Fungal and Parasitic Infections

• Fungi – usually immunosuppressed patients; causes basilar meningitis (cranial nerve symptoms)
• Candida – most common
• normally found in GI, skin, genitals
• causes multiple microabscesses, rarely meningitis
• Histoplasma – pulmonary, rare in CNS
• basilar meningitis, parenchymal granulomas
• Blastomyces – causes abscesses rather than meningitis
• asymmetric single bud
• Cryptococcus – most frequent fungal meningitis, can involve parenchyma in AIDS patients
• India ink test
• does not cause cerebral swelling
• usually immunocompromised
• center with mucopolysaccharide capsule
• may be within macrophage
• Coccidiomyces – San-Joachin valley or Arizona
• causes meningitis/cerebritis/CNS granulomas in 1/3 of cases
• half die
• see sporangia filled with endospores
• double-walled cystic mass with endospores
• Aspergillus – rarely diagnosed before death
• angioinvasive causing hemorrhagic cerebritis, rarely meningitis; branching septate hyphae
• hemorrhagic lesions
• 45 degree branching hyphae (have septae)
• angiotrophic organism
• Mucormyces – rhinocerebral involvement
• associated with acidotic condition (diabetes, diarrhea)
• angioinvasive with necrosis/ischemic strokes
• nonseptate right-angle branching large hyphae
• larger hyphae, weakly septated
• DM patients predisposed; often near cribriform
• Parasites
• Nematodes
• Trichinosis – undercooked pork, rare in CNS
• Angiostrongylus – rat lung worm, causes eosinophilic meningitis
• Strongyloid – usually mixed infection with bacteria
• Platyhelminths
• Cestodes (tapeworms)
• Cysticercosis – most frequent parasitic infection worldwide; T. soleum; definitive host is human (adult tapeworms in GI causing taeniasis), intermediate host is pig (cysts); humans can get cysticercosis due to eating undercooked pork or human fecal contamination
• Echinococcus – hydatid disease; E. granulosum (dog tapeworm); definitive host is dog, intermediate host is sheep; humans can get intermediate disease due to eating fecal contamination; cyst has multiple larvae, hydatid sand can rupture to produce more cyst; usually involves liver/lung (rarely brain)
• Trematodes (flukes)
• Schistosomiasis – can involve spinal cord (S. hematobium or mansoni) or brain (S. japonicum); human definitive host, freshwater snails intermediate host; live in blood vessels
• Paragonomiasis – lung fluke; humans get by eating raw fish; rarely to brain by traveling through basal foramina
• Protozoa
• Toxoplasmosis – intracellular; cat is definitive host; humans get by eating cat feces or raw meat
• 50% of population has been exposed, but immunosuppressed can get meningitis or abscess
• most frequent mass lesion in AIDS
• congenital: brain necrosis, periventricular calcification, hydrocephalus, hydrancephaly, chrioretinitis, hepatosplenomegaly
• Most commonly encountered neurologic opportunistic infection
• Seen in 30% of all AIDS patients
• Etiology: Toxoplasma gondii an obligate intracellular protozoan
• Most adults in the US have antibodies indicating prior exposure
• Disease believe to represent a reactivation of latent primary infection
• History: Subacute course (days to weeks) of progressive hemiparesis, sensory loss, aphasia, seizures
• Diagnosis: LP shows mononuclear pleycytosis with mildly elevated protein (Warning: LP can be fatal in patients with large mass lesions and increased ICP)
• MRI shows multiple ring-enhancing lesions with predilection for basal ganglion and gray-white matter junction

· Pathology: masses without liquefaction, speckled spheres (organisms in macrophages); need extracellular speckling for diagnosis

• CSF/serum toxo titers
• Brain biopsy diagnostic
• Treatment: Pyrimethamine and sulfadiazine
• Amoeba

§ multiple cortical hemorrhagic lesions

§ cells larger than macrophages, motile

§ target-like nucleus

§ acanthamoeba – in immunosuppressed patients

• Naegleria fowler – swimming in freshwater pond; erodes cribriform plate to cause basilar meningitis
• Acanthamoeba/E. hystolytica – rarely involve CNS
• Malaria – plasmodium; cause capillary obstruction, seizures/encephalitis, fever
• Trypanosomiasis – T. brucei (sleeping sickness), T. rhobesiense (meningoencephalitis), T. gambiense (chorea), T. cruzi (chagas from reduviid bug with cardiomyopathy/megacolon)