Infections Flashcards
What is GALT?
Gut associated lymphoid tissue- made up of payers patches and mesenteric lymph nodes- a collection of macrophages, T cells, plasma cells, mast cells and dendritic cells found within the large colon, which recognises pathogens and dont react to commensals.
What should be asked in the history of someone with a GI infection?
- Travel history
- Food and location history (animals)
- Diarrhoea (type of poo, frequency, consistancy, duration, onset)
- Evidence of deyhdration
- Co- morbities
state functions of commensals in the gut
- billirubin metabolism
- competition for pathogens
- ferment polysacchardies (creates variety of useful products)
What is gastroenteritis?
A combination of nausea, vomiting, diarrhoea and abdominal pain
What is the most common cause for gastroenteritis
50-70% is viral, of this the most common causative virus is norovirus, but also rotavirus and adenovirus may cause it
What is the difference in incubation periods between viral, bacterial and protozoan causes of infections?
viral- 12-24 hrs
Bacterial- 2-4 days
Protozoal- 7 days
State 5 bacteria and 4 protozoa that may cause gastroenteritis?
Bacteria- sallmonella, camplyobacter, shigella, enterotoxigenic E. Coli, C. diff
Protozoa: Cryptosporidium, Giardia, cyclospora, entamoeba
What is the gram stain of shigella
gram neg (red) red (non motile)
How does shigella spread?
faecal oral, contaminated food, water, fomites, secual contact ect
Describe the pathogenesis of shigella dysenteriae?
Invade and destroy mucosa of large intestine by producing 3 effector proteins which cause enterocytes to engulf them. They dont often invade deep and cause bacteraemia.
How does shigella normally present?
- may have recent travel or know someone else ill
- incubation of 1-3 days
- water diarrhoea (if inc blood- dysentery)
- abdo pain
- fever and malaise
What is treatment for shigella?
supportive, may take a week to get better, if immunocompromised= ciprofloxacin
What is the causative organism of salmonella?
salmonella enteritidis
How is salmonella transmitted?
some associated with animals, others faecal oral
What is the pathogenesis for salmonella?
Invade enterocytes and cause localised disease. They may be taken up by phagocytes and taken to lymph nodes where they multiply and can then become systemic and cause enteric fever
How quickly does gastroenteritis due to salmonella tend to resolve?
within a day
How is enteric fever caused by salmonella treated?
B- lactams
What is the pathogenesis for enterotoxigenic E coli
Colonise small intestine w/ help from pili, this is mediated by enterotoxins. They then cause prolonged hypersecretion of Cl- whilst inhibiting Na+ absorbtion.
What is the most common cause of travellers diarrhoeas?
enterotoxigenic E. Coli
What is the definition of travellers diarrhoea
Three or more unformed stools per day combined with one clinical sign, such as abdominal cramps, fever,
nausea, or vomiting.
How should travellers diarrhoea by managed- prevention and treatment
Prevention- alcohol gel, careful what you eat, prophylaxis if immunocompromised
Antibiotics may be given to be taken if they get infected
When should antibiotics be given and not given for E.coli and which antibiotic is best?
They should be given if very severe or host immunocompromised- give ciprofloxacin or trimethaprim.
They should not be given if blood in diarrhoea or high fever as different strain of E. coli and anti biotics will make it worse. Generally the illness will only last 4 days or so so self limiting.
What type of organism is camplyobacter (gram stain)?
a gram negative rod
From where are campylobacter infections commonly obtained from?
Uncooked chicken (theyre a commensal to chicken)- also contact w/ contaminated food, water or animals.
What are the 2 main species of camplyobacter?
C. jejuni and C. coli
What is the pathogenesis of campylobacter infection?
it releases an enterotoxin, which is stimilar to that released by E. coli. This increases adeylyl cyclase activity which causes electrolyte imbalances
What is the incubation period of campylobacter?
between 1 and 7 days
How is campylobacter identified in a stool sample?
There is an agar which will only allow camplyobacter to grow.
What antibiotic is used to treat severe campylobacter infections?
ciprofloxacin
List complications of campylobacter infections
cholecystis, peritonitis, rash
later complications inc reactive arthiritis and guillian barre syndrome
What is the difference between food poising and a food infection?
Food poisoning is caused by ingestion of a toxin, usually from staph A or clostridium botulinum. Symptoms occur within 2-12 hrs.
Food infections require colonisation of bacteria
What is the route of transmission for norovirus?
faecal/ vomit- oral- particles will aerosolise from stool and vomit forming fomites which contaminate the environment and are resistant to freezing, heating and alcohol.
What is the incubation period for norovirus
48hrs
In which population is rotavirus common?
In young children and infants. Nearly everyone gets it but develops immunity to it so subsequent infections are less severe.
Where is giardia common?
USA
Where can you get giardia from?
Food, water or soil which has been contaminated by faecal matter of carriers
How is giardia diagnosed?
often clinicaly, immunoassay useful, microscopy of stool may see cysts or trophozoities but is often negative
How can severe giardia be treated?
metronidazole
Do giardia invasive the epithelium?
No, they just attach.
Most infections are relatively mild, but some can cause severe mucosal damage. They mostly affect the duodenum
What causes amebic dysentery?
Entamoeba histolytica
What is the pathogenesis of entamoeba?
they feed on intestinal bacteria and may invade the epithelium and cause ulceration. They can further spread to the liver and cause ulceration.
Protozoa are generally resistant to chlorine, how can they be destroyed?
High concentrations of chlorine or UV light.
How can entamoeba be diagnosed?
- Cysts found in stool sample
- serology
- biopsies of abcesses
In which country is cyclospora a common cause of traveller diarrhoea?
mexico
How is cyclospora transmitted?
Faecal oral- whith oocytes particularly invading food chain in water, leafy greens and vegetables.
What is the incubation period for cyclospora and how long do symptoms tend to last
incubation period tends to be 7 days, with illness lasting 7 weeks on avg
How is cyclospora diagnosed?
acid fast staining of stool sample
How is cyclospora infections of someones who’s immunocompromised treated?
trimethoprim
How can cyclospora infections be avoided?
wash foods, avoid buffets, drink filtered and bottled water
How is cryptosporidium transmitted?
Eating contaminated food and water (farm run off has been implicated), also swallowing contaminated pool water
What is the incubation period, length of illness and severity of a cryptosporidium infection?
incubation period is 2-10 days, illness lasts 1-2 weeks and generally not very severe
How long should a person with gastroenteritis wait before returning to work?
48hrs
