Amebiasis (Entamoeba Histolytica Infection)

E. histolytica can survive in the colon (large intestine) without damaging the gut. Sometimes, however, it can invade the colon wall and cause colitis, acute dysentery, or persistent diarrhea. 

The infection can potentially reach the liver via the bloodstream. Rarely, it may spread to other organs, such as the brain or lungs.

Amebiasis affects people everywhere but is more prevalent in tropical regions with crowded housing and subpar sanitation (India, Mexico, Africa, and parts of South America). The parasite may spread through:

• Water or food tainted with stools
• Using human waste-based fertilizer
• Contact with the mouth or genital region of an infected person

The following are risk factors for severe amebiasis:

• Malnutrition
• Old or young age
• Pregnancy
• Cancer
• Alcohol consumption
• Recent travel to a tropical location
• Use of corticosteroid medication to reduce immune response
• Men who have sex with men
• People who live in institutions with poor sanitary conditions

Amebiasis is more prevalent in the United States in those who reside in institutions or have visited regions where the disease is widespread.

Most people with the infection do not experience symptoms at all. On average, the incubation period is 2-4 weeks. However, some people may not show any symptoms for months or even years after the initial infection. 

Mild symptoms may include:

• Abdominal pain
• Diarrhea (passing 3-8 partially formed stools a day or passing soft stools with mucus and sporadic blood)
• Tenesmus (rectal pain when going to the bathroom)
• Excessive gas
• Fatigue
• Unintended weight loss

Severe symptoms may include:

• Abdominal tenderness
• Moving 10- 20 bloody loose stools a day
• Vomiting
• Fever

Amoebiasis can be diagnosed with an examination of E. histolytica cysts and trophozoites in feces, liver abscess aspirates, and biopsy samples. 

E. histolytica and E. dispar, a nonlethal strain, cannot be detected under a microscope. To confirm an E. histolytica infection, your healthcare provider must use one of three methods: serology, antigen detection, or identification of E. histolytica genetic material.

• Blood tests: E. histolytica immunoglobulins (antibodies), which are formed in response to the infection, can be found via serology assays (blood tests). After successful treatment, detectable E. histolytica-specific antibodies may continue to exist for years. The presence of antibodies does not always signify a current infection.
• Stool samples: Stool samples can be used to detect E. histolytica antigens.
• Polymerase chain reaction test: A polymerase chain reaction test can support a diagnosis by detecting genetic traces of E. histolytica in biopsy samples, liver abscess aspirates, and feces.

The primary treatment of symptomatic amebiasis is the use of tinidazole and metronidazole along with hydration. Doses for these two drugs are as follows:

• 500 mg of metronidazole every 6-8 hours for 7-14 days
• 2 grams of tinidazole daily for 3 days

Other treatment options may include:

• Luminal agents, such as paromomycin
• Aspiration under CT guidance and metronidazole for an amoebic liver abscess
• Surgery for liver abscesses, toxic megacolon, perforated colon, or substantial gastrointestinal bleeding when percutaneous drainage is inadequate

The following precautions can help reduce the likelihood of amoebiasis spreading:

When at home

• Thoroughly wash your hands with soap and hot running water for at least 15 seconds after using the restroom or changing a baby's diaper.
• Regularly clean toilets and bathrooms. Pay close attention to the taps and seats on the toilets.
• Do not share towels.

When preparing food

• Thoroughly wash your hands with soap and hot running water before handling food.
• Clean and thoroughly cook raw vegetables 
• Make sure to reheat foods until the internal temperature reaches at least 167 F.

When traveling to developing countries

• Avoid consuming raw food, especially fruits and vegetables.
• Only consume prepackaged beverages, boiled water, or water that has been chlorinated and filtered.
• Avoid drinks with ice.