Amebiasis Pathogenesis and pathology

Etiology

· Infection is established by ingestion of Entamoeba histolytica cysts that release trophozoites.

· The amebic cysts are resistant to low temperature and chlorine that are commonly used in water purification.

· Trophozoites are actively motile organisms and colonize the lumen of large intestine and may invade its mucosal lining.

Pathogenesis and pathology

Once the trophozoites invade the intestinal mucosa, they produce tissue destruction      (ulcers) with little local inflammatory response.

· The organisms multiply and spread through the wall underneath the intestinal epithelium to produce flask shaped ulcers.

· These lesions are commonly seen in the caecum, transverse colon, and sigmoid colon.

· Amebae may produce similar lytic lesions if they reach the liver.

· Rarely the infection may extend extraintestinally to lungs and brain.

Clinical manifestations

1- Intestinal amebiasis

2- Hepatic amebiasis

Diagnosis

· Patients with invasive colitis show occult blood in stools.

· Detection of the parasite or cysts in the stools.

· When stool samples are negative for 3 days, segmoidoscopy is done and biopsy is taken.

· Indirect hemagglutination test may be helpful in the diagnosis of invasive intestinal amebiasis and amebic liver abscess.

Treatment

Drug	Dose (oral)
Metrnidazole	Colitis or liver abscess: 50mg/kg/day in 3 divided doses for 7-10 days
Or Tinidazole	Colitis : 50mg/kg/day once daily for 3 days
	Liver abscess : 50mg/kg/day once daily for 5 days
Followed by
Paromomycin (preferred)	30mg/kg/day in 3 divided doses for 7 days
Or
Diloxanide furoate in children >2 yrs	20mg/kg/day in 3 divided doses for 7 days
Or
Iodoquinol	30mg/kg/day in 3 dividsd doses for 20 days