WK 5- Gastrointestinal Infections Flashcards
What is gastroenteritis
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
What is diarrhoea
Frequent faecal discharge +/-fluid stools (small bowel)
What is dysentery
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
Differentiate infection and intoxication
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.
What are 7 host defences present in the GIT to protect from infection
- peristalsis
- IgA
- normal flora
- mucous
- gastric acidity
- digestive enzymes
What pathogen is resistant to bile acid and what is the consequence
salmonella–> allows for survival in the GIT
What pathogen has motility as a virulence factor and what is the consequence
V.cholerae-> allows for movement to reach the site of attachment and the production of cholera toxins
What pathogen is acid resistant and what is the consequence
H.Pylori-> allows for survival in the GIT
-does this by producing urease that will convert urea to ammonia
What are the mechanisms by which pathogens cause host damage
multiplication and spread, exotoxin production, obstruction (like hookworm), local inflammation and invasion
Do pathogens entering bound to food require a small or large conc
Small–> the pathogen will be protected by the food and allow entrance into the stomach
Do pathogens entering in water require a small or large conc
Large- due to majority being eliminated in the stomach
What are the 5 at risk groups for GIT infection and why
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
Do infections or intoxications cause most rapid symptoms- and why
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
What is an example of a pathogen that causes intoxication via ingestion (toxin is already pre formed)
eg. S. aureus, B.cereus) →often found in things like rice
- cause rapid onset vomiting and diarrhea
What is an example of a pathogen that causes infection via ingestion
-toxin is produced in situ
V.cholerae–> takes time for symptoms to develop as the bacteria must multiply and then produce a toxin
How does V.cholera cause it’s symptoms
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.
What are the 2 most common pathogens that cause food related infection
Salmonella and and C.jejuni
What pathogen causes typhoid
-what are the symptoms of typhoid
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
What is enterocolitis
-cause and symptoms
- caused by Salmonella typhimurium, Salmonella paratyphi
- presents as fever and chills for 1-3 weeks
What is listeriosis
- cause
- 3 main types/symptom groups
-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
Who is most affected by listeriosis
The fetus- mother will only have a mild non-specific illness
What is the leading cause of gastroenteritis and most common cause of diarrhoea
Rotavirus
What is rotavirus
double stranded RNA virus that is transmitted person to person or fomites (things that can carry infection, like clothes or utensils)
How does rotavirus create such severe diarrhoea
: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)
How does rotavirus infection cease
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
What is the transmission of rotavirus
faecal-oral route through direct contact with contaminated faeces or indirect through contact with contaminated surfaces (taps, toys, toilet lids)
How can rotavirus be prevented?
Vaccination
Hand hygiene
Sanitation
What is the norovirus
virus with is a posItive sense ssRNA with a non-segmented genome
What are the symptoms of norovirus
include nausea, vomiting, abdominal pain and cramping, diarrhea, fever→ IP is 24-48 hours and symptoms last around 3 days
Why is norovirus difficult to eradicate and how can it be prevented
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
What virus causes Hepatitis A
-how is it transmitted
Picornavirus→ is an ssRNA virus that can be transmitted via person-person contact ie. Hand contact, contaminated food/water, sexual contact, household contact
How is hepatitis E spread
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
If a country has high level of parasitic infections, what does this indicate
Poor hygiene and sanitation within the country due to parasitic infections being mainly faecally derived
What is giardia- how does it cause illness
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.
What is shigella flexneri
- 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.
What is entamoeba hystolytica
- 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.
What is the lifecycle of whipworm
- 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
Why would a helminthic infection reduce the efficacy of vaccinations
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
What is the lifecyle of cryptosporidium
- 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.
What are the symptoms associated with cryptosporidium
Watery diarrhea is the most frequent symptom, and can be accompanied by dehydration, weight loss, abdominal pain, fever, nausea and vomiting
What is the lifecyle of ascaris lumbricodes (round worm)
- 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
What is the presentation of ascaris
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.
What is the lifecyle of ancylostoma- hookworm
- 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
What is the clinical features of ascaris
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
What is the lifecyle of strongyloides sterocalis
- 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)
