Showing papers in "Parasitology in 1977"

Plasmodium falciparum gametocytes: their longevity and infectivity.

Abstract: The longevity and infectivity of isolated populations of Plasmodium falciparum gametocytes were studied. Following chloroquine treatment gametocyte numbers fell with a constant rate of loss over a period of 16–24days; the populations had a half-life of 2·4 days. The sex ratio stayed constant throughout at 4 female:1 male. The ability of the microgametocytes to exflagellate and the infectivity of the population to mosquitoes persisted for 3 weeks. Antibodies to the gametocytes were detected but not in every patient studied. It was concluded that the gametocytes of P. falciparum are both long-lived and show persistent infectivity to mosquitoes. They can stimulatae antibody production but the immune response appears to play no part in their elimination, which probably takes place in the spleen as a part of the normal process of removing old, damaged and malformed red cells.

The formation and turnover of the membranocalyx on the tegument of Schistosoma mansoni.

Abstract: The multilaminate vesicles present in the tegument cytoplasm appear to fuse with side channels projecting out into the cytoplasm from the base of the surface pits. Their lamellate contents then unroll and spread out to form a trilaminate membranocalyx lining the pits and covering the tegument surface. The plant lectin concanavalin A appears to stabilize the process of vesicle fusion leading to an aggregation of multilaminate vesicles trapped in the lumen of the surface pits. The membranocalyx can be labelled with cationized ferritin. Chase incubations in normal medium indicate that by 4 h most of the label and the membranocalyx to which it is bound have been lost to the medium. This suggests that under the conditions of these experiments the membranocalyx has a half-life of 2-3 h.

Protection of mice against Babesia spp. and Plasmodium spp. with killed Corynebacterium parvum.

Abstract: Mice which had been pre-treated with killed Corynebacterium parvum given intravenously or intraperitoneally, but not subcutaneously, were completely resistant ot infection withBabesia microti or B. rodhaini, and protected from death caused by Plasmodium vinckeior P. chabaudiinfection. There is evidence that the parasites died within circulating erythrocytes. This occurred much too soon for a specific antibody response to be evoked, and no antibody could be detected by the indirect fluorescent-anitbody technique. Thus it is suggested that a non-secific soluble mediator may play an important role in the protection observed.

Impairment of primary expulsion of Trichuris muris in mice concurrently infected with Nematospiroides dubius.

Abstract: Primary immune expulsion of Trichuris muris was markedly delayed by concurrent infection with Nematospiroides dubius. Maximum delay of expulsion was dependent on size and timing of N. dubius infection relative to T. muris infection. In NIH mice infection with 400 N. dubius larvae immediately before or after T. muris infection was found to be most effective in suppressing expulsion. Infection on day 8 of T. muris infection, when mice are sensitized to T. muris, also impaired expulsion. From this evidence it is suggested that the larvae of N. dubius are immunosuppressive and that the efferent role of the immune response to T. muris is inhibited. The results are discussed in terms of non-specific immunosuppression and their relevance to the tropical disease situation is emphasized.

The relationship between duration of infection with Trypanosoma brucei in mice and the efficacy of chemotherapy.

Abstract: Relapse of infection after drug treatment of trypanosome infections under conditions precluding re-infection has usually been ascribed to drug resistance on the part of the parasite or to under-dosage of the drug. With Trypanosoma brucei infection in mice we have obtained evidence of another type of relapse. In infections resulting from the inoculation of 1 × 105 trypanosomes, derived from a stabilate T. brucei TREU 667, treatment with diminazene aceturate (Berenil) at 40 mg/kg at either 3 or 7 days after infection elicited a permanent cure. If, however, treatment was delayed later than 14 days after infection, then all the mice relapsed. These relapses generally occurred between 20 and 50 days after treatment, but some mice remained aparasitaemic for up to 60 days. The relapsed infections were apparently not due to the survival of ‘drug-resistant’ trypanosomes, as infections derived from a stabilate isolated from a relapsed Berenil-treated mouse were also permanently cured with Berenil if treated 3 days after infection; however, if treatment was delayed until 21 days post-infection, all the mice relapsed. The cause of relapse was not related to the number of parasites inoculated, as infection resulting from initial inocula of 1 × 105 to 1 × 108 trypanosomes were all cured if treated at 3 days after infection, and all eventually relapsed if treatment was delayed until day 21. This type of relapse phenomenon was not confined to T. brucei TREU 667 but also occurred with 5 other stabi-lates of T. brucei after Berenil treatment. Treatment of T. brucei TREU 667 infections with Ethidium and Prothidium at dose levels of 7.5 and 10 mg/kg respectively was also followed by relapse if treatment was delayed for 3 weeks after infection. The possible causes of relapse under these conditions, and its implications in the study of the natural disease, are discussed.

Schistosoma mansoni: a comparative study of artificially transformed schistosomula and schistosomula recovered after cercarial penetration of isolated skin.

Abstract: A comparison was made of the ultrastructure, development and antigenic nature of the surfaces and of the viability of three types of Schistosoma mansoni: schistosomula formed after cercariae had penetrated isolated skin (SS) schistosomula produced after mechanical separation of cercarial tails from bodies (MS), and schistosomula transformed from cercariae after incubation in fresh rat serum (RS). Within 2h of transformation, the surface membranes of all three types of schistosomula had changed from trilaminate to heptalaminate structures and SS and MS had lost their cercarial glycocalyx. Initially a dense amorphous material was demonstrated on the surfaces of RS, which was thought to be the result of an interaction between a factor in rat serum and the glycocalyx; this material was greatly reduced within 2 h of transformation. The pre-acetabular glands of SS were emptied while those of MS and RS retained their contents. Immunofluorescent studies showed that all schistosomula bound serum from mice immune to S. mansoni, but the binding was stronger with MS and RS. The mixed agglutination reaction demonstrated the presence of human A and B blood group-like antigenic determinants on approximately 30% of 3h old SS; these determinants were not detected on MS or RS. In vitro, the development of MS and RS was similar to SS; the first schistosomula reached the "gut-closed" stage by day 10; 50-70% of SS reached this stage by day 12, in contrast to only 25-50% of MS and RS. Between 28 and 45% of all schistosomula developed to maturity when injected intravenously into mice. It was concluded that the two types of artificially prepared schistosomula fulfil the main criteria of transformation from cercaria to schistosomulum. Further, it is suggested that MS are the most appropriate source of material for immunochemical and physiological studies.

Transfer of immunity to Trichinella spiralis in the mouse with mesenteric lymph node cells: time of appearance of effective cells in donors and expression of immunity in recipients.

Abstract: Cells capable of transferring immunity to Trichinella spiralis, i.e. of accelerating adult worm expulsion, were present in the mesenteric lymph nodes of mice infected for 4, 6 or 8 days, but not in mice infected for only 2 days. The time-course of worm expulsion in mice infected on the day of transfer was similar in recipients of day 4 or day 8 cells, expulsion becoming marked only when the recipients had been infected for at least 6 days. Transfer of cells 4 or 6 days after infection did not result in an accelerated worm expulsion; transfer 1 or 2 weeks before infection did not enhance the level of immunity in recipient mice. In contrast to the results obtained with mesenteric lymph node cells (MLNC) on immunity was transferred when recipients were given spleen cells taken from donors infected for 8 days. It is suggested that MLNC do not cause worm expulsion directly, but cooperate with another component of the host's defence mechanism. Accelerated expulsion in recipients of cells was accompanied by a premature decline in fecundity of female worms. Evidence is presented to show that worm expulsion and impaired reproduction may represent independent aspects of the immune response to T. spiralis.

The in vivo and in vitro analysis of immunity to Trichinella spiralis in mice and rats.

Abstract: Wistar-Furth strain male rats and CFW strain male mice were immunized against Trichinella spiralis using an antigenic fraction derived from a cell-free homogenate of mature muscle larvae. In rats, animals immunized with 250 mug of antigen harboured significantly fewer (135000) muscle larvae 30 days after oral challenge than controls (231000). Further 7-day-old adult worms derived from immunized rats shed 48% fewer (P less than 0.001) newborn larvae over a 24h period in vitro than adult worms from non-immunized animals. Mice were injected with either 10 or 100 mug of antigen. In comparison with non-immunized controls, mice immunized with 100 mug of antigen harboured significatnly fewer adult worms at days 7 and 9 after oral challenge infection, while female worms recovered from immune mice on days 6-10 after challenge shed fewer newborn larvae in vitro. Finally, mice immunized with 100 mjg of antigen harboured significantly fewer (10391) muscle larvae at 30 days after challenge than did controls (47750). Immunization of mice with 10 mug of antigen did not induce a statistically significant reduction in adult worms at either day 7 or 9 after challenge (P less than 0.5). However, adult female worms from mice receiving 10 mug of antigen still shed fewer larvae than did adults from control mice (P less than 0.05). Mice immunized with 10 mug of antigen harboured significantly fewer (13700) recoverable muscle larvae than did controls at 30 days after challenge (39000).

Dynamical aspects of host-parasite associations: Crofton's model revisited

Abstract: Although superseded by more recent and biologically realistic studies, Crofton's (1971 b ) model of host–parasite associations remains of interest as the simplest model which captures the essentials. Even if its simplifying assumptions are all accepted, Crofton's model has two defects: the first is that its general conclusions are drawn from numerical simulations for a very restricted range of parameter values; the second is that the probability for a parasite transmission stage to succeed in establishing itself in a host is not constrained to be less than unity, as biologically it must be. The present paper remedies these two defects, by giving analytical results valid for all values of the parameters, and by demanding that the parasite transmission factor indeed saturates to unity. Some of Crofton's conclusions remain intact, others are significantly altered. (1) Crofton (1971 b ) has presented a mathematical model which aims to exhibit some of the essential dynamical properties of host–parasite associations. The extreme biological simplicity of this model (e.g. hosts and parasites have the same generation time) makes it applicable to few real systems, and later models (Anderson & May, 1977; May & Anderson, 1977) have added many more general biological features in an effort to makecontact with empirical data. Nevertheless, Crofton's model retains pedagogical value as the basic model. (2) Even within its own framework ofsimple assumptions, Crofton's model has two defects. The first is thatthe general conclusions about its dynamical behaviour are drawn from numerical stimulations for a re stricted, and not necessarily representative, range of parametervalues. The second is that the factor describingthe input of parasite transmission stages into the next generation of hostsdoes not saturate to unity, as its biological definition implies it must. Thepresent paper gives an analytical account of the dynamical behaviour of Crofton's model, valid for all values of the relevant biological parameters, and with a parasite trans mission factor that does saturate to unity. The ensuing conclusions are in several respects significantly differentfrom Crofton's (3) The intrinsic growth rates of the host and parasite populations are defined as λ and A ; the negative binomial parameter k measures the overdispersion of parasites among hosts (small k corresponds to high overdispersion); and L characterizes thelethal level of parasites per host.Then unless λ1+1/ k λ A exp (– 1[ L ) no equilibrium state is possible, andthe host population undergoes Malthusiangrowth that the parasites cannot check. This inequality tends to be satisfied if k is not too small, λ not too large, and A significantly larger than λ: see Figs 1, 2, and 4.This aspect of the model derives from the saturation of the parasite transmission factor, and is omitted fro Crofton's discussion. (4) When an equilibrium does exist, the following observations can be made. The equilibrium host population H * is given by eq. (15): it de creases with increasing A ; increases with increasing λ; is roughly inde pendent of L ; and increases with increasing parasite overdispersion for small k ( k k for larger k . Theequilibrium number of parasites per host m * is given by eq. (9): it is independent of A ; increases roughly linearly with L ; increases with increasing overdispersion or λ for small k ( k k , for larger k . The totalpopulation of parasites at equilibrium is given by P * = H * m * . (5) The stability of the equilibrium, i.e. its ability to recover from disturbance, depends mainly on λ and on k , as illustrated in Fig. 4. Except for values of λ and k perilously close to the boundary where no equili brium is possible, the disturbed host and parasite populations will return to their equilibrium values by undergoing damped oscillations. The damping will tend to be weak if k is large, or if λ is small. (6) These conclusions accord with those derived from more detailed and realistic host–parasite models. (7) The general process, whereby thehost–parasite association can be stabilized by overdispersion of parasites, is dynamically similar to that whereby prey–predator or host–parasitoid associationscan be stabilized by differential aggregation of predators or by explicit refuges for the prey.

A comparative analysis of various developmental stages of Schistosoma mansoni with respect to their protein composition.

Abstract: The protein composition of Schistosoma mansoni was analysed by electrophoresis in polyacrylamide slab gel in the presence of sodium dodecyl sulphate. A high degree of identity existed between protein patterns obtain from immature and adult parasites of the two sexes. Some stage-and sex-specific components were indentified and their possible origin discussed.

The water dynamics of stages of Ditylenchus dipsaci and D. myceliophagus during desiccation and rehydration

Abstract: Interference microscopy has been used to study the rate at which water enters and is lost from larval and adult stages of Ditylenchus dipsaci and D. myceliophagus . It is shown that the cuticle of the dry nematode, irrespective of stage, is completely permeable to water. In contrast, marked intra– and interspecific differences were found in the rate at which stages dry at 0 and 50% relative humidity. All stages of D. myceliophagus dry very rapidly: in this species, death, as a consequence of severe desiccation, appears to be linked to a lack of any marked ability to control water loss. For D. dipsaci , those stages known to survive desiccation will appear to be the slower dryers. In general, the “order of performance” in slowing the rate of drying is the same as the order previously found for survival of desiccation. Both the 4th– and, to a lesser extent, the 3rd–stage larvae of D. dipsaci show evidence of an intrinsic ability to control water loss. An analysis of the drying curve for 4th–stage larvae of D. dipsaci supports the indications of interference photographs that the rate of drying is slowed by a decrease in permeability of the drying cuticle. Vacuum desiccation studies further demonstrate the remarkable ability of the 4th–stage larva of D. dipsaci to control its rate of drying. The survival of 4th– and 3rd–stage larvae of D. dipsaci is diminished by very rapid drying, and the survival of other stages of this species and larval and adult stages of D. myceliophagus is precluded. The decrease in survival of the 4th–stage larvae of D. dipsaci is shown to be associated with a more rapid rate of water loss.

Desiccation survival of larval and abult stages of the plant parasitic nematodes, Ditylenchus dipsaci and D. myceliophagus

Abstract: The effect of different relative humidities on the survival of individual larvae and adults of Ditylenchus dispasci and D. myceliophagus has been examined; experiments were carried out at 5 and 18°C with D. myceliophagusand at 18°C with D. dipsaci. Survival of both species was enhanced when they were dried at high humidities and, for D. myceliophagus, by the lower temperature. The survival of all stages of D. myceliophagus was poor. Generally it was expressed in minutes only; 4th-and 3rd-stage larvae, however, were marginally better at surviving drying than adults and much better than 2nd-stage larvae.Although the 4th-stage larva of D. dipsaci was overwhelmingly superior to all other stages, the 3rd stage, and to a lesser extent, the adult of this species also showed remarkable powers of survival to desiccation. In general, survival of 4th-, 3rd- and 2nd-stage larvae could be expressed in weeks, days and minutes respectively; for adults, survival was expressed in hours at relative humidites under 50% but in days at higher relative humidites.The results are discussed in relation to the survival value of the aggregations formed by these species; the validity of the term ‘resistantstage’ as applied to the 4th-stage larva of D. dipsaci is assessed.

Effect of the expulsion phase of Trichinella spiralis on Hymenolepis diminuta infection in mice.

Abstract: The effect of the intestinal changes brought about by the expulsion of Trichinella spiralis in rats was studied in relation to the growth and survival of a concurrent infection with Hymenolepis diminuta, a cestode not normally rejected by the rat in low-level infections. Growth of H. diminuta was stunted in rats given T. spiralis just before, or after, infection with H. diminuta, the stunting being more pronounced when the cestode was given closer to the period of inflammation. There was no loss of the cestode from dual-infected rats and no evidence for destrobilation was found. Lower T. spiralis burdens had a correspondingly weaker effect on growth of H. diminuta, and stunting was abolished by administration of the anti-inflammatory drug cortisone acetate. It is concluded that the stunting of H. diminuta is probably due to the non-specific inflammatory component of the rat's response to T. spiralis infection.

Immunodepression in Babesia microti infections.

Abstract: Infection with the avirulent piroplasm Babesia microti in mice is accompanied by a marked depression in the ability of the mice to mount an immune response to sheep red blood cells. The period of immunodepression begins 3 days after peak parasitaemia and is maximal 4 days later. There-after, there is a slow return to normal immune responsiveness, correlated with the gradual disappearance of the parasites from the blood. Both IgM and IgG responses are depressed. Cell-mediated responses as determined by contact sensitivity to oxazolone and allograft survival are apparently unaffected. Phagocytic activity as measured by carbon clearance tests is increased, and is correlated with the parasitaemia.

Intra-erythrocytic death of the parasite in mice recovering from infection with Babesia microti.

Abstract: As mice recover from infection with Babesia microti, abnormal forms of the parasite are present in some red cells. These forms are non-infective, indistinguishable by light microscopy from those present after treatment with amicarbalide, a babesicidal drug, and persist in splenectomized mice. Electron microscopy confirmed that these abnormal forms are degenerating intra-erythrocytic parasites. In the absence of evidence for death of B. microti elsewhere in the body, it appears that infections of mice with this parasite are normally terminated by their death within circulating red cells. This has important implications for the mechanism of immunity to both this parasite and those Plasmodium spp. with which it cross-protects in this host.

Development of Theileria parva (Theiler, 1904) in the gut of Rhipicephalus appendiculatus (Neumann, 1901)

Abstract: The life-cycle of Theileria parva in the gut of the tick Rhipicephalus appendiculatus was investigated in Giemsa-stained smears and in wet preparations under the phase-contrast microscope. The different developmental stages of T. parva were seen in a large proportion of specially-selected R. appendiculatus tickes. After the intra-erythorcytic merozoites were engorged by the ticks during a blood meal, the following development was observed. (1) In the lumen of the gut of infected nymphs, spindle-shaped microgamonts developed out of the ring-forms. These broke up into several thread-like microgameters after nuclear division and development of thread-like cytoplasmic projections. The ring-froms developed into round-forms of 3–4 μm in diameter which are considered to be macrogametes. (2) From the 6th day after repletion, zygotes with a clear zone in the centre appeared in the epithelial cells of the tick's gut. A steady increase in size and a progressively denser cytoplasm were observed up to the 3rd day after moulting to adult ticks. (3) Subsequently a slightly angular, retort-like stage developed by invagination inside the rounded zygotes, and from the 5th day after moulting this stage developed further into a club-shaped kinete. The kinetes propelled themselves in the gut by active gliding movements.

The source and nature of some functional antigens of Trichuris muris

Abstract: Vaccination with whole male worm extract (AMA), stichoseome extract (SA) and a short-term inculbation fluid (EXA) of adult Trichuris muris induced a high degree of protective immunity in mice as assessed by reduction in larval worm burden. Immunodiffusion of AMA against rabbit anti-AMA serum revealed five precipitin lines, one of which was common to both EXA and SA with which only single lines were obtained. Physico-chemical tests suggested that the antigen is a protein and that carbohydrate, lipid and DNA do not contribute to its antigenicity. Partial fractionation was obtained with ammonium sulphate. All preparations with immunogenic activity showed the common line of EXA on immunodiffusion. It is concluded that one of the protective immunogens is a protein which can be associated with the precipitin line and originates in the stichosome.

Vaccination of lambs against infection with Taenia ovis using antigens collected during short-term in vitro incubation of activated T. ovis oncospheres.

Abstract: Activated oncospheres of Taenia ovis were incubated for 24 h or 48 h at 37-5 degress C in Medium 858 alone or in Medium 858 enriched with 20% lamb serum or foetal calf serum. Antigens contained in the supernatant medium from these incubations were concentrated, emulsified in Freund's incomplete adjuvant and injected intramuscularly into lambs. These lambs developed a very high level of immunity to subsequent challenge infection with T. ovis eggs.

Flight muscle ultrastructure of susceptible and refractory mosquitoes parasitized by larval Brugia pahangi.

Abstract: On parasitization with larval Brugia pahangi the infected flight muscle fibres of ‘resistant’ Anopheles labranchiae atroparvus undergo the following ultrastructural changes. The fibres become almost totally devoid of glycogen, their sarcoplasmic reticulum becomes elongate and closely associated with muscle fibrils. These fibrils degenerate and vesicles appear both within the degenerate fibril and within elements of the sarcoplasmic reticulum. Vesicles accumulate around the worm and degenerate to a uniform mass which eventually becomes melanized from its inner edge (next to the parasite) outwards. The infected flight muscle fibres of both ‘resistant’ Aedes aegypti and ‘susceptible’ Aedes togoi are almost totally devoid of glycogen granules, but show no other ultrastructural change from the uninfected state.

Antibody dependent cell-mediated cytotoxicity against Trypanosoma cruzi.

Abstract: This paper describes in vitro antibody dependent cytotoxicity against Trypanosoma cruzi epimastigotes by normal mouse splenic lymphocytes. Cytotoxicity was expressed as the percentage reduction in the number of motile parasites upon incubation with lymphocytes at 37 °C in a denned medium. Failure of the non-motile parasites to regain motility and their ensuring degeneration at 28 °C in liver infusion tryptose (LIT) medium confirmed loss of motility as a criterion of cytotoxicity. Incubation of T. cruzi at 37 °C for 18 h in a defined medium per se did not interfere with motility but was followed by a lag phase of the growth curve in LIT medium at 28 °C. The lag phase was prolonged for T. cruzi which had previously been incubated at 37 °C in the absence of cells.

Nutrition of the mite Unionicola intermedia , Koenike and its relationship to the inflammatory response induced in its molluscan host Anodonta anatina , L.

Abstract: The structure and staining properties of the epithelium of the midgut in Unionicola intermedia are described. Intracellular non-specific esterase, acid and alkaline phosphatase are present and confined to vacuoles. Extracellular enzymes are absent. Nymphal and adult stages of U. intermedia feed principally on the haemocytes (= amoebocytes) and mucus of their molluscan host, Anodonta anatina. Feulgen-positive material recorded from the lumen and midgut cells of the mites is believed to be derived from the nucleated haemocytes and to undergo intracellular digestion in the midgut cells. Starved mites show steadily decreasing amounts of Feulgen-positive material in the vacuoles. Haemocytes are present in large numbers below the site of attachment of the mites, their presence represents an inflammatory response, and the mite feeds on the products of this response. Large amounts of bound iron are present in the midgut cells but the origin and role of this is unknown.

Strain variation within Eimeria meleagrimitis from the turkey

Abstract: During the course of a field study of coccidiosis in turkeys, Eimeria oocysts were found which had much smaller dimensions that any previously recorded isolate from the turkey. These oocysts were purified by single oocyst infection of a turkey. The first oocysts (mean dimensions 16-15 X 14-75 micrometer) were recovered 103 h later. Inoculation of between 0-5 and 2-5 X 10(5) oocysts of this isolate caused severe effects on body weight gain. Cross-immunity studies showed the parasite to be a strain of E. meleagrimitis. Electrophoretic analyses of two enzymes showed that the strain could be differentiated from another strain of E. meleagrimitis (Weybridge strain B). The results show that strain variation occurs within the species E. meleagrimitis and extreme caution should be used in identifying species of Eimeria from the turkey by the oocyst characters.

Stimulation of the activity of Schistosoma mansoni miracidia by snail–conditioned water

Abstract: A dark-ground photographic technique was used to analyse the reactions of Schistosoma mansoni miracidia to homogeneous solutions of snail-conditioned water (SCW). The most significant effect of this water was to increase miracidial turning. This effect was maintained under both acid and alkaline conditions, after passage of the SCW through a mixed bed resin and after chelation of either calcium or both calcium and magnesium ions. The stimulant in the water was unaffected by trypsin but was protease-sensitive, suggesting its possible identity as a peptide. The importance of 'active spaces' rather than concentration gradients in miracidial host-location was emphasized.

Translation in a reticulocyte cell-free system of RNA isolated from blood and culture forms of Trypanosoma brucei.

Abstract: RNA with messenger activity has been extracted from both blood and culture (insect mid-gut) forms of Trypanosoma brucei and translated in a reticulocyte cell-free system. The products of this cell-free system have been compared, and many common polypeptides demonstrated. A major polypeptide of 58000--65000 molecular weight was made when both blood and culture form RNA was added to the cell-free system. Antiserum raised against purified variant antigen from a cloned variant (MIAG 099) was used to detect specific products of this system. A major polypeptide of approximately 58000-65000 molecular weight was precipitated when the homologous trypanosome (MIAG 099) blood form RNA was used in the cell-free system. No such polypeptide was precipitated when RNA from a heterologous strain culture or blood form was used in the system. Competition experiments, in which excess purified variant antigen was addded after incubation but before addition of specific antiserum, confirmed that the polypeptide of 58000--65000 molecular weight is the variant antigen.

Schistosoma mansoni: differential cell death associated with in vitro culture and treatment with Astiban (Roche).

Abstract: A simple technique for the maintenance in vitro of mature Schistosoma mansoni is described and critically assessed at the ultrastructural level. Females were cultured for 4--6 days with no apparent ultrastructural change, but after this period changes appeared in the cells of the ovary and vitelline gland. At a later stage (10--12 days) lipid bodies appeared in the parenchyma cells. These changes occurred in worms which were active, paired with males and were egg-laying. Thus the activity, pairing behaviour and egg-laying characteristics are not adequate to reveal the true morphological condition and presumably the physiological and biochemical status of cultured worms. This technique was used to study the effect of Astiban on females and the results were compared with worms treated in vivo. Astiban concentrations greater than 30 microgram/ml killed worms within 7--20 h and acted non-selectively. Astiban at low concentrations (10 microgram/ml) during short-term culture (1--3 h) resulted in a selective action of the drug on maturing vitelline cells. Thus, although the degree of cell damage caused by drug treatment was more severe and occurred earlier than the effects observed in worms cultured in vitro without drugs, both treatments resulted in differential cell death.

The anticoccidial effects of amprolium, dinitolmide and monensin against Eimeria maxima, E. brunetti and E. acervulina with particular reference to oocyst sporulation

Abstract: Chicks infected with the Weybridge strains of Eimeria maxima and E. acervulina were not protected by the normal levels of amprolium, but the sporulation of the oocysts was inhibited. With higher drug concentrations, fewer oocysts were produced. E brunetti was not so markedly affected, although oocyst sporulation was reduced by the higher dosage levels. The effects were not enhanced by the inclusion of ethopabate. With dinitolmide the phenomenon was not so marked, although oocysts of E. maxima and E. acervulina were reduced in numbers by the normal drug concentration and sporulation was reduced when this level was increased. Much higher drug levels were required to obtain these effects with E. brunetti. Monensin at 120 ppm affected neither oocyst numbers nor their sporulation in any of the species tested. The significance of the effects of anticoccidial drugs on gametogony and sporogony is discussed.

The longevity of Hymeonlepis microstoma in mice, and its immunological cross-reaction with Hymenolepis diminuta

Abstract: Hymenolepis microstoma was found to live for at least 728 days in a mouse, but an initial infection of 10 worms per mosue decreased exponentially for approximately the first 110 days to a level of 3–5 worms, after which little further loss occurred.A primary infection of six H. microstoma, expelled with anthelmintic on day 21, strongly protected against a single worm H. diminuta challenge; worms in 80 ‘immunized’ mice weighed less than 5% of the weight of worms from 80 control mice. However, a primary (5-worm) H. diminuta infection led only to a small, though statistically significant, decrease in weight of the 3-worm H. microstoma challenge.The results are interpreted as indicating that H. microstoma evokes a strong immunological response which cross-reacts with H. diminuta. The failure of H. diminutato protect strongly against a 3-worm challenge by H. microstoma suggests, as does the long survival of a primary infection when it is reduced to approximately 4 worms, that H. microstoma survives in low infection because it is able to avoid the immune response. This could be due to antigen camounflage, ability to repair immune damage or to the low permeability of the bile duct wall to components of the immune response. The worm loss which occurs from heavy infection until only 3–5 worms remain may be physiologically rather than immunologiacally mediated.

Evidence for the involvement of a bone marrow-derived cell population in the immune expulsion of Trichinella spiralis.

Abstract: When mice were irradiated immediately before infection with Trichinella spiralis there was a profound and long-lasting interference with their ability to expel adult worms from the intestine. Irradiation given after the fifth day of infection was progressively less effective in this respect. The ability to expel worms was not restored when mesenteric lymph node cells (MLNC) were transferred (a) on the day of infection in mice irradiated one day previously, or (b) on day 7 of an infection in mice irradiated on day 6, even though the MLNC transferred immunity to intact recipients. Transfer of bone marrow (BM) alone was also without effect. However, worm expulsion was restored if, following irradiation and injection of BM, 10 days were allowed for BM differentiation before transfer of MLNC. This restoration was effective even after lethal levels of irradiation and was clearly dependent upon a donor-derived BM component cooperating with, or responding to, the activity of the transferred MLNC. The possibility that the BM component is non-lymphoid in nature is discussed.

The immune response of plaice (Pleuronectes platessa L) to the metacercariae of Cryptocotyle lingua and Rhipidocotyle johnstonei.

Abstract: The humoral immune response of plaice to infestations of selected metacercariae was studied. Precipitating antibodies to both Cryptocotyle lingua and Rhipidocotyle johnstonei were demonstrated using agar gel diffusion techniques. Immunochemical investigations of these antibodies indicated they were macroglobulins, resembling immunoglobulin M (IgM) of mammals. The rate and magnitude of antibody production by the host was determined by the ambient temperature.