The alimentary tract of female Culicoides nubeculosus is simple. There is much similarity between it and that of other nematoceran and brachyceran bloodsucking flies.

Among the interesting features observed are the following:

1. The mid-gut is composed of two portions, a tubular anterior segment and a dilated stomach, which show structural differences.

2. The peritrophic membrane, which is absent in the unfed female, forms around the ingested blood. Its substance is secreted by the epithelium of the stomach.

3. A simple rectal valve guards the opening of the small intestine into the rectum.

4. The Malpighian tubules are two in number, and they give attachment to muscular branches from different sources.

5. There are six accessory glands arranged in a rosette around the mouth of each salivary gland proper. Some of them may sometimes function as reservoirs for the secretion of the salivary glands proper.

In one specimen, tumours at the base of the stomach and abnormal features in the Malpighian tubules were observed.

The haemocytic reactions of larvae of Drosophila algonquin leading to encapsulation and melanization of eggs of the hymenopterous parasite Pseudeucoila bochei are characterized in part by the premature mass differentiation of plasmatocytes to lamellocytes. Normally this transformation of blood cells occurs at the time of pupation. The data suggest the haemocytes are stimulated to differentiate by chemotactic means. In susceptible host larvae the parasite appears activately to inhibit the immune reactions by blocking cellular differentiation.

The potential of a recombinant Schistosoma bovis-derived glutathione S-transferase (rSb28GST) to protect cattle against S. mattheei infection was tested in Zambia. All animals were challenged 2 weeks after the second inoculation with either 0·250 mg rSb28GST in adjuvants (vaccinated calves, n=14) or adjuvants alone (controls, n=14). In a first experiment, 7 vaccinated and 7 control animals were exposed to 10000 S. mattheei cercariae percutaneously. All animals developed clinical schistosomiasis 7–8 weeks after challenge. At perfusion, 12 weeks after challenge, vaccinated and control groups had averages of 887 and 541 eggs per gramme (epg) faeces, 6515 and 5990 worms, and 4·2 and 3·4 million tissue eggs, respectively. These results indicate that the immunization protocol used did not protect these calves against the massive single experimental challenge. In a second experiment, another 2 groups (n=7) of vaccinated and control animals were challenged naturally over a period of 9 months on a farm known to be endemic for S. mattheei. The natural infections were much lighter in intensity, as indicated by the mean faecal egg count (13 epg), worm count (139) and tissue egg count (294000) in non-vaccinated controls. In vaccinated calves, significant reductions in female worm burdens (50%), faecal egg counts (89%) and miracidial counts (93%) were recorded. Total tissue egg counts were also reduced by 42% in vaccinated animals. It therefore appears that the rSb28GST can provide significant protection in cattle against S. mattheei under conditions of low to moderate natural infection.

Caryophyllids are widely distributed cestodes of the fresh water siluriform and cypriniform fishes of the world. There are about 126 species and 45 genera and they constitute approximately 25% of the cestode fauna of fresh water fish (Mackiewicz, 1972). Benthic-feeding fish become infected by eating tubificid worms (Annelida; Oligochaeta) that harbour the cercomer-beariug, infective stage; the tubificids, in turn, are infected by eating the operculated eggs in mud. Such a brief synopsis belies the fact that these well-known tapeworms are at the very heart of important questions concerning the evolution of Cestoidea. One has but to read Bazitov (1976), Freeman (1973), Kulakovskaya & Demshin (1978), Mameav (1975), Malmberg (1974) and Mackiewicz (1981) to appreciate that great differences still exist as to how caryophyllids evolved and what role they may have played in the evolution of the more numerous strobilate tapeworms.

The histological anatomy of the female reproductive system of an oxyuroid nematode, Aspiculuris tetraptera, Schulz, has been described.

The process of egg-shell formation in this animal has been followed in detail while the structural and chemical characteristics of the egg-shell have been studied by histochemical and other methods. It is shown that there are three layers: a lipoprotein layer, a ‘chitinous’ layer and the so-called vitelline (glycosidal) membrane. Evidence is presented for the exogenous origin of the lipoprotein layer: this being formed by the cells of the upper uterus which are shown to be secretory.

The question of quinone-tanning in the egg-shell of A. tetraptera and in other oxyuroids and ascarids is considered. It is shown that neither a polyphenol oxidase nor a high concentration of phenolic substances (apart from protein tyrosine) exists in this system. The significance of these and other observations is discussed in relation to the mechanism of tanning as elucidated in insects and trematodes.

I have to acknowledge with gratitude the support of many during these investigations. To Dr P. Tate for his encouragement and provision of facilities at the Molteno Institute; to Dr D. L. Lee, for much useful discussion and permission to refer to some of his unpublished electron micrographs of nematodes; to Professor J. D. Smyth, who kindly read through the manuscript; to the Cambridge Philosophical Society for a grant that made possible the translation of Fauré-Frémiet's classical study on Ascaris; and to the Department of Technical Cooperation for financial assistance.

The truncated negative binomial distribution is used to demonstrate water mite-induced mortality in a field population of the mosquito host Anopheles crucians. Consistent changes in the parameters of this distribution and in the number of hosts expected in higher mite load classes as truncation is applied to successively lower mite load classes suggest that many heavily parasitized individuals were missing from field samples. These changes are not observed in distributions derived from an association between parasitic larvae of another water mite, Hydrachna conjecta, and the insect Sigara ornata, which is apparently immune to this parasite. Although the method discloses parasite-induced mortality that is non-linearly related to parasite load, it fails to reveal linear parasite-induced mortality in a hypothetical example.

The complexity of the life-cycle of many parasitic helminths has driven the evolution of several well-documented adaptations serving to facilitate the completion of each difficult step in the cycle. In some trematode taxa, selection has even favoured the truncation of the life-cycle: progenetic larval stages (metacercariae) are capable of producing eggs inside their usual intermediate hosts, eliminating the need to be transmitted by predation to a definitive host. In some species, progenesis is shown by all individuals, whereas in other species both the normal and truncated life-cycles coexist in the same populations. Here, the strategies chosen by normal and progenetic metacercariae of the trematode Coitocaecum parvum are investigated and compared. Normal metacercariae, i.e. metacercariae that only develop into adults following ingestion by a suitable fish definitive host, were not capable of manipulating the behaviour of their amphipod intermediate host in ways that could facilitate their capture by fish. These metacercariae were associated with increased mortality in amphipods. Progenetic metacercariae, on the other hand, showed lower virulence levels than normal metacercariae. At the time of their death, amphipods harbouring progenetic metacercariae contained close to the maximum number of eggs that can be produced by progenetic metacercariae, suggesting that the parasite lowers its virulence to keep its host alive long enough to maximize egg output. The maintenance of the 2 strategies in the C. parvum population suggests that they may have equal fitness payoffs: progenesis and low virulence guarantee the production of at least some eggs, whereas the normal life-cycle and its associated higher virulence in the intermediate host provides a low probability of much higher fecundity.

Understanding disease transmission is important to species management and human health. Host body condition, nutrition and disease susceptibility interact in a complex manner, and while the individual effects of these variables are well known, our understanding of how they interact and translate to population dynamics is limited. Our objective was to determine whether host relative body condition influences epidemic dynamics, and how this relationship is affected by food availability. Poecilia reticulata (guppies) of roughly similar size were selected and assembled randomly into populations of 10 guppies assigned to 3 different food availability treatments, and the relative condition index (Kn) of each fish was calculated. We infected 1 individual per group (‘source’ fish) with Gyrodactyus turnbulli and counted parasites on each fish every other day for 10 days. Epidemic parameters for each population were analysed using generalized linear models. High host Kn—particularly that of the ‘source’ fish—exerted a positive effect on incidence, peak parasite burden, and the degree of parasite aggregation. Low food availability increased the strength of the associations with peak burden and aggregation. Our findings suggest that host Kn and food availability interact to influence epidemic dynamics, and that the condition of the individual that brings the parasite into the host population has a profound impact on the spread of infection.

During recent investigations on Endamoeba blattae (Bütschli) Leidy of the common cockroach, Blatta orientalis, there were observed in the hindgut of the host, two other distinct amoebic species. Both appear to be truly entozoic, but contrast strikingly with E. blattae both in morphological features and life cycle. They are interesting not only in being among the comparatively few species yet reported from insects, but also in their relationships to certain of the amoebae of vertebrates.

It is now slightly more than 60 years since Piaget described as Haematomyzus elephantis an extraordinary insect found by him living as an ectoparasite upon an African elephant in the Zoological Garden of Rotterdam. The insect was considered by its describer to be a sucking louse, and this assignment has been accepted by almost all of the few entomologists who have since been privileged to examine specimens. Walker, who in ignorance of Piaget'os work, redescribed the species as Idolocoris elephantis, regarded it as constituting a new family of Hemiptera Heteroptera near the bed bugs. Since that time no one has questioned the belief that it is a sucking louse and for it Enderlein named a family, the Haematomyzidae, in the Anoplura.

The population dynamics of Trichuris suis in pigs was studied during long-term experimental infections. Twenty-three 10-week-old pigs were inoculated with 5 T. suis eggs/kg/day. Seven, 8, and 8 pigs were necropsied at weeks 4, 8, and 14 post-start of infection (p.i.), respectively. The median numbers of worms in the colon were 538 (min–max: 277–618), 332 (14–1140) and 0 (0–4) at 4, 8, and 14 weeks p.i. respectively, suggesting an increased aggregation of the worms with time and acquisition of nearly sterile immunity. The serum levels of T. suis specific antibodies (IgG1, IgG2 and IgA) peaked at week 8 p.i. By week 14 p.i. the IgG2 and IgA antibody levels remained significantly elevated above the level of week 0. The population dynamics of T. suis trickle infections in pigs is discussed with focus on interpretation of diagnostic and epidemiological data of pigs, the use of pigs as a model for human Trichuris trichiura infections and the novel approach of using T. suis eggs in the treatment of patients with inflammatory bowel disease.

For some years past in Northern Province, Nyasaland, work has been in progress to determine the mortality amongst native cattle due to east coast fever (Wilson, 1944). As an integral part of such a survey, routine tick collections were made during cattle inspections. It was then intended to map the various species of tick concerned in the hope that their geographical distribution might offer a partial explanation for the prevalence or absence of east coast fever in certain areas. Such a map for the western portion of Kenya Colony has been provided by Lewis (1939), ‘according to the groups of dominant species of ticks’; but in Kenya, climate, soils and vegetation show wide contrasting variations, and conditions are scarcely comparable to those existing in the smaller territory of Nyasaland.

The sequential, quantitative histological analysis of adult Hyalomma anatolicum anatolicum feeding sites on rabbits showed that the cellular reactions at tick feeding sites change in character and magnitude with time after attachment, and differ considerably from primary infestation to tertiary infestation. Neutrophils (62–68%) followed by mononuclear cells (22–24%) were the major component of the cellular infiltrate throughout primary infestation. Eosinophils accounted for 10% of the cellular infiltrate at 24 h after attachment. Their proportions declined thereafter, forming 9% of the infiltrate at 72 h and 5% at 144 h. Basophil infiltration in most of the feeding lesions was noticed by 24 h, but always in low numbers. Despite a slight increase in absolute numbers the proportion of basophils fell from 3% at 24 h to 2– at 144 h. In contrast to primary infestation the cellular reactions on tertiary infestations were characterized by a significant increase in the numbers of basophils and eosinophils and marked degranulation of mast cells and basophils as early as 24 h after attachment. As the feeding advanced there was an increase in the mean proportions of basophils from 4% to 9% and mononuclear cells from 22% to 38%, and a decrease in the proportion of eosinophils from 21% to 9%. However, neutrophils (42–53%) remained the major component of the cellular infiltrate. There was no significant difference in the nature and sequence of cellular events in the feeding sites of male and female ticks, although the lesions produced by feeding males were 5–10 fold smaller than those of females. Mast cells, basophils and eosinophils appeared to be the major host cells involved in the resistance response, manifested by protracted feeding, reduced engorgement weight and poor egg laying. The mechanisms by which these cells might interact to mediate resistance are suggested and discussed.

That quinine has little or no destructive action against gametocytes of Plasmodium Falciparum (crescents) has been known for a long time. Marchiafava & Bignami (1900) pointed out that quinine (grains xxx daily) over a period of time did not perceptibly affect the sexual parasites of P. falciparum. Darling (1914), working in the Panama Zone, showed that Anopheles albimanus readily became infected when fed upon carriers of M.T. crescents who were taking xxx grains of quinine daily. These and other experiments showed that quinine, even in large doses, has no direct destructive action on crescents, and does not prevent mosquitoes from becoming infected once the.crescents are formed and are present in the peripheral circulation. However, quinine given in heavy doses during the first day or two of a primary attack, restricts and reduces the asexual source of supply.

Host location by parasites can be achieved by either active or passive mechanisms. In spite of their significance, the efficacy of these methods has been little researched. High fecundity in parasites is discussed in terms of the role it plays in dispersal and transmission. Some concepts developed by mainstream behavioural ecologists are outlined and their relevance to parasitology is indicated. ‘Reproductive value’ is recommended as an appropriate measure of the costs and benefits of behavioural acts. Although costs of reproduction have been rarely studied in parasites, they are likely to occur in cosexual insects, nematodes and crustaceans. Experiments using captive hosts and/or in vitro cultivation could help in the construction of realistic optimality models. We suggest that r- and K-selection theory could assist in the study of the evolution of parasite behaviour. We discuss how parasite populations are dispersed and controlled and consider the implications of overdispersion. WTe outline three sources of signals to which parasites may respond and suggest that understanding evolutionary mechanisms and community organisation of parasites and hosts requires evaluation of fundamental behavioural responses to environmental signals. The study of closely related groups of parasites and their hosts may advance our knowledge of the evolution of parasite life cycles and the evolutionary costs and benefits of behavioural acts.

Microfilariae of Brugia malayi were obtained from the peritoneal cavities of infected gerbils and were then injected intravenously into mice. A sub-periodic, nocturnal microfilaraemia was produced. The level of microfilaraemia was proportional to the number of parasites injected, with approximately 1–3% of microfilariae being found in the peripheral circulation. The duration of microfilaraemia was proportional to the number of parasites injected; it subsided by 30 days after injection of 104 microfilariae but was still present at a low level 120 days after injection of 2 × 105 microfilariae. A transient splenomegaly developed after injection of microfilariae. Histopathological examination revealed large numbers of microfilariae free in the lumens of pulmonary small blood vessels and without any accompanying inflammatory reaction. Lesser numbers of microfilariae were seen in the cardiac blood and hepatic and renal blood vessels for the first few days after injection. There was cellular proliferation in the splenic white pulp and vascular congestion of the red pulp. Microfilariae labelled with 51Cr were injected intravenously; 57% of radioactivity was found in the lungs, 8·5% in the liver and 2·9% in the spleen. Mice developed immediate hypersensitivity reactions to B. malayi antigen by 4 weeks after injection, but Arthus and delayed hypersensitivity reactions were not seen at any time. When mice which had been injected 5 months previously were challenged with a 2nd injection of microfilariae, there was an accelerated clearance of parasites over 2 weeks and a marked peripheral blood eosinophilia developed. In contrast with natural infections, in which the continuous production of microfilariae complicates assessment, this model provides a system in which factors controlling the circulation of microfilariae in the bloodstream can be studied independently.

The plasma of mice infected with pleomorphic Trypanosoma brucei brucei contains a peptidase which has the same electrophoretic mobility on starch gels as a parasite peptidase. An enzyme with this electrophoretic mobility was not detected in the plasma of uninfected mice. The molecular weight of this enzyme in either parasite lysate or plasma from infected mice was approximately 40000 Da when assayed on a size exclusion column using high-performance liquid chromatography. The enzyme can cleave the dipeptides leu-ala, val-leu and pro-leu, but not the dipeptide phe-ala. The enzyme also cleaved the tripeptides tyr-tyr-tyr and leu-gly-gly. Another parasite peptidase which migrates on starch gels to a different position than the above-mentioned peptidase cleaved the dipeptides leu-ala, val-leu and pro-leu but could not cleave the tripeptides tyr-tyr-tyr or leu-gly-gly. Furthermore, incubation of this parasite peptidase with normal mouse plasma at 37 °C resulted in an apparent loss of detectable activity. It is postulated that the plasma of mice modifies either the charge or enzymic activity of this peptidase. We speculate that the parasite peptidase present in the plasma of mice infected with T. brucei could contribute to pathogenesis.

The tapeworm Raillietina trapezoides was studied in a Tunisian population of the fat sand rat Psammomys obesus. Seasonal changes in the abundance of parasite and host were monitored in a longitudinal field survey lasting 20 months. In total 582 intestinal samples were collected during 10 trapping sessions between May 1995 and January 1997 and examined. The impact of abiotic and biotic factors on the prevalence and parasite burden were explored, using generalized linear models. R. trapezoides showed a seasonal pattern with most transmission occurring in summer and autumn. In August–September when the rodents were at low density and most adult (90–100%) were infected. In winter, infections with R. trapezoides were highly prevalent in the cohort of adults only. The worm burden by number was also high in late summer and autumn. Prevalence and parasite burden by number or by biomass were highly age dependent. Season and age act in synergy so that the rodents were highly infected in late summer and autumn. Unusually dry conditions in winter seemed to increase prevalence and to reduce the number of worms. There was no difference between males and females in prevalence or parasite burden (by number or by biomass). Prevalence was not correlated with the relative density of the hosts whereas parasite burden depended upon their densities. The more numerous the worms were, the smaller they were individually, reflecting a crowding effect. The possibility of an immune response regulating P. obesus is discussed, in regard to the very high natural prevalence and the variation in worm burden, and compared with other parasite–host systems.

The present paper is the outcome of my examination of a collection of trematodes from various parts of Japan (including Formosa). The species of monostome came from a turtle caught in Singapore. Of the material certain species are left unidentified chiefly owing to the paucity of specimens. It may be mentioned that in the following description the parasites are arranged according to their hosts.

Soil-transmitted helminthiasis (STH) is a scourge to the health and well-being of infants and pre-schoolchildren throughout many parts of sub-Saharan Africa. To improve maternal and child health, regular de-worming is recommended and often delivered from mother and child health (MCH) clinics, yet there have been few studies monitoring the progress and impact of interventions on local levels of disease. A cross-sectional parasitological survey, supplemented with questionnaires, was therefore conducted across 10 Ungujan villages examining mothers (n=322) and their pre-school children (n=359). Within children, mean prevalence of ascariasis, trichuriasis and hookworm was 8·6% (95% CI 5·5–11·8), 18·9% (95% CI 14·5–23·4) and 1·7% (95% CI 0·2–3·5) while in mothers mean prevalence was 6·7% (95% CI 3·7–9·7), 11·9% (95% CI 8·0–15·8) and 1·9% (95% CI 0·2–3·5), respectively. There was, however, significant spatial heterogeneity of STH by village, 2 villages having much elevated levels of infection, although general access to anthelminthics and utilization of village MCH clinics was good. Levels of parasite aggregation (k) were determined and a multilevel logistic regression model identified access to a household latrine [OR=0·56 (95% CI 0·32–0·99)] and having an infected household member [OR=3·72 (95% CI 2·22–6·26)] as observed risk factors. To further investigate worm burdens of Ascaris lumbricoides, adult worms were expelled using Combantrin® and measured. A negative relationship between mean worm burden and mean worm mass was found. Villages in the north of Unguja represent locations where there is elevated prevalence of both ascariasis and trichuriasis and it appears that local factors are particularly favourable for transmission of these helminths. From a perspective of control, in such locations, intervention efforts should be stepped up and greater efforts placed upon improving household sanitation.