First Swedish case of fatal equine parasitic encephalitis by Halicephalobus gingivalis

Halicephalobus gingivalis is a nematode with zoonotic potential which can cause fatal opportunistic infections in various mammals. The parasite has never been diagnosed in Sweden, in any species, prior to the presented case. An imported 21-year-old Icelandic mare developed severe neurological signs. The horse was eventually euthanized and submitted for post-mortem examination where severe lesions in the kidneys were noted. Histopathology revealed the presence of H. gingivalis in both kidneys and the brain. Phylogenetic analysis of the parasite determined it to belong to Lineage 1. With the occurrence of H. gingivalis in Sweden, the disease should be added to the list of differential diagnoses in cases with acute onset of neurological disease in both horses and other mammals including humans.