Amebiasis

Background

The life-cycle of various intestinal Entamoeba species.

• Fecal oral transmission of Entamoeba histolytica cyst
• Most infection asymptomatic
• Excystation in intestinal lumen
• Trophozoites adhere and colonizes large intestine forming new cysts or invade the intestinal mucosa to cause colitis or abscesses
• Liver abscess - 10x more common in men
• Incubation period usually 2-4 weeks, but may range from a few days to years

Clinical Features

• Asymptomatic vs. dysentery vs. extraintestinal abscesses
• Intestinal- several weeks of crampy abdominal pain, weight loss, watery or bloody diarrhea
• Liver abscess-fever, cough, RUQ or epigastric pain, right-sided pleural pain or referred shoulder pain +/- GI upset
  • Hepatomegaly with tenderness over the liver a typical finding
  • Abscess rupture can involve associated peritoneum, pericardium, or pleural cavity
• Extrahepatic amebic abscesses in the lung, brain, and skin are rare

Differential Diagnosis

Dysentery

• Infectious- shigella, salmonella, campylobacter, E. Coli.
• Noninfectious- Inflammatory bowel disease, ischemic colitis, diverticulitis, AV malformation.

Hepatic abscess

• Pyogenic abscess
  • Aerobic: Escherichia coli, Klebsiella, Pseudomonas
  • Anaerobic: Enterococcus, bacteroides, anaerobic streptococci
• Echinococcosis
• Amebiasis
• Benign cysts/malignancy
• Tuberculosis
• Mycosis

Fever in traveler

• Normal causes of acute fever!
• Malaria
• Dengue
• Leptospirosis
• Typhoid fever
• Typhus
• Viral hemorrhagic fevers
  • Ebola virus disease
  • Marburg virus disease
  • Lassa fever
  • Crimean-Congo hemorrhagic fever
• Chikungunya
• Yellow fever
• Rift valley fever
• Q fever
• Amebiasis
• Zika virus

Acute diarrhea

Infectious

• Viral (e.g. rotavirus)
• Bacterial
  • Campylobacter
  • Shigella
  • Salmonella (non-typhi)
  • Escherichia coli
    • E. coli 0157:H7
  • Yersinia enterocolitica
  • Vibrio cholerae
  • Clostridium difficile
• Parasitic
  • Giardia lamblia
  • Cryptosporidium
  • Entamoeba histolytica
  • Cyclospora
  • Microsporidium
• Toxin
  • Staphylococcus aureus
  • Bacillus cereus

Noninfectious

• GI Bleed
• Appendicitis
• Mesenteric Ischemia
• Diverticulitis
• Adrenal Crisis
• Thyroid Storm
• Toxicologic exposures
• Antibiotic or drug-associated

Watery Diarrhea

• Enterotoxigenic E. coli (most common cause of watery diarrhea)
• Norovirus (often has prominent vomiting)
• Campylobacter
• Non-typhoidal Salmonella
• Enteroaggregative E. coli (EAEC)
• Enterotoxigenic Bacteroides fragilis

Traveler's Diarrhea

• Giardia lamblia
• Cryptosporidiosis
• Entamoeba histolytica
• Cyclospora

Evaluation

Labs

• CBC
• Chem
• LFTs
• Stool PCR
  • Diagnostic gold standard
  • 100% sensitive and specific
• Stool or abscess microscopy
  • <60% SN; unreliable diagnostic test
• Stool, serum, or abscess fluid antigen
• Indirect hemagglutination (antibody)

Imaging

• Abdominal Ultrasound
  • 58-98% SN for liver abscess (depending on size/location)
• Abdominal CT
  • Alternative to ultrasound; equally effective in identifying abscess

Management

Asymptomatic colonization

• Paromomycin or diloxanide

Colitis

• Metronidazole

Liver abscess

• Flagyl, tinidazole, paromomycin, or diloxanide
• Consider drainage of abscess by IR if no response to antibiotics in 5 days, abscess > 5cm, or left lobe involvement

Disposition

• Admission
  • Admit if signs of shock, sepsis, or peritonitis
  • Patients with toxic megacolon should be admitted for surgical intervention.
• Discharge
  • Patients who are non-toxic and able to tolerate oral hydration/PO meds can be discharged with outpatient follow-up

External Links

• Merk Manual - Amebiasis