Mucosal mast cell response to Hymenolepis diminuta infection in different rat strains.

Five-week-old DA male rats infected with 10 Hymenolepis diminuta cysticercoids showed significant mastocytosis 6 weeks post-infection and low persistence of worms. In F344/N rats, however, no mastocytosis and no worm loss occurred during a 6 week infection. Mucosal mast cells appear to be associated with the expulsion of H. diminuta from DA rats.     

Biochemical effects of thiabendazole and cambendazole on Hymenolepis diminuta (Cestoda) in vivo

An investigation of the chemotherapeutic and biochemical effects of two benzimidazole anthelmintics, thiabendazole (TBZ) and cambendazole (CBZ), on Hymenolepis diminuta in experimentally infected rats is reported. Thiabendazole was active against H. diminuta at a relatively high dosage. A single oral dose of TBZ at 250 mg/kg body weight on day 15 of infection eliminated 100% of the tapeworms as determined at necropsy 5 days after treatment. The chemotherapeutic actions of TBZ on H. diminuta were accompanied by marked changes in worm weight and chemical composition. Tapeworms recovered from rats that had received a therapeutically effective dose of TBZ 24 hr earlier were significantly smaller and contained much less glycogen (as a percent of the wet weight) than worms from unmedicated controls. Protein concentrations increased in TBZ-treated worms and at a rate sufficient to offset the decline in glycogen concentration. Glycogen/protein ratios in TBZ-treated worms were significantly lower than the corresponding control values. Cambendazole proved to be five times more potent than TBZ against H. diminuta and produced the same basic changes in worm weight and chemical composition within 18 hr of treatment of the host. Administration of a single oral dose of TBZ or CBZ to the host produced in H. diminuta another change, the onset of which coincided with, or preceded, the gross alterations in worm weight and chemical composition. That change, observed in in vitro studies carried out 14 hr after treatment, revealed that tapeworms from drug-treated rats absorbed and metabolized much smaller quantities of exogenous glucose than did the controls, and the ability of the worm to accumulate glucose against a concentration difference was significantly depressed.     

Possible immunological damage to the tegument of Hymenolepis diminuta in mice and rats.

Opaque or darkened areas (DA) of variable size and position occur on Hymenolepis diminuta in mice and rats. In mice DA normally first appear in the neck region of the worm but subsequently they appear elsewhere and increase in number until destrobilation or worm expulsion. The posterior of destrobilated worms is often darkened. In the more immunogenic infections with six cysticercoids there are more DA per worm than in infections with one cysticercoid. DA are areas of the tegument with a homogeneous increase in electron density; abnormal mitochondria; reduced granular endoplasmic reticulum, Golgi complexes and discoidal secretory bodies; and accumulation of lipid droplets. DA disappear from worms maintained for up to 4 h in Hanks' balanced salt solution and can be induced by mechanical damage to the worms. As the numbers of DA increase with the duration and intensity of infection and have similarities with types of cell injury, they are probably sites of worm pathology induced by host immunity.     

Delayed expulsion of Hymenolepis diminuta in Trypanosoma brucei infected mice

An experiment was conducted to study the effect of Trypanosoma brucei on the expulsion of Hymenolepis diminuta in the mouse. The study showed that T. brucei given 8 days before infection with H. diminuta resulted in a significant delay in the expulsion of the H. diminuta worm burden. This finding is suggested to be due to the immunosuppressive effect of the trypanosome.     

Scanning electron microscope studies of the mucosa of rats infected with Hymenolepis diminuta (Cestoda)

The intestinal morphology of rats given one, 10 or 100 cysticercoids of hymenolepis diminuta was examined by scanning electron microscopy. The presence of this tapeworm causes extensive villous atrophy and fusion. The most extreme changes in mucosal architecture were observed adjacent to the mature proglottides of the worm and in these areas the villi were reduced either to flattened plate-like structures or to low irregularly shaped undulations. The presence of one large H. diminuta resulted in more severe pathological damage than caused by several smaller worms. Colonization of the upper region of the ileum by long filamentous bacteria was also observed in rats infected with H. diminuta.     

Study of the effects of insulin on the migration of Hymenolepis diminuta in rats

The effects of insulin on worm (Hymenolepis diminuta) migration was studied. Insulin injection (20 U/kg, s.c.) significantly increased gastric acid output but did not affect the serotonin content of blood, intestinal lumen or worms. The drug produced, dose-dependently, posteriad migration of the worms in rats without pylorus-ligation but ligation of the pylorus prevented this migration. It is concluded that the hypersecretion of gastric acid induced by insulin is responsible for the posteriad migration of H. diminuta in rats.     

Characterization of the immuno-regulatory response to the tapeworm Hymenolepis diminuta in the non-permissive mouse host

Hymenolepis diminuta is spontaneously expelled from mice; concomitant with worm expulsion was protection against colitis induced by dinitrobenzene sulphonic acid (DNBS). Here we examined the immune response mobilized by Balb/c and C57Bl/6 male mice in response to H. diminuta and assessed the requirement for CD4+ cells (predominantly T cells) in worm expulsion and the anti-colitic effect. Wild-type (CD4+) or CD4 knock-out (CD4-/-) mice received five H. diminuta cysticercoids and segments of jejunum and mesenteric lymph nodes (MLNs), or spleen, were excised 5, 8 and 1l days later for mRNA analysis and cytokine production, respectively. In separate experiments uninfected and infected mice received DNBS by intra-rectal infusion and indices of inflammation were assessed 3 days later (i.e. 11 days p.i.). Infection of Balb/c mice resulted in a time-dependent increase in intestinal mRNA for Foxp3, a marker of natural regulatory T cells, and markers of alternatively activated macrophages (arginase-1, FIZZ1), while concanavalin-A activation of MLN cells revealed a significant increase in T helper 2 (TH2) type cytokines: IL-4, -5, -9, -10, -13. MLN cells showed a reduced ability to induce Foxp3 expression upon stimulation. CD4-/- mice did not display this response to infection, but surprisingly did expel H. diminuta. Moreover, DNBS-induced colitis in CD4-/- mice (wasting, tissue damage, elevated myeloperoxidase) was not reduced by H. diminuta infection, whereas time-matched infected CD4+ C57Bl/6 mice had significantly less DNBS-induced inflammation. In conclusion: (i) in addition to stereotypical TH2 events, H. diminuta-infected Balb/c mice develop a local immuno-regulatory response; and (ii) CD4+ cells are not essential for H. diminuta expulsion from mice but are critical in mediating the anti-colitic effect that accompanies infection in this model.     

The effect of the expulsion phase of Trichinella spiralis on Hymenolepis diminuta infection in rats.

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.     

Immunity to adult cestodes: basic knowledge and vaccination problems. A review.

Immunity in mammals to intestinal cestodes has been reviewed using the normal final host infected with the tapeworms Hymenolepis diminuta in rats and H. microstoma and H. nana in mice as a model. Primary infections up to a certain level continue to live as long the host, while most worms in infections with larger doses are destrobilated and expelled. It has been argued that concomitant immunity against a superimposed infection exists in rats and mice infected with H. diminuta and H. microstoma, respectively, and suggested that it also takes place in humans infected with Taenia spp. Immunity to secondary infections after expulsion of a primary infection occurs, but immunological memory is rather short-lived, although depression of worm growth occurs for at least two third of the rat's life. Serum antibodies have been shown to produce a direct precipitate on the surface of cestodes in vitro, but a direct effect of antibodies in vivo or the relationship with e.g. host effector cells, like mast cells and eosinophils, is unknown. It has been shown that peritoneal exudate cells from rats are able to kill H. diminuta in vitro. Very little is known about the mechanisms of tapeworms to counteract host immunological responses, but the tegumental glycoconjugates and discoidal secretory bodies are possible candidates. Passive transfer of immunity by mesenteric lymph node cells has only been successful using cells from H. nana egg-infected mice and has shown that only short-lived proliferating cells are responsible for transferring immunity. Vaccination procedures and problems are discussed with special reference to E. granulosus in dogs.     

Strain-dependent differences in susceptibility of mice to experimental Angiostrongylus costaricensis infection

Experimental Angiostrongylus costaricensis infection was carried out in inbred strains of mice (C57BL/6 BALB/c, DBA/2 and C3H/He). All strains became infected with this parasite. Marked differences in mortality and in worm burden were found among inbred strains of mice tested. A significant reduction was shown in worm length from mice compared to that from cotton rats.     

The occurrence and distribution of 5-hydroxytryptamine in Hymenolepis diminuta and H. nana

The presence of 5-HT in Hymenolepis diminuta and Hymenolepis nana was detected by 2 biochemical methods and as yellow fluorescence in a histochemical method. In H. diminuta, 5-HT was found in a concentration of about 1.2 micron/g; this amount did not vary significantly in worms aged 6 to 18 days or more or in various regions of the worm. In H. nana, 5-HT was found in a concentration of about 1.8 micron/g. It was histochemically localized in H. diminuta and H. nana in a pattern similar to that of acetylcholinesterase previously described in these 2 cestodes, and it may be the opposing neuro-transmitter to acetylcholine. The lack of 5-HT in the vestigial rostellum of H. diminuta may be correlated with loss of function of this organ.     

Inflammatory responses in the intestine during tapeworm infections. Mucosal mast cells and mucosal mast cell proteases in Sprague-Dawley rats infected with Hymenolepis diminuta.

Comparative studies were made of two populations of Sprague-Dawley rats infected with Hymenolepis diminuta. The time course of infection, the development of mucosal mastocytosis and the levels of rat mucosal mast cell (MMC) protease (RMCP II) in serum and in jejunal mucosal tissues were monitored at intervals after infection with 40 cysticercoids of the tapeworm. Worm expulsion patterns differed markedly between the two populations, rats of New Zealand origin showing an abrupt and clear-cut loss of worms, rats of English origin showing a more gradual decline over a longer time period. In both populations, however, numbers of MMC and levels of tissue RMCP II were positively correlated with time after infection and negatively correlated with worm numbers. In only one of the three experiments (using English strain rats over a short time period) did levels of serum RMCP II change with time. In the other two experiments, in which English-strain and New Zealand-strain rats were used, there were no correlations between serum RMCP II and time, numbers of MMC, numbers of worms or levels of tissue RMCP II. The absence of correlation between serum RMCP II and worm loss in these experiments implies that MMC have no direct role in expulsion of H. diminuta. The data do show, nevertheless, that this purely luminal tapeworm is fully capable of activating the mucosal T lymphocyte-MMC precursor axis to elicit a mucosal mastocytosis.     

Structure-activity relationships of benzothiazole and benzimidazole anthelmintics: a molecular modeling approach to in vivo drug efficacy

An investigation of the biochemical effects of an anthelmintic, tioxidazole (TIOX, methyl 6-[n-propoxy]benzothiazole-2-carbamate), on Hymenolepis diminuta in experimentally infected rats is reported. The chemotherapeutic actions of TIOX on H. diminuta in vivo were accompanied by marked changes in worm weight and chemical composition. Tapeworms recovered from rats that had received a therapeutically effective dose of TIOX 24 hr earlier were significantly smaller and contained much less glycogen (as a percentage of the wet weight) than worms from untreated controls. In TIOX-treated worms, protein concentrations rose at a rate sufficient to offset the decline in glycogen concentration. Glycogen/protein ratios in TIOX-treated worms were considerably lower than the corresponding control-values. Differences in the absolute amounts of glycogen and protein between control and drug-treated worms were even more pronounced. Administration of a subcurative dose of TIOX to the rat produced in H. diminuta another change, the onset of which preceded the gross alterations in worm weight and chemical composition. In vitro studies, carried out 18 hr after treatment, revealed that TIOX-treated worms absorbed and metabolized much smaller quantities of exogenous glucose than did the controls and that the ability of the worm to accumulate glucose against a concentration difference was significantly depressed. A mode of action common to the structurally related benzothiazole and benzimidazole anthelmintics is indicated by the similarity of their biochemical and physiological effects on the tapeworms and their time course of action when administered to rats infected with H. diminuta. Molecular modeling revealed that the benzothiazole and benzimidazole anthelminitics are congruent electronically and structurally. In vivo drug efficacy depends upon the magnitude of the molecular dipole moment and the percentage of polar surface area. Within the benzimidazole series, structural and electronic congruence is found between the 2-thiazolyl and 2-methyl carbamate groups, suggesting that these groups behave similarly in transport to, and binding at, the active site. Finally, anthelmintics that have the 5' substituents twisted out-of-plane were more active than those anthelminitics with 5' substituents in-plane. All of these factors implicate a highly polar, L-shaped cleft to which the anthelmintics bind at the active site.     

Hymenolepis diminuta: lack of sulphate activation and sulphotransferase activity

There is no evidence that Hymenolepis diminuta can carry out sulphoconjugation reactions. Neither whole worms nor worm extracts were able to sulphate 4-methylumbelliferone. No sulphotransferase activity could be demonstrated in H. diminuta using a variety of substrates, nor was H. diminuta capable of synthesising the sulphate donor 3'-phosphoadenosine-5'-phosphosulphate from ATP and inorganic sulphate. Possible alternative sources of active sulphate in this parasite are discussed.     

Neutralizing anti-IL-10 antibody blocks the protective effect of tapeworm infection in a murine model of chemically induced colitis

There is increasing evidence that parasitic helminth infection has the ability to ameliorate other disease conditions. In this study the ability of the rat tapeworm, Hymenolepis diminuta, to modulate dinitrobenzene sulfonic acid (DNBS)-induced colitis in mice is assessed. Mice receiving DNBS (3 mg intrarectally) developed colitis by 72 h after treatment. Mice infected 8 days before DNBS with five H. diminuta larvae were significantly protected from the colitis, as gauged by reduced clinical disease, histological damage scores, and myeloperoxidase levels. This anticolitic effect was dependent on a viable infection and helminth rejection, because no benefit was observed in mice given killed larvae or in infected STAT6 knockout mice or rats, neither of which eliminate H. diminuta. The anticolitic effect of H. diminuta was associated with increased colonic IL-10 mRNA and stimulated splenocytes from H. diminuta- plus DNBS-treated mice produced more IL-10 than splenocytes from DNBS-only treated mice. Coadministration of an anti-IL-10 Ab blocked the anticolitic effect of prophylactic H. diminuta infection. Also, mice infected 48 h after DNBS treatment showed an enhanced recovery response. Finally, using a model of OVA hypersensitivity, we found no evidence of concomitant H. diminuta infection enhancing enteric responsiveness to subsequent ex vivo OVA challenge. The data show that a viable infection of H. diminuta in a nonpermissive system exerts a profound anticolitic effect (both prophylactically and as a treatment) that is mediated at least in part via IL-10 and does not predispose to enhanced sensitivity to bystander proteins.     

The role of the host in the regulation of end-product formation in two strains of the rat tapeworm, Hymenolepis diminuta

Individual worms from rats infected with different strains of Hymenolepis diminuta were incubated in vitro and the products lactate, succinate, acetate and ammonia assayed. Variability in excretion was not confined to differences between strains. Two metabolic types were identified. Where succinate was above 20 mumol g-1 h-1, lactate excretion was low. Where succinate was not detected, lactate excretion was high. Acetate excretion was variable. Lactate and ammonia excretion were positively correlated. All worms from one rat were of the same type but could be of either type from different rats. The host strain had no effect. A relationship was shown between lactate excretion and the number of worms from a standard inoculum present at 21 days of infection. The incidence of high lactate excretion was increased in worms from secondary infections. Components of the host immune response may thus exert effects on the metabolism of H. diminuta, manifest as shifts in emphasis on cytosolic and mitochondrial metabolism.     

Susceptibility of several strains of mice to Echinostoma hortense infection

Susceptibilities of 5 different mice strains, including C3H/HeN, BALB/c, C57BL6, FvB and ICR, to Echinostoma hortense infection, was evaluated. The worm expulsion rate, worm size and egg production were observed from 1 to 8 weeks after infection with 30 metacercariae. C3H/HeN and ICR mice showed the highest worm maturation rates. The worm recovery rate and the number of eggs per gram (EPG) of feces was also higher in C3H/HeN and ICR mice than in BALB/c, C57BL6, and FvB mice. It is suggested that E. hortense is highly infectious to ICR and C3H/HeN mice, but not to the other strains of mice. Based on the results obtained, we believe that the susceptibility of different mouse strains to E. hortense infection is dependent on the genetic and immunologic background of mice.     

Phloretin inhibition of glucose transport by the tapeworm Hymenolepis diminuta: a kinetic analysis

Phloretin non-competitively inhibits glucose and methionine absorption by Hymenolepis diminuta (Ki = 0.24 and 1.48 mM, respectively). Inhibition of glucose transport by phloretin is reversible. Phloretin and phlorizin binding sites on the surface of H. diminuta are distinct. Phloretin does not inhibit Na+ transport independent of glucose transport in H. diminuta. The data suggest that phloretin inhibits absorptive functions across the surface of H. diminuta via non-specific binding sites associated with the lipid portion of the worm outer membrane.     

Inhibition of growth of a tapeworm Hymenolepis diminuta in its normal host (rat).

The biomass of 8-day-old worms of Hymenolepis diminuta in secondary infections, administered to rats 3-10 days after chemotherapeutically expelling a primary infection, was 70-90% less, and the worms were more posteriorly distributed, than in naive controls. The strong depressive effect on growth waned rapidly over 2-5 weeks, but even in rats not challenged until 17 months later, worm growth was weakly depressed by 30%. The extent to which growth was depressed in a secondary infection was independent of the number of worms in the challenge but increased with number of worms in the immunizing infection up to four to eight worms. Further increase up to 64 worms had little effect. This suggests, as it is known that the biomass of worms in a rat reaches a maximum with infections of between five and 10 worms, that the change in the intestine is proportional to biomass, not number, of worms. It is argued that partially suppressed immuno-inflammatory changes in the intestine, which will affect secondary worms so strongly, will also have depressed growth and fecundity effects on the primary worms, that a dynamic equilibrium is reached between the strength of the intestinal response and the biomass of the tapeworm, and that it is reaching this equilibrium, not a 'crowding effect', which limits H. diminuta to a level compatible with the survival of the rat.     

Parasite populations in the brown rat Rattus norvegicus from Doha, Qatar between years: the effect of host age, sex and density

A total of 179 urban rats were sampled in the city of Doha in Qatar across the winter seasons (February-April) of 2002 and 2003. Only two parasites were identified, with overall prevalences of 35.8% and 41.3% for the cestode Hymenolepis diminuta and the flea Xenopsylla astia respectively. The prevalence of H. diminuta was markedly influenced by both year of study and host age, being higher in 2003 and amongst older rats. The abundance of infection of H. diminuta was influenced by the year of study, host age and sex. Worm burdens in adult rats were almost twice as heavy in males compared with females and adults of both sexes harboured heavier infections than juveniles. The prevalence of X. astia was influenced by both year and host age, being higher in juvenile rats in 2002 and in adults in 2003. The abundance of X. astia was significantly higher in 2003 and both male and female rats showed similar abundances, but in 2003 females were more heavily infested. Reasons for this are discussed in relation to the differing foraging strategies shown by male and female rats. The prevalence and abundance profiles for both H. diminuta and X. astia were higher overall in 2003 due to a significant increase in the rat population density, although this did not reflect in any increase in parasite species richness. Rats that were infected with H. diminuta were almost twice as likely to be infected with X. astia than those without the cestode, but when controlled for the effects of year, host age and sex, no quantitative interactions were detected between the two parasite species.