Bacterial and Viral Infections of the GIT

Question 1

Intoxication

Answer 1

Ingestion of food containing biologically active toxins which cause disease.

Question 2

Infection

Answer 2

Ingestion of live microbes which can multiply readily on food prior to consumption or use food only as a means of getting to a live host.

Question 3

How can antibiotics reserved for severe prolonged symptoms worsen disease?

Answer 3

They can worsen disease by prolonging duration, promoting toxin release, increasing antibiotic resistance and disturbing natural flora.

Question 4

Oral rehydration treatment/therapy

Answer 4

Electrolytes and glucose increase the resorption of fluids into the intestinal wall. Fruit juices, coconut water, and other indigenous solutions are alternatives.

Question 5

Personal measures to avoid infection.

Answer 5

Hand hygiene, cook food properly, avoid cross contamination, “wash food, peel food, cook it or forget it”.

Question 6

Public health measures to avoid infection.

Answer 6

Pasteurisation of milk and dairy products, proper sewage disposal, provision of safe clean drinking water and vaccination.

Question 7

Norovirus: transmission? Classification? Pathogenesis? Clinical presentation? 

Answer 7

• Transmission - by person-to-person (faecal-oral and aerosolised), foodborne, and water. Outbreaks occur in hospitals, care homes, and cruise ships. Continuing antigenic variation results in immunity lasting less than a year.
• Classification - single-stranded RNA virus.
• Pathogenesis - affects all ages and previously healthy. Infectious dose very small (10-100 virions). Survives well in environment (including alcohol gel).
• Clinical Presentation - projectile vomiting, diarrhoea, abdominal cramps, headache, muscle aches. Infectious period from onset till 48 hours after symptoms stop.

Question 8

Rotavirus: Transmission? Classification? Pathogenesis? Clinical presentation?

Answer 8

• Transmission - by person-to-person (faecal-oral or aerosolised). Most common cause of diarrhoeal illness in developing countries. Infection occurs in children. Increased cases in winter. 
• Classification - double-stranded RNA virus
• Pathogenesis - mainly affects young children, elderly and immunocompromised. Infectious dose very small (10-100 virions).
• Clinical Presentation - Watery diarrhoea, vomiting, abdominal cramps, fever. Incubation is two days. Duration of symptoms 3 to 8 days.

Question 9

Adenovirus: Transmission? Classification? Pathogenesis? Clinical presentation?

Answer 9

• Transmission - 10% of community acquired diarrhoea is in young children. No seasonal incidence. Only first infection symptomatic except in elderly and immunocompromised. A symptomatic infection is common although nearly everyone has been infected by the age of five, only a few have had symptomatic infection.
• Classification - double-stranded DNA virus.
• Pathogenesis - Mainly affects young children, elderly, and immunocompromised. Infectious dose is very small (10-100 virions).
• Clinical Presentation - mild prolonged diarrhoea.

Question 10

Campylobacter: Transmission? Classification? Pathogenesis? Clinical Presentation?

Answer 10

• Transmission - campylobacter jejuni is the most common bacterial foodborne infection. Transmitted via animals (poultry) and contaminated food.
• Classification - gram negative curved bacilli with flagella.
• Pathogenesis - invasion of the bowel leads to inflammation and ulceration.
• Clinical presentation - bloody diarrhoea, abdominal pain and fever. Incubation period is 2 to 11 days. Duration of symptoms can last between 3 to 21 days.

Question 11

What characterises the histological appearance of campylobacter?

Answer 11

Neutrophil rich inflammatory response involving the entire mucosa. Villus atrophy and necrotic debris in crypts.

Question 12

Vibrio Cholerae: Transmission? Classification? Pathogenesis? Clinical Presentation?

Answer 12

• Transmission - human only pathogen with large infective dose. Asymptomatic human reservoir. Spread via contaminated food or water. Prompt oral or intravenous rehydration is life-saving. Clean drinking water supply and proper sanitation or key preventative measures.
• Classification - Gram negative bacilli. Serotype O1 is the most common Serotype. Sucrose fermenter.
• Pathogenesis - polar flagella and mucinase facilitate penetration of intestinal mucus. Disease caused by exotoxin.
• Clinical Presentation - severe, profuse, watery diarrhoea (rice water stool). Profound fluid and electrolyte loss. Hypovolaemic shock and cardiac failure.

Question 13

Salmonella:  Transmission? Classification? Pathogenesis? Clinical Presentation?

Answer 13

• Transmission - found in a range of animals. Salmonella has more than 2000 serotypes (S.typhi and paratyphi have only human reservoirs and cause typhoid fever). Transmission via contaminated food (especially meat and dairy), waterborne and person-to-person.
• Classification - gram negative bacilli. Member of the enteribacteriaceae. Non-lactose fermenter.
• Pathogenesis - invasion and inflammation of the bowel.
• Clinical Presentation - watery diarrhoea, vomiting and fever. Incubation: 1-2 days. Duration of symptoms: 2-7 days.

Question 14

Pathogenesis of salmonella infection.

Answer 14

Ingestion of a large number of bacteria which is then absorbed into the terminal ileum. Bacteria multiply is in Peyer’s patches (lymphoid follicles). Inflammatory response mediates release of prostaglandins which stimulates cyclic AMP and releases fluid and electrolytes causing watery diarrhoea.

Question 15

Clinical features of typhoid and paratyphoid.

Answer 15

Malaise, headache, cough, rose spot rash, fever, bradycardia, severe lethargy, constipation, hepatosplenomegaly and intestinal haemorrhage.

Question 16

Shigella: Transmission? Classification? Pathogenesis? Clinical Presentation?

Answer 16

• Transmission - human-only pathogen. Most often spread via faecal-oral route and less often by contaminated food and water. Associated with low infectious dose.
• Classification - gram negative bacilli. Member of the enterobacteriaceae. Non-lactose fermenter.
• Pathogenesis - production of shiga toxin damagesthe intestinal epithelium. Shiga toxin can target the glomerular endothelium causing haemolytic uraemic syndrome.
• Clinical Presentation - watery followed by bloody diarrhoea, crampy abdominal pain and fever. Incubation: 1-4 days. Duration of symptoms: 2-3 days.

Question 17

Escherichia Coli: Transmission? Classification? Pathogenesis? Clinical presentation?

Answer 17

• transmission - important component of gut flora. Some strains possess virulence factors which enable them to cause infections. Six different diarrhoeagenic groups of E.coli have been described.
• classification - gram negative bacilli. Member of enterobacteriaceae.
• pathogenesis - six different strains which cause disease by differemt mechanism.
• clinical presentation - vary depending on strain.

Question 18

Enterotoxigenic E. Coli (ETEC): Transmission? Classification? Pathogenesis? Clinical presentation?

Answer 18

• Transmission - major bacterial cause of diarrhoea in children and infants on developing world. Major cause of “Travellers” diarrhoea.
• Classification - gram negative bacilli. Member of enterobacteriaceae.
• Pathogenesis - diarrhoea due to action of toxins. Heat-labile (LT): structural and functional analogue of cholera toxin. Heat-stable (ST): produced in addition to or instead of LT, similar mode of action.
• Clinical Presentation - watery diarrhoea, abdominal pain, vomiting, no fever associated. Incubation: 1-7 days. Duration of symptoms: 2-6 days.

Question 19

Enterohaemorrhagic E.coli (EHEC): Transmission? Classification? Pathogenesis? Clinical presentation?

Answer 19

• Transmission - Large animal reservoirs especially cattle and sheep. Transmitted by contaminated food, water, dairy products and direct contact with animal faeces e.g. petting zoos. Avoid antibiotics as they promote toxin release.
• Classification - gram negative bacilli, member of enterobacteriaceae. Best known as E. coli O157:H7
• Pathogenesis - production of shiga-like toxins. Toxins can target the glomerular endothelium causing haemolytic uraemic syndrome.
• Clinical presentation - bloody diarrhoea, abdominal pain, vomiting. Incubation: 3-4 days. Duration of symptoms: 5-10 days.

Question 20

Yersinia Enterocolitica: Transmission? Classification? Pathogenesis? Clinical presentation?

Answer 20

• Transmission - mainly affects younger children. Infection from wide range of animals including pets, undercooked pork and unpasteurised milk. Mimics appendicitis due to right iliac fossa pain. Only supportive therapy required.
• Classification - gram negative bacilli, member of enterobacteriaceae.
• Pathogenesis - invades terminal ileum with inflammation of mesenteric lymph nodes.
• Clinical presentation - bloody diarrhoea, abdominal pain and fever. Mesenteric adenitis may mimic acute appendicitis. Incubation: 4-7 days. Duration of symptoms: 7-14 days.

Question 21

Helicobacter Pylori Eradication Therapy

Answer 21

one week with proton pump inhibitor and two of the following antibiotics: Omeprazole, Clarithromycin, Amoxicillin (if penicillin allergy then Metronidazole).

Question 22

Helicobacter Pylori Pathogenesis

Answer 22

• Flagella allows movement through viscous mucus.
• Urease generates ammonia from urea and elevates local gastric pH.
• Adhesins enhance binding to gastric epithelium.
• Cytotoxins cause damage to gastric epithelium.

Question 23

Helicobacter Pylori: Transmission? Classification? Pathogenesis? Clinical presentation?

Answer 23

• Transmission - one of the most common infections (70% prevalence). Transmission by faecal-oral or oral-oral. Infection acquired in childhood and persists lifelong unless treated. Diagnosis by faecal antigen, serology testing, c-urea breath test, culture from biopsy.
• Classification - gram negative spiral shaped bacilli, urease positive.
• Pathogenesis - involves cytotoxin production, and a range of factors to promote adhesion and colonisation.
• Clinical presentation - asymptomatic unless peptic ulceration develops. Cause of 70-90% of peptic ulcers. Gastric cancer risk.

Question 24

Listeria Monocytogenes: Transmission? Classification? Pathogenesis? Clinical presentation?

Answer 24

• Transmission - important infection in pregnant (with possible placental transmission) and immunocompromised patients. Transmitted by contaminated foods: unpasteurised milk and soft cheeses, pate and dips such as hummus, and cooked meats. Outbreaks from contaminated ready to eat foods and produce. Intravenous antibiotics (usually ampicillin and synergistic gentamicin) are required.
• Classification - gram positive coccobacilli.
• Pathogenesis - <1000 organisms may cause disease. Invasive infection results in systemic spread via bloodstream.
• Clinical presentation - initial flu-like illness with or without diarrhoea. Severe systemic infection (septicaemia/meningitis). Incubation: 14-28 days. Duration of symptoms: 7-14 days.

Question 25

Staphylococcus Aureus: Transmission? Classification? Pathogenesis? Clinical presentation?

Answer 25

• Transmission - via food (especially cooked meats and pastries) contaminated by carriers. Bacteria multiply at room temperature and produce toxins.
• Classification - gram positive cocci.
• Pathogenesis - heat stable and acid-resistant protein toxins results in emetic disease.
• Clinical presentation - profuse vomiting and abdominal cramps. No diarrhoea or fever. Incubation: 15mins-6hours. Duration of symptoms: 12hours - 1 day.

Question 26

Clostridium Difficile: Transmission? Classification? Pathogenesis? Clinical presentation?

Answer 26

• Transmission - spores resistant to heat, dryinh, alcohol gel. Up to 30% of hospitalised patients are carriers. Lab diagnosis based upon toxin detection. Control measures include; patient isolation, hand hygiene, use of PPE, cleaning and disinfection with bleach. Treatment; stop precipitating antibiotics, oral metronidazole or vancomycin (severe cases), faecal transplant (for refractory disease).
• Classification - anaerobic spore-forming gram positive bacilli.
• Pathogenesis - disruption of normal protective gut flora due to antibiotics, chemotherapy or antacids. Release of potent toxins (A and B).
• Clinical Presentation - mild to severe diarrhoea. Psuedomembranous colitis, toxic colonic dilation, perforation.

Question 27

Clostridium Botulinum: Transmission? Classification? Pathogenesis? Clinical presentation?

Answer 27

• Transmission - two types of food related botulism: Foodborne (preformed toxins in improperly processed canned foods) and Infant (associated with organisms germinating of gut of babies fed honey containing spores and toxins are produced in gut). Diagnosisby toxin detection. Treatment with anti-toxin and urgent intensive supprotive care due to difficulties breathing and swallowing.
• Classification - anaerobic spore-forming gram positive bacilli.
• Pathogenesis - produces powerful heat-labile protein neurotoxin. Absorbed toxins spread via bloodstream and enter peripheral nerves where they cause neuromuscular blockade at the synapses.
• Clinical presentation - neuromuscular blockade results in flaccid paralysis and progressive muscle weakness. Can result in respiratory failure. High mortality if untreated.