Toxoplasma gondii is a common intracellular protozoan that preferentially infects the central nervous system (CNS). In immunodeficient patients it may cause encephalitis; it also can cause local disease such as chorioretinitis and pneumonia. Clinical disease usually occurs through reactivation of latent infection in patients who have CD4 counts of <100 cells/µL. Toxoplasma seroprevalence varies widely, from 11% in the United States to 75% in some European countries, and even higher in certain resource-limited countries. In the absence of prophylaxis, toxoplasmic encephalitis occurs in more than 30% of patients with advanced HIV infection who are seropositive for T. gondii. There have been case reports of CNS toxoplasmosis in the setting of immune reconstitution on antiretroviral therapy (ART); see chapter Immune Reconstitution Inflammatory Syndrome.

Toxoplasma has an infectious reservoir in almost all animals; humans acquire infection either through ingestion of tissue cysts contained in undercooked meat (usually pork, lamb, or beef) or oocysts on contaminated vegetables or through exposure to cat feces containing oocysts. There is no transmission by person-to-person contact.

CNS toxoplasmosis is an AIDS-defining condition that can be progressive and fatal. However, antimicrobial therapy, especially if given in conjunction with ART that results in immune reconstitution, can be successful in treating toxoplasmosis. Specific prophylaxis and effective ART also may be used to prevent toxoplasmosis in patients with advanced AIDS who have latent T. gondii infection (as demonstrated by the presence of anti-Toxoplasma immunoglobulin G [IgG] antibodies; see chapter Preventing Exposure to Opportunistic and Other Infections).

S: Subjective

The patient may complain of subacute onset of dull, constant headache, fever, visual changes or other focal neurologic symptoms, confusion, or disorientation. Seizures may occur. Caregivers may report subtle alterations in mental status or mood.

Take a careful history from the patient and caregivers about the symptoms listed above and their duration, progression, and severity. Inquire about other related symptoms. Ask whether the patient is taking Toxoplasma prophylaxis or ART.

O: Objective

  • Measure vital signs (temperature, heart rate, blood pressure, respiratory rate).
  • Perform a full physical examination including a thorough neurologic examination, looking for focal or nonfocal neurologic deficits, particularly weakness, cranial nerve abnormalities, visual field defects, gait disturbances, and abnormalities in speech, cognitive, or affective functions.
  • Review previous laboratory values, particularly the following:
  • CD4 count (usually <50-100 cells/µL in patients with toxoplasmosis)
  • Toxoplasma IgG (>95% of patients with toxoplasmosis have positive IgG)

A: Assessment

Rule out other infectious or neoplastic causes of headache, fever, and neurologic changes. A partial differential diagnosis includes the following:

  • CNS lymphoma
  • Cryptococcal meningitis
  • Progressive multifocal leukoencephalopathy (PML)
  • Tuberculous meningitis
  • Brain abscesses of bacterial, fungal, or mycobacterial etiologies
  • Herpes simplex virus or cytomegalovirus (CMV) encephalitis
  • Primary HIV encephalopathy
  • AIDS dementia complex
  • Cerebrovascular accident secondary to hemorrhage, hypoxia, or emboli from vegetative endocarditis
  • Neurosyphilis
  • Other causes of chorioretinitis such as CMV, HIV, and cryptosporidiosis

P: Plan

Diagnostic Evaluation

Definitive diagnosis requires identification of T. gondii in tissue biopsy or body fluid samples from a patient with a compatible clinical presentation. Brain biopsy usually is not performed if toxoplasmosis is strongly suspected; instead, presumptive diagnosis is made on the basis of clinical presentation, laboratory and imaging tests, and response to therapy. Brain biopsy should be considered for patients who do not respond to therapy and for those whose diagnosis is unclear.

  • Serum Toxoplasma IgG antibody test results are positive in nearly all patients with toxoplasmic encephalitis. A negative IgG test result makes the diagnosis very unlikely but does not rule it out. (Antibody titer changes are uncommon in reactivation disease and are not useful in making a diagnosis.)
  • CNS imaging with computed tomography (CT) typically shows multiple contrast-enhancing mass lesions, but may show a single lesion or no lesions. Magnetic resonance imaging (MRI) is more sensitive than CT for CNS toxoplasmosis. Other imaging studies, such as single photon emission CT (SPECT), may be useful in distinguishing toxoplasmic lesions from CNS lymphoma.
  • If possible, cerebrospinal fluid should be checked for T. gondii by polymerase chain reaction (PCR).
  • Other diagnostic tests should be performed as indicated to rule out other potential causes of the patient's symptoms.
  • Patients with toxoplasmic encephalitis typically respond quickly to treatment. If clinical improvement is not seen after 10-14 days of appropriate treatment, or if clinical worsening is seen in the first week, consider brain biopsy for alternative diagnoses.


Treatment consists of two phases: acute therapy and chronic maintenance therapy. If possible, consult with an expert on the management of toxoplasmosis.

Presumptive treatment often is begun on the basis of clinical presentation, positive Toxoplasma IgG, and results of brain imaging studies. If patients do not respond quickly to treatment, other diagnoses should be considered. The following recommendations are based on treatment guidelines published by the Centers for Disease Control and Prevention, National Institutes of Health, and HIV Medicine Association/Infectious Diseases Society of America (see "References," below).

Acute Therapy

Acute therapy should be given for at least 6 weeks, and until the patient has shown improvement by clinical and radiographic measures.


  • Pyrimethamine 200 mg PO as a single loading dose, then 50 mg (<60 kg body weight) or 75 mg (>60 kg body weight) QD + sulfadiazine 1,000 mg (<60 kg body weight) or 1,500 mg (>60 kg body weight) PO Q6H + folinic acid (leucovorin) 10-25 mg QD

Dosage adjustments to the lower end of therapeutic range of pyrimethamine and sulfadiazine may be considered for patients who have significant bone marrow suppression despite folinic acid supplementation. Monitor patients carefully for cytopenias, especially if they are taking other agents that cause bone marrow suppression, such as zidovudine, valganciclovir, and ganciclovir.

Note: Patients at risk of G6PD deficiency should be checked for G6PD deficiency before starting pyrimethamine.


  • Pyrimethamine + folinic acid (administered as described above) + clindamycin 600 mg PO or IV Q6H; recommended for patients with significant allergic reactions to sulfa medications
  • Trimethoprim-sulfamethoxazole (TMP-SMX) 5 mg/kg TMP and 25 mg/kg SMX PO or IV BID. TMP-SMX can be considered when the availability of other regimens is limited or when patients need IV therapy
  • Atovaquone 1,500 mg PO BID + pyrimethamine + folinic acid (pyrimethamine and folinic acid as described above)
  • Atovaquone 1,500 mg PO BID + sulfadiazine 1,000-1,500 mg PO Q6H (sulfadiazine dosing as above)
  • Atovaquone 1,500 mg PO BID
  • Pyrimethamine + leucovorin (dosing as above) + azithromycin 900-1,200 mg PO QD

Note: The regimens that contain sulfadiazine, TMP-SMX, or atovaquone also are effective in preventing Pneumocystis jiroveci pneumonia (PCP), so patients on these regimens do not need additional PCP prophylaxis.

Adjunctive corticosteroids (e.g., dexamethasone 4 mg PO or IV Q6H) may be indicated for patients with CNS mass effect or edema. Use is based on clinical judgment and should be discontinued as soon as it is feasible to do so.

Anticonvulsant therapy should be given to patients with a history of seizures (but not to those who have not had seizures).

Ventilatory support may be necessary if severe CNS symptomatology is present.

Chronic Maintenance Therapy

After at least 6 weeks of initial therapy and significant clinical and radiologic improvement, chronic maintenance therapy can be considered.


  • Pyrimethamine 25-50 mg PO QD + sulfadiazine 2,000-4,000 mg PO daily in 2-4 divided doses + folinic acid 10-25 mg PO QD (also effective as PCP prophylaxis)


  • Pyrimethamine 25-50 mg PO QD + clindamycin 600 mg PO Q8H + folinic acid 10-25 mg PO QD
  • TMP-SMX double-strength 1 tablet PO BID
  • Atovaquone 750-1,500 mg PO BID + pyrimethamine 25-50 mg PO QD (+ folinic acid 10-25 mg PO QD)
  • Atovaquone 750-1,500 mg PO BID + sulfadiazine 2,000-4,000 mg PO daily in 2-4 divided doses (also effective as PCP prophylaxis)
  • Atovaquone 750-1,500 mg PO BID

For patients who complete acute therapy successfully, have resolution of signs and symptoms of toxoplasmosis, and have immune reconstitution (with CD4 counts >200 cells/µL) for more than 6 months on ART, it is reasonable to consider discontinuing maintenance therapy. Some specialists would require resolution of CNS lesions on radiologic studies before discontinuation of therapy. Patients must be observed for recurrence of symptoms, and treatment should be restarted if the CD4 count decreases to <200 cells/µL.

Considerations During Pregnancy

All pregnant women should be tested for T. gondii. If the result is positive, evaluate the pregnant woman for signs or symptoms of toxoplasmosis and the neonate for evidence of congenital infection. Perinatal transmission usually occurs only with acute maternal infection, but in advanced HIV, it may occur with reactivation of chronic infection. If T. gondii infection occurs during pregnancy, consult with maternal-fetal and infectious disease specialists. Treatment for pregnant women is the same as for nonpregnant adults (see above). Note that sulfadiazine taken at the time of delivery may increase the risk of neonatal hyperbilirubinemia and kernicterus.

Patient Education

  • Advise patients that antimicrobial therapy alone will not eradicate toxoplasmosis, but should decrease symptoms and improve quality of life. If medications are discontinued, the disease is likely to recur, unless the CD4 count increases to >100-200 cells/µL in response to ART.
  • Inform patients that suppressive therapy must be continued to prevent recurrence. The duration of this therapy may be lifelong.
  • It is essential for patients to take all medicines exactly as prescribed. If doses are missed, or if the medications are stopped and restarted, Toxoplasma can develop resistance to the medications. If patients are having trouble taking the medication on schedule, they should contact their health care provider immediately.
  • Educate patients about the benefits of ART in strengthening the immune system and preventing opportunistic infections such as toxoplasmosis.
  • Advise patients to contact the clinic promptly if symptoms worsen or if new symptoms develop.
  • Toxoplasmosis is a late-stage HIV opportunistic infection that indicates profound immune suppression. Some patients may not respond to treatment or to ART. As with any patient who is at risk of a life-threatening HIV-related disease, clinicians should discuss advance directives and durable power of attorney with patients. Referral to a social worker, mental health clinician, or chaplain experienced in such issues may facilitate this discussion.