During 1988 and 1989, the mesenteric veins of 901 cattle were examined for the presence of schistosomes at the Kandy slaughterhouse (Sri Lanka). The overall prevalence of infection was 31·2%. Animals younger than 2 years were less infected (21·3%) than those older than 5 years (47·9%). Based on the number of paired worms counted, three intensities of infection were recognized: low (1–20 pairs), moderate (21–100 pairs) and heavy (> 100 pairs). Intensities increased with the age of the animals but remained low (average 10 worm pairs). The worm burden increased by approximately 20% for each step in age group. The number of miracidia/100 g faeces was measured in 85 animals of all age groups and intensities of infection; 77% of the samples contained less than 100 miracidia. Miracidia counts decreased with age; moderately and heavily infected animals in each age group had the highest and the lowest counts, respectively. This may be due to a host immune response. The results raise questions on the sensitivity of faecal egg counts as a diagnostic method for visceral schistosomiasis in cattle.

Ecological specialization is hypothesized to result from the exploitation of predictable resource bases. For parasitic organisms, one prediction is that parasites of large-bodied host species, which tend to be long-lived, should specialize on these hosts, whereas parasites of small host species, which represent more ephemeral and less predictable resources, should become generalists. We tested this prediction by quantifying the association between the level of host specificity of fleas and the mean body mass of their mammalian hosts, using published data from 2 large, distinct geographical regions (South Africa and northern North America). In general, we found supporting evidence that flea host specificity, measured either as the number of host species exploited or their taxonomic distinctness, became more pronounced with increasing host body mass. There were, however, some discrepancies among the results depending on the different measures of host specificity, the geographical region studied, or whether we used the raw values or phylogenetically independent contrasts. These are discussed with respect to other forces acting on the evolution of host specificity in parasites, as well as in the context of the regions' contrasting evolutionary histories. Overall, though, our findings indicate that the exploitation of large-bodied, and therefore long-lived, host species has promoted specialization in fleas, most likely because these hosts represent predictable resources.

The response of the plant parasitic nematode, Meloidogyne incognita (J2 stage) to avermectin B2a-23-one is triphasic, comprising an initial loss of locomotor activity where the juveniles remain sensitive to touch, a recovery phase and a final loss of activity where the juveniles are relatively insensitive to touch. In contrast, the acetylcholinesterase inhibitor, oxamyl, causes initial hyperactivity of juveniles followed by a progressive decline in movement. The addition of bicuculline and to a lesser extent picrotoxin, both antagonists of γ-aminobutyric acid (GABA), blocks the action of avermectin on M. incognita.

Recent publications demonstrated that a fragment of a Neospora caninum ROP2 family member antigen represents a promising vaccine candidate. We here report on the cloning of the cDNA encoding this protein, N. caninum ROP2 family member 1 (NcROP2Fam-1), its molecular characterization and localization. The protein possesses the hallmarks of ROP2 family members and is apparently devoid of catalytic activity. NcROP2Fam-1 is synthesized as a pre-pro-protein that is matured to 2 proteins of 49 and 55 kDa that localize to rhoptry bulbs. Upon invasion the protein is associated with the nascent parasitophorous vacuole membrane (PVM), evacuoles surrounding the host cell nucleus and, in some instances, the surface of intracellular parasites. Staining was also observed within the cyst wall of ‘cysts’ produced in vitro. Interestingly, NcROP2Fam-1 was also detected on the surface of extracellular parasites entering the host cells and antibodies directed against NcROP2Fam-1-specific peptides partially neutralized invasion in vitro. We conclude that, in spite of the general belief that ROP2 family proteins are intracellular antigens, NcROP2Fam-1 can also be considered as an extracellular antigen, a property that should be taken into account in further experiments employing ROP2 family proteins as vaccines.

Cylicospirura heydoni (Baylis) is redescribed, from what is assumed to be paratype material (Queensland) and from Dasyurus quoll (Tasmania) and Dasyurops maculatus (N.S. Wales). Cyathospirura dasyuridis, sp.nov., is described from the same host spp., from N.S.W. and Tasmania.

Some specimens and some intact nodules were sent by Mr Green of Queen's Museum, Launceston, Tasmania. Skinned animals were given to me for dissection by Mr Peter Aitken, Curator of Mammals, at the South Australian Museum. To both of these collectors I am most grateful.

Types of the new species will be deposited in the South Australian Museum.

The grass in the vicinity of the town of Lourenço Marques is often infested by larval ticks, especially in places frequented by cattle. These ticks are so numerous as to constitute a veritable scourge, since they attack a variety of animals, and man is frequently a victim to their onslaughts. The ticks are especially prevalent in July and August. Their bites may produce merely a local effect, but in some persons general symptoms may follow.

1. The dorsal plate which probably represents a rudimentary scutum in some Argasid larvae is discussed and described.

2. The respiratory system of the larvae of some species of Argas and Ornithodorus is described.

3. The systematic position of the lahorensis group of the genus Ornithodorus is discussed and the use of the name Alveonasus with an emended diagnosis for this group is suggested.

4. Ornithodorus procaviae n.sp. is described. Two other probably new species are described provisionally, but not named.

5. New records for other species of Argasidae in Israel are given.

Babesia rodhaini infected mouse and rat red cells were non-infective after receiving 40 or 60 krad irradiation from a 60Co source.

Rats inoculated with irradiated infected red cells were subsequently found to show strong resistance to homologous challenge.

Mice, which are more susceptible to B. rodhaini, showed less resistance to challenge, following immunization with irradiated B. rodhaini infected red cells.

Splenectomized rats were immunized with irradiated infected blood. There was a delay compared with the controls in the onset of acute fatal parasitaemias in these rats. A population of parasites was isolated by taking and mixing blood from each of the splenectomized rats during the patent parasitaemia following challenge. This population appeared to be an antigenic variant of the original immunizing population.

I thank Mrs J. Page for excellent technical assistance and Dr K. N. Brown for criticizing the manuscript.

On day 10 of a primary infection of Trichinella spiralis in NIH mice, when adult worms were in the process of being expelled, their fecundity was markedly depressed. Upon transplantation to new host mice, the worms were able to establish successfully in their usual position in the anterior small intestine, even if originally recovered from the large intestine of mice expelling their worms, and these worms fully recovered their fecundity after 7 days in recipients. On day 5 of secondary and tertiary infections, immediately before loss of worms began, the adult worms were stunted and had a depressed fecundity. However, such worms, when transplanted, were able to establish in normal numbers and in a normal position in the intestine of recipient mice. Additionally, these worms were found to have developed a fecundity, and grown to a length, comparable to that of normal worms, but slightly less than that of control worms transplanted from day 7 of a primary infection, after 7 days in a new host. Electron microscopy showed that worms taken at the time of expulsion in primary and tertiary infections showed structural abnormalities, including large quantities of lipid in intestinal cells and somatic musculature and decreased quantities of stored glycogen. Upon transplantation to new host mice, these worms were found to have recovered a normal ultrastructural appearance within 7 days, although there was still evidence of a slightly elevated lipid and depressed glycogen content. It is concluded that immune expulsion of T. spiralis from mice does not involve irreversible damage to the worms.

The survival of the free-living stages of Trichostrongylus colubriformis under defined conditions of temperature and relative humidity was investigated. The survival of embryonated eggs was poor at 0, 33 and 54·5 % relative humidity (rel. hum.) at 20 °C but hatching occurred from a proportion of eggs even after exposure for 104 days to 76 and 98% rel. hum. at 20 °C. Second-stage larvae were desiccation-susceptible and were killed within 6 h even at 98% rel. hum. and 20 °C. Infective larvae, dried separately or in clumps, survived prolonged exposure to desiccation at 33–98% rel. hum. and 20 °C with 50% survival times of 58–164 days. Clump formation did not enhance survival in this range. Infective larvae also survived exposure to vacuum desiccation with 50% survival times of 8·8 h in clumps and 4·5 h when dried separately. The infective larva thus readily survives desiccation and may prove a useful model for the study of anhydrobiosis.

Hatching of eggs of Anguillicola crassus was studied at temperatures between 5 and 30°C. Hatching occurred between 10 and 30°C and the incubation time was inversely related to temperature. Survival, spontaneous and excitatory rate of activity of 2nd-stage larvae of A. crassus were also affected by temperature. The percentage of larvae eaten by Paracyclops fimbriatus was not always influenced by the activity of the larvae. Penetration efficiency into the haemocoel of the intermediate host was highest for freshly hatched larvae and declined gradually with age. Completely non-active larvae were still able to penetrate, although penetration efficiency was lower.

The specific composition of the parasitic helminth fauna of wild ruminants in Britain has not been examined for 30 years, and the series of surveys to be described were undertaken to provide data on this aspect of helminth epidemiology. With the increase in interest in conservation of wild stock, and especially ruminants, in recent years, information on the epidemiology of their helminth infections is an essential adjunct to any schemes for their protection and husbandry.

The common roe deer, Capreolus capreolus capreolus, is distributed throughout Europe and Asia, the other subspecies, G. c. pygargus, the Siberian roe, G. c. bedfordi, the Manchurian roe, and C. c. melanotis, the Szechwan roe, being limited in range. It is indigenous to Britain, and over the centuries its populations have undergone great numerical fluctuations. Though at one time nearly extinct in England except in the counties on the Scottish marches it appears at present to be in a period of resurgence, and the range is extending from dense foci in the south and south-east to join the northern population. It has always been numerous in mainland Scotland and a few of the Western Isles, but is extinct in Wales and Ireland (Whitehead, 1964). The roe is the smallest of our indigenous deer and differs from the others in its breeding habits, not forming herds, but grouping as family units of buck, doe and offspring. On the mainland of Europe, however, herding does take place, and a limited migration has even been observed in Russian roe (Flerov, 1952). Its habitat is essentially woodland, but it grazes open areas to some extent and, not-withstanding its timid character, lives in close proximity to man in agricultural and even in urban areas.

Golden hamsters were given plerocercoids of Diphyllobothrium dendriticum either singly or in groups of 2, 4, 8 or 15. There was a higher rate of recovery of worms from hamsters given many (8 and 15) than from those given few (1, 2 or 4) plerocercoids. The difference in rate of recovery of worms was present from 2 h after administration of plerocercoids and persisted up to day 20 when experiments were ended. Denser tapeworm populations had the smallest individuals and some of them contained worms with primary strobilae at the start of egg production. The size of the tapeworm population did not influence the prepatent time. Also, with the common gull there was a higher rate of recovery of worms when plerocercoids were given in groups. These results are discussed in relation to aspects of the life-cycle of D. dendriticum where the natural final host is most probably normally infected by a larger number of plerocercoids at the same time.

During their growth in vitro, promastigotes of Leishmania amazonensis undergo differentiation from complement-susceptible to complement-resistant forms. Here, we demonstrate that both forms bind comparable amounts of C3 on their surfaces, with the predominant molecule species being the haemolytically active C3b. Likewise, equivalent amounts of C9 are deposited on both forms of promastigotes. However, while C9-bearing complexes are exposed on the cell surface of resistant promastigotes, they are cryptic in the susceptible stage of the parasites. The membrane fraction of complement-resistant promastigote lysates has the ability to inhibit complement-mediated haemolysis, blocking C9, but not C3 deposition to complement-activating complexes. Moreover, the membrane fraction of complement-resistant promastigote lysates can inhibit the late steps of guinea-pig erythrocyte lysis much more efficiently than complement-susceptible ones. Our results indicate that L. amazonensis promastigotes evade complement killing by inhibiting the cytolytic pathway of the complement cascade.

Adults of the monogenean genus Protopolystoma infecting Xenopus species occur in an extremely space-limited habitat, the urinary bladder. Xenopus wittei, from a population in Rwanda naturally infected with Protopolystoma fissilis and Protopolystoma simplicis, were exposed to reinfection in captivity (for 1–3 months post-capture) and then monitored in the laboratory for up to 5 months in transmission-free conditions. The two parasites co-occurred in individual bladders less frequently than expected if they were dispersed randomly. Distribution of bladder infections was significantly non-independent (n=157) and gravid worms of both species were never found in the same host. This pattern might be explained by interference competition between the parasites or by genetic differences in susceptibility within the host species, which is of allopolyploid origin. Other distributional data for sympatric polystomatid species pairs, including P. fissilis and P. ramulosus, show concurrent infections at frequencies consistent with random distributions (i.e. no evidence of interspecific competition or variability in species-specific susceptibility of the hosts). Interference between P. fissilis and P. simplicis (assuming host genetic factors are not involved) may therefore result from a mechanism specific to this species pair. Observations on infection turnover in captive hosts suggest that loss of adult worms may be related to the arrival of juveniles (of either species) in the urinary bladder. Ectopic infection of the host urinary ducts by adult and subadult P. fissilis was observed in some single-species infestations and may be density related. However, the use of an ectopic-site ‘refugium’ has never been observed in concurrent polystomatid infections.

In the intestine of freshwater fishes, two morphologically different types of diplomastigine flagellates have so far been found to exist: Hexamita salmonis (Moore, 1920) specific for fishes, and Spironucleus elegans Lavier, 1936, identical with the flagellate from amphibia.

The identity of the Spironucleus from fishes and amphibia has been demonstrated by infecting Pterophyllum scalare with flagellates from newts per os, per rectum and with contaminated food.

A redescription of motile stages of both Hexamita salmonis and Spironucleus elegans is presented, together with a list of existing findings of fish diplomastigines, and a brief discussion.

The genotypes of both host and parasite may influence the outcome of parasitic infections, but few attempts have been made to quantify the effect of parasite genotype on macroparasite infections of socio-economic importance. We examined variation in particular traits during the infection in pigs with the parasitic nematode Ascaris suum. We infected 26 pigs with mixtures of equal proportions of embryonated eggs from 4 single female worms each with a unique mtDNA haplotype – the eggs from each female worm were a mixture of siblings and half-siblings. Pigs were necropsied on days 14, 17 and 28 following inoculation, which corresponded to time-points before, during and after the main immune responses against the nematode. A total of approximately 11 000 worms were recovered at necropsy. The location in the small intestine was recorded for all worms and the length and mtDNA haplotype were determined for about 4200 individual worms. There were significant differences in the distribution and abundance of the 4 individual haplotypes among individual pigs demonstrating strong interactions between parasite and host. We found significant differences in the abundance and position in the small intestine as well as the size of worms among haplotypes. We conclude that both parasite and host effects as well as the interplay between them play important roles in determining the characteristics and outcome of infection.

We tested whether the prevalence of ticks can be predicted reliably from a simple epidemiological model that takes into account only mean abundance and its variance. We used data on the abundance and distribution of larvae and nymphs of 2 ixodid ticks parasitic on small mammals (Apodemus agrarius, Apodemus flavicollis, Apodemus uralensis, Clethrionomys glareolus and Microtus arvalis) in central Europe. Ixodes trianguliceps is active all year round, occurs in the study area in the mountain and sub-mountain habitats only and inhabits mainly host burrows and nests, whereas Ixodes ricinus occurs mainly during the warmer seasons, occupies a large variety of habitats and quests for hosts outside their shelters. In I. ricinus, the models with k values calculated from Taylor's power law overestimated prevalences. However, if moment estimates of k corrected for host number were used instead, expected prevalences of both larvae and nymphs I. ricinus in either host did not differ significantly from observed prevalences. In contrast, prevalences of larvae and nymphs of I. trianguliceps predicted by models using parameters of Taylor's power law did not differ significantly from observed prevalences, whereas the models with moment estimates of k corrected for host number in some cases under-estimated relatively lower larval prevalences and over-estimated relatively higher larval prevalences, but predicted nymphal prevalences well.

Both individuals of a pair of Diplozoon paradoxum Nord., 1832, when parasitizing the gills of Rutilus rutilus, are normally attached to the same hemibranch but never to the same surface of one primary lamella. A preference is shown for attachment to certain gills and also to particular locations on the gills.

Diplozoon paradoxum displays asymmetry of its haptor when attached to the gills of the roach but the haptor assumes bilateral symmetry when unattached. As in Discocotyle, this impermanent asymmetry is facultative to the left or right, dependent upon the incidence of the gill-ventilating current, so that the body of a worm will present the least amount of resistance to the water as it passes across the gills. It is probable that impermanent, facultative asymmetry occurs in other species of the genus Diplozoon, and the usefulness of the asymmetrical nature of the haptor as a taxonomic criterion is therefore extremely limited.

It is a pleasure to record my thanks to Dr F. G. Rees, University College of Wales, Aberystwyth, for her encouragement and guidance and to Dr J. Llewellyn, University of Birmingham, for his valuable help and critical reading of the manuscript. I am indebted to Mr D. Haigh for supplying me with fishes. This work was done while receiving a grant from the Department of Scientific and Industrial Research.

Many vector-borne pathogens whose primary vectors are generalists, such as Ixodid ticks, can infect a wide range of host species and are often zoonotic. Understanding their transmission dynamics is important for the development of disease management programmes. Models exist to describe the transmission dynamics of such diseases, but are necessarily simplistic and generally limited by knowledge of vector population dynamics. They are typically deterministic SIR-type models, which predict disease dynamics in a single, non-spatial, closed patch. Here we explore the limitations of such a model of louping-ill virus dynamics by challenging it with novel field data. The model was only partially successful in predicting Ixodes ricinus density and louping-ill virus prevalence at 6 Scottish sites. We extend the existing multi-host model by forming a two-patch model, incorporating the impact of roaming hosts. This demonstrates that host movement may account for some of the discrepancies between the original model and empirical data. We conclude that insights into the dynamics of multi-host vector-borne pathogens can be gained by using a simple two-patch model. Potential improvements to the model, incorporating aspects of spatial and temporal heterogeneity, are outlined.