Gastrointestinal Infections & Enteric Pathogens – Key Vocabulary

Vocabulary flashcards covering bacterial, viral, and eukaryotic agents of gastrointestinal infection, their virulence factors, clinical consequences, and control measures.

Toxinosis

Disease caused solely by a pre-formed bacterial toxin without the need for bacterial colonisation (e.g., Staphylococcal food poisoning, botulism).

Botulism

Life-threatening toxinosis characterised by flaccid paralysis; results from ingestion, in-situ production, or wound contamination with Clostridium botulinum toxin.

Clostridium botulinum

Gram-positive, spore-forming, obligate anaerobic rod that produces botulinum neurotoxin in low-oxygen environments.

Botulinum neurotoxin (BoNT)

Most potent known toxin; blocks acetylcholine release at neuromuscular junctions, causing flaccid paralysis.

Antitoxin Therapy

Passive immunisation with antibodies that neutralise circulating botulinum toxin; main treatment for botulism.

Escherichia coli

Gram-negative, facultative anaerobe; includes commensal strains and six major pathogenic pathovars that cause extra- and enteric diseases.

Pathovar

A bacterial subgroup defined by characteristic virulence factors and disease profile (e.g., ETEC, EPEC, EHEC).

Enterotoxigenic E. coli (ETEC)

Non-invasive pathovar that adheres to small-bowel enterocytes and secretes heat-stable (ST) and heat-labile (LT) enterotoxins, causing traveller’s diarrhoea.

Heat-labile enterotoxin (LT)

ETEC toxin that activates adenylate cyclase → ↑cAMP → CFTR activation → chloride & water secretion.

Heat-stable enterotoxin (ST)

ETEC toxin that activates guanylate cyclase → ↑cGMP, producing watery diarrhoea.

Enteropathogenic E. coli (EPEC)

Attaching-and-effacing pathovar of E. coli that disrupts microvilli and may produce cytolethal distending toxin; common in infant diarrhoea.

Enterohemorrhagic E. coli (EHEC)

Attaching-and-effacing pathovar that produces Shiga-like toxin; can lead to bloody diarrhoea and haemolytic uremic syndrome (HUS).

Shiga-like toxin (SLT)

Phage-encoded cytotoxin of EHEC that inhibits protein synthesis, damaging vascular endothelium and precipitating HUS.

Haemolytic Uremic Syndrome (HUS)

Triad of acute renal failure, microangiopathic haemolytic anaemia, and thrombocytopenia; severe complication of EHEC infection.

Enteroinvasive E. coli (EIEC)

Partially invasive pathovar resembling Shigella; invades colonic epithelium, escapes phagosomes, and spreads cell-to-cell, causing dysentery-like illness.

Type III Secretion System

Needle-like apparatus used by EPEC/EHEC to inject effector proteins into host cells, inducing actin pedestal formation and ion transport disruption.

Serotype (e.g., O157:H7)

Classification based on surface O (LPS), H (flagellin), and K (capsule) antigens; does not necessarily indicate relatedness.

Colonisation Factors

Fimbriae, pili, or adhesins (e.g., EtpA) on ETEC that mediate initial attachment to intestinal epithelium.

Attaching-and-Effacing (A/E) Lesion

Destruction of microvilli with pedestal formation beneath bound bacteria; hallmark of EPEC/EHEC infection.

Viral Gastroenteritis

Inflammation of stomach and intestines caused by viruses such as rotavirus, norovirus, adenovirus, or astrovirus; leads to acute diarrhoea and vomiting.

Rotavirus

Double-stranded RNA virus (Reoviridae) with triple-layer capsid; leading cause of severe diarrhoea in children under five worldwide.

NSP4

Rotavirus non-structural protein acting as viral enterotoxin; disrupts Ca²⁺ homeostasis, tight junctions, and SGLT1, promoting diarrhoea.

Rotavirus Vaccine (e.g., Rotarix, RotaTeq)

Oral live-attenuated vaccine series recommended by WHO; dramatically reduces childhood rotavirus mortality.

Norovirus

Highly contagious calicivirus; most common cause of acute viral gastroenteritis in adults; transmitted via faecal-oral route, surfaces, and aerosols.

Oral Rehydration Therapy (ORT)

Simple glucose-salt solution that replaces fluids/electrolytes lost during diarrhoea; cornerstone of gastroenteritis management.

Giardia duodenalis

Flagellated protozoan causing giardiasis; transmitted by cyst-contaminated water, food, or direct faecal-oral contact.

Giardiasis

Diarrhoeal illness featuring malabsorption and abdominal pain; results from trophozoite attachment to small-intestinal mucosa.

Cryptosporidium parvum / hominis

Apicomplexan protozoa producing oocysts; cause cryptosporidiosis, a watery diarrhoea especially severe in immunocompromised hosts.

Kato-Katz Technique

Microscopy method to detect helminth eggs in stool; standard diagnostic for soil-transmitted helminths.

Albendazole / Mebendazole

Broad-spectrum anthelmintic drugs used for treatment of soil-transmitted helminth infections.

Soil-Transmitted Helminths (STH)

Group of intestinal worms (Ascaris, Trichuris, hookworms) whose eggs or larvae develop in contaminated soil and infect humans.

Ascaris lumbricoides

Large roundworm causing ascariasis; adult worms may migrate, causing intestinal obstruction or biliary complications.

Ascariasis

Helminth infection marked by abdominal discomfort, cough from larval lung migration, and growth impairment in children.

Trichuris trichiura

Whipworm responsible for trichuriasis; heavy infections can cause Trichuris dysentery syndrome and rectal prolapse.

Hookworms (Ancylostoma duodenale & Necator americanus)

Blood-feeding nematodes that penetrate skin as L3 larvae; cause iron-deficiency anaemia and growth stunting.

Colonisation Resistance

Protective effect of normal gut microbiota that prevents pathogenic bacteria from establishing in the intestine.

Heat Treatment (≥85 °C for >5 min)

Food-safety measure that destroys C. botulinum spores/toxin, preventing food-borne botulism.

Ventilator Support

Mechanical assistance for respiration; often required for months in severe botulism cases with respiratory muscle paralysis.

ID50 (Infectious Dose 50)

Number of pathogen particles required to infect 50 % of exposed hosts; as low as 10 particles for rotavirus.

Child Mortality from Diarrhoeal Disease

Third leading global cause of death in children; declining due to vaccines, sanitation, and ORT.

NSP (Non-structural Proteins)

Rotavirus proteins crucial for replication (e.g., NSP1 interferon antagonist) and pathogenesis (e.g., NSP4 enterotoxin).

Cyclospora cayetanensis

Coccidian protozoan causing prolonged watery diarrhoea; often linked to contaminated fresh produce.

Enteric Adenovirus

Serotypes 40/41; cause paediatric diarrhoea, usually less severe than rotavirus.

Blepharospasm

Involuntary eyelid twitch treated therapeutically with local botulinum toxin injections.