Black Death Survivors: Genetic Resistance and the CCR5 Connection

Historical Context

The Black Death (1347–1351) killed ~30–50% of Europe's population (~25–50 million). Strong selective pressure likely shaped human genetics.

CCR5-Δ32 Mutation

• 32-base-pair deletion in CCR5 gene → nonfunctional CCR5 receptor.
• Homozygotes (Δ32/Δ32): Highly resistant to HIV-1 (R5-tropic).
• Frequency: ~10% in Europeans; absent in Africans, East Asians.

Link to Plague? Controversial

• Hypothesis: CCR5-Δ32 conferred survival advantage against Yersinia pestis (plague) or smallpox → positive selection.
• Evidence: Ancient DNA studies show Δ32 existed pre-Black Death; frequency rise may align with plague pandemics.
• Counter: Y. pestis doesn't use CCR5; smallpox (variola) uses chemokine receptors but evidence weak.
• Current consensus: Selection driver uncertain; possibly multiple pathogens over millennia.

Clarification from Source Text

The original text incorrectly states "individuals without CCR5 could not be infected by HIV which would go on to cause millions of deaths... during the black plague period." HIV emerged in 20th century; the text conflates timelines. The CCR5-Δ32 mutation is a real genetic factor with historical selective interest, but its link to plague survival remains debated.