Gastritis and Gastric Ulcers

• Causative Organism: Helicobacter pylori.
• Mode of Transmission: Oral–oral or oral–fecal route.
• Virulence Factors: Adhesins and urease.
• Culture/Diagnosis: Direct Antigen test on stool or urea breath test.
• Prevention: None.
• Treatment: Clarithromycin and acid suppression.
• Signs and Symptoms: Sharp or burning abdominal pain and mucosal lesions

Bacterial Acute Diarrhea (Salmonella)

• Causative Organism: Salmonella
• Mode of Transmission: Vehicle (contaminated food or beverage) and fecal–oral route.
• Virulence Factors: Adhesins and endotoxin.
• Culture/Diagnosis: Stool culture (though not always necessary).
• Prevention: Strict food hygiene and personal hygiene.
• Treatment: Primarily rehydration; for complicated cases, ciprofloxacin is used.
• Usually, a fever is present, and there is sometimes blood in the stool
• Signs and Symptoms: Ranges from mild gastroenteritis (vomiting, diarrhea, and mucosal irritation) to severe fever and septicemia

Bacterial Acute Diarrhea (Shigella)

• Causative Organism: Shigella species (e.g., Shigella dysenteriae).
• Mode of Transmission: Fecal–oral route and direct contact.
• Virulence Factors: Endotoxins, enterotoxins, and Shiga toxins (in some strains).
• Culture/Diagnosis: Stool culture and antigen testing for Shiga toxin.
• Prevention: Food hygiene and personal hygiene.
• Treatment: Azithromycin or ciprofloxacin.
• Signs and Symptoms: Frequent watery stools, fever, intense abdominal pain, nausea, and vomiting; frequently involves dysentery (bloody stools)

Bacterial Acute Diarrhea (Shiga)

• Causative Organism: Shiga-Toxin-Producing Escherichia coli (STEC) E. coli O157:H7 and other strains.
• Mode of Transmission: Vehicle (contaminated food/beverages) and fecal–oral route.
• Virulence Factors: Shiga toxins and specialized proteins for attachment, secretion, and effacement.
• Culture/Diagnosis: Stool culture and antigen testing for Shiga toxin.
• Prevention: Thoroughly cooking meat, cleaning vegetables, and monitoring food recalls.
• Treatment: Antibiotics are contraindicated; supportive measures and rehydration are used.
• Signs and Symptoms: Fever and bloody diarrhea; a serious complication is hemolytic uremic syndrome (HUS), which can lead to kidney failure

Bacterial Acute Diarrhea (Non-Shiga E. coli)

• Causative Organism: Other E. coli (non-shiga-toxin producing)
• Mode of Transmission: Vehicle, fecal–oral
• Virulence factors: Various: proteins for attachment, secretion, effacement; heat-labile, and/or heat-stable exotoxins; invasiveness
• Culture/Diagnosis: Stool culture not usually necessary in absence of blood, fever
• Prevention: Food and personal hygiene
• Treatment: Rehydration, antimotility agent
• Signs and Symptoms: Different strains of E. coli cause distinct diarrheal diseases: ETEC causes traveler’s watery diarrhea, EIEC causes dysentery with blood and mucus, EPEC leads to profuse watery diarrhea by damaging intestinal surfaces, EAEC causes chronic diarrhea (especially in children and AIDS patients), and DAEC is linked to diarrhea and urinary tract infections.

Bacterial Acute Diarrhea (Campylo)

• Causative Organism: Campylobacter jejuni.
• Mode of Transmission: Vehicle (food or water) and fecal–oral route.
• Virulence Factors: Adhesins, exotoxins, and the induction of autoimmunity.
• Culture/Diagnosis: Stool culture (not usually required) and dark-field microscopy.
• Prevention: Food and personal hygiene.
• Treatment: Rehydration; azithromycin is reserved for severe cases.
• Signs and Symptoms: Frequent watery stools, fever, vomiting, headaches, and severe abdominal pain; can lead to Guillain–Barré syndrome, a type of paralysis

Bacterial Acute Diarrhea (Cholera)

• Causative Organism: Vibrio cholerae.
• Mode of Transmission: Vehicle (contaminated water and certain foods) and fecal–oral route.
• Virulence Factors: Cholera toxin (CT), which causes intestinal cells to shed large amounts of electrolytes.
• Culture/Diagnosis: Clinical diagnosis, microscopic techniques, and serological detection of antitoxin.
• Prevention: Comprehensive water and food hygiene.
• Treatment: Intensive oral rehydration therapy; possibly doxycycline.
• Signs and Symptoms: Vomiting and copious watery feces known as "rice-water stools", leading to extreme dehydration, hypotension, and shock

Bacterial Acute Diarrhea (Chostridioides)

• Causative Organism: Clostridioides difficile.
• Mode of Transmission: Endogenous (part of normal biota, but triggered by antibiotic use).
• Virulence Factors: Enterotoxins A and B.
• Culture/Diagnosis: Stool culture, PCR, or ELISA for toxins in the stool.
• Prevention: N/A (avoiding broad-spectrum antibiotic misuse is key).
• Treatment: Withdrawal of the causative antibiotic; treatment with vancomycin or fidaxomicin, or fecal transplants for recurrent cases.
• Signs and Symptoms: Diarrhea with prominent mucus; can progress to pseudomembranous colitis

Bacterial Acute Diarrhea (Vibrio choler)

• Causative Organism: Vibrio cholerae
• Modes of Transmission: Vehicle (water and some foods), fecal–oral
• Virulence Factors: The primary virulence factor is the cholera toxin (CT), which disrupts the normal physiology of intestinal cells, causing them to shed massive amounts of electrolytes.
• Culture and Diagnosis: Clinical diagnosis, microscopic techniques, serological detection of antitoxin
• Prevention: Water and food hygiene
• Treatment: Rehydration and possibly doxycycline
• Signs and Symptoms: Vomiting, Copious watery feces, “rice-water stool”, Profuse water loss, Loss of blood volume, acidosis, potassium depletion,
  muscle cramps, severe thirst, flaccid skin, and sunken eyes; convulsions and coma in young children, Hypotension, tachycardia, cyanosis, shock

Bacterial Acute Diarrhea (Non-Cholera Vibrio)

• Causative Organism: Non-cholera Vibrio species such as V. vulnificus and V. parahaemolyticus.
• Mode of Transmission: Vehicle (contaminated food, particularly raw shellfish, or natural bodies of water).
• Virulence Factors: Not explicitly listed.
• Culture/Diagnosis: Culture of stool or blood.
• Prevention: Avoiding the consumption of raw shellfish.
• Treatment: Doxycycline.
• Signs and Symptoms: Fever; potential for sepsis to follow the initial infection

Nonbacterial Acute Diarrhea (Cryptosporidium)

• Causative organism: Cryptosporidium
• Mode of Transmission: Vehicle (water, food), fecal–oral
• Virulence Factors: Intracellular growth
• Culture/Diagnosis: Acid-fast staining, ruling out bacteria
• Prevention: Water treatment, proper food handling
• Treatment: None or nitazoxanide
• Signs and Symptoms: headache, sweating, vomiting, severe
  abdominal cramps, and diarrhea

Nonbacterial Acute Diarrhea (Rotavirus)

• Causative organism: Rotavirus
• Mode of Transmission: Fecal–oral, vehicle, fomite
• Virulence Factors: N/A
• Culture/Diagnosis: Rapid antigen test
• Prevention: Oral live-virus vaccine
• Treatment: Rehydration
• Signs and Symptoms: Watery diarrhea, vomiting, low–moderate fever, abdominal cramps, dehydration (dry mouth, decreased urination, sunken eyes, lethargy)

Nonbacterial Acute Diarrhea (Norovirus)

• Causative organism: Norovirus
• Mode of Transmission: Indirect, vehicle (food), direct contact
• Virulence Factors: Limited immunity to reinfection
• Culture/Diagnosis: Rapid antigen test
• Prevention: Hygiene
• Treatment: Rehydration
• Signs and Symptoms: Profuse, watery diarrhea for 3 to 5 days, vomiting in the
  early stages, mild fever

Acute Diarrhea w/ vomiting caused by exotoxin (Staph)

• Causative organism: Staphylococcus aureus exotoxin
• Mode of Transmission: Vehicle (food)
• Virulence Factors: Heat-stable exotoxin
• Culture/Diagnosis: Usually based on
  epidemiological evidence
• Prevention: Proper food handling
• Treatment: Supportive
• Signs and Symptoms: Acute diarrhea with prominent vomiting caused by the exotoxin of Staphylococcus aureus has a rapid onset (1–6 hours) with severe nausea, abdominal cramps, mild non-bloody diarrhea, and little to no fever.

Acute Diarrhea w/ vomiting caused by exotoxin (Bacillus)

• Causative organism: Bacillus cereus exotoxin
• Mode of Transmission: Vehicle (food)
• Virulence Factors: Heat-stable toxin, heat-labile toxin
• Culture/Diagnosis: Microscopic analysis of food or stool
• Prevention: Proper food handling
• Treatment: Supportive
• Signs and Symptoms: Acute diarrhea with vomiting caused by the exotoxin of Bacillus cereus has a rapid onset (1–6 hours) with prominent nausea and vomiting, mild diarrhea, abdominal cramps, and little to no fever.

Acute Diarrhea w/ vomiting caused by exotoxin (Clostridium)

• Causative organism: Clostridium perfringens exotoxin
• Mode of Transmission: Vehicle (food)
• Virulence Factors: Heat-labile toxin
• Culture/Diagnosis: Detection of toxin in
  stool
• Prevention: Proper food handling
• Treatment: Supportive
• Signs and Symptoms: Acute diarrhea with vomiting caused by exotoxin from Clostridium perfringens typically has a slower onset (8–16 hours) with abdominal cramps and watery diarrhea, while vomiting and fever are uncommon.

Chronic Diarrhea (EAEC)

• Causative Organism: Enteroaggregative E. coli.
• Mode of Transmission: Vehicle (food and water) or the fecal–oral route.
• Virulence Factors: This organism adheres to human cells in aggregates rather than single cells and stimulates the production of large amounts of mucus in the gut.
• Culture/Diagnosis: It is difficult to distinguish from other E. coli strains during diagnosis.
• Prevention: Not specifically listed in the sources.
• Treatment: Rehydration or ciprofloxacin.
• Signs and Symptoms: Chronic diarrhea, particularly common in young children, the malnourished, and patients with AIDS

Chronic Diarrhea (Cyclospora)

• Causative Organism: Cyclospora cayetanensis (an emerging protozoan pathogen).
• Mode of Transmission: Fecal–oral transmission via contaminated fresh produce and water.
• Virulence Factors: Invasiveness.
• Culture/Diagnosis: Stool examination or PCR; oocysts in the feces can be visualized when exposed to UV light.
• Prevention: Thoroughly washing and cooking food, along with personal hygiene.
• Treatment: TMP-SMZ.
• Signs and Symptoms: Watery diarrhea, stomach cramps, bloating, fever, and muscle aches

Chronic Diarrhea (Giardia)

• Causative Organism: Giardia duodenalis (also known as G. intestinalis or G. lamblia).
• Mode of Transmission: Vehicle, fecal–oral route, and direct or indirect contact. It is frequently isolated from animal reservoirs like beavers and cattle, and epidemics are often traced to mountain streams or chlorinated municipal water.
• Virulence Factors: Attachment to the intestines, which alters the mucosa.
• Culture/Diagnosis: Stool examination or ELISA.
• Prevention: Water and personal hygiene.
• Treatment: Tinidazole or nitazoxanide.
• Signs and Symptoms: Long-duration diarrhea, abdominal pain, and flatulence; a hallmark sign is greasy, malodorous (foul-smelling) stools

Chronic Diarrhea (Entamoeba)

• Causative Organism: Entamoeba histolytica.
• Mode of Transmission: Vehicle or fecal–oral route; infection typically occurs through food and water contaminated with cysts.
• Virulence Factors: Lytic enzymes that dissolve tissues, induction of apoptosis, and invasiveness.
• Culture/Diagnosis: PCR, stool examination, ELISA, or serology.
• Prevention: Water and personal hygiene.
• Treatment: Metronidazole or paromomycin.
• Signs and Symptoms: Intestinal amoebiasis involves dysentery (bloody, mucus-filled stools), abdominal pain, fever, and weight loss. It can also lead to extraintestinal forms where the amoeba invades the liver

Hepatitis A

• Causative organism: Hepatitis A or E virus
• Mode of Transmission: Fecal–oral, vehicle
• Virulence Factors: N/A
• Culture/Diagnosis: IgM serology
• Prevention: Hepatitis A vaccine or combined; HAV/HBV vaccine
• Treatment: HAV: hepatitis A vaccine or
  immune globulin; HEV: immune globulin
• Signs and Symptoms: Subclinical or vague, flu-like symptoms and Jaundice in only 10% of cases w/ incubation period of 2–4 weeks

Hepatitis B

• Causative organism: Hepatitis B virus
• Mode of Transmission: Parenteral (blood contact), direct contact (especially sexual), vertical
• Virulence Factors: Latency
• Culture/Diagnosis: ELISA
• Prevention: HBV recombinant vaccine
• Treatment: Interferon, tenofovir, or entecavir
• Signs and Symptoms: Fever, chills, malaise, anorexia, abdominal discomfort, diarrhea, and nausea, rashes, and arthritis may occur, and cause hepatocellular carcinoma w/ incubation period of 1-6 months

Hepatitis C

• Causative organism: Hepatitis C virus
• Mode of Transmission: Parenteral (blood contact), vertical
• Virulence Factors: Core protein suppresses immune function?
• Culture/Diagnosis: Serology, also PCR
• Prevention: N/A
• Treatment: Sofosbuvir + simeprevir
• Signs and Symptoms: Similar to hepatitis B virus and 75% to 85% remain infected indefinitely w/ incubation period of 2-8 weeks

Intestinal Distress (pinworm)

• Causative organism: Enterobius vermicularis (pinworm)
• Mode of Transmission: Cycle A: vehicle (food, water), fomites, self-inoculation
• Virulence Factors: N/A
• Culture/Diagnosis: Adhesive tape + microscopy
• Prevention: Hygiene
• Treatment: Mebendazole, piperazine
• Signs and Symptoms: pronounced anal itching

Intestinal Distress (whipworm)

• Causative organism: Trichuris trichiura (whipworm)
• Mode of Transmission: Cycle A: vehicle (soil), fecal–oral
• Virulence Factors: Burrowing and invasiveness
• Culture/Diagnosis: Blood count, serology, egg or worm detection
• Prevention: Hygiene, sanitation
• Treatment: Mebendazole
• Signs and Symptoms: localized hemorrhage of the bowel, dysentery, loss of muscle tone, rectal prolapse (can be fatal in children)

Intestinal Distress (fish tapeworm)

• Causative organism: Diphyllobothrium latum (fish tapeworm)
• Mode of Transmission: Cycle C: vehicle (seafood)
• Virulence Factors: Vitamin B12 usage
• Culture/Diagnosis: Blood count, serology, egg or worm detection
• Prevention: Cook meat
• Treatment: Praziquantel
• Signs and Symptoms: abdominal discomfort or nausea, anemia

Intestinal Distress (Hymenolepis)

• Causative organism: Hymenolepis nana and H. diminuta
• Mode of Transmission: Cycle C: vehicle (ingesting insects), fecal–oral
• Virulence Factors: N/A
• Culture/Diagnosis: Blood count, serology, egg or worm detection
• Prevention: Hygienic environment
• Treatment: Praziquantel
• Signs and Symptoms: Infection with Hymenolepis nana (or other Hymenolepis species) often causes mild or no symptoms, but can include abdominal pain, diarrhea, irritability, loss of appetite, nausea, and sometimes anal itching—especially in heavy infections.

Intestinal Distress Plus Migratory Symptoms (Toxo)

• Causative organism: Toxocara species
• Mode of Transmission: Cycle A: dog or cat feces
• Virulence Factors: N/A
• Culture/Diagnosis: Blood count, serology, egg or worm detection
• Prevention: Hygiene
• Treatment: Albendazole
• Signs and Symptoms: may cause mild intestinal distress (nausea, abdominal discomfort, diarrhea) along with “migratory” flu-like symptoms such as fever, fatigue, muscle aches, and swollen lymph nodes due to systemic spread of the parasite after ingestion.

Intestinal Distress Plus Migratory Symptoms (Ascaris)

• Causative organism: Ascaris lumbricoides (intestinal roundworm)
• Mode of Transmission: Cycle A: vehicle (soil/fecal–oral), fomites, self-inoculation
• Virulence Factors: Induction of hypersensitivity, adult worm migration, abdominal obstruction
• Culture/Diagnosis: Blood count, serology, egg or worm detection
• Prevention: Hygiene
• Treatment: Albendazole
• Signs and Symptoms: can cause intestinal distress (abdominal pain, nausea, diarrhea, or bowel obstruction in heavy infections) plus migratory respiratory symptoms during larval lung migration, including cough, wheezing, fever, and eosinophilic pneumonia (Löffler syndrome).

Intestinal Distress Plus Migratory Symptoms (Necator)

• Causative organism: Necator americanus and Ancylostoma duodenale (hookworms)
• Mode of Transmission: Cycle B: vehicle (soil), fomite
• Virulence Factors: Induction of hypersensitivity, adult worm migration,
  abdominal obstruction
• Culture/Diagnosis: Blood count, serology, egg or worm detection
• Prevention: Sanitation
• Treatment: Albendazole
• Signs and Symptoms: causes intestinal distress such as abdominal pain, diarrhea, and iron-deficiency anemia, along with migratory symptoms during larval lung passage including cough, wheezing, and eosinophilic inflammation (Löffler-like syndrome).

Cysticercosis

• Causative organism: Taenia solium (pork tapeworm)
• Mode of Transmission: Cycle C: vehicle (pork), fecal–oral
• Virulence Factors: N/A
• Culture/Diagnosis: Blood count, serology, egg or worm detection
• Prevention: Cook meat, avoid pig feces
• Treatment: Praziquantel
• Signs and Symptoms: subcutaneous nodules, muscle pain, and especially seizures, headaches, and neurologic deficits when the brain is involved (neurocysticercosis).

Liver and Intestinal Disease (Opis)

• Causative organism: Opisthorchis sinensis, Clonorchis sinensis
• Mode of Transmission: Cycle D: vehicle (fish or crustaceans)
• Virulence Factors: N/A
• Culture/Diagnosis: Blood count, serology, egg or worm detection
• Prevention: Cook food, sanitation of water
• Treatment: Praziquantel
• Signs and Symptoms: Slow to develop, thickening of the lining of the bile duct, granuloma formation in areas of the liver, and bile duct may be blocked

Liver and Intestinal Disease (Fasciola)

• Causative organism: Fasciola hepatica
• Mode of Transmission: Cycle D: vehicle (water and water plants)
• Virulence Factors: N/A
• Culture/Diagnosis: Blood count, serology, egg or worm detection
• Prevention: Sanitation of water
• Treatment: Triclabendazole
• Signs and Symptoms: vomiting, diarrhea, hepatomegaly, and bile obstruction if infected with a large number of flukes

Muscle and Neurological Symptoms Disease

• Causative organism: Trichinella species
• Mode of Transmission: Vehicle (food)
• Virulence Factors: N/A
• Culture/Diagnosis: Serology combined with clinical picture; muscle biopsy
• Prevention: Cook meat
• Treatment: Mebendazole, steroids
• Signs and Symptoms: Symptoms range from unnoticeable to life-threatening:
  • First phase: diarrhea, nausea, abdominal pains, fever, and sweating
  • Second phase: puffiness around the eyes, intense muscle and joint pain, shortness of breath, and eosinophilia

Schistosomiasis Liver Disease

• Causative organism: Schistosoma mansoni, S. japonicum
• Mode of Transmission: Cycle D: vehicle (contaminated water)
• Virulence Factors: Antigenic “cloaking”
• Culture/Diagnosis: Identification of eggs in feces, scarring of intestines detected by endoscopy
• Prevention: Avoiding contaminated vehicles
• Treatment: Praziquantel
• Signs and Symptoms: Itchiness in the area where the worm enters the body,
  fever, chills, diarrhea, and cough
  • Chronic infection: hepatomegaly, liver disease,
  splenomegaly, bladder obstruction, and blood in the urine, and can cause a granulomatous response in the nervous system and heart