The anatomy, histology and digestive enzymes of the mid-intestine of the tsetse-fly have been investigated, and an attempt has been made to determine the functions of the various parts and to observe the changes to which they are subject during the digestion of blood.

Histologically the mid-gut of Glossina consists of three regions:

(i) An anterior segment of small, pale-staining, irregularly columnar cells, which comprises about half the total length of the mid-gut. The zone of giantcells containing bacteroids, which is very limited in extent, lies at about the middle of this region.

(ii) A middle segment of large, deeply staining cells, heaped together in the resting state, which is separated abruptly from the anterior segment.

(iii) A posterior segment, arising by gradual transition from the middle segment, composed of regular columnar cells.

After a meal the blood is concentrated by the removal of fluid in the anterior segment but it shows no other change in this region. The giant-cells are greatly flattened but they do not regularly discharge the bacteroids which they contain and there is no evidence that these organisms play any part in the digestion of blood. Their possible function has been discussed.

During digestion the cells in the middle segment contain globules of secretion, and vacuolated buds of cytoplasm are set free and disintegrate in the lumen. The blood shows an abrupt change on reaching this region; it turns black where it is in contact with the epithelium and amorphous masses of altered blood pigment are deposited.

In the posterior segment, the epithelial cells become greatly vacuolated later in digestion and are probably concerned chiefly in absorption.

The distribution of digestive enzymes agrees with these histological observations. The salivary glands and proventriculus contain no digestive enzymes, and the anterior and posterior segments of the mid-gut also are practically inactive. But the middle segment produces a very active tryptase which agrees in its pH-activity curve and other properties with the tryptase of the cockroach. A peptidase also is present but, except for a very weak amylase, enzymes acting upon carbohydrates are absent. The contents of the mid-gut are always slightly acid (about pH 6·5) and the tryptase present is well adapted to work at this reaction.

These findings have been contrasted with those in a non-blood-sucking muscid (Calliphora). Here the salivary glands secrete an active amylase and the mid-gut is rich in amylase, invertase and maltase, whereas the proteolytic enzymes are extremely weak.

Some observations have been made upon the tracheal supply to the walls of the gut. The epithelial cells of the middle segment have been shown to contain a very rich supply of intracellular tracheoles. These are usually difficult to make out in the resting cells but after a large meal the surface of the cells is ruptured and blood pigment enters the tracheoles and may extend to the sub-epithelial tracheoles and tracheae or even to quite large tracheal trunks. As the epithelial cells are flattened by the pressure of the meal, this pigment is set free in the lumen in the form of dark rods of haematin, which often bear a superficial resemblance to bacteria. The pigment in the deeper tubes appears to be slowly absorbed later. Intracellular tracheoles similar to these are present also in the mid-gut of Calliphora.

The proventriculus in Glossina is a complex and has always been a puzzling structure. It has been shown that it acts as a sphincter between the fore-gut and mid-gut and that it is responsible for the production of the peritrophic membrane. This membrane, which is composed of chitin but contains a small quantity of protein, is secreted in the form of a fluid by the ring of large epithelial cells at the base of the proventriculus. The fluid is pressed and condensed to form a uniform membrane by being drawn through the cleft between the wall of the proventriculus and the funnel-shaped invagination of the fore-gut.

The function of the peritrophic membrane has been discussed and it has been shown that it is freely permeable to digestive enzymes and to haemoglobin.

The parasite, Neospora caninum is an important cause of abortion in cattle. It is transmitted vertically or horizontally and infection may result in abortion or the birth of a live, healthy but infected calf at full-term. Only a proportion of infected cattle abort and the pathogenesis of abortion is not understood. Groups of cattle were infected with 107N. caninum tachyzoites intravenously at different times relative to gestation. Intravenous inoculation was chosen to reproduce the putative haematogenous spread of N. caninum following either recrudescence of endogenous infection or de novo infection. In all cattle, infection was accompanied by high γ-interferon and lymphoproliferative responses, and a biased IgG2 response indicating that N. caninum infection is accompanied by a profound Th1 helper T cell-like response. Infection at 10 weeks gestation resulted in foetopathy and resorption of foetal tissues 3 weeks after infection in 5 out of 6 cows. Infection at 30 weeks gestation resulted in the birth of asymptomatic, congenitally-infected calves at full term in all 6 cows, whereas the 6 cows infected before artificial insemination gave birth to live, uninfected calves. These results suggest that the reason some cows abort is related to the time during gestation when they become infected or an existing infection recrudesces.

Cutaneous and visceral leishmaniasis are amongst the most devastating infectious diseases of our time, affecting millions of people worldwide. The treatment of these serious diseases rely on a few chemotherapeutic agents, most of which are of parenteral use and induce severe side-effects. Furthermore, rates of treatment failure are high and have been linked to drug resistance in some areas. Here, we reviewed data on current chemotherapy practice in leishmaniasis. Drug resistance and mechanisms of resistance are described as well as the prospects for applying drug combinations for leishmaniasis chemotherapy. It is clear that efforts for discovering new drugs applicable to leishmaniasis chemotherapy are essential. The main aspects on the various steps of drug discovery in the field are discussed.

Recently, some authors (Kennedy, 1981; Price & Clancy, 1983) have argued that there are fundamental differences between the communities of helminths in fish and bird hosts. Such differences are foreshadowed by the work of Dogiel (1964) and are apparent from survey data (e.g. Threlfall, 1967; Bakke, 1972; Hair & Holmes, 1975 on birds, and compare Chubb, 1963; Mishra & Chubb, 1969; Wootten, 1973; Ingham & Dronen, 1980 on fish). Questions still remain, however, as to whether the distinctions are truly justified and whether the differences are really fundamental. In this paper, we address these questions by examining helminth diversity in a series of hosts. We then discuss and provide explanations for the observed differences.

After infection with the nematode Trichuris muris 70–75% of mice of the Schofield strain developed an immunity to the parasite and eliminated the worms between the 16th and 19th days after infection. In these mice the acquired immunity persisted for at least 3 months and prevented the establishment of subsequent infections.

In 25–30% of the mice immunity was not produced and infections developed into mature worms. These non-resistant mice remained susceptible to further infection.

The development and action of the immune response were suppressed completely by the administration of cortisone acetate.

Parasite-induced modifications of host behaviour are known from a wide range of host-parasite associations. In many cases, these behavioural changes are thought to be adaptive and. benefit the parasite by increasing its probability of successful transmission. However, in many cases, energy spent on host manipulation will not be available for other functions, such as growth. These trade-offs suggest that in the absence of other constraints, natural selection will optimize, and not maximize, the influence of parasites on host behaviour. This argument is developed and expanded into theoretical considerations of the evolution of host behaviour manipulation by parasites. Among populations of the same parasite species or among closely-related species, the optimal investment into manipulation, or optimal manipulative effort (ME*), of individual parasites is predicted to increase as (1) typical infrapopulation size decreases, (2) prevalence increases, (3) the longevity of the infected host, or of the parasite in its host, decreases, (4) passive transmission rates decrease, and (5) parasite fecundity decreases. This evolutionary analysis indicates that ecological and life history variables may have played an important role in the evolution of manipulation of host behaviour by parasites.

Search behaviour of two entomopathogenic nematode species with different foraging strategies was compared by measuring parameters of unrewarded search after contact with host cues. Steinernema glaseri cruises in search of hosts. Steinernema carpocapsae ambushes hosts. Nematodes should respond to contact with relevant host cues by shifting their search from ranging to localized after contact with them. We predicted that cruising foragers rely on chemical cues more heavily than ambushers. These species were also tested for host affinities. Nematodes were tracked by image analysis after exposure to faeces, cuticle or food of either Popillia japonica or Spodoptera exiqua. Steinernema glaseri responded to selected host cues by shifting from ranging to localized search, characterized by decreased locomotory rate, distance travelled, search area and the proportion of the test period spent moving. Steinernema carpocapsae did not respond to host cues. Steinernema glaseri responds to selected chemical host cues for host location, whereas S. carpocapsae does not.

Life history traits expressed by organisms vary due to ecological and evolutionary constraints imposed by their current environmental conditions and genetic heritage. Trematodes often alter the life history of their host snails by inducing parasitic castration. Our understanding of the variables that influence the resulting changes in host growth, fecundity and survivorship is insufficient to confidently predict specific outcomes of novel snail–trematode combinations. In a literature review of the last 30 years, we found 41 publications examining various life history characteristics of trematode-infected snails. These publications reported 113 different field and laboratory experiments involving 30 snail species and 39 trematode species and provided a data set for assessing factors that potentially affect life history outcomes. Analysis of the diverse responses across various snail–trematode systems and experimental conditions teased out general patterns for the expression of host growth, fecundity and survival. These were used to address existing hypotheses and develop several new ones relating the response of snail-trematode interactions to environmental and genetic factors. Finally, we propose directions for future experiments that will better assess the ecological and evolutionary factors influencing snail life history responses to trematode parasitism.

Cryptic species, belonging to the 37 collar-spine Echinostoma group, were distinguished using nuclear rDNA ITS (884 bases) and mtDNA CO1 (257 bases) and ND1 (530 bases) sequences. Sequences were obtained from five 37 collar-spine species, Echinostoma trivolvis, E. paraensei, E. caproni, E. revolutum and E. sp.I, a parthenogenetic isolate from Africa. Three geographic isolates of E. caproni were compared. Average sequence divergence among the 37 collar-spine species range from 2·2% in the rDNA ITS through 8% for the CO1 and 14% for the ND1. In addition, genes were sequenced from 2 non 37 collar-spine species, E. hortense and an undescribed Australian species, E. sp. (Aus). For each gene, distances of terminals from a predicted ancestral sequence were calculated. These indicated that ND1 is diverging significantly faster than the other 2 regions. In the CO1 gene most substitutions are synonymous and saturation has been reached for the majority of pairwise comparisons. The ND1 gene exhibits greater pairwise divergence but less evidence of saturation due to weaker conservation of first and second codon positions. The ITS has no amino acid coding constraints and displays no evidence of saturation. Although all 3 regions successfully distinguished the nominal species, ND1 appears to be the most informative region for investigating relationships within the 37 collar-spine group.

Echinococcus granulosus exhibits substantial genetic diversity that has important implications for the design and development of vaccines, diagnostic reagents and drugs effective against this parasite. DNA approaches that have been used for accurate identification of these genetic variants are presented here as is a description of their application in molecular epidemiological surveys of cystic echinococcosis in different geographical settings and host assemblages. The recent publication of the complete sequences of the mitochondrial (mt) genomes of the horse and sheep strains of E. granulosus and of E. multilocularis, and the availability of mt DNA sequences for a number of other E. granulosus genotypes, has provided additional genetic information that can be used for more in depth strain characterization and taxonomic studies of these parasites. This very rich sequence information has provided a solid molecular basis, along with a range of different biological, epidemiological, biochemical and other molecular-genetic criteria, for revising the taxonomy of the genus Echinococcus. This has been a controversial issue for some time. Furthermore, the accumulating genetic data may allow insight to several other unresolved questions such as confirming the occurrence and precise nature of the E. granulosus G9 genotype and its reservoir in Poland, whether it is present elsewhere, why the camel strain (G6 genotype) appears to affect humans in certain geographical areas but not others, more precise delineation of the host and geographic ranges of the genotypes characterised to date, and whether additional genotypes of E. granulosus remain to be identified.

Transmission of leishmaniasis is effected by a specific developmental stage, the metacyclic promastigote. The precursors of metacyclic promastigotes were a distinct subpopulation of parasites, identified for the first time as a new stage in the life-cycle and named leptomonad promastigotes. Microdissection of infected sandflies into 4 midgut regions and foregut allowed precursor-product relationships to be established for amastigote-procyclic promastigote, procyclic-nectomonad promastigote, nectomonad-leptomonad promastigote and leptomonad-metacyclic promastigote developmental switches. Metacyclic promastigotes occurred mainly in the thoracic midgut and cardia, coincident with the accumulation of a promastigote secretory gel (PSG) plug in these anterior regions. The gel-like plug was isolated from flies with mature infections and found to contain predominantly leptomonad promastigotes. The PSG plug also contained the majority (75%) of the total metacyclic promastigote population in the sandflies, which were concentrated at the anterior pole. The PSG plug was found to be the main site of metacyclogenesis, and acted as a reservoir of leptomonad promastigotes from which metacyclic forms differentiated and migrated forward to promote the infective potential of the fly. The PSG plug occluded and distorted the midgut, forcing the stomodeal valve open and affecting the feeding success of the sandflies, such that they experienced difficulty in taking a full meal. Collectively, these data support the role of the PSG in the transmission of leishmaniasis, by conditioning the midgut environment for metacyclogenesis and altering the feeding ability of infected sandflies.

There is evidence that faecal egg counts of Schistosoma mansoni vary considerably from day to day, which results in poor sensitivity of single stool readings. Intra-specimen variation of S. mansoni egg counts may also be considerable, but has previously been considered as the less important component. We quantified the relative contribution of these two sources of variation among 96 schoolchildren from an area in Côte d'Ivoire highly endemic for S. mansoni. Stool specimens were collected over 5 consecutive days, and 5 egg-counts were made in each specimen by the Kato–Katz technique. The point prevalence of the first sample was 42.7% and the cumulative prevalence after the maximum sampling effort was 88.5%. Using generalized linear mixed models we found that the presence of S. mansoni eggs in a stool sample varied much more between days than within specimens, indicating that stool sample examination over multiple days is required for accurate prevalence estimates. However, using the same approach, we found that among infected children intra-specimen variation in egg counts was 4.3 times higher than day-to-day variation. After praziquantel administration, day-to-day variation was more important than before, since most infections were very light and thus likely to be missed altogether by stool examination on a single day. We conclude that diagnostic sensitivity in high transmission areas is maximized by making several stool readings on several days, but examining 1 stool specimen several times can make reasonable estimates of infection intensity.

Many studies have identified various host behavioural and ecological traits that are associated with parasite infection, including host gregariousness. By use of meta-analyses, we investigated to what degree parasite prevalence, intensity and species richness are correlated with group size in gregarious species. We predicted that larger groups would have more parasites and higher parasite species richness. We analysed a total of 70 correlations on parasite prevalence, intensity and species richness across different host group sizes. Parasite intensity and prevalence both increased positively with group size, as expected. No significant relationships were found between host group size and parasite species richness, suggesting that larger groups do not harbour more rare or novel parasite species than smaller groups. We further predicted that the mobility of the host (mobile, sedentary) and the mode of parasite transmission (direct, indirect, mobile) would be important predictors of the effects of group sizes on parasite infection. It was found that group size was positively correlated with the prevalence and intensity of directly and indirectly transmitted parasites. However, a negative relationship was observed between group size and mobile parasite intensity, with larger groups having lower parasite intensities. Further, intensities of parasites did not increase with group size of mobile hosts, suggesting that host mobility may negate parasite infection risk. The implications for the evolution and maintenance of sociality in host species are discussed, and future research directions are highlighted.

This paper reviews the work published over the past decade on the use of parasites as biological tags in population studies of marine fish, mammals and invertebrates. Fish hosts are considered in taxonomic and ecological groups as follows: demersal, anadromous, small pelagic, large pelagic and elasmobranch. Most studies were carried out on demersal fish, particularly on members of the genera Merluccius (hake), Sebastes (rockfish) and on Atlantic cod Gadus morhua L., but Pacific salmonids and small pelagic fish of the genus Trachurus are also well-represented. A current multidisciplinary study of the population biology of horse mackerel Trachurus trachurus in European waters, which includes the use of parasites as tags, is described. Two studies recognize the potential for using parasites as tags for cetaceans but, in spite of the considerable potential for this approach in population studies of elasmobranchs, no original study has been carried out on this group for over ten years. Studies of parasites as tags for marine invertebrates have concentrated on squid. Recent trends in the use of parasites as biological tags for marine hosts are discussed.

The potential of various quantitative lateral flow (LF) based assays utilizing up-converting phosphor (UCP) reporters for the diagnosis of schistosomiasis is reviewed including recent developments. Active infections are demonstrated by screening for the presence of regurgitated worm antigens (genus specific polysaccharides), whereas anti-Schistosoma antibodies may indicate ongoing as well as past infections. The circulating anodic antigen (CAA) in serum or urine (and potentially also saliva) is identified as the marker that may allow detection of single-worm infections. Quantitation of antigen levels is a reliable method to study effects of drug administration, worm burden and anti-fecundity mechanisms. Moreover, the ratio of CAA and circulating cathodic antigen (CCA) is postulated to facilitate identification of either Schistosoma mansoni or Schistosoma haematobium infections. The UCP-LF assays allow simultaneous detection of multiple targets on a single strip, a valuable feature for antibody detection assays. Although antibody detection in endemic regions is not a useful tool to diagnose active infections, it gains potential when the ratio of different classes of antibody specific for the parasite/disease can be determined. The UCP-LF antibody assay format allows this type of multiplexing, including testing a linear array of up to 20 different targets. Multiple test spots would allow detection of specific antibodies, e.g. against different Schistosoma species or other pathogens as soil-transmitted helminths. Concluding, the different UCP-LF based assays for diagnosis of schistosomiasis provide a collection of tests with relatively low complexity and high sensitivity, covering the full range of diagnostics needed in control programmes for mapping, screening and monitoring.

Cercariae, like miracidia, are non-parasitic larval stages implicated in the life cycle of all trematodes for the host-to-host parasite transmission. Almost all cercariae are free-living in the external environment. With a few exceptions (cercariae of Halipegus occidualis (Halipegidae) can live several months, Shostak & Esch, 1990a), cercariae have a short active life during which they do not feed, living on accumulated reserves. Most cercariae encyst as metacercariae in second intermediate hosts which are prey of the definitive host; in certain species, the interruption of the active life is achieved by an encystment in the external environment (or a simple immobile waiting strategy in a few species). In some two-host life cycles, the cercariae develop into adults after penetration (this is the case for various species causing human schistosomiasis). Some cercariae do not leave the mollusc which must then be ingested by the definitive host.

Angiostrongylus cantonensis is a metastrongyloid nematode found widely in the Asia-Pacific region, and the aetiological agent of angiostrongyliasis; a disease characterized by eosinophilic meningitis. Rattus rats are definitive hosts of A. cantonensis, while intermediate hosts include terrestrial and aquatic molluscs. Humans are dead-end hosts that usually become infected upon ingestion of infected molluscs. A presumptive diagnosis is often made based on clinical features, a history of mollusc consumption, eosinophilic pleocytosis in cerebral spinal fluid, and advanced imaging such as computed tomography. Serological tests are available for angiostrongyliasis, though many tests are still under development. While there is no treatment consensus, therapy often includes a combination of anthelmintics and corticosteroids. Angiostrongyliasis is relatively rare, but is often associated with morbidity and sometimes mortality. Recent reports suggest the parasites’ range is increasing, leading to fatalities in regions previously considered Angiostrongylus-free, and sometimes, delayed diagnosis in newly invaded regions. Increased awareness of angiostrongyliasis would facilitate rapid diagnosis and improved clinical outcomes. This paper summarizes knowledge on the parasites’ life cycle, clinical aspects and epidemiology. The molecular biology of Angiostrongylus spp. is also discussed. Attention is paid to the significance of angiostrongyliasis in Australia, given the recent severe cases reported from the Sydney region.

1. Evidence from previous literature shows that puppies are commonly infected with larvae of Toxocara canis at birth and that prenatal infection can be produced by feeding embryonated eggs to pregnant bitches.

2. Observations on fifty-eight dogs in Brisbane showed that all of twenty-nine puppies 1–6 months old were infected, while only three out of twenty-nine dogs over 6 months old were infected.

3. In naturally infected puppies, 1–3 weeks old, it was found that at birth third-stage larvae were present in the lungs. Third-stage larvae continued to appear in the lungs for the first week of life; their length was 0·6–1·3 mm.

4. Third-stage larvae were found in the stomach on the day after birth; at 3 days after birth fourth-stage larvae were found in the intestine.

5. It appeared likely that the second moult occurs in puppies before birth, and that the third moult takes place at a length of 1·0–1·3 mm. in the lungs and stomach within the first week of life.

6. By the beginning of the second week, fourth-stage larvae were fully grown and had commenced the fourth moult at a length of 5–7 mm.

7. Throughout the second and third weeks, adults grew rapidly, reaching a length of about 67 mm. by the end of the third week, but no eggs had appeared in the faeces at this time.

8. Experimental infection of mice with eggs showed that the larvae were distributed to the somatic tissues, few reaching the alimentary tract. The larvae did not progress beyond the second stage in the tissues of mice.

9. Experimental infection of dogs with eggs showed that in dogs over 5 weeks old the larvae were distributed to the somatic tissues and did not reach the alimentary tract. The larvae did not progress beyond the second stage, though some of them showed signs of commencing the second moult. In contrast, 1 to 3-week-old puppies infected in the same way were found to harbour larvae in the alimentary tract. Though some of these larvae were probably derived from a naturally acquired prenatal infection, it was evident from the progress of development that the experimental infection resulted in the presence of second-stage larvae in the liver and lungs and that these larvae underwent the second moult, commenced development as third-stage larvae in the lungs, migrated into the stomach and developed to the adult stage in the intestine.

10. Experimental infection of dogs and foxes with mice harbouring second-stage larvae in the tissues showed that, in some instances, development of larvae proceeded in the alimentary tract. No evidence of somatic migration was found in dogs infected in this way, but in foxes second-stage larvae were found in the lungs.

11. The structure and development of the second, third and fourth stage is described in detail and found to resemble closely the development of T. cati larvae (Sprent, 1956). Second-stage larvae from dog tissues had a length of 0·34–0·44 mm. and the second moult occurred at a length of 0·37–0·44 mm. Third-stage larvae varied in length from 0·46 to 1·36 mm., and the third moult occurred at a length of 0·98–1·3 mm. Fourth-stage larvae measured 1·2–6·3 mm., though moulting fourth-stage larvae were observed up to a length of 7·4 mm. Sexual differentiation occurred during the fourth stage and was evident at a length of about 1·5 mm.

12. The migratory behaviour of the larvae of T. canis and T. cati is compared and discussed in relation to their wide range of hosts. It is concluded that differences in migratory behaviour are adaptations to prevailing modes of nutrition and it is suggested that the somatic migration occurring in dogs is an adaptation to the non-predatory habits of this particular host.

The ultrastructure of the reproductive system of mature (54-day-old), immature (32-day-old) and females from unisexual infections of Schistosoma mansoni is described in detail. The uterus is tegumentary in structure but the vitelline duct and oviduct are complex and possess cilia as well as lamellae on their luminal surfaces. The characteristics of the cells forming the walls of the ducts suggests that they may have a digestive function. The posterior portion of the oviduct of the adult worm contains sperm which become enveloped by lamellae. The vitelline cells of the adult contain vitelline droplets, much lipid and little glycogen. A second type of body derived from endoplasmic whorls is also present. Mehlis's gland contains only one type of gland cell and these cells pass through the ootype wall and open into its lumen. The female from unisexual infections has an incompletely developed Mehlis's gland, an ovary in which the Golgi complexes do not produce typical cortical granules and has vitelline cells which remain immature. The oviduct, ootype and uterus are well developed in contrast to the vitelline duct.A comparison with young, but not inseminated worms, suggests that the presence of sperm in the oviduct is not the major stimulus which induces maturation of the female worm.

Intestinal helminths of fish are of increasing interest as potential bioindicators for heavy metal contamination in aquatic habitats. Among these parasites cestodes and acanthocephalans in particular have an enormous heavy metal accumulation capacity exceeding that of established free living sentinels. Metal concentrations several thousand times higher in acanthocephalans than in host tissues were described from field and laboratory studies. Whereas larval stages inside their intermediate hosts are not able to take up high quantities of metals, young worms begin to take up metals immediately after infection of the final host. After four to five weeks of exposure, the parasites reach a steady-state concentration orders of magnitude higher than the ambient water level. Thus, acanthocephalans are not only very effective in taking up metals, but they can also respond very rapidly to changes in environmental exposure. The mechanism which enable acanthocephalans to take up metals from the intestinal lumen of the host appears to be based on the presence of bile acids, which form organo-metallic complexes that are easily absorbed by the worms due to their lipophilicity. Investigations of the environmental conditions affecting metal uptake have shown that the parasites are more consistent and reliable indicators for metal pollution than the host tissues as metal levels of the latter are much more dependent on the water chemistry. Thus, after some years of research on the uptake of metals by acanthocephalans and on the factors affecting metal accumulation in intestinal parasites it should be asked if acanthocephalans meet the criteria commonly accepted for sentinels. If parasites can be considered as promising sentinels, we need reasons for the establishment of ‘new’ indicators. Therefore, this review summarises the present knowledge about parasites as bioindicators and compares the accumulation properties of parasites and established free living indicators. Finally, this review presents possible answers to the question why it could be advantageous to have new and even more sensitive indicators for environmental monitoring purposes.