Protozoal diseases

Disease Description (Causes and Symptoms)

• Definition: Protozoa are unicellular eukaryotic microorganisms that cause gastrointestinal infections, hematogenous spread, or tissue invasion in humans. Representative protozoa include Trypanosoma spp., Trypanosoma cruzi, Toxoplasma gondii, Giardia intestinalis, Entamoeba histolytica, and Cryptosporidium spp.
• Routes of infection: Transmission by insects (tsetse flies, reduviid bugs, etc.), mosquitoes (some species), ingestion of contaminated water or food, contact with infected animals (cats), blood transfusion, vertical transmission, etc.
• Pathophysiology summary: Intestinal protozoa damage the mucosa, causing diarrhea and abdominal pain (e.g., Giardia, Entamoeba), while protozoa that spread through the blood or invade tissues affect the lymph nodes, heart, and central nervous system, causing systemic symptoms and serious complications (e.g., Trypanosoma spp., T. cruzi, Toxoplasma). When the central nervous system is involved, sleep–wake rhythm disturbances, headache, and neurological deficits may occur.
• Major symptoms (vary depending on the cause): Fever (irregular fever), chills, rash, headache, daytime sleepiness (sleeping sickness), enlarged lymph nodes, abdominal pain and diarrhea, weight loss, and cardiac or cerebral complications (myocarditis, meningoencephalitis, etc.).

Treatment Methods and Precautions

• Diagnostic approach: Check symptoms and exposure history (travel, exposure to vector insects) → perform appropriate tests
  • Blood smear (peripheral blood smear, staining) or PCR (blood/tissue)
  • Stool testing (stool O&P, antigen testing) — intestinal protozoa
  • Serologic testing (antibody testing) — toxoplasmosis and some chronic infections
  • Lumbar puncture or tissue biopsy when necessary (if central nervous system involvement is suspected)
• Drug treatment (selected according to the pathogen, disease stage, and patient condition)
  • Sleeping sickness (African trypanosomiasis)
    • Early stage (hemolymphatic stage): Pentamidine or suramin, etc.
    • With central nervous system involvement (late stage): Melarsoprol or eflornithine/nifurtimox combination therapy, etc. — drug selection depends on the strain (T. b. gambiense vs. T. b. rhodesiense) and disease stage
  • Chagas disease (Chagas, T. cruzi): Benznidazole or nifurtimox — effective mainly during the acute stage and in some chronic-stage cases
  • Toxoplasmosis: Pyrimethamine + sulfadoxine (or sulfadiazine) + leucovorin, etc.; management during pregnancy and in immunocompromised patients is handled separately
  • Intestinal protozoa
    • Giardiasis: Metronidazole or tinidazole
    • Amebiasis (invasive): Metronidazole, etc. (after treatment of the invasive infection, elimination of intestinal organisms with a luminal agent is required)
    • Cryptosporidiosis: Nitazoxanide in immunocompetent patients; in immunocompromised patients, treatment of the underlying disease (e.g., HIV) and supportive care should be provided concurrently
• Supportive care: Fluid and electrolyte replacement, nutritional management, and control of fever and pain
• Treatment precautions and drug adverse effects
  • Pyrimethamine: Bone marrow suppression (supplemented by concurrent administration of leucovorin)
  • Melarsoprol: May cause severe encephalopathy
  • Pentamidine, suramin, etc.: Hypoglycemia, nephrotoxicity, hepatotoxicity, etc.
  • Benznidazole/nifurtimox: Skin reactions, neurotoxicity, etc.
  • In pregnant or breastfeeding patients, children, and immunocompromised patients, drug selection, dosage, and timing of treatment must be determined carefully
• Infection control: Screening of blood transfusions and blood products, caution when handling patients’ bodily fluids and blood, and isolation measures when necessary

Checklist Before an Outpatient Visit (Including Items to Bring and Sample Questions)

• Items to bring
  • List of medications currently being taken and allergy history
  • Recent travel destinations (country/region and period of stay) and records of vector exposure (such as insect bites)
  • Notes on the date symptoms began and their progression (fever pattern, frequency and characteristics of diarrhea, changes in sleep, etc.)
  • Previous test results (blood tests, stool tests, chest X-ray, ECG, etc.) and information on antibiotics/antiprotozoal drugs taken
  • Possibility of pregnancy or recent pregnancy (women)
  • Presence of immunocompromise (HIV, use of immunosuppressants, etc.)
• Key items to confirm at the outpatient visit (information to tell the doctor in advance)
  • Recent history of blood transfusion, childbirth or miscarriage, and contact with pets (especially cats)
  • Exposure to unsafe drinking water or food (raw meat, unhygienic drinking water)

Examples of General Questions to Ask the Doctor

• "What do the tests I received mean, and what additional tests are needed?"
• "What are the recommended treatment options and expected treatment duration? What are the side effects?"
• "When and how should repeat or follow-up testing be performed after treatment?"
• "Is there a risk of transmission to other people (family members)? Are isolation or other precautions needed?"

Examples of Disease-Specific Questions

• If sleeping sickness/trypanosomiasis is suspected: "Is a lumbar puncture necessary to determine whether the central nervous system (brain and spinal cord) is involved? How will treatment differ depending on the lumbar puncture results?"
• If Chagas disease is suspected or diagnosed: "Are ECG, echocardiography, or additional tests needed to evaluate cardiac or gastrointestinal complications (myocarditis, ECG abnormalities, esophageal/colonic dilation)?"

Note: Testing and treatment for protozoal diseases vary considerably depending on the causative organism, disease stage, and the patient’s condition (including pregnancy and immune status). Please consult a doctor (such as an infectious disease specialist) to identify the exact cause and receive appropriate antiprotozoal treatment.