An ideal culture medium for Leishmania promastigotes should retain the basic characteristics of promastigotes found in sandflies (morphology and infectivity). Furthermore, the media should not create a bias in experimental settings, thus enabling the proper extrapolation of results. To assess this we studied several established media for promastigote growth. We analysed morphology, viability, cell cycle progression, metacyclic profile, capacity to differentiate into axenic amastigotes and infectivity. Furthermore, using a rational approach from the evaluated media we developed a simple serum-free medium (cRPMI). We report that parasites growing in different media present different biological characteristics and distinct in vitro and in vivo infectivities. The developed medium, cRPMI, proved to be a less expensive substitute for traditional serum-supplemented media for the in vitro maintenance of promastigotes. In fact, cRPMI is ideal for the maintenance of parasites in the laboratory, diminishing the expected loss of virulence over time typical of the parasite cultivation. Ultimately this report is a clear warning that the normalization of culture media should be a real concern in the field as media-specific phenomena are sufficient to induce biological bias with consequences in infectivity and general parasite biology.

Malaria remains one of the most significant global public health burdens, with nearly half of the world's population at risk of infection. Malaria is not however a monolithic disease – it can be caused by multiple different parasite species of the Plasmodium genus, each of which can induce different symptoms and pathology, and which pose quite different challenges for control. Furthermore, malaria is in no way restricted to humans. There are Plasmodium species that have adapted to infect most warm-blooded vertebrate species, and the genus as a whole is both highly successful and highly diverse. How, where and when human malaria parasites originated from within this diversity has long been a subject of fascination and sometimes also controversy. The past decade has seen the publication of a number of important discoveries about malaria parasite origins, all based on the application of molecular diagnostic tools to new sources of samples. This review summarizes some of those recent discoveries and discusses their implication for our current understanding of the origin and evolution of the Plasmodium genus. The nature of these discoveries and the manner in which they are made are then used to lay out a series of opportunities and challenges for the next wave of parasite hunters.

Human–wildlife interactions have reached unprecedented levels, and humans are influencing the earth's ecosystems more rapidly and extensively than ever before. This situation is cause for serious concern, especially since disease interactions between wildlife and humans have been recognized as major conservation threats. In this study, long-tailed macaques, Macaca fascicularis, from 2 forest parks located in north-eastern Thailand were investigated to determine the influence of habitat modification by humans on helminth parasite associations in non-human primates. Macaque populations with contact to anthropogenically modified environments were compared with sylvatic groups in nearby natural environments. In order to test for human–non-human primate transmission of parasites, the local human populations were also examined. Humans were infected with a number of potentially pathogenic parasites, including Opisthorchis viverrini and Strongyloides stercoralis. However, eggs of these helminths were not detected in macaque feces. Thus, no direct parasite transfer from humans to non-human primates could be confirmed. However, macaque groups with more frequent contact with human-modified habitats, and a higher portion of human-provided food in their diet, had significantly higher prevalences and intensities of Strongyloides fuelleborni and of an intestinal fluke (probably Haplorchis sp.) than sylvatic groups. Positive correlations were found between the time foraging on the ground and infection with S. fuelleborni, and the amount of human-provided food and intestinal fluke infection. Human alteration of habitat and associated modifications in non-human primate behaviour are likely to play a role in determining the occurrence, prevalence and intensity of zoonotic helminth infection of wild non-human primates.

Factors such as the particular combination of parasite–mosquito species, their co-evolutionary history and the host's parasite load greatly affect parasite transmission. However, the importance of these factors in the epidemiology of mosquito-borne parasites, such as avian malaria parasites, is largely unknown. Here, we assessed the competence of two mosquito species [Culex pipiens and Aedes (Ochlerotatus) caspius], for the transmission of four avian Plasmodium lineages (Plasmodium relictum SGS1 and GRW11 and Plasmodium cathemerium-related lineages COLL1 and PADOM01) naturally infecting wild house sparrows. We assessed the effects of parasite identity and parasite load on Plasmodium transmission risk through its effects on the transmission rate and mosquito survival. We found that Cx. pipiens was able to transmit the four Plasmodium lineages, while Ae. caspius was unable to transmit any of them. However, Cx. pipiens mosquitoes fed on birds infected by P. relictum showed a lower survival and transmission rate than those fed on birds infected by parasites related to P. cathemerium. Non-significant associations were found with the host–parasite load. Our results confirm the existence of inter- and intra-specific differences in the ability of Plasmodium lineages to develop in mosquito species and their effects on the survival of mosquitoes that result in important differences in the transmission risk of the different avian malaria parasite lineages studied.

That part of the physiological life history of the tick, Ixodes ricinus, which is dealt with in the present paper, falls into three distinct phases: maturation of the gonads, oviposition, and development of the egg; these three are collectively referred to as “reproduction”.

Histological studies using horse-radish peroxidase (HRP) as a marker, injected iontophoretically through a recording electrode, have indicated the origins of potentials encountered upon advancement of the electrode into and beneath the dorsal surface of adult male Schistosoma mansoni. The first potential encountered, having a value of – 51 ± 0·6 mV originates across the outer tegumental membrane. The next potential has a value of — 28 ± 0·6 mV and originates in the muscle masses underlying the tegument. Finally, a potential having the value — 10 ± 0·5 mV originates within the basal lamina and the interstitial fibres and extracellular space surrounding the muscle. Altering ion concentrations in the bathing medium (i.e. high K+, low Na+, zero Ca2+, low Cl−, high Li+) depolarizes all three potentials. External applications of ouabain and the anti-schistosomal, praziquantel, also cause depolarization of the potentials. It appears that the muscle potential and the tegumental potential are primarily K+-dependent. The depolarizing effects of ouabain, LiCl and low Na+ suggest that active transport is important in the maintenance of the muscle potential, just as is the case for the tegumental potential. There appears to be a close correlation between changes in the tegumental, muscle and extracellular space potentials. The correlation between tegument and muscle potential changes might be explained by junctional complexes between tegumental cell bodies and muscle cell bodies.

The total lipids and the amount of neutral lipids of male and female N. brasiliensis, from 7-day and 15-day infections, have been studied quantitatively. There is an increase in total lipids from 10·9 ± 2 to 15·5 ± 2 % in females and an increase from 8·4 ± 1 to 14·6 ± 2 % in males. In both sexes there is a rise in cholesterol and trigylceride content and a fall in free fatty acid content. These changes are discussed with reference to the development of immunity of the host to this nematode.

I wish to thank Mrs B. Fisher, Mr A. W. Pearson and Mr N. Sykes for assistance during this work. These results form part of a programme of work supported by the A.R.C. while I was at the Molteno Institute, University of Cambridge, and continued at the Houghton Poultry Research Station. I wish to thank Dr P. Tate for accommodation at the Molteno Institute during the early part of this work.

By a variety of microscopical techniques, an initial survey has been made of the functional organization of ovarian balls from mature, inseminated female Moniliformis dubius and Polymorphus minutus. On the basis of evidence from observations made with the transmission electron microscope, we have concluded that the ovarian ball consists of three components; these are two separate, multinucleate syncytia and a cellular zone. The inner region is considered to be an oogonial syncytium from which the germ-line cells arise to form the cellular zone. The oogonial syncytium and the cellular elements are embedded in a supporting syncytium which also forms the boundary of the ovarian ball. Details of the ultrastructure of these components, observations on fertilization and a hypothesis to account for the main events occurring in an acanthocephalan ovarian ball are also presented.

Acanthocephalans are dioecious parasites which become sexually mature in the alimentary tract of vertebrates. After insemination, individual female worms begin to release embryonated eggs at rates which have been estimated to vary, on average, from 2000 per day in the case of Polymorphus minutus (Crompton & Whitfield, 1968) to 260000 per day in the case of Macracanthorhynchus hirudinaceus (Kates, 1944). Irrespective, however, of the species of acanthocephalan and the number of eggs produced, a most interesting mode of ovarian development and multiplication is believed to exist (see Bullock, 1969). Within the female worm, the primordial ovarian tissue gives rise to separate ovaries which are often termed ovarian balls. These in turn give rise to more ovarian balls and the process continues until large numbers have been formed. The ovarian balls of a mature female have no permanent attachment to the tissues of the worm. They are contained in the fluid of the body cavity either freely, or loosely constrained in large membranous chambers known as ligament sacs.

Few investigations have been made into the structure and cytology of the ovarian balls of the Acanthocephala. Early observations on the histology of the germ-line constituents of ovarian balls were made by Hamann (1891), Kaiser (1893) and Meyer (1928), each of whom suggested that some of the developing oogonial stages were arranged in a syncytial manner. In a study of the embryology of P. minutus. Nicholas & Hynes (1963) interpreted preparations of ovarian balls, which had been subjected to the Feulgen reaction, as indicative of syncytial tissue in the central region of the ball. They also recorded their uncertainty about whether an ovarian ball has a bounding membrane or not. More recently, Robinson (1964, 1965) described mitotic and meiotic divisions in oogonia and oocytes from ovarian balls of Mac. hirudinaceus and Moniliformis dubius and Stranack (1972) included an electron micrograph of part of an ovarian ball of Pomphorhynchus laevis in a description of the nature of the egg envelopes of that species. In this paper, we present a general survey, based largely on evidence obtained with the electron microscope, of the functional organization of the ovarian balls of mature M. dubius and P. minutus.

The metacercaria of Holostephanus lühei Szidat (1936) is described together with comments on both its linear and tissue distribution within the host (Gasterosteus aculeatus L.), host-parasite reaction and numbers of cysts in relation to the size of the fish.

The adult of Holostephanus lühei Szidat (1936) (syn. H. bursiformis Szidat, 1936) obtained experimentally from the duck and pigeon, is re-described in detail. It is noted that this species is amphitypic and it is suggested that H. dubius (Szidat, 1936) (syn. Cyanocotyloides Dubius, Szidat, 1936) should be reduced to synonymy with H. lühei.

Grateful acknowledgement is expressed to Dr G. Dubois for his interest, advice and valuable opinions given in connexion with this study.

In the ideal situation, the development of new amoebicides, or more accurately anti-amoebic compounds which are compounds with activity against Entamoeba histolytica, should initially proceed with the study of parasite-specific metabolic pathways and their inhibition, followed by whole parasite in vitro studies, experimental in vivo models and finally clinical trial. However, there are considerable gaps in our knowledge which will be discussed below, and consequently many investigators consider that empirically selected compounds should be tested experimentally in addition to specifically designed compounds. Before clinical trials can begin, extensive examination of the candidate amoebicide in experimental animals is required in order to investigate possible toxicological hazards.

In addition to inhibiting the amoebic parasite, the drug has to reach the parasite in several different sites in the body, thus there is also a problem of pharmacokinetics and distribution. Prior to the discovery of the nitroimidazole class of amoebicides, the multi-site attack was solved by the use of several drugs, sometimes in sequence during the treatment of an individual case (Powell, 1972). The discovery of the nitroimidazole class of compound changed the situation dramatically and these have shown a clinical and parasitological effect against extra-intestinal and intestinal wall infections. The effect on intralumenal infection (that is mildly symptomatic or asymptomatic infections) of the large intestine is, however, less certain (Finegold, 1977; Spillman, Ayala & Sanchez, 1976).

Although the treatment of amoebiasis appears to be satisfactory at the present time, it is difficult to predict problems which might arise in the future, and therefore it is valuable to continue the pre-clinical development, especially the investigation of parasite metabolism, in order to define parasite-specific points of chemotherapeutic attack.

The chemotherapy of amoebiasis was reviewed comprehensively by Woolf (1963, 1965). The present account of the development of amoebicides therefore starts from the Woolfe reviews.

The immature stages of Caraphractus cinctus Walker are described.

Four larval stages have been observed which may correspond to three or four instars. In no stage have mandibles been observed.

The first-instar larva is elongated and active. In the second-instar oral lobes are present. In the next stage the larva becomes shapeless and rather transparent. In the last stage the wall of the mid-gut shows conspicuous opaque spots which consist of single cells containing spherical concretions, probably the products of excretion.

These concretions later become free in the gut of the pupa and are discharged in the meconium when the imago emerges from the host egg.

The effects of parasitism on the host eggs of different ages is discussed. In newly laid host eggs all the contents are consumed by the parasitic larvae. In advanced eggs of Agabus the egg of Caraphractus is laid in the mid-gut of the host embryo where the parasitic larva develops, the hard parts of the host larva remaining intact. Parasitism in advanced eggs of Dytiscus is rarely successful.

The larvae of other Mymaridae are discussed and their main features compared. The first-instar larva of Caraphractus does not correspond to any of the previously described types of mymarid larvae.

The seasonal history is described, with the sequence of hosts parasitized throughout the year. From four to six generations of Caraphractus have been bred indoors during the year. The winter is passed as a diapausing prepupa. In some cases diapause may be prolonged. Fertility is high: 121 imagines have been bred from one female of Caraphractus.

I have much pleasure in acknowledging my gratitude to the late Dr W. D. Hincks for his kindness in reading the typescript of this paper: the comments by such a well-known authority on Mymaridae have been most valuable. I am very grateful to Mr O. Bakkendorf for allowing me to reproduce several of his figures of Mymarid larvae from the valuable work he devoted to the biology of Danish hymenopterous egg-parasites. I am also grateful to Miss B. A. Trott of the Commonwealth Institute of Entomology for the help she has so kindly given me with references.

1. Suspensions made from infected caecal material, derived from chickens which had been artificially infected with Histomonas meleagridis by the administration of embryonated Heterakis ova, can be used to transmit the organisms to other chickens when administered per os.

2. Infections with histomonad suspensions can only be obtained in chickens that have been starved, or in chickens that are feeding but have received an alkali mixture immediately before the suspension is administered. The highest incidence of infections is obtained by administering suspensions to starved chickens that have received 1 g. alkali mixture beforehand.

3. Successful infection appears to depend upon the pH of the gizzard and, possibly, of the upper intestine. The incidence of lesions produced by feeding suspension is increased as the contents of the gizzard become alkaline. It is also suggested that the consistency of the food may play a part, as coarse food, along with the infective material, is retained in the gizzard until it is completely ground up and mixed with the gastric juice.

4. In one series of passages the suspension became attenuated after fourteen passages through chickens. In other cases suspensions became attenuated after only six passages through chickens.

5. The courses of infections produced by histomonad suspensions and Heterakis ova are compared.

6. The advantages of the method of using histomonad suspensions are discussed in their relation to the screening of chemotherapeutical agents.

An ultrastructural study of numerous serial sections of Plasmodium chabaudi trophozoites at various growth stages, followed by 3-dimensional reconstruction, allowed us to describe more precisely the internalization process of the erythrocytic stroma, both in space and in time. Two endocytotic processes are apparent. (1) Pinocytosis — as soon as the merozoite has become a young trophozoite (ring stage), small double membrane-bound vesicles can be seen budding off around the whole periphery of the parasite. After the inner membrane of the vesicle has disappeared, the contents alter and a pigment crystal appears. (2) Cytostomal system — this phenomenon coexists with, and eventually replaces, pinocytosis. It consists of invagination of the membrane of the parasitophorous vacuole and of the plasmalemma, through a typical cytostome, in order to form a cytostomal vacuole. This extends into a long tube, the cytostomal tube, which eventually digitates. When the tube reaches its maximal size, the cytostome disappears and the tube remains open to the erythrocytic stroma by a simple aperture. A new cytostome can form elsewhere on the parasite surface and another tube can extend. Two or three such tubes can coexist in a trophozoite although only one cytostome is functional at one time. At the end of the tubes vesicles bud off, the contents of which become modified as described previously. The residual product of haemoglobin degradation is the malarial pigment.

The influence of the late components of complement (C) on percutaneous primary infections with Schistosoma mansoni was studied in inbred mice genetically deficient or intact in C5. Worm recoveries were diminished in C5-deficient male mice as compared to C5-intact animals. Twenty-four-day-old parasites were also shorter following growth in C5-deficient animals. At 7 weeks after infection, female schistosomes, but not male parasites, were shorter and fewer eggs/schistosome pair were deposited in the livers of C5-deficient as compared to C5-intact male mice. In addition to the presence of C5, the mouse sex was found to influence the outcome of an infection. Schistosomes showed a reduced infection rate and were relatively stunted after 24 days of growth in female mice of the two strains as compared to male mice of the corresponding strains. The results suggest that C5 plays no role in defence against a primary infection in mice.

The parameters of species richness, abundance and diversity of the intestinal helminth infracommunities of a sample of 269 Common gulls, Larus canus, were examined over one season at Agdenes, Norway. The communities developed rapidly in unfledged gulls and the diversity parameters were of similar magnitude in immature and adult birds. All parameters were low in the early part of the season, reached maxima in June or July and fluctuated erratically or declined thereafter. Comparison of summary parameters with those from other species of gulls indicated that helminth community diversity in Common gulls is fairly typical of gulls in general. In gulls as a group, helminth communities show common features of high species richness, low abundance, few or no core species and a number of species that occur rarely and in low numbers. Expectations of particularly high parasite community diversity were not fully realised because species lists and diversity of the component community are not a very good basis for predicting diversity at the infracommunity level.

There are comparatively few studies concerned specifically with chemotherapy of parasitic infections and its relationship with the immune status of the host being treated. In one sense this is hardly surprising. The disciplines of chemotherapy and immunology have developed independently, and the search for effective drugs has for the most part been an empirical process; when a compound showing some activity has emerged the tendency has been to look for analogues with even greater parasiticidal properties rather than to consider whether effectiveness of the parent compound could be improved if the immune status of the host were different. In many cases, test systems for drug development have actually been selected to reduce as far as possible the complications f an immune response. Thus acute, fatal infections are commonly used for the screens, and questions such as the level of specific resistance at the time of treatment, immunodepression by the parasite, and increased resistance to challenge following chemotherapy are generally irrelevant.

1. The bucephalid cercaria from Crassostrea virginica (Gmelin), the commercial oyster of the Atlantic and Gulf coasts of North America, has been called Bucephalus haimeanus Lacaze-Duthiers and Bucephalopsis haimeana (Lacaze-Duthiers). Neither of these names is correct. Bucephalus haimeanus Lacaze-Duthiers, 1854, is a parasite of the European oyster, Ostrea edulis L. (and possibly of cockles, Cardium spp.) in oceanic or near-oceanic habitats, while the American species is a parasite of an estuarine oyster and is found almost entirely in the least saline parts of its host's range. The correct name of the American oyster bucephalid is Bucephalus cuculus McCrady, 1874.

2. The life cycles of all European marine bucephalids are still unknown. The life cycles described in the European literature are based entirely on morphological resemblances which are not close enough to be convincing, and none of them has been tested by experiment. Bucephalid cercariae do not show any of the features which are used to distinguish genera. So far as present evidence goes, Bucephalopsis haimeana is just as likely to develop into a Rhipidocotyle, a Bucephalus, or a Prosorhynchus as it is to develop into a member of the genus Bucephalopsis Nicoll, 1914, nec Diesing, 1855.

3. Bucephalopsis Diesing, 1855, is the name proposed by Diesing for a subgenus created especially for the cercaria Bucephalus haimeanus Lacaze-Duthiers, 1854. Nicoll had no right to use this name for the genus of gasterostomes which, as adults, have a muscular sucker at the anterior end and do not have accessory structures such as a hood or papillae. Up to the present, there is still no evidence that this genus has any connexion with Lacaze-Duthiers's cercaria, other than common membership in the family Bucephalidae. Therefore the new name Bucephaloides Hopkins has been proposed to replace the generic name Bucephalopsis Nicoll, 1914, nec Diesing, 1855, with Bucephaloides gracilescens (Rudolphi, 1819) as the type species. This genus does not include Bucephalus haimeanus Lacaze-Duthiers because the metacercaria and the adult form of that species remain unknown.

4. Tennent (1905, 1906, 1909) did not prove that there was any connexion between the oyster cercaria, Bucephalus cuculus McCrady, and the immature bucephalids in Menidia or the adult bucephalids in Strongylura. His drawings show that at least some of the bucephalids which Tennent studied had a hood and therefore belong in Rhipidocotyle. Re-examination of the bucephalids in Strongylura marina reveals that at least three species of bucephalids occur as adults in that host; these are described in this paper as Rhipidocotyle transversale Chandler, 1935, R. lintoni Hopkins, and Bucephaloides strongylurae Hopkins. Rhipidocotyle transversale and Bucephaloides strongylurae were also found in an immature (metacercaria) stage in Menidia, and were the only bucephalids found in Menidia during this study. The excretory systems of the three species in Strongylura all have features which exclude the possibility that they could develop from the oyster cercaria, Bucephalus cuculus.

5. Tennent's (1906) drawing (fig. 46) of an adult bucephalid from Strongylura marina, which Eckmann (1932) mentions as the best representation of the species characteristics of Bucephalopsis haimeana (Lacaze-Duthiers), was probably made from a specimen of Rhipidocotyle lintoni.

6. Tennent (1909) proved that eggs or larvae from an unknown adult bucephalid in Lepisosteus osseus could infect oysters, Crassostrea virginica, and develop into sporocysts which would grow in oysters for at least one month. This is the only experimental proof of a connexion between an adult bucephalid in a fish and a larval bucephalid in an oyster. Until the present, no bucephalid from a gar (Lepisosteus) had ever been described. In the present paper Rhipidocotyle lepis-ostei Hopkins is described from adults in Lepisosteus spatula, the alligator gar, in Louisiana. The metacercariae of Rhipidocotyle lepisostei are abundant in the fin rays of mullets, Mugil cephalus and M. curema. The excretory system of this species is not identical with that of Bucephalus cuculus, but is not so different as to exclude the possibility that the oyster cercaria might develop into R. lepisostei. If, in the future, R. lepisostei is proved to be the adult form of Bucephalus cuculus, the name of the species will become Rhipidocotyle cuculus (McCrady), and R. lepisostei will become a synonym.

E. praeox has been isolated in Britain for the first time and is similar in regard to its oocyst size, prepatent time, life-cycle and the development of host immunity to the reports of Tyzzer et al. (1932). Oocysts had mean dimensions of 20·4 × 17·45 μm and the first oocysts were discharged 83½ h after infection.

Oocyst production and life-cycle studies suggest that at least three generations of schizogony precede gametogony and that at least one further generation of schizogony is needed to explain the oocyst reproduction resulting from a small dose of oocysts. Young chickens 1½–3 weeks of age were not such suitable hosts as older chickens (6 weeks) and the reproduction of the parasite was seriously reduced when large numbers (e.g. 105, 106) were used to infect chickens. A high degree of resistance to reinfection occurred after a single exposure to infection.

Sporozoite infections of the caeca or cloaca resulted in the infection of the usual small intestine site; there was no development at the site of inoculation and attempts to infect the embryo allantois did not succeed.

I wish to thank Dr M. Elaine Rose for the surgery required for the caecal infections, for her interest throughout and for help with the manuscript; Dr R. F. Gordon for help with the manuscript and permission to publish and Mr B. J. Millard for skilled technical assistance.

The feral Soay sheep (Ovis aries L.) population on Hirta, St Kilda, is host to a diverse component parasite community, but previous parasitological studies of the population have only focussed on the metazoan species. This paper reports the first epidemiological study of the protozoan species comprising Cryptosporidium parvum, Giardia duodenalis and 11 species of Eimeria in Soay sheep across 3 years of varying host population density. Prevalence and intensity of almost all species of protozoa significantly decreased with host age, with the exception of E. granulosa, which increased in prevalence with host age. The prevalence of C. parvum appeared to vary positively with host population density but that of G. duodenalis did not vary significantly with density. Most species of Eimeria showed a distinct lag in infection level following the host population crash of 2002, taking up to 2 years to decrease. Mixed Eimeria species intensity and diversity were highest in 2002, a year of low host density. Parasite diversity decreased with host age and was higher in males. There were 5 positive pair-wise associations between protozoa species in terms of prevalence. The results of this study highlight the potential for protozoal infection to shape the evolution of parasite resistance in wild host populations harbouring diverse parasite species.

The activation of peritoneal macrophage effector functions after therapy with free PZQ and PZQ incorporated in liposomes (lip.PZQ) was studied in the Mesocestoides corti–mouse model system. Each drug formulation was administered to an infected group of mice in 6 daily doses from day 14 p.i. Phagocytic activity of macrophages increased significantly after the administration of both drug formulations, more after lip.PZQ with an earlier peak observed for PZQ (day 3) than for lip.PZQ (day 6). Empty liposomes had no significant effect. The average counts of ingested particles in phagocytosing cells were significantly higher only after lip.PZQ administration. The pattern of changes in phagocytic activity correlated with the reduction of parasite numbers in the peritoneal cavity, with the highest observed on day 6 after therapy with lip.PZQ. Phagocytosis of lip.PZQ in vivo stimulated significantly the respiratory burst in peritoneal macrophages, with the highest concentration of superoxide anions recorded on day 1 after the last dose, whereas therapy with PZQ itself did not increase this process significantly. The capacity for the respiratory burst declined in all groups with progressing infection. It is proposed that the phagocytic activity of peritoneal macrophages after therapy was stimulated indirectly as a consequence of activation of the specific immune response. The larvicidal effect of lip.PZQ on the tetrathyridia in the peritoneal cavity was synergistic with the phagocytic activity and might be the result of double action of drug and superoxide anions generated during the respiratory burst stimulated by this drug formulation.