pathogens and host Flashcards
what are some features of clinical infection?
inflammation
pain
pyrexia → (raised body temperature)
tachycardia → (raised heart rate over 100 beats)
rigours → (feeling cold with shivering)
increased white cell count
increased C reactive protein (CRP)
Two types: latent or subclinical
what is a pathogen and commensal?
pathogens - an organism which can cause disease
commensal - an organism which is part of normal flora
e.g. E. coli in the gut, Staph aureus in the nose, axilla.
what is pathogenicity and its requirements?
the capacity of a micro-organism to cause an infection.
Requirements:
infectivity
- ability to become established on or within a host
1- Attachment (fimbriae & receptors)
→ E. coli
2- Acid resistance (evasion of acid which has Urease enzyme)
→ Helicobacter pylori
virulence
- ability to cause harmful effects (disease) once established
Conferred by virulence factors
– Genetically determined microbial components
1- Invasiveness
2- Toxin production
3- Evasion of the immune system
- Specific to strains, not species (different strains of one species can vary in their virulence)
what are the 3 types of toxins?
exotoxins are released extracellularly by the micro-organism
enterotoxins are exotoxins which enter via the GI tract then spread to other tissues
e.g. polio spreads to neuronal tissue - paralysis
endotoxins are structurally part of the Gram-negative cell wall
what are the sites of viral entry? give examples
Respiratory Tract: Influenza, SARS-CoV-2.
Gastrointestinal Tract: Rotavirus, poliovirus.
Skin: Human papillomavirus (HPV) via micro-abrasions.
Mucous Membranes: HIV through sexual contact.
Blood: Hepatitis B, Zika virus via transfusion or insect vectors.
how do viruses induce tumours? give examples
Integration of viral DNA into the host genome disrupts tumour suppressor genes.
Viral proteins inactivating p53 and Rb (e.g., HPV E6/E7).
Human papillomavirus → Cervical cancer.
Epstein-Barr Virus (EBV) → Burkitt’s lymphoma, nasopharyngeal carcinoma.
what is humoral and cell-mediated immunity? both acquired
Humoral Immunity:
B cells produce antibodies (IgG, IgA, IgM).
Neutralization, opsonization, complement activation.
Cell-Mediated Immunity:
T cells (CD4+ and CD8+) eliminate intracellular pathogens.
CD4+ T-helper cells stimulate other immune cells.
CD8+ cytotoxic T cells kill infected cells.
Describe the features of acute viral infections with the use of examples:
Features: Rapid onset, short duration, self-limited.
Influenza: Fever, respiratory symptoms, clears within 1-2 weeks.
Rhinovirus: Common cold, mild symptoms, resolves in days.
