GI Infections: Protozoa - Microbiology

Snapshot

A 26-year-old woman presents to the emergency room for large amounts of watery, nonbloody diarrhea, abdominal cramping, and lots of flatulence. She was trying to hydrate with water and sports drinks; however, she started feeling lightheaded and was brought to the hospital for treatment. She recently did a 5-day hike in Patagonia in South America. On physical exam, she demonstrated signs of dehydration but otherwise has no significant findings. Stool studies are sent and return with cysts on microscopy. (Giardia lamblia infection)

Introduction

Protozoa
- single-celled eukaryotes, often parasitic, that feed on organic tissues

Infections of Protozoa
Central Nervous System	Gastrointestinal	Visceral Infections	Hematologic Infections	Sexually Transmitted Diseases
Toxoplasma gondii Naegleria fowleri Trypanosoma brucei Acanthamoeba	Giardia lamblia Entamoeba histolytica Cryptosporidium	Trypanosoma cruzi Leishmania donovani	Plasmodium Babesia	Trichomonas vaginalis

Giardia lamblia

Introduction
- clinical syndrome
  - giardiasis
- demographics
  - very common, especially in South America and Southeast Asia
- transmission
  - ingestion of cysts in contaminated water
- pathogenesis
  - only requires a few cysts to cause giardiasis
- risk factors
  - camping and hiking
  - poor sanitation
  - IgA deficiencies
    - Burton agammaglobulinemia
    - common variable immunodeficiency
    - selective IgA deficiency
Presentation
- 1-2 weeks after exposure
- abdominal pain and bloating
- flatulence
- large-volume, watery, foul-smelling, fatty diarrhea
Studies
- stool microscopy
  - microscopy multinucleated trophozoites
  - cysts
- stool antigen test
Treatment
- metronidazole
  - first-line
  - if asymptomatic, patients may not need treatment unless they are at risk for severe disease (immunosuppression)
- paromomycin
  - pregnant women

Entamoeba histolytica

Introduction
- clinical syndrome
  - amebiasis
  - hepatic abscess
- demographics
  - tropical areas
- transmission
  - ingestion of cysts in contaminated water
  - fecal-oral
- risk factors
  - poor sanitation
  - pregnancy
  - immunosuppression
Presentation
- fever
- bloody or watery diarrhea
- right upper quadrant pain
  - should raise suspicion for liver abscess
Imaging
- abdominal computed tomography (CT) or ultrasound
  - liver abscess
Studies
- stool antigen test
- stool detection of DNA with polymerase chain reaction (PCR)
- stool microscopy
  - trophozoites with ingested red blood cells in the cytoplasm
  - cysts with multiple nuclei
- histology
  - flask-shaped lesions
Treatment
- metronidazole
  - symptomatic patients
- paromomycin or iodoquinol
  - asymptomatic patients with cysts detected in stool
- needle aspiration or percutaneous drainage of abscess
  - liver abscess often has an “anchovy paste” or red-brown exudate

Cryptosporidium

Introduction
- clinical syndrome
  - cryptosporidiosis
- transmission
  - ingestion of oocysts in contaminated water
  - fecal-oral
- risk factors
  - immunosuppression
  - HIV/AIDS
- Prevention
  - filter all drinking water
Presentation
- immunosuppressed patients
  - severe and prolonged nonbloody diarrhea
  - may be fatty
  - weight loss
- immunocompetent patients
  - mild watery diarrhea
Studies
- acid-fast stain
  - oocysts
- detection of antigen
Treatment
- nitazoxanide
  - immunocompetent patients

Microsporidium

Introduction
- clinical syndrome
  - microsporidiosis
- transmission
  - fecal-oral
- risk factors
  - immunosuppression
  - HIV/AIDs
  - organ transplant
Presentation
- weight loss
- nonbloody and watery diarrhea
- nausea and vomiting
- can also cause keratoconjunctivitis
Studies
- stool detection of DNA with polymerase chain reaction (PCR)
- stool microscopy with trichrome stain
  - ovoid spores with bright red walls
  - gram-positive
Treatment
- albendazole
  - first-line
- topical fumagillin
  - keratoconjunctivitis

Blood, Plasma, Serum	Reference Range
ALT	8-20 U/L
Amylase, serum	25-125 U/L
AST	8-20 U/L
Bilirubin, serum (adult) Total // Direct	0.1-1.0 mg/dL // 0.0-0.3 mg/dL
Calcium, serum (Ca²⁺)	8.4-10.2 mg/dL
Cholesterol, serum	Rec: < 200 mg/dL
Cortisol, serum	0800 h: 5-23 μg/dL //1600 h: 3-15 μg/dL 2000 h: ≤ 50% of 0800 h
Creatine kinase, serum	Male: 25-90 U/L Female: 10-70 U/L
Creatinine, serum	0.6-1.2 mg/dL
Electrolytes, serum
Sodium (Na⁺)	136-145 mEq/L
Chloride (Cl^-)	95-105 mEq/L
Potassium (K⁺)	3.5-5.0 mEq/L
Bicarbonate (HCO₃^-)	22-28 mEq/L
Magnesium (Mg²⁺)	1.5-2.0 mEq/L
Estriol, total, serum (in pregnancy)
24-28 wks // 32-36 wks	30-170 ng/mL // 60-280 ng/mL
28-32 wk // 36-40 wks	40-220 ng/mL // 80-350 ng/mL
Ferritin, serum	Male: 15-200 ng/mL Female: 12-150 ng/mL
Follicle-stimulating hormone, serum/plasma	Male: 4-25 mIU/mL Female: premenopause: 4-30 mIU/mL midcycle peak: 10-90 mIU/mL postmenopause: 40-250
pH	7.35-7.45
PCO₂	33-45 mmHg
PO₂	75-105 mmHg
Glucose, serum	Fasting: 70-110 mg/dL 2-h postprandial:<120 mg/dL
Growth hormone - arginine stimulation	Fasting: <5 ng/mL Provocative stimuli: > 7ng/mL
Immunoglobulins, serum
IgA	76-390 mg/dL
IgE	0-380 IU/mL
IgG	650-1500 mg/dL
IgM	40-345 mg/dL
Iron	50-170 μg/dL
Lactate dehydrogenase, serum	45-90 U/L
Luteinizing hormone, serum/plasma	Male: 6-23 mIU/mL Female: follicular phase: 5-30 mIU/mL midcycle: 75-150 mIU/mL postmenopause 30-200 mIU/mL
Osmolality, serum	275-295 mOsmol/kd H₂O
Parathyroid hormone, serume, N-terminal	230-630 pg/mL
Phosphatase (alkaline), serum (p-NPP at 30° C)	20-70 U/L
Phosphorus (inorganic), serum	3.0-4.5 mg/dL
Prolactin, serum (hPRL)	< 20 ng/mL
Proteins, serum

Hematologic	Reference Range
Bleeding time	2-7 minutes
Erythrocyte count	Male: 4.3-5.9 million/mm³ Female: 3.5-5.5 million mm³
Erythrocyte sedimentation rate (Westergren)	Male: 0-15 mm/h Female: 0-20 mm/h
Hematocrit	Male: 41%-53% Female: 36%-46%
Hemoglobin A1c	≤ 6 %
Hemoglobin, blood	Male: 13.5-17.5 g/dL Female: 12.0-16.0 g/dL
Hemoglobin, plasma	1-4 mg/dL
Leukocyte count and differential
Leukocyte count	4,500-11,000/mm³
Segmented neutrophils	54%-62%
Bands	3%-5%
Eosinophils	1%-3%
Basophils	0%-0.75%
Lymphocytes	25%-33%
Monocytes	3%-7%
Mean corpuscular hemoglobin	25.4-34.6 pg/cell
Mean corpuscular hemoglobin concentration	31%-36% Hb/cell
Mean corpuscular volume	80-100 μm³
Partial thromboplastin time (activated)	25-40 seconds
Platelet count	150,000-400,000/mm³
Prothrombin time	11-15 seconds
Reticulocyte count	0.5%-1.5% of red cells
Thrombin time	< 2 seconds deviation from control
Volume
Plasma	Male: 25-43 mL/kg Female: 28-45 mL/kg
Red cell	Male: 20-36 mL/kg Female: 19-31 mL/kg

Cerebrospinal Fluid	Reference Range
Cell count	0-5/mm³
Chloride	118-132 mEq/L
Gamma globulin	3%-12% total proteins
Glucose	40-70 mg/dL
Pressure	70-180 mm H₂O
Proteins, total	< 40 mg/dL

Sweat	Reference Range
Chloride	0-35 mmol/L
Urine
Calcium	100-300 mg/24 h
Chloride	Varies with intake
Creatinine clearance	Male: 97-137 mL/min Female: 88-128 mL/min
Estriol, total (in pregnancy)
30 wks	6-18 mg/24 h
35 wks	9-28 mg/24 h
40 wks	13-42 mg/24 h
17-Hydroxycorticosteroids	Male: 3.0-10.0 mg/24 h Female: 2.0-8.0 mg/24 h
17-Ketosteroids, total	Male: 8-20 mg/24 h Female: 6-15 mg/24 h
Osmolality	50-1400 mOsmol/kg H₂O
Oxalate	8-40 μg/mL
Potassium	Varies with diet
Proteins, total	< 150 mg/24 h
Sodium	Varies with diet
Uric acid	Varies with diet
Body Mass Index (BMI)	Adult: 19-25 kg/m²