STEPTRACKERMICROBIOLOGY + NEUROLOGY + CARDIOLOGY | TISSUE PROTOZOA | HIGH-YIELD REVIEW

CNS & Tissue Protozoa

Protozoa that reach the brain, eye, heart and skin — cats and undercooked meat, warm freshwater, contact lenses, and insect vectors in Africa and the Americas.

FOCUS ON
Toxoplasma gondii: cat feces (oocysts) or undercooked meat (cysts) → congenital (chorioretinitis, hydrocephalus, diffuse intracranial calcifications) and AIDS encephalitis (multiple ring-enhancing lesions, CD4 < 100) → pyrimethamine + sulfadiazine + leucovorin. Naegleria fowleri: warm freshwater swimming, nasal irrigation → cribriform plate → fatal meningoencephalitis in days. Acanthamoeba: contact lens keratitis; granulomatous encephalitis. Trypanosoma brucei (tsetse fly; African sleeping sickness), T cruzi (kissing bug; Chagas → cardiomyopathy, megacolon, megaesophagus). Leishmania (sandfly; skin ulcers or visceral kala-azar).
PARASITE · DISEASE
TRANSMISSION · MECHANISM
CLINICAL PICTURE
DIAGNOSIS · TREATMENT
Toxoplasmosis — healthy host
Cat litter oocysts, undercooked pork/lamb cysts, unwashed produce
Usually asymptomatic or mono-like with lymphadenopathy
Serology
Congenital toxoplasmosis
Primary maternal infection in pregnancy → transplacental
Classic triad: chorioretinitis, hydrocephalus, diffuse intracranial calcifications; ± seizures
Pregnant women: avoid litter boxes and raw meat · spiramycin (mother), pyrimethamine-sulfadiazine (fetus)
Toxoplasma encephalitis
Reactivation of tissue cysts, CD4 < 100, IgG ⁺
Headache, confusion, fever, focal deficits; multiple ring-enhancing lesions at gray-white junction and basal ganglia
Pyrimethamine + sulfadiazine + leucovorin · prophylaxis TMP-SMX
Toxoplasma chorioretinitis
Congenital or reactivated
Focal necrotizing retinitis, "headlight in the fog" vitritis
Most common infectious posterior uveitis
Primary amebic meningoencephalitis
Naegleria fowleri in warm lakes, hot springs, poorly treated pools, neti pots → through cribriform plate
Healthy young swimmer: headache, fever, anosmia, rapid coma and death within days
Motile trophozoites in CSF · amphotericin B + miltefosine (rarely survived)
Acanthamoeba keratitis
Contact lenses rinsed with tap water, homemade saline
Severe eye pain out of proportion, ring-shaped corneal infiltrate
Cysts on corneal scraping · topical biguanides
Granulomatous amebic encephalitis
Acanthamoeba or Balamuthia in immunocompromised
Subacute focal brain lesions
—
African sleeping sickness
T brucei gambiense / rhodesiense via tsetse fly; antigenic variation (VSG) → cyclic fevers
Chancre → fever, posterior cervical nodes (Winterbottom sign) → CNS: somnolence, coma
Blood smear trypomastigotes · suramin/pentamidine early; melarsoprol, fexinidazole for CNS
Chagas disease
T cruzi in feces of reduviid (kissing) bug, rubbed into bite or eye; Latin America; transfusion, congenital
Acute: unilateral periorbital swelling (Romaña sign) · chronic: dilated cardiomyopathy, apical aneurysm, arrhythmias, megaesophagus, megacolon (myenteric plexus loss)
Blood smear (acute), serology (chronic) · benznidazole, nifurtimox
Cutaneous leishmaniasis
Leishmania via sandfly; amastigotes in macrophages
Painless papule → ulcer with raised border at bite site
Amastigotes on biopsy · sodium stibogluconate, miltefosine
Visceral leishmaniasis (kala-azar)
L donovani; spreads to spleen, liver, marrow
Fever, weight loss, massive splenomegaly, pancytopenia, darkened skin
Amphotericin B (liposomal)

Mechanism — Chagas destroys nerves and muscle

Kissing bug feces in wound
→
T cruzi invades cellsMyocytes, ganglion cells
→
Myocarditis → dilated heart
Myenteric plexus lossMegaesophagus, megacolon

Vector → protozoan

VECTOR
PARASITE
DISEASE
Tsetse fly
T brucei
Sleeping sickness
Reduviid bug
T cruzi
Chagas
Sandfly
Leishmania
Cutaneous, visceral
Anopheles mosquito
Plasmodium
Malaria
Ixodes tick
Babesia
Babesiosis

How it's tested

COMMON CONFUSIONCongenital toxoplasmosis (diffuse calcifications, hydrocephalus) vs congenital CMV (periventricular calcifications, microcephaly, hearing loss).
THE TRAPNaegleria hits healthy young swimmers and kills in days — think of it with rapid meningitis after warm freshwater, even with a normal immune system.
YOUR APPROACHExposure (cat/meat, freshwater, lenses, vector, region) → organ → stage → drug.

If you see… think…

Newborn with chorioretinitis, hydrocephalus, scattered calcifications → congenital toxoplasmosis
AIDS, CD4 50, multiple ring-enhancing lesions → Toxoplasma encephalitis
Pregnant woman told to avoid litter boxes → Toxoplasma
Teen swam in a warm lake, dies of meningoencephalitis in 5 days → Naegleria fowleri
Contact lens wearer with severe pain and ring corneal infiltrate → Acanthamoeba
Fever, posterior cervical nodes, then somnolence in an African traveler → T brucei
Unilateral eyelid swelling after a bug bite in Bolivia → Romaña sign (Chagas)
Latin American immigrant with dilated cardiomyopathy and megacolon → chronic Chagas
Massive spleen, pancytopenia, darkened skin → visceral leishmaniasis
Painless ulcer after sandfly bites in Afghanistan → cutaneous leishmaniasis