Plague and Non-enteric Pathogens

Plague and Non-enteric Pathogens

1. Yersinia pestis

   • Cause of the plague
   • Transmitted via animals
     • Sylvatic plague - from wild animals
     • Urban plague - from domestic/semi-domestic animals or humans
     • Found in 200 species of animals (rodents) without causing disease
   • Fleas are vector
     • Bacteria replicates in gut
       • Coagulase causes blood clotting which blocks the oesophagus
         • Flea becomes ravenous
   • 3-50 bacilli
   • Bubonic
     • Bacilli multiplies in flea bite
       • Bacteria enters lymphatic system
         • Causes swelling and necrosis in groin/axilla (a bubo)
   • Septicemic
     • Progression to massive bacterial growth
       • Virulence factors cause intravascular coagulation, subcutaneous haemorrhage and purpura
     • Black plague
   • Pneumonic
     • Infection localized to lungs
     • Highly contagious
     • Fatal without treatment
   • Diagnosis depends on patient history, symptoms and lab findings from bubo aspirate
   • Treated with streptomycin, tetracycline or chloramphenicol
     • Prevention of spread by quarantine and control of rodent population
   • Killed/attenuated vaccine available

2. Non-enteric Pathogens

   • Pasterurella multocida
     • Normal flora in animals
     • Opportunistic pathogen
     • Animal bites cause local abcesses that spread to bones, joints and lymph nodes
     • Immunocompromised are at risk of septicaemia and complications
     • Treated with penicillin and tetracycline
   • Haemophilus
     • Tiny, Gram -ve pleomorphic rods
     • Fastidious - sensitive to drying, temperature extremes and disinfectants
     • Grows on chocolate agar - require hemin, NAD or NADP
     • Some species are normal flora of upper respiratory tract/vagina
     • Other species are involved in conjunctivitis (H. aegyptius), childhood meningitis and chancroid (H. ducreyi)
       • H. influenzae - acute bacterial meningitis, epiglottitis, otitis media, sinusitis, pneumonia, bronchitis
         • Hib vaccine
       • H. parainfluenzae and H. aphrophilus - normal oral and nasopharangeal flora but can cause infective endocarditis