4.1 Infections of the GI tract PART I

Question 1

What can be used to classify stools?

What do these indicate?

Answer 1

The Bristol Stool Chart

Type 1: separate hard lumps, indicates very constipated
Type 3 and 4: NORMAL
Type 7: liquid consistancy with NO solid pieces, indicates inflammation

Question 2

Define gastroenteritis

What is the primary manifestation?

Answer 2

A nonspecific term for various pathological states of the GI tract.

Defined as-Inflammation of the mucous membrane of both the stomach and intestine, usually causing diarrhea, nausea, vomiting and abdominal cramps

Primary manifestation is diarrhea but often accompanied by symptoms above

Question 3

Give 4 causes of Gastroenteritis

Answer 3

1) GI Obstruction
2) Trauma
3) Food poisoning
4) GI Inflammation

Question 4

What are the 2 main causes of Infectious Gastroenteristis?

Answer 4

Pre-formed toxins (food poisoning)

Living Organisms (helminths, virus, bacteria)

Question 5

List the non-invasive and invasive mechanisms organisms can use to infect the GI tract

List one organism for each

Answer 5

Non-invasive:

• organisms colonize the gut and produce the toxin (e.coli)
• organisms bind to brush border (cryptosporidium)

Invasive:

• organisms penetrate the mucosal layer (shigella) or deeper (S.typhi)

Question 6

What are nematodes? Name 4 types

Answer 6

Round bodied worms

1. Hookworms
2. Roundworms
3. Pinworms
4. Whipworm

Question 7

What are Hookworms and how are they commonly contracted?

What feature of hookworms makes them able to infect and how does it do this?

What is a common sign

Answer 7

These are round bodied nematodes contracted through contaminated food

The mouth area has the ability to grasp onto the epithelia ➞ the egg or cyst is ingested and in the right environment will hatch into small worms

Sign: red appearance on skin due to worms moving and burrowing through

Question 8

What are round worms and how are they commonly contracted?

What is a common symptom and why?

Why can they lead to breathing problems?

What is a visible sign that can be seen in severe cases?

Answer 8

These are a type of round bodied nematode that are commonly contracted through ingestion of contaminated soil or meat

Symptom: “acute abdominal pain” due to build up of worms within intestines that cause severe blockages

They can circulate body and reach other sites such as lungs leading to breathing problems

In severe cases the worms can be seen by the naked eye moving throughout body (eg. through nasal cavity)

Question 9

What are pinworms are who do they commonly affect?

How do they travel and why are they particularly spreadable?

What are 4 signs of pinworms?

Answer 9

These are roundbodied nematodes that commonly affect children

Ingestion of egg travels through intestines and resides ➞ at night female worms will travel through intestine to the anus and lay eggs in a sticky substance ➞ this substance has a small reaction with the skin, causing itchiness ➞ itching causes transfer of eggs onto fingernails and anywhere the hand touches after

Signs: visible detection in faeces, malaise, anaemia, development of darkness under eyes

Question 10

Which type of nematode is associated with an anal prolapse?

Answer 10

Whipworm (Trichuris trichiura)

Question 11

What are cestodes and how are they spread?

Name one example and how it is commonly spread

Answer 11

Cestodes are segmented flat-bodied worms that are commonly spread through the ingestion of meats

Eg. tapeworm

Question 12

What are trematodes and give 2 examples?

Answer 12

Trematodes are flatworms that are non-segmented

Eg. flukes or schistosomes

Question 13

What immune cell is key in defending against parasitic worms?

What is its structure and how does this aid function?

Answer 13

Eosinophils: bi-lobed nucleus and cytoplasm filled with granules containing enzymes and proteins

They contain a chemical compound directed at the nervous system of worms

Question 14

What are Schistosomiasis and how are they commonly contracted?

Name 3 signs of this infection

Answer 14

Schistosomes are trematodes that flatbodied are non-segmented

They are ususally a tropical disease and commonly infect ‘intermediates’ (such as snails and soil). These can then infect humans through skin touch.

Signs: swollen abdomen, increased vascularisation, rashes

Question 15

What is the difference between: food poisoning, food infection and food intoxication?

Answer 15

Food Poisoning is any illness resulting from the consumption of food

Food infection refers to the presence of bacteria or other microbes which infect the body after consumption

Food intoxication refers to the ingestion of toxins contained within the food

Question 16

Which organism is the leading bacterial cause of food poisoning, give 4 features of this bacteria

How does infection by this bacteria lead to common symptoms of food poisoning?

How would you treat and why?

Answer 16

Staphylococcal aureus

It is a commensal bacteria that is salt tolerant, heat stable and produces five enterotoxins (A-E) making it resistant to gut enzymes. It also changes its genes very fast

Entertoxins stimulate intestinal muscle contractions ➞ leads to nausea, abdominal cramping, vomiting and diarrhea. Onset is ususally 1-6hours

Treatment is usually just replacement of fluids and electrolytes as the infection is normally mild and self-limiting

Question 17

Give 6 general symptoms of food poisoning

Answer 17

nausea, vomiting, diarrhoea, abdominal cramping, bloating, fever

Question 18

How do enterotoxins pass through the villi and how does this result in vomiting and watery diarrhoea?

Answer 18

Enterotoxin utilises goblet cells and epithelial cells to passage through into lamina propria

Once in lamina propria two thing happen:

1) Immune response ➞ increase in 5HT acts on vagus nerve which stimulates vomiting
2) Inflammatory response ➞ disrupts passage of substances through epithelia causing damage and leading to watery diarrhoea

Question 19

Venous blood gas status depends on whether we have more vomiting or diarrhoea

What would an ABG show if vomitting is the main cause of fluid loss?

What would an ABG show if diarrhoea is the main cause of fluid loss?

Answer 19

Vomiting: hypochloremia, metabolic alkalosis, hypokalemia (low Cl-, K+ H+)

Diarrhoea: metabolic acidosis and hypokalemia (high H+ and low K+)

Question 20

Why is reheating food an ineffective method of preventing food poisoning by S. aures?

Answer 20

Reheating food eliminates the staphylococci but NOT the enterotoxin produced

Question 21

Describe the stucture of Clostridium Perfringes

Answer 21

gram +, rod shaped, spore forming and anaerobic

Question 22

Describe the mechanism of infection by clostridium perfringes and how this results in watery diarrhoea

Answer 22

1) once ingested produces an enterotoxin which can enter the natural protective layer of our microbiota, through epithelium and lamina propria
2) triggers an inflammatory response which weakens epithelial cells making them prone to furthur entry of C.perfringes
3) Increased bacterial invasion, replication and enterotoxins results in more inflammation which furthur dirupts and damages epithelium
4) eventually there is complete breakdown of epithelium ➞ incorrect passage of ions ➞ large amounts of water enters lumen ➞ watery diarrhoea

Question 23

What is meant by “emetic” and “diarrhoeal” causes?

Answer 23

Emetic: cooked food left at room temperature too long

DiarrhoeaI: meat and ready prepared meals that have been incorrectly stored

Question 24

What is the most common cause of infectious diarrhea in the western world?

How are they commonly contracted?

Answer 24

Viral gastroenteritis: specifically the Norovirus which is the leading non-bacteria cause of gastroenteritis

Commonly contracted through contaminated food/water

Viral gastroenteritis produces symptoms similar to bacterial gastroenteritis but are much milder

Question 25

What is the general mechanism viruses use that cause gastroenteritis?

Answer 25

They infect epithelia of the proximal small intestine

They do not fully invade, but use natural biofilm in the GIT to attach their LPS (antigen) to the gut wall. They use the biofilm as co-factors that stabilise them and allow them to hide

Question 26

List the 4 categories of viral gastroenteritis (CANE)

Answer 26

1) Norovirus
2) Claicivirus (such as the Rotavirus)
3) Astrovirus
4) Enteric adenovirus

Question 27

What is the main cause of Travellers’ Diarrhoea?

How does it present?

Answer 27

80-90% are cause by Bacterial pathogens, 5–8% are viral

Both presents with the sudden onset of symptoms ranging from mild cramps and urgent loose stools to severe abdominal pain, fever, vomiting, and bloody diarrhoea

Question 28

What can be used to determine whether gastroenteristis is bacterial, viral or protozoal?

Answer 28

Onset and duration of diarrhoea may be an indicator of the pathogen involved.

• Untreated bacterial diarrhoea lasts 3–7 days.
• Viral diarrhoea generally lasts 2–3 days.
• Protozoal diarrhoea can persist for weeks to months without treatment

Question 29

Describe the structure of Norovirus and how it is contracted

What is the classic presentation and what is its effect on the GIT?

Answer 29

Norovirus is a type of Claicivirus that is contracted through ingestion of infected food/water

• RNA virus
• Icosahedral nucleocapsid
• non-enveloped and non segmented
• contains 9 genes

Classic presentation: projectile vomiting (+ slows passage of food, feeling of a full stomach)

It the GIT it leads to local infection and inflammation in proximal small intestine

Question 30

Why does viral gastroenteritis cause vomiting?

Answer 30

They cause irritation and inflammation of the GI tract and stomach lining, so when we eat/drink the region is further irritated causing you to expel the contents of your stomach

Question 31

What is the most common cause of diarrhoea in young children?

Describe the structure of this virus and how it is spread

How is it diagnosed and treated?

Answer 31

Rotavirus ➞ RNA virus with an Icosahedral nucleocapsid. It is non-enveloped and segmented and belongs to the family Reovirdidea

It is highly contagious and is spread by the fecal-oral route

Diagnosed by EIA antigen in stool and treated with oral rehydration or IV

Question 32

Where in the GIT does Rotavirus infect and what 3 things can this lead to?

What specific toxin is responsible for the symptoms produced?

Answer 32

Infects villus cells of the proximal small intestine, replicates within them and then lyses the cells

Leads to:

• Impaired absorption of carbohydrates and nutrients
• vomiting followed by diarrhoea (no blood)
• dehydration and hospitalization

Symptoms are principally induced by the viral enterotoxinNSP4