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PubMed2004

Infective larvae of the human hookworms Necator americanus and Ancylostoma duodenale differ in their orientation behaviour when crawling on surfaces.

The infective third stage larvae of hookworms infect their hosts by active skin invasion, and they find and recognize their hosts by the behavioural phases of activation, directed crawling, and penetration. Here we analyse the orientation of the infective larvae of the human hookworms Necator americanus and Ancylostoma duodenale when crawling on surfaces. Their behaviour differed from that of the larvae of the dog hookworm Ancylostoma caninum, but the two species also differed from each other. N. americanus crawled towards light, but A. duodenale did not. Both species migrated towards the warm ends of thermal gradients, and this response was more sensitive than in other skin-invading helminths (threshold 0.09 degrees C/cm). However, A. duodenale turned back and accumulated at higher temperatures than N. americanus [turn-back 45.7 (44.5-49.9) vs 41.5 (38.5-43.9) degrees C; accumulation 43.6 (41.6-46.0) vs 39.5 (37.9-43.0) degrees C]. In contrast to other skin-invading helminths, both species showed no chemo-orientation towards skin compounds when crawling on surfaces. This behaviour may reflect adaptations for reaching the skin surface from hairs or adhering material, but the differences in the orientation of the two species could not be attributed to differing transmission strategies.

Ancylostoma↗
PubMed2004

Behavioural strategies used by the hookworms Necator americanus and Ancylostoma duodenale to find, recognize and invade the human host.

The infective third-stage larvae of the hookworms Necator americanus and Ancylostoma duodenale infect their human hosts by active skin invasion, but A. duodenale is in addition capable of oral infection. The behaviour of the larvae when crawling on surfaces has already been described. Here we analyse in various in vitro systems the other behavioural invasion phases: activation, penetration, and orientation within the host. The larvae normally remained in a motionless, energy-saving, resting posture. An activation to sinusoidal locomotion was stimulated in both species by similar cues such as touch, vibration, water currents, heat, light, and chemicals. Human breath in addition stimulated searching and waving ("nictating") behaviour, which facilitates a change-over to the host. Activating cues in air streams were warmth and moisture; CO2 activated only in combination with warmth and/or moisture. Penetration behaviour in both species was stimulated by warmth and skin extracts. The stimulating components of skin extracts were fatty acids, but their stimulating characteristics differed from those inducing schistosome cercarial skin penetration. After penetration into agar substrates, both species showed thermo-orientation, but only A. duodenale followed gradients of serum. The directing serum cues were not amino acids and glucose (the supposed cues for schistosome blood vessel localization), but Ringer's solution attracted the larvae. The host-finding and host-invasion behaviour of both hookworm species is well adapted to the invasion of the human skin, and there seems to be no particular adaptation of A. duodenale behaviour to the oral infection mode. Hookworm host-finding behaviour is not as complex as that of schistosome cercariae but seems well adapted to the ecological conditions in the transmission sites.

Ancylostoma↗
PubMed2001

Parasite-specific antibody and cellular immune responses in human infected with Necator americanus and Oesophagostomum bifurcum.

In this study parasite-specific antibody, cellular reactivity and Thl-type or Th2-type cytokine responses were investigated in humans concurrently infected with Necator americanus and Oesophagostomum bifurcum. The prospects for O. bifurcum-specific serodiagnosis based on IgG4 and IgE were evaluated. IgG4 showed low specificity for O. bifurcum due to antigen cross-reactivity with N. americanus, while IgE specifically distinguished between hookworm and O. bifurcum, and, in doubly infected patients, levels of O. bifurcum-specific as well as N. americanus-specific IgE were significantly elevated compared to those with N. americanus mono-infections. Cellular immunity was not strictly dominated by a Thl- or Th2- type reactivity. In co-infected patients cellular unresponsiveness to parasite antigens was observed, while cellular production of tumour necrosis factor alpha (TNF-alpha) and gamma-interferon (IFN-gamma) was greater in those doubly infected. Th2-type cytokines (interleukin-5 and interleukin-10) were produced in equal amounts by peripheral blood mononuclear cells from individuals with mono- and coinfections. Such mixed Thl-type and Th2-type immune responsiveness associated with persisting gastrointestinal parasitic nematodes may reflect a state of infection at which parasite-induced inflammatory and enteropathogenic responses co-exist, and furthermore, helminth coinfection will not only suppress parasite-specific cellular responsiveness but may also direct cytokine production towards a "permissive Th1-type cytokine profile" that favours parasite persistence.

Adolescent↗
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↗
PubMed1993

Sensitivity to ivermectin and pyrantel of Ancylostoma ceylanicum and Necator americanus.

Experiments were carried out in the hamster to compare the relative susceptibility of Necator americanus and Ancylostoma ceylanicum to treatment with ivermectin. A. ceylanicum was found to be 300 times more sensitive to the anthelmintic with a 50% effective dose (ED50) of the order of 10-15 micrograms kg-1 body weight whilst that for N. americanus approximated to 3-5 mg kg-1. Furthermore, whereas complete clearance of A. ceylanicum was observed with a dose of 100 micrograms kg-1, N. americanus was not totally removed after treatment with 25 mg kg-1, the highest dose tested. Both parasites proved equally sensitive to pyrantel with an ED50 of 1-12 mg kg-1 for A. ceylanicum and 5-25 mg kg-1 for N. americanus. Treatment with pyrantel at 100 mg kg-1 completely eliminated worms of both species and doses of 25-50 mg kg-1 were > 90% effective. In addition to worm burdens, changes in host weight and PCV were also recorded and it was shown that both parameters could be used to evaluate the success/failure of treatment.

Ancylostoma↗
PubMed1995

In vitro studies on the relative sensitivity to ivermectin of Necator americanus and Ancylostoma ceylanicum.

Experiments were carried out to compare the sensitivity of Ancylostoma ceylanicum and Necator americanus to ivermectin (IVM) and pyrantel in vitro. Loss of motility and inhibition of ingestion by IVM were compared and A. ceylanicum was found to be approximately 40-50 times more sensitive to IVM than N. americanus. Both species showed a similar sensitivity to pyrantel. Uptake of [3H]IVM across the cuticle was compared and shown to be unlikely to account for the differences in sensitivity to IVM between the two species.

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↗
PubMed2004

Comparison of mitochondrial cytochrome oxidase 1 DNA sequences from Necator americanus hookworms maintained for 100 generations in golden hamsters (Mesocricetus auratus) and hookworms from natural human infections.

The human hookworm Necator americanus was maintained through one hundred generations in the golden hamsters. The strain is now routinely maintained in laboratory hamsters through serial passage, and is the laboratory strain of choice for vaccine studies. Comparison of the mitochondrial cytochrome oxidase 1 (cox-1) sequences was shown previously to be useful for comparing the genetic structure of populations of N. americanus in China. Cytochrome oxidase 1 genes were amplified by the polymerase chain reaction, and the sequences compared to those of N. americanus recovered from infected humans from several regions in China. Sequence comparison revealed little difference between the laboratory strain and the field isolates at the cox-1 locus, but also indicated that the laboratory strain is represented by a single cox-1 haplotype. These results suggest that the laboratory strain of N. americanus has undergone a severe genetic bottleneck, and that the genetic diversity in other genes, including potential vaccine antigens, could be similarly limited.

Animals↗
PubMedDate not supplied

Necator americanus: maintenance through one hundred generations in golden hamsters (Mesocricetus auratus). II. Morphological development of the adult and its comparison with humans.

Through 100 passages, the human hookworm Necator americanus was adapted to the golden hamster, Mesocricetus auratus, without either the requirement for exogenous steroids or other immunosuppressive agents, nor the requirement to infect hamsters as pups. Adult N. americanus recovered from infected hamsters were morphologically similar to those from infected humans in Sichuan Province, China, although they were smaller and the females produced fewer eggs. The natural history and kinetics of N. americanus infection was different in female and male hamsters. Female hamsters supported low intensity infections that lasted for approximately two months. In contrast, the peak intensity of infection in male hamsters was high, but this situation lasted less than for 4 weeks at which time many of the hookworms were expelled. However, even after the major parasite expulsion, the total number of hookworms consistently remained higher in chronically infected male hamsters compared with female hamsters. The hamster model of N. americanus is potentially useful for studying the development of new anthelminthic drugs and vaccines.

Animals↗
PubMed2005

Necator americanus: optimization of the golden hamster model for testing anthelmintic drugs.

Laboratory golden hamsters (Mesocricetus auratus) were infected with Necator americanus under several different parasite and host conditions to optimize the model for testing anthelminthic drugs. The results confirmed that male hamsters were more susceptible to infection than females. Host age in the range of 5-15 weeks was not a factor that impacted on adult worm burden, and similar worm burdens were achieved using doses of 150, 250 or 500 N. americanus L3 (NaL3). The largest numbers of adult hookworms were recovered on days 21-28 post-infection, with a significant decrease at days 40-50 post-infection. Therefore adult worm recovery is maximal approximately 11-18 days prior to patency and host blood loss. From these studies a drug evaluation protocol was developed using 150 NaL3 as the infectious dose and then evaluating the anthelminthic effects of the drugs albendazole, tribendimidine, and pyrantel pamoate on days 21-28 post-infection. The model confirms the anthelminthic activity of albendazole, tribendimidine, and pyrantel pamoate and has the potential as a laboratory animal model to detect emerging drug resistance.

Age Factors↗