Protozoal Infections Toxoplasmosis

Toxoplasmosis is one of the commonest opportunistic infections in immunocompromised individuals, mainly in patients with AIDS (Fig. 6.28). The infection by Toxoplasma gondii is acquired through the ingestion of undercooked meat infected with parasitic cysts. In a healthy host, the infection usually remains asymptomatic and seldom presents with meningeal or encephalo-

TABLE 6.7.

Protozoal Diseases

Diseases

Protozoa

Mode of Infection

Neuropathology

Toxoplasmosis

Toxoplasma gondii

Ingestion of meat contaminated with T cysts

Multifocal necrotizing encephalitis, granulomas, abscesses, microglial nodular encephalitis

Amoebiasis

Entamoeba histolytica

Ingestion of E cysts

Abscess

Naegleria fowleri

Olfactory mucosa

Meningoencephalitis

Acanthamoeba

Respiratory tract

Granulomatous encephalitis

Malaria

Plasmodium falciparum

Mosquito bite

Vascular necrosis Petechial hemorrhages Dürck (microglial) nodule

American

Trypanosoma crusii

Insect bite

Acute: microglial nodular

trypanosomiasis

Transfusion

encephalitis

Chagas disease

Organ transplant Transplacental Breast feeding

Chronic: autonomic nervous system involvement Cerebral infarct Reactivated: hemorrhagic meningoencephalitis

African

Trypanosoma brucili

Insect bite

Meningoencephalitis

trypanosomiasis

Sleeping sickness

TABLE 6.8

Helminthic Infections of the CNS

Diseases

Helminths

Mode of Infection

Pathology

Cysticercosis

Taenia solium

Ingestion of contaminated food

Cysticercus cysts, granulomas,

with T solium eggs

calcifications, meningoencephalitis,

(fecal-oral route)

granular ependymitis, vasculitis,

obstructive hydrocephalus

Echinococcosis

Taenia echinococcus

Ingestion of contaminated food

Hydatid cysts; solitary or multiple

with T eggs (fecal-oral route)

Trichinosis

Trichinella spiralis

Ingestion of undercooked

Eosinophilic meningoencephalitis,

pork meat contaminated

vascular necrosis, thrombosis,

with T larvae

ischemic/hemorrhagic lesions,

granulomas

Schistosomiasis

Schistosoma species

Cutaneous infection

Clusters of ova, multiple granulomas,

necrotizing vasculitis

Strongyloidiasis

Strongyloides

Cutaneous infection

Granulomas, abscesses, microinfarcts

Stercoralis

pathic symptoms. A high percentage of population (20% to 70%) are seropositive for toxoplasmosis. In immunocompromised individuals, toxoplasmosis presents with meningeal and encephalitic symptoms or with signs of solitary or multiple mass lesions. The diagnosis is confirmed with serial serologic tests on serum and CSF. CT scan and MRI localize the lesions, which may display ring or homogeneous enhancement. Calcifications are found in the parenchyma and beneath the ventricles. The diagnostic value of brain biopsy is questionable. Because untreated cases have a fatal outcome, empirical therapy is justified.

The pathology may present as solitary or multiple necrotizing abscesses, coagulative necrotic granulomas, and microglial nodular encephalitis (Fig. 6.28). Toxo-plasma organisms within cysts or freely dispersed in the parenchyma are demonstrated in sections stained with HE or by the Wright-Giemsa stain, but most reliably using immunohistologic methods.

Congenital toxoplasmosis is acquired transplacen-tally, either from an acute or reactivated infection of the mother. Characteristic clinical features are microcephaly, mental retardation, seizures, variable neurologic deficits, and chorioretinitis. Pathologic features are micrencephaly, extensive coagulative necrosis with calcifications, and hydrocephalus (see Chapter 14).

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