[Ultra-pathological study on the syncytium of Schistosoma mansoni exposed to cyclosporin Ain vitro]

OBJECTIVE

To study the ultra-pathological changes of syncytium of Schistosoma mansoni after cyclosporin A (CsA) treatment.

METHODS

MF1 mice were infected with Schistosoma mansoni cercariae. Six weeks later, the adult worms were recovered by portal vein perfusion. After the worms were exposed to CsA of 20 micrograms/ml for 24 h, the drug-induced damage of the worm surface was observed by SEM and TEM.

RESULTS

Incubation of male and female schistosomes with 20 micrograms/ml of CsA for 24 h resulted in disruption of the tegument and rupture of the spines. Progressive surface damage and swelling and vacuolization of the tegument led to eventual disruption of the syncytium.

CONCLUSION

The antischistosomal action of CsA is direct, the syncytium is the main site for CsA attack.

[Chronobiological studies on effect of cyclosporin A (CsA) against adult male worms of Schistosoma mansoni in vitro]

AIM

To study the action mode of cyclosporin A (CsA) against Schistosoma mansoni in vitro.

METHODS

MF1 mice were infected with Schistosoma mansoni cercariae for 6 weeks when the adult worms were recovered by portal perfusion. The male worms of S. mansoni recovered were exposed to varying concentrations of CsA at 8, 16, and 24 h in vitro. Drug induced damage to the male worm surface was chrono-biologically observed throughout these experiments by SEM.

RESULTS

After the male worms of S. mansoni were incubated with 1 microgram/ml CsA for 8-24 h, the tegument showed swelling of ridges with appearance of holes on their surface and detachment of a part of spines. The above damage of the tegument became more evident in male worms after incubation with 10, 15, 20 micrograms/ml CsA for 8-24 h. Moreover, incubation of male worms with 25 micrograms/ml CsA for 8-24 h resulted in significant deformation and disruption of tegument, rupture of ridges and detachment of spines. The tegumental damage of male worms of S. mansoni was dose- and time-dependent.

CONCLUSION

The antischistosomal action of CsA is direct, the schistosome tegument appears to be the main site for CsA attack.

Mode of action of cyclosporin A against Hymenolepis microstoma (Cestoda): relationship between cyclophilin binding and drug-induced damage

Cyclosporin A (CsA) is a widely investigated experimental anti-parasitic drug whose mode of action remains unresolved. The immunosuppressive action of CsA depends on the drug binding to the intracellular receptor cyclophilin (CyP). This study investigates whether complexing of CsA with parasite CyP is equally essential for its anthelmintic action. The correlation between initial cyclosporin-induced damage in vitro and drug binding to parasite CyP has been examined. CsA and the analogues B-5-49, CsH and CsA-acetate all induced similar damage to the tapeworm Hymenolepis microstoma in vitro in incubations between 2 h and 4 days. The initial foci of drug damage were the parasite surface and mitochondria in the syncytium. In a competitive binding assay only B-5-49 displaced [H3]-CsA from either crude parasite cytosolic CyP or affinity-purified CyP while CsH and CsA-acetate had no effect. These data suggest strongly that cyclosporins act on the surfaces of helminth parasites but that drug action does not involve complex formation with CyP. An alternative drug-binding site must therefore be identified which may lead to the rational design of novel anthelminitic drugs.

Anorexia in rats infected with the nematode, Nippostrongylus brasiliensis: experimental manipulations

Nippostrongylus brasiliensis induces a biphasic anorexia in laboratory rats, the first phase coincident with lung invasion (ca day 2) and the second when the worms mature in the intestine (ca day 8). Using the anthelminthic, mebendazole (MBZ), N. brasiliensis infections of the rat were eliminated between the first and second anorexic episodes. This intervention prevented the expression of the second phase of anorexia. Rats exposed to a second infection with N. brasiliensis, 3 weeks after the primary infection, exhibited only a first phase anorexic response which was not influenced by MBZ termination of the primary infection. The lower cumulative food intake and weight gain of all infected rats after 8 days of infection were accompanied by elevated plasma insulin and, in some individuals, by elevated plasma leptin, compared with uninfected controls and previously-infected MBZ-treated rats. Messenger RNA levels for neuropeptide Y were higher in the hypothalamic arcuate nucleus of 8-day infected rats than in recovering MBZ-treated animals. Inoculation of rats with heat-killed N. brasiliensis larvae failed to induce anorexia and did not alter the severity of biphasic anorexia on subsequent injection of viable larvae. The first anorexic episode is therefore dependent upon viable migrating larvae. The second phase of anorexia clearly requires the continuing presence of the parasite beyond the lung phase. Viable migrating larvae are also required to confer 'resistance' to reinfection.

Appetite and parasite

Molecular techniques have dramatically advanced our knowledge of the mechanisms that regulate appetite and body weight, yet human obesity, a significant healthcare problem, still lacks an effective science-based treatment. Infectious agents, including worm parasites, seem capable of overwhelming these regulatory systems. Can the study of parasites extend our understanding of what makes animals feed?

Mucosal mast cell responses and release of mast cell protease-I in infections of mice with Hymenolepis diminuta and H. microstoma: modulation by cyclosporin A

The dynamics of intestinal mucosal mast cells and the major mucosal mast cell protease were followed during the course of laboratory infections of mice with Hymenolepis diminuta and H. microstoma. The effects of the drug cyclosporin A (CsA), which is both immunosuppressive and selectively anthelmintic depending upon dose regime, were determined. In H. diminuta infections worm expulsion occurred around day 9 and coincided with peak mastocytosis and peak mMCP-I concentrations in tissues and serum. Immunosuppressive treatment with CsA prevented worm expulsion, permitting some individuals to reach maturity, and abrogated mast cell proliferation and mMCP-I production and release. By contrast, H. microstoma infections persisted for 64 days in spite of a considerable mastocyosis in both intestine and bile duct tissues accompanied by a high level of mMCP-I in tissues and serum. A subimmunosuppressive regime of CsA had only limited effects on worms and mast cell numbers and activity. Together these data shed light on the variable mast cell response to gastrointestinal infections and on the potential significance of parasite location in evasion of mast cell action. Use of CsA reveals the contributions of both T cell-dependent mechanisms, including mast cell proliferation and activation, and T cell-independent events in regulating intestinal helminth infections.

Parasite-induced anorexia: leptin, insulin and corticosterone responses to infection with the nematode, Nippostrongylus brasiliensis

The nematode parasite, Nippostrongylus brasiliensis, induces a biphasic anorexia in its rat host. The mechanisms, underlying this anorexia and its possible advantages to the host or parasite are unknown. We have investigated the effect of acute (12-24 h) and chronic (2-17 days) infections on plasma concentrations of leptin, insulin and corticosterone, and on hypothalamic expression of neuropeptide Y, galanin and corticotrophin-releasing factor genes. Plasma leptin was elevated in infected rats relative to uninfected ad libitum-fed controls and pair-fed controls in 12 h infections initiated at dark onset and in infections of 2 days' duration. At other times prior to parasite expulsion, plasma leptin in infected and pair-fed rats was lower than that of uninfected ad libitum-fed controls, reflecting the existing state of negative energy balance. Elevated plasma leptin concentrations in infected rats at day 2 post-infection were accompanied by reduced neuropeptide Y gene expression in the hypothalamic arcuate nucleus compared with both ad libitum control and pair-fed animals, and by lowered corticotrophin-releasing factor gene expression in the paraventricular nucleus relative to pair-feds. Twelve hour infections were characterized by a substantial increase in plasma corticosterone that was independent of reduced food intake, and in 12 h infections initiated at dark onset, where plasma leptin was elevated, there was also increased plasma insulin concentration in infected rats. In longer infections, differences between the groups in plasma insulin and corticosterone concentration were only observed at day 4 post-infection. In summary, perturbations to leptin, insulin and corticosterone signals early in infection may have a causative role and might feed back onto hypothalamic gene expression, whereas subsequent changes in these parameters are more likely to be secondary to negative energy balance.

Characterization of calcineurin from Hymenolepis microstoma and H. diminuta and its interaction with cyclosporin A

The drug cyclosporin A (CsA) exerts its immunosuppressive action by binding to the cytosolic protein, cyclophilin (CyP) and, as a complex, binding to and inhibiting the calcium/calmodulin-dependent serine threonine phosphatase, calcineurin. It is unknown whether a similar mode of action occurs during the drug's antiparasite activity. Calmodulin-binding proteins from the helminth parasites Hymenolepis microstoma and H. diminuta were purified by affinity chromatography, yielding single polypeptide bands of 60000 M(r), according to SDS-PAGE. These proteins were tested for calcineurin activity by the dephosphorylation of the RII peptide (part of the catalytic subunit of cAMP-dependent protein kinase). Both proteins were calcium- and calmodulin-dependent and were inhibited by mammalian cyclophilin complexed with cyclosporin A (IC50 values of 0.75 microgram CyP for H. microstoma and 0.90 microgram CyP for H. diminuta). However, neither of the parasite calcineurins was inhibited by H. microstoma cyclophilin/CsA. These data suggest the anthelmintic mode of action of CsA in these helminth models does not involve the inhibition of a signal transduction pathway requiring interaction with calcineurin.

The antiparasite effects of cyclosporin A: possible drug targets and clinical applications

1. The immunosuppressive drug cyclosporin A, and some of its nonimmunosuppressive derivatives, are potent inhibitors of a range of parasites of humans. 2. Cyclosporin A and the structurally unrelated immunosuppressant FK506 are known to act on T-lymphocytes as complexes with their binding proteins, cyclophilins and FKBPs, respectively. 3. Cyclophilins and FKBPs have been structurally identified in a number of parasites and, in some instances, are believed to play roles in the antiparasitic actions of these drugs. 4. Nonimmunosuppressive cyclosporins and FK506 derivatives may have clinical potential in certain parasitic diseases, especially malaria and schistosomiasis, and identification of the targets of these drugs in parasites may lead to development of novel chemotherapeutic agents.

Synergistic action of cyclosporin A and polyspecific rabbit anti-sera against murine Schistosoma mansoni

The efficacy of cyclosporin A (CsA) treatment against Schistosoma mansoni in mice was compared with treatments that included co-administration of one of two anti-sera (infected rabbit serum (IRS) obtained by repeated infection and a worm membrane antigen anti-serum (WSS) obtained by immunization with worm surface supernatants). These two sera recognized a number of worm antigens but differed in precise detail. Administration of CsA alone to mice harbouring mature infections of S. mansoni reduced worm burdens and preferentially targeted female worms. Sera administered alone had no effect on worm burdens. Co-administration of worm membrane antigen anti-serum (WSS) with CsA reduced worm burden significantly compared with drug treatment alone. Male worms were more susceptible to this combined treatment regime. Anti-infection serum (IRS) had a lesser stimulatory activity in combination with CsA which was not statistically different from the effects of CsA alone on worm burdens. The data suggest that CsA-induced surface damage to the parasite may reveal specific antigens that were previously unavailable for host attack.

Hymenolepis diminuta and H. microstoma: uptake of cyclosporin A and drug binding to parasite cyclophilins

Cyclosporin A (CsA) acts as a powerful immunosuppressant through its binding to the cytosolic isomerase, cyclophilin (CyP), forming a complex which inhibits the phosphatase activity of calcineurin. The drug is also selectively anti-parasitic but its mode of action remains unknown. The mouse tapeworm, Hymenolepis microstoma is sensitive to CsA, but the rat tapeworm, H. diminuta is not susceptible either in rats, mice or in vitro. Using these two tapeworm models, the uptake and binding of CsA were examined in relation to parasite cyclophilins. Uptake and compartmentalization of the drug were markedly different in the two species: H. microstoma takes up more drug than does H. diminuta and sequesters more drug into intracellular compartments. Characterization of cyclophilins using both CsA binding and isomerase activity assays reveals that H. microstoma possesses two cyclophilin isoforms (M(r) 17,700 and 21,400) with isomerase activity that is inhibited by CsA. using identical assays, we have been unable to demonstrate CsA-binding proteins or CsA-sensitive isomerase activity in H. diminuta. These data suggest that the anthelmintic action of CsA relates in some way to the presence and function of parasite cyclophilins.

Anorexia induced by the parasitic nematode, Nippostrongylus brasiliensis: effects on NPY and CRF gene expression in the rat hypothalamus

Infections of the gastrointestinal nematode, Nippostrongylus brasiliensis, in the laboratory rat result in a characteristic biphasic anorexia which is followed by hyperphagia once the worm burden has been cleared. Despite the importance of parasite-induced anorexia, relatively little is known of the underlying mechanisms. We have investigated the involvement of the central appetite drive in this anorexia by studying the gene expression of two neuropeptides with opposing actions on energy balance, NPY and CRF. Gene expression was assessed by in situ hybridization at 2, 8 and 16 days post-infection (p.i.) in infected rats, in uninfected controls, and in a group with food intake restricted to match that taken voluntarily by the parasitize animals. The sampling intervals corresponded to each of the two phases of maximum anorexia and the period of compensatory hyperphagia. Surprisingly, we found that increases in NPY gene expression in the hypothalamic arcuate nucleus (ARC) accompany anorexia in rats infected with N. brasiliensis; there was a significant relationship between degree of anorexia and induction of NPY mRNA after 8 days of infection. Furthermore, ARC NPY mRNA levels in parasitized animals were similar to those in pair-fed individuals with food intake restricted to match the infected rats. The number of larvae used to establish the infection affected both the degree of anorexia and the level of NPY mRNA at 8 days p.i. in a dose-dependent manner. NPY gene expression remained elevated in infected rats during at least the initial stages of compensatory hyperphagia. This suggests that animals detect a state of energy deficit during the early stages of the infection, yet do not feed, but become hyperphagic coincident with worm loss. The failure of anorectic parasitized animals to feed in response to activation of the NPYergic system makes this a novel system in which to study the regulation of hypothalamic NPY by physiological challenge. There were no significant differences in CRF gene expression between the groups at any of the sampling intervals.

Identification and preliminary characterization of a chitinase gene in the Autographa californica nuclear polyhedrosis virus genome

A functional chitinase gene (chiA) has been identified in the genome of the Autographa californica nuclear polyhedrosis virus (AcMNPV). It is expressed in the late phase of virus replication in insect cells. High levels of both endo- and exochitinase activity were detected by 12 hr p.i. and remained stable throughout infection. An AcMNPV chiA protein-specific antibody was prepared using recombinant material prepared in bacteria. This was used to demonstrate that a product of approximately 58 kDa was synthesised in virus-infected cells. Immunofluorescence analysis of virus-infected cells showed that most chitinase was located in the cytoplasm. Primer extension analysis of mRNA from AcMNPV-infected cells confirmed that transcription initiated from a baculovirus late start site (TAAG), 14 nucleotides upstream from the putative translation initiation codon. The predicted protein sequence of the AcMNPV chiA shares extensive sequence similarity with chitinases from bacteria and, in particular, the Serratia marcescens chitinase A (60.5% identical residues). Phylogenetic analyses indicate that AcMNPV, or an ancestral baculovirus, acquired the chitinase gene from a bacterium via horizontal gene transfer.

Cyclosporin A: drug treatment in vivo affects the kinetics of [14C]glucose transport in Hymenolepis microstoma in vitro

The transport of [14C]glucose by Hymenolepis microstoma in vitro following in vivo treatment with cyclosporin A (CsA) was determined over a range of concentrations. For untreated (control) worms glucose uptake showed saturation kinetics with a small diffusion component. Estimates of the maximum velocity of glucose uptake (Vmax) and the affinity of substrate for the glucose transporter (Kt) revealed that untreated 8-day-old worms had a Vmax twice that of 15-day-old worms and that younger worms had a lower Kt. An inverse relationship was demonstrated between log10 worm weight and the rate of uptake of [14C]glucose, reflecting the relatively greater number of glucose transporters due to the larger surface area:volume ratio of smaller worms. Treatment of H. microstoma with CsA in vivo significantly increased the diffusion component of glucose uptake in vitro. Parasites from drug-treated mice had a significantly lower Vmax for glucose uptake than size-matched controls. The affinity of glucose for its transporter in CsA-treated worms (Kt) was not significantly different from size-matched controls. Both juvenile and adult worms underwent transient depletion in total glycogen content after CsA treatment in vivo. The data confirm that CsA treatment in vivo disrupts the functional integrity of the worm tegument, one facet of which is impaired acquisition of glucose.

Human tumor necrosis factor alpha influences rainbow trout Oncorhynchus mykiss leucocyte responses

Human recombinant tumor necrosis factor alpha (rTNF alpha) and rainbow trout macrophage activating factor (postulated gamma-interferon (gamma-IFN) analogue) synergised to elevate the respiratory burst activity of trout macrophages. This elevated response may parallel phenomena described in mammals where TNF alpha and gamma-IFN commonly synergise. Human rTNF alpha also synergised with mitogenic stimuli to heighten proliferation responses of trout head kidney leucocytes. These data are indicative of a conserved TNF alpha receptor on trout leucocytes (and possibly the TNF alpha molecule itself) and support the notion of an interactive cytokine network regulating immune responses in fish.

Anthelmintic effects of cyclosporin A on protoscoleces and secondary hydatid cysts of Echinococcus granulosus in the mouse

Cyclosporin A (CsA), employed primarily as an immunosuppressant during the management of organ and graft transplants, exhibits anthelmintic properties. However, its efficacy against tapeworm infections in laboratory models is variable. A preliminary investigation has been undertaken to assess the action of CsA on the establishment and growth of protoscoleces and secondary hydatid cysts of ovine Echinococcus granulosus in mice. Administration of CsA in five consecutive daily doses, beginning 2 days prior to infection, resulted in significant reduction in cyst establishment (measured in terms of cyst masses, cyst numbers and cyst wet weights), when mice were autopsied 20 weeks post-infection. None of these parameters were significantly reduced when the drug was administered 18 weeks post-infection, although wet weight decreased by 42%. Ultrastructural examination of the germinal membrane and laminated layer of late-treated E. granulosus revealed abnormalities in all cysts studied whereas control and early-treated hydatids were normal. A case is made for the consideration of a clinical use for CsA for post-operative control of secondary hydatidosis and its efficacy against hydatid cysts is discussed.

Chitinolytic activities in Heligmosomoides polygyrus and their role in egg hatching

The occurrence of chitin in the eggshell of Heligmosomoides polygyrus has been determined by histochemical and biochemical techniques. Approximately 5% of the egg dry weight was chitin. Staining with Calcofluor white showed the chitin in the eggshell to be more accessible to the stain after hatching or rupturing of the eggshell. Chitinolytic activity has been detected using fluorescent substrates in extracts of adult males (at low levels), females and eggs. Enzyme activity in situ, within the developing larvae, was visualised with the same substrates. It was localized in discrete granules about 1 micron in diameter which occurred as groups in areas of about 5 microns in diameter, in the posterior third of the larvae. The chitinolytic activity in the eggs increased with the age of the egg and was released into the medium when the eggs hatched. The chitinase activities were very sensitive to inhibition by allosamidin, a specific chitinase inhibitor, with an IC50 for the crude egg extract of 2.2 nM. However, treatment of eggs with 250 microM allosamidin resulted in a slowing but not cessation of egg hatching.

Effects of cyclosporin A on the morphology and tegumentary ultrastructure of Hymenolepis microstoma in vivo

Cyclosporin A (CsA) induced significant changes in parasite morphology when administered to mice infected with Hymenolepis microstoma. Gross morphological damage consisted of proglottis swelling and the formation of protuberances from the worm surface, visible with a low-power dissecting microscope, occurring most frequently in the posterior third of the strobila. Gross morphology and ultrastructure were examined further using scanning and transmission electron microscopy. Swollen proglottides exhibited areas covered in small pits and fissures (diameter approximately 1-2 microns) but it was not possible to establish the significance of this damage. The brush-border and distal cytoplasm appeared largely intact although some evidence of swelling of the basal membrane invaginations and possible fluid accumulation was seen in drug-treated TEM sections. The apparent oedematous condition of many of the proglottides from drug-treated mice may indicate that CsA treatment mediates permeability changes in the worm surface membrane but the mechanisms by which this may occur remain to be elucidated. The effects of CsA on the morphology of H. microstoma correlate with the previously described anthelmintic activity of the drug against this parasite where CsA treatment dramatically reduces worm growth, retards migration into the bile duct and limits parasite survival.

Preface: positive interactions between anti-infection drugs and the immune response: an emerging paradigm

In the third and fourth decades of this century chemotherapy began to be established as one of the greatest success stories in medicine. Now unfortunately severe problems compromise the efficacy of drugs used to treat infectious diseases, two of the most serious handicaps being the rapidity with which target pathogens can develop drug-resistance and the slow rate at which replacement products are appearing on the market. Increased understanding of the ways in which existing drugs act may help both to prolong their usefulness and to generate novel therapeutic strategies.

Cyclosporin A: antiparasite drug, modulator of the host-parasite relationship and immunosuppressant

Cyclosporin A (CsA), a cyclic undecapeptide with powerful properties of immunosuppression, acts on parasitic infections in laboratory animals in various ways. The outcome of drug administration in vivo varies with timing of treatment relative to infection, route of administration, dose and number of treatments applied. CsA is clearly antiparasitic against malaria, schistosomes, adult tapeworms, metacestodes and filarial nematodes. By contrast, it acts as an immunomodulator against trypanosomes and Giardia, by exacerbating infection; in the case of Leishmania spp. the drug acts variously. In some other infections CsA acts both as an antiparasite drug and as an immunosuppressant (Toxoplasma, avian coccidiosis and gastrointestinal nematodes). This range of activities is reviewed and possible modes of action discussed in the light of emerging data on in vitro drug activity and on putative receptor binding. The potential value of a non-immunosuppressive analogue of CsA in the control of parasitic infections of humans and domestic animals is considered but this paper lays particular stress on the seminal role of CsA as a laboratory tool.

Studies on the infectivity of Diplostomum spathaceum in rainbow trout (Oncorhynchus mykiss)

The infectivity of Diplostomum spathaceum (Digenea: Trematoda) cercariae to rainbow trout and the efficacy of the diplostomule migration to the lens following different routes of administration was examined. The optimum age of infectivity for cercariae was between 0-5 h after liberation from the snail and for intraperitoneally injected diplostomules, 5 h post-transformation in vitro through fish skin. After exposure of the entire fish body or head to cercariae, metacercariae first appeared in the lens at 5 h and their numbers gradually increased until 22 h. Following exposure of the tail region of rainbow trout to cercariae, metacercariae first appeared in the lens at 14 h. Significantly more metacercariae established in the lens of fish following exposure of the fish head compared with the tail region; 40% of penetrating cercariae reached the lens of fish following exposure of the head or entire body, 20% of cercariae or diplostomules injected either intraperitoneally, intramuscularly or intracardially reached the lens while only 5% of cercariae established as metacercariae following exposure of the tail region.

Effect of water temperature on the ability of Diplostomum spathaceum miracidia to establish in lymnaeid snails

The effects of water temperature on the ability of Diplostomum spathaceum miracida to infect and establish patent infections in Lymnaea peregra and L. stagnalis were investigated. Snails were infected over a range of temperatures (6-20 degrees C) and kept thereafter at 20 degrees C or were infected at 20 degrees C and kept at either 14, 20, or 25 degrees C. Infection success was determined after 8 weeks by either observing cercarial shedding or examining snail viscera for sporocysts. The establishment of miracidia declined at lower water temperatures despite maintenance for 8 weeks at 20 degrees C while exposure of snails to miracidia at 20 degrees C and maintenance at different temperatures had little apparent effect. Infection success under these conditions was related more to the numbers of miracidia to which the snails were exposed. However, under this latter experimental regime, the time taken for the infection to become patent clearly depended upon maintenance temperature.

The larvicidal activity of cyclosporin A against Schistosoma mansoni in mice

Treatment of BALB/c or MF1 mice with cyclosporin A (CsA) around the time of infection with Schistosoma mansoni conferred almost complete protection. The migration kinetics of L-[75Se]selenomethionine-labelled infective cercariae were investigated by compressed tissue autoradiography. Similar levels of skin penetration were achieved by cercariae in control and drug-treated individuals. CsA arrested 87-94% of the worms in the skin and ultimately all of these died in this site. Few worms (7-14%) migrated from the skin to the lungs and none completed migration to the liver. Nevertheless, the autoradiograms revealed a limited degree of lateral cutaneous migration by the worms present in the skins of CsA-treated mice. Results of perfusion recovery experiments carried out during the course of infection reinforced the tracking data.

Action of cyclosporin A on the tapeworm Hymenolepis diminuta in mice

Cyclosporin A (CsA), administered in 5 daily subcutaneous doses of 50 mg/kg to MF1 mice immediately following infection with Hymenolepis diminuta enhanced parasite growth relative to controls. Drug administered at 24 h intervals for 10 days, and thereafter every 48 h to MF1 and CBA/Ca mice infected with H. diminuta, increased worm survival and growth, delayed host-mediated expulsion of the parasite and enabled some worms to develop to patency. Worm survival and weight both increased in a dose-dependent manner following daily CsA treatment of infected CBA/Ca and BALB/c mice (0-150 mg/kg CsA/day). Delay in parasite elimination was accompanied by increased frequency of worm-attachment in the anterior small intestine (MF1 mice given 5 daily doses of CsA [0-150 mg/kg] following infection); posteriad migration of worms was restricted in a dose-dependent manner. The data presented contrast markedly with the action of the same drug on H. microstoma in mice. Thus CsA treatment acts in opposing ways on two closely related parasites in the same host; this possibly reflects the mechanistic antagonism between immunosuppression and anthelmintic activity. This paper reports the first use of a specific T cell-suppressive drug on H. diminuta in the mouse, implicating the role of T cells in protective immunity to this parasite.

Praziquantel treatment of Biomphalaria glabrata infected with Schistosoma mansoni--influence on snail fecundity

Praziquantel, administered over a 72 h period in the food of mature Biomphalaria glabrata harbouring 7-week-old Schistosoma mansoni infections, dramatically reduced the numbers of cercariae shed. Doses of 20-30 micrograms/g body weight (including shell weight) reduced shedding by 85-95% over 5 weeks before recovery was evident. Suppression of cercarial shedding in these infections was accompanied by the temporary recovery of the snail reproductive regression due to S. mansoni infection. Snail fecundity was subsequently re-suppressed 2 weeks prior to recovery of the parasite as evidenced by a resumption of cercarial shedding. Praziquantel destroyed mature and developing cercariae within the daughter sporocysts but had no apparent effect on daughter sporocysts; this may account for the eventual resumption of cercarial production. Reproductive failure of the snail is apparently related to the latter stages of cercarial development specifically. Reproductive recovery did not occur when snails were infected as juveniles or when mature-infected snails harboured 12.5 week i.e. older infections: drug treatment temporarily inhibited cercarial production but no snails produced eggs.

Anti-schistosomal activity of cyclosporin A: studies on murine spleen cells and the influence of a cyclosporin antagonist on resistance to infection

Mice were treated with 5-day courses of cyclosporin A (CsA) around the time of infection with Schistosoma mansoni. Recovery of lung-stage worms 4-8 days post-infection (p.i.) was substantially reduced (80%) and no sexually mature adults were recovered from the hepatic portal system at 7 weeks p.i. Flow cytometric analysis of spleen cells from CsA-treated animals during the period of maximal parasite attrition revealed transient reductions in CD3+ and CD4+ cells and in the CD4+: CD8+ ratio compared with drug vehicle-treated, infected controls. No significant numerical changes in B cells, macrophages or eosinophils were detected relative to vehicle-treated infected mice. Transfer of spleen cells from CsA-treated donors 8 days after infection failed to confer increased resistance to S. mansoni infection on untreated recipients. Moreover, concomitant administration of CsA and an inducer of interleukin-2 production (ADA-202-718) did not interfere with the anti-schistosomal effect of CsA. Despite our incomplete understanding of the in vivo properties of CsA and reports of its paradoxical effects on immune responses, these new data indicate that the influence of CsA in schistosomiasis is unlikely to be mediated by modulation of host cell mediated immunity. This contrasts with certain other anti-parasitic effects of CsA which appear to be mediated by an action on T cells.

Action of cyclosporin A on the tapeworms Hymenolepis microstoma, H. diminuta and Mesocestoides corti in vivo

The in vivo activity of two cyclosporins, cyclosporin A (CsA) and a non-immunosuppressive derivative of dihydrocylosporin A (DHCsA-d) against three tapeworms, Hymenolepis microstoma, H. diminuta and Mesocestoides corti, has been assessed. CsA reversibly reduced the dry weight of H. microstoma in the mouse, briefly delayed oviposition and had a statistically significant effect on worm numbers recovered. Oral and subcutaneous treatments of both CsA and DHCsA-d were effective in reducing worm weight; juvenile worms were most susceptible but worms of all ages responded to drug by a dramatic reduction in weight from which they recovered. Multiple courses of CsA were no more active than single courses of treatment but dose response suggested that a threshold level of drug was necessary to evoke activity. By contrast, H. diminuta in the rat was completely unaffected by CsA but no explanation for the differences in drug response by these two closely related helminths is forthcoming. Mesocestoides corti responded reversibly to CsA in the mouse by a reduction in asexual proliferation of both liver and peritoneal cavity tetrathyridia. The data presented argue in favour of a range of anti-parasitic activities by cyclosporins but the details of the various putative modes of action remain to be defined.

Chitinase in female Onchocerca gibsoni and its inhibition by allosamidin

Chitinase activity has been detected in female worms of Onchocerca gibsoni. With 3,4-dinitrophenyl-tetra-N-acetylchitotetraoside as substrate 50% of maximum activity was achieved at about 25 microM substrate, with inhibition above 50 microM substrate. The antibiotic allosamidin very strongly inhibited the chitinase activity, 50% inhibition being achieved by 200 pM allosamidin in the presence of 45 microM substrate.

Immunophenotypic analysis of blood and spleen lymphocyte subsets in rats protected against schistosomiasis by cyclosporin A

The antischistosomal property of a short course of cyclosporin A (CsA), administered at the time of infection was demonstrated in the rat. In comparison with vehicle-treated controls, no schistosomes were recovered from CsA-treated animals, 18-19 days post infection. Flow cytometric analysis of blood and spleen lymphocyte populations from rats protected by CsA revealed no significant changes in functional T lymphocyte subsets, B cells or Ia-positive cells. Moreover, there were no significant differences in eosinophil numbers between the two experimental groups. These data add credence to the view that the unexplained antischistosomal property of cyclosporins is not mediated immunologically.

The interactions between drugs and the parasite surface

The interrelationships between drugs and parasite surfaces are considered under the headings of (a) effects on membrane transport, (b) drug uptake mechanisms and (c) effects on surface morphology and function: praziquantel is discussed under a separate heading. The range of chemotherapeutic compounds that cause permeability changes and concomitant morphological disruption is discussed in terms of mode of drug action. Interpretation of the available data renders it difficult to identify the primary mode of action in the drugs considered. Drug uptake mechanisms are known for relatively few compounds; drug resistance as a function of drug acquisition is discussed. The role of the parasite surface as a specific drug target is argued.

Prophylactic and therapeutic effects of ciclosporin A in murine Schistosomiasis mansoni: studies on bisexual and unisexual infections and the hepatic inflammatory response

Ciclosporin A (CsA), administered subcutaneously as 5 daily injections of 50 mg.kg-1, reduced the numbers of Schistosoma mansoni perfused from MF1 mice at 7 weeks post-infection. The timing of drug administration revealed that the antischistosomal effects were greater when CsA treatment coincided with or was within a few days of infection with the parasite. CsA exerted a clear prophylactic effect, which decreased with time and was virtually abolished by 4 months pre-infection. Adult worms treated in vivo were partially susceptible to CsA. In addition to its antiparasite action, CsA reduced hepatosplenomegaly due to schistosomiasis and diminished the granulomatous inflammatory response of mice to parasite eggs in the liver. The mode of action of CsA is not understood but evidence is presented that supports the proposition that the antiparasite effects are perhaps host-mediated.

Chitin in egg shells of Onchocerca gibsoni and Onchocerca volvulus

Chemical analysis of adult females of Onchocerca gibsoni gave estimated chitin contents of 200-500 micrograms (g dry weight)-1. Egg shells from both O. gibsoni and Onchocerca volvulus stained with Calcofluor white and with fluorescent wheat germ agglutinin as shown by fluorescent light microscopy, and bound gold-labelled wheat germ agglutinin as shown by electron microscopy, under conditions specific for chitin. The egg shells appeared as single electron dense layers from 50 to 85 nm in thickness. Purified chitinase digested these egg shells, leaving coiled microfilariae unattacked. We conclude that chitin is a major component of the egg shells.

Dosage, timing, and route of administration of cyclosporin A and nonimmunosuppressive derivatives of dihydrocyclosporin A and cyclosporin C against Schistosoma mansoni in vivo and in vitro

The prophylactic and therapeutic effects of cyclosporin A (CsA) against percutaneous Schistosoma mansoni infection in MF1 mice were dose related and dependent on the temporal relationship between drug administration and infection. Antischistosomal activity, assessed by worm recovery from the host 6 weeks after infection, was most effective (complete worm elimination) when CsA was administered at the time of infection. Oral administration of CsA was less effective than subcutaneous injection, and no prophylactic activity was demonstrated by the former route. Derivatives of dihydrocyclosporin A and cyclosporin C, which have been reported to exert only poor immunosuppressive activity, exhibited efficacy against S. mansoni similar to that of CsA and were also less effective when given orally. Subcutaneous, but not oral CsA reduced cercarial skin penetration and transformation success; the derivative of dihydrocyclosporin A, however, was without effect. Moreover, CsA, but not the derivative of dihydrocyclosporin A, reduced the number of worms established after intraperitoneal injection of cercariae. These data provide further insight into the antischistosomal activity of cyclosporins, which appears to be distinct from their immunomodulatory properties, since parasite killing was retained both in immunologically disparate mice and with poorly immunosuppressive cyclosporin derivatives.

Silver enhancement of lectin-gold and enzyme-gold cytochemical labelling of eggs of the nematode Onchocerca gibsoni

Wheat germ agglutinin-gold and chitinase-gold complexes were used to demonstrate the presence of chitin on the surfaces of eggs of the animal parasitic nematode Onchocerca gibsoni. The gold complexes were enhanced by silver intensification and examined by light microscopy (LM), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Distinctive labelling of the egg surfaces was obtained with both probes in all three microscope modes. The results indicate that the small colloidal gold markers (3-10 nm) commonly used for high resolution TEM studies may be silver enhanced and also used for sensitive LM and SEM studies.

Diplostomum spathaceum (Rud. 1819): effects of physical factors on the infection of rainbow trout (Salmo gairdneri) by cercariae

The relationship between infection rates of rainbow trout (Salmo gairdneri) by Diplostomum spathaceum and cercarial concentration, water flow rate and temperature were investigated by means of controlled infections within a flume. A linear relationship was obtained between cercarial concentration and mean abundance of metacercariae/fish. A biphasic relationship occurred between flow rate and abundance of metacercariae. Within the confines of the flume, it was possible to control the infection rate of trout with D. spathaceum cercariae by manipulating flow rate, suggesting that it may be a possible method of controlling diplostomiasis on fish farms. No infection occurred in fish infected and maintained below 10 degrees C and the optimum infection temperature was approximately 17.5 degrees C. Infections became established in fish infected at 7.5 and 5 degrees C but maintained at 15 degrees C prior to examination. Trout were infected at 7.5 degrees C for 10-50 min and all attached cercariae were washed off and removed from the flume. Following infection, fish were either maintained at 7.5 degrees C or 15 degrees C prior to examination. Using this method, it was possible to ascertain that it was migration and not penetration which was inhibited at water temperatures below 10 degrees C.

The epidemiology of diplostomiasis in farmed rainbow trout from north-east Scotland

An epidemiological survey of the distribution and abundance of Diplostomum spathaceum in farmed rainbow trout (Salmo gairdneri) from Mill of Cantray trout farm (Nairn, Morayshire) involved monthly sampling of fish over a 3-year period. Diplostomum metacercariae were present in both the lens and aqueous humour of infected fish, and these have been treated separately throughout the study. The infection period was normally between May and September each year and transmission of the parasite from snail to fish did not occur at temperatures below 10 degrees C. The prevalence and abundance of both lens and humour metacercariae reached a maximum in September. The cleansing and application of a molluscicide (copper sulphate) to the raceways in spring resulted in a 56% reduction in the numbers of metacercariae infecting trout during the following summer. However, no further improvement in parasite control was recorded when the treatment was repeated in the following year. Experiments using caged fish indicated that diplostomiasis was confined to certain areas of the farm only and that the infection rate of rainbow trout with D. spathaceum cercariae was correlated (P less than 0.01) with water temperature. The results of the study indicated that it is possible by regular cleaning and use of molluscicides to keep the intensity of diplostomiasis at such a level that rainbow trout do not become severely affected. However, as with other parasitic diseases, a combination of control methods will probably be required to eradicate the disease completely from trout farms.

Schistosoma mansoni: uptake in vitro and incorporation of adenine by adults

The rates of adenine uptake and incorporation into nucleic acids by adult male and female Schistosoma mansoni were determined during periods of up to 10 days in vitro, and comparisons were made between paired and separated worms. Adenine uptake by separated males and females exceeded that exhibited by equivalent paired worms. The rate of incorporation of adenine into nucleic acids was higher in separated females than in paired females. In contrast, the state of pairing had little effect on adenine incorporation by male S. mansoni. There was no correlation between rates of adenine uptake and incorporation and the reproductive activity of S. mansoni adults in vitro. Uptake and incorporation rates appeared to reflect the changing somatic requirements of both male and female worms.

Schistosoma mansoni: effect of maintenance in vitro on the uptake and incorporation of leucine by adult worms

The rates of leucine uptake and incorporation into protein by adult male and female Schistosoma mansoni were not affected by maintenance in vitro for up to 10 days' duration, despite the decline in the protein content of male and female worms of approximately 35 and 55%, respectively, during this period. The effect of maintenance in vitro was obscured in paired female schistosomes by the apparent shielding of the female tegument within the gynaecophoral canal of the male. Incorporation rates were reduced by 50% in the presence of 2 mM cycloheximide whereas uptake rates were unaffected. Adult schistosomes are unable to maintain their in vivo protein levels purely by recourse to exogenous amino acids absorbed across the tegument in vitro, and the rates of uptake and incorporation of leucine appear to reflect the changing somatic requirements of the worms and are probably not correlated with the reproductive activity of adult worms in vitro. The possible role of alimentary rather than tegumental nutrition in egg production in vivo is discussed.

Schistosoma mansoni: effect of maintenance in vitro on the physiology and biochemistry of adult worms

In Medium 199 supplemented with calf serum (+10%), adult Schistosoma mansoni produced a mean total of 400 eggs/worm pair during maintenance for 10 days in vitro. During the period of egg deposition in vitro, the dry weight of worm pairs decreased by 35%. Biomass decreases were proportionally greater in female worms than in males. Declines in the dry weight of female worms were mainly due to decreases in protein content, while biomass decreases in males resulted from losses of both protein and glycogen. Glucose was depleted from the maintenance medium at a rate of approximately 200 micrograms/worm pair/day during each of the first 3 days in vitro, while concentrations of glucose in the medium of above 1 g/litre did not affect the degree of glycogen depletion observed in adult S. mansoni during culture for 24 h. The contribution of the loss of schistosome gut contents in vitro to the observed changes is discussed. The work described represents part of an attempt at logical design of in vitro culture.

Schistosoma mansoni: incorporation and metabolism of protein amino acids in vitro

1. The amino acid composition of total proteins in six stages of the life cycle of Schistosoma mansoni was determined by routine autoanalysis of acid hydrolysates. Aspartate, glutamate and glycine were consistently the most abundant protein amino acids in all stages. 2. Incorporation of each of the protein amino acids into adult and egg proteins was determined using 72 hr cultures in complex media. Incorporation rates varied widely and there was no correlation between abundance in protein and the rate of incorporation. 3. Only five amino acids were interconverted to other amino acids which were themselves incorporated into worm and egg proteins (ala, arg, asp, gly, ser); of these only two (glu from ala and pro from arg) appeared to be of quantitative significance. Exogenous glucose yielded only three protein amino acids (ala, asp, glu). 4. The data are considered in the light of differences in egg and adult protein synthesis and with particular regard to potential chemotherapy at this level.

Schistosoma mansoni: in vitro uptake and incorporation of glycine by adult worms

1. The uptake of [3H]glycine into an ethanol-extractable intracellular pool and its simultaneous incorporation into protein (TCA insoluble fraction) have been measured in adult male and female Schistosoma mansoni incubated, in vitro, in complex media. 2. The patterns of uptake and incorporation were similar in male and female schistosomes incubated in media containing serum, and also in male worms incubated in the presence or absence of serum. 3. The amounts of [3H]glycine uptake and incorporation were directly proportional to the extracellular glycine concentration and were identical in male worms (in the presence or absence of serum) and female worms. 4. Emetine at a concentration producing a 95% inhibition of protein synthesis was without effect on the uptake of [3H]glycine into the ethanol-extractable pool in male worms.