Plague
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Plague is caused by Yersinia pestis. The main animal reservoir is the rat but the vector is the rat flea, Xenopsylla cheopis.
Bubonic plague is the more common form. The other forms are pneumonic, septicaemic, and meningeal.
Virulence of Y.pestis depends on V and W antigens whose genes are plasmid mediated. The bacterial cell wall contains a potent lipopolysaccharide endotoxin which may cause Gram negative shock. Exotoxins are also produced.
Cases of plague should be isolated because person to person spread may occur.
