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PubMed1999

Necator americanus (human hookworm) aspartyl proteinases and digestion of skin macromolecules during skin penetration.

The infective larvae of Necator americanus were shown to secrete all mechanistic classes of proteolytic enzymes with two overall pH optima of 6.5 and 8.5 using fluorescein isothiocyanate-labeled casein as the substrate. Since infective larvae are obligate skin penetrators, the effect of each of these enzyme classes against macromolecules derived from human skin was examined. Larval secretions were shown to degrade collagen types I, III, IV, and V, fibronectin, laminin, and elastin. All the skin macromolecules tested were hydrolyzed by aspartyl proteinase activity, which was inhibitable by pepstatin A. Collagen and elastin was also hydrolyzed by metalloproteinase activity, while the serine proteinase activity hydrolyzed only elastin. As a consequence of these experiments, the effect of proteinase inhibitors on the penetration of live larvae through hamster skin was tested. Larval penetration was significantly inhibited only by pepstatin A, confirming the importance of the aspartyl proteinase activity during the skin penetration process.

Animals↗
PubMed2002

Influence of parasitic life style on the patterns of codon usage and base frequencies of Ancylostoma and Necator species.

Parametric analyses were used to investigate the nucleotide, codon, and amino acid composition of coding sequences corresponding to hook-worms. Ancylostoma caninum and Necator americanus. Although genomic research has become prevalent within the scientific community, few studies have dealt directly with parasitic species. Parasites have existed throughout the history of mankind due to their wide range of distribution in nature and their ability to evade immune detection. An AT nucleotide bias was identified in both A. caninum and N. americanus sequences. A similar AT bias was also identified in both datasets when considering relative synonymous codon usage. However, the codon bias was much more pronounced in N. americanus as compared to A. caninum. Bias was also present at the amino acid level, and appeared to be partially independent of the nucleotide-based biases. Analysis of parasite genomes will facilitate the development of vaccines against larval forms of parasites. Moreover, the examination of the parasite genes in general, will allow for a more in-depth understanding of the evolution of the parasites and parasitism.

Ancylostoma↗
PubMed1992

Secretion of metalloproteases by living infective larvae of Necator americanus.

Fresh living third-stage larvae of Necator americanus released a significant amount of label within 2 hr of their incubation on 125I-labeled gelatin-coated polystyrene plastic plates. This protease activity was primarily susceptible to o-phenanthroline, which identifies the activity as predominantly metalloprotease.

Animals↗
PubMed2003

[Polymorphism analysis of cytochrome C oxidase 1 (COI) gene in Necator americanus collected from 5 provinces in China].

OBJECTIVE: To detect and compare the COI gene sequences of Necator americanus collected from the provinces of Sichuan, Hainan, Yunnan, Hubei and Jiangsu, and to analyze the genetic diversity of the geographic isolates. METHODS: COI genes of N. americanus were amplified from the genomic DNA by PCR and sequenced. RESULTS: The COI gene sequences of N. americanus from five provinces were 97%-99% identical over 595 bp, and base variation occurred in 19 nucleotide sites in which the transition was more frequent than the transversion. The difference between the sequences ranged from 1.34% to 2.18%. CONCLUSION: The COI gene sequences show high identity among the geographic isolates of N. americanus with some difference at specific nucleotide sites.

Animals↗
PubMed2006

Dose-ranging study for trials of therapeutic infection with Necator americanus in humans.

Epidemiological studies suggest that a hookworm infection producing 50 eggs/gram of feces may protect against asthma. We conducted a dose-ranging study to identify the dose of hookworm larvae necessary to achieve 50 eggs/gram of feces for therapeutic trials of asthma. Ten healthy subjects without asthma or airway hyperresponsiveness to inhaled methacholine received 10, 25, 50, or 100 Necator americanus larvae administered double blind to an area of skin on the arm. Subjects were seen weekly for 12 weeks and were then treated with mebendazole. Skin itching at the entry site and gastrointestinal symptoms were common at higher doses. Lung function did not change. Levels of blood eosinophils and IgE increased transiently, and levels of IgG increased progressively. All doses resulted in at least 50 eggs/gram of feces in the eight subjects who completed the study. Infection with 10 N. americanus larvae is well tolerated, elicits a modest host eosinophil response, and is potentially suitable for use in preliminary clinical therapeutic trials.

Adult↗
PubMed1989

Effect of single-dose albendazole and single-dose mebendazole on Necator americanus.

One hundred two children (43 males and 59 females) aged 6 to 14 years with positive stool examination by Kato-Katz and/or Harada-Mori culture techniques for N. americanus, were randomly divided into two groups. Group I with 48 children were treated with a single dose albendazole, 400 mg. Group II, 54 children, received a single dose mebendazole, 600 mg. After treatment, repeated stool examination was performed on Day 14, Day 21 and Day 28. The children were considered cured when stool examination was negative on all three occasions by both methods. The cure rate was 64% in Group I and 11% in Group II. The difference was statistically significant (p less than 0.05). The eggs reduction rate was 98% in Group I and 95% in Group II. Mild and transient side effects such as nausea, dizziness and headache were observed in both groups. Albendazole, 400 mg, as a single dose treatment was shown to be superior to mebendazole, 600 mg, single dose for the mass treatment of hookworm infection, especially that of Necator americanus, in an endemic area.

Adolescent↗
PubMed1989

[Light and electron microscopic observations on effects of tribendimidin on cuticle of Necator americanus and small intestinal mucosa of infected golden hamsters].

Golden hamsters infected with Necator americanus were treated orally with a new anthilmintic tribendimidin (N, N'-[bis-4'-(1-dimethyl amino ethylidene amino)phenyl] 1,4-phenyene dimethylidyne amine) at a single dose of 150 mg/kg. One h after medication, some worms showed cuticular swelling, fusion of transverse striations and attachment of host leucocytes onto the worm's damaged cuticular surface. Four h post treatment, the cuticle revealed a moderate swelling or even erosion. Meanwhile, the ventral cutting plates appeared to be swollen. After 8-24 h, severe cuticular swelling, erosion and peeling in female worm tails and male copulatory bursa were seen. No increases in lesions in the small intestinal mucosa of infected golden hamsters were observed 4-8 h after medication.

Animals↗
PubMed1985

Necator americanus and Ancylostoma ceylanicum: development of protocols for dual infection in hamsters.

Two-day-old baby hamsters were infected initially with the infective larvae of hamster-adapted human hookworm, Necator americanus (NaL3). After a specified period they were again infected orally with infective larvae of Ancylostoma ceylanicum (AcL3). Three weeks after the second infection they were killed and the establishment of N. americanus and A. ceylanicum was assessed. The effect of different infection levels and exposure period of N. americanus on the concurrent establishment of A. ceylanicum was also examined. An infection with 50 NaL3 percutaneously, and 3 weeks later, a second infection with 50 AcL3 orally has produced reasonably equal number of hookworms (no statistical difference in the burden of N. americanus and A. ceylanicum) in the intestine of hamsters. Thus this protocol of dual infection was found suitable to develop two species of hookworms in hamsters for anthelmintic screening.

Ancylostoma↗
PubMed1985

Site of resistance to Necator americanus in hamsters.

Resistance to the development of human hookworm, Necator americanus was examined in 3- to 6-week-old young adult hamsters. Only 3% of N. americanus infective third stage larvae (NaL3) reached maturity in the intestines of young adults as opposed to as many as 60% in 2-day-old baby hamsters. This seemingly effective resistance prevailing in young adults was investigated in some detail. The skin, the first site of contact for the invading NaL3, was bypassed during the infection process. Completely in vitro exsheathed NaL3 (ExNaL3) were used, and young adult hamsters were infected parenterally, by-passing the skin. Even after exsheathing the larvae artificially before infection and by-passing the skin, no improvement was seen in the development of N. americanus in the intestines of young adults. Higher infection doses also did not increase the worm burden. Some of the factors limiting the development of parasites in young adults were examined. N. americanus were monitored in lungs and intestines during various intervals after infection. Similar parasite burdens were apparent in lungs of baby as well as young adult hamsters. In the intestines, a significantly lower burden of N. americanus was seen during various intervals in young adults compared to the baby hamsters. Moreover, N. americanus were expelled soon after reaching the intestine. This comparative monitoring revealed the intestine as the seat of resistance against the establishment of N. americanus in young adult hamsters.

Age Factors↗
PubMed1987

The response of adult and free-living stages of Necator americanus, in vitro, to anthelmintics.

The in vitro response of adults (males and females) and free-living stages of Necator americanus one of the human hookworms, to a wide variety of 20 broad and narrow spectrum anthelmintics was tested. Almost all the broad spectrum anthelmintics influenced males, females and free-living stages at different levels and showed good activity with EC50 values varying from about 0.0002 and 0.0007 mg/l for pyrantel pamoate and tricofenol piperazine respectively to about 8.47 and 7.6 mg/l for morantel tartrate and amoscanate respectively. Certain drugs (emetine, praziquantel and suramin) exerted their effect either on male or female or free-living stages at 10.0 mg/l level. It is concluded that either sex or life-cycle stage alone may not be an effective criteria for screening of anthelmintics which have been employed at large; and females of nematodes (in particular those of N. americanus) should be taken into account for proposing EC50 as they were found to require relatively highest EC50 level in almost all the instances studied presently.

Animals↗
PubMed1987

Adherence of human eosinophils to infective filariform larvae of Necator americanus in vitro.

Eosinophilia is common in hookworm infection but the interaction between eosinophils and the larval stage of the parasite is poorly understood. The present study was conducted to test the ability of the eosinophils to adhere to infective filariform larvae of Necator americanus in vitro. Adherence of eosinophils to the larvae was found to be serum dependent. Antibody facilitated eosinophil adherence but this was maximal in the presence of complement. The adherence was greatly diminished by EGTA treated normal human serum (NHS) and was completely abolished when NHS was treated with either EDTA or heat-inactivation, suggesting that the process can be facilitated through complement activation via the alternative pathway. As with other nematodes, the surface of hookworm larvae appeared to be both antigenic and complement-activating. Although it is not known whether eosinophil adherence has any larvicidal effect, the present study demonstrated for the first time a definite interaction between human eosinophils and hookworm filariform larvae.

Animals↗
PubMed1972

Distribution of Necator americanus and Ancylostoma duodenale in Liberia.

In the first country-wide survey of hookworm infection in Liberia, diagnosis by test-tube filter-paper cultivation revealed a prevalence of more than 90%. This sensitive technique also permitted differential species determination. Necator americanus was found to occur in all regions and in a high proportion of the persons examined. Ancylostoma duodenale was mainly confined to a narrow coastal belt, and usually parasitized individuals harbouring N. americanus as well. The average number of eggs per gram of faeces (EPG) of infected individuals was lowest in the population of the hinterland. During the latter part of the studies a modified test-tube filter-paper cultivation technique was used in combination with dilution counting to obtain data on intensity of infection separately for the 2 species. For N. americanus there was little regional difference in the intensity of infection, but the EPG for A. duodenale was much higher in people living in the coastal area.

Adolescent↗
PubMedDate not supplied

[Necator americanus uncinariasis in an infant born and residing in Mexico City].

A six-month-old infant is reported with the unquestionable diagnosis diagnosis of Necator americanus uncinariasis. The mother was also infected with the same hookworm. The patient was born and has always dwelt in Mexico City, where helminthiasis is considered extremely rare. The epidemiologic studies determined that the dwelling conditions were inadequate for the transmittal of the agent through the soil. The authors emphasize the importance of the presumptive diagnosis in those cases suggesting the disease and to carry out studies to confirm the existence of other infectious means

Adult↗
PubMed1994

Effect of albendazole on the larvae and eggs of Necator americanus in golden hamster.

When golden hamsters infected with adult Necator americanus were treated ig with albendazole(Alb) 75 or 150 mg/kg, the efficacy rates were 83.8% and 100%, respectively. Three days before treatment, the mean numbers of larvae recorded from the incubation of feces from 2 treated groups were 29,716 +/- 3,299 and 28,256 +/- 118 per gram of feces, while in the control group, it was 8,828 +/- 2,659. Within 3 days after treatment, no larva was detected in the 2 treated groups, but in the control group the mean larva number was 9,066 +/- 7,416. Furthermore, in 2 treated groups none or only a few degenerated eggs could be found using saturated saline solution method. when infected golden hamsters were treated ig with Alb at a single dose of 150 or 300 mg/kg on day 3, 7 or 14 after infection with the third stage larvae, the egg positive rates in the feces were 0-9.1%, while the worm reduction rates were 96.8-100%.

Albendazole↗
PubMed1993

New observations on proteases of the human hookworm Necator americanus.

Two protease populations have been identified in the somatic products of adult Necator americanus. One population (158, 138, 34 and 31 kDa) loses, whereas the other population (107, 74, 51 and 20 kDa) retains, its proteolytic activity after elution from substrate gels. The present study warns that hookworm proteases may oligomerise and/or lose their activity under the conditions necessary for their purification. We suggest that following assessment of protease activity on substrate gels, the protease of interest should be eluted from plain gels; their isolation from substrate gels may lead to a reduced or no yield.

Animals↗
PubMed1996

Differentiation between the human hookworms Ancylostoma duodenale and Necator americanus using PCR-RFLP.

There are 2 major species of hookworms that infect humans. Ancylostoma duodenale and Necator americanus. Although traditionally considered to be identical for treatment purposes, there are significant life history differences between the species that must be considered for the rational design of chemotherapeutic and immunoprophylactic control strategies. However, identification of the species infecting a particular population has been problematic, as the eggs of the 2 species cannot be reliably differentiated by classical parasitological methods. A PCR-based technique for the differentiation of hookworm species that infect humans is reported. A fragment of the 3' untranslated region of the cAMP-dependent protein kinase catalytic subunit gene was amplified from A. duodenale and N. americanus genomic DNA using primers derived from the corresponding A. caninum cDNA. Digestion of the amplified DNA with the restriction enzymes HpaII, MboI, TaqI, and ThaI generated specific restriction fragment patterns unique to each species. The technique can distinguish between pure and mixtures of hookworm DNA and can amplify DNA from a single egg. The primers also amplify the fragment from the DNA of several other species of hookworms that infect humans and other animals. The technique is fast, simple, and hookworm specific and represents a considerable savings in time over current methods used for distinguishing between human hookworm infections.

Ancylostoma↗
PubMed1996

IgG4 responses to antigens of adult Necator americanus: potential for use in large-scale epidemiological studies.

Described is an epidemiological investigation of hookworm infections in a rural community in Zimbabwe, where Necator americanus is the only human helminth species present. Among a cohort of 120 individuals the overall prevalence of infection was 78%. Intensity of infection was quantified both as egg counts (range: 0-2563 eggs per g of stool) and worm burden (range: 0-100 worms). Although both these measures provide useful quantitative data, they are tedious to determine in large-scale epidemiological studies and may present social and logistic difficulties. As an alternative screening method, we therefore investigated isotype-specific responses to adult worm antigens of N. americanus. The results show that specific IgG4 responses correlate positively and significantly with both measures of intensity and may be a useful marker of hookworm infection.

Animals↗
PubMed1997

Characterization of Oesophagostomum bifurcum and Necator americanus by PCR-RFLP of rDNA.

Esophagostomiasis in humans due to infection with Oesophagostomum bifurcum (nodular worm) is of major human health significance in northern Togo and Ghana, where Necator americanus (human hookworm) also exists at high prevalence. Yet, very little is known about the transmission patterns of O. bifurcum, which is in part due to the difficulties in diagnosis and in differentiating some life-cycle stages of O. bifurcum from N. americanus using morphological features. As a first step toward developing a molecular-diagnostic assay, it was evaluated whether ribosomal (r)DNA could provide genetic markers for the identification of O. bifurcum and N. americanus to species. Internal transcribed spacer rDNA (plus flanking and intervening sequences) was analyzed by polymerase chain reaction-linked restriction fragment length polymorphism (PCR-RFLP) using several restriction endonucleases. The analysis showed that there was no detectable intraspecific difference in the size of the PCR products among multiple samples, that there was a consistent size difference in the products (of 110 bp or 350 bp, depending on region amplified) between the species, and that there was no significant variation in restriction patterns within each species. These results indicate that the rDNA spanning the internal transcribed spacers provides useful genetic markers for the identification of O. bifurcum and N. americanus to species, which has important implications for developing PCR-based tools to study the epidemiology and population biology of O. bifurcum.

Animals↗