Nematode infections: Neurological involvement and neurobiology

Abstract

Nematode parasite infections in the central nervous system (CNS) are rare and often neglected. Of the over ten species of nematode parasites known to infect CNS, the genuine neurotropic species is Angiostrongylus cantonensis. Other species can, as larvae, accidentally migrate into or disseminate via systemic circulation to CNS. Nematode parasites are generally prevalent in rural areas of tropical and subtropical countries, but some species like roundworm of dogs and cats (Toxocara canis and T. cati) are also common in pet animals in the high-income countries. Ease of global transport has increased the incidence of neuronematodiases among travellers and immigrants. Clinical manifestations of neuronematodiasis are similar regardless of causative species. The patients can present with symptoms of space-occupying lesions, meningitis, encephalitis or myelitis. Computed tomography and/or magnetic resonance imaging are helpful in the diagnosis. Neurological symptoms with eosinophilia, and in particular eosinophilic pleocytosis in cerebrospinal fluid (CSF), are suggestive for the helminth infections. The history of patients resident or traveling to endemic areas, eating habits or ethnic dishes, field activities, are helpful for diagnosis. Direct detection of the causative parasite is the gold standard for diagnosis, but is rarely successful. In practice, diagnosis can be made by the combination of radio-imaging and immuno-diagnosis to detect parasite-specific antibodies in serum and/or CSF, although the availability of immunodiagnostic kits and access to laboratories are limited in endemic countries. Molecular diagnostic techniques are under exploration.