Current Diagnosis and Treatment of Amebiasis

Treatment of Amebiasis

Drug therapy of invasive amebiasis is different from that of non-invasive infection, and is summarized in Table 1. Asymptomatic infection should be treated because of its potential to progress to invasive disease. Luminal agents—such as paromomycin, iodoquinol, or diloxanide furoate—that are not absorbed are best suited for such a therapy.

Metronidazole, a nitroimidazole, is the mainstay of therapy for invasive amebiasis.³⁴ Tinidazole has also recently been approved by the US Food and Drug Administration (FDA) for intestinal or extraintestinal amebiasis. Other nitroimidazoles with longer half-lives—i.e. secnidazole and ornidazole— are currently unavailable in the US. Nitroimidazole therapy leads to clinical response in ~90% of patients with mild to moderate amebic colitis. Nitroimidazole therapy does not eradicate the intraluminal parasites, and should be followed by treatment with a luminal agent such as paromomycin or diloxanide furoate to prevent a relapse. Dehydroemetine has been used successfully, but is not preferred due to its potential myocardial toxicity.

Broad-spectrum antibiotics may be added to treat bacterial superinfection in cases of fulminant amebic colitis and suspected perforation. Bacterial co-infection of amebic liver abscess has occasionally been observed (both before and as a complication of drainage), and it is reasonable to add antibiotics to the treatment regimen in the absence of a prompt response to nitroimidazole therapy.

Surgical intervention is required for acute abdominal pain due to perforated amebic colitis, massive gastrointestinal bleeding, or toxic megacolon. Toxic megacolon is rare, and is typically associated with the use of corticosteroids. Surgical attempts to correct amebic bowel perforation or peritonitis should be avoided, although some patients may benefit from peritoneal lavage.³⁵ Unlike pyogenic liver abscess, amebic liver abscess generally responds to medical therapy alone, and drainage is seldom necessary. The indications for drainage of amebic liver abscess include presence of left-lobe abscess, size >10cm in diameter, impending rupture, and abscess that does not respond to medical therapy within three to five days. Imaging-guided percutaneous treatment (needle aspiration or catheter drainage) has replaced surgical intervention as the procedure of choice for reducing the size of an abscess.³⁶

Preventive Strategies in Amebiasis

Improved sanitation is critical to preventing fecal–oral transmission of organisms such as E. histolytica. Travelers to developing countries should be advised to avoid consumption of unsafe food and water and sexual practices that may lead to fecal–oral transmission.

Development of a vaccine for invasive amebiasis is still in its infancy. Many components of the ameba are immunogenic and may serve as targets for a future vaccine, including the (Gal/GalNAc) lectin, the serinerich E. histolytica protein, cysteine proteinases, lipophosphoglycans, amebapores, and the 29kDa protein.³⁷ Progress in vaccine development has been facilitated by new animal models that allow better testing of potential vaccine candidates and by the application of recombinant technology to vaccine design. Oral vaccines utilizing amebic antigens— either co-administered with some form of cholera toxin or expressed in attenuated strains of Salmonella or Vibrio cholera—have been developed and tested in animals for mucosal immunogenicity.³⁸ ■