Parasitic Diseases in Immunosuppressed Patients

Parasitic infections cause significant morbidity and mortality in immunosuppressed hosts due to impaired cellular immunity (CD4+ T-cell depletion in HIV/AIDS, calcineurin inhibitors in transplant, anti-TNF biologics, B-cell depleting therapies, corticosteroids, chemotherapy). Three main mechanisms: (1) opportunistic infections in severely immunocompromised hosts (toxoplasmosis, cryptosporidiosis, cystoisosporiasis, microsporidiosis, leishmaniasis), (2) reactivation of latent parasitic infections acquired during periods of normal immunity (Strongyloides stercoralis hyperinfection, Trypanosoma cruzi/Chagas reactivation, Leishmania reactivation, Toxoplasma reactivation), (3) accelerated/atypical presentations of common parasitic infections (severe giardiasis, visceral leishmaniasis with atypical features, complicated malaria).

Toxoplasmosis (Toxoplasma gondii): in HIV with CD4 <100/uL or transplant recipients with seropositive donor/seronegative recipient mismatch, reactivation causes cerebral toxoplasmosis with focal neurological deficits, headache, fever, seizures, ring-enhancing lesions on brain MRI (basal ganglia, corticomedullary junction), often mistaken for primary CNS lymphoma. Diagnosis: serology (IgG indicates exposure, but reactivation can occur), brain MRI, response to empirical treatment (in HIV) or brain biopsy (in transplant). Treatment: pyrimethamine + sulfadiazine + folinic acid for 6 weeks acute, lifelong secondary prophylaxis (TMP-SMX) until CD4 >200 for 6 months. Pre-transplant screening of donor and recipient mandatory; primary prophylaxis with TMP-SMX or alternative for high-risk recipients.

Strongyloides stercoralis hyperinfection syndrome: latent infection (acquired in tropical/subtropical regions including Mediterranean, Southeast Asia, Caribbean, Africa) reactivates in corticosteroid therapy, HTLV-1 infection, malignancy, transplantation, causing massive autoinfection with disseminated disease, gram-negative bacteremia (gut bacteria translocation through compromised intestinal barrier), septic shock, mortality 50-90% if not recognized. Symptoms: gastrointestinal (severe diarrhea, abdominal pain, vomiting, ileus), pulmonary (cough, dyspnea, hemoptysis, ARDS, larvae in BAL), cutaneous (purpura, larva currens), neurologic (meningitis from gram-negative bacteria), hyperinfection with eosinophilia (often suppressed by steroids). Diagnosis: serology (most sensitive for screening), stool examination (low sensitivity, multiple samples), Baermann concentration, agar plate culture, larvae in respiratory secretions during hyperinfection, PCR. Pre-immunosuppression screening essential for at-risk patients (history of tropical residence). Treatment: ivermectin 200 mcg/kg daily until clear (1-2 doses for uncomplicated, prolonged for hyperinfection), thiabendazole or albendazole alternatives, supportive care including antibiotics for concomitant bacteremia. Prevention: pre-immunosuppression screening of all at-risk patients with serology, treatment of seropositive patients before initiating immunosuppression.

Cryptosporidiosis (Cryptosporidium parvum/hominis): in HIV with CD4 <100/uL, severe chronic watery diarrhea (>4 L/day), weight loss, malabsorption, dehydration, electrolyte abnormalities, biliary tract involvement (sclerosing cholangitis-like), pancreatitis, respiratory involvement. Treatment: nitazoxanide (limited efficacy without immune recovery), antiretroviral therapy with immune reconstitution is most effective. Microsporidiosis (Encephalitozoon, Enterocytozoon): chronic diarrhea, biliary disease, ocular keratoconjunctivitis, disseminated disease in severely immunocompromised. Treatment: albendazole for Encephalitozoon, fumagillin for Enterocytozoon, immune reconstitution. Visceral leishmaniasis (Leishmania donovani/infantum): atypical presentations with fever, hepatosplenomegaly, pancytopenia, mucocutaneous involvement, frequent relapses; treated with liposomal amphotericin B with maintenance therapy. Chagas reactivation (Trypanosoma cruzi): in heart or kidney transplant recipients from endemic areas (Latin America), reactivation with myocarditis, encephalitis, skin lesions; treatment with benznidazole or nifurtimox. Pre-transplant screening of donors and recipients from endemic areas mandatory.