Halicephalobus gingivalis is a free-living nematode often found in the soil that has occasionally been identified as a cause of serious disease in horses. Reported infections have been limited to approximately 30 cases involving horses and 3 fatal infections in people. Infection of other species has not been reported. Cases have been recorded worldwide, including North and South America, Asia, Europe, and the Middle and Far East.

In horses H gingivalis appears to have a predilection for the skin, mucous membranes, the eyes, and the central nervous system (CNS) and the kidneys. Most often horses suffering from infection are examined for CNS disorders. The disease progresses rapidly in horses and invariably is fatal. Alternative disease manifestations that have included facial swelling, lameness from arthritis, inflammation of the glans of the penis, testicles, and renal disease. Renal involvement in a horse that was detected during meat inspection has also been reported.

This disease, though rarely reported, may be more common than thought and when diagnosed usually results in a fatal disease of the CNS. Early recognition of the disease as a peripheral granulomatous infection and proper treatment may improve the outcome.

How H gingivalis establishes an infection is unknown. A likely mechanism is the nematode is picked up during grazing, colonizes ingesta trapped in the buccal cavity and then gains entry to the horse through penetrating lacerations in the buccal mucosa. The airways are another possible route of infection. In 2 of 3 infected humans, decubital ulcers and deep penetrating wounds were thought to have provided access for the nematode. Often H gingivalis infection is preceded by focal diseases on the head. The most common course once infection is diagnosed the horse develops neurologic deficits and either dies or euthanized.

Clinical signs and diagnosis How the infection gets to the CNS or other internal organs is unknown but through the blood stream (hematogenous dissemination) is increasingly thought to be the mechanism.