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

The herd reproductive ratio (R_h) 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 R_h 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 R_h and the cluster analyses provide quantitative estimates of the self-limiting nature of FMD spread in a susceptible but vaccinated population.