Strongyloidiosis by Strongyloides stercoralis is a disease of increasing interest in human and animal medicine. The scientific knowledge on canine strongyloidiosis is hindered by the poor diagnostics available. To assess the most sensitive and specific diagnostic method, feces and blood from 100 shelter dogs were screened for S. stercoralis by coprological, molecular and serological tests. Thirty-six dogs (36%) scored positive to S. stercoralis by coprology (22.3% to Baermann) and/or 30% to real time-polymerase chain reaction (rt-PCR). According to two composite reference standards (CRS) based on all coprological methods and rt-PCR (first CRS) or in combination with serology (second CRS), the most sensitive test was IFAT (93.8%; CI 82.8–98.7), followed by rt-PCR (80.6%; 95% CI 64–91.8) and Baermann (60.6%; 95% CI 42.1–77.1). The inconsistent shedding of L1 during the 4-week follow-up in infected dogs suggests the importance of multiple faecal collections for a reliable diagnosis. A combination of serological and coprological tests is recommended for the surveillance and diagnosis of S. stercoralis infection in dogs.

Host-mediated responses and parasite density-dependent processes can have a major influence on the growth and fecundity of parasitic nematodes. However, host characteristics and parasite intensity consistently change during the course of an infection and these could affect worm length and number of eggs in a non-constant way. We used a free-living population of rabbits naturally infected with Trichostronglyus retortateformis and examined how adult nematode length and the number of eggs in utero were affected by host characteristics (i.e. age, sex, breeding status) and parasite intensity, in a seasonal environment, between 2004 and 2007. Nematode length and number of eggs in utero decreased exponentially with host age; in contrast, parasite intensity increased, peaked in juveniles and decreased in older hosts. These patterns were consistent between rabbit cohorts. A negative relationship was observed between parasite intensity and nematode length, as well as number of eggs. Nematode length was strongly affected by nematode sex and host age, while the number of eggs was mainly influenced by nematode length. The direct influence of host-mediated effects appeared quantitatively more important than parasite density dependence in controlling length and egg production in naturally infected wild rabbits. However, their relative contribution changed during the course of the infection such that, while host immunity still influenced worm numbers, the direct effect of density-dependent interactions contributed the most at high parasite intensities.

The development of second generation schizonts of Eimeria necatrix and E. tenella was studied with the electron microscope. Invasion of the crypt epithelial cells by merozoites of the first generation schizonts caused changes in the morphology of the infected cells and stimulated their migration into the lamina propria through breaks which appeared in the basement membrane of the crypts. Second generation schizonts developed in the lamina propria within these crypt cells whose epithelial origin was confirmed by their interconnection by desmosomes and tight junctions and by their possession of characteristic microvilli. A comparison is made between this invasion of the lamina propria by parasitized cells and invasion of connective tissue by malignant epithelial cells; the possible mechanisms involved are discussed.

Using biochemical genetic methods, we have distinguished 2 sibling species in the complex Bothrimonus nylandicus (Schneider, 1902), which infest 2 congeneric species of sole (Solea lascaris and Solea impar) on European coasts (Atlantic and Mediterranean). Neither of the parasite species is specific for either of the sole species, but one of them is present all year round, whereas the other is absent in the autumn and winter and only appears in the spring, subsequently disappearing at the end of the summer. Only S. impar lives in the Mediterranean, and is equally infested by both cestodes, whereas both species occur in the Atlantic and each of them is preferentially infested by 1 species of cestode. The shortness of the adult stage of the parasite in the definitive host and the presence of 2 life-cycles associated with competition between the 2 hosts in the Atlantic could be responsible for the biological differences observed and for maintaining the sibling species in sympatry.

A chloroform extract of molluscicidal plant secondary compounds from the seeds of a West African legume Millettia thonningii was used to attenuate cercariae of Schistosoma mansoni prior to infection of NMRI female mice. Exposure of cercariae to 0·3, 0·6, 1·3, 2·5, 10 or 20 mg/l concentrations of extract for 30 mm, immediately before standardized infection, was associated with a concentration-dependent decline in worm establishment at 55 days post-infection. The mean numbers of adult worms established declined from about 17 worms/mouse with control cercariae and those exposed to 0·3 mg/l Millettia to 0·1 worms/mouse after 10 mg/l pre-treatment. Mice exposed to cercariae after 20 mg/l pre-treatment had no adult worms at 55 days post-infection. The activities of cercariae 30 mm after exposure to Millettia extract at concentrations up to 2·5 mg/l were similar to those of control larvae: none was immobile. Exposure to higher concentrations of Millettia progressively reduced swimming activity and increased the proportion of immobile cercariae. After pretreatment with 20 mg/l Millettia the majority of larvae were immobile. Levels of anti-parasite antibodies (estimated by ELISA assay using an adult worm-based antigen preparation) rose between 21 and 55 days p.i. with control cercariae and those pre-treated with 2·5 mg/l Millettia. After 5 mg/l pre-treatment, cercariae induced a reduced antibody rise, while mice exposed to cercariae after 10 mg/l pre-treatment showed no rise in anti-parasite antibody levels. These results are discussed in the context of protocols which could possibly use Millettia-attenuated cercariae to induce useful levels of protection in mice towards further cercarial challenge.

The entomopathogenic nematode Heterorhabditis megidis may undergo several rounds of reproduction within a single host. Infective juveniles (IJs) are formed within each generation during a process referred to as endotokia matricida, which involves the progressive consumption of the parent hermaphrodite or female by the developing IJs prior to emergence from the host cadaver. The present study examines the extent to which within-host population dynamics exhibit density-dependent variation. Particular attention is paid to the effect of infection density on the relative production of IJs and ‘normal’, non-infective offspring within each generation and on the emergence of the IJs from the host. Fecundity was found to be negatively density dependent across generations. However, at high infection density the first generation hermaphrodites invested relatively more in IJs at the expense of producing non-infective offspring. It is suggested that this pattern resulted from an adaptive, phenotypically plastic allocation of reproductive investment between offspring types in response to increased competition. The F1 and F2 IJs were also shown to emerge from the host in relatively discrete pulses.

Morphological features of the bladder wall of Cysticercus fasciolaris and carbohydrate analysis of the contained fluid are described. The bladder fluid was found to have a higher concentration of glucose than the plasma of the respective host animal. The bladder wall has a prominent duct system with numerous cytoplasmic extensions and interconnections. It is suggested that the bladder may function in the nutrition of the developing cysticercus by providing a reservoir of raw material which may be utilized by the growing strobila.

The authors wish to thank Dr Theodor von Brand for many helpful discussions, and Dr Harley G. Sheffield and Mr Ned M. Etherington for their advice and technical assistance in the preparation of the electron micrographs.

1. The life cycle of Gigantobilharzia huronensis Najim, 1950, was determined experimentally. The snail, Physa gyrina (Say), served as the intermediate host. The natural definitive hosts were goldfinches (Spinus tristis tristis) and the cardinals (Richmondena cardinalis). Chicks and canaries served as susceptible hosts in the laboratory

2. The shortest time recorded for the hatching of eggs in water is about 20 min. Cercariae were liberated from the snail as early as 24 days after exposure. Eggs were found in the faeces of the definitive host 31 days after the first exposure to the cercariae.

3. Adult worms are elongate and filiform. Females are longer than males, and in both sexes the oral and ventral suckers are absent. The cuticle has no spines. A short gynaecophoric canal is present. Up to 300 testes are present in the male and the cirrus is spiny. Laurer's canal is present and vitelline follicles fill most of the body of the female. Eggs are spherical to very broadly ovoid in shape and averaged 93µ in length by 88µ in width. The uterus contains from one to several eggs at a time, and the genital pore is located shortly posterior to the mouth opening.

4. The miracidium has a peculiar wide gap between the second and third rows of epidermal plates. The body covering consists of twenty-two epidermal plates arranged in four rows of 6:9:4:3. The mother sporocyst has an elongate, sac-like body. A birth pore is present in the mature mother sporocysts. The daughter sporocyst also has an elongate body, but the anterior end is covered with spines. A birth pore is present in the mature daughter sporocysts.

5. The cercaria is an apharyngeal, furcocercous, brevifurcate, distome with pigmented eyespots; the body averaging 240µ in length by 72·5µ in width; the tail stem averaging 268·5µ in length by 30µ, in width; the furca averaging 146·8µ in length by 15µ in width. The furcae have fin folds. The body and tail are covered with spines. There are five pairs of penetration glands and an oral gland. The excretory system is usually 2[(2) + (2+1)]. The cercaria attaches to the surface film of the water with the body parallel to it and the tail hanging downward at different angles. The cercaria is a dermatitis producer in human skin.

Psoroptic sheep scab and psoroptic otoacariasis of domestic rabbits occur in the same geographical regions of Switzerland. To address the question as to whether Psoroptes mites are naturally transmitted between sheep and rabbits, we determined the sequences of the rDNA second internal transcribed spacer (ITS-2) from psoroptic mites from sheep (5 field isolates from Switzerland and 2 laboratory isolates from Ireland and the UK) and from rabbits (8 field isolates from Switzerland). The ITS-2 sequences for all Psoroptes mites originating from sheep were identical and differed at 1 nucleotide position from all the sequences of the rabbit-derived isolates. A statistically significant difference between a rabbit-derived isolate and isolates originating from sheep was also obtained by morphometric analysis of the lengths of the outer opisthosomal setae. For comparative purposes, the ITS-2 sequences from Chorioptes and Sarcoptes collected in Switzerland were also determined. No intraspecies variation was found in 6 sarcoptic isolates from red foxes, with a sequence identity of 41% as compared to Psoroptes. The ITS-2 sequences of 3 chorioptic isolates differed by 24–29% from the Psoroptes sequence. Identical sequences were found for the Chorioptes isolates from sheep and a camel, which differed by 18% from the sequence of an isolate from a cow. These genetic data of psoroptic mites originating from sheep and rabbits from the same geographical area suggest the existence of epidemiologically separated populations.

A strain of Trypanosoma avium isolated from Corvus frugilegus in England was readily cultivated in vitro in diphasic blood agar, or blood nutrient agar, media at 28 °C.

In both media, small trypanosomes appeared which morphologically resembled the metacyclic forms from the insect vector and which were infective to canaries. They were more numerous, and developed more regularly, in the medium with the nutrient agar base.

At 40–41 °C a few of these small trypanosomes apparently developed into large trypanosomes similar to, but not identical with, those seen in the blood of infected birds.

The genus Monospora (= Monosporella renamed) was founded by Metschnikoff in 1884 to designate a parasitic fungus which he discovered in Daphnia magna. This monocellular fungus, of which he described only one species, Monospora bicuspidata, lives free in the body cavity of its host, where it multiplies actively by budding in a yeast-like manner (Fig. I, 1, 2, 3).

The ultrastructure of the lappets of Apatemon gracilis minor Yamaguti, 1933, has been described. The tegument covering the lappets is characterized by the presence of long seta-like structures and unicellular gland cells which exhibit a holocrine type of secretion. The setae contain extensions of the tegument cytoplasm and are supported by a bundle of fibrils. The unicellular gland cells are pear-shaped with the tapering neck supported by a ring of 50–60 microtubules. The secretion consists of relatively large, membrane bounded bodies containing a fine granular material.

The lappets are regarded as representing a specialized host–parasite interface in which adaptation exists for attachment to the host tissue and the discharge of secretion from the parasite at this region. The concept of the specialized host–parasite interface is discussed and extended to include Apatemon gracilis minor.

The author wishes to acknowledge the research grant provided by the S.R.C. for the purchase of a vacuum coating unit and an AEI EM 6 electron microscope. The progress of this study was greatly facilitated by the excellent assistance of Mr T. Davies and Miss C. Green. The stereoscan micrograph (P1. 1, fig. 2) is published by permission of the Cambridge Instrument Company.

In a recent paper1, written jointly with Dr P. P. Laidlaw, methods were described for cultivating Entamoeba histolytica, and various other entozoic amoebae of man and monkeys, from the encysted forms. We there showed that cultures of all the species studied can be readily obtained by merely incubating such cysts in any of the media suitable for the cultivation of the corresponding active forms—provided that certain precautions are taken.

An account is given of the bacterial flora isolated from the blood-sucking Reduviid bugs, Triatoma infestans and T. protracta, and the predatory Reduviid, Sinea diadema. The micro-organisms which have been found in Triatoma spp. differ from that found in Rhodnius prolixus (Actinomyces rhodnii), in both specific identity and in their relation to the cells of the mid-gut. The symbiont occurring most frequently in T. infestans has been identified as a diphtheroid organism resembling Coryne-bacterium hofmannii, and sections show this organism inside vacuoles within some of the endothelial cells of the insect's intestine. The organism occurring in R. prolixus, on the other hand, cannot be found in this situation, but remains in the lumen of the gut. While the occurrence of the bacteria found in T. infestans in so intimate a connexion with the cells of its host seems to suggest a more highly organized state of affairs, T. infestans does not show the fixed association with one species of micro-organism which is shown by R. prolixus. Other bacteria occur commonly in T. infestans, although they do not occur in cell-vacuoles; and the range of bacterial types is so great that it seems unlikely that the species recorded in this paper are the only ones that may occur. The presence of these other bacteria may be due either to the anti-biotic action of the Corynebacterium sp. being weaker than that of A. rhodnii, or to masking of the anti-biotic action by the cell wall that encloses the organisms. The situation in R. prolixus shows clearly that a constant symbiotic association with a micro-organism can be maintained without the presence of specialized organs of the mycetome type.

With regard to the predatory species, no general conclusion can be reached on the evidence so far available. Compared with the blood-sucking Reduviids, insects of this kind usually have powerful proteolytic enzymes secreted in the anterior mid-gut, while the same region of the blood-suckers is a simple storage and concentration sac, digestion taking place lower down the intestine. Thus the region of the gut where bacteria are found in blood-suckers might not be a favourable situation for them in predatory bugs. Hence it is perhaps significant that most of the few successful isolations from a predatory type were from the rectum of the insect. It is the usual opinion that insects with a predatory diet do not need bacterial symbionts, but the aim in examining the predatory Reduviidae has been to find out whether they show a condition which might have evolved into that found in their blood-sucking relatives. The search is still in progress for a rather unspecialized type of predatory Reduviid in which the salivary and anterior mid-gut digestion is less strongly developed than in those species which have been available for study up to the present.

Experiments were performed to determine at what phase or phases of its parasitic development Boophilus microplus becomes infected with Babesia bigemina. Problems due to Boophilus microplus being a one-host tick were overcome by artificially transferring ticks from one host to a second just prior to a moult. In several experiments, a babesiacide was used to eliminate parasites so that the exposure of ticks to infection could be restricted to one phase of their development. Further information was obtained by correlating the presence or absence of patent parasitaemia in the bovine with the presence or absence of infection in ticks which fed on it.

It was found that ticks were susceptible to infection for approximately the last day of their parasitic life. Infection at other times, that is, during larval, nymphal and the major part of the adult stages was not usual. Four of five attempts to infect larvae and all five attempts to infect nymphs were negative.

Infection of ticks always resulted when a patent parasitaemia coincided with the last day of parasitic life. Ticks were infected in all thirteen instances when these conditions existed but in only seven of eighteen instances when the animal was a carrier but was not showing parasitaemia.

Stage-to-stage transmission did not occur, although suitable conditions for this existed on nine occasions.

Specific antisera, directed against the highly conserved C-terminal hexapeptide amide of mammalian pancreatic poly-peptide (PP) and the invertebrate peptide FMRFamide, have been used in conjunction with post-embedding, IgG-conjugated colloidal gold immunostaining to demonstrate peptide immunoreactivity at subcellular level in the nervous system of adult Diclidophora merlangi. Gold labelling revealed that immunoreactivity for PP and FMRFamide was localized exclusively in dense-cored vesicles occupying the majority of axons in the central nervous system. Double-labelling demonstrated an apparent co-localization of PP and FMRFamide in the same dense-cored vesicles. Antigen pre-absorption experiments indicated cross-reactivity of the two antisera as unlikely, and that some if not all of the PP/FMRFamide immunostaining in the parasite was due to a neuropeptide F-like peptide.

We have identified and partially sequenced 8 ABC transporters from an EST dataset of Sarcoptes scabiei var. hominis, the causative agent of scabies. Analysis confirmed that most of the known ABC subfamilies are represented in the EST dataset including several members of the multidrug resistance protein subfamily (ABC-C). Although P-glycoprotein (ABC-B) sequences were not found in the EST dataset, a partial P-glycoprotein sequence was subsequently obtained using a degenerate PCR strategy and library screening. Thus a total of 9 potential S. scabiei ABC transporters representing the subfamilies A, B, C, E, F and H have been identified. Ivermectin is currently used in the treatment of hyper-infested (crusted) scabies, and has also been identified as a potentially effective acaricide for mass treatment programmes in scabies-endemic communities. The observation of clinical and in vitro ivermectin resistance in 2 crusted scabies patients who received multiple treatments has raised serious concerns regarding the sustainability of such programmes. One possible mechanism for ivermectin resistance is through ABC transporters such as P-glycoprotein. This work forms an important foundation for further studies to elucidate the potential role of ABC transporters in ivermectin resistance of S. scabiei.

On the available data from south Wales and southeast England, the tick Ixodes hexagonus Leach has spring and autumn peaks of activity on hedgehogs, stoats and weasels.

One or more stages of this tick have been recorded on fifteen mammalian hosts. All stages have been collected from hedgehogs, stoats, foxes, polecats and ferrets. The weasel is probably the smallest habitual host. No specimens of I. hexagonus have been found on birds.

Man is an ‘accidental’ host and records of this tick on man in the London area are given. From the present information it seems that ill-effects following the bite of this parasite are rare. In built-up areas the probable sources of infestation are dogs, cats and hedgehogs. Air-raid shelters and similar constructions which have harboured these hosts at one time or another may provide a centre of infestation of man. Our observations indicate that the number of ticks in most hedgehogs' nests is not large. Nothing is known of the tick population in the habitats of other hosts. It is suggested tentatively that the ticks may drop off hedgehogs away from the nest and that after further development (i.e. hatching of eggs and metamorphoses of later stages) they are picked up by such animals as foxes, stoats, weasels.

The records of this tick in Britain are summarized and they indicate that I. hexagonus is a southern species.

1. The development of resistance to metachloridine (3-metanilamido-5-chloropyrimidine) was studied in two clones of Plasmodium gallinaceum derived from single erythrocytic parasites and maintained by serial inoculation in young chicks. Resistance developed with equal facility and similarly in the two clones.

2. In thirteen strains of these clones an enhancement of resistance was obtained after three to five courses of treatment, each of seven doses of metachloridine over a period of 3½ days.

3. The effect of the size of the inoculum (2·5 × 107–109 parasites), and of the dose of drug upon the rate of development of resistance was studied. Although the number of courses of treatment required to produce an enhancement of resistance was not always related to the size of the inoculum, with the largest inoculum an enhancement of resistance was observed after the minimum number of courses of treatment (three), whereas with the smallest inoculum no enhancement of resistance was obtained. The rate of the development of resistance did not appear to be related to the size of the dose of drug.

4. In some strains the increase in resistance was sudden, whereas in others it was more gradual. Resistance was retained when parasites of a newly resistant strain were transmitted through Aëdes aegypti or maintained for 43 days in the absence of the drug.

5. A comparison of the development of resistance in populations of normal parasites, and of populations composed of mixtures of known numbers of resistant and normal parasites, indicated that the pattern of the development of resistance in normal populations could be explained by the selections of mutations of a frequency of less than 1 in 5 × 107, or probably less than 1 in 109 parasites.

It is proposed that, for many species of parasites, evasion of the host immune response may be achieved passively through enhanced survival within host individuals that have a genetically determined low responsiveness to infection. Evasion by this means may contribute significantly to continued transmission of infection in man and domestic animals and influence the severity of pathology. Low responsiveness plays an important role in determining over-dispersion of parasites within host populations, and the common occurrence of this form of distribution is seen as supporting evidence for the proposition, although few of the examples available provide conclusive proof. The extensive individual and strain variation in response to parasitic infection in laboratory strains of mice is tak as a homologue of the natural situation and allows analysis of the mechanisms underlying low responsiveness. Two examples are considered in detail. In Leishmania infections both non-H-2 and H-2-linked genes influence resistance, but the primary expression of genetically determined low response is at the level of the macrophage. Genetic influences upon acquired immunity regulate macrophage–T-cell interactions. In Trichinella spiralis H-2-linked and non-H-2 genes influence development of the intestinal responses necessary for expulsion of the adult worm, the former through the response of helper T-cells to worm antigen and the amplification of this response through other T-cells, the latter through an effect upon the response of myeloid stem cells to T-cell signals. Modification of genetically determined low responsiveness is discussed in terms of (a) improving host responsiveness through vaccination or non-specific immunostimulation and (b) altering host genotype through selective breeding or the introduction of resistance alleles into a population.