Herd reproduction ratio and time-space analysis of a foot-and-mouth disease epidemic in Peru in 2004.

Abstract

The herd reproductive ratio (Rh) and spatio-temporal clustering were estimated in the 2004 foot-and-mouth disease (FMD) epidemic in Peru. The epidemic lasted 39 days and involved 26 herds. Movement of cattle was restricted, all susceptible species within a 25-km buffer zone were revaccinated, and infected animals with clinical signs of FMD were killed or destroyed to control and eradicate the disease. The Rh declined from 5.3 on the second day of the epidemic to 1.31 on the 25th day. Spatio-temporal clustering of cases was detected at a critical distance of 0.5 km and critical times of 7 and 14 days. Cases were clustered in space (P=0.006) but not in time (P=0.498). The space-time scan method detected a spatio-temporal cluster that included consecutive case numbers 13, 14 and 15, located at the temporal midpoint of the epidemic. The values estimated for Rh and the cluster analyses provide quantitative estimates of the self-limiting nature of FMD spread in a susceptible but vaccinated population.