Lecture 6.1: Infectious Diseases of the GI Flashcards
What is Infection?
The process whereby a pathogenic organism invades and multiplies in or on host tissue
Transmission Routes of Infection
- Endogenous Infection
- Air-borne Spread
- Faeco-oral Spread
- Vector Borne
- Direct Person to Person
- Indirect Person to Person
- Direct Inoculation (e.g bite)
- Consumption of Infected Material
Pathogenic Mechanisms: Epithelial Attachment
- Attach via adhesion molecules (adhesins) of either pili or fimbrae
- Some bacteria have the ability to produce a protective slime
- Specific organs e.g. buccal plates of hookworms
Pathogenic Mechanisms: Colonization and Invasion
- May travel to intracellular locations
- May remain extracellular
- May enter blood/lymph circulations
Pathogenic Mechanisms: Tissue Dysfunction
• Cell lysis
• Production of toxins
• Endotoxins = cell wall compounds of G-ve bacteria which generate an
inflammatory response in the host
• Exotoxin = secreted proteins (act both locally and at a distance)
What is Gastroenteritis?
Irritation/inflammation of the stomach resulting in cramping pain, nausea and
vomiting and diarrhoea
What is Diarrhoea?
Abnormal faecal discharge characterised by frequent and/or fluid stool >3/day)
Bristol Stool Chart: Type 1
- Separate Hard Lumps
* Very Constipated
Bristol Stool Chart: Type 2
- Lumpy and Sausage-like
* Slightly Constipated
Bristol Stool Chart: Type 3
- Sausage shape with cracks on surface
* Normal
Bristol Stool Chart: Type 4
- Like a smooth sausage/ snake
* Normal
Bristol Stool Chart: Type 5
- Soft blobs with clear-cut edges
* Lacking fibre
Bristol Stool Chart: Type 6
- Mushy consistency with ragged edges
- Inflammation
- Diarrhoea
Bristol Stool Chart: Type 7
- Liquid with no solids
- Inflammation
- Diarrhoea
What are the 4 Groups of Viruses associated with Gastroenteritis?
- Rotaviruses (groups A, B and C)
- Enteric Adenoviruses (types 40 and 41)
- Calici Viruses (noroviruses, sapoviruses)
- Astroviruses
Rotavirus
• Major cause of infantile gastroenteritis worldwide (>200K deaths in children
<5)
• Asymptomatic infections are common (more so in breast-fed babies)
How can Rotavirus Infections be detected? (2)
- Infection can be established via genome amplification
* ELISA for detection in faeces
What are the 3 different ways diarrhoea is caused?
- Mucosal adherence
- Mucosal invasion
- Production of toxins
What are the 2 syndromes Bacterial Gastroenteritis can be divided into?
- Watery diarrhoea (toxins or adherence)
* Dysentery (mucosal invasion and damage)
What is the Salmonella Bacteria?
Salmonella is a genus of rod-shaped Gram-negative bacteria of the family Enterobacteriaceae
What is a Salmonella Infection caused by?
Salmonella infection is usually caused by eating raw or undercooked meat, poultry, and eggs or egg products or by drinking unpasteurized milk
Symptoms of Salmonella
- Symptoms commence 12-48 hours after infection
- Nausea
- Cramping
- Diarrhoea (watery->bloody)
- Fever
How often does Bacteraemia occur in Salmonella?
May occur in 1-4% of cases
How to diagnose Salmonella?
Specific diagnosis from culture of the organism from faeces or blood
What is Food Poisoning?
Any disease of an infective or toxic nature caused by or thought to be caused by the consumption of food and water
What are Helminthic Infections? Where are they most common?
- Infections caused by different species of parasitic worms
* Common in developing countries (affects humans & domestic animals)
What are the most common Helminthic Infections?
- Nematodes (Roundworms)- have mouthparts + guts
- Trematodes (Flukes)- have mouthparts + guts
- Cestodes (Tapeworms)- absorb nutrients across body surface
How long can worms live?
Have the potential to live for ~30 years in some cases
What are Nematodes? Mechanism of Infection?
- Also termed soil-helminthes or geohelminthes
- Ingestion of eggs that have matured in soil
- Eggs hatch in soil and larvae penetrate skin directly
Enterobius (Threadworm or Pinworm)
Nematodes
Ova transferred from perianal area to fomites
Worm 2-12mm in length
Larvae develop in small intestine, adults reside in colon
Symptoms and Treatment of Enterobius (Threadworm or Pinworm)
- Perianal Irritation
- Weightloss
- Bedwetting
- Mebendazole
- Piperazine
- Good Hygiene
What are Fomites?
Objects or materials which are likely to carry infection, such as clothes, utensils, and furniture
What are Trematodes?
Flat, leaf-shaped worms
Liver Flukes
- Freshwater snails are intermediate hosts
- Encyst on aquatic vegetation that is then consumed by humans
- Penetrate gut wall and migrate to live (produces systemic allergic symptoms)
What are Cestodes?
- Flatworm Phylum
* 15 to 50 mm Long
How do Cestodes attach to intestines?
They have four ‘suckers’ to adhere to the gut wall
How do Cestodes infect humans?
- Arising from anterior region are segmets called proglottids
- These distally contain eggs
- Eggs released into faeces and consumed by intermediate hosts
- Eventually consumed by host (cattle, pigs)
- Humans consume undercooked meat
- Results in infection and development usually of a single tapeworm
Symptoms of having a Cestode Infection? (9)
- Nutritional Deficiencies
- Intestinal blockage if intense infestation
- Nausea
- Weakness
- Abdominal Pain
- Diarrhoea
- Dizziness
- Salt Craving
- Weight Loss
Types of Protozoal Infections? (5)
- Amoebea – Entamoeba histolytica (Amboebiasis)
- Flagellates – Giardia intestinalis (Giardiasis)
- Coccidia – Cryptosporidium parvum (Cryptosporidiosis)
- Cilliates – Balantidium coli (Balantidisis)
- Microspora – Enterocytozoon bieneusi (Microsporidiosis)
What is Giardiasis?
- Most common parasitic infection of travellers returning to UK
- Diarrhoeal disease caused by the microscopic parasite Giardia duodenalis
- When in gut it can change morphology, mild partial villous atrophy
Symptoms and Treatment of Gisardiasis
- Diarrhoea
- Nausea
- Anorexia
- Abdominal Pain
- If illness is prolonged steatorrhoea is seen
- Metronidazole 2g/day, 3 days usually does the job
What is Steatorrhoea?
It is an increase of fat excretion in the stools
