Pathophysiology
1) infection with obligate intracellular protozoa Toxoplasma gondii 2) exists as oocyst, tachyzoite, and bradyzoite forms 3) tachyzoite form occurs in acute infection forms groups of rapidly multiplying organisms 4) bradyzoite form occurs in chronic infection with organization into cysts 5) oocyte is the sexual phas that occurs in cats
Signs and Symptoms
1) most infections are asymptomatic 2) can produce significant disease in immunocompromised (usually a latent infection that becomes reactivated) or fetus Normal adults – 3) nontender lymphadenopathy (especially cervical) 4) fever 5) sore throat 6) hepatosplenomegaly 7) headache 8) myalgia 9) abdominal pain Fetus – 10) mental and motor retardation 11) visual deficiences up to blindness owing to choroid retinopathy 12) seizures 13) adrenal necrosis 14) hydrocephalus Immunocompromised – 15) brain abscess/necrosis/hemorrhage 16) confusion 17) seizures 18) severe headaches 19) cranial nerve palsies 20) aphasia 21) ataxia 22) hydrocephalus
Characteristic Test Findings
Radiology – 1) calcification in infant brain Eye exam – 2) retina shows fluffy whitish patches and black spots near posterior retinal pole Laboratory – 3) increased sed rate 4) positive IgG and IgM serology 5) increased transaminases
Histology/Gross Pathology
1) epitheliod macrophages abutting the reactive germinal centers in lymph nodes (Piringer-Kuchinka lesion) 2) perisinusoidal B cell hyperplasia 3) follicular hyperplasia 4) paraventricular necrosis and calcification in fetal thalamus and basal ganglia 5) multiple abscesses in cerebral cortex
Associated Conditions
1) myocarditis 2) myositis 3) hepatitis 4) pneumonitis 5) HIV/AIDS
Inheritance/Epidemiology
1) infects many animals, especially cats 2) in developed countries infection is by eating undercooked lamb or pork or by contact with infected cat feces 3) bradyzoites from contaminated meat or sporulated oocytes from contaminated soil are converted into tachyzoites in GI tract 4) yearly affects 2000 pregnancies in USA
Treatment
Normal adults – 1) no treatment if lymphadenopathy only or in mild systemic symptoms Immunocompromised – 2) high-dose pyrimethamine and sulfadiazine plus leucovorin for one month and then life-long, low-dose pryimethamine/sulfadizine Fetal – 3) pyrimethamine and sulfadiazine for one year
Tips for USMLE
1) toxoplasmosis is part of the TORCHES complex, which causes severe birth defects – toxoplasmosis, others, rubella, cytomegalovirus, herpes simplex virus, syphilis 2) rapidly fatal in AIDS if not treated early and aggressively
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