5. Diarrheal Diseases

found in areas that lack access to safe drinking water

• developing countries:
• suffer most of burden from diarrheal diseases
• majority of mortality

• developed countries:
• burden is mostly economic
• contributing factors - centralization of food production and large food distribution network

• humans, non-human animals, environment
• primarily fecal-oral
• - fecal contamination of hands or food products

more liquid bowel movements than normal for the individual in a day

• secretory diarrhea - acute, watery, lasts hours or day
• invasive (inflammatory) diarrhea - acute, bloody
• persistent diarrhea - lasts 14 days or longer

• segregated from the internal body
• mediates selective exchange - absorb nutrients, exclude pathogens

• high acidity of stomach
• antibody IgA
• phagocytic cells and tissues rich in lymphocytes underneath the mucosal membrane
• endogenous (commensal) organisms in the intestine - compete with pathogens for nutrients, space, can have direct antimicrobial effects on pathogens

• leading cause of severe, acute diarrhea among infants and young children
• dsRNA
• 5 species (A-E) - Type A causes most infections in humans

• reservoir = human
• transmission = fecal-oral
• - small infectious dose, can survive a long time on hands, intermediate vehicles important

infect small intestine, cause inflammation -> blunting of microvilli

immunity - most children have antibody by age 2

• diarrhea
• occasional vomiting
• additional risks for immunocompromised children

diagnosis - enzyme immunoassay, latex agglutination, DNA probes, RT-PCR

treatment - IV fluids, oral rehydration therapy

• breastfeeding
• vaccines

• ssRNA
• 5 distinct genotypes, 3 infect humans
• most common cause of outbreaks of viral gastroenteritis in adults

reservoir = human

• transmission = fecal-oral
• -infectious vomit, food, low infectious dose, survives well on surfaces, resistant to disinfectants

• small intestine disease
• immunity - most people seem highly susceptible to infection

• milder than rotavirus
• vomiting
• diarrhea
• shorter duration of symptoms
• occasional deaths
• asymptomatic infection

diagnosis - clinical, RT-PCR

treatment - oral rehydration with fluids, IV fluids, palliative (antisecretory agents)

• food-handler restrictions
• food and water precautions
• person-to-person and environmental control
• no vaccine

• severe, watery diarrhea
• caused by Vibrio cholerae

biotypes = classical and El Tor - based on agglutination

serotypes = based on O antigens,

reservoir = free-living in brackish waters and estuaries, associated with copepods

• transmission = fecal-oral
• - water usually intermediate vehicle
• sometimes food

• residence in cholera endemic area
• host factors - gastric acidity, blood group O, bottle feeding infants
• strain factor - El Tor more asymptomatic infection

• infects small intestine
• adherence factors = toxin co-regulated pilus, other pili
• cholera toxin - activates adenylate cyclase, increased cAMP
• infection can provide long-term immunity against same biotype

diagnosis - clinical, rapid test kits, culture

treatment - oral rehydration therapy

• patients - disinfection of feces and anything it contacts
• warnings about contaminated water sources
• proper sewage treatment
• water purification
• surveillance to identify epidemics
• vaccines