Parasitic Infection of the CNS

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Parasitic infection of the nervous system by protozoa and metazoa is increasing in Western countries

Infection of the nervous system by protozoa was formerly uncommon in Western countries, but is being seen increasingly because of international travel and increased risk of infection in patients with immunosuppression. 

Toxoplasma can cause a congenital infection resulting in hydrocephalus and cerebral calcifications. It is also now frequently seen in patients with AIDS, causing cerebritis and brain abscesses.

Worldwide, Malaria is the most common protozoan disease to involve the brain (particularly infection with Plasmodium falciparum), causing vascular thromboses with petechial haemorrhages (cerebral malaria). Trypanosomiasis may be associated with an encephalomyelitis in acute disease.

Entamoeba histolytica can cause an amoebic abscess by spread from the gut, whereas a meningitis is caused by free-living amoebae such as Naegleria, usually acquired by swimming in contaminated pools in warm climates.

The two main metazoan parasites to infect the brain are {\I Echinococcus granulosus} (causing hydatid disease) and the larval form of the pork tapeworm, Taenia solium (causing cysticercosis).


Infection of the nervous system with TB may cause meningitis or abscess.

Infection of the CNS by Mycobacterium tuberculosis is by blood spread from a site of primary infection, most commonly the lung. There are two main types of infection.

Meningitis is characterized by numerous granulomas in the leptomeninges, with features of a chronic meningitis. Infection is most marked around the base of the brain and, even when infection is treated, there is often development of meningeal fibrosis to cause hydrocephalus.

Tuberculous abscess (tuberculoma) forms with infection of the brain parenchyma. A tuberculoma is typically a firm, lobulated mass of granulomatous inflammation with central caseous necrosis, up to several centimetres in diameter, and walled off by fibrous tissue. Lesions occur within the cerebral hemispheres, but are most common in the cerebellum. Treatment with antibiotics is usually ineffective and surgical excision is required.
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Revised: 02-11-2014.