Enteric and Diarrhoeal Disease Flashcards
Define gasterenteritis. Name the primary manifestation and three things it is often accompanied by
A nonspecific term for various pathological states of the GI tract, defined as inflammation of the mucous membrane of both the stomach and intestine. The primary manifestation is diarrhea but is often accompanied by nausea, vomiting and abdominal cramps
List the non-invasive and invasive mechanisms organisms affect the GI tract and list one organism for each
Non-invasive:
- organisms colonize the gut and produce the toxin (e.coli)
- organisms bind to brush border (cryptosporidium)
Invasive:
1. organisms penetrate the mucosal layer (shigella) or deeper (S.typhi)
What are nematodes? Name 4 types
Round bodied worms
- Hookworms
- Roundworms
- Pinworms
- Whipworm
Which type of nematode is associated with an anal prolapse?
Whipworm
Why are pinworms particularly spreadable?
Once ingested the female travels through the intestine. At night, it lays its eggs just outside the anus using a sticky substance that has a small reaction with the skin - causing itchiness. Eggs can then transfer onto fingernails and anywhere the hand touches after
What are cestodes? Name one example and how it is commonly spread
Cestodes are flat-bodied worms that are segmented, one example is tapeworm commonly spread through the ingestion of meat (and was once sold as a slimming product)
What are trematodes? Name two common examples
Trematodes are flatworms that are not segmented, two common examples are blood flukes or schistosomes
How do eosinophils target worms without overly harming the surrounding tissue?
They have a chemical compound within their granules that directly attacks the nervous system of worms. They also have specific receptors including Fc and complement receptors which bind the target (antibody or complement-coated parasite), and the granule’s contents are then released into the space between the cell and the parasite to target the parasite membrane.
How is schistosomiasis commonly contracted? Name 3 signs of this infection
Schistosomes commonly infects ‘intermediates’ (such as snails and soil) that are ingested, causing
- swollen abdomen
- increased vascularisation
- rashes
Which organism is the leading cause of food poisoning and why?
Staph aureus as it produces enterotoxin and has the ability to change its genes very quickly. Given the right environment it can turn on genes responsible for producing enterotoxin (less than one microgram needed to cause disease)
How do enterotoxins pass through the villi?
They use goblet and epithelial cells to go into the lamina propria…
1. Triggers an immune response which increases 5-HT -> acts on the VAGUS nerve which signals to the body (and particularly the nervous system in the stomach) to vomit
- Inflammatory response disrupts the passage of substances through epithelia -> more water in lumen -> watery diarrhea
Why is reheating food an ineffective method of preventing disease?
Reheating food eliminates the staphylococci but NOT the enterotoxin produced
Describe the basic pathophysiology when infected with clostridium perfringes
Once ingested it produces a toxin that goes through the protective layer of the microbiota and through the epithelia into the lamina -> produces an immune response -> weakens epithelia, making them more susceptible to the bacteria entering -> increased rate of bacteria and toxin production in the lamina -> increased inflammation and damage to the epithelial structure -> water in the lumen -> watery diarrhea
What is the most common cause of infectious diarrhea in the western world? What is this pathogen’s basic mechanism and how is it commonly contracted?
Viral gastroenteritis (viruses), they often infect epithelia (hindering their function and causing watery diarrhea) of the small intestine without invading fully but attaching to LPS in the microbiota (a virulent factor).
Commonly contracted through contaminated food/water
List the 4 categories of viral gastroenteritis
- Norovirus
- rotavirus
- astrovirus
- enteric adenovirus
Describe the two classical presentations of norovirus and list two other symptoms that may occur, how long do symptoms usually last? How many genes does the virus have and why is it so contagious?
Projectile vomiting (once ingested it also slows down the passage of food so you have a full stomach…) and profuse diarrhea. Patients may also have abdominal cramps and a low-grade fever. Overall symptoms usually last 1-3 days. It’s also partly so contagious as you only need to internalize ~20 norovirus particles to be infected.
9 genes
Why do viral ilnesses cause vomiting?
They cause irritation and inflammation of the GI tract and stomach lining, so when you eat/drink the region is further irritated causing you to expel the contents of your stomach
Which symptoms of a GI infection make the body prone to going into metabolic acidosis and alkalosis?
Which symptom makes the body more prone to going into hypochloremia?
Metabolic acidosis: occurs from diarrhea since stools have a higher bicarbonate concentration than plasma
Metabolic alkalosis: occurs from vomiting and depleting the stomach HCl (along with hypochloremia)
What ion imbalance can both vomiting and diarrhea cause?
Hypokalemia
What and where are enteric bacteria? How can they cause disease? List two examples
They are gram (-) bacteria of the intestines/gut flora that can be either opportunistic (by acquiring a virulence factor) or always obligate (causing disease). They have large molecules consisting of LPS which helps adhere to the epithelia and is a toxin (composed of O antigen)
E.g; salmonella, shigella
Describe the 3 antigens enteric bacteria can have
O antigen: on the surface, inhibits phagocytosis and provides a degree of heat stability
K antigen: part of the capsule (capsules are good at creating a sticky layer to attach to cells or an existing biofilm)
H antigen: in those with a flagellum, useful for attachment and provides a degree of protection against macrophages
List 3 main disease outcomes that can result from an enteric bacterial infection
- Sepsis
- UTIs
- many intestinal infections (and meningitis if there’s inflammation of the meninges)
What are the 2 types of salmonellosis? What differentiates them and which is more common?
- Acute gastroenteritis: more common and results from a foodborne infection/intoxication
- Enteric Fever (Typhoid): results from a bacterial invasion into the bloodstream
What are the main two signs of a GI infection?
Vomiting and changes in bowel habits
Name three symptoms that acute gastroenteritis usually causes
Watery diarrhea, nausea and vomiting
Describe the overall two general ways one can contract infectious gastroenteritis, how does the onset of the disease vary in each? Name two organisms that cause each.
- Pre-formed toxins in food poisoning: onset very rapid (usually in small number of hours). Toxins may come from Staphyloccocus and clostridium.
- Contact with a living organism; helminths, viruses, bacteria: onset can take up to 48 hours. Most common organisms are strains of salmonella, campylobacter
Why did hookworms attain their name and how do they infect?
They have little teeth that act as hooks to grip onto the epithelia they come in contact with, they are spread through ingestion/contamination with an egg or cyst
What is ascaris and a complication of being infected by one? How are they commonly spread?
Round worm, a type of nematode. A major complication arises from their ability to build up in the intestine and cause severe blockages, they can also travel throughout the body and colonize other organs. Commonly spread through contamination with soil or meat
Name three signs of a pinworm infection
Visibly detectable in the feces, signs of being worn down, dark eyes, etc
Define the following terms:
A) Food poisoning
B) Food infection
C) Food Intoxication
A) any illness resulting from the consumption of food
B) presence of bacteria or other microbes which infect the body after consumption
C) ingestion of toxins contained within the food
Describe the common presentation of staphylococcal food poisoning
Symptoms such as nausea, abdominal cramping, vomiting and diarrhea occur 1-6 hours following ingestion. The illness is usually mild (lasting a few hours to a day) but can become more severe
What is the leading cause of non bacterial gastroenteritis in the developed world?
Norovirus
Describe the basic pathology of being infected with rotavirus, what it commonly presents with and how it can be diagnosed and managed
Uses particular attachments that allow the virus to enter villus of the proximal SI -> replicates within and lyses cells -> impaired absorption of carbohydrates and nutrients + diarrhea and vomiting (no blood)
Commonly presents with severe dehydration
Diagnosed with the EIA antigen in the stool, treated with oral rehydration or IV. Oral vaccine is also now available
What differentiates norovirus and rotavirus from astrovirus and enteric adenovirus?
Astrovirus and enteric adenovirus have longer signs and symptoms typically lasting 1 week - 10 days, whereas norovirus and rotavirus tend to last 3-4 days if uncomplicated
List two examples of opportunistic and obligate enterobacteria
Opportunistic: E.coli, Klebsiella pneumonia
Obligate: Salmonella, Shigella (and some e.coli strains)
Which subgroups of salmonella cause typhoid fever, paratyphoid fever and salmonellosis?
S.typhi: typhoid fever
S. Paratyphi A, B and C: paratyphoid fever
S. Typhimurium, S. montevideo: salmonellosis
Describe their basic pathology of how salmonellosis infects
- Ingestion of contaminated food/water
- Salmonella attaches to epithelia cells and induces phagocytosis into a vacuole
- Once bacteria is within the cell it causes cell death (inducing diarrhea), PAMPs and DAMPs activated
- Sometimes bacteria moves into bloodstream and inflammation begins
What is the difference in how S.typhi affects the body in comparison to other salmonella subgroups?
Once the immune system recognizes this bacteria, WBCs phagocytose the bacteria and carry it to the liver, spleen and bone marrow where they bacteria can reproduce. In the liver, the bacteria tends to invade the biliary system and live within the gall bladder (provides a nice environment for this particular organism). Every time bile salts are sent to the SI, a small amount of bacteria is sent with it - and so many individuals are asymptomatic but it can progress to ‘Typhoid fever’
Describe briefly the classic four stages of typhoid fever, how long does each last?
Each lasts about a week
1. Slow rising temperature, relative bradycardia, malaise, acute haemorrhaging from nostrils in 1/4
- Temp increases, distension of abdomen (massive inflammatory response and intestine damage is causing fluid imbalance), weight loss (gut is no longer absorbing nutrients), delirium, continued bradycardia
- Intestinal haemorrhaging (epithelia continually breaking down), intestinal perforation, high fever, dehydration and increased delirium, encephalitis (inflammation of brain)
- Very high fever, possible death
Name five other complications tend to be involved as typhoid fever progresses to stage 4
Pneumonia, intestinal bleeding and perforation, kidney failure, peritonitis (inflammation of peritoneum), overwhelming infections
What has been the major intervention in preventing further cases of Typhoid fever?
Ensuring access to clean water (chlorination of water inhibits microorganism growth)
Define a ‘carrier’, how many individuals infected with S.typhi become carriers? How are both carriers and symptomatic infected individuals of S.typhi treated?
A carrier is usually a healthy person who survived the disease but whom the bacteria are able to survive without causing further symptoms (3-5% of those infected become carriers). They are treated with prolonged antibiotics and removal of the gall bladder or site of infection
Describe the following aspects of shigella:
Type, motility, spore forming ability, catalase and oxidase, aerobic/anaerobic
Which symptom is shigella predominantly responsible for?
Gram -, nonmotile (no H antigen), non spore forming, catalase positive and oxidase negative, anaerobic
Responsible for dysentery
Compare diarrhea and dysentery
TFL-CD-VB-T
Type: Diarrhea is watery with no blood and mucus whereas dysentery is a mucoid stool which may be accompanied by blood
Fever: less common in diarrhea, more common in dysentery
Location: Diarrhea tends to affect small bowel and the infection is located only in the intestinal lumen and upper epithelial cells. Dysentery affects the colon and targets upper epithelial cells and causes colon ulceration
Cell death: No cell death in diarrhea (infection is only caused by the release of toxins by the pathogen). In dysentery, the upper epithelial cells are attacked and destroyed by the pathogen
Viral/Bacterial: Diarrhea is mostly viral, dysentery is mostly bacterial
Treatment: diarrhea doesn’t need antibiotics but dysentery almost always does. The antimicrobial given to treat diarrhea doesn’t eradicate toxin left behind, but treatment for dysentery can eradicate the pathogen and stop inflammation
Describe the basic pathology when infected by shigella
- Through contamination it enters system and attaches to cells (first colonizes cells of the small then large intestine)
- Has an antigen on its surface which triggers cell phagocytosis
- Multiplies within the cell and releases a chemical that breaks down the actin fibres - causing the connection between cells to break down so shigella can invade the epithelia laterally
- An abscess forms as epithelia are killed by the infection (very painful) and shigella may enter the blood where it is quickly phagocytized
Shigatoxin is also a neurotoxin and can affect the nervous system
What is shigella’s main virulence factor? How does it spread so efficiently and how is it diagnosed?
Virulence factors include enterotoxins such as shigatoxin. Since there aren’t many immune cells within the host cell itself the bacteria has time to grow and replicate before being intercepted by immune cells in circulation. Diagnosis is based on symptoms and presence of shigella in the stools
Name 5 factors that contribute to the pathogenicity of e.coli
- O, H and K antigens
- Often acquire plasmids to increase virulence
- Some e.coli produce shiga-like toxin (can disrupt the PM)
- Have receptors for attachment
- Has LPS: so even when its degraded/broken down by immune system your exposing it to LPS which causes an inflammatory response
Name the four major classifications of E.coli, which is responsible for traveller’s diarrhea (also define traveller’s diarrhea)?
Which causes dysentery and is clinically identical to shigella? Which classification of e.coli is the most extreme and what other disease can it cause?
- ETEC: enterotoxigenic - traveller’s diarrhea: production of three or more loose watery stools during or shortly after travelling abroad
- EPEC: enteropathogenic - moderately invasive
- EIEC: enteroinvasive - causes dysentery and is identical to shigella
- EHEC: enterohemorrhagic; has shiga toxin which produces a major inflammatory response leading to mass haemorrhaging and can cause hemolytic uremic syndrome
Name the two toxins produced by enterotoxigenic e.coli, what pathogen are they similar to and what type of diarrhea do they cause?
Briefly describe the mechanism by which this bacterium causes diarrhea
Some strains produce one and some produce both: Heat labile toxin (LT) and heat stable toxin (ST), similar to cholera and produces watery diarrhea (without blood or mucus) but no fever
- ETEC bacteria colonized the mucosal surface of the SI, using projections (fimbrial adhesions) to bind to enterocytes
- Enterotoxins are transferred into the epithelial cell stimulating the release of liquid into the lumen.
How is V.cholera spread and how can it be prevented? Which parts of the GI tract is affected and how?
*include one unique characteristic of infected individual’s stools
Usually through water (organism survives in water supplies) in developing areas, prevention includes access to clean drinking water and improved sanitation.
The SI is affected; V.cholerae stays in the lumen but produces cholera toxins A and B; toxin B binds to cell surface receptors facilitating the entry of toxin A which irreversibly activates adenylyl cyclase - generating excess cAMP. This stimulates Cl- secretion through CFTR, which is followed by Na+, K+ and water. The result is profound diarrhea that can cause life threatening dehydration.
Stools look like ‘rice water’ as it’s made up of intestinal secretions and mucus
Name 5 clinical signs that might be present in a patient infected with cholera, what is the man treatment and how is it administered?
- Dehydration
- Watery diarrhea smells of fish and contains white flecks
- Hypotension
- Circulatory failure
- Pyrexia, although it is uncommon and raises suspicion of a secondary infection
Main treatment is fluids, usually oral in large amounts
Name three complications that might result from a cholera infection
Hypokalemia, hypoglycaemia, renal failure
Define the following terms:
A) endemic
B) epidemic
C) pandemic
A) diseases that are always found in a particular locality or amongst certain races
B) diseases affecting large numbers of people in a particular locality at one time
C) an epidemic that has spread so widely that many people in different countries are affected
Are neutrophils in the stool more indicative of a viral or bacterial infection?
Neutrophils are more commonly present in bacterial infections as most viruses causing diarrhea don’t cause ulceration or invade the mucosa
Which pathway gives rise to eosinophils?
The myeloid pathway
What would your initial investigations be for a patient with suspected traveller’s diarrhea? *Name 3 main things
Name four things you would do to manage this patient while awaiting results
- Stool for microscopy and culture
- EIA test for antigen
- Blood; FBC, urea and electrolytes, LFT, CRP
Management:
- Maintain adequate hydration (oral or IV if dehydration is significant or unable to tolerate oral fluids)
- As symptoms improve introduce bland foods
- Avoid anti-motility agents
- Consider antibiotics in those with severe or prolonged symptoms
Describe the pathophysiology for H.pylori
H.pylori induces chronic inflammation which upsets gastric acid secretory physiology and can lead to chronic gastritis. For some, this stays asymptomatic and does not progress. However, in some cases altered gastric secretion coupled with tissue injury leads to peptic ulcer disease. Gastritis can also progress to atrophy, intestinal metaplasia and eventually gastric carcinoma (and rarely due to persistent immune stimulation of gastric lymphoid tissue, gastric lymphoma)
How do antacids affect the growth of H.pylori?
It can increase the risk of bacterial overgrowth
How is the norovirus spread and what is its normal incubation period
Fecal-oral, person-person contact and via aerosolization. Normal incubation period is 1-2 days
How would a GP determine whether a patient is dehydrated and signs of shock in severely dehydrated?
For dehydration can assess mucous membranes, skin turgor, presence of sunken eyes, and assessing the frequency/colour of the patient’s urine
Signs of shock in severely dehydrated patients may also include tachycardia and tachypnoea
Other than diarrhea, namer four other less common but potential symptoms that may be experienced with an ETEC infection. How long does the illness usually last?
Abdominal cramping, fever, vomiting, muscle aches. Illness usually lasts 3-4 days following exposure but can last up to 3 weeks.
Name three common causes for traveller’s diarrhea
- ETE
- Shigella
- Salmonella
