Halicephalobus gingivalis




Rev 03/02/2021

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Morphology and Anatomy Life Cycle

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Halicephalobus gingivalis
Stefanski, 1954
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Morphology and Anatomy:




Adults of Halicephalobus spp. are very small for panagrolaimids, (235–460 mm length).
The genital tract in the advanced fourth stage of H. gingivalis has two branches reflexed at the terminal ends.
Female monovarial, prodelphic, ovary reflexed. No spermatheca.
In the parthenogenic adult the posterior branch forms a short ovary, whereas most of the anterior branch becomes a combined uterus-oviduct (Anderson et al., 1993).
Short cylindrical stoma. 
Long tapering corpus with no offset metacorpus.  Valve in postcorpus
Tail conical but asymmetrical, shorter on ventral side.    

 Although H. gingivalis appears morphologically distinct among the described species of the genus, morphometrics do not distinguish well among nominal species.  Molecular markers and morphological characters variable even in offspring of a single individual – cultures started from single individuals. (Anderson et al., 1998; Fonderei and Bert, pers. comm.).





Reported median body size for this species (Length mm; width micrometers; weight micrograms) - Click:


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Common in composts; H. gimgivalis is an opportunistic parasite of horses and other equine species. 

Halicephalobus infection apparently is a worldwide phenomenon; it has been reported on five continents in seven different countries : the United States , the United Kingdom, Japan , Egypt, Switzerland, The Netherlands, and Colombia.


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Commonly found in compost, not as active as typical soil panagrolaims. Also isolated from soil, plants, or moist organic-rich habitats.

They can be cultured on E. coli and other bacteria, human blood plasma and liquid C. elegans media
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Biology and Ecology:

Halicephalobus gingivalis (Stefanski, 1954) is a freeliving panagrolaimid nematode capable of infecting and reproducing in horses, zebras, donkeys, and humans  (Nadler et al., 2003; Fonderie, pers. comm.). 

Some relatively recent case reports refer to this species as Micronema deletrix or Halicephalobus deletrix. However,  Anderson, et al., 1998 provided evidence that Halicephalobus species reported in horses and humans is H. gingivalis and that H. deletrix (=Micronema deletrix) is its synonym (Nadler et al., 2003).



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Life Cycle:

Ecophysiological Parameters:

For Ecophysiological Parameters for this species, click If species level data are not available, click for genus level parameters
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Ecosystem Functions and Services:

Inflammation of the central nervous system is a consistent feature of Halicephaiobus infection in human beings.  In horses, infection of the brain is common followed by the e kidneys, oral and nasal cavities, lymph nodes, lungs, spinal cord, and adrenal gland, and also reports of infection of heart, liver, stomach and bone (Dunn et al., 1993). 



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Interestingly, all Halicephalobus species tested appear to be resistant to anthelminthics, even those not associated with horses (Wim Bert, pers. comm.).


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Anderson, R.C., Linder, K.E., Peregrine, A.S. 1998.  Halicephalobus gingivalis (Stefanski, 1954) from a fatal infection in a horse in Ontario, Canada with comments on the validity of H. deletrix and a review of the genus.  Parasite 5::255-261.

Dunn, D.G., Gardiner, C.H., Dralle, K.R., Thilsted, J.P. 1993.  Nodular granulomatous posthitis caused by Halicephalobus (syn. Micronema) sp. in a horse.  Vet Pathol 30:207- 208.

Nadler, S.A., Carreno, R.A., Adams, B.J., Kinde, H., Baldwin, J.G., Mundo-Ocampo, M.  2003. Molecular phylogenetics and diagnosis of soil and clinical isolates of Halicephalobus gingivalis (Nematoda: Cephalobina: Panagrolaimoidea), an opportunistic pathogen of horses.  International Journal for Parasitology 33:1115–1125.


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Copyright © 1999 by Howard Ferris.
Revised: March 02, 2021 .