Encephalitis due to parasites

Parasites are common pathogens of humans and contribute extensively to morbidity and mortality in developing countries, as well as in industralized nations with a high rate of immigrant influx from endemic areas. Parasites are classified into protozoa and helminths. The latter are further classified as stodes (tapeworms), nematodes (roundworms), and trematodes (flukes). Most parasites require two or more hosts to complete their life cycles, and humans may act as either intermediate or definitive hosts. The variable nature of the immunological reaction of the host against parasites, as well as the many pathological lesions that these microorganisms may cause in humans, make these conditions highly pleomorphic. Parasitic invasion of the central nervous system (CNS) may cause encephalitis, meningitis, spaceoccupying brain lesions, stroke, and myelopathy (1,2). Encephalitis due to parasitic infections usually have an acute onset followed by a rapidly progressive course that may cause the death of the patient in a few days. Occasionally, encephalitis evolves over weeks or months, causing slowly progressive brain damage. Clinical manifestations of encephalitis are related to either diffuse brain swelling or to multiple foci of necrosis in the brain parenchyma, and include seizures, delirium, stupor, and coma. Patients may also present with meningeal signs due to involvement of the brain coverings, or with focal neurologic deficits related to the development of spaceoccupying brain lesions.