The frequently predicted spread of tropical and subtropical diseases to temperate regions, possibly related to global warming, appears to be becoming a reality. The midge vector of the cattle disease, bluetongue has spread out of the tropics and subtropics, and the disease reached the UK in 2007. Now the viral disease, chikungunya, has spread to northern Italy (G Rezza and colleagues. Lancet 2007;370:1840–6; see also Comment ibid: 1805–6).

Chikungunya virus (CHIKV) was …