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Protozoa (Overview (Single-celled parasites, Multi-stage life cycle - may…
Protozoa
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Diagnosis
Intestinal protozoa
Stool sample (3 fresh on different days) for Microscopy, Ag detection, PCR, +/- serology
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ImmunoC
Impairment of host T-cell immune response (HIV, SOT, SCT) at higher risk of:
- Acquisition if infection after exposure
- Severe disease
- Disseminated infection
- Chronic carriage and reactivation
Toxoplasma gondii
Pathogenesis
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Humans aquire via... ingestion of undercooked meats from intermediate host (e.g. pork), ingestion of oocysts from cat faeces, transplacental, blood transfusion, organ transplantation (ip heart)
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Complications
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HIV
if HIV+, CD4<100, toxoplasma IgG +ve: 30% risk
of reactivation
- Sx
- CNS (mc) - subacute obset with headache, confusion, fever, focal neuro deficits, seizures, altered mental state.
- chorioretinitis, hepatitis, pulmonary infection
- Dx
Definitive: Sx + ≥ 1 mass lesion on brain imaging + detection of organism in brain biopsy
OR
CD4 < 100, toxoplasma IgG positive, not on effective prophylaxis, typical appearance on brain imaging (MRI > CT, multiple ring enhancing lesions)
Transplant
Cx: Primary infection from D+, R- (ip heart transplant), reactivation.
Sx: myocarditis, encephalitis, pneumonitis. May have disseminated disease.
Management
Pyrimethamine and sulfadiazine (+ folinic acid to prevent haematological toxicity) for 6 weeks followed by chronic suppressive therapy.
Prevention: avoid primary infection (avoid cat faeces, cook meat, wash fruit + veg, pre-transplant try matching with seronegative reciprient)
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Cryptosporidium parvum
Pathogenesis
Life Cycle: No resevoir/intermediate hosts. Human ingests oocyst, it sets up infection in intestines, new oocysts excreted and contaminate water etc. Ingested again
Transmission: H2O, food, person-person
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Clinical Features
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Sometimes watery self-limiting diarrhoea, crampy abdominal pain, low grade fever, nausea and anorexia, malaise
Risk of severe disease in ImmunoC: chronic diarrhoea +/- biliary tract involvement. May see Biliary tract infection + pancreatitis
Diagnosis
Visualisation of parasite (modified acid-fast stain, immunofluorescent antibody) + PCR
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Management
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Chronic infection: nitazoxanide, paromomycin
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Prevention: Good hygiene, avoid recreational water supply - lakes, streams, swimming pools
Giardia lamblia
Management
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Prevention: Good hygiene, avoid drinking water from lakes, rivers, streams
Overview
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Associated with poor sanitation, inadequate water treatment facilities.
Pathogenesis
Transmission: Foodborne, waterborne, faecal-oral
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Diagnosis
Visualisation of parasite - Routine O&P (trophozoites, cysts)
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Clinical Features
Asymptomatic, acute diarrhoea, chronic diarrhoea – malabsorption, weight los