Halicephalobus gingivalis

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.

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.

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]

H. gingivalis is uncommon in humans so far. However, its rare effects are lethal, as there is widespread inflammation of the central nervous system, leading to brain dysfunction and meningoencephalomyelitis. This disease shows 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 homeless, alcohol-abusing man who died of meningitis were transplanted into two recipients.[8][9]

As of 2015 six cases had been described in humans.

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]

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.

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.