The manner by which Kuhnia scombri (Kuhn, 1829) Sproston, 1945, attaches itself to the gills of Scomber scombrus L. is described.

The parasite lies between the primary gill lamellae with its posterior attachment organs ‘upstream’ with respect to the gill ventilating current of the host.

The adhesive mechanism consists of two sets of organs which become attached to the secondary lamellae: a pair of hooks, provided with powerful muscles, perforates three or four secondary lamellae; and each of the members of four pairs of hinged clamps, operated by its own extrinsic muscle, grasps one or two secondary lamellae.

The description of the adhesive mechanism given differs substantially from that given by Sproston. Sproston's classification of the Diclidophoroidea, being based mainly on her interpretation of the structure of the clamps of Kuhnia, is therefore open to criticism.

The erythrocytes and plasma of a British and Brahman crossbred steer were labelled with 51Cr and 125I respectively. The radioactivity levels were subsequently maintained as constant as feasible by injecting the steers with calculated amounts of the appropriate labelled material on 3 consecutive days. The steers had previously been heavily infested with Boophilus microplus to ensure that all stages in the parasite's life-cycle would be present during the 4-day period, when the steers were being treated with isotopes.

Various stages of B. microplus larvae, nymphs and adults were collected and the uptake of red cells and plasma at each stage assessed by radioassay. In certain calculations, corrections were made for the uptake of blood fractions before the animals were made radioactive.

A relationship between the weight of the tick and its dietary intake was established. At all the stages of larval and nymphal feeding the plasma content of the diet was greater than that of the host blood. However, erythrocytes were detectable even in the earliest larval stages examined. Dropped fully engorged adult females contained more red cells per individual, and generally also more plasma, than engorged ticks removed from the host.

Fully engorged adult females took up as much as twice their own weight of blood components, but in none of the earlier stages did the tick concentrate its blood meal.

No obvious differences could be demonstrated statistically between the behaviour of the parasites on the two hosts. However, indications are that recently attached larvae took up more erythrocytes from the British animal.

We wish to thank Messrs A. K. Duffield, A. J. Short, B. Wilson, and Miss S. J. Shepherd, for skilful technical assistance.

The ultrastructure of the intra-erythrocytic stage of a haemogregarine in the gecko, Gehyra variegata, has been studied and numerous points of similarity to Plasmodium, Toxoplasma, Sarcocystis, Lankesterella, Eimeria and the M-organism were found. The protozoon was invested by a triple-layered pellicle, and possessed at least two micropyles. A conoid and apical rings were observed at the anterior end. Other cell constituents included nucleus, microtubules, endoplasmic reticulum, mitochondria, toxonemes and a variety of vacuoles. Loosely surrounding the parasite was an unusual convoluted membrane, which in appropriate planes of section, displayed corrugations on both surfaces. It was not clear whether this membranous structure should be regarded as an integral part of the protozoon or as an external coat which could be discarded upon emergence from the host red cell. Within its external sheath, the parasite lay in a periparasitic vacuole which was limited by a conventional unit membrane from the host red cell cytoplasm. The parasite did not exhibit any evidence of pinocytosis or phagocytosis.

Our sincere thanks are due to Dr E. H. Mercer, Professor J. D. Smyth and Dr M. J. Mackerras for advice. Miss N. Carroll gave technical assistance.

1. The exrectory system of Anoplocephala perfoliata has been re-described and shown to consist of a dorsal ‘network’ system of vessels to which the flame cells are connected and a ventral pair of longitudinal vessels linked only by a transverse vessel in each proglottid.

2. The two excretory systems unite only in the apical ramifying vessels of the scolex.

3. Alkaline phosphatase activity was demonstrated in the cuticular microvilli, the subcuticular region and in the excretory vessels.

4. Non-specific esterase, insensitive to 10−4m E 600, was located in the lappets and embryonated eggs and esterases, inhibited by 10−4m E600, in parts of the cuticle and subcuticular region and parenchyma.

5. Cholinesterases were found in the nervous system and in the reproductive ducts.

6. Aminopeptidase was found in the neck region, in the undifferentiated proglottids, the active testes and ovaries, the male reproductive ducts and in the region of high metabolic activity in the fringe of the proglottid.

Forty Theileria schizont-infected lymphocyte culture isolates from Zimbabwe were characterized using a panel of antischizont monoclonal antibodies (MAbs) and 4 Theileria parva DNA probes containing cloned extrachromosomal element, Tpr repetitive, ribosomal and telomeric sequences. The Theileria isolates were assigned as T. parva or T. taurotragi on the basis of reactivities with MAbs and restriction fragment length polymorphisms (RFLPs) detected using the extra chromosomal element probe. Cattle-derived T. parva isolates were relatively homogeneous on the basis of reactivities with MAbs and RFLPs detected using Tpr repetitive and ribosomal DNA probes. In contrast to previous results from Kenya, most of the cattle-derived isolates from Zimbabwe exhibited very similar Tpr restriction fragment patterns, although the Tpr genotypes of buffalo-derived isolates were heterogeneous. This suggests that selection for a particular Tpr genotype may be occurring in cattle. Many isolates with similar Tpr genotypes were differentiated by RFLPs detected using the telomeric DNA probe. The T. parva Boleni immunizing stock was distinguished from all other isolates by telomeric RFLPs. The T. parva Boleni Tpr repetitive DNA probe cross-hybridized with T. taurotragi DNA and detected RFLPs between different T. taurotragi isolates.

Three distinct muscle types have been identified within the metacestode of Grillotia erinaceus. These consist of peripheral somatic myofibres plus two muscle systems directly involved in parasite attachment to the host, i.e. the tentacular bulb and its antagonistic retractor muscle. In common with other cestodes the somatic muscle consists of smooth-type fibres running longitudinally and obliquely to the main body axis. The retractor muscle consists of myofibres with centrally displaced nuclei. Upon contraction these latter fibres become spirally orientated causing the muscle to coil and lateral membranes to become elevated as spikes. Definitive nerve processes have not been identified within somatic or retractor muscle. Individual tentacular bulbs form the proximal terminus for a closed hydraulic system. Each bulb consists of overlapping, contrarotating myofibres which display obvious striations; the striations appear in alternate fibres to be in transverse and oblique planes. Adjacent myofibres are separated by approximately 0·5 μm, possess abundant mitochondria and have shallow t-tubules plus associated vesicles of sarcoplasmic reticulum at each Z line. Thick myofilaments are surrounded by 13, shared, thin myofilaments. Close neuronal control for the bulb muscle is suggested by the presence of obvious motor end-plates which contain both lucent and dense neurovesicles.

1. A survey of 227 rooks (Corvus frugilegus frugilegus L.) and seventy jackdaws (C. monedula spermologus Vieill.) was conducted in Hertfordshire. The birds were examined by means of cultures of their peripheral blood, or (in the case of eleven rooks and one jackdaw only) bone-marrow, on N.N.N. medium. Twenty-seven rooks (11·9%) and six jackdaws (8·6%) were found to be infected.

Some of the rooks were examined at a time of year when the trypanosomes are not present in the peripheral circulation; other rooks were examined in the first year of their life before adults of Ornithomyia avicularia (the vector of this parasite) were present. Ignoring birds of these two groups, twenty-six out of seventy-eight (33·3 %) adult rooks were found to be infected. This value probably approximates to the natural infection rate among adult rooks (and perhaps jackdaws).

2. The trypanosome in question is a large spindle-shaped form, measuring an average of 48·2µ in length (excluding flagellum) and 5·5µ in width. There is a tapering aflagellar region extending 14·1µ (on the average) beyond the kineto-plast. This trypanosome is assigned to the species T. avium Danilewsky, 1885.

Periodicity of occurrence in the final host has been observed in only a few of the known Acanthocephala of fish (Van Cleave, 1916; Steinstrasser, 1936; Komarova, 1950; Shulman & Shulman-Albova, 1953). The periodicity appears to be due to the simultaneous operation of a complex of physiological, developmental and ecological factors.

In the present investigation a detailed study has been made of both the occurrence and the developmental cycle of Echinorhynchus truttae in its hosts in a small trout stream, Afon Terrig, in North Wales. An attempt has also been made to ascertain to what extent some of the various and varying ecological and physiological factors influenced the incidence, degree of parasitization and the development of the worm in nature.

Samples of the intermediate host, Gammarus pulex pulex L., and the final host the brown trout, Salmo trutta L., were taken monthly at three points or stations where the stream was readily accessible. Station I was at Rhydtalog as far upstream as practicable. Station III was at the opposite end of the stream near Caegwydd and station II was about mid-way between the other two sampling points. To ensure that each host sample was examined in as fresh a condition as possible, autopsy of the intermediate host was completed before the definitive host was taken.

Within the first week of each month from November 1961 to January 1963, shrimps were taken from over a stretch of about 30 m at each station.

The shore crabs, Hemigrapsus oregonensis and H. nudus, sometimes kill the female endoparasitic entoniscid isopod, Portunion conformis, a parasitic castrator. Studies of host populations from Baja California, Mexico to Vancouver Island, Canada, show that the incidence of parasitized hosts with dead parasites and the percentage of the parasite population found dead vary markedly with locality but only occasionally with season. Both higher incidences of hosts with dead P. conformis and higher proportions of the total parasite population found dead are associated with (1) high prevalence of parasitism, (2) female hosts and (3) large hosts. Within a host, the proportion of the parasites that are dead is not related to the degree of multiple infection. Typically, either all or none of the parasites in a multiple infection are dead. Supernumerary juvenile parasites do not suffer differential mortality. The developmental stage of the female parasite does not seem to influence the likelihood of death. The presence of dead parasites may not confer an acquired immunity to re-infection. These features suggest that parasite death is typically the result of activation of a successful host defensive process rather than indicative of a defect on the part of the parasites. Parasitized female hosts can regain their reproductive capabilities following death of the parasite. Post-parasitic broods are smaller than normal. Reproductive recovery is presumed to provide the selective pressure favouring evolution of a lethal host response. The host-produced sheath surrounding female parasites is a haemocytic response. Sheaths enclosing dead parasites are thicker and more electron dense than those containing healthy parasites. The sheath of a healthy P. conformis may actually protect the parasite from a more intense host response.

Malaria is one of the most serious infectious diseases with ~250 million clinical cases annually. Most cases of severe disease are caused by Plasmodium falciparum. The blood stage of Plasmodium parasite is entirely responsible for malaria-associated pathology. Disease syndromes range from fever to more severe complications, including respiratory distress, metabolic acidosis, renal failure, pulmonary oedema and cerebral malaria. The most susceptible population to severe malaria is children under the age of 5, with low levels of immunity. It is only after many years of repeated exposure, that individuals living in endemic areas develop clinical immunity. This form of protection does not result in sterilizing immunity but prevents clinical episodes by substantially reducing parasite burden. Naturally acquired immunity predominantly targets blood-stage parasites and it is known to require antibody responses. A large body of epidemiological evidence suggests that antibodies to Plasmodium antigens are inefficiently generated and rapidly lost in the absence of ongoing exposure, which suggests a defect in the development of B cell immunological memory. This review summarizes the main findings to date contributing to our understanding on cellular processes underlying the slow acquisition of humoral immunity to malaria. Some of the key outstanding questions in the field are discussed.

Insecticide-treated nets (ITNs) are a major tool to control malaria. Over recent years increased ITN coverage has been associated with decreased malaria transmission. However, ITN ‘misuse’ has been increasingly reported and whether this emergent behaviour poses a threat to successful malaria control and elimination is an open question. Here, we use a game theory mathematical model to understand the possible roles of poverty and malaria infection protection by individual and emerging ‘community effects’ on the ‘misuse’ of malaria bednets. We compare model predictions with data from our studies in Lake Victoria Islands (LVI), Kenya and Aneityum, Vanuatu. Our model shows that alternative ITN use is likely to emerge in impoverished populations and could be exacerbated if ITNs become ineffective or when large ‘community effects’ emerge. Our model predicted patterns of ITN use similar to the observed in LVI, where ‘misuse’ is common and the high ITN use in Aneityum, more than 20 years after malaria elimination in 1990. We think that observed differences in ITN use may be shaped by different degrees of economic and social development, and educational components of the Aneityum elimination, where traditional cooperative attitudes were strengthened with the malaria elimination intervention and post-elimination surveillance.

The ultrastructure of the merozoite of Eimeria tenella has been studied by means of electron microscopy. The first-generation merozoite is approximately 3·4 μm in length, and 1·2 μm in width, while the second-generation merozoite is approximately 10·5 μm in length and 1·5 μm in width.

The cell wall of the merozoite consists of a double membrane, but at the anterior extremity the existence of a fluted collar gives the appearance of two narrow double membranes separated by a zone of less electron-dense material. Twenty-four surface fibrils are distributed around the periphery; they extend along the entire length of the organism and lie beneath the double limiting membrane.

The anterior end of the merozoite is distinguished by a conoid apparatus which includes several components. A bulbiform outer annulus is invested by a fluted collar, and itself encloses an extrusible papilla. Two osmiophilic fibrils, the paired organelles, arise within the extrusible papilla and extend longitudinally into the cytoplasm. Twenty-four smaller fibrils, or toxonemes, also arise within the conoid and pass back into the main body of the organism.

The cytoplasm of the merozoite includes mitochondria, glycogen, dense elliptical granules and endoplasmic reticulum, together with a definite Golgi complex. A nucleus is located in the posterior third of the organism and is enclosed by a perforated double membrane. At the posterior extremity the double membrane which bounds the organism is broken by a pore 700 A in diameter.

Our sincere thanks are due to Mr P. Richmond for technical assistance, and we are grateful to the Central Veterinary Research Laboratory, Weybridge, for supplying the strain of Eimeria tenella.

Larvae of the cattle tick Boophilus microplus will attach to thin (0·3–0·5 mm) slices of cattle skin and engorge on a partially denned medium at 35 °C. Forty-seven to 83% of the larvae had engorged by 8 days, and 51–71% of these moulted to nymphs. Tissue culture medium alone allowed little growth unless supplemented with dialysed, freeze dried bovine serum (7%, w/v). This medium could be further defined by substituting purified bovine serum albumin (Cohn fraction V) for the dialysed bovine serum. In one experiment, nymphs of Haemaphysalis longicornis engorged and later moulted to adults. Skin slices were used fresh or after freeze-drying and storing at − 25 °C. The possible uses of the culture method are discussed.

Plasmodium vinckei infections, which usually kill mice within 7 days, can be terminated in the majority of cases by a single injection of chloroquine phosphate equivalent to 10 mg/100 g body weight. After such drug treatment the parasites disappear from the blood for 6–11 days, after which a recrudescence with a low peak occurs. Most animals overcome this second parasitaemia and the parasites finally disappear completely. After recovery, mice exhibit an immune response to a challenge infection and, after a short period of parasitaemia during which a low peak is reached, the animals recover completely. This immunity, once acquired, apparently persists for the lifetime of the host. The establishment of the immune state depends on the period of patent parasitaemia during the primary infection and the longer this period the greater is the chance of a solid immunity developing. Immunity may be exhibited by mice treated with chloroquine as early as the 3rd day of infection. Killed parasites have no immunizing effect. Mice splenectomized before infection are capable of an immune response, and mice splenectomized after radical cure are also able to overcome a challenge infection. In both these cases more than one injection of chloroquine is required. The immunity produced in mice is that of the true sterile type, equivalent to that produced against P. berghei in rats, and is species-specific, conferring no resistance to infection with P. berghei. P. vinckei infections in mice provide a useful immunological model for laboratory studies. The immune response is predictable and easy to induce, and this parasite is therefore superior to P. berghei for immunological studies. Attention is drawn to the fact that in P. vinckei the infection is brought under control by the immune response and not by the antimalarial drug; therefore this ought to be taken into consideration in the assessment of drug trials.

1. Ixodes hexagonus is a three-host tick.

2. The length of the pre-oviposition period is fairly constant at 19° C. in a saturated atmosphere, varying between 12 and 14 days.

3. Oviposition takes place as in I. ricinus and, at room temperatures at 18–20° C., R.H. 100%, the number of eggs laid varies from 880 to 1449. Experiments on the effects of different temperatures and humidities on egg-laying are described.

4. Eggs hatch in 52–59 days under the conditions stated above.

5. The larvae gorge for 3–6 days, the majority becoming replete on the third and fourth days after attachment.

6. The metamorphosis of the larva is prolonged by cold conditions and is hastened during warm weather. In a saturated atmosphere at 15, 20, 22 and 25° C., the mean times for moulting are respectively 60, 33, 27 and 23 days.

7. The nymphs gorge for 5–7 days, the greater number dropping off between the sixth and seventh days.

8. At 18° C. and 100% R. H. moulting of the nymph takes place about 32 days after repletion.

9. After metamorphosis the adults rest for 8–12 days, and feeding lasts 8–16 days.

Toxoplasmosis is a significant public health threat for Inuit in the Canadian Arctic. This study aimed to investigate arctic seals as a possible food-borne source of infection. Blood samples collected from 828 seals in 7 Canadian Arctic communities from 1999 to 2006 were tested for Toxoplasma gondii antibodies using a direct agglutination test. Polymerase chain reaction (PCR) was used to detect T. gondii DNA in tissues of a subsample of seals. Associations between seal age, sex, species, diet, community and year of capture, and serological test results were investigated by logistic regression. Overall seroprevalence was 10·4% (86/828). All tissues tested were negative by PCR. In ringed seals, seroprevalence was significantly higher in juveniles than in adults (odds ratio=2·44). Overall, seroprevalence varied amongst communities (P=0·0119) and by capture year (P=0·0001). Our study supports the hypothesis that consumption of raw seal meat is a significant source of infection for Inuit. This work raises many questions about the mechanism of transfer of this terrestrial parasite to the marine environment, the preponderance of infection in younger animals and the natural course of infection in seals. Further studies to address these questions are essential to fully understand the health risks for Inuit communities.

Myxosporean parasites are significant parasites of fishes not only for their apparent high diversity but also for their potential impact on fish health and/or marketability. Regardless, our knowledge of most myxosporeans, especially those found in elasmobranch hosts, is superficial. A study of multivalvulidan diversity in a range of elasmobranchs from Queensland, Western Australia and the Northern Territory (Australia) was conducted to address this knowledge gap. Specimens were collected from a total of 3 orders, 9 families and 31 species of elasmobranchs. Myxosporean infections referable to the genus Kudoa were discovered in host muscle and characterized morphologically and genetically. Both small subunit (SSU) and large subunit (LSU) rDNA sequences were used in molecular phylogenetic analyses. Kudoa spp. infected 27 of the 31 species of elasmobranchs examined, representing new records of this parasite genus in 26, of the 27, host species. Kudoids were observed in all 3 orders, and 7 out of the 9 families of elasmobranchs investigated. This paper reports the first 2 multivalvulidan species to be formally described from elasmobranchs, Kudoa hemiscylli n.sp. characterized from Hemiscyllium ocellatum (and 8 other host species) and Kudoa carcharhini n. sp. characterized from Carcharhinus cautus (and 2 other host species). Phylogenetic analyses revealed that kudoids from elasmobranchs form a separate lineage to those of teleosts, but are anchored within the overall kudoid clade.

TaqMan minor groove binder probes were evaluated as to their suitability for the real-time allelic discrimination of the β-tubulin codon 200 TTC/TAC single nucleotide polymorphism in cyathostomin species. Amplification of titrated cloned full-length β-tubulin cDNA revealed that the TaqMan minor groove binder PCR is capable of specifically detecting as few as 10 copies. Testing of DNA from single adult and larval stages of several different species of cyathostomin allowed reproducible genotyping of individual worms. Using the real-time PCR approach, the throughput of samples was considerably increased compared with conventional post-PCR readout procedure. Only 7·8% homozygous TAC L3 were found among 102 L3 which were genotyped from phenotypically BZ-resistant small strongyle populations. The percentages of the homozygous TTC and heterozygous TTC/TAC were 41·3% and 50·9%, respectively. This resulted in a total TAC-allele percentage of only 33·3%. These findings correspond to data obtained by genotyping of an experimentally selected BZ-resistant cyathostomin population. It is concluded that the β-tubulin codon 200 polymorphism is not the sole mechanism involved in the process of BZ resistance in cyathostomins.

An artificial skin of hardened gelatine was used to examine the factors affecting penetration of skin by cercariae of the bird schistosome, Austrobilharzia terrigalensis.

The percentage of cercariae able to penetrate through a gelatine membrane was increased by a factor of 3–4 by coating the membrane with a thin layer of lipid collected from the surface of chicken skin.

The free sterol fraction, isolated from chicken skin surface lipid by thin-layer chromatography, stimulated penetration to the same extent as whole skin lipid.

Cholesterol was detected in the sterol fraction by mass spectrometry and pure cholesterol had the full stimulating effect on cercarial penetration.

Skin lipid, from which free sterols had been removed, lost the stimulatory effect on cercariae, but full activity was recovered by adding cholesterol to the sterol-free lipid. Fractions of skin lipid containing free fatty acids or triglycerides, wax esters and sterol esters similarly failed to stimulate penetration.

These results establish that penetration of A. terrigalensis cercariae is greatly stimulated by the free sterols present in the surface lipid of chicken skin but cholesterol may not be the only active sterol. Cholestanol and the plant sterols campesterol and β-sitosterol were also detected in chicken skin surface lipid. These sterols were not tested for activity on cercariae because samples free from cholesterol could not be obtained.

Some cercariae were able to penetrate plain gelatine membranes not coated with cholesterol but small amounts of free sterol were detected in the gelatine itself. This sterol could not be completely removed by prolonged solvent extraction and consequently it is not known whether any cercariae are able to penetrate in the complete absence of sterols.

Temperature had a marked effect on penetration of cercariae; lowering the temperature from 40 to 25 °C reduced the number of successful penetrants by a factor of 4.

I am grateful to Miss V. Bowen for excellent technical assistance and to Dr J. McLeod of the Research School of Chemistry, Australian National University, who performed and interpreted the mass spectrometry. This investigation was partly supported by a research grant from the World Health Organization.