WK 5- Gastrointestinal Infections

Question 1

What is gastroenteritis

Answer 1

Usually a self-limiting infection with nausea, vomiting, diarrhea and abdominal cramps→ inflammation of the GI tract→ can be a result of microbes or exposure to toxins/drugs

Question 2

What is diarrhoea

Answer 2

Frequent faecal discharge +/-fluid stools (small bowel)

Question 3

What is dysentery

Answer 3

Diarrhoea containing blood +/-pus, mucous→ accompanied by pain, fever, abdominal cramps (large bowel)→ due to invasive organism that burrows into the enterocytes→ more systemic type infection

Question 4

Differentiate infection and intoxication

Answer 4

Intoxication= ingesting preformed toxins produced by pathogens in food/materials 
Infection= occurs when a person eats food containing harmful microorganisms, which then grow in the intestinal tract and cause illness.

Question 5

What are 7 host defences present in the GIT to protect from infection

Answer 5

• peristalsis
• IgA
• normal flora
• mucous
• gastric acidity
• digestive enzymes

Question 6

What pathogen is resistant to bile acid and what is the consequence

Answer 6

salmonella–> allows for survival in the GIT

Question 7

What pathogen has motility as a virulence factor and what is the consequence

Answer 7

V.cholerae-> allows for movement to reach the site of attachment and the production of cholera toxins

Question 8

What pathogen is acid resistant and what is the consequence

Answer 8

H.Pylori-> allows for survival in the GIT

-does this by producing urease that will convert urea to ammonia

Question 9

What are the mechanisms by which pathogens cause host damage

Answer 9

multiplication and spread, exotoxin production, obstruction (like hookworm), local inflammation and invasion

Question 10

Do pathogens entering bound to food require a small or large conc

Answer 10

Small–> the pathogen will be protected by the food and allow entrance into the stomach

Question 11

Do pathogens entering in water require a small or large conc

Answer 11

Large- due to majority being eliminated in the stomach

Question 12

What are the 5 at risk groups for GIT infection and why

Answer 12

Hospital nurseries: infection via birth canal, staff, siblings, formula and having an immature immune system- fomite based group
Day care centres: close contact, toilet training, infection control
Travellers: unfamiliar organisms, public health issues
Hospitalised patients: antibiotic therapy (clostridium difficile)
People with AIDS or other immunocompromised conditions: due to immunosuppression

Question 13

Do infections or intoxications cause most rapid symptoms- and why

Answer 13

Intoxications as the toxin is already present-> there will be more vomiting and diarrhoea to rapidly id the toxin
-Infection required growth and colonisation before toxin can be produced

Question 14

What is an example of a pathogen that causes intoxication via ingestion (toxin is already pre formed)

Answer 14

eg. S. aureus, B.cereus) →often found in things like rice

- cause rapid onset vomiting and diarrhea

Question 15

What is an example of a pathogen that causes infection via ingestion
-toxin is produced in situ

Answer 15

V.cholerae–> takes time for symptoms to develop as the bacteria must multiply and then produce a toxin

Question 16

How does V.cholera cause it’s symptoms

Answer 16

symptoms are caused by an enterotoxin→ toxin binds to and activates the G protein Gs through an ADP-ribosylation reaction that acts to lock the G protein in its GTP-bound form→ will continually stimulate the adenylate cyclase to produce cAMP→ The high cAMP levels activate the cystic fibrosis transmembrane conductance regulator (CFTR), causing a dramatic efflux of ions and water from infected enterocytes into the lumen, leading to watery diarrhoea.

Question 17

What are the 2 most common pathogens that cause food related infection

Answer 17

Salmonella and and C.jejuni

Question 18

What pathogen causes typhoid

-what are the symptoms of typhoid

Answer 18

caused by salmonella typhi

• typhoid presents with fever, rose spots, delirium and bowel perforation
• carried in macrophages-> means the host can be a chronic carrier

Question 19

What is enterocolitis

-cause and symptoms

Answer 19

• caused by Salmonella typhimurium, Salmonella paratyphi

- presents as fever and chills for 1-3 weeks

Question 20

What is listeriosis

• cause
• 3 main types/symptom groups

Answer 20

-caused by listeria monocytogenes- a gram post cocco-bacillus (mix between cocci and bacillus-short rod)
-causes:
Maternal listeriosis: causes fever in mother→ if adequately treated, will prevent and treat foetal disease
Foetal listeriosis: depending on the gestational age, can have a 25-35% mortality rate→ if in 3rd trimester will result in abortion or neonatal death
Neonatal listeriosis: may present as sepsis or meningitis with severe sequels and high fatality rate

Question 21

Who is most affected by listeriosis

Answer 21

The fetus- mother will only have a mild non-specific illness

Question 22

What is the leading cause of gastroenteritis and most common cause of diarrhoea

Answer 22

Rotavirus

Question 23

What is rotavirus

Answer 23

double stranded RNA virus that is transmitted person to person or fomites (things that can carry infection, like clothes or utensils)

Question 24

How does rotavirus create such severe diarrhoea

Answer 24

:1. Ingested virus infects cell at the tip of the villi (the enterocytes) in the small intestine and spreads to infect large numbers (of villi)→ 2. Viral particles are released into the lumen→ 3. Infected enterocytes are damaged and then die off, leaving immature enterocytes with reduced absorptive capacity for water/sugars/salts→ 4. Fluid accumulation in the lumen (due to the decreased movement of solutes into cells, meaning low conc gradient)→ 5. Causes diarrhoea and dehydration (lasting 2-4 days)

Question 25

How does rotavirus infection cease

Answer 25

After 6-7 days the virus replication ceases due to multiple factors (Ab, interferon, infection of all possible cells) and the cells ill being to repopulate villi, causing regaining of normal structure

Question 26

What is the transmission of rotavirus

Answer 26

faecal-oral route through direct contact with contaminated faeces or indirect through contact with contaminated surfaces (taps, toys, toilet lids)

Question 27

How can rotavirus be prevented?

Answer 27

Vaccination
Hand hygiene
Sanitation

Question 28

What is the norovirus

Answer 28

virus with is a posItive sense ssRNA with a non-segmented genome

Question 29

What are the symptoms of norovirus

Answer 29

include nausea, vomiting, abdominal pain and cramping, diarrhea, fever→ IP is 24-48 hours and symptoms last around 3 days

Question 30

Why is norovirus difficult to eradicate and how can it be prevented

Answer 30

the virus can withstand hot and cold temps and multiple disinfectants→ can persist in the environment for weeks
-Prevented through Practice proper hand hygiene, Take care in the kitchen, Do not prepare food while infected, Clean and disinfect contaminated surfaces, Wash laundry thoroughly

Question 31

What virus causes Hepatitis A

-how is it transmitted

Answer 31

Picornavirus→ is an ssRNA virus that can be transmitted via person-person contact ie. Hand contact, contaminated food/water, sexual contact, household contact

Question 32

How is hepatitis E spread

Answer 32

Most cases associated with consuming water contaminated with faeces→ prevalent in east and south asia
-Minimal person to person contact and infections only normally arise after travel to endemic areas→ causes a normally mild disease

Question 33

If a country has high level of parasitic infections, what does this indicate

Answer 33

Poor hygiene and sanitation within the country due to parasitic infections being mainly faecally derived

Question 34

What is giardia- how does it cause illness

Answer 34

a trophozite that adheres to the brish border of the SI and creates cysts that are passed in faeces
-attachment of trophozoites causes villus flattening and inhibition of enzymes that break down disaccharide sugars in the intestines and programmed death of enterocytes→ alteration of the villi leads to an inability of nutrient and water absorption from the intestine, resulting in diarrhea→ Characteristically, the stools are loose, foul-smelling and often fatty.

Question 35

What is shigella flexneri

Answer 35

• Shigellae attach to, and invade, the mucosal epithelium of the distal ileum and colon, causing inflammation and ulceration
• causes damage to the intestinal epithelium and glomerular endothelial cells→causes water diarrhea that can later contain mucus and blood→ Lower abdominal cramps can be
  severe. The disease is usually self-limiting, but dehydration can occur, especially in the young and elderly. Complications can be associated with malnutrition.

Question 36

What is entamoeba hystolytica

Answer 36

• trophozite that can live harmlessly in the LI and have asymptomatic carriers
• Invasion of the mucosa by E. histolytica may produce small localized superficial ulcers or involve the entire colonic mucosa with deep ulcers
• more severe invasion causing deeper ulcers causes amoebic dysentery’, which is characterized by mucus and blood in the stools.
• Complications include perforation of the intestine, leading to peritonitis, and extraintestinal invasion.

Question 37

What is the lifecycle of whipworm

Answer 37

1. Adults in cecum pass around 200,000 fertilised eggs in the faeces→ 2. Eggs in faeces in the environment are unembryonated→ 3. Require time in environment to become infective → 4. Acquire infective egg (where the embryo has matured and developed) by ingestion→ 5. The larvae will leave the egg in the SI and migrate to the LI

Question 38

Why would a helminthic infection reduce the efficacy of vaccinations

Answer 38

Helminth infection triggers Th2 immune response, causes decrease in Th1→ results in vulnerability to viruses/intracellular pathogens→ if there is small Th1 levels, vaccinations will not be seroconverted (Th1 is required for immunisations to be effective)→ need to treat the helminth before giving the vaccine

Question 39

What is the lifecyle of cryptosporidium

Answer 39

1. Ingest the thick walled oocyst→ 2. excystation occurs and the sporozoites are released and parasitize epithelial cells of the gastrointestinal tract or other tissues such as the respiratory tract→ 3. The parasites will undergo multiplication and fertilization and produce oocysts that can develop → oocysts can be thick-walled, which is commonly excreted from the host or thin-walled which is primarily involved in autoinfection. Oocysts are infective upon excretion, thus permitting direct and immediate fecal-oral transmission.

Question 40

What are the symptoms associated with cryptosporidium

Answer 40

Watery diarrhea is the most frequent symptom, and can be accompanied by dehydration, weight loss, abdominal pain, fever, nausea and vomiting

Question 41

What is the lifecyle of ascaris lumbricodes (round worm)

Answer 41

1. Adult worms live in the lumen of the small intestine→ 2. A female may produce approximately 200,000 eggs per day, which are passed with the feces. Unfertilized eggs may be ingested but are not infective. Fertile eggs embryonate and become infective after 18 days to several weeks depending on the environmental conditions (optimum: moist, warm, shaded soil) → 3.After infective eggs are swallowed the larvae hatch and invade the intestinal mucosa, and are carried via the portal, then systemic circulation to the lungs → 4. The larvae mature further in the lungs (10 to 14 days), penetrate the alveolar walls, ascend the bronchial tree to the throat, and are swallowed back into the intestine→ 5 Upon reaching the small intestine, they develop into adult worms

Question 42

What is the presentation of ascaris

Answer 42

Ascaris often show no symptoms. If symptoms do occur they can be light and include abdominal discomfort. Adults can pass adult worms. Heavy infections can cause intestinal blockage and impair growth in children. Other symptoms such as cough are due to migration of the worms through the body.

Question 43

What is the lifecyle of ancylostoma- hookworm

Answer 43

1. Adults are in SI and eggs are passed in the stool and under favorable conditions (moisture, warmth, shade), larvae hatch in 1 to 2 days in the environment→ 2. The released rhabditiform larvae grow in the faeces and/or the soil and after 5 to 10 days (and two molts) they become filariform (third-stage- infective form) larvae that are infective → 3. These infective larvae can survive 3 to 4 weeks in favorable environmental conditions. → 4. On contact with the human host, the larvae penetrate the skin and are carried through the blood vessels to the heart and then to the lungs. → 5. They penetrate into the pulmonary alveoli, ascend the bronchial tree to the pharynx, and are swallowed → 6. The larvae reach the small intestine, where they reside and mature into adults. Adult worms live in the lumen of the small intestine, where they attach to the intestinal wall with resultant blood loss by the host

Question 44

What is the clinical features of ascaris

Answer 44

iron deficiency anemia (caused by blood loss at the site of intestinal attachment of the adult worms) is the most common symptom of hookworm infection, and can be accompanied by cardiac complications. Gastrointestinal and nutritional/metabolic symptoms can also occur

Question 45

What is the lifecyle of strongyloides sterocalis

Answer 45

1. Adults are in the GIT, and eggs are passed by the adult worm→ 2. Eggs will hatch in the GIT (don’t need to leave)→ 3. Larvae leave the eggs and move through the GIT into circulation where they can move back to the SI and mature into adults OR the eggs that hatch release larvae that is passed in faeces–> in enviro the larvae mature and lay eggs which will hatch into larvae that can penetrate the skin of the host and move to the GIT to mature into adults (cycle repeats)