Diarrhea Workshop
Viral Etiology
Reoviridae (dsRNA)
Rotavirus can cause vomiting and watery diarrhea. Viral nsP4 protein is the viral enterotoxin that causes the diarrhea. Usually infants less than 2 y.o. Dx. By immune EM. Clumping of virus Ag with virus specific Ab: RT-PCR.
Adenoviridae (DNA virus)
Enteric adenovirus types 40 & 41 infect the Peyer’s patches. Causes acute viral gastroenteritis similar to rotavirus (especially in infants). Dx. ELISA assays to detect viral Ag or Ab. Tx. w/ Abs.
Caliciviridae (ssRNA +)
Sapovirus and Norovirus infect intestinal brush border. Prevent proper absorption of water and nutrient. No seasonal incidence. Dx. ELISA assays to detect viral Ag or Ab. Tx. No vaccines or antiviral drugs available.
HEV is fecal oral transmission. Similar entry through GI tract. Moves to liver infx.
Astroviruses (small, +ssRNA) cause outbreaks of diarrhea in children, most often in the winter. Dx. ELISA assays to detect viral Ag or Ab in patient specimens.
Picornaviridae
Hepatitis A Virus can cause diarrhea. The big thing here is to look at Jaundice. A biopsy gives a good indicator of disease severity. Dx. IgM Ab to HAV Ag in acute phase.
Pharmacologic etiology
Erythromycin is a GI motilist, causing diarrhea.
Bacteriologic Etiology
Bacillus cereus causes two types of common food-borne intoxications. The short-incubation form is heat stable enterotoxin that is associated with nausea, vomiting, and abdominal cramps. Most often after rice contamination. Resembles S. aureus in its symptoms and incubation period (1-6 hrs). The long-incubation form is diarrheal, heat-labible enterotoxin. Resembles C. perfringens. Incubation of 8-16 hrs. Toxin stimulates the adenylate cyclase-cAMP cycle in the intestinal epithelium. Illness is usually self-limiting, less than 24 hrs. of onset. Tx. Maintain fluids.
Clostridium perfringens, Gm+ anaerobic rod, nonmotile, resistant endospores. Fecal contaminated water. Many potent toxins. Alpha toxin conveys destruction (lecithinase) that lyses the host cells and increases vascular permeability. One of most commonly reported food borne illness. Presents w/in 8-24 hrs. Intense abdominal cramps and diarrhea. Usually self limiting.
Clostridium difficile induces diarrhea from toxins. C. diff colonizes the colon after normal gut flora decimated by AB like clindamycin. Heat-resistant spores. Tx. metronidazole (1st) and Vancomycin (2nd). A toxin is enterotoxin that causes inflammation. Toxin B kills. Pseudomembranous colitis is caused by leukocytic infiltration into lamina propria, elaboration of fibrin, mucus, and leukocytes. Patches of pseudomembrane form on the mucosa. Dx. Volcano-like lesions. Loose stool frequency of 3 or more daily for at least 1-2 days. Anaerobic culture of stool that displays cytotoxic activity. PCR of stool for toxins is possible too but expensive.
Tropheryma whippelii Gm+ rod, doesn’t Gm stain well, infects macrophages in GI. Causes malbasorption and diarrhea. Dx. By intestinal biopsy for PAS-positive macrophage inclusions. Confirm with PCR. Tx. Penicillin/streptomycin with long term trimeth-sulfa.
Campylobacter jejuni is the number 1 cause of bacterial gastroenteritis in the US. Causes dysentery. Fever, abdominal pain that can mimic appendicitis, diarrhea (often bloody). Self limiting, symptoms last about a week. Low ID50. Transmission via contaminated food, especially chicken. Person to person spread is rare. Damages mucosal surfaces of the jejunum and colon (ulcerated and bloody). Infiltration of lamina propria with neutrophils, monocytes, and eosinophils. Cytolethal distending toxin (CDT) delivers DNAse to host cell blocking mitosis and triggering apoptosis (killing cells). Can lead to Guillain-Barre Syndrome where macrophages move to nerves where demyelination occurs. Why? Because C. jejuni looks like self. Tx. With rehydration and erythromycin or azithromycin if necessary.
Vibrio cholerae is Gm- comma shaped motile rod, facultative anaerobe with single flagellum. Presents 2-4 days after ingestion of food, water, or improperly cooked shellfish. Abrupt onset of watery diarrhea and vomiting. Rice water stools (loaded with mucus flecks). Severe dehydration. Tx. With IV fluids and electrolytes. AB exotoxin. B binds to intestinal cells. A is internalized. Locks the adenylate cyclase in the “ON” phase, so its always producing cAMP therefore pumping out water and electrolytes. Very acid sensitive, most in stomach will die. Therefore large ID50. Secretory Diarrhea.
Vibrio parahaemolyticus is self limiting (3 days). Explosive onset of watery diarrhea w/in 24 hrs. Leading cause of gastro w/ raw shellfish. Tx. Rehydration.
Vibrio vulnificus causes diarrhea, nausea, vomiting, abdom. cramps after ingestion. In immunocompromised patients can cause blistering skin wounds. Can cause necrotizing fasciitis if enters a wound. Tx. Tetracycline+ fluoroquinolone or cefotaxime.
Yersinia pestis causes diarrhea. Also fever, weakness, and severe pain with rashes. Tx. Streptomycin.
Escherichia
Shigella
Salmonella
Staphylococcus
Listeria