Toxoplasmosis
The Common Vein Copyright 2010
Definition
Toxoplasmosis is an infection caused by Toxoplasma gondii, an obligate intracellular parasite that multiplies in nucleated cells. When the host develops immunity, proliferation ceases and “tissue cysts” are formed, which can persist for years, especially in heart, muscle and brain. The reactivation of latent infection occurs in people with immune deficiency, mostly HIV+ patients.
It is usually transmitted from animals to humans through various routes of infection, being the definitive host the cat and some other feline species. However, transmission most often occurs through contaminated food: undercooked meat, poorly washed fruits and vegetables. There can also be transplacental transmission of the parasite during pregnancy.
It causes a wide range of manifestations ranging from lymphadenopathy, pneumonitis, hepatitis, chorioretinitis, myocarditis, involvement of the CNS, and is potentially lethal. In cases of congenital transmission, newborns carry a number of malformations resultant from the intracellular infection and consequent generalized cell death – hydrocephaly, mycrocephaly, deafness, choreoretinitis, microphtalmia are some examples.
The presence of focal neurological signs in HIV seropositive patients should lead to consideration of a potential toxoplasmosis infection, given its high prevalence in these patients. Clinically, patients present with headaches, fever, encephalopathy, confusion, stupor or coma, visual changes and focal deficits.
Neuroimaging studies are very useful in the evaluation of a clinical suspicion of neurotoxoplasmosis. Brain CT with contrast can reveal single or multiple rounded lesions, with a surrounding ring formed by contrast (corresponding to surrounding edema), with a stronger predilection to the basal ganglia and frontotemporal area. MRI has some advantages over CT, to demonstrate some visible injuries to the latter technique.
Diagnosis is then confirmed with PCR amplification from a CSF sample.
Treatment is done with with pyrimethamine plus sulfadiazine, with an initial cycle of 4 to 6 weeks or until proven radiographic improvement.