Amebiasis

Amebiasis, or amoebic dysentery, is an infection caused by the parasite Entamoeba histolytica. Transmission is through the fecal-oral route or by consumption of contaminated food and water. Most patients infected with E. histolytica are asymptomatic, but about 10% may develop dysentery. Invasive infections are characterized by abdominal pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain, fever Fever Fever is defined as a measured body temperature of at least 38°C (100.4°F). Fever is caused by circulating endogenous and/or exogenous pyrogens that increase levels of prostaglandin E2 in the hypothalamus. Fever is commonly associated with chills, rigors, sweating, and flushing of the skin. Fever, and bloody diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea, and can lead to serious complications including liver Liver The liver is the largest gland in the human body. The liver is found in the superior right quadrant of the abdomen and weighs approximately 1.5 kilograms. Its main functions are detoxification, metabolism, nutrient storage (e.g., iron and vitamins), synthesis of coagulation factors, formation of bile, filtration, and storage of blood. Liver abscesses, intestinal fistulas, or fulminant colitis. Diagnosis is usually made based on stool studies or the detection of immunologic markers. Treatment consists of both an absorbable amebicidal agent such as metronidazole and an intraluminal amebicidal agent such as paromomycin.

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Editorial responsibility: Stanley Oiseth, Lindsay Jones, Evelin Maza

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Overview

Epidemiology

  • Annually, over 50 million cases of amebiasis occur worldwide.
  • Annually, over 100,000 deaths occur worldwide due to amebiasis or an amebiasis-related complication.
  • Endemic regions include India, Mexico, and areas of Central and South America, likely because of poor sanitation and low socioeconomic conditions.

Etiology

Causative organism: anaerobic protozoan parasites of the Entamoeba genus

  • Most common species causing symptomatic disease: E. histolytica
  • Most common species causing infection worldwide: E. dispar
    • E. dispar has a lifecycle similar to that of E. histolytica but is noninvasive.
    • E. dispar infection is almost always asymptomatic.
  • Other species worldwide:
    • E. moshkovskii
    • E. bangladeshi

Transmission occurs through the ingestion of cysts:

  • Fecal-oral route
  • Contaminated food or water

Risk factors and high-risk populations:

  • Geographic:
    • Inhabitants of an endemic region
    • Travelers who spend more than 1 month in an endemic region
    • Institutionalized patients
  • Health status:
    • Men who have sex with men
    • Advanced age
    • Pregnancy Pregnancy Pregnancy is the time period between fertilization of an oocyte and delivery of a fetus approximately 9 months later. The 1st sign of pregnancy is typically a missed menstrual period, after which, pregnancy should be confirmed clinically based on a positive β-hCG test (typically a qualitative urine test) and pelvic ultrasound. Pregnancy: Diagnosis, Maternal Physiology, and Routine Care
    • Corticosteroid use
    • Malignancy
    • Malnutrition Malnutrition Malnutrition is a clinical state caused by an imbalance or deficiency of calories and/or micronutrients and macronutrients. The 2 main manifestations of acute severe malnutrition are marasmus (total caloric insufficiency) and kwashiorkor (protein malnutrition with characteristic edema). Malnutrition in children in resource-limited countries
    • Alcoholism

Pathophysiology

Life cycle of Entamoeba species (spp.)

The life cycle of Entamoeba spp. is dependent on the infection of a host because transition through the life stages occurs within the host’s intestinal tract. 

Cyst stage:

  1. Found in formed and diarrheal stools from an infected host
  2. Ingested via the fecal-oral route or contaminated water and food: Ingestion of just 1 cyst is sufficient to cause infection.
  3. Ingested cysts become trophozoites in the small intestine Small intestine The small intestine is the longest part of the GI tract, extending from the pyloric orifice of the stomach to the ileocecal junction. The small intestine is the major organ responsible for chemical digestion and absorption of nutrients. It is divided into 3 segments: the duodenum, the jejunum, and the ileum. Small Intestine.

Trophozoite stage:

  1. Trophozoites migrate to the large intestine Large intestine The large intestines constitute the last portion of the digestive system. The large intestine consists of the cecum, appendix, colon (with ascending, transverse, descending, and sigmoid segments), rectum, and anal canal. The primary function of the colon is to remove water and compact the stool prior to expulsion from the body via the rectum and anal canal. Colon, Cecum, and Appendix.
  2. In 10% of cases, trophozoites invade the intestinal mucosa causing bloody diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea, local tissue destruction, and other complications.
  3. Trophozoites undergo binary fission and produce cysts; both forms are excreted in the diarrheal stool.
  4. Trophozoites quickly die outside the GI tract, but the cysts can survive for weeks.

Pathogenesis of invasive infection

  1. Trophozoites colonize the large intestine Large intestine The large intestines constitute the last portion of the digestive system. The large intestine consists of the cecum, appendix, colon (with ascending, transverse, descending, and sigmoid segments), rectum, and anal canal. The primary function of the colon is to remove water and compact the stool prior to expulsion from the body via the rectum and anal canal. Colon, Cecum, and Appendix and secrete proteases to invade mucosal cells and cause necrosis and apoptosis.
  2. Trophozoites then release lytic enzymes Enzymes Enzymes are complex protein biocatalysts that accelerate chemical reactions without being consumed by them. Due to the body's constant metabolic needs, the absence of enzymes would make life unsustainable, as reactions would occur too slowly without these molecules. Basics of Enzymes that allow penetration into the intestinal vasculature.
  3. A chain reaction of tissue destruction ensues, including the breakdown of intercellular tight junctions that leads to “flask-shaped” ulcers and fistulas.
  4. Trophozoites that have entered the portal circulation may migrate to infect other organs.
Pathogenesis of entamoeba histolytica

The pathogenesis of invasive Entamoeba histolytica infection:
In 10% of cases, E. histolytica colonizes the large intestine Large intestine The large intestines constitute the last portion of the digestive system. The large intestine consists of the cecum, appendix, colon (with ascending, transverse, descending, and sigmoid segments), rectum, and anal canal. The primary function of the colon is to remove water and compact the stool prior to expulsion from the body via the rectum and anal canal. Colon, Cecum, and Appendix mucosa and invades via secretion of proteinases and lytic enzymes Enzymes Enzymes are complex protein biocatalysts that accelerate chemical reactions without being consumed by them. Due to the body's constant metabolic needs, the absence of enzymes would make life unsustainable, as reactions would occur too slowly without these molecules. Basics of Enzymes. This causes cellular necrosis and lysis of the membranes, respectively. This chain of events induces mucosal cell apoptosis and disrupts tight junctions between cells, allowing for flask-shaped ulcers, abscesses, and fistulas to form. Invasion may reach the portal venous system, through which E. histolytica can spread to other organs.

Image by Lecturio. License: CC BY-NC-SA 4.0

Clinical Presentation

The incubation period is usually 2–4 weeks once ingested, but symptoms may develop up to 1 year after infection.

90% of all Entamoeba infections are asymptomatic:

  • E. histolytica has the highest likelihood of causing symptoms (approximately 10% of cases).
  • E. dispar infections are almost always asymptomatic/noninvasive.

Clinical amebiasis

  • Onset: 2–4 weeks
  • Symptoms may include:
    • Loose stools, ranging from mild to severe diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea (94%–100% of cases)
    • Abdominal pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain, often in the RUQ (12%–80%)
    • Bloody stools (94%–100%)
    • Weight loss (50%)
    • Fever (up to 38%)

Complications

  • Superimposed bacterial intestinal infections as a result of mucosal breakdown
  • Amebic dysentery:
    • Severe diarrhea with visible blood and mucus
    • Trophozoites present in the stool
  • Fulminant colitis:
    • Bowel necrosis
    • Bowel perforation leading to peritonitis (0.5%)
    • Toxic megacolon
  • Persistent diarrhea, weight loss, and abdominal pain, such that they become chronic conditions
  • Abscesses:
    • Liver: “anchovy paste” exudate (> 4%)
    • Rarely, abscesses may occur in the lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs, spleen Spleen The spleen is the largest lymphoid organ in the body, located in the LUQ of the abdomen, superior to the left kidney and posterior to the stomach at the level of the 9th-11th ribs just below the diaphragm. The spleen is highly vascular and acts as an important blood filter, cleansing the blood of pathogens and damaged erythrocytes. Spleen, or brain.
  • Fistulas with neighboring organs due to invasive destruction of the intestinal walls

Diagnosis

The diagnosis of amebiasis is based on clinical suspicion as well as confirmatory testing. Several testing modalities may be used.

  • Stool antigen testing:
    • Rapid, 90% sensitive, specific
    • Can differentiate between causative species
    • May involve:
      • ELISA
      • Radioimmunoassay
      • Immunofluorescence
  • Stool PCR:
    • 100% sensitive and specific
    • Expensive
    • Detects DNA DNA The molecule DNA is the repository of heritable genetic information. In humans, DNA is contained in 23 chromosome pairs within the nucleus. The molecule provides the basic template for replication of genetic information, RNA transcription, and protein biosynthesis to promote cellular function and survival. DNA Types and Structure or RNA RNA Ribonucleic acid (RNA), like deoxyribonucleic acid (DNA), is a polymer of nucleotides that is essential to cellular protein synthesis. Unlike DNA, RNA is a single-stranded structure containing the sugar moiety ribose (instead of deoxyribose) and the base uracil (instead of thymine). RNA generally carries out the instructions encoded in the DNA but also executes diverse non-coding functions. RNA Types and Structure in stools
    • Can differentiate between causative species
  • Stool microscopy:
    • Demonstration of cysts or trophozoites
    • RBCs within the cytoplasm are suggestive of an E. histolytica infection.
    • A minimum of 3 samples per day is needed for accuracy.
  • Serology:
    • Presence of antiamebic antibodies Antibodies Immunoglobulins (Igs), also known as antibodies, are glycoprotein molecules produced by plasma cells that act in immune responses by recognizing and binding particular antigens. The various Ig classes are IgG (the most abundant), IgM, IgE, IgD, and IgA, which differ in their biologic features, structure, target specificity, and distribution. Immunoglobulins is suggestive of an E. histolytica infection.
    • E. dispar does not generally invoke antibody production.
    • Antibodies are detected 5–7 days after infection.
      • Antibodies may persist for years after an acute infection.
      • Serology cannot distinguish between acute and prior infections.
  • Colonoscopy with histologic examination:
    • Not performed routinely due to risk of perforation of amebic ulcerations
    • Biopsies are performed to obtain samples for microscopy or antigen testing.
    • Mucosal thickening and flask-shaped ulcers may be visible.

Management and Prevention

Management

All E. histolytica infections should be treated regardless of the absence or severity of symptoms; however, E. dispar infections do not need to be treated.

  • Medical approach (both are needed):
    1. Absorbable amebicides Amebicides Amebicides are drugs toxic to amoebas such as Entamoeba histolytica (the causative organism of amebiasis). Parasites enter the GI tract where trophozoites can penetrate the intestinal wall and cause an invasive infection. Amebicides are classified based on where the drug is most effective: intestinal lumen or tissues. Amebicides, such as metronidazole, can be used to treat infections within the tissue.
    2. Luminal amebicides Amebicides Amebicides are drugs toxic to amoebas such as Entamoeba histolytica (the causative organism of amebiasis). Parasites enter the GI tract where trophozoites can penetrate the intestinal wall and cause an invasive infection. Amebicides are classified based on where the drug is most effective: intestinal lumen or tissues. Amebicides, such as paromomycin, can eliminate cysts and trophozoites within the intestinal lumen.
  • Surgical approach:
    • Drainage of abscesses that resist antibiotic treatment
    • Repair of bowel perforation
    • Colectomy for toxic megacolon Megacolon Megacolon is a severe, abnormal dilatation of the colon, and is classified as acute or chronic. There are many etiologies of megacolon, including neuropathic and dysmotility conditions, severe infections, ischemia, and inflammatory bowel disease. Megacolon

Prevention

  • Primary prevention is based on the avoidance of uncooked food and untreated water in endemic areas.
  • Water may be treated with iodine before consumption. Amebic cysts are not susceptible to chlorine treatment.
  • A previous infection may confer partial immunity through IgA antibodies Antibodies Immunoglobulins (Igs), also known as antibodies, are glycoprotein molecules produced by plasma cells that act in immune responses by recognizing and binding particular antigens. The various Ig classes are IgG (the most abundant), IgM, IgE, IgD, and IgA, which differ in their biologic features, structure, target specificity, and distribution. Immunoglobulins, but recurrent infections and persistent intestinal colonization have been documented.

Differential Diagnosis

All conditions that cause nonspecific or bloody diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea are differential diagnoses for amebiasis.

  • Nonspecific diarrhea: diarrhea is a common GI problem in all age groups and is defined by the occurrence of > 3 episodes of loose stools in a day. Infectious causes include bacterial, viral (most common), or parasitic etiologies. Nonspecific diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea may also be physiologic (e.g., in response to stress) or caused by dietary factors. Most episodes of diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea without concerning features such as fever Fever Fever is defined as a measured body temperature of at least 38°C (100.4°F). Fever is caused by circulating endogenous and/or exogenous pyrogens that increase levels of prostaglandin E2 in the hypothalamus. Fever is commonly associated with chills, rigors, sweating, and flushing of the skin. Fever or bloody stools can be treated with supportive care. 
  • Bacterial infections:
    • Shigellosis: an infection caused by Shigella Shigella Shigella is a genus of gram-negative, non-lactose-fermenting facultative intracellular bacilli. Infection spreads most commonly via person-to-person contact or through contaminated food and water. Humans are the only known reservoir. Shigella that spreads through interpersonal contact or contaminated food and water. Shigellosis leads to inflammation Inflammation Inflammation is a complex set of responses to infection and injury involving leukocytes as the principal cellular mediators in the body's defense against pathogenic organisms. Inflammation is also seen as a response to tissue injury in the process of wound healing. The 5 cardinal signs of inflammation are pain, heat, redness, swelling, and loss of function. Inflammation and invasion of the intestinal mucosa, causing fever Fever Fever is defined as a measured body temperature of at least 38°C (100.4°F). Fever is caused by circulating endogenous and/or exogenous pyrogens that increase levels of prostaglandin E2 in the hypothalamus. Fever is commonly associated with chills, rigors, sweating, and flushing of the skin. Fever, abdominal pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain, and bloody diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea. Diagnosis is made using Gram staining, culture, or PCR. Treatment of shigellosis includes rehydration, electrolyte replacement, and antibiotic therapy with ciprofloxacin, ceftriaxone, or cefixime.
    • Typhoid fever Typhoid Fever Typhoid (or enteric) fever is a severe, systemic bacterial infection classically caused by the facultative intracellular and Gram-negative bacilli Salmonella enterica serotype Typhi (S. Typhimurium, formerly S. typhi). S. paratyphi serotypes A, B, or C can cause a similar syndrome. Enteric Fever (Typhoid Fever) or enteric fever Enteric Fever Typhoid (or enteric) fever is a severe, systemic bacterial infection classically caused by the facultative intracellular and Gram-negative bacilli Salmonella enterica serotype Typhi (S. Typhimurium, formerly S. typhi). S. paratyphi serotypes A, B, or C can cause a similar syndrome. Enteric Fever (Typhoid Fever): an infection caused by Salmonella Salmonella Salmonellae are gram-negative bacilli of the family Enterobacteriaceae. Salmonellae are flagellated, non-lactose-fermenting, and hydrogen sulfide-producing microbes. Salmonella enterica, the most common disease-causing species in humans, is further classified based on serotype as typhoidal (S. typhi and paratyphi) and nontyphoidal (S. enteritidis and typhimurium). Salmonella that spreads via fecal-oral transmission and consumption of contaminated food and water. Typhoid fever Typhoid Fever Typhoid (or enteric) fever is a severe, systemic bacterial infection classically caused by the facultative intracellular and Gram-negative bacilli Salmonella enterica serotype Typhi (S. Typhimurium, formerly S. typhi). S. paratyphi serotypes A, B, or C can cause a similar syndrome. Enteric Fever (Typhoid Fever) leads to invasion of the intestinal mucosa and possibly the bloodstream, causing abdominal pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain, diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea, and sepsis Sepsis Organ dysfunction resulting from a dysregulated systemic host response to infection separates sepsis from uncomplicated infection. The etiology is mainly bacterial and pneumonia is the most common known source. Patients commonly present with fever, tachycardia, tachypnea, hypotension, and/or altered mentation. Sepsis and Septic Shock. Diagnosis is generally made with stool cultures. Treatment includes rehydration, electrolyte replacement, and antibiotic therapy with fluoroquinolones Fluoroquinolones Fluoroquinolones are a group of broad-spectrum, bactericidal antibiotics inhibiting bacterial DNA replication. Fluoroquinolones cover gram-negative, anaerobic, and atypical organisms, as well as some gram-positive and multidrug-resistant (MDR) organisms. Fluoroquinolones.
    • Gastroenteritis Gastroenteritis Gastroenteritis is inflammation of the stomach and intestines, commonly caused by infections from bacteria, viruses, or parasites. Transmission may be foodborne, fecal-oral, or through animal contact. Common clinical features include abdominal pain, diarrhea, vomiting, fever, and dehydration. Gastroenteritis/enterocolitis: conditions that include abdominal pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain, nausea, vomiting, and watery to bloody diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea, which do not typically lead to sepsis Sepsis Organ dysfunction resulting from a dysregulated systemic host response to infection separates sepsis from uncomplicated infection. The etiology is mainly bacterial and pneumonia is the most common known source. Patients commonly present with fever, tachycardia, tachypnea, hypotension, and/or altered mentation. Sepsis and Septic Shock in otherwise healthy patients. Some notable bacterial etiologies include Campylobacter Campylobacter Campylobacter ("curved bacteria") is a genus of thermophilic, S-shaped, gram-negative bacilli. There are many species of Campylobacter, with C. jejuni and C. coli most commonly implicated in human disease. Campylobacter spp., Yersinia Yersinia Yersinia is a genus of bacteria characterized as gram-negative bacilli that are facultative anaerobic with bipolar staining. There are 2 enteropathogenic species that cause yersiniosis, Y. enterocolitica and Y. pseudotuberculosis. Infections are manifested as pseudoappendicitis or mesenteric lymphadenitis, and enterocolitis. Enterobacteriaceae: Yersinia spp./Yersiniosis spp., and Escherichia spp. These gram-negative bacilli spread via the consumption of undercooked food and contaminated food and water. The diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea is generally self-limiting, but treatment may include rehydration, electrolyte replacement, and ciprofloxacin if indicated.
    • Pseudomembranous colitis Pseudomembranous colitis Pseudomembranous colitis is a bacterial disease of the colon caused by Clostridium difficile. Pseudomembranous colitis is characterized by mucosal inflammation and is acquired due to antimicrobial use and the consequent disruption of the normal colonic microbiota. C. difficile infections account for the most commonly diagnosed hospital-acquired diarrheal illnesses. Pseudomembranous Colitis: an infection caused by C. difficile. Although the causative organism is commonly found in the normal gut microbiome, pathogenesis occurs when there is an overabundance. Common symptoms include foul-smelling and non-bloody diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea, abdominal pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain, and nausea with vomiting. Diagnosis is made using stool PCR or enzyme assays. Treatment generally consists of discontinuing the offending antibiotic and commencing oral vancomycin.
  • Parasitic infections:
    • Giardiasis Giardiasis Giardiasis is caused by Giardia lamblia (G. lamblia), a flagellated protozoan that can infect the intestinal tract. The hallmark symptom of giardiasis is foul-smelling steatorrhea. Patients who develop chronic infections may experience weight loss, failure to thrive, and vitamin deficiencies as a result of malabsorption. Giardia/Giardiasis: an infection caused by Giardia, which are flagellated protozoans causing infections after the consumption of cysts via the fecal-oral route or contaminated water. The hallmark symptom is foul-smelling steatorrhea resulting from malabsorption Malabsorption Malabsorption involves many disorders in which there is an inability of the gut to absorb nutrients from dietary intake, potentially including water and/or electrolytes. A closely related term, maldigestion is the inability to break down large molecules of food into their smaller constituents. Malabsorption and maldigestion can affect macronutrients (fats, proteins, and carbohydrates), micronutrients (vitamins and minerals), or both. Malabsorption and Maldigestion. Diagnosis is made based on stool microscopy or antigen testing. Treatment is with supportive care and antibiotics such as metronidazole. 
    • Strongyloidiasis Strongyloidiasis Strongyloidiasis is a common parasitic disease caused by infection with the roundworm Strongyloides stercoralis. Transmission occurs through skin penetration. Strongyloides has a unique life cycle that can be entirely completed in the human host, migrating from the skin to the pulmonary system and then to the GI system. Strongyloidiasis: an infection caused by Strongyloides stercoralis, which is transmitted via the fecal-oral route, penetration through the skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Structure and Function of the Skin, or penetration through the alveoli of the lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs. Strongyloidiasis Strongyloidiasis Strongyloidiasis is a common parasitic disease caused by infection with the roundworm Strongyloides stercoralis. Transmission occurs through skin penetration. Strongyloides has a unique life cycle that can be entirely completed in the human host, migrating from the skin to the pulmonary system and then to the GI system. Strongyloidiasis leads to a constellation of nonspecific symptoms depending on the organ system that is most affected. Diagnosis can be made with a skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Structure and Function of the Skin biopsy, stool studies, or serologic studies. Treatment includes the antihelmintic drugs, ivermectin and albendazole.
  • Colonic ischemia: hypoperfusion to areas of the colon Colon The large intestines constitute the last portion of the digestive system. The large intestine consists of the cecum, appendix, colon (with ascending, transverse, descending, and sigmoid segments), rectum, and anal canal. The primary function of the colon is to remove water and compact the stool prior to expulsion from the body via the rectum and anal canal. Colon, Cecum, and Appendix without redundant sources of arterial blood, known as “watershed” areas, due to thrombosis, embolism, or hypotension Hypotension Hypotension is defined as low blood pressure, specifically < 90/60 mm Hg, and is most commonly a physiologic response. Hypotension may be mild, serious, or life threatening, depending on the cause. Hypotension. The acute phase is characterized by a classic triad of severe abdominal pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain, vomiting, and diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea that may be bloody, and a history of cardiovascular disease. Diagnosis is generally made with laboratory studies and CT with angiography. Treatment includes fluid replacement, antibiotics, systemic anticoagulation, and often surgery.
  • Inflammatory bowel disease:
    • Crohn’s disease: a chronic, inflammatory, autoimmune disease that causes transmural inflammation Inflammation Inflammation is a complex set of responses to infection and injury involving leukocytes as the principal cellular mediators in the body's defense against pathogenic organisms. Inflammation is also seen as a response to tissue injury in the process of wound healing. The 5 cardinal signs of inflammation are pain, heat, redness, swelling, and loss of function. Inflammation and may involve any segment of the GI tract. The terminal ileum and proximal colon Colon The large intestines constitute the last portion of the digestive system. The large intestine consists of the cecum, appendix, colon (with ascending, transverse, descending, and sigmoid segments), rectum, and anal canal. The primary function of the colon is to remove water and compact the stool prior to expulsion from the body via the rectum and anal canal. Colon, Cecum, and Appendix are typically involved. Presents present with crampy abdominal pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain, non-bloody diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea, and extraintestinal symptoms. Definitive diagnosis is made using colonoscopy with biopsies, and treatment may involve antibiotics, corticosteroids, and/or immunomodulators.
    • Ulcerative colitis Ulcerative colitis Ulcerative colitis (UC) is an idiopathic inflammatory condition that involves the mucosal surface of the colon. It is a type of inflammatory bowel disease (IBD), along with Crohn's disease (CD). The rectum is always involved, and inflammation may extend proximally through the colon. Ulcerative Colitis: a chronic, inflammatory, autoimmune disease that causes mucosal ulceration that always involves the rectum Rectum The rectum and anal canal are the most terminal parts of the lower GI tract/large intestine that form a functional unit and control defecation. Fecal continence is maintained by several important anatomic structures including rectal folds, anal valves, the sling-like puborectalis muscle, and internal and external anal sphincters. Rectum and Anal Canal. Unlike those observed in Crohn’s disease, the ulcerations in ulcerative colitis are continuous. Patients present with colicky abdominal pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain, bloody diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea, and tenesmus. Definitive diagnosis is made using colonoscopy with biopsies, and treatment may involve corticosteroids, immunomodulators, and resection surgery.
  • Appendicitis Appendicitis Appendicitis is the acute inflammation of the vermiform appendix and the most common abdominal surgical emergency globally. The condition has a lifetime risk of 8%. Characteristic features include periumbilical abdominal pain that migrates to the right lower quadrant, fever, anorexia, nausea, and vomiting. Appendicitis: an acute inflammation Inflammation Inflammation is a complex set of responses to infection and injury involving leukocytes as the principal cellular mediators in the body's defense against pathogenic organisms. Inflammation is also seen as a response to tissue injury in the process of wound healing. The 5 cardinal signs of inflammation are pain, heat, redness, swelling, and loss of function. Inflammation of the appendix often due to obstruction by fecal matter. Appendicitis Appendicitis Appendicitis is the acute inflammation of the vermiform appendix and the most common abdominal surgical emergency globally. The condition has a lifetime risk of 8%. Characteristic features include periumbilical abdominal pain that migrates to the right lower quadrant, fever, anorexia, nausea, and vomiting. Appendicitis presents with periumbilical pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain that migrates to the RLQ, and with fever Fever Fever is defined as a measured body temperature of at least 38°C (100.4°F). Fever is caused by circulating endogenous and/or exogenous pyrogens that increase levels of prostaglandin E2 in the hypothalamus. Fever is commonly associated with chills, rigors, sweating, and flushing of the skin. Fever, anorexia, nausea, and vomiting. Diagnosis is typically made clinically and is aided by either an ultrasound or CT scan. Treatment involves surgical appendectomy Appendectomy Appendectomy is an invasive surgical procedure performed with the goal of resecting and extracting the vermiform appendix through either an open or a laparoscopic approach. The most common indication is acute appendicitis. Appendectomy, but antibiotic therapy alone may be used in some cases.
  • Diverticulitis: an inflammation Inflammation Inflammation is a complex set of responses to infection and injury involving leukocytes as the principal cellular mediators in the body's defense against pathogenic organisms. Inflammation is also seen as a response to tissue injury in the process of wound healing. The 5 cardinal signs of inflammation are pain, heat, redness, swelling, and loss of function. Inflammation of the diverticula (small outpouching regions of the colon Colon The large intestines constitute the last portion of the digestive system. The large intestine consists of the cecum, appendix, colon (with ascending, transverse, descending, and sigmoid segments), rectum, and anal canal. The primary function of the colon is to remove water and compact the stool prior to expulsion from the body via the rectum and anal canal. Colon, Cecum, and Appendix) often due to obstruction with fecal matter. Diverticulitis presents with abdominal pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain often in the LLQ, nausea, and diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea that may be bloody. The definitive diagnosis is usually based on the findings in a CT scan. Treatment involves bowel rest, IV fluids IV fluids Intravenous fluids are one of the most common interventions administered in medicine to approximate physiologic bodily fluids. Intravenous fluids are divided into 2 categories: crystalloid and colloid solutions. Intravenous fluids have a wide variety of indications, including intravascular volume expansion, electrolyte manipulation, and maintenance fluids. Intravenous Fluids, and antibiotic therapy.

References

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  2. Parija, S.C., Mandal, J., Ponnambath, D.K. (2014). Laboratory methods of identification of Entamoeba histolytica and its differentiation from look-alike Entamoeba spp. Tropical Parasitology, 4(2), 90–95. https://doi.org/10.4103/2229-5070.138535
  3. Leder, K., Weller, P.F. (2021). Intestinal Entamoeba histolytica amebiasis. UpToDate. Retrieved April 11, 2021, from https://www.uptodate.com/contents/intestinal-entamoeba-histolytica-amebiasis
  4. Bercu, T.E., Petri, W.A., Behm, J.W. (2007). Amebic colitis: New insights into pathogenesis and treatment. Current Gastroenterology Reports, 9(5), 429–433. https://doi.org/10.1007/s11894-007-0054-8
  5. Salit, I.E., Khairnar, K., Gough, K., Pillai, D.R. (2009). A possible cluster of sexually transmitted Entamoeba histolytica: Genetic analysis of a highly virulent strain. Clinical infectious diseases: an official publication of the Infectious Diseases Society of America, 49(3), 346–353. https://pubmed.ncbi.nlm.nih.gov/19580413/
  6. Kantor, M., Abrantes, A., Estevez, A., Schiller, A., Torrent, J., Gascon, J., Hernandez, R., Ochner, C. (2018). Entamoeba Histolytica: Updates in clinical manifestation, pathogenesis, and vaccine development. Canadian Journal of Gastroenterology & Hepatology, 4601420. https://www.researchgate.net/publication/329370117_Entamoeba_Histolytica_Updates_in_Clinical_Manifestation_Pathogenesis_and_Vaccine_Development
  7. Stanley S.L. Jr. (2003). Amoebiasis. Lancet (London, England), 361(9362), 1025–1034. https://pubmed.ncbi.nlm.nih.gov/12660071/
  8. Chandnani, S., Udgirkar, S., Jain, S.S., Sonthalia, N., Contractor, Q., Rathi, P.M., Chapekar, A. (2019). Massive lower gastrointestinal bleeding due to fulminant necrotizing amebic colitis: A diagnostic and therapeutic challenge. The Journal of the Association of Physicians of India, 67(4), 79–81.
  9. Nespola, B., Betz, V., Brunet, J., Gagnard, J.C., Krummel, Y., Hansmann, Y., Hannedouche, T., Christmann, D., Pfaff, A.W., Filisetti, D., Pesson, B., Abou-Bacar, A., Candolfi, E. (2015). First case of amebic liver abscess 22 years after the first occurrence. Parasite (Paris, France), 22, 20. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4472968/
  10. Taherian, M., Samankan, S., Cagir, B. (2020). Amebic Colitis. In StatPearls. StatPearls Publishing.
  11. Stanley S. L. Jr. (2001). Protective immunity to amebiasis: New insights and new challenges. The Journal of Infectious Diseases, 184(4), 504–506. https://pubmed.ncbi.nlm.nih.gov/11471109/

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