Strongyloides

  

Contents

  

Rev 05/26/2023

  Classification Biology and Ecology
Morphology and Anatomy Life Cycle
Return to Strongyloides Menu Ecosystem Functions and Services
Distribution Management
Return to Strongyloididae Menu Feeding  References
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Classification:

Chromadorea

  Rhabditia

    Rhabditida

Tylenchina

      Strongyloidoidea

        Strongyloididae

       
Strongyloides Grassi, 1879
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Morphology and Anatomy:

A genus of animal-parasitic nematodes that, unusually, has a free-living adult generation.

The genus has around 50 species of obligate gastrointestinal parasites of vertebrates that infects mammals, birds, reptiles and amphibians. Most species have rather narrow host ranges and infect either one, or very few, host species (Speare, 1989)

 

Males:

Free-living Male:

  • Slightly smaller than female, up to 1.2 mm in length by 55 um wide, with shorter, broader tail ventrally curved when fixed.

  • Reproductive system single, straight. Testis blunt at beginning, shortly behind esophagus, ex tends to near middle of body.

  • Spicules equal, short, blade-like with laterally bent, knob-like anterior ends

  • Gubernaculum laterally com-pressed with short wing-like structures extending laterally from posterior half of dorsal edge.

  • Genital papillae consist of one unpaired medio-ventral preanal and six pairs as follows: one sub-ventral preanal, two subventral adanal, one lateral postanal, one subventral postanal, one subdorsal postanal

Female:

Free-living Female:

  • Body small, up to 1.5 mm long by 85 um wide, spindle-shaped.

  • Cuticle thin, cuticle with fine transverse striations.

  • Lateral chords broad, flat.

  • Head with two lateral cephalic lobes projecting beyond mouth, each bearing a small inconspicuous papilla in sub dorsal, lateral, and subventral positions.

  • Mouth dorsoventrally elongated; stoma subglobular, laterally compressed, with thickened posterior wall.

  • Collar-like cuticular structure (collaret) surrounds anterior part of stoma.

  •  Esophagus rhabditoid; a short muscular portion, set off from corpus by slight constriction, surrounds posterior part of stoma; muscles of corpus and bulbus coarser than those of isthmus.

  • In anterior portion of corpus, radii of esophageal lumen terminate distally in incomplete tube-like structures with thickened cuticular walls. These "tubes" arch distally and decrease in caliber as they extend posteriorly. Isthmus about one-half as long as corpus. Bulbus with well-developed valvular apparatus.

  • Intestine composed of 22 intestinal cells in two rows (dorsal and ventral), each with single nucleus.

  • Rectum short, compressed dorsoventrally. Anus subterminal, with small liplike swelling along posterior edge of transverse opening.

  • Phasmids lateral, near middle of gradually tapering, finely-pointed tail.

  • Reproductive system didelphic with opposed, equal uteri and reflected ovaries; anterior branch on right side of intestine, posterior branch on left. Vulva near middle of body; vagina very short; end of each uterus, at junction with oviduct, serving as seminal receptacle.

Parasitic Female:

  • Parthenogenetic, embedded in mucosal epithelium of gastrointestinal tract of host.

  • Slender, up to 6 mm in length by 75 um wide

  • Body wall thin, cuticle finely striated. Tail short, abruptly tapered.

  •  Head with circumoral elevation.

  •  Mouth dorsoventrally elongated, stoma shallow. Four very small papillae, paired right and left subventrals and subdorsals near outer margin of head; lateral papillae absent;

  • Amphids at lateral margins of head

  •  Esophagus long, filariform. Subventral glands empty into lumen of esophagus at junction of glandular and muscular portions; dorsal gland empties into lumen near stoma.

  •  Excretory system composed of single renette cell and lateral canals extending anteriorly and posteriorly in lateral chords

  • Lateral chords broad and thick in living worms, often collapsed in preserved specimens.

  • Reproductive system similar to that of free-living female but longer and lacking seminal receptacles.

Ref: Little, 1966
   

Body size range for the species of this genus in the database - Click:
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Distribution:

 

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Feeding:

A genus of animal-parasitic nematodes that, unusually, has a free-living adult generation.

The genus has around 50 species of obligate gastrointestinal parasites of vertebrates that infect mammals, birds, reptiles and amphibians. Most species have rather narrow host ranges and infect either one, or very few, host species (Speare, 1989)

 

 

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Biology and Ecology:

Two species of Strongyloides stercoralis and S. fuelleborni infect humans. of these, S. stercoralis his widely distributed in tropical and subtropical regions while S. fuelleborni occurs in African primates where infection can be shared with humans (Pampiglione and Ricciardi, 1972) and subspecies S. fuelleborni kellyi occurs exclusively in humans in New Guinea (Ashford and Barnish 1989).

Around 100-200 million individuals are infected worldwide with Strongyloides, however the infections can be difficult to detect, so these may be underestimates (Crompton, 1987; Albonico et al., 1999; Requena-Mendez et al., 2013). For comparison, global human infection with the gastro-intestinal nematodes Ascaris lumbricoides, Trichuris trichiura, and hookworms (Ancylostoma duodenale and Necator americanus) are 1.4, 1.0, and 1.4 billion, respectively (Albonico et al., 1999; Viney and Lok, 2015).

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Life Cycle:

The life cycle of Strongyloides, based primarily on studies of S. ratti, is complex:

 

 
Life cycle of Strongyloides ratti.  Gray boxes represdent developmental switches to either (1) sex determination and sexual development, or (2) female only asexual development.  Larval stages are designated as L1 through L4. afer Harvey et al (2000) and (Vinney and Lok, 2015).
For Ecophysiological Parameters for this genus, click 
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Ecosystem Functions and Services:

 

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Management:

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References:

Albonico, M., Crompton, D.W.T., and Savioli, L. 1999. Control strategies for human intestinal nematode infections. Adv. Parasitol. 42: 277-341.

Ashford, R.W., and Barnish, G.1989. Strongyloides fuelleborni and similar parasites in animals. In: Strongyloidiasis a major roundworm infection of man, D.I. Grove, ed. (London: Taylor and Francis), pp. 271-286.

Chitwood, B.G. and M.B. Chitwood. 1950. An Introduction to Nematology. Section !. Anatomy. Monumental Printing Baltimore. 213 p.

Chitwood, B.G. and McIntosh. 1934. A new variety of Alloionema (Nematoda: Diplogasteridae) with a note on the genus. Proc. Helm Soc, Wash 1.37-38.

Harvey, S.C., Gemmill, A.W., Read, A.F., and Viney, M.E. 2000. The control of morph development in the parasitic nematode Strongyloides ratti. Proc. Biol. Sci. 267, 2057-2063.

Little, M.D. 1966. Comparative morphologhy of six species of Strongyloides (Nematoda) and redefinition of the genus. J. Parasitol. 52:69-84.

Pampiglione, S., and Ricciardi, M.L. 1972. Geographic distribution of Strongyloides fuelleborni in humans in tropical Africa. Parasitologia 14: 329-338.

Speare, R. 1989. Identification of species of Strongyloides. In Strongyloidiasis a major roundworm infection of man, D.I. Grove, ed. (London: Taylor and Francis), pp. 11-84,

Viney M.E., Lok J.B. The biology of Strongyloides spp. (July 16, 2015), WormBook, ed. The C. elegans Research Community, WormBook, doi/10.1895/wormbook.1.141.2, http://www.wormbook.org.

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Copyright 1999 by Howard Ferris.
Revised: May 26, 2023.

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