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Infectious Diseases of the
Digestive System
GI Tract
U.S. Foodborne-Disease Outbreaks
Typhoid Mary
• Human carrier
(and reservoir) of
Salmonella typhi
Typhoid Fever and
Salmonellosis
Salmonella enterica serovars
• Infect domestic animals
• Eggs and contaminated
meat
• One of the most
prevalent causes of foodborne illnesses
• Transmission dose as
few as 10 organisms
• Attachment is key
virulence factor
Salmonella enterica serovars.
• Gram negative bacillus
• Classification based on serology and
phage susceptibility assays
Salmonellosis
•
•
•
•
40,000 cases annually in US
Invades intestinal epithelial cells
Nausea, cramps, diarrhea
Recovery in a few days but may
shed organism for 6 months
Campylobacter jejuni
• Small curved
Gram negative
rod
• Lives in large
intestine of birds
and mammals
• Fecal
contamination of
water and foods
Campylobacteriosis
• Leading bacterial cause of human
gastroenteritis in the world
• 2.4 million U.S. cases/year
• Undercooked poultry, shellfish,
unpasteurized dairy products,
contaminated water
• Waterybloody diarrhea
• Treated with antibiotics
Rotavirus
• virus
• Primary cause of diarrhea
morbidity and mortality
• 1 million cases per year; 70,000
hospitalizations
• Fecal-oral transmission
• Most serious in infants 6-24
months
Hepatitis
• Inflammation
of the liver
• Multiple
viruses
Hepatitis A Virus
• “Infectious”
hepatitis
• Small RNA virus
• Transmitted by
fecal-oral route
• New effective
vaccine
Hepatitis A in US
Hepatitis A Worldwide
Hepatitis B Virus
• “Serum” hepatitis
• Enveloped DNA
virus
• Can result in
chronic infection
and liver cancer
• Recombinant
vaccine
Hepatitis C Virus
• “Serum” hepatitis
• More likely than
HBV to become
chronic
• Also causes liver
cancer
• No vaccine
Hepatitis C
• Treated with
Interferon alpha
and ribavirin
• No cure but slows
liver damage
Giardia lamblia
• Protozoan
• Cysts survive in
environment
– Insensitive to
chlorine
• Contaminated
water source of
infection
Giardiasis
• Shed by wild animals
into water supply as well
as by infected humans
• G. lamblia attaches to
human intestinal wall
• Diarrhea lasting for
weeks
• Treated with antiparasitic drugs
HELMINTHES
Flat worms and Round worms
Hermaphroditic Flukes
FLAT WORMS
Phylum Platyhelminthes = Flat worms
Class Cestoda = Tape worms
Scolex contained in egg
holdfast structure with
hooks
and suckers
Proglottids major body of
tapeworm
contains both ovaries and
testes = hermaphroditic
Eggs can penetrate intestine of host
FIGURE 13-57 Taenia solium scolex (X64).
The Taenia solium scolex has two rings of hooks and four suckers.
Hookworms
• Ancylostoma duodenali and Necator
americanus Old world and new world
hookworms differ only in their geographic
location.
Human phase of this worm begins with a
filaform larvae penetrating the skin, enters
circulation, carried to the lungs, coughed up
and swallowed, develops to adulthood in
small intestine. Adult worms lay between
10,000 and 20,000 eggs per day. Daily blood
loss 0.2ml/adult/day. Microcytic hypochromic
Biblical worm
• Trichinella spiralis etiological agent
of trichinosis. Infectious larva is
present in the striated muscle of
carnivorous and omnivorous
mammals. Swine most common
organism to transmit to humans.
Encysted larvae live for many
years. Polar bears and walruses
are accounting for new human
infestations in our Alaskan artic
regions.
FIGURE 13-68 Trichinella spiralis larva in skeletal muscle (W.M., X260).
The spiral juvenile and its nurse cell are visible in this preparation.
Pin worms or Seat worms
• Enterobius vermicularis most common
helminthic infestation in America, 500
million cases annually globally second
globally to Ascaris infestations.
Eggs are ingested mainly fecaloral.Egg laden dust can be inhaled.
Autoinfection occurs frequently.
“Scotch Tape Test” from perianal folds
of diagnostic value.
Ascaris Lumbricoides
• Large worms 25cm – 45cm in length. Most
common helminth with over a billion infested
a year. Prevalent in areas where sanitation is
poor and human waste is used as fertilizer.
• Ingested egg releases a larva that penetrates
the duodenal wall and carried to the liver and
the heart, enters the pulmonary system,
enters the alveoli where they molt and
mature. They are coughed up, swallowed and
returned to the small intestine. Adults can be
passed out into the feces.
Helminth Transmission
• Intestine -->
environment -->
ingested
• Examples:
whipworm
Helminth Transmission
• Intestine -->
environment -->
skin penetration
• Example:
hookworms
Helminth Transmission
• Intestine -->
environment -->
food animal
muscle -->
ingested
• Example:
tapeworm
Helminth Transmission
• Various organs -> environment -->
ingestion or
penetration
• Example: flukes
Treatment of Inflammatory
Bowel Disease with Worms?
• Pig whipworm causes transient, noninvasive, non-infective human disease
• Improved IBD symptoms