morphology, staining and molecular testing have been developed. Treatment with trimethoprim–sulfamethoxazole (TMP–SMX) effectively cures C. cayetanensis infection, whereas ciprofloxacin is less effective than TMP–SMX, but is suitable for patients who cannot tolerate co-trimoxazole. Here, we review the biological characteristics, clinical features, epidemiology, detection methods and treatment of C. cayetanensis in humans, and assess some risk factors for infection with this pathogen.

A dilution medium for the cultivation in vitro of the erythrocytic stages of P. knowlesi has been simplified to contain the following: a balanced salt solution, glucose, isoleucine, methionine, adenosine, p-aminobenzoic acid, biotin and calcium pantothenate. The medium, in the presence of plasma gave better results than the Harvard medium for the growth of P. knowlesi during one asexual cycle and also allowed the subculture of the parasites through three asexual cycles before a reduction in the number of parasites was observed.

We should like to thank Dr F. Hawking and Dr K. N. Brown for their advice and Mr T. J. Scott-Finnigan for technical assistance. One of us (P.I.T.) received financial assistance from the World Health Organization.

The pre-feeding and feeding periods of larvae, nymphs and adults of Rhipicephalus appendiculatus on rabbits (Oryctolagus cuniculus) were investigated. Larvae and nymphs required at least 8–9 days after hatching and moulting respectively before they could attach and start feeding, while adults required at least 6–9 days. But longer periods of starvation improved the proportion of ticks that successfully fed.

After attachment, there was always an initial period of slow feeding, which was followed by a phase of very rapid feeding before the engorged ticks detached from the host. Larvae detached 4–5 days after attachment, nymphs detached after 5–6 days and adults detached 7–9 days after attachment.

A cDNA encoding a cysteine protease inhibitor (cystatin) was identified by immunoscreening a Haemonchus contortus cDNA library with antisera from lambs vaccinated with a protective membrane protein complex (H-gal-GP) derived from the gut of the parasite. The cDNA sequence, designated Cys-1, showed significant levels of similarity with cystatins from several species of nematode as well as with human cystatinNucleotide and amino acid sequence data reported in this paper are available in the GenBankTM database under the accession number AF035945.. Recombinant H. contortus cystatin was expressed in Escherichia coli in a soluble and functionally active form, which proved to be a potent inhibitor of both mammalian cathepsin B and native H. contortus cysteine proteases. Immunolocalization studies using antisera raised against recombinant H. contortus cystatin showed that the inhibitor was predominantly expressed in the cytoplasm of intestinal cells. To determine whether H. contortus had any protective capacity against infection, lambs were vaccinated with the recombinant molecule and subsequently given a single challenge infection. Although vaccination did not confer any protection against infection with H. contortus, as judged by faecal egg output or worm counts, cystatin will be a valuable tool in the analysis of the function of the cysteine proteases which are the subject of on-going study as potential vaccine components.

Infection of an intracellular parasitic nematode, Trichinella spiralis, resulted in severe damage in muscle cells which was followed by activation and proliferation of satellite cells. The repairing process, shortly after the damage, histopathologically resembled those seen after mechanical injury. Resemblance was also true for kinetics of expression of myogenic regulatory factors (MyoD, myogenin and MRF4). The difference resided in the next step where the muscle cell infected with T. spiralis transformed to a unique cell which is parasitologically known as the nurse cell, and the proliferated satellite cells did not differentiate to the muscle cell but to the nurse cell (misdifferentiation). Thus the nurse cell was a fusion of the transformed infected muscle cell and misdifferentiated satellite cells. Infection with another species of Trichinella, T. pseudospiralis, also caused cell damage, but more extensively involving the entire length of the infected muscle cells because no septum was formed to minimize the affected area. Therefore, a large number of satellite cells were activated and proliferated. The myogenic regulatory factors such as MyoD and myogenin were activated for a longer period than in the case with T. spiralis infection. The infected muscle cell transformed to the nurse cell, whose cytoplasm was characterized by extensive smooth endoplasmic reticulum. Satellite cells misdifferentiated to the nurse cell, whose cytoplasm was amorphous, void of distinct cell organelles. The two kinds of cytoplasm did not fuse as examined thus far. Thus infection with T. spiralis and T. pseudospiralis caused misdifferentiation of satellite cells, but in a different way.

The more important points that have emerged in the course of our investigations may now be assembled.

(1) An adhesion phenomenon has been described in which, in certain circumstances, red blood corpuscles adhere to trypanosomes.

(2) We believe this red-cell adhesion to be a manifestation of the adhesion phenomenon already described by other workers both with trypanosomes and spirochaetes.

(3) The substance responsible for this phenomenon of adhesion is designated in this paper adhesin.

(4) The red-cell adhesion test has been studied in relation to several strains of polymorphic trypanosomes, all of which were either recently isolated from naturally infected man or animals, or had been recently passed cyclically through tsetse.

(5) It is shown that the adhesion phenomenon is irregular and uncertain in its appearance. A single or even a number of negative observations do not exclude trypanosomiasis. A positive reaction, on the other hand, indicates recent or actual infection with a trypanosome of the same group, but not necessarily specifically identical with that employed as antigen in the test. Thus T. gambiense adhesin bloods not uncommonly react with T. rhodesiense trypanosomes and also on occasion with the Damba strain: the converse is apparently of less common occurrence.

(6) Adhesins appear in an animal's blood in the course of its infection with trypanosomes, whether the animal be treated with trypanocidal drugs or not. When sterilising doses of such drugs are employed the adhesins gradually disappear in the course of a few months; but in untreated infections of T. gambiense they have been shown to persist in an active form for more than two years.

(7) With our material it was found impossible to distinguish between “passage” and “relapse” strains by means of the adhesion test. On the contrary it was found, at all events with T. gambiense, that the best way to call forth the reaction in the blood of animals long infected is to employ trypanosomes from a very early infection.

(8) Guinea-pigs have been found to be unsatisfactory animals in which to demonstrate adhesins; they are, however, useful as a source of sensitive trypanosomes. When only guinea-pig elements are present in a test a positive reaction is indicated by platelet not by red-cell adhesion.

(9) The presence of adhesins in the blood has no apparent relation to immunity against the homologous trypanosome.

(10) The test has been applied to over 200 human cases of trypanosomiasis in the Uganda Protectorate, and with six of these repeated observations were made. Some of these human cases reacted both to T. gambiense and T. rhodesiense, but none to T. rhodesiense alone.

(11) A partial analysis has been made of the mechanism of red-cell adhesion, which has been shown to be in some way associated with the presence of the red corpuscles of primates. This fact probably explains why other workers appear not to have noticed red-cell adhesion in the extreme form we have described in this paper.

We present an analysis of the survival and migration rates of the infective (L3) stages of Oslertagia ostertagi and Cooperia oncophora. Although the majority of laboratory studies show that the survival of the L3 stage depends upon temperature, moisture and the age of the larvae, a simple mathematical model of larval demography, in which their mortality and migration rates are held constant, provides as good agreement between observed and predicted larval counts as models in which these rate processes are made explicit functions of larval age and microclimate. Maximum-likelihood estimates of larval mortality rates in the faeces and on the herbage are 0·0284/day and 0·00887/day respectively. The average migration rate from faeces to herbage under temperate Northern European conditions is estimated as 0·00884/day. Finally, we discuss the probable scale of L3 larval losses due to desiccation and lavage (active or passsive migration into the soil).