GI Infections
Host Defences
Diseases
Gastritis
Aetiological agent; H. Pylori (neutralised acidity by ammonia (by product of urea)
Diagnosis; biopsy (invasive), breath test (testing for presence of carbon) & antibody test
Gastroenteritis
Multi-aetiologies, presents with diarrhoea and/or vomiting, common following food poisening
Oesophagitis
Usually in predisposed pt, following antibiotic course > superinfection with oral thrush
Immunocompromised pt > occurrence of ulcers
Aetiological agents; C. Albicans, Herpes, CMV, EBV etc
Peridontal Disease
Chronic inflammatory condition
Pockets of pus under the gum line > gingivitis 
Aetiology; excessive enzyme production > weaken tissue-teeth hold > opens space between gum/teeth > allows for anaerobic bacteria to grow
Tooth Decay
Most common infection (dental caries)
Production of flaque (biofilm) > bacteria metabolise sugar > forms acid
S. Mutans (common aetiological agent) > breaks down glucose (in wall) > produces lactic acid > initiates tooth decay
Inflammatory Conditions
Infection w/ Protozoa
Infection w/ Multicellular Parasites
Infection w/ Viruses
Gastric Acidity
Normally less than 4.0pH
Acidity is reduced with food, in neonates, pt with pernicious anaemia & following gastric resection
Gut Microbiota (Flora)
Function as mechanical barrier, occupying possible binding sites, produce antibacterial compounds & some essential host vitamins
Immune System
Comprised of IgA secreted onto mucosal surface, leukocyte migration & presence of antibodies in colostrum/breast milk
GIT Mobility
Including fibre into diet = enhances gut motility
Inflammatory Intestinal Disease
Presents with dysentery & colitis
Occurs in large intestine
Bacterial; cells invaded & destroyed by cytotoxin, organism grows in lumen > releasing cytotoxin (E.g C. Difficile (spore former) = pseudomembranous colitis > Ab associated diarrhoea
Protozoa; penetrate mucosa > destroying colonic cells (E.g Entamoeba histolytica; amoebic dysentery 
Non-Inflammatory Intestinal Disease
TOXIN-MEDIATED = reducing fluid & salts
Occurs in small intestine
Bacterial; produce toxin > interferes with fluid absorption > net excretion of fluid
Protozoa; attach to epithelium & block fluid absorption 
Viruses; infect & destroy microvilli cells
Giardiasis
Occurs in duodenum/upper jejunum
Pt may present as a carrier (no symptoms) OR with diarrhoea & abdominal pain, bloating & smelly flatulence
With malabsorption syndrome; faeces may appear pale (increased fat)
Treatment; w/ metronidazole (Flagyl)
Amoebic Dysentery
May invade peritoneum > abscess formation = Blood/mucosal containing diarrhoea (AKA dysentery
Cryptosporidium Infections
Causes severe chronic diarrhoea in immuno-compromised pt
Usually infection occurs after exposure to contaminated water (E.g. in pool, as can survive chlorination)
Enterobius Bermicularis 
AKA threadworm or pinworm
Life-cycle with single host, from anus to mouth of same host or others
Trichuris Trichiura
AKA whipworm
Predominant symptom is anaemia
Sometimes used to treat ulcerative colitis, as autoimmune disease appears 'distracted' when parasite present  
Ascaris Lumbricoides
Largest worm > may cause intestinal obstruction or allergic pneumonitis
Hookworm
Caused iron-deficiency anaemia, usually presents with itchy skin, abdominal pain, diarrhoea, loss of appetite & weight loss
Taenia Saginata
AKA beef tapeworm
Requires another host to complete lifecycle
Organism found in cattle muscle > undercooked meat > larvae developed in humans
Taenia Solium
AKA pork tapeworm
Requires another host to complete lifecycle
Undergoes cysticerosis in human tissue stage 
Fasciola Hepatica
Requires another host to complete lifecycle
Presents normally as the sheep liver fluke & larvae in water snails
If found in humans > can obstruct bile duct > leading to hepatomegaly 
Rotavirus
Most common cause of gastroenteritis (in children)
Treatment/Preventative measures; cohorting, separation from non-infected, individual equipment for infected & hand hygiene 
Norovirus
Causes gastroenteritis in both adults & children
Presents with sudden onset of nausea & diarrhoea
Treatment; w/ hypochlorite as viricide 
Infection w/ Bacteria
Salmonella Infection
High infective dose (unless in young/elderly/immunocompromised), symptoms present due to toxins (if involves GIT, referred to as enterotoxin)
Symptoms present delayed as entertoxin pentrates mucosal layer (invasion) > causing inflammation
Reptiles have a high salmonella carrying capacity
Typhoid Fever (Enteric)
Limited to human species, infected pt is either human case or chronic carrier (E.g Typhoid Mary)
Symptoms present as influenza-like (and abdominal 'rose spots', neuropsychiatric, intestinal perforation etc)
Chronic carriers (3% of infected) tend to excrete bacteria from gall bladder, and can be treated with antibiotics
Campylobacter Enteritis
Most common cause of food poisoning (10:1 compared to Salmonella)
Symptoms present more severly & prolonged with abdominal colic and fever in severe cases
Delayed process as agent requires low oxygen & high carbon dioxide conditions to grow
Outbreaks have occurred through raw/undercooked chicken, contaminated water & unpasteurised milk
Presentation; acute watery/bloody diarrhoea ( due to spiral shape/flagella invading mucosa > producing cytotoxin = inflammation)
Bacillary Dysentery 
Aetiological agents; Shigella (E.g. Bali belly), Amoeba
All have low infective dose (about 2 only)
E. Coli
Part of normal flora, but new bacteria can colonise from different countries causing mild diarrhoea = travellers diarrhoea (due to enterotoxigenic strains)
Types; Enteroinvasive E. Coli (EIEC) > blood dysentery, high infective dose > possible kidney failure. Enterohaemorrhagic E. Coli (EHEC) > severe haemorrhagic diarrhoea & haemolytic uraemic syndrome
Listeria Infection
Found in dairy foods, deli-style foods & raw seafood
No GIT symptoms, but may present with septicaemia and/or meningitis in immunocompromised, premature foetal death if pregnant woman ingests
Diseases Caused by Ingested Toxin
1. Staphyloccocal aureus; found in salty, high fat & CHO foods > induces acute vomiting (within 1-6 hours post)
2. Bacillus cereus; spore forming bacterium (can survive boiling) > time left at room temp > toxin production = acute vomiting 1-6hrs post
3. Clostridium botulinum; spore-forming bacterium, produces most toxic substance, grows in neutral anaerobic foods, comsumption of neurotoxin > paralysis with no intestinal symptoms
Diseases Caused by Toxins Produced in the Intestine
1. Clostridium perfringens (Gas gangrene), high amount required for disease to occur as difficult to survive intestinal passage, toxin production in duodenum = diarrhoea 8-16hrs post
2. Cholera (Vibrio Cholera); requires large infective dosage (killed w/ stomach acid), no invasion, only toxin release, causes massive fluid excretion > fluid loss & dehydration 
Symptoms appear 16-72 hrs post
Treatment; rapid electrolyte & water replacement
3. Infant botulism; occurs in large intestine due to lowered normal flora & bile secretion), spores may be sources from honey
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