In this discussion include (1) the amebiasis that causes the disease, (2) how the disease is transmitted, (3) the signs/symptoms of the disease, and (4) means of prevention/treatment if present

2) references

1) AMEBIASIS

Causative agent: Entamoeba histolytica

Mode of transmission: Fecal-oral route and oro-anal sexual practices

• Ingestion of viable E. histolytica cysts from contaminated water, food, or hands

Signs and symptoms:

• Intestinal Amebiasis: lower abdominal pain, diarrhea, body malaise, weight loss, back pain, fever
• Amebic Liver Abscess: fever, right-upper quadrant abdominal pain and tenderness, jaundice, diarrhea, weight loss, liver enlargement or hepatomegaly

Treatment:

• Asymptomatic carriage: Iodoquinol (650 mg orally three times daily for 20 days), or paromomycin (500 mg orally three times daily for 10 days)
• Acute colitis/intestinal amoebiasis: Metronidazole (750 mg orally or IV three times daily for 5-10 days), or tinidazole (2 grams orally once daily for 3 days), plus either iodoquinol or paromomycin with the above indicated dosages
• Amebic liver abscess: Metronidazole (750 mg orally or IV for 5-10 days), or tinidazole (2 grams orally once), or ornidazole (2 grams orally once), plus either iodoquinol or paromomycin with the above indicated dosages

Prevention:

• Adequate sanitation and proper implementation of hygienic practices in food preparation
• Treatment of asymptomatic carriers
• Avoidance of unpeeled fruits and vegetables in high risk areas
• Consumption of bottled water, instead of tap water in high risk areas
• Disinfection of water with iodination (tetraglycine hydroperiodide)

2) Reference: Harrison's Principles of Internal Medicine 20th edition Chapter 218

Step-by-step explanation

Amebiasis is an infection caused by the intestinal protozoan, Entamoeba histolytica. This typically affects underdeveloped countries in tropical areas with poor sanitation and hygiene practices. Children <5 years of age, travelers to these countries, and men who have sex with men are at risk for this infection. Amebiasis is the second most common cause of death due to a parasite, second only to malaria.

This infection is acquired after ingestion of viable E. histolytica cysts from water, food, or hands that have been contaminated with feces. When infected food handlers shed cysts, they transfer these organisms to the food they are preparing. Another way food becomes exposed to E. histolytica is when they are grown in areas with fecally contaminated soil, fertilizer or water. These infectious cysts are capable of surviving for several weeks in a moist environment.

Amebiasis is typically asymptomatic in nature, with people passing infectious E. histolytica cysts in their stools despite not having any symptoms. However, others may manifest with the disease either as intestinal amebiasis and amebic liver abscess.

For intestinal amebiasis or amebic colitis, this follows 2-6 weeks after ingestion of viable cysts. Patients then gradually develop lower abdominal pain and mild diarrhea. This is followed by body malaise, weight loss, and back pain or persistence of the lower abdominal pain. In more severe cases, patients will develop a high fever and pass 10-12 stools in a day, mainly consisting of blood and mucus.

For amebic liver abscess, this is found in 95% of travelers about 5 months after leaving an E. histolytica-endemic area. Most patients present with fever and right-upper quadrant abdominal pain and tenderness. This pain may radiate to the shoulder. Some may develop a right pleural effusion, while fewer may develop jaundice. Despite the colon being the site initially infected, less than one-third of patients have diarrhea. In older patients, they may develop weight loss and hepatomegaly (liver enlargement) over 6 months.

Treatment of amebiasis mainly involves the use of luminal amebicides. These drugs are poorly absorbed, thus are able to maintain increased concentrations in the bowel. Only two of these drugs are available in the United States: iodoquinol and paromomycin. These drugs eradicate the cysts in both symptomatic and asymptomatic patients.

Tissue amebicides, such as metronidazole and tinidazole, reach high concentrations in blood and tissue and are able to act on cases of invasive amebiasis. Majority of the patients greatly improve with metronidazole therapy, with decreases in both pain and fever in 72 hours. Side effects to this drug include nausea, vomiting, and abdominal discomfort.

As amebiasis is spread by ingestion of fecally contaminated food and water, it is important to treat asymptomatic carriers as they may excrete millions of cysts per day. Adequate sanitation and hygienic food preparation practices are also important to reduce the chances of infection. In areas considered high-risk, avoiding consumption of unpeeled fruits and vegetable, and using bottled water also minimizes infection. As cysts are resistant to the usual levels of chlorine, water can be disinfected using tetraglycine hydroperiodide.