We studied nestedness and its relationships with beta-diversity in flea communities harboured by three closely related rodent species (Rhabdomys pumilio, Rhabdomys intermedius, Rhabdomys dilectus) at two spatial scales (within and among host populations) in South Africa and asked (a) whether variation in species composition of flea communities within and among host populations follows a non-random pattern; if yes, (b) what are the contributions of nestedness and species turnover to dissimilarity (= beta-diversity) among flea communities at the two scales; and (c) do the degree of nestedness and its contribution to beta-diversity differ among host species (social vs solitary) and between scales. We found that nestedness in flea assemblages was more pronounced (a) in social than solitary host species and (b) at lower (among host individuals within populations) than at higher scale (among host populations). We also found that higher degree of nestedness was associated with its higher contribution to beta-diversity. Our findings support earlier ideas that parasite community structure results from the processes of parasite accumulation by hosts rather than from the processes acting within parasite communities.

Parasite transmission can be altered via the removal of parasites by the ambient communities in which parasite–host interactions take place. However, the mechanisms driving parasite removal remain poorly understood. Using marine trematode cercariae as a model system, we investigated the effects of consumer and host body size on parasite removal rates. Laboratory experiments revealed that consumer or host body size significantly affected cercarial removal rates in crabs, oysters and cockles but not in shrimps. In general, cercarial removal rates increased with consumer (crabs and oysters) and host (cockles) body size. For the filter feeding oysters and cockles, the effects probably relate to their feeding activity which is known to correlate with bivalve size. Low infection levels found in cockle hosts suggest that parasite removal by hosts also leads to significant mortality of infective stages. The size effects of crab and shrimp predators on cercarial removal rates were more complex and did not show an expected size match-mismatch between predators and their cercarial prey, suggesting that parasite removal rates in predators are species-specific. We conclude that to have a comprehensive understanding of parasite removal by ambient communities, more research into the various mechanisms of cercarial removal is required.

1. The morphology and life history of a new haplosporidian parasite, Nephri-diophaga xenoboli sp.nov. from the gut of a millipede, Xenobolus carnifex are described.

2. The earliest stage hatched from the spore is a free uninucleate amoebula which penetrates the gut epithelium and grows into a multinucleate plasmodium.

3. The uninucleate gametes are formed by a process of endogeneous budding in the centre of the plasmodium and the sporoblast is formed as a result of fusion of two such gametes.

4. A characteristic cyst membrane enclosing about forty to fifty sporoblasts is formed immediately after fertilization is completed which is accompanied by a disintegration of the peripheral layer of the cytoplasm of the plasmodium.

5. Each sporoblast develops into a bivalved simple spherical spore, 3·0μ in diameter.

The presence of Ellobiopsis chattoni is recorded on Undinula vulgaris var. major for the first time.

The presence of this parasite in shallow tropical water, within a temperature range of 25·92–26·28° C. (salinity range 35·43–36·38‰) is recorded for the first time.

It is noted that the parasite was completely species specific to its host.

Table l analyses the incidence of the parasite in a population of Undinula vulgaris.

It was found that the parasite affected egg production in the ovaries. The suggestion is that it produces a starvation effect on the copepod, this effect being reversible.

The tegument of the metacercaria of Gorgoderina vitelliloba contains S1, S2, S3 and S4 secretory bodies. Between the parenchymal cells 2 types of tegumental cyton occur. Type 1 contains S1 and S3 secretory bodies, whilst S2 and S4 bodies are limited to Type 2. Type 1 cytons and S1 secretory bodies disappear at excystment. Post-metacercariae contain a third type of tegumental cyton in which a new secretory body, S5, occurs. This cyton type disintegrates 1–5 days after infection. The maintenance and development of the outer anucleate layer after this period is the responsibility of Type 2 cytons. Type 2 cytons and S2 and S4 secretory bodies have also been found within the cercarial body. When juvenile flukes migrate from the kidney to the bladder of their frog definitive host 21 days after infection, the outer anucleate layer increases in electron density. Within the bladder, however, the tegument of the adult fluke appears normal. The distribution of mitochondria within the outer anucleate layer changes during the fluke's migration. The mitochondria, which have a random distribution in the metacercaria, are located adjacent to the outer and basal plasmalemmas in the early kidney stages. In late kidney stages and bladder stages mitochondria occur only against the former membrane. The mitochondria increase in size in the adult fluke.

This paper describes a compartmental model incorporating biological details of the transmission of canine visceral leishmaniasis in southern France. In contrast to earlier, empirical models (Jolivet, 1977; Rioux, Croset & Lanotte, 1977) the new model (1) predicts a threshold density of sandflies below which transmission cannot be sustained, (2) suggests that, until better data become available, the maximum prevalence of infection obtained at high sandfly density should be considered an unknown quantity.

The material which forms the basis of the following account consists of two tubes of tapeworms collected from ostriches at the Veterinary Pathological Laboratory, Nairobi, British East Africa. One tube contained approximately 12 scolices and the anterior portions of the strobilae attached to them, together with several fragments of the more posterior portions: these are described under the name Davainea beddardi n. sp. The other tube contained one large fragment of a Davainea and several smaller pieces but no scolices: these are described under the heading Davainea sp. For this material I am indebted to Professor G. H. F. Nuttall, F.R.S. to whom I wish here to express my thanks. I have also to acknowledge my indebtedness to the Librarian of the Royal College of Veterinary Surgeons for allowing me to consult literature unobtainable elsewhere.

The evolution of faecal egg output, worm burdens and tissue egg counts in young calves was monitored during the first year of natural exposure to Schistosoma mattheei infection on a Zambian farm. According to the duration of their stay on the farm, these calves were classified into 2 groups of 14 temporary tracers (TT calves) which were introduced on a 2-monthly basis for residential periods of 2 months, and 12 permanent tracers (PT calves) introduced either at the beginning of the experiment (Group A) or 2 months later (Group B) and gradually removed after residential periods of 2, 4, 6, 8, 10 and 12 months on the farm. Worm counts in the TT calves showed that infection occurred throughout the year on the farm and that levels of infection acquired during each period of 8 weeks correlated well with the respective infected snail densities observed at the main transmission site. Marked differences in worm population dynamics were recorded between the 2 groups of PT calves. In Group B animals which apparently were initially exposed to heavy transmission, according to the results from TT calves, much higher worm counts and greater susceptibility to reinfection were observed than in Group A animals initially exposed to lighter exposure. These results suggest that the development of resistance to natural infection with S. mattheei may depend on the initial exposure to the parasite. Low initial exposures may lead to resistance whereas high initial exposures may result in decreased immune responses resulting in susceptibility to infection.

Theileria annulata was transmitted transtadially by an Israeli strain of Hyalomma excavatum from larvae to nymphs and from nymphs to adults. However, the adults developing from larvae which engorged on infected calves and fed during the nymphal stage on non-infected calves, rabbits or gerbils (Meriones tristrami), did not transmit theileriosis. Suspensions of infected unfed nymphs or adults did not produce theileriosis but both nymphs and adults of the same batch became infective to cattle after 2 days of feeding. Suspensions of salivary glands or of whole ticks derived from infected adults that remained attached to rabbits for more than 7 days, were not infective to cattle.

In the present study, the diagnostic value of Trypanosoma cruzi recombinant protein (Tc24) was examined. Although antibodies against Tc24 were detected during natural and experimental T. cruzi infections, specificity studies revealed that sera from T. rangeli-infected mice also recognized to some extent Tc24 protein. In addition, sera from Tc24-immunized mice reacted against a 21 kDa polypeptide in T. rangeli extracts. Detailed analysis of the antibody response against 20—40 peptide localized in the Tc24 amino-terminal domain suggests that this sequence is not expressed by T. rangeli 21 kDa antigen. Therefore, the PCR reaction using oligonucleotides corresponding to a 20–26 peptide clearly demonstrated the specificity of the oligoprobes for T. cruzi identification. Positive signals were also found when using blood samples from T. cruzi-infected mice. Taken together, these results suggest that the PCR-based 20–26 assay may be useful in the specific diagnosis of Chagas' disease.

The response of individual adult males of the potato cyst nematodes, Globodera rostochiensis and G. pallida, to sex pheromones from adult females was investigated using electrophysiological techniques. Each male nematode was pierced with an electrode close to the cephalic region and then exposed to pheromones from virgin females. Cellular responses in the form of action potentials were recorded as spike activity. The spike frequency produced by G. rostochiensis and G. pallida males increased significantly after the application of their homospecific pheromone. The spike frequency produced by G. pallida males also increased significantly after the application of G. rostochiensis female sex pheromone. In contrast, males of G. rostochiensis showed no significant response to G. pallida female sex pheromone. The electrophysiological results support and considerably extend information from agar plate behavioural bioassays.

The intimate cell relationships of Hymenolepis diminuta are described and occur between cells of the parenchyma, excretory system, muscle and tegument. The cell relationships are of three types: (a) a tight junction or zonula occludens; (b) a desmosome-like structure without tonofibrils or intercellular dense line; (c) a junctional complex with modified unit membranes and an intercellular region of dense granules and fibres.

This research was begun while one of us (L.T.T.) was a Visiting Lecturer in the Biology Department, Rice University, and completed in the Zoology Department, Queen's University, Belfast. We should like to thank Dr C. W. Philpott for allowing us the full use of the facilities of his electron-microscope unit and Mr W. Ferguson for photographic assistance.

Transmission of Trypanosoma cruzi, the causal agent of Chagas disease, has expanded from rural endemic to urban areas due to migration. This so-called urban Chagas is an emerging health problem in American, European, Australian and Japanese cities. We present a mathematical model to analyse the dynamics of urban Chagas to better understand its epidemiology. The model considers the three clinical stages of the disease and the main routes of inter-human transmission. To overcome the complexities of the infection dynamics, the next-generation matrix method was developed. We deduced expressions which allowed estimating the number of new infections generated by an infected individual through each transmission route at each disease stage, the basic reproduction number and the number of individuals at each disease stage at the outbreak of the infection. The analysis was applied to Buenos Aires city (Argentina). We estimated that 94% of the new infections are generated by individuals in the chronic indeterminate stage. When migration was not considered, the infection disappeared slowly and R 0 = 0·079, whereas when migration was considered, the number of individuals in each stage of the infection tended to stabilize. The expressions can be used to estimate different numbers of infected individuals in any place where only inter-human transmission is possible.

Human strongyloidiasis is a neglected tropical disease with global distribution and this infection is caused by the parasitic nematode Strongyloides stercoralis. The aim of this study was to determine the prevalence of strongyloidiasis in Dhaka, Bangladesh. Sera from 1004 residents from a slum (group A) and 299 from city dwellers (group B) were tested for total IgG and IgG subclasses to Strongyloides antigen. There was a significant difference (P < 0·001) in IgG seroprevalence between group A (22%) and group B (5%). Reactive IgG subclasses (IgG1 and IgG4) were also higher in group A (P < 0·05). The seroprevalence of strongyloidiasis in group A increased with age but was unrelated to sex. The presence of reactive IgG to Strongyloides antigen had no correlation with either socio-economic or personal hygiene factors. However, a history of diarrhoea in a family member, in the past 6 months, but not in the respondents was associated with detection of antibodies to S. stercoralis (P < 0·01). None of the sera from either group had an HTLV-I reaction. This study demonstrates that strongyloidiasis is prevalent in Dhaka, especially among slum dwellers, but concurrent infection with HTLV-I was not found. Future epidemiological studies should identify individual risk factors and other communities at risk so that appropriate interventions can be planned.

Several specimens of Phyllobothrium dohrnii (Oerley) were obtained from the intestine of Hexanchus griseus caught in the deep-sea fishing grounds on the Porcupine Bank to the west of Ireland. The species was first described by Oerley in 1885. Since then, several cestodes which are probably synonymous with this species, have been described by various writers. They are Crossobothrium laciniatum Linton (1889) from Odontaspis littoralis (the sand shark) at Wood's Hole, Mass., Crossobothrium campanulatum Klaptocz (1906) from Hexanchus griseus in the Gulf of Trieste, and Orygmatobothrium velamentum Yoshida (1917) from Cynias manazo (the bleeker) of Hiroshima, Japan.

Bluetongue is a disease of major economic concern in Europe. Its causative agent, bluetongue virus (BTV), is transmitted by several Culicoides species (mainly Culicoides imicola and Culicoides obsoletus in Europe). The application of insecticides on animals may reduce transmission of BTV, however, no formulation is currently licensed specifically against Culicoides midges. The present study assesses the susceptibility of C. obsoletus to deltamethrin using an adapted World Health Organization (WHO) susceptibility test. Midges were exposed to different dosages of deltamethrin for 1 h, and mortality after 1 h and 24 h was recorded. Results indicated that deltamethrin is highly toxic to C. obsoletus since a dose of 1·33×10−4% was enough to kill 50% of the population (LD50) in 24 h. The deltamethrin concentration needed to kill 90% of the population (LD90) was 5·55×10−4%. The results obtained in the present work could help to create a system that can be used to assess insecticide resistance and susceptibility of Culicoides biting midges.

Population growth, in vitro, of three Paramoeba perurans cultures, one polyclonal (G) and two clonal (B8, CE6, derived from G), previously shown to differ in virulence (B8 > G > CE6), was compared at 10 and 15 °C. B8 showed a significantly higher increase in attached and in suspended amoebae over time at 15 and 10 °C, respectively. CE6 and G also had significantly higher numbers of suspended amoebae at 10 °C compared with 15 °C at experiment termination. However, in contrast to B8, numbers of attached amoebae were significantly higher at 10 °C in CE6 but showed a similar trend in G at the end of the experiment. Numbers of both suspended and attached amoebae were lower in B8 compared with CE6 and G. Significant differences in bacterial community composition and/or relative abundances were found, between cultures, between temperatures and between the same culture with and without amoebae, based on 16S rRNA Illumina MiSeq sequencing. Bacterial diversity was lower in B8 and CE6 compared with G, possibly reflecting selection during clonal isolation. The results indicate that polyclonal P. perurans populations may contain amoebae displaying different growth dynamics. Further studies are required to determine if these differences are linked to differences seen in the bacterial communities.

Invasive parasites can spill over to new hosts in invaded ecosystems with often unpredictable trophic relationships in the newly arising parasite-host interactions. In European seas, the intestinal copepod Mytilicola orientalis was co-introduced with Pacific oysters (Magallana gigas) and spilled over to native blue mussels (Mytilus edulis), with negative impacts on the condition of infected mussels. However, whether the parasite feeds on host tissue and/or stomach contents is yet unknown. To answer this question, we performed a stable isotope analysis in which we included mussel host tissue and the primary food sources of the mussels, microphytobenthos (MPB) and particulate organic matter (POM). The copepods were slightly enriched in δ15N (mean Δ15N ± s.d.; 1·22 ± 0·58‰) and δ13C (Δ13C 0·25 ± 0·32‰) with respect to their host. Stable isotope mixing models using a range of trophic fractionation factors indicated that host tissue was the main food resource with consistent additional contributions of MPB and POM. These results suggest that the trophic relationship of the invasive copepod with its mussel host is parasitic as well as commensalistic. Stable isotope studies such as this one may be a useful tool to unravel trophic relationships in new parasite-host associations in the course of invasions.