What is the treatment for microsporidiosis, especially in immunocompromised patients?

Treatment of Microsporidiosis in Immunocompromised Patients

Albendazole is the first-line treatment for microsporidiosis, particularly for infections caused by Encephalitozoon intestinalis and other microsporidia species, with the exception of Enterocytozoon bieneusi. 1

Species-Specific Treatment Approach

For Encephalitozoon intestinalis and other non-E. bieneusi species:

• First-line treatment: Albendazole 400 mg orally twice daily (7.5 mg/kg twice daily for persons weighing <60 kg; maximum 400 mg twice daily) 1
• Duration: At least 2-4 weeks, with treatment continued until symptoms resolve and CD4 counts improve in HIV patients
• Albendazole decreases diarrhea and can sometimes eradicate the organism completely 1

For Enterocytozoon bieneusi:

• First-line treatment: Fumagillin 20 mg orally three times daily for 2 weeks 1
  • Note: Fumagillin is not available in the United States but has shown efficacy in placebo-controlled studies 1
• Alternative: Nitazoxanide has been used with some success 1

Treatment in Special Populations

HIV-infected patients:

• Immune reconstitution through antiretroviral therapy is the cornerstone of treatment 2
• For persistent infection despite immune recovery:
  • Continue albendazole for non-E. bieneusi species
  • Consider lifelong suppressive therapy with albendazole in patients with severe immunosuppression if immune function cannot be restored 1

Children:

• Albendazole 15 mg/kg/day divided twice daily for 7 days has shown efficacy in immunocompetent children with microsporidial diarrhea 3
• Clinical improvement typically occurs within 48 hours of initiating therapy 3

Ocular microsporidiosis:

• Topical fumagillin eye drops prepared from Fumidil-B® have been used successfully 1
• Combined with systemic albendazole for disseminated disease

Monitoring and Follow-up

• Monitor clinical symptoms, particularly diarrhea frequency and volume
• Follow-up stool examinations to confirm parasite clearance
• In HIV patients, monitor CD4 counts as immune reconstitution is critical for long-term success

Treatment Efficacy Considerations

• Albendazole is highly effective for Encephalitozoon species but has limited activity against E. bieneusi 4, 5
• Fumagillin has broader anti-microsporidian activity but causes dose-related bone marrow toxicity (thrombocytopenia and neutropenia) 1
• Response rates vary based on:
  1. Species of microsporidia
  2. Immune status of the host
  3. Site of infection

Common Pitfalls and Caveats

• Misidentification of the microsporidian species can lead to ineffective treatment choices
• Failure to address underlying immunosuppression, particularly in HIV patients, will result in poor outcomes
• Inadequate duration of therapy is a common cause of treatment failure
• Bone marrow toxicity must be monitored when using fumagillin
• Expecting complete cure with albendazole in E. bieneusi infections is unrealistic, as the drug has limited efficacy against this species

Emerging Treatments

Research is ongoing for new therapeutic targets including:

• Methionine aminopeptidase type 2 (MetAP2) inhibitors
• Triosephosphate isomerase inhibitors
• Topoisomerase IV inhibitors
• Chitin synthase inhibitors 4

The treatment of microsporidiosis requires species identification when possible, appropriate drug selection based on the infecting species, and addressing the underlying immune status of the patient to achieve the best outcomes in terms of morbidity, mortality, and quality of life.