Entamoeba spp./Amebiasis

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 Sanitation The development and establishment of environmental conditions favorable to the health of the public. Hepatitis E Virus and low socioeconomic conditions.

Etiology

Causative organism: anaerobic protozoan parasites of the Entamoeba Entamoeba A genus of ameboid protozoa characterized by the presence of beaded chromatin on the inner surface of the nuclear membrane. Its organisms are parasitic in invertebrates and vertebrates, including humans. Nitroimidazoles 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 Cysts Any fluid-filled closed cavity or sac that is lined by an epithelium. Cysts can be of normal, abnormal, non-neoplastic, or neoplastic tissues. Fibrocystic Change:

• Fecal-oral route Fecal-oral route Echovirus
• 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 Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship
• Health status:
  • Men who have sex Sex The totality of characteristics of reproductive structure, functions, phenotype, and genotype, differentiating the male from the female organism. Gender Dysphoria with men
  • Advanced age
  • Pregnancy Pregnancy The status during which female mammals carry their developing young (embryos or fetuses) in utero before birth, beginning from fertilization to birth. Pregnancy: Diagnosis, Physiology, and Care
  • Corticosteroid use
  • Malignancy Malignancy Hemothorax
  • 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 Alcoholism A primary, chronic disease with genetic, psychosocial, and environmental factors influencing its development and manifestations. The disease is often progressive and fatal. It is characterized by impaired control over drinking, preoccupation with the drug alcohol, use of alcohol despite adverse consequences, and distortions in thinking, most notably denial. Each of these symptoms may be continuous or periodic. Wernicke Encephalopathy and Korsakoff Syndrome

Pathophysiology

Life cycle Cycle The type of signal that ends the inspiratory phase delivered by the ventilator Invasive Mechanical Ventilation of Entamoeba Entamoeba A genus of ameboid protozoa characterized by the presence of beaded chromatin on the inner surface of the nuclear membrane. Its organisms are parasitic in invertebrates and vertebrates, including humans. Nitroimidazoles species (spp.)

The life cycle Cycle The type of signal that ends the inspiratory phase delivered by the ventilator Invasive Mechanical Ventilation of Entamoeba Entamoeba A genus of ameboid protozoa characterized by the presence of beaded chromatin on the inner surface of the nuclear membrane. Its organisms are parasitic in invertebrates and vertebrates, including humans. Nitroimidazoles 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 Fecal-oral route Echovirus or contaminated water and food: Ingestion of just 1 cyst is sufficient to cause infection.
3. Ingested cysts Cysts Any fluid-filled closed cavity or sac that is lined by an epithelium. Cysts can be of normal, abnormal, non-neoplastic, or neoplastic tissues. Fibrocystic Change become trophozoites Trophozoites Cells or feeding stage in the life cycle of sporozoan protozoa. In the malarial parasite, the trophozoite develops from the merozoite and then splits into the schizont. Trophozoites that are left over from cell division can go on to form gametocytes. Amebicides 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: Anatomy.

Trophozoite stage:

4. Trophozoites Trophozoites Cells or feeding stage in the life cycle of sporozoan protozoa. In the malarial parasite, the trophozoite develops from the merozoite and then splits into the schizont. Trophozoites that are left over from cell division can go on to form gametocytes. Amebicides 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: Anatomy.
5. In 10% of cases, trophozoites Trophozoites Cells or feeding stage in the life cycle of sporozoan protozoa. In the malarial parasite, the trophozoite develops from the merozoite and then splits into the schizont. Trophozoites that are left over from cell division can go on to form gametocytes. Amebicides invade the intestinal mucosa Intestinal Mucosa Lining of the intestines, consisting of an inner epithelium, a middle lamina propria, and an outer muscularis mucosae. In the small intestine, the mucosa is characterized by a series of folds and abundance of absorptive cells (enterocytes) with microvilli. Small Intestine: Anatomy causing bloody diarrhea Bloody diarrhea Diarrhea, local tissue destruction, and other complications.
6. Trophozoites Trophozoites Cells or feeding stage in the life cycle of sporozoan protozoa. In the malarial parasite, the trophozoite develops from the merozoite and then splits into the schizont. Trophozoites that are left over from cell division can go on to form gametocytes. Amebicides undergo binary fission Binary fission Cell Types: Eukaryotic versus Prokaryotic and produce cysts Cysts Any fluid-filled closed cavity or sac that is lined by an epithelium. Cysts can be of normal, abnormal, non-neoplastic, or neoplastic tissues. Fibrocystic Change; both forms are excreted in the diarrheal stool.
7. Trophozoites Trophozoites Cells or feeding stage in the life cycle of sporozoan protozoa. In the malarial parasite, the trophozoite develops from the merozoite and then splits into the schizont. Trophozoites that are left over from cell division can go on to form gametocytes. Amebicides quickly die outside the GI tract, but the cysts Cysts Any fluid-filled closed cavity or sac that is lined by an epithelium. Cysts can be of normal, abnormal, non-neoplastic, or neoplastic tissues. Fibrocystic Change can survive for weeks.

Pathogenesis of invasive infection

1. Trophozoites Trophozoites Cells or feeding stage in the life cycle of sporozoan protozoa. In the malarial parasite, the trophozoite develops from the merozoite and then splits into the schizont. Trophozoites that are left over from cell division can go on to form gametocytes. Amebicides 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: Anatomy and secrete proteases Proteases Proteins and Peptides to invade mucosal cells and cause necrosis Necrosis The death of cells in an organ or tissue due to disease, injury or failure of the blood supply. Ischemic Cell Damage and apoptosis Apoptosis A regulated cell death mechanism characterized by distinctive morphologic changes in the nucleus and cytoplasm, including the endonucleolytic cleavage of genomic DNA, at regularly spaced, internucleosomal sites, I.e., DNA fragmentation. It is genetically-programmed and serves as a balance to mitosis in regulating the size of animal tissues and in mediating pathologic processes associated with tumor growth. Ischemic Cell Damage.
2. Trophozoites Trophozoites Cells or feeding stage in the life cycle of sporozoan protozoa. In the malarial parasite, the trophozoite develops from the merozoite and then splits into the schizont. Trophozoites that are left over from cell division can go on to form gametocytes. Amebicides then release Release Release of a virus from the host cell following virus assembly and maturation. Egress can occur by host cell lysis, exocytosis, or budding through the plasma membrane. Virology 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 Penetration X-rays into the intestinal vasculature.
3. A chain reaction of tissue destruction ensues, including the breakdown of intercellular tight junctions Tight junctions Cell-cell junctions that seal adjacent epithelial cells together, preventing the passage of most dissolved molecules from one side of the epithelial sheet to the other. The Cell: Cell Junctions that leads to “flask-shaped” ulcers and fistulas.
4. Trophozoites Trophozoites Cells or feeding stage in the life cycle of sporozoan protozoa. In the malarial parasite, the trophozoite develops from the merozoite and then splits into the schizont. Trophozoites that are left over from cell division can go on to form gametocytes. Amebicides that have entered the portal circulation Circulation The movement of the blood as it is pumped through the cardiovascular system. ABCDE Assessment may migrate to infect other organs.

Clinical Presentation

The incubation Incubation The amount time between exposure to an infectious agent and becoming symptomatic. Rabies Virus period is usually 2–4 weeks once ingested, but symptoms may develop up to 1 year after infection.

90% of all Entamoeba Entamoeba A genus of ameboid protozoa characterized by the presence of beaded chromatin on the inner surface of the nuclear membrane. Its organisms are parasitic in invertebrates and vertebrates, including humans. Nitroimidazoles infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease are asymptomatic:

• E. histolytica has the highest likelihood of causing symptoms (approximately 10% of cases).
• E. dispar infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease 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 Abdominal Pain Acute Abdomen, often in the RUQ (12%–80%)
  • Bloody stools (94%–100%)
  • Weight loss Weight loss Decrease in existing body weight. Bariatric Surgery (50%)
  • 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 (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: Anatomy, 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: Anatomy, or brain Brain The part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem. Nervous System: Anatomy, Structure, and Classification.
• 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 Antigen Substances that are recognized by the immune system and induce an immune reaction. Vaccination testing:
  • Rapid, 90% sensitive, specific
  • Can differentiate between causative species
  • May involve:
    • ELISA ELISA An immunoassay utilizing an antibody labeled with an enzyme marker such as horseradish peroxidase. While either the enzyme or the antibody is bound to an immunosorbent substrate, they both retain their biologic activity; the change in enzyme activity as a result of the enzyme-antibody-antigen reaction is proportional to the concentration of the antigen and can be measured spectrophotometrically or with the naked eye. Many variations of the method have been developed. St. Louis Encephalitis Virus
    • Radioimmunoassay Radioimmunoassay Classic quantitative assay for detection of antigen-antibody reactions using a radioactively labeled substance (radioligand) either directly or indirectly to measure the binding of the unlabeled substance to a specific antibody or other receptor system. Non-immunogenic substances (e.g., haptens) can be measured if coupled to larger carrier proteins (e.g., bovine gamma-globulin or human serum albumin) capable of inducing antibody formation. Immunoassays
    • Immunofluorescence
• Stool PCR Stool PCR Norovirus:
  • 100% sensitive and specific
  • Expensive
  • Detects DNA DNA A deoxyribonucleotide polymer that is the primary genetic material of all cells. Eukaryotic and prokaryotic organisms normally contain DNA in a double-stranded state, yet several important biological processes transiently involve single-stranded regions. DNA, which consists of a polysugar-phosphate backbone possessing projections of purines (adenine and guanine) and pyrimidines (thymine and cytosine), forms a double helix that is held together by hydrogen bonds between these purines and pyrimidines (adenine to thymine and guanine to cytosine). DNA Types and Structure or RNA RNA A polynucleotide consisting essentially of chains with a repeating backbone of phosphate and ribose units to which nitrogenous bases are attached. RNA is unique among biological macromolecules in that it can encode genetic information, serve as an abundant structural component of cells, and also possesses catalytic activity. RNA Types and Structure in stools
  • Can differentiate between causative species
• Stool microscopy Stool Microscopy Giardia/Giardiasis:
  • Demonstration of cysts Cysts Any fluid-filled closed cavity or sac that is lined by an epithelium. Cysts can be of normal, abnormal, non-neoplastic, or neoplastic tissues. Fibrocystic Change or trophozoites Trophozoites Cells or feeding stage in the life cycle of sporozoan protozoa. In the malarial parasite, the trophozoite develops from the merozoite and then splits into the schizont. Trophozoites that are left over from cell division can go on to form gametocytes. Amebicides
  • RBCs RBCs Erythrocytes, or red blood cells (RBCs), are the most abundant cells in the blood. While erythrocytes in the fetus are initially produced in the yolk sac then the liver, the bone marrow eventually becomes the main site of production. Erythrocytes: Histology within the cytoplasm are suggestive of an E. histolytica infection.
  • A minimum of 3 samples per day is needed for accuracy.
• Serology Serology The study of serum, especially of antigen-antibody reactions in vitro. Yellow Fever Virus:
  • 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: Types and Functions is suggestive of an E. histolytica infection.
  • E. dispar does not generally invoke antibody production.
  • 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: Types and Functions are detected 5–7 days after infection.
    • 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: Types and Functions may persist for years after an acute infection.
    • Serology Serology The study of serum, especially of antigen-antibody reactions in vitro. Yellow Fever Virus cannot distinguish between acute and prior infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease.
• Colonoscopy Colonoscopy Endoscopic examination, therapy or surgery of the luminal surface of the colon. Colorectal Cancer Screening with histologic examination:
  • Not performed routinely due to risk of perforation Perforation A pathological hole in an organ, blood vessel or other soft part of the body, occurring in the absence of external force. Esophagitis of amebic ulcerations
  • Biopsies are performed to obtain samples for microscopy or antigen Antigen Substances that are recognized by the immune system and induce an immune reaction. Vaccination testing.
  • Mucosal thickening and flask-shaped ulcers may be visible.

Management and Prevention

Management

All E. histolytica infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease should be treated regardless of the absence or severity of symptoms; however, E. dispar infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease 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 Metronidazole A nitroimidazole used to treat amebiasis; vaginitis; trichomonas infections; giardiasis; anaerobic bacteria; and treponemal infections. Pyogenic Liver Abscess, can be used to treat infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease within the tissue.
  2. Luminal amebicides Luminal Amebicides Amebicides, such as paromomycin Paromomycin An aminoglycoside antibacterial and antiprotozoal agent produced by species of streptomyces. Amebicides, can eliminate cysts Cysts Any fluid-filled closed cavity or sac that is lined by an epithelium. Cysts can be of normal, abnormal, non-neoplastic, or neoplastic tissues. Fibrocystic Change and trophozoites Trophozoites Cells or feeding stage in the life cycle of sporozoan protozoa. In the malarial parasite, the trophozoite develops from the merozoite and then splits into the schizont. Trophozoites that are left over from cell division can go on to form gametocytes. Amebicides within the intestinal lumen.
• Surgical approach:
  • Drainage of abscesses that resist antibiotic treatment
  • Repair of bowel perforation Bowel perforation Perforated viscus or GI perforation represents a condition in which the integrity of the GI wall is lost with subsequent leakage of enteric contents into the peritoneal cavity, resulting in peritonitis. The causes of perforated viscus include trauma, bowel ischemia, infections, or ulcerative conditions, all of which ultimately lead to a full-thickness disruption of the intestinal wall. Perforated Viscus
  • Colectomy for toxic megacolon Toxic megacolon An acute form of megacolon, severe pathological dilatation of the colon. It is associated with clinical conditions such as ulcerative colitis; Crohn disease; amebic dysentery; or Clostridium enterocolitis. Megacolon

Prevention

• Primary prevention is based on the avoidance of uncooked food and untreated water in endemic areas.
• Water may be treated with iodine Iodine A nonmetallic element of the halogen group that is represented by the atomic symbol I, atomic number 53, and atomic weight of 126. 90. It is a nutritionally essential element, especially important in thyroid hormone synthesis. In solution, it has anti-infective properties and is used topically. Thyroid Hormones before consumption. Amebic cysts Cysts Any fluid-filled closed cavity or sac that is lined by an epithelium. Cysts can be of normal, abnormal, non-neoplastic, or neoplastic tissues. Fibrocystic Change are not susceptible to chlorine treatment.
• A previous infection may confer partial immunity through IgA IgA Represents 15-20% of the human serum immunoglobulins, mostly as the 4-chain polymer in humans or dimer in other mammals. Secretory iga is the main immunoglobulin in secretions. Immunoglobulins: Types and Functions 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: Types and Functions, but recurrent infections Recurrent infections Common Variable Immunodeficiency (CVID) and persistent intestinal colonization Colonization Bacteriology have been documented.

Differential Diagnosis

All conditions that cause nonspecific or bloody diarrhea Bloody diarrhea 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 Infectious Febrile Infant 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 Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease:
  • Shigellosis Shigellosis Shigella: 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 Shigellosis Shigella 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 Intestinal Mucosa Lining of the intestines, consisting of an inner epithelium, a middle lamina propria, and an outer muscularis mucosae. In the small intestine, the mucosa is characterized by a series of folds and abundance of absorptive cells (enterocytes) with microvilli. Small Intestine: Anatomy, 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 Abdominal Pain Acute Abdomen, and bloody diarrhea Bloody diarrhea Diarrhea. Diagnosis is made using Gram staining Gram staining Bacteriology, culture, or PCR PCR Polymerase chain reaction (PCR) is a technique that amplifies DNA fragments exponentially for analysis. The process is highly specific, allowing for the targeting of specific genomic sequences, even with minuscule sample amounts. The PCR cycles multiple times through 3 phases: denaturation of the template DNA, annealing of a specific primer to the individual DNA strands, and synthesis/elongation of new DNA molecules. Polymerase Chain Reaction (PCR). Treatment of shigellosis Shigellosis Shigella includes rehydration Rehydration Dengue Virus, electrolyte replacement, and antibiotic therapy with ciprofloxacin Ciprofloxacin A broad-spectrum antimicrobial carboxyfluoroquinoline. Fluoroquinolones, ceftriaxone Ceftriaxone A broad-spectrum cephalosporin antibiotic and cefotaxime derivative with a very long half-life and high penetrability to meninges, eyes and inner ears. Cephalosporins, or cefixime.
  • Typhoid Typhoid 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) 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 enteric 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: 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 Typhoid 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) 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 leads to invasion of the intestinal mucosa Intestinal Mucosa Lining of the intestines, consisting of an inner epithelium, a middle lamina propria, and an outer muscularis mucosae. In the small intestine, the mucosa is characterized by a series of folds and abundance of absorptive cells (enterocytes) with microvilli. Small Intestine: Anatomy and possibly the bloodstream, causing abdominal pain Abdominal Pain Acute Abdomen, 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 Systemic inflammatory response syndrome with a proven or suspected infectious etiology. When sepsis is associated with organ dysfunction distant from the site of infection, it is called severe sepsis. When sepsis is accompanied by hypotension despite adequate fluid infusion, it is called septic shock. Sepsis and Septic Shock. Diagnosis is generally made with stool cultures Cultures Klebsiella. Treatment includes rehydration Rehydration Dengue Virus, 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 Enterocolitis Inflammation of the mucosa of both the small intestine and the large intestine. Etiology includes ischemia, infections, allergic, and immune responses. Yersinia spp./Yersiniosis: conditions that include abdominal pain Abdominal Pain Acute Abdomen, nausea Nausea An unpleasant sensation in the stomach usually accompanied by the urge to vomit. Common causes are early pregnancy, sea and motion sickness, emotional stress, intense pain, food poisoning, and various enteroviruses. Antiemetics, vomiting Vomiting The forcible expulsion of the contents of the stomach through the mouth. Hypokalemia, and watery to bloody diarrhea Bloody diarrhea Diarrhea, which do not typically lead to sepsis Sepsis Systemic inflammatory response syndrome with a proven or suspected infectious etiology. When sepsis is associated with organ dysfunction distant from the site of infection, it is called severe sepsis. When sepsis is accompanied by hypotension despite adequate fluid infusion, it is called septic shock. Sepsis and Septic Shock in otherwise healthy patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship. 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. Yersinia spp./Yersiniosis spp., and Escherichia spp. These gram-negative bacilli Bacilli Shigella 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 Self-Limiting Meningitis in Children, but treatment may include rehydration Rehydration Dengue Virus, electrolyte replacement, and ciprofloxacin Ciprofloxacin A broad-spectrum antimicrobial carboxyfluoroquinoline. Fluoroquinolones if indicated.
  • Pseudomembranous colitis Colitis Inflammation of the colon section of the large intestine, usually with symptoms such as diarrhea (often with blood and mucus), abdominal pain, and fever. Pseudomembranous Colitis: an infection caused by C. difficile. Although the causative organism is commonly found in the normal gut microbiome Microbiome Commensal organisms living in and on the body Innate Immunity: Barriers, Complement, and Cytokines, 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 Abdominal Pain Acute Abdomen, and nausea Nausea An unpleasant sensation in the stomach usually accompanied by the urge to vomit. Common causes are early pregnancy, sea and motion sickness, emotional stress, intense pain, food poisoning, and various enteroviruses. Antiemetics with vomiting Vomiting The forcible expulsion of the contents of the stomach through the mouth. Hypokalemia. Diagnosis is made using stool PCR Stool PCR Norovirus or enzyme assays. Treatment generally consists of discontinuing the offending antibiotic and commencing oral fidaxomicin or vancomycin Vancomycin Antibacterial obtained from streptomyces orientalis. It is a glycopeptide related to ristocetin that inhibits bacterial cell wall assembly and is toxic to kidneys and the inner ear. Glycopeptides.
• Parasitic infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease:
  • Giardiasis Giardiasis An infection of the small intestine caused by the flagellated protozoan giardia. It is spread via contaminated food and water and by direct person-to-person contact. Giardia/Giardiasis: an infection caused by Giardia Giardia A genus of flagellate intestinal eukaryotes parasitic in various vertebrates, including humans. Characteristics include the presence of four pairs of flagella arising from a complicated system of axonemes and cysts that are ellipsoidal to ovoidal in shape. Nitroimidazoles, which are flagellated protozoans Protozoans Cell Types: Eukaryotic versus Prokaryotic causing infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease after the consumption of cysts Cysts Any fluid-filled closed cavity or sac that is lined by an epithelium. Cysts can be of normal, abnormal, non-neoplastic, or neoplastic tissues. Fibrocystic Change via the fecal-oral route Fecal-oral route Echovirus or contaminated water. The hallmark symptom is foul-smelling steatorrhea Steatorrhea A condition that is characterized by chronic fatty diarrhea, a result of abnormal digestion and/or intestinal absorption of fats. Diarrhea resulting from malabsorption Malabsorption General term for a group of malnutrition syndromes caused by failure of normal intestinal absorption of nutrients. Malabsorption and Maldigestion. Diagnosis is made based on stool microscopy Stool Microscopy Giardia/Giardiasis or antigen Antigen Substances that are recognized by the immune system and induce an immune reaction. Vaccination testing. Treatment is with supportive care and antibiotics such as metronidazole Metronidazole A nitroimidazole used to treat amebiasis; vaginitis; trichomonas infections; giardiasis; anaerobic bacteria; and treponemal infections. Pyogenic Liver Abscess. 
  • 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 Strongyloides stercoralis A species of parasitic nematode widely distributed in tropical and subtropical countries. The females and their larvae inhabit the mucosa of the intestinal tract, where they cause ulceration and diarrhea. Strongyloidiasis, which is transmitted via the fecal-oral route Fecal-oral route Echovirus, penetration Penetration X-rays 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. Skin: Structure and Functions, or penetration Penetration X-rays through the alveoli Alveoli Small polyhedral outpouchings along the walls of the alveolar sacs, alveolar ducts and terminal bronchioles through the walls of which gas exchange between alveolar air and pulmonary capillary blood takes place. Acute Respiratory Distress Syndrome (ARDS) 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: Anatomy. 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. Skin: Structure and Functions biopsy Biopsy Removal and pathologic examination of specimens from the living body. Ewing Sarcoma, stool studies, or serologic studies. Treatment includes the antihelmintic drugs, ivermectin Ivermectin A mixture of mostly avermectin h2b1a (rn 71827-03-7) with some avermectin h2b1b (rn 70209-81-3), which are macrolides from streptomyces avermitilis. It binds glutamate-gated chloride channel to cause increased permeability and hyperpolarization of nerve and muscle cells. It also interacts with other chloride channels. It is a broad spectrum antiparasitic that is active against microfilariae of onchocerca volvulus but not the adult form. Anthelmintic Drugs and albendazole Albendazole A benzimidazole broad-spectrum anthelmintic structurally related to mebendazole that is effective against many diseases. Anthelmintic Drugs.
• Colonic ischemia Ischemia A hypoperfusion of the blood through an organ or tissue caused by a pathologic constriction or obstruction of its blood vessels, or an absence of blood circulation. Ischemic Cell Damage: 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: Anatomy without redundant sources of arterial blood, known as “watershed” areas, due to thrombosis Thrombosis Formation and development of a thrombus or blood clot in the blood vessel. Epidemic Typhus, 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 Acute phase Short Bowel Syndrome is characterized by a classic triad of severe abdominal pain Abdominal Pain Acute Abdomen, vomiting Vomiting The forcible expulsion of the contents of the stomach through the mouth. Hypokalemia, 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 Angiography Radiography of blood vessels after injection of a contrast medium. Cardiac Surgery. Treatment includes fluid replacement, antibiotics, systemic anticoagulation Anticoagulation Pulmonary Hypertension Drugs, and often surgery.
• Inflammatory bowel disease:
  • Crohn’s disease: a chronic, inflammatory, autoimmune disease that causes transmural inflammation Transmural inflammation Crohn’s Disease and may involve any segment of the GI tract. The terminal ileum Ileum The distal and narrowest portion of the small intestine, between the jejunum and the ileocecal valve of the large intestine. Small Intestine: Anatomy 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: Anatomy are typically involved. Presents present with crampy abdominal pain Abdominal Pain Acute Abdomen, 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 Colonoscopy Endoscopic examination, therapy or surgery of the luminal surface of the colon. Colorectal Cancer Screening with biopsies, and treatment may involve antibiotics, corticosteroids Corticosteroids Chorioretinitis, and/or immunomodulators.
  • Ulcerative colitis Colitis Inflammation of the colon section of the large intestine, usually with symptoms such as diarrhea (often with blood and mucus), abdominal pain, and fever. Pseudomembranous Colitis: a chronic, inflammatory, autoimmune disease that causes mucosal ulceration Ulceration Corneal Abrasions, Erosion, and Ulcers 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: Anatomy. Unlike those observed in Crohn’s disease, the ulcerations in ulcerative colitis Colitis Inflammation of the colon section of the large intestine, usually with symptoms such as diarrhea (often with blood and mucus), abdominal pain, and fever. Pseudomembranous Colitis are continuous. Patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship present with colicky abdominal pain Abdominal Pain Acute Abdomen, bloody diarrhea Bloody diarrhea Diarrhea, and tenesmus. Definitive diagnosis is made using colonoscopy Colonoscopy Endoscopic examination, therapy or surgery of the luminal surface of the colon. Colorectal Cancer Screening with biopsies, and treatment may involve corticosteroids Corticosteroids Chorioretinitis, 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 Acute Inflammation Inflammation of the appendix Appendix A worm-like blind tube extension from the cecum. Colon, Cecum, and Appendix: Anatomy 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 An unpleasant sensation induced by noxious stimuli which are detected by nerve endings of nociceptive neurons. Pain: Types and Pathways 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 Anorexia The lack or loss of appetite accompanied by an aversion to food and the inability to eat. It is the defining characteristic of the disorder anorexia nervosa. Anorexia Nervosa, nausea Nausea An unpleasant sensation in the stomach usually accompanied by the urge to vomit. Common causes are early pregnancy, sea and motion sickness, emotional stress, intense pain, food poisoning, and various enteroviruses. Antiemetics, and vomiting Vomiting The forcible expulsion of the contents of the stomach through the mouth. Hypokalemia. 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 Diverticulitis Inflammation of a diverticulum or diverticula. Diverticular Disease: 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: Anatomy) often due to obstruction with fecal matter. Diverticulitis Diverticulitis Inflammation of a diverticulum or diverticula. Diverticular Disease presents with abdominal pain Abdominal Pain Acute Abdomen often in the LLQ, nausea Nausea An unpleasant sensation in the stomach usually accompanied by the urge to vomit. Common causes are early pregnancy, sea and motion sickness, emotional stress, intense pain, food poisoning, and various enteroviruses. Antiemetics, 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.