Toxoplasmosis Disease Facts

Study Notes

Toxoplasmosis

Caused by infection with the protozoan Toxoplasma gondii, an obligate intracellular parasite.
Only 10-20% of toxoplasmosis cases in adults and children are symptomatic.
Toxoplasmosis is a serious and often life-threatening disease in immunodeficient patients.
Congenital toxoplasmosis may manifest as a mild or severe neonatal disease, with onset during the first month of life or with relapse of a previously undiagnosed infection at any time during infancy or later in life.

Life Cycle of Toxoplasma gondii

T. gondii has two distinct life cycles: the sexual cycle occurs only in cats, the definitive host, and the asexual cycle occurs in other mammals (including humans) and various strains of birds.
The asexual cycle consists of two forms: tachyzoites (the rapidly dividing form observed in the acute phase of infection) and bradyzoites (the slowly growing form observed in tissue cysts).

Transmission

T. gondii oocysts, tachyzoites, and bradyzoites can cause infection in humans.
The tissue cysts are up to 60μm in diameter, each containing up to 60,000 organisms.
Extracellular tachyzoites are cleared from host tissues, and intracellular parasites differentiate into occult bradyzoite forms.

Changes in T-Lymphocyte Levels

Alterations in subpopulations of T lymphocytes are profound and prolonged during acute acquired T. gondii infection.
These have been correlated with disease syndromes but not with disease outcome.

Retinochoroiditis

Retinochoroiditis usually results from reactivation of congenital infection, although cases have been recorded that were part of acute infection.
There are five hypotheses related to the inflammatory process of ocular toxoplasmosis.

Signs and Symptoms

In immunocompetent personnel:
- Cervical lymphadenopathy
- Fever, malaise, night sweats, and myalgias
- Sore throat
- Retroperitoneal and mesenteric lymphadenopathy with abdominal pain
- Retinochoroiditis
In immunodeficient patients:
- CNS toxoplasmosis occurs in 50% of patients
- Seizure, dysequilibrium, cranial nerve deficits, altered mental status, focal neurologic deficits, headache
- Encephalitis, meningoencephalitis, or mass lesions
- Hemiparesis and seizures have been reported
- Visual changes

Congenital Toxoplasmosis

This is most severe when maternal infection occurs early in pregnancy.
15-55% of congenitally infected children do not have detectable T. gondii –specific IgM antibodies at birth or early infancy.
Approximately 67% of patients have no signs or symptoms of infection.
Retinochoroiditis occurs in about 15% of patients, and intracranial calcifications develop in 10%.

Ocular Toxoplasmosis

Patients develop retinochoroiditis (focal necrotizing retinitis).
Symptoms include:
- Impaired vision - Either sudden or gradual, depending on the site of infection
- Blurred vision
- Scotoma
- Pain
- Photophobia
- Floaters
- Red eye
- Metamorphopsia

Diagnosis

Direct detection of T. gondii organisms in blood, body fluids, or tissue using PCR.
Indirect detection of immunoglobulin G (IgG) is possible within 2 weeks of infection using ELISA test.
Diagnostic procedures:
- Lumbar puncture
- Brain biopsy
- Lymph node biopsy
- Amniocentesis

Treatment

Act primarily against the tachyzoite form of T. gondii; thus, they do not eradicate the encysted form (bradyzoite).
Pyrimethamine is the most effective agent.
Leucovorin (ie, folinic acid) should be administered concomitantly to prevent bone marrow suppression.

Prevention

Avoid eating raw meat, unpasteurized milk, and uncooked eggs, oysters, clams, and mussels.
Wash hands after touching raw meat.
Wear gloves when gardening or handling soil and wash hands afterwards.
Wash fruits and vegetables.
Avoid contact with cat feces.

Description

Learn about the causes, symptoms, and risks of toxoplasmosis, a disease caused by the protozoan Toxoplasma gondii. This quiz covers the basics of toxoplasmosis and its impact on immunodeficient patients.