Infection and Inflammation
Topic 18 — Gram-Positive Rods, Zoonotic and Directly Contagious Infections
Connect the organism, pathogenic mechanism, clinical clue, diagnosis and preventive action for rapid KMU revision.
1. THE TOPIC IN ONE CONNECTED FLOW
This topic connects different infections through one simple idea: identify the source or organism, understand its key pathogenic mechanism, recognize the characteristic clinical effect, choose an appropriate diagnostic clue, and then interrupt disease through prevention. Some organisms mainly act through toxins, while others persist within cells, spread through vectors or produce disease after repeated close-contact transmission.
2. KEY CLINICAL CONNECTIONS
B. anthracis spores → edema and lethal toxin effects → tissue edema and necrosis → anthrax.
C. tetani toxin → loss of inhibitory neurotransmission → rigidity and painful spasms.
C. diphtheriae toxin → inhibited protein synthesis → pseudomembrane ± systemic cardiac or neural injury.
Unpasteurized dairy or infected livestock → Brucella exposure → prolonged febrile illness → blood culture/serology.
Rodent–flea exposure → Y. pestis → lymph-node involvement → bubo aspirate supports diagnosis.
Rabies exposure → peripheral nerve entry → CNS spread → prompt wound care + vaccination ± immunoglobulin prevents progression.
Tetanus-prone wound → spore germination risk → appropriate active immunization ± passive immune protection reduces toxin-mediated disease.
Leprosy → peripheral nerve involvement → sensory loss and disability → early detection and treatment limit progression.
Repeated trachoma → conjunctival fibrosis → entropion/trichiasis → corneal damage → SAFE measures interrupt this pathway.
3. AIM HIGH-YIELD INTEGRATION REVIEW
Do not confuse the neurological effects of the clostridial toxins: tetanus produces spastic paralysis through loss of inhibitory neurotransmission, while botulism produces flaccid paralysis through impaired acetylcholine release.