ACUTE INFECTIOUS DISEASE Flashcards
- passage of abnormally liquid or unformed stools at an increased frequency
- Stool weight >200 g/day
DIARRHEA
TWO COMMON CONDITIONS, USUALLY ASSOCIATED
WITH THE PASSAGE OF STOOL TOTALING <200 G/D
|. Pseudodiarrhea
2. Fecal Incontinence
- frequent passage of small volumes of |
- often associated with rectal urgency, tenesmus, or a feeling of incomplete evacuation
- accompanies IBS or proctitis
PSEUDODIARRHEA
- involuntary discharge of rectal contents
- most often caused by neuromuscular disorders or structural anorectal problems
FECAL INCONTINENCE
DURATION OF DIARRHEA
- acute if <2 weeks
- persistent if 2-4 weeks
- chronic if >4 weeks in duration.
- > 90% of cases of acute diarrhea are caused by infectious agents vomiting, fever, and abdominal pain.
- 10% are caused by medications, toxic ingestions, ischemia, food indiscretions, and other conditions.
sACUTE DIARRHEA
PATHOGENIC MECHANISMS OF ACUTE DIARRHEA
- INOCULUM SIZE
- ADHERENCE
- TOXIN PRODUCTION
- INVASION
INOCULUM SIZE: 10-100 bacteria or cysts
Shigella, enterohemorrhagic Escherichia coli, Giardia lamblia, or Entamoeba
INOCULUM SIZE
105-108
Vibrio organism
INOCULUM SIZE:
The infective dose varies widely, depending on the species, host and food vehicle
Salmonella
ADHERENCE
specific surface adhesins, including the toxin-coregulated pilus
V. cholerae
ADHERENCE
produces an adherence protein called colonization factor antigen
Enterotoxigenic E. coli
ADHERENCE
produce virulence determinants
Enteropathogenic/Enterohemorrhagic E. coli
TOXIN PRODUCTION
cause watery diarrhea by acting directly on secretory mechanisms in the intestinal mucosa.
Enterotoxin
TOXIN PRODUCTION
cause destruction of mucosal cells and associated inflammatory diarrhea
Cytotoxins
TOXIN PRODUCTION
which act directly on the central or peripheral nervous system
Neurotoxins
- prototypical enterotoxin
- heterodimeric protein composed of one A and five B subunits
Cholera toxin
Cholera toxin contains the enzymatic activity of the toxin
A subunit
Cholera toxin binds holotoxin to the enterocyte surface receptor, the ganglioside GMI, increase in cAMP
B subunit pentamer
similar to cholera toxin and causes secretory diarrhea by the same mechanism.
heat-labile enterotoxin (LT)
one form of which causes diarrhea by activation of guanylate cyclase and elevation of intracellular cGMP
heat-stable enterotoxin (ST)
- destroy intestinal mucosal cells and produce the syndrome of dysentery
- Shigella dysenteriae type |, Vibrio parahaemolyticus,
and Clostridium difficile.
BACTERIAL CYTOTOXINS
produce potent cytotoxins and have been associated with outbreaks of hemorrhagic colitis and hemolytic-uremic syndrome
S. dysenteriae type I and Shiga toxin-producing strains of E. coli
- usually produced by bacteria outside the host and therefore cause symptoms soon after ingestion
- which act on the central nervous system to produce vomiting.
- staphylococcal and Bacillus cereus toxins
Neurotoxins
Bacteria cause Neurotoxins
- staphylococcal
- Bacillus cereus toxins
INVASION
invasion of mucosal epithelial cells, intraepithelial multiplication, and subsequent spread to adjacent cells
Shigella and enteroinvasive E. coli
INVASION
causes inflammatory diarrhea by invasion of the bowel mucosa, but generally is not associated with the destruction of enterocytes or the full clinical syndrome of dysentery.
Salmonella
INVASION
can penetrate intact intestinal mucosa, multiply intracellularly in Peyer’s patches and intestinal lymph nodes, and then disseminate through the bloodstream to cause ENTERIC FEVER
- Salmonella Typhi
- Yersinia enterocolitica
asyndrome characterized by fever, headache, abdominal
pain, splenomegaly, and leukopenia, relative bradycardia
(faget’s sign).
ENTERIC FEVER
HOST DEFENSES
- Intestinal Microbiota
- Gastric Acid
- Intestinal Motility
- Intestinal Mucin
- Immunity
- Genetic Determinants
- act as an important host defense mechanism, preventing colonization by potential enteric pathogens.
- Persons with fewer intestinal bacteria: infants or patients receiving antibiotics
INTESTINAL MICROBIOTA
- Alterations in gastric pH due to Gastric surgery have increased frequency to Salmonella, G. lamblia, and a variety of helminths
- Antacids, proton pump inhibitors, or H2 blockers
- Rotavirus- a microorganisms that can survive the extreme acidity of the gastric environment and is highly stable to acidity.
GASTRIC ACID
- Impaired intestinal motility the frequency of bacterial overgrowth and infection of the small bowel with enteric pathogens is increased.
- Opiates
- Antimotility drugs
- Anatomic Abnormalities
- Hypomotility states
INTESTINAL MOTILITY
- A complex layer of mucus, produced by specialized secretory cells
- Comprises glycoproteins and a range of antimicrobial molecules and secreted immunoglobulins directed against specific microbial antigens
- pathogens can penetrate the mucus layer by secreting enzymes to degrade the mucus or through flagella-mediated motility.
- Shigella, secrete toxins that can diffuse through the mucus layer and disrupt the underlying epithelium.
INTESTINAL MUCIN
systemic IgG and IgM as well as secretory IgA.
Humoral immunity
may be the first line of defense against many gastrointestinal pathogens.
Mucosal immune system
show increased susceptibility to disease due to V. cholerae, Shigella, E. coliO\57, and norovirus.
blood group O
