Opportunistic Infections

Toxoplasma gondii infection

• Disease occurs almost exclusively because of reactivation of latent tissue cysts. Primary infection occurs after eating undercooked meat containing tissue cysts or ingestion of oocysts that have been shed in cat feces.

• Clinical disease is rare among patients with CD4+ T lymphocyte counts >200 cells/μL. The greatest risk is among patients with a CD4+ T lymphocyte count less than 50.
  

• The most common clinical presentation of T. gondii infection among patients with AIDS is of a focal encephalitis.

• Patients with TE are almost uniformly seropositive for anti-toxoplasma IgG antibodies. The absence of IgG antibody makes a diagnosis of toxoplasmosis unlikely but not impossible. Anti-toxoplasma IgM antibodies are usually absent.

• CT/MRI scan can demonstrate mass lesion.

• CT guided brain biopsy can demonstrate Toxoplasma Gondi. Detection of T. gondii by PCR in cerebrospinal fluid has produced disappointing results.
  

• Differentials includes CNS lymphoma, mycobacterial infection (especially TB), fungal infection (e.g. cryptococcosis), Chagas disease, bacterial abscess, and rarely PML, which can be distinguished on the basis of imaging studies (PML lesions typically involve white matter rather than gray matter, are noncontrast enhancing, and indicate no mass effect).

• The initial therapy of choice consists of the combination of pyrimethamine plus sulfadiazine plus leucovorin. Acute therapy should be continued for at least 6 weeks, if there is clinical and radiologic improvement. Longer courses might be appropriate if clinical or radiologic disease is extensive or response is incomplete at 6 weeks.

Cryptosporidiosis

• Those at greatest risk for disease are patients with advanced immunosuppression (i.e., CD4+ T lymphocyte counts generally less than 100.
  

• Feces from infected animals, including humans, can contaminate water supplies and recreational water with viable oocysts despite standard chlorination.

• The most common presentation of cryptosporidiosis is the acute or subacute onset of profuse, nonbloody watery diarrhea. Cholangitis and pancreatitis occur among patients with prolonged disease.

• Diagnosis of cryptosporidiosis is primarily based on microscopic identification of the oocysts in stool or tissue. Cryptosporidial enteritis can be diagnosed on small intestinal biopsy.

• ART with immune restoration is associated with complete resolution and all patient should be offered ART. Chemotherapeutic and Immunotherapeutic agent does not have consistent success.

Microsporidiosis

• They are ubiquitous organisms and are likely zoonotic and/or waterborne in origin.

• The most common manifestation of microsporidiosis is diarrhea but encephalitis, ocular infection, sinusitis, myositis, and disseminated infection are also described.

• In gastrointestinal disease, examination of three stools with chromotrope and chemofluorescent stains is often sufficient for diagnosis. If stool examination is negative and microsporidiosis is suspected, a small bowel biopsy should be performed.

• ART with immune restoration is associated with complete resolution and all patient should be offered ART. Albendazole is also recommended for initial therapy.

Progressive Multifocal Leukoencephalopathy Caused by JC Virus

• PML is the only known disease caused by the JC virus. This disease has an insidious onset and characterized by cognitive dysfunction, dementia, seizures, ataxia, aphasia, cranial nerve deficits, hemiparesis or quadriparesis, and eventually coma.

• Typical computed tomographic abnormalities include single or multiple hypodense, nonenhancing cerebral white matter lesions, although cerebellum and brain stem are occasionally involved.

• Brain biopsy can demonstrate characteristic pathologic foci of demyelination and oligodendrocytes with enlarged nuclei and basophilic-staining intranuclear material. PCR detection of JC virus DNA in CSF provides supportive diagnostic information.

• No effective therapy for JC virus exists.