Shedding of antibody complexes by Strongyloides ratti (Nematoda) larvae

Antigens on the epicuticular surface of Strongyloides ratti infective third-stage larvae (L3) could be demonstrated by an indirect fluorescent antibody technique under certain conditions. Infective L3 shed anti-antibody complexes at room temperature, but not at 4 C or in the presence of sodium azide or colchicine. Shedding of antibody did not appear to involve epicuticular antigens, and only occurred when anti-rat IgG was complexed to rat anti-larval antibody. However, parasitic L3 removed from rats did not exhibit this shedding reaction, suggesting that an important developmental change in cuticle physiology occurs during the transition from a free-living existence to a parasitic mode. The ability to shed foreign objects from the epicuticle of free-living infective L3 may be a defensive or protective response to soil microorganisms.     

Demonstration of collagenase activity in adult Strongyloides ratti (Nematoda:Strongyloididae) and its absence in the infective larvae

Larvae and adults of Strongyloides ratti were examined for collagenolytic activity on 14C proline-labelled, native, guinea-pig skin collagen substrate. The activity was measured by determining either the amount of hydroxyproline released or the amount of radioactivity in the solubilized fraction of the collagen substrate. Bacterial collagenase was used for enzyme control and trypsin served as substrate control. No collagenolytic activity was found in living larvae, their extracts or metabolites. The collagenolytic activity of the metabolites of adult worms appeared weak, whereas that of the extracts of the adults was pronounced. It is suggested that collagenase is active in the adult females at the time of migration in the intestinal mucosa during oviposition.     

Experimental evolution of parasite life-history traits in Strongyloides ratti (Nematoda)

Evolutionary ecology predicts that parasite life-history traits, including a parasite's survivorship and fecundity within a host, will evolve in response to selection and that their evolution will be constrained by trade-offs between traits. Here, we test these predictions using a nematode parasite of rats, Strongyloides ratti, as a model. We performed a selection experiment by passage of parasite progeny from either early in an infection ('fast' lines) or late in an infection ('slow' lines). We found that parasite fecundity responded to selection but that parasite survivorship did not. We found a trade-off mediated via conspecific density-dependent constraints; namely, that fast lines exhibit higher density-independent fecundity than slow lines, but fast lines suffered greater reduction in fecundity in the presence of density-dependent constraints than slow lines. We also found that slow lines both stimulate a higher level of IgG1, which is a marker for a Th2-type immune response, and show less of a reduction in fecundity in response to IgG1 levels than for fast lines. Our results confirm the general prediction that parasite life-history traits can evolve in response to selection and indicate that such evolutionary responses may have significant implications for the epidemiology of infectious disease.     

The response of intact Strongyloides ratti infective (L3) larvae to substrates and inhibitors of respiratory electron transport.

Live, intact third-stage larvae (L3s) of Strongyloides ratti in the absence of exogenous substrates consumed oxygen at a rate (E-QO₂) of 181.8 ± 12.4 ng atoms min⁻¹ mg dry weight⁻¹ at 35°C. Respiratory electron transport (RET) Complex I inhibitor rotenone (2 μ ) produced 33 ± 6.5% inhibition of the E-QO₂. Unusually the rotenone-induced inhibition was not relieved by 5 μ -succinate. The E-QO₂ of intact L3s was refractory to RET Complex III inhibitor antimycin A at 2 μ ; 4 μ -antimycin inhibited ≤ 10% of the E-QO₂. The electron donor couple ascorbate/TMPD augmented the E-QO₂ in the presence of rotenone (2 μ ) and antimycin A (4 μ ) by 110%. Azide (1 m ) stimulated the antimycin A refractory QO₂ by 36.6 ± 7.2% which was only partially inhibited by 1.0 m -KCN ( ). The data suggest the presence of classical (CPW) and alternate (APW) electron transport pathways in S. ratti L3s.     

Strongyloides ratti: chemokinesis of glycolytic enzyme- and lectin-treated third-stage infective larvae in vitro

The infective third-stage larvae (L3s) of Strongyloides ratti, a parasitic nematode in rodents, showed two types of chemokinesis on a gradient of sodium chloride (NaCl) in an in vitro agarose tracking assay. The types were a consistent directional avoidance behavior under unfavorable environmental conditions and a reduced avoidance behavior under favorable conditions. We examined the effects of treatments with glycolytic enzymes and lectins by analyzing the avoidance behavior. L-Fucose dehydrogenase, hyaluronidase, beta-glucosidase, alpha-mannosidase, beta-galactosidase, concanavalin A, wheat germ agglutinin and soybean agglutinin exhibited inhibitory or enhancive effects on chemokinesis. We also confirmed the sites of the amphids of L3s aside from the mouth at the anterior end by scanning electron microscopy, and that concanavalin A-binding sites existed in the vicinity of the amphids using lectin-histochemistry. The carbohydrate moieties in the amphids of S. ratti L3s may play an important role as chemosensors in perceiving environmental cues.     

Loss of surface coat by Strongyloides ratti infective larvae during skin penetration: evidence using larvae radiolabelled with 67gallium

The optimal conditions for labelling infective larvae of Strongyloides ratti with 67gallium citrate were determined. Radiolabelled larvae were injected s.c. into normal and previously infected rats. The distribution of radioactivity in these animals was compared with that in rats infected subcutaneously with a similar dose of free 67Ga by using a gamma camera linked to a computer system. Whereas free 67Ga was distributed throughout the body and excreted via the hepatobiliary system, the bulk of radioactivity in rats injected with radiolabelled larvae remained at the injection sites. Direct microscopical examination of these sites, however, revealed only minimal numbers of worms. When rats were infected percutaneously with radiolabelled larvae, it was found that most radioactivity remained at the surface, despite penetration of worms. When infective larvae were exposed to CO2 in vitro and examined carefully by light microscopy, loss of an outer coat was observed. It was concluded that infective larvae lose an outer coat on skin penetration.     

Chemokinetic behavior of the infective third-stage larvae of Strongyloides ratti on a sodium chloride gradient.

The movements of the infective third-stage larvae (L3) of a rodent parasitic nematode Strongyloides ratti were examined on a sodium chloride (NaCl) gradient set up on agarose plates. The movements of larvae were followed by observing their tracks on the surface of the agarose. The direction of movement depended on the NaCl concentration at the point of their initial placement on the gradient. Larvae placed at between 230 and 370 mM NaCl tended to migrate towards areas of lower concentration. On the other hand, when placed at concentrations less than 20 mM NaCl, larvae tended to migrate initially towards higher concentrations but did not linger in areas where the concentration was over approximately 80 mM NaCl. It seems that S. ratti L3, tested in vitro, prefer regions with a concentration of NaCl below 80 mM NaCl. Two typical chemokinetic behaviors are seen; a unidirectional avoidance movement when initially placed in unfavorable environmental conditions and a random dispersal movement when placed within an area of favorable conditions. Track patterns were straight in the avoidance movement but included multiple changes of direction and loops in the dispersal movement. This study introduces an assay system suitable for studying chemokinetic behavior of larvae of Strongyloides ratti.     

Electron microscopical studies of Strongyloides ratti infective larvae: loss of the surface coat during skin penetration

Previous indications using radiolabelled larvae that Strongyloides ratti free-living infective larvae lose a surface coat during penetration of the skin were further investigated by transmission electron microscopy of the cuticle of S. ratti infective larvae in the free-living stage, after penetration of mouse skin, and after migration to the lungs. These studies demonstrated the presence of a faint electron-dense surface coat external to the epicuticle on free-living worms which was absent from larvae recovered from the skin and lungs. When free-living infective larvae were incubated in 10% CO2 at 37 C and then examined with phase-contrast microscopy, worms were observed in the process of losing this coat. These observations confirm the hypothesis that S. ratti infective larvae lose a surface coat during penetration of the skin.     

Tracking radioactive larvae of Strongyloides ratti in the host

Infective larvae of homogonic Strongyloides ratti grown in faecal culture with 32P or 75Se acquired a significant amount of radioactivity which was firmly attached to them. Heating removed most of the 32P but left 75Se in place. Subcutaneous injection of virgin and nursing mother rats with living and heat-killed radioactive larvae resulted in a pattern of labelling in the small intestine of injected animals and, in the case of 75Se, those of suckling pups, which can only be explained if labelled worms follow the natural migratory routes. The use of this tool in migratory studies is discussed, with precautions to allow for flaws in the technique.     

No evidence for specificity between host and parasite genotypes in experimental Strongyloides ratti (Nematoda) infections

A key requirement for several theories involving the evolution of sex and sexual selection is a specificity between host and parasite genotypes, i.e. the resistance of particular host genotypes to particular parasite genotypes and the infectivity of particular parasite genotypes for particular host genotypes. Determining the scope and nature of any such specificity is also of applied relevance, since any specificity for different parasite genotypes to infect particular host genotypes may affect the level of protection afforded by vaccination, the efficacy of selective breeding of livestock for parasite resistance and the long-term evolution of parasite populations in response to these control measures. Whereas we have some evidence for the role of specificity between host and pathogen genotypes in viral and bacterial infections, its role in macroparasitic infections is seldom considered. The first empirical test of this specificity for a vertebrate–nematode system is provided here using clonal lines of parasite and inbred and congenic strains of rat that differ either across the genome or only at the major histocompatibility complex. Although significant differences between the resistance of host genotypes to infection and between the fitness of different parasite genotypes are found, there is no evidence for an interaction between host and parasite genotypes. It is concluded that a specificity between host and parasite genotypes is unlikely in this system.     

Strongyloides ratti: chemotactic responses of third-stage larvae to selected serum proteins and albumins

Experiments were carried out in vitro to investigate whether the sera of several animals as well as albumins and peptides might act as attractants for larvae of Strongyloides ratti. Samples of sera from several mammal species were dialysed and the aliquots were further centrifuged using ultrafiltration cartridges to remove any remaining small molecules. Additional test substances included commercially obtained ovalbumin, rat and bovine serum albumins, polypeptides such as peptone, tryptone and tryptose, amino nitrogens, monosaccharides, and reduced glutathione (triaminopeptide). Larvae were strongly attracted to the dialysed mammalian sera, which mainly consisted of serum albumin and globulins. Ov- and serum albumins, and polypeptides also acted as attractants. On the other hand, reduced glutathione, 16 kinds of amino acids and four kinds of monosaccharides did not attract this nematode.