Rapamycin exposure to host and to adult worms affects life history traits of Heligmosomoides bakeri

Parasite life history can be affected by conditions of the host and of the external environment. Rapamycin, a known immunosuppressant of mammals, was fed to laboratory mice that were then infected with the Trichostrongylid nematode Heligmosomoides bakeri to determine if host rapamycin exposure would affect parasite survival, growth, and reproduction. In addition, adult worms from control fed mice were directly exposed to rapamycin to assess if rapamycin would affect worm viability and ex vivo reproduction. We found that host ingestion of rapamycin did not affect H. bakeri survival or growth for male or female worms, but female worms had increased reproduction both in vivo and when removed from the host and cultured ex vivo. After direct rapamycin exposure, motility of female worms was greater at low levels of rapamycin compared to high levels of rapamycin or high levels of DMSO (the vehicle used to solubilize rapamycin) in control media, but was similar to females in low levels of DMSO in control media. Male motility was not affected by the presence of rapamycin or DMSO in the media. Ex vivo egg deposition was higher when exposed to rapamycin than when cultured in control media that contained DMSO, regardless of DMSO dose. Overall, we conclude that host ingestion of rapamycin or direct exposure to rapamycin was generally favorable or neutral for parasite life history traits.

Anthelmintic potential of three plants used in Nigerian ethnoveterinary medicine

CONTEXT

The leaves of Irvingia gabonensis Baill. Ex Lanen (Irvingiaceae), Ficus exasperata Vahl (Moraceae), and Vernonia amygdalina Delile (Asteraceae) are folklorically used in treating worm infestation in Eastern Nigeria. The anthelmintic potential of the ethanol extracts of the leaves of I. gabonensis, F. exasperata, and V. amygdalina was investigated.

MATERIALS

Acute toxicity tests were done in mice using 10, 100, and 1000 mg/kg/bw of extracts. In vitro larval assays of Heligmosomoides bakeri larvae at various extract concentrations (125, 250, and 500 mg/kg) were done. Mice experimentally infected with H. bakeri were treated with F. exasperata extract (200, 400, 800 mg/kg).

RESULTS

At concentrations of 500, 250, and 125 mg/ml F. exasperata caused 100% larval mortality. V. amygdalina extract caused 71.43, 57.14, and 57.14% larval deaths while I. gabonensis extract caused 71.43, 57.14, and 42.9% larval deaths at the same concentrations. There was no significant difference in the fecal egg output, packed cell volumes and body weights of the F. exasperata treated mice when compared with the infected untreated group.

DISCUSSION AND CONCLUSION

Leaf extracts of F. exasperata, V. amygdalina, and I. gabonensis exhibited varying degrees of larvicidal activities on the infective stage larvae of H. bakeri in vitro whereas F. exasperata showed no activity on the parasites in vivo.

In vitro anthelminthic efficacy of Dichrocephala integrifolia (Asteraceae) extracts on the gastro-intestinal nematode parasite of mice: Heligmosomoides bakeri (Nematoda, Heligmosomatidae)

OBJECTIVE

To evaluate the ovicidal and larvicidal activities of aqueous and ethanolic extracts of leaves of Dichrocephala integrifolia (D. integrifolia) against the eggs (fresh and embryonnated), the first and second larval stages of Heligmosomoides bakeri. In order to verify if this medicinal plant possesses active compounds capable of inhibiting the embryonation and hatching of eggs or to induce the mortality of larvae (L1 and L2).

METHODS

dried extracts were diluted in distilled FIV water to obtain five different concentrations: 625, 1,250, 2,500, 3,750 and 5,000 µg/mL. Fresh eggs obtained from artificially infected mice feces were exposed to these different concentrations for 48 h. Time of contact for embryonated eggs was 6 h while L1 and L2 larvae were exposed for 24 h. Distilled water (placebo) and 1.5% DMSO were used as negative controls.

RESULTS

Distilled water, and 1.5% DMSO had no effect on embryonation, hatching and larval survival. Aqueous extracts of D. integrifolia showed a weak activity against all stages of the parasite at all concentrations tested. On the contrary, the ethanolic extract of D. integrifolia inhibited the embryonation of 87.5% of fresh eggs, the hatching of 81.1% of embryonated eggs and induced the mortality of 98.1% and 98% of L1 and L2 larvae respectively at 5,000 µg/mL.

CONCLUSIONS

The results of the present study indicate that the ethanolic extracts of D. integrifolia contained compounds with ovicidal and larvicidal properties. In spite of these results, in vivo tests, studies on toxicity and mechanism of action of active compounds are also needed to validate the utilisation of this medicinal plant by population of Dschang-Cameroon to treat gastro-intestinal parasites.

The life cycle of Ohbayashinema erbaevae (Nematoda, Heligmosomoidea, Heligmosomidae) in Ochotona rufescens rufescens (Ochotonidae)

The morphogenesis and the chronology of the life cycle of Ohbayashinema erbaevoe Durette-Desset et al, 2000, a parasite of Ochotona daurica from Buriatia were studied in detail in an experimental host, Ochotona rufescens rufescens. Worm-free pikas were each infected per os with O. erbaevae larvae and were killed at one day post infection (DPI 1) and every 12 hours from 1.5 to 8 days post infection. By DPI 1, all the larvae were exsheathed and in the small intestine. The third moult occurred in 2.5-3.0 days. The last moult occurred in 4.0-4.5 days. The prepatent period was eight days and the patent period lasted between two and 12 weeks. The distribution of O. erbaevae along the small intestine of the pikas was assessed. For each experiment, a morphological description of the different stages of the life cycle was provided. The morphogenesis and the chronology of the life cycle of O. erbaevae appear to be identical with those of two other genera of the family of the Heligmosomidae, Heligmosomum Railliet & Henry, 1909 and Heligmosomoides Hall, 1916. They confirm that the three genera belong to the same family. The presence of an abortive posterior genital branch in the female of O. erbaevae, which represents the posterior part of the genital primordium of the didelphic females, supports the systematic position of the genus Ohbayashinema between the didelphic genus Citellinema Hall, 1916 and the monodelphic genera Heligmosomum and Heligmosomoides.

Heligmosomoides polygyrus: retarded development and stunting of larvae by antibodies specific for excretory/secretory antigens

The migration of young adult-stage Heligmosomoides polygyrus from beneath the muscularis mucosa to the lumen of the intestine was monitored to compare the rate of development and maturation of larvae in normal and previously infected mice. The development of surviving larvae was significantly retarded in mice that had experienced one or more previous infections and the adult worms arising from a challenge infection were stunted and appeared anaemic. Identical effects were observed with worms recovered from mice that had been injected with immune mouse serum at the time of challenge, and the magnitude of these effects was related to the amount of serum given. Larval maturation was also retarded in mice immunized with larval excretory/secretory (ES) antigens, even though the antibody response was poor due to the very small (submicrogram) amounts of antigen available for injection. In contrast, larvae developed at a normal rate in mice that had been hyperimmunized with killed exsheathed larvae. These mice had serum antibody titres against both "internal" and cuticular antigens similar to those of highly immune (4x-infected) mice, but they had no detectable antibody against ES antigens. The results indicate that the growth and development in vivo of H. polygyrus larvae are retarded by antibodies specific for larval ES antigens. Stunting is permanent, with female worms being affected more severely than males and egg output per worm correspondingly reduced.

The microbial environment and intestinal nematode infections of Heligmosomoides polygyrus in laboratory mice

The difficulty of establishing primary infections of Heligmosomoides polygyrus (= Nematospiroides dubius) in ASH/CSI mice in the Laboratory Animal House at Royal Holloway and Bedford New College during a recent autumn and spring period was associated with a syndrome of worm distortion, together with zero or low worm establishment and reduced fecundity (eggs/female worm). The eggs produced were non-viable and the egg capsule comprised a rumpled lipid and ruptured chitin layer. The egg size and peaks of egg production were also reduced and the total egg output ceased entirely by day 28 post-infection in male mice. The syndrome was repeated when control LACA mice harbouring 'normal' infections of H. polygyrus were housed on the same source of peat bedding material as the ASH/CSI mice. An increase in H. polygyrus egg production in ASH/CSI mice, removed from the peat or treated with 0.04% oxytetracycline hydrochloride suggested that the cause of the syndrome was microbial in origin. A microbiological assay of the peat, which was the common denominator of all syndrome infections, revealed an abundance of chitinase secreting species of bacteria (Bacillaceae). Bacterial chitinase was therefore likely to rupture the chitin layer of the egg capsule producing nonviable eggs and either abnormal or no larvae. Preliminary in vitro studies using chitinase from Streptomyces griseus indicated that the hatching success of eggs of H. polygyrus was reduced as the concentration of chitinase increased.

Heligmosomoides polygyrus (Nematoda): the influence of dietary protein on the dynamics of repeated infection

The influence of the protein component in the diet of the host on the population dynamics of gastrointestinal helminth infection was studied by using a mouse-H. polygyrus experimental model. Mice fed a 2% (by mass) protein diet ad libitum maintained body weight during the experiment, but gained weight steadily when fed a diet containing 8% (by mass) protein. When repeatedly infected with 5, 10, 20 or 40 larvae every 2 weeks, the mice fed the 2% (by mass) protein diet accumulated adult worms in direct proportion to exposure to the infective stages. Under similar infection régimes, mice fed an 8% (by mass) protein diet acquired a partly effective immunity to reinfection by the nematode. Acquired immunity was principally manifest as a reduction in the survival of adult worms, although a slight increase in the mortality rate and/or the development time of the tissue-dwelling larval phase was observed. Worm fecundity per head was significantly depressed in hosts fed the 8% protein diet. In conclusion, in these experiments it is demonstrated that the nutritional status of the host can influence the population dynamics of helminth infection.

Heligmosomoides polygyrus (Nematoda): the dynamics of primary and repeated infection in outbred mice

The population dynamics of Heligmosomoides polygyrus were studied in outbred male MF1 mice subject either to primary or repeated experimental infection. Little variability in susceptibility was observed between mice, but heterogeneity increased with both duration and intensity of primary infection; this result indicates that there are differences in parasite survival between hosts. The rate of parasite-induced host mortality was 4 X 10(-4) per parasite per host per parasite lifespan. The mortality rates of male and female larvae during their development in the intestinal wall were estimated as 0.033 and 0.021 per parasite per day respectively, and estimates of the expected lifespans of the adult male and female parasites in primary infection of 11.22 and 9.92 weeks were obtained. Approximately 40% of female worms were observed in copula at any one time, although this proportion was significantly depressed in hosts harbouring fewer than 50 parasites and during the first four weeks of infection. Parasite fecundity was markedly age-dependent; each female worm produced approximately 31,000 eggs during its lifespan. No density dependence in either worm survival or fecundity in primary infection was apparent. The only detectable effect of worm density was in association with spatial distribution in the intestine; high levels of infection were associated with a posterior shift in the location of a proportion of the parasite population. Characterization of the dynamics of primary infection allowed predictions to be made about the expected dynamics of repeated infection. The comparison of predicted results and observed data revealed unequivocal epidemiological evidence for the density-dependent regulation of parasite population growth during repeated infection, affecting both parasite survival and parasite fecundity. The results also demonstrated the existence of two types of host individual in which the dynamics of repeated infection were markedly different. It is concluded that immunological differences between mice (possibly under genetic control) may be responsible for the observed effects; approximately 25% of MF1 mice seem unable to generate any protective immunity against H. polygyrus, whereas 75% become almost completely refractory to reinfection. This experimental system could be used for quantitative investigation of the impact of acquired immunity and genetic heterogeneity on helminth population dynamics. Both are of obvious relevance with respect to the control of infections of medical and veterinary significance.