What treatment is recommended for Blastocystis (B.) hominis and other parasites after traveling to Mexico?

Treatment for Blastocystis hominis and Other Parasites After Travel to Mexico

For Blastocystis hominis and other intestinal parasites acquired during travel to Mexico, metronidazole is the recommended first-line treatment at a dose of 500-750 mg three times daily for 7-10 days. 1

Diagnosis and Assessment

• Diagnosis of B. hominis is typically made through microscopic examination of stool samples, looking for the vacuolar form, cyst form, or multivacuolar form 2
• Consider obtaining multiple stool samples (at least 3) to increase diagnostic yield
• For persistent symptoms, stool testing should include:
  • Stool culture for bacterial pathogens
  • Ova and parasite examination
  • Giardia and Cryptosporidium antigen testing 3

Treatment Algorithm for Parasitic Infections

First-line Treatment for B. hominis:

• Metronidazole 500-750 mg three times daily for 7-10 days 1
  • This regimen has shown effectiveness in making patients asymptomatic with negative follow-up stool examinations

For Other Common Parasites:

1. Strongyloides stercoralis (common co-infection):

   • Ivermectin 200 μg/kg daily for 1-2 days 4

2. Giardia lamblia:

   • Metronidazole 250 mg three times daily for 5-7 days OR
   • Tinidazole 2 g single dose

3. For persistent symptoms after initial treatment:

   • Consider adding albendazole 400 mg twice daily for 5 days if symptoms persist after metronidazole therapy 3

Treatment Considerations

• The pathogenicity of B. hominis is debated, but treatment is warranted when:

  • Large numbers of organisms are present in stool
  • Patient has persistent gastrointestinal symptoms
  • No other causative pathogen is identified 1, 5

• Common symptoms of B. hominis infection include:

  • Abdominal pain (most common)
  • Diarrhea
  • Constipation or alternating diarrhea/constipation
  • Fatigue 1

• Treatment failures with metronidazole have been reported; in such cases, consider:

  • Extending treatment duration
  • Alternative agents such as trimethoprim-sulfamethoxazole or paromomycin

Prevention of Reinfection

• Consume only thoroughly cooked foods and fruits that you peel yourself
• Avoid raw fruits, vegetables, undercooked seafood/meat, and street vendor food
• Drink only bottled beverages, hot coffee/tea, or properly boiled water
• Practice frequent handwashing, especially before eating and after using the bathroom 3

Important Caveats

• B. hominis may be an opportunistic pathogen, with higher infection rates in immunocompromised individuals 6
• Endoscopy typically does not show significant intestinal inflammation in B. hominis infection 7
• Consider co-infections, as B. hominis is frequently found alongside other parasites, particularly Strongyloides stercoralis 6
• If symptoms persist despite appropriate antiparasitic treatment, consider other causes of gastrointestinal symptoms

Follow-up

• Repeat stool examination 2-4 weeks after completing treatment to confirm clearance
• If symptoms persist or worsen despite treatment, consider referral to an infectious disease specialist

Remember that while B. hominis is commonly found in stool samples, its role as a pathogen remains controversial. Treatment should be considered when symptoms are present and no other cause is identified.