SUPERStudy: Toxoplasmosi

Introduction: Toxoplasmosis is an infection caused by the protozoan parasite Toxoplasma gondii. It is one of the most common parasitic infections worldwide, often asymptomatic in immunocompetent individuals but potentially severe in immunocompromised patients and during congenital transmission.

Epidemiology: In the United States, T gondii is estimated to infect 1.1 million persons each year

Etiology and Life Cycle

Causative Agent: Toxoplasma gondii is an obligate intracellular parasite, with 3 distinct life forms: trophozoite, cyst, and oocyst. 

Hosts:

• Definitive Hosts: Cats and other felines, where the parasite completes its sexual life cycle in the intestinal tract.
• Intermediate Hosts: Humans and other mammals, where the parasite exists in tissue cysts.

Transmission:

• Ingestion of oocysts from contaminated soil, water, or food (e.g., unwashed vegetables).
• Exposure to oocysts in cat feces 
• Consumption of undercooked or raw meat containing tissue cysts.
• Vertical transmission from mother to fetus during pregnancy (congenital toxoplasmosis).
• Rarely through organ transplantation or blood transfusion.

Clinical Manifestations

1.Asymptomatic Toxoplasmosis:

• Acute infection is asymptomatic in 80% – 90% of healthy adults. 
• Most immunocompetent individuals have no symptoms.
• Latent infection with tissue cysts persists lifelong without causing disease.

2.Acute Toxoplasmosis (Immunocompetent Host):

• When symptomatic, acute disease resembles mononucleosis. 
• Flu-like symptoms: low-grade fever, fatigue, malaise, headache, sore throat, rash, myalgias, hepatosplenomegaly, and atypical lymphocytosis.
• Lymphadenopathy, particularly cervical lymph nodes.

3.Congenital Toxoplasmosis:

• Transmission risk is lowest in the first trimester and highest in the third trimester. However, the congenital disease is most severe if acquired in the first trimester and least severe if acquired in the third trimester. 

Symptoms in the neonate:

• Chorioretinitis (The most common late presentation of congenital toxoplasmosis is retinochoroiditis) 
• Hydrocephalus.

• Intracranial calcifications (classic triad).

• Other: Growth restriction or developmental delays, seizures, psychomotor retardation, deafness, hepatosplenomegaly, lymphadenopathy 

4.Toxoplasmosis in Immunocompromised Patients: 

• Often due to reactivation of latent infection.Reactivated toxoplasmosis occurs in patients with AIDS, cancer, or those taking immunosuppressive drugs. Toxoplasmosis in an AIDS patient is nearly always a reactivation disease, so if a patient has a negative toxoplasma IgG test, it essentially rules out the diagnosis. Toxoplasmosis is the most common cause of secondary CNS infection in AIDS. In advanced AIDS, the most common manifestation is encephalitis, with multiple necrotizing brain lesions. 
• Severe manifestations include:
• Encephalitis with multiple brain abscesses (toxoplasmic encephalitis).
• Pneumonitis.
• Chorioretinitis.

Diagnosis

1.Serology:

• IgG Antibodies: Indicate past exposure or chronic infection.
• IgM Antibodies: Suggest recent infection but can persist for months, requiring confirmatory tests.

2.Molecular Testing:

• PCR: Detects parasite DNA in blood, amniotic fluid, or cerebrospinal fluid (CSF), especially in congenital or severe cases.

3.Imaging Studies:

• Brain MRI or CT: In immunocompromised patients, shows multiple ring-enhancing lesions consistent with toxoplasmic encephalitis.

4.Histopathology:

• Demonstration of tachyzoites or tissue cysts in biopsy specimens. The demonstration of tachyzoites indicates acute infection; cysts may represent either acute or chronic infection. 

Treatment

1.Asymptomatic or Mild Disease:

• Generally does not require treatment in immunocompetent hosts.

2.Acute or Severe Toxoplasmosis:

• Combination Therapy: Pyrimethamine + Sulfadiazine + Leucovorin (to prevent folate deficiency). Pyrimethamine is not used during the first trimester of pregnancy due to its teratogenicity.To prevent sulfonamide crystal-induced nephrotoxicity, good urinary output should be maintained.
• Clindamycin may replace sulfadiazine if the patient has an allergy. Another alternative is trimethoprim-sulfamethoxazole 

3.Congenital Toxoplasmosis:

• Spiramycin is used during pregnancy to reduce vertical transmission.It reduces the frequency of transmission to the fetus by about 60%. It does not cross the placenta. 
• Neonates with confirmed infection are treated with pyrimethamine and sulfadiazine.

4.Prophylaxis in Immunocompromised Patients:

• TMP-SMX (trimethoprim-sulfamethoxazole) for patients with HIV and CD4 counts <100 cells/µL.

Prevention

• Avoid consumption of raw or undercooked meat.
• Wash hands and cooking utensils thoroughly after handling raw meat.
• Wash fruits and vegetables before eating.
• Pregnant women should avoid contact with cat litter and soil contaminated by cats.
• Use prophylaxis in high-risk immunocompromised individuals.

Prognosis

• In immunocompetent individuals, the infection is usually self-limiting with an excellent prognosis.
• In congenital infections, prognosis depends on the timing of maternal infection and treatment. Severe cases can result in long-term neurological damage.
• Immunocompromised patients are at high risk for life-threatening complications, requiring aggressive treatment and prophylaxis.

Summary: Toxoplasmosis is often asymptomatic but can cause severe complications in immunocompromised individuals and during congenital transmission. Diagnosis is primarily serological, with molecular testing and imaging used in severe or atypical cases. Treatment is based on a combination of antiparasitic drugs, with prophylaxis essential for high-risk groups.

SUPERPoint: Toxoplasmosis, caused by Toxoplasma gondii, is often asymptomatic but can lead to severe complications like congenital defects and encephalitis, requiring diagnosis through serology or imaging and treatment with pyrimethamine-based regimens or prophylaxis in high-risk individuals.

SUPERFormula: Infection caused by the protozoan parasite Toxoplasma gondii + Transmitted through ingestion of oocysts (contaminated food or water), tissue cysts (undercooked meat), or vertically from mother to fetus + Commonly asymptomatic in immunocompetent individuals but can cause flu-like symptoms or lymphadenopathy + Severe manifestations include congenital toxoplasmosis (chorioretinitis, hydrocephalus, intracranial calcifications) and toxoplasmic encephalitis in immunocompromised patients + Diagnosed using serology (IgG, IgM), PCR, and imaging (ring-enhancing brain lesions) + Treated with pyrimethamine, sulfadiazine, and leucovorin for severe cases, with spiramycin for pregnancy and TMP-SMX for prophylaxis in high-risk patients + Prevented by avoiding raw meat, washing produce, and practicing hygiene around cats = Toxoplasmosis

References: 

Current Medical Diagnosis & Treatment 2025, Philip J. Rosenthal

First Aid for the® Medicine Clerkship, 4th Edition

Matthew S. Kaufman, Latha Ganti, Dennis Chang, Alfredo J. Mena Lora