Plague

Question 1

plague

Answer 1

• the most explosive disease in human history

Question 2

Yersina pestis

Answer 2

• Gram -ve Enterobacteriaceae
• discovered by Alexandre Yersin, 1894 (plague outbreak in Hong Kong)
• mammalian + arthropod hosts
• resistant to mammalian immune attack; produces a range of endo- and exo-toxins
• three forms of human infection:
  pneumonic (lungs); septicaemic (bloodstream); and bubonic (lymph nodes)
• highly virulent
• 60% of infected individuals die within 10 days

Question 3

genetics of Yesinia pestis

Answer 3

• genetically monomorphic bacterium; very closely related to Y. pseudotuberculosis
• clonal population structure: no horizontal gene transfer
• 3.5Mb chromosome
• 3x plasmids; encode many virulence factors

Question 4

Reconstructing Y. pestis historically

Answer 4

• reconstructs perfect phylogeny in modern/ancient DNA
• 3 biovars of plague each associated with a specific pandemic; not quite congruent

Question 5

A point on phylogeny

Answer 5

HGT and recombination messes it up

Question 6

Plague transmission

Answer 6

• epizootic + zoonotic
• human-to-human transmission can occur
• has never become permanently established

Question 7

epizootic plague

Answer 7

• obligate pathogen of rodents and lagomorphs
• transmitted by infected fleas
• main host in central Asia: gerbils
• boom bust cycles; increased transmission amoungst gerbil pops by fleas
• rodent collapse; fleas migrate to other hosts

Question 8

zoonotic plague

Answer 8

• an accidental pathogen of humans
• normally a dead-end host
• spillover events due to food and density

Question 9

Pneumonic form of plague

Answer 9

• establishment