The Black Death

Flea to human transmission‣Flea blood meal blocks the foregut‣Yesinia hms locus encodes proteins that bind to flea haemin as well aspromoting bacterial aggregation by increasing the hydrophobicity of thebacterial cell wall; this clumping blocks the foregut‣Dose delivered by flea bite ? ~20,000 bacilli ?‣Neutrophils kill bugs, macrophages don’t (still not clear why)--PhoP/PhoQsystem implicated‣Massive inflammation causes huge influx of cells into the lymph nodes,causing the characteristic “buboes”‣Bacteria have type-III secretion system that inhibits phagocytosis – this isupregulated as the disease progresses‣This allows entry of effector proteins (Yops) into the host macrophagewhich inhibits the cell cytoskeleton, down-regulates the inflammatoryresponse, and induces macrophage apoptosisY.pestis has a “remarkable ability to survive and grow in a diversity ofhost environments”