Infectious Diseases of the Digestive System GI Tract

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 • 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 (X 64). 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. 2 ml/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. , X 260). 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 25 cm – 45 cm 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