During 1987 a total of 1393 cattle was examined for Schistosoma nasale infection at the Kandy slaughterhouse, Sri Lanka. The overall prevalence was 12·6% (monthly range 3–17%). Based on the appearance of macroscopic lesions, 6 types (0–5) were recognized; type 5 being the most severe, with cauliflower-like growths obstructing the nasal cavity. Older bovines with 8 permanent incisors were more heavily infected (29·%) than younger ones with no permanent incisors (6·0%). The severity of the lesions increased also with the age of the animals. Observations on the localization of the lesions showed that the first sessile nodular areas appear on the medial septum, on the dorsal edge of the ventral nasal concha and on the lateral wall of the middle meatus of the nasal cavity. Later, they gradually spread over the whole mucosal surface of the anterior part of the cavity but were rarely found further than 10 cm posterior to the nasal opening. The histopathology showed that granuloma formation due to the presence of eggs was the most common feature of the respiratory mucosa.

An acoustic actograph was used to monitor for 17 days after infection the spontaneous flight activity of the mosquito Anopheles stephensi parasitized with the rodent malaria Plasmodium yoelii. Activity fell to approximately two-thirds of control levels at about day 10 post-infection – when oocysts were reaching maximum size and starting to rupture (mean number of oocysts = 92) – and thereafter remained at this reduced level. The circadian activity pattern was not affected by the parasitism.

We investigated local adaptation in the spatially structured natural Biomphalaria glabrata/Schistosoma mansoni host-parasite system in the marshy forest focus of Guadeloupe using cross-transplantation experiments. We demonstrated strong and highly significant variations in susceptibility/infectivity of host and parasite populations, respectively, but found no evidence of local adaptation neither for S. mansoni nor for B. glabrata. Environmental as well as genetic factors are discussed to explain susceptibility/infectivity variations between both host and parasite populations. The absence of local adaptation is discussed in relation to the metapopulation dynamics of both host and parasite, in particular their relative rates of dispersal at the scale under scrutiny. Our study constitutes the first cross-transplantation experiment concerning this host-parasite system of which both hosts and parasites came directly from the wild, excluding laboratory generations and experimental host passages.

My attention was first directed to this Cestode in 1906 when I was asked to examine several specimens of edible fish which had been exposed for sale in the public markets and had been condemned as human food on account of the presence of obvious, intrusive bodies in the flesh. In three of these cases the muscles of the flesh of the fishes—a Halibut, a Megrim and a Hake—contained cysts which enclosed the larvae of a Tetrarhynchid, and on examination the latter was identified as T. erinaceus from the peculiar nature of the armature of the proboscides. In another case the wall of the stomach of a Halibut was also infected with the same larvae. Acting on an obsolete principle of Border Law the Fish Inspectors promptly condemned the fishes and then caused them to be examined. I do not think there was any valid reason for the condemnation of the articles of food, for I can find no reference in the literature to the presence of Tetrarhynchids in the human alimentary canal, and there does not appear to be any question of a possible communication of a parasite by the consumption, as food, of such infected flesh. Further the number of larvae present was far too few to lead to any emaciation of the fish, or to the likelihood of the production of toxic substances in the flesh of the animal. Nevertheless the Inspectors probably acted in the interests of the public health in condemning such articles of food as contained obvious cyst-like structures in the flesh, as to the precise nature of which they were ignorant, since there is always the possibility that these bodies might be detrimental to the health of those eating them.

Control programmes generally use a school-based strategy of mass drug administration to reduce morbidity of schistosomiasis and soil-transmitted helminthiasis (STH) in school-aged populations. The success of school-based programmes depends on treatment coverage. The community-directed treatment (ComDT) approach has been implemented in the control of onchocerciasis and lymphatic filariasis in Africa and improves treatment coverage. This study compared the treatment coverage between the ComDT approach and the school-based treatment approach, where non-enrolled school-aged children were invited for treatment, in the control of schistosomiasis and STH among enrolled and non-enrolled school-aged children. Coverage during the first treatment round among enrolled children was similar for the two approaches (ComDT: 80·3% versus school: 82·1%, P=0·072). However, for the non-enrolled children the ComDT approach achieved a significantly higher coverage than the school-based approach (80·0 versus 59·2%, P<0·001). Similar treatment coverage levels were attained at the second treatment round. Again, equal levels of treatment coverage were found between the two approaches for the enrolled school-aged children, while the ComDT approach achieved a significantly higher coverage in the non-enrolled children. The results of this study showed that the ComDT approach can obtain significantly higher treatment coverage among the non-enrolled school-aged children compared to the school-based treatment approach for the control of schistosomiasis and STH.

The presence of haemoparasites belonging to the taxa Anaplasma, Bartonella and Trypanosoma was determined among 76 common shrews (Sorex araneus) from Northwest England. Anaplasma phagocytophilum DNA was recovered from the blood of 1 shrew (1·3%), with the amplified 16S rRNA sequence identical to one previously reported from a bank vole (Clethrionomys glareolus). Trypanosoma spp. DNA was detected in 9 shrews (11·8%), the amplified 18S rDNA fragments being indistinguishable from one another, and distinct from previously published data. This represents the first report of trypanosome infection in S. araneus and suggests they are susceptible to an uncharacterized Trypanosoma species. Blood from 11 shrews (14·5%) yielded Bartonella spp., with characterization of isolates using comparative sequence analysis of partial gltA and 16S-23S rRNA intergenic spacer regions revealing 2 different genotypes. Phylogenetic inference from alignment of partial gltA sequences found that both UK S. araneus types formed a well-supported cluster with Bartonella sp. isolated from S. araneus in Sweden. No significant effect of host age, sex, or year of collection was found on prevalence of Bartonella or trypanosome infections. The results of this survey demonstrate that common shrews in the UK are susceptible to haemoparasitic infections, at prevalences similar to those reported from sympatric rodents.

Parasites of marine fishes have attracted, comparatively speaking, but little attention among scientists. This is true especially for the parasites of those fishes which live in the open seas, and are therefore less accessible to investigation than their relatives inhabiting coastal waters. On many occasions, when chance has brought such a parasite to the attention of a research worker, the scarcity of data allowed no more than mere recording of the existence and a brief description of the parasitic species. Now, when investigations into the parasite fauna of marine fishes are being intensified, it is possible to add to our knowledge of such forgotten species of parasites, in order to appreciate more clearly their possible importance to their hosts and, indirectly, to the economics of the stocks of our food fishes.

The small group of Trematodes here discussed comprises new species of the genera Megalocotyle, Calicotyle and Microcotyle.

Adhesion of parasitized red blood cells to vascular endothelium is thought to play an important role in the development of the ischaemic complications associated with severe falciparum malaria. Using a novel, flow-based assay, we have investigated the adhesion of parasitized red blood cells to formalin-fixed human umbilical vein endothelial cells (HUVEC), for isolates obtained from 32 Gambian subjects with mild or severe falciparum malaria. Red cells infected with wild strains of Plasmodium falciparum were able to adhere to HUVEC under physiologically relevant flow conditions, but the level of adhesion was highly variable, ranging from 1 to 688 adherent cells per mm2 of HUVEC. Within isolates, some adherent parasitized cells remained stationary, whilst other formed less stable interactions and rolled slowly over the cell surface. There was no significant difference in adhesion of parasitized cells between isolates obtained from mild or severe cases of malaria, although a subset of isolates did show very high levels of adhesion. The results suggest that there is not a simple relationship between the adhesion of parasitized cells to cultured endothelial cells (presumably via the receptor ICAM-1) and the clinical severity of the disease, although variation in microvascular adhesion in vivo may still be a determinant of ischaemic complications.

Biozzi mice of Selections 1 and 3, each exhibiting either high- or low- antibody responses to a wide range of antigens, were exposed to primary, secondary and tertiary infections of the nematode, Nematospiroides dubius. The course of these infections was followed by monitoring egg output and by examination of the worm burdens on the 14th day after each exposure to the parasite. When exposed to a primary infection, high and low responders were equally susceptible to the parasite, and the egg production of the infections was similar in all groups. However, when the mice were exposed to a 2nd infection of N. dubius, marked differences in the susceptibility of the hosts were seen. The high-responder mice of both Selections 1 and 3 were significantly more resistant to infection, far less adult worms being found in these. Resistance to a 3rd and final infection of the parasite was amplified appreciably in all groups but, again, the high-responder mice were significantly more resistant than the low responders. These results imply that host antibodies play an essential role in immunity to this parasite and that resistance cannot be attributed solely to non-specific macrophage activity or cell-mediated immune reactions, since the latter are equivalent in high and low lines and the macrophages of the Ab/L line of Selection 1 are hyperactive.

Pentastomids are arthropod parasites which attain maturity in the respiratory tracts of vertebrates. All pentastomids exhibit an obvious sexual dimorphism in that fully mature females are invariably much bigger than males. Unusually though, copulation, which happens only once in the lifetime of females, occurs when both sexes are approximately the same size and the uterus of the female is undeveloped. This is because sperm is stored in spermathecae which, being positioned at the junction of the oviduct and uterus, become more remote from the vagina as the uterus elongates during development. The provision of spermathecae for sperm storage allows oocytes, shed continuously from the ovary, to be fertilized from time to time. What renders this process quite remarkable, and possibly unique, is the extreme length of the patent period. In one species this can extend up to an estimated 10 years and is associated with an egg production of about 106 eggs/female/year. Spermathecal structure provides some clues as to how prolonged sperm storage and the continuous fertilization of oocytes is accomplished. The upper region of the access duct is a narrow, chitinized tube which tapers to as little as 3 μm diameter at the point of entry into the spermatheca. The chitinous (?) lining of the spermatheca is relatively impermeable and apparently functions to totally isolate sperm from external influences: stored sperm are arranged in bundles and whorls and remain totally quiescent and inactive during the storage period. The entire spermatheca is invested by muscle fibres, the contraction of which will express small numbers of sperms through the narrow access duct. These are then reactivated by secretions from the female reproductive tract: the extreme narrowness of the spermathecal duct provides the fine adjustment of the system. The narrowness of the duct also creates problems during the process of insemination, since sperm discharged directly into the female reproductive tract would be unlikely to find the spermatheca through such a structure. Accordingly, the male cirrus is much modified to directly penetrate the spermathecal duct during copulation. Sperms, stored in the male seminal vesicle, are apparently activated prior to sperm transfer, and swim along the cirrus to be guided directly into the spermathecal lumen. Some unusual variations on the normal pentastomid life-cycle are discussed.

In the savanna areas of tropical Africa, cattle are frequently infected with the filaria Onchocerca ochengi. This parasite is closely related to Onchocerca volvulus, the causative agent of human onchocerciasis (river blindness), and is capable of developing in the same vector, Simulium damnosum s.l. In North Cameroon, where both O. ochengi and O. volvulus are endemic, we carried out a field study (reported in this and 2 following papers) to examine to which extent the transmission of the 2 parasite species overlap and what influence this has on the epidemiology of human onchocerciasis. In this paper we report our experiments to determine which of the S. damnosum species in North Cameroon act as vectors of O. ochengi, how efficiently they do so and whether other Simulium species play a vector role. To this end, infected cattle were exposed near 5 rivers in different geographical areas. Among 14 Simulium species identified as aquatic and/or adult stages at these rivers, only 6 (S. squamosum, S. damnosum s.s., S. sirbanum, S. bovis, S. wellmanni and S. hargreavesi) were found to bite cattle in important numbers in at least 1 of the sites. The 3 species of the S. damnosum complex were all capable of ingesting microfilariae (mf) of O. ochengi and developing a proportion of them to infective larvae (L3). Whereas S. squamosum and S. damnosum s.s., the prevailing vectors in the Guinea and Sudan savanna respectively, showed a high vector competence (17% of ingested mf developed to L3), S. sirbanum, which was much rarer in both areas, appeared to have a much lower susceptibility (2%). Other boophilic Simulium species were only seen in certain sites and seasons, being either incapable of ingesting important numbers of O. ochengi mf from body regions where these mf were abundant (S. bovis, S. hargreavesi); not able to support the development of ingested mf to L3 (S. wellmanni), or bit cattle preferentially in the ears, where O. ochengi mf do not occur (S. hargreavesi). We conclude that in North Cameroon members of the S. damnosum complex are the only important vectors of O. ochengi, with S. squamosum and S. damnosum s.s. being the main vectors.

The influence of host dietary protein on acquired immunity and intestinal helminth population dynamics during repeated infection was studied using the mouse–Trichuris muris experimental model. CBA/Ca mice fed a 2% (by mass) protein diet ad libitum maintained body weight during the experiment, but when fed diets containing either 4% or 16% (by mass) protein gained weight steadily. Infection with T. muris did not affect the growth of the latter mice but significantly reduced the growth of animals fed on the 2% protein diet. When repeatedly infected with either 5 or 50 eggs every 10 days, the mice fed the 2% or 4% protein diet accumulated adults in proportion to infection dose. The results show that this is due to both the establishment of larvae at each repeated infection and the survival of established adults. In contrast, very few worms were recovered from animals fed the 16% protein diet, principally as a result of the development of strong acquired immunity to reinfection. T. muris egg output/mouse increased with infection dose in animals fed the low protein diets, but no parasite eggs were detected in the faeces of hosts fed the 16% protein diet. Mouse antibody reponses to adult worm excretory/secretory antigen were time- and infection dose-dependent in all 3 dietary groups. The major finding was that the specific antibody response was more intense, both quantitatively (serum OD levels) and qualitatively (antigen recognition by IgG1), in mice fed the low protein diets, even though they remained susceptible to infection. This study shows that host dietary protein deficiency, even at levels irrelevant to normal growth, can markedly potentiate the transmission of T. muris via alterations in host resistance. The high levels of antibody in susceptible animals suggest that this defect in resistance is unlikely to be due to nutrient deficiency-associated defects in humoral immunity.

The sequences for the entire intergenic spacer (IGS) and 3′ end region of the large subunit (28S) ribosomal RNA gene are presented for Schistosoma intercalatum, S. haematobium and S. mansoni. The IGS was found to have at least 2 size formats for S. intercalatum and S. haematobium and the region for all 3 species contains numerous repeats and evidence of recombination. An A+T rich sequence found in S. intercalatum and S. haematobium is described and its possible function and origins are discussed. The amplification of this region by means of the polymerase chain reaction can be used to discriminate clearly between the 3 species involved in this study. The putative end of the 28S gene is identified.

Extreme variation in reproductive success (VRS) has been reported as a common feature of populations. Few individuals producing most of the offspring for the next generation has potential consequences for the population dynamics, genetics, and evolution of a group of organisms. High VRS has been described as a normal feature of helminth populations, although studies have focused largely on parasites of vertebrate hosts. Paragordius varius, a parasite of crickets, was used as a model system to study VRS. In this life cycle, worms absorb and store resources for reproduction from their hosts before being released into water. Egg output varied significantly with worm length, indicating that female length is an excellent predictor of fecundity. Analyses using the Lorenz curve and Gini coefficient suggest that there were no marked fecundity differences. This result was supported by data collected from a natural gordiid population, Gordius difficilis, suggesting that within gordiid populations the offspring of the next generation are contributed nearly equally by females. In addition, male body length appeared to be limited by intensity, whereas females showed no length limitation by crowding. These results contrast previous studies of parasites.

Ticks display a distinct type of host-seeking behaviour called questing. It has been proposed that the questing behaviour of Ixodes scapularis explains the geographic variation in Lyme disease (LD) risk in the eastern USA because the northern population has been shown to quest more often than the southern population. The height at which questing occurs is variable and this study aimed to characterize questing height for I. scapularis. Ticks were collected from a northern and southern state (i.e. Maryland and Texas) and bioassays were conducted. We report that nymphs from Texas quested at lower heights compared to nymphs from Maryland. In addition, only Texas nymphs exhibited a behaviour we call ‘hiding behaviour’. These results may reflect the different composition of hosts between these two areas as the south has a higher abundance of lizards. In contrast, there was no significant difference in questing height between Maryland adults and Texas adults which was to be expected since adults are feeding on white-tailed deer in both locations. If all southern I. scapularis nymphs are questing at lower heights, this might make them less likely to come into contact with humans and this may be contributing to the geographical difference in LD prevalence.

The free pool amino acids of Taenia crassiceps metacestodes (advanced larvae) were analyzed quantitatively. In addition, the uptake of L-glutamic acid, L-proline, L-phenylalanine, L-lysine, and L-methionine was studied. Proline and glutamic acid absorption followed straight-line kinetics with respect to substrate concentration, and were not inhibited by their own molecular species. Lysine, phenylalanine and methionine were found to enter larvae by a combination of diffusion and mediated processes. Lysine absorption was inhibited only by lysine, arginine and ornithine. Phenylalanine and methionine uptake was not inhibited by lysine or arginine, but was inhibited by several other amino acids. The data suggested the presence of a basic amino acid transport locus and two distinct transport loci for methionine absorption. In addition, both immature and advanced larvae were found to be impermeable to [14C]inulin (M.W. ca. 5000). These results are discussed and compared with the results of earlier investigations of protein and amino acid absorption by T. crassiceps larvae.

The ecology of the tick Ixodes trianguliceps Bir. is described from material collected at two localities in Wytham Estate near Oxford. The hosts examined were bank voles, Clethrionomys glareolus Schr., field voles, Microtus agrestis (L.), and field mice, Apodemus sylvaticus (L.).

The seasonal distribution of the tick is biannual, with spring and autumnal peaks as found in Ixodes ricinus (L.). Larvae occur throughout the year but principally in spring and autumn. Nymphs are found only from late spring until the autumn, and adults principally in the spring with a small peak in autumn.

Larvae and nymphs of I. trianguliceps were more abundant on male than on female bank voles, but there was no significant difference in the infestation of males and females by adult ticks. Similarly there was no significant difference in the infestation of adult and juvenile bank voles.

Larvae and nymphs occur principally on the ears, but the adult ticks are found mainly on the neck or body, although the ears were not excluded from infestation.

The seasonal distribution and life-history is discussed with reference to similar studies made in the Soviet Union and in Poland. Male ticks were found in copula on the host, and both males and nymphs were collected from the nests of voles.

A tentative summary of the life-history of I. trianguliceps is given based on known facts for the hedgehog tick, Ixodes hexagonus Leach, which has a similar seasonal occurrence.

We wish to thank Professor Don Arthur for identification of much of the tick material, especially in the early stages of this study, and for useful criticism of the draft manuscript. The work was carried out while one of us (M.J.C.) was a research student in the Hope Department of Entomology, Oxford, and the other (C.H.S.W.) a research student at the Bureau of Animal Population, Oxford. For facilities in both departments we wish to express our gratitude.

This study investigated the significance of the genetic differences between assemblages A, B and E on intestinal growth and virulence. Intestinal growth and virulence were studied in 2 laboratory (AI: WB and B: GS/M-83-H7) and 6 field isolates of assemblage subtype AI, AII, B and EIII. Intestinal trophozoite burdens, body weight and faecal consistency were monitored until day 29 post-infection (p.i.), morphological (mucosal architecture and inflammation) and functional (disaccharidase and alkaline phosphatase enzyme activity) damage to the small intestine were evaluated on days 7 and 18 p.i. The assemblage subtypes AI and B were more infectious and produced higher trophozoite loads for a longer period compared to the subtypes AII and EIII. The body weight of infected gerbils was significantly reduced compared to uninfected controls, but did not differ between the assemblage subtypes. Consistent softening of the faeces was only observed with assemblage B. Assemblage B next to assemblage subtype AI elicited relatively higher pathogenicity, characterized by more extensive damage to mucosal architecture, decreased brush-border enzyme function and infiltration of inflammatory cells. Assemblage EIII and AII isolates showed relatively low virulence. The Giardia assemblage subtypes exhibit different levels of growth and virulence in the gerbil model.

Previous experimental gametocyte infections of Anopheles arabiensis on 3 volunteers naturally infected with Plasmodium falciparum were conducted in Senegal. They showed that gametocyte counts in the mosquitoes are, like macroparasite intakes, heterogeneous (overdispersed). They followed a negative binomial distribution, the overdispersion coefficient seeming constant (k=3·1). To try to explain this heterogeneity, we used an individual-based model (IBM), simulating the behaviour of gametocytes in the human blood circulation and their ingestion by mosquitoes. The hypothesis was that there exists a clustering of the gametocytes in the capillaries. From a series of simulations, in the case of clustering the following results were obtained: (i) the distribution of the gametocytes ingested by the mosquitoes followed a negative binomial, (ii) the k coefficient significantly increased with the density of circulating gametocytes. To validate this model result, 2 more experiments were conducted in Cameroon. Pooled experiments showed a distinct density dependency of the k-values. The simulation results and the experimental results were thus in agreement and suggested that an aggregation process at the microscopic level might produce the density-dependent overdispersion at the macroscopic level. Simulations also suggested that the clustering of gametocytes might facilitate fertilization of gametes.