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At least 19 recordsLinked to original sources
PubMed1990

The survivability of the ectoparasitic flagellate Ichthyobodo necator on chum salmon fry (Oncorhynchus keta) in seawater and comparison to Ichthyobodo sp. on Japanese flounder (Paralichthys olivaceus).

Experimental studies revealed that a freshwater ectoparasitic flagellate Ichthyobodo necator (Henneguy, 1883) could survive and reproduce in seawater after infected chum salmon fry, Oncorhynchus keta (Walbaum), were transferred directly from fresh water to 33% seawater. Minor morphological changes (slight reduction in body width, loss of twistlike wrinkles on body surface, and reduction in contractile vacuoles) were observed in the attached form of I. necator following transfer to seawater. The field survey also confirmed that I. necator occurs on chum salmon fry in seawater estuaries (salinity 17-34%) and in freshwater habitats. It was assumed that I. necator acquired salinity tolerance as a result of adapting to the migratory behavior of its anadromous host. Two morphologically similar bodonids, I. necator from chum salmon and Ichthyobodo sp. from marine Japanese flounder, Paralichthys olivaceus (Temminck and Schlegel), were differentiated by cross-infection experiments. Thus, the parasite from marine flounder should be regarded as a separate species from I. necator.

Animals↗
PubMed1992

Skin penetration by ensheathed third-stage infective larvae of Necator americanus, and the host's immune response to larval antigens.

In vitro experiments were conducted to assess skin penetration by ensheathed third-stage infective larvae (L3) of Necator americanus. The fact that only a small proportion of larval sheaths was recoverable from the outer skin surface suggested that some larvae penetrate mouse skin without undergoing exsheathment. Penetration by ensheathed larvae was confirmed visually using a novel fluorescein isothiocyanate (FITC)-labelling technique in which viable ensheathed larvae were fluoresceinated, applied onto intact mouse skin, and their progress monitored in frozen skin sections. This direct observation that the L2-derived sheath can present antigens to the host's immune system was also monitored by immunoassay to provide confirmatory information regarding skin penetration by ensheathed larvae. Sera from humans infected with Necator americanus were shown to react in ELISA against antigens stripped by detergent (cetyltrimethylammonium bromide) from the sheath surface, and with antigens contained in L3-exsheathing fluid. These data suggest that the host's immune response, as a result of antigenic stimulation by the cast sheath and exsheathing fluid, could in fact be diverted away from the potentially vulnerable L3 stage.

Animals↗
PubMed2026

Identification of genetic determinants that promote biofilm growth under heterotrophic conditions in Cupriavidus necator using transposon enrichment.

Cupriavidus necator is a metabolically versatile β-proteobacterium of growing interest for auto- and heterotrophic bioprocesses, yet the genetic determinants governing its biofilm formation remain largely uncharacterized, particularly under process-relevant heterotrophic conditions. Here, we applied a forward-genetics transposon-enrichment approach to identify loci which promote surface-associated growth. A high-density mini-Tn5 mutant library (26,185 insertion clones, exceeding the >17,000 required for genome-wide coverage) was cultivated as a biofilm in a microfluidic flow-cell system on fructose for 168 h, and the surface-associated community was characterized by deep sequencing. Twelve genes showed significantly elevated insertion frequencies, several with documented links to biofilm formation in other bacteria, including the ferrous-iron uptake system (feoA/feoB), galU, and a GSDEF/EAL dual-domain protein. The gene B2043 (E6A55_RS29530), encoding this c-di-GMP-metabolizing protein, was selected for validation by markerless deletion. Under static conditions, the ΔB2043 mutant showed a 1.69 ± 0.06-fold increase in biofilm-associated biomass (p = 5.16 × 10-15). Under flow-through conditions, the mutant attached faster, entered exponential growth ∼10 h earlier, reached its biovolume plateau ∼16 h earlier than the wild-type, and formed distinct tower-like structures. These results identify B2043 as a negative regulator of biofilm formation acting predominantly during attachment, provide the first experimental evidence for c-di-GMP-dependent biofilm regulation in C. necator H16, and establish a functional-genomics framework - together with eleven further candidate loci - for engineering productive biofilms in this organism.

Biofilm formation↗
PubMed1990

Epidemiology and immunology of Necator americanus infection in a community in Papua New Guinea: humoral responses to excretory-secretory and cuticular collagen antigens.

Baseline data from an immuno-epidemiological study of hookworm infection in a rural village in Madang Province, Papua New Guinea are reported. Necator americanus was found to be the commonest helminth infection, with a prevalence of near 100% and intensity of 40 worms per host in adults. Enterobius vermicularis, Ascaris lumbricoides and Trichuris trichiura were also present, at prevalences of 53, 10 and 3% respectively; Ancylostoma duodenale was absent. The frequency distribution of N. americanus was highly over-dispersed, and was well described by a negative binomial distribution with aggregation parameter, k, of 0.370. Intensity of infection was significantly related to host age, but did not differ between the sexes. Haemoglobin levels and haematocrit values were indicative of anaemia in the community, but were unrelated to hookworm infection. Levels of antibodies (IgG, IgA and IgM combined) against adult Necator cuticular collagen and excretory-secretory (ES) products were determined. Serum concentrations of the two types of antibody were significantly correlated with each other. Significant positive correlations were found between anti-ES antibody levels and hookworm egg production, and between anti-collagen antibody levels and host age. It is suggested that the level of anti-collagen antibodies may reflect cumulative exposure to infection, whereas levels of anti-ES antibodies may be more dependent on current worm burden. No evidence was found to suggest that either antibody response is important in regulating parasite population growth. Similarly, the presence of a positive correlation between eosinophil concentration and infection intensity in adults indicates that eosinophilia reflects, rather than determines, the host's worm burden.

Adolescent↗
PubMed1986

The recognition of antigens on the surface of adult and L4 Necator americanus by human and hamster post-infection sera.

The surface antigens of adult Necator americanus were recognized by post-infection hamster sera and resolved at molecular weight 93,000, 67,000, 46,000, 43,000, 32,000 and 25,000. L4 larvae in contrast had one major surface antigen, resolving at 93,000. These antigens were also recognized by a range of human sera, although on a differential basis. This suggests that the human sera tion. However, the results do indicate that the hamster model might be of immunological relevance to the human disease state, in that infected hamster recognized the full cuticular antigen spectrum of adult Necator. This, at least, gives the experimenter a convenient reference point from which to conduct further experiments incorporating parameters such as re-infection, anthelmintic treatment and genetic variability to study the effect of these modifications on the serological response.

Animals↗
PubMed1987

Antigen expression during development of the human hookworm, Necator americanus (Nematoda).

The accumulated and de novo synthesized antigens expressed by L3, L4 and adult Necator americanus, recognized by both the natural host, man, and the experimental host, the hamster, were identified by immunoblotting and immunoprecipitation analysis. Following infection of neonatal hamsters serum samples were taken on days 17, 35 and 117. Only serum taken 117 days after infection showed significant reactivity in immunoblotting experiments, recognizing adult epitopes of 30,000, 33,000, 48,000 and 69,000 mol. wt thereby suggesting that few accumulated antigens are shared between developmental stages. By contrast, immunoprecipitation analysis of metabolically labelled proteins suggested that L3 and in particular L4 larvae synthesize some antigens which comigrate with those synthesized and accumulated by adult worms. In addition, L4 larvae synthesize a 41,000 mol. wt excretory/secretory (ES) stage specific antigen. Parallel experiments using serum samples from infected humans, demonstrated that hamsters and man recognize many antigens of identical molecular weight. Notable in this respect are accumulated adult antigens of 30,000, 33,000, 48,000 and 69,000 and de novo synthesized antigens of 30,000, 33,000, 44,000, 46,000 and 69,000 mol. wt. Some individual human sera mainly recognized L3 antigens of 47,000-69,000 mol. wt in immunoblotting experiments whilst others simultaneously recognized adult epitopes. This differential recognition of developmental stages by individual human sera suggests that genetic or epidemiological factors are operative and warrants further study. Overall, these studies confirm the pronounced immunogenicity of Necator americanus in both man and an animal model and pave the way for analysis of the relevance of these antigens to field situations.

Animals↗
PubMed1975

The topographic distribution of Necator americanus and Ancylostoma duodenale in the human intestine.

During an investigation in Dar es Salaam, Tanzania, 28 human intestinal tracts were systematically inspected on the presence of hookworms. In total, 643 hookworms (508 Necator americanus and 135 Ancylostoma duodenale) were isolated from 19 intestinal tracts. The localization of these hookworms was determined. N. americanus worms were concentrated in the duodenum and jejunum, whereas A. duodenale worms rather prefer the jejunum and proximal ileum. Some preference of hookworms for the antimesenteric site of the intestinal wall was found. The relative distance between adjoining worms in the observed hookworm populations was 3.8 cm on the average for Necator and 5.5 cm for Ancylostoma. The distribution of the sexes in the worm-population revealed no monosexual or bisexual prevalence of the hookworms.

Ancylostoma↗
PubMed1990

Radiolabeling of Necator americanus third stage larvae with 75Se-methionine.

Third stage larvae of Necator americanus were radiolabeled with 75Se-methionine by two methods. Larvae labeled in aqueous cultures contained 188 and 25 cpm per sheathed and ex-sheathed larva, respectively. Larvae labeled in coproculture incorporated 25 and 18 cpm per sheathed and ex-sheathed larva, respectively. All of the label was decayed in 5 days from larvae labeled in aqueous cultures, whereas appreciable amounts of radioactivity were still detectable at day 7 of chase period in coproculture labeled larvae.

Animals↗
PubMed1987

Necator americanus: temperature, pH, light, and larval development, longevity, and desiccation tolerance.

The effect of incubation temperature and pH on the hatch rate of eggs of Necator americanus, and the desiccation tolerance of the resulting infective stage-3 larvae were investigated in the laboratory under controlled conditions. Hatching did not occur below 15 C and above 35 C. A 21% hatch rate was obtained at 15 C while a 10.6% hatch rate was obtained at 35 C. The highest hatch rate (93.7%) was obtained at 30 C. The optimum pH for hatching was 6.0, but the larvae did not reach the infective stage. Incubation temperature of the eggs affected the longevity and desiccation tolerance of resultant infective larvae. Larvae hatched at 30 C and maintained at 26 C under bright fluorescent light had a 50% survival time (S50) of 4 days. In the dark or shade, the S50 for larvae raised at 30 C was 5 weeks, while that of larvae hatched at 20 C was 7 weeks. Incubation temperature also affected the desiccation tolerance of larvae. Larvae developed at 20 C were more resistant to desiccation at various relative humidity values than larvae hatched at 30 C.

Animals↗
PubMed1992

The partial characterization of proteases present in the excretory/secretory products and exsheathing fluid of the infective (L3) larva of Necator americanus.

Following the observation that live third-stage larvae (L3) could digest gelatin in vitro, gelatinolytic protease activity has been demonstrated at pH 8.5, in both exsheathing fluid (EF) and excretory/secretory (ES) products of infective L3 of Necator americanus. EF resolved as a single band of proteolytic activity, with a mol. wt of 116 kDa, while L3 ES products exhibited multiple bands of proteolysis, at 219, 200, 195, 166, 137, 92, 72 and 62 kDa; weak bands were detectable at 92 and 72 kDa. The EF protease was characterized as cysteine, whereas ES apparently possessed one serine (195 kDa) and seven (219, 200, 166, 137, 92, 72 and 62 kDa) cysteine protease bands and a combination of metallo- and cysteine proteases of approximately the same mol. wts (62, 137 and 219 kDa). Though EF was not able to cleave immunoglobulins, ES was shown to cleave IgG, IgA and IgM, but not IgD or IgE. The activity appeared to be directed toward the Fc portion of the molecule, and was inhibited by PMSF, which is indicative of serine protease activity. The significance of the presence of such apparently diverse proteases in larval products is discussed.

Animals↗
PubMed1992

Metabolism of lipid peroxidation products by the gastro-intestinal nematodes Necator americanus, Ancylostoma ceylanicum and Heligmosomoides polygyrus.

Somatic extracts of the three parasitic nematodes Necator americanus, Ancylostoma ceylanicum and Heligmosomoides polygyrus were able to detoxify a model hydroperoxide and a putative natural peroxide by glutathione-dependent peroxidase activity while cytotoxic carbonyls could be metabolized by NADPH-linked reduction activities. Unlike cestodes and digeneans, the nematodes in this study could not enzymatically conjugate carbonyls with glutathione. The results indicate that the three nematodes can protect themselves against possible host-immune initiated lipid peroxidation of their membranes at the level of the hydroperoxide and at the level of cytotoxic carbonyl, although other protective enzymatic mechanisms are also likely to exist (superoxide dismutase and catalase).

Ancylostoma↗
PubMed1978

Antibody responses in self-infections with Necator americanus.

Antibody responses were measured in a volunteer infected four times with Necator americanus over a 27-month period. The main source of antigen was culture fluid in which living adult N. americanus had been maintained for several days. Antibodies to worm acetylcholinesterase and IgE antibodies were detected only with this material, but antibodies were identified by the enzyme-linked immunosorbent (ELISA) assay, with either adult worm secretions or extracts of third-stage infective larvae. The total serum IgE level fell after the first infection, but although it then increased during subsequent infections, it never rose above 600 U per ml. None of the antibody responses suppressed the rat of worm development to maturity, or reduced the fecundity of the parasites. However, it is suggested that the development of the immune response may be associated with the waning of the severe gastro-intestinal symptoms which were experienced in this infection, and which are frequently characteristic of hookworm infections.

Acetylcholinesterase↗
PubMed1986

The growth and migration of Necator americanus following infection of neonatal hamsters.

Necator americanus was studied in neonatally infected hamsters in order to determine precisely the growth and migration of the parasite in this laboratory host. Most larvae stayed at the skin infection site for at least 48 hours following administration of larvae and the movement to the lungs commenced on day 3. There was no significant growth at the skin site or during the first two days in the lungs. 98% of the larvae were recovered from the lungs by day 6 and showed signs of some growth and development. Moulting larvae were seen in the lungs on days 7 and 8, but intestinal worms, which were first detected on day 7, were all L4 larvae. These worms were significantly longer than the lung stages and henceforth grew rapidly. Over 80% of the worms were recovered from the intestine on day 9, only small numbers of larvae persisting in the lungs until day 12. Moulting worms were observed in the intestine on days 17 to 21, after which growth continued and did not slow until about the fifth week. Small quantities of eggs were occasionally detected as early as day 34 and continuous egg production commenced in the seventh week of infection reaching a peak by about the 10th week.

Animals↗
PubMed1987

Necator americanus in neonatally infected hamsters. The time-course of infection and antibody response to the surface antigens of L4 and adult worms.

Neonatal hamsters were infected with a hamster-adapted strain of Necator americanus, and the time-course of infection was followed by worm and faecal egg counts. Parasite eggs were first recorded during the 6th week of infection, increasing rapidly thereafter to peak in weeks 7-10. Male hamsters excreted more eggs than females, but both sexes were equally susceptible to infection and harboured comparable worm burdens. Faecal egg counts declined from week 10 onwards and this was associated with a loss of worms from animals with heavy infections. Low level infections were stable over the first 114 d of infection but worm fecundity nevertheless still declined over this period. Both hamster sexes responded similarly to surface antigens on adult worms, the antibody levels rising from week 5 onwards to reach a plateau in weeks 6-7, which persisted until the experiments were terminated. The major antigens recognised on the surface of adult worms had molecular masses corresponding to 25 kDa, 32 kDa, a doublet with the heaviest polypeptide resolving at 46 kDa, and a triplet with the heaviest at 67 and 93kDa. In contrast L4 had only 2 major cuticular antigens resolving at 41 and 93kDa. The 93kDa molecule on L4 and adult worms may be antigenically related.

Animals↗
PubMedDate not supplied

Antigenic cross-reactivity between Necator americanus and Ascaris lumbricoides in a community in Papua New Guinea infected predominantly with hookworm.

Sero-epidemiological data are presented in which antigenic cross-reactivity between Necator americanus and Ascaris lumbricoides has been investigated in a community in Papua New Guinea infected predominantly with N. americanus. It is our contention that the antigenic cross-reactivity which undoubtedly exists between these species accounted for (i) a peak in antibody levels against N. americanus in 10-13 years old children (driven by infection with A. lumbricoides), and (ii) the maintenance of apparent antibody levels against A. lumbricoides in older age groups (driven by infection with N. americanus in the absence of overt infection with A. lumbricoides). Cross-reactivity was analysed further, and apparently N. americanus-specific epitopes identified, by immunoblotting. These observations could have considerable bearing on the interpretation of data from sero-epidemiological studies which failed to take account of concurrent infection with these parasites.

Adolescent↗
PubMedDate not supplied

The epidemiology and population biology of Necator americanus infection in a rural community in Zimbabwe.

Baseline data from an epidemiological study of hookworm infection in a rural community in Zimbabwe are presented. The infection status of an age-stratified sample of the community was assessed using anthelmintic expulsion techniques. Necator americanus was the only helminth parasite found to be present. The age-prevalence and intensity profiles rose asymptotically to an adult prevalence of about 80% and adult mean burden of 7.7 worms per host. The overall mean burden was 4.8 worms per host. The frequency distribution of N. americanus was overdispersed and well described by the negative binomial distribution with a value for the aggregation parameter, k, of 0.346. Separate estimates of k were lower in males and older hosts. The distribution patterns were difficult to reconcile with any simple process of age-dependent acquisition of an effective immune response. A significant negative correlation was recorded between per caput fecundity and worm burden, providing evidence for a density-dependent regulation of female worm fecundity. The basic reproductive rate (R0 congruent to 2) was found to be similar to estimates from other geographical areas.

Adolescent↗
PubMed1986

Identification of hookworm (Necator americanus) antigens and their translation in vitro.

During in vitro culture adult (day 35) Necator americanus synthesise a wide range of protein species many of which are excreted or secreted into the culture medium. Both post infection (day 117) hamster sera and sera from infected humans precipitate antigens of 15, 30, 33, 44, 46 and 69 kDa although individual human sera exhibit some variability in absolute specificity. In immunoblotting experiments antigens of 33 kDa are routinely recognised by human sera although two-dimensional gel analysis suggests that more than one polypeptide is involved. RNA isolated from adult worms direct the in vitro synthesis of numerous polypeptides possessing antigenic determinants recognised by sera from infected hamsters and humans. Post-translational modification of N. americanus encoded polypeptides is not, therefore, a prerequisite for antigenicity.

Animals↗
PubMed1988

Cuticle preparations from Necator americanus and their immunogenicity in the infected host.

Cuticle samples have been prepared from the human parasitic nematode Necator americanus using detergent solubilisation with sodium dodecyl sulphate and subsequent reduction of disulphide bonds using 2-beta-mercaptoethanol. It would appear that N. americanus, like many other nematodes, relies on relatively small collagenous proteins, linked by disulphide bonds, to maintain the integrity of its cuticle. These molecules are normally hidden from the immune system during the course of infection but are potentially immunogenic. It is suggested that waves of antibodies, firstly with specificity against superficial cuticular epitopes followed by antibodies against deeper lying, structural elements, should be induced during vaccination to effectively destroy the nematode at the cuticular level.

Animals↗