Biology:Halicephalobus gingivalis

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Short description: Species of roundworm

Halicocephalus gingivalis
Scientific classification
H. gingivalis
Binomial name
Halicocephalus gingivalis
(Stefanski, 1954)

Micronema deletrix, Halicephalobus deletrix.[1]

Halicephalobus gingivalis is a free-living saprophagous nematode species identified and named in 1954 by Stefanski. It is a facultative parasite of horses, invading the nasal cavity, and sometimes numerous other areas, where it produces granulomatous masses. On rare occasion, it can infect humans as well, in whom it is invariably fatal. Based on studies performed on infected horses in Florida, the parasite is associated with swampland environments. These worms are dioecious, with female and male organs having been found in separate individuals. Eggs and immature larvae have been found in tissue samples, indicating an asexual reproductive cycle [clarification needed], and free-living males have been found in soil environments, indicating that sexual reproduction also occurs. The site of entry for the parasite is thought to be through breaks in the skin or through mucous membranes.[2] This nematode is now distributed worldwide, as cases of equine infections have been found in Canada, Florida, the Nordic regions, and Arabian horses alike.[3][4][5]


The genital tract in the advanced fourth stage female of H. gingivalis is Uterus didelphys (twinned uteri) and amphidelphic (uteri opposed) and terminal ends of the uterine horns are reflected, the anterior one ventrally, the posterior one dorsally.[6] Adults are 235–460 μm long. In the parthenogenic adult, the posterior branch forms a short ovary, whereas most of the anterior branch becomes a combined uterus–oviduct.[6] The worm has a conical, asymmetrical tail that is shorter on the ventral side.[citation needed]

Life cycle and habitation

This is a facultative parasite whose stages remain unclear. It dwells actively in soil, around plants and other organically rich environments [4] including manure and compost.

Prevalence of infection

According to a 1997 paper, neurohelminthiases in general are more prevalent where environmental factors and poor sanitation assist the spread of parasitism between man and animals, and have been facilitated by population shifts and improved transport. Neurohelminthiases are often not diagnosed because they are unfamiliar; diagnostic tests are not easily available.[7] Neurohelminthiases in general are not common in the United States.[5]

Effects on health

H. gingivalis is a rare infection in humans, but causes a universally lethal meningoencephalitis. This disease shows greatly increased concentration of eosinophils in the cerebrospinal fluid.[4] In horses (where the parasite is most studied), infection of the brain is common, followed by the kidneys, oral and nasal cavities, lymph nodes, lungs, spinal cord, and adrenal gland, and also reports of infection of heart, liver, stomach and bone.[6] An extremely rare triple fatality from Halicephalobus was reported in Wales after previously rejected, infected kidneys from a man experiencing homelessness who consumed excessive alcohol who ultimately died of meningitis were transplanted into two recipients.[8][9]

As of 2015 six cases had been described in humans.[citation needed]


All known cases of human infections were only found post mortem and had been fatal; they had not been treated with antihelminthic drugs (such as ivermectin and benzimidazole). In animals, these drugs are mostly ineffective, as they do not cross the blood–brain barrier.[5]

Further research

When there is occurrence of a neurohelminthic disease, it is fatal, as there exist no tests that can be done to identify these species and apply effective treatment. These nematodes seem to exhibit neurotropism, but their life cycle, mode of infection and risk factors are not yet clearly understood.[5]


This organism was described in 1954 by Stefanski.[citation needed]


  1. Monoranu, Camelia-Maria; Müllges, Wolfgang; Keppler, Marc; Brehm, Klaus; Ondrejka, Sarah L.; Muntau, Birgit; Tannich, Egbert; Müller-Hermelink, Hans Konrad et al. (2015). "Fatal Human Meningoencephalitis due to Halicephalobus Nematodes, Germany". Open Forum Infectious Diseases 2 (2): ofv061. doi:10.1093/ofid/ofv061. PMID 26125032. "Halicephalobus gingivalis (formerly Micronema deletrix)". 
  2. Craig R. Reinemeyer; Martin Krarup Nielsen; Debra C. Sellon (2007). "Nematodes". Equine Infectious Diseases. St. Louis, MO: Saunders Elsevier. pp. 480–494. ISBN 978-1-4160-2406-4. 
  3. Matthías Eydal; Slavko H. Bambir; Sigurdur Sigurdarson; Eggert Gunnarsson; Vilhjámur Svansson; Stefán Fridriksson; Ellert Thór Benediktsson; Ólöf G. Sigurdardóttir (2012). "Fatal infection in two Icelandic stallions caused by Halicephalobus gingivalis". Veterinary Parasitology 186 (3–4): 523–527. doi:10.1016/j.vetpar.2011.11.024. PMID 22305655. 
  4. 4.0 4.1 4.2 Howard Ferris. "Halicephalobus gingivalis". Nemaplex (University of California, Davis). Retrieved December 2, 2013. 
  5. 5.0 5.1 5.2 5.3 Bhavesh Papadi; Carole Boudreaux; J. Allan Tucker; Blaine Mathison; Henry Bishop; Mark E. Eberhard (2013). "Halicephalobus gingivalis: a rare cause of fatal meningoencephalomyelitis in humans". American Journal of Tropical Medicine and Hygiene 88 (6): 1062–1064. doi:10.4269/ajtmh.12-0730. PMID 23509120. 
  6. 6.0 6.1 6.2 R. C. Anderson; K. E. Linder; A. S. Peregrine (1998). "Halicephalobus gingivalis (Stefanski, 1954) from a fatal infection in a horse in Ontario". Parasite 5 (3): 255–261. doi:10.1051/parasite/1998053255. PMID 9772725. 
  7. Nishimura, K & Hung, T. (1997). Current views on geographic distribution and modes of infection of neurohelminthic diseases. Journal of the Neurological Sciences, 145. [1]
  8. The Guardian newspaper: Rare parasitic worm killed two kidney donor patients, inquest hears, 18 November 2014
  9. "'Worm-infected kidneys' given to south Wales men, say solicitors". BBC News Online. 14 November 2014. 

Lim CK, Crawford A, Moore CV, Gasser RB, Nelson R, Koehler AV, Bradbury RS, Speare R, Dhatrak D, Weldhagen GF. 2015. First human case of fatal Halicephalobus gingivalis meningoencephalitis in Australia. J Clin Microbiol 53:1768 –1774. doi:10.1128/JCM.00032-15.

Wikidata ☰ Q16753245 entry