Toxoplasmosis Symptoms
Most infected individuals (70-90%) are completely asymptomatic at birth or at initial infection, but the majority will develop serious late complications—including vision loss, neurologic impairment, and intellectual disability—with onset ranging from months to years after infection. 1, 2
Clinical Presentation by Population
Congenital Toxoplasmosis in Infants and Children
Asymptomatic at Birth (Most Common)
- 70-90% of congenitally infected infants show no symptoms at birth, creating a dangerous false reassurance 1, 2
- The absence of newborn symptoms does NOT exclude infection—ongoing surveillance is critical even in apparently healthy infants 2
Late-Onset Manifestations (Months to Years Later)
Chorioretinitis (eye disease): The predominant late complication, appearing as white retinal lesions with minimal hemorrhage that can cause progressive visual loss 2
- New or recurrent eye lesions develop years after birth even in treated children—recurrence rates reach 36% in severely affected children and 9% in those with mild disease at birth 2
- Isolated ocular toxoplasmosis is rare; CNS involvement usually coexists, requiring neurologic examination in all children with Toxoplasma chorioretinitis 2
Neurologic deterioration: Progressive microcephaly, intellectual impairment, and motor deficits develop if untreated 2
Symptomatic at Birth (10-30% of Cases)
- Hepatosplenomegaly, jaundice, thrombocytopenia 3
- Microcephaly with intracranial calcifications 3
- Hydrocephalus visible on brain imaging 4
- Chorioretinitis present from birth 3
Immunocompromised Patients (HIV/AIDS, Transplant Recipients)
Toxoplasmic Encephalitis
- Consider this diagnosis in ALL HIV-infected patients presenting with new neurologic findings, regardless of whether focal or diffuse 1
- Fever, reduced alertness, confusion 2
- Seizures (new-onset or worsening) 2
- Focal neurological deficits: hemiparesis, speech disturbances, visual field defects (most common presentation) 1
- Headache and altered consciousness 2
- Brain imaging shows multiple, bilateral, ring-enhancing lesions, especially in basal ganglia and cerebral corticomedullary junction 4
Critical Pitfall: Cases of Toxoplasma encephalitis occur in persons without detectable Toxoplasma-specific IgG antibodies—negative serology does NOT exclude the diagnosis 4, 2
Immunocompetent Adults and Older Children
Acute Infection (Primary Toxoplasmosis)
- Most adults remain completely asymptomatic 5, 6
- When symptomatic: mild flu-like illness with lymphadenopathy 7
- Self-limited course in immunocompetent hosts 5
Ocular Toxoplasmosis
- Can cause blindness even in immunocompetent individuals 5, 6
- Presents as chorioretinitis with visual complaints 2
Pregnant Women
- The majority of infected pregnant women show NO symptoms, making screening and high clinical suspicion essential 3
- Maternal-fetal transmission risk is 29% overall (95% CI: 25%-33%) 1
- Transmission risk increases sharply with gestational age—from 2-6% in first trimester to as high as 81% when infection occurs in final weeks of pregnancy 1
- However, early infection causes more severe fetal disease despite lower transmission rates 1
Key Clinical Pearls
Do not assume a normal newborn screen excludes TORCH infection—most affected infants are asymptomatic at birth and develop problems later 2
Maintain high clinical suspicion for toxoplasmosis in any child presenting with unexplained neurologic deterioration, new-onset seizures, visual complaints, developmental regression, or hearing loss 2
Do not dismiss mild symptoms (single seizure, transient ataxia, headache) as they may represent milder forms of encephalitis requiring treatment 2
In HIV-infected children, toxoplasmic encephalitis is uncommon (<1% of pediatric AIDS cases) but should still be considered with new neurologic findings 2