Patterns of spread and persistence of foot-and-mouth disease types A, O and Asia-1 in Turkey: a meta-population approach.
Despite significant control efforts, foot-and-mouth disease (FMD) persists in Turkey, and new strains of serotypes A, O and Asia-1 are periodically reported to enter the country from the east. The status of FMD in Turkey is important regionally because the country forms a natural bridge between Asia where the disease is endemic, and Europe which has disease-free status. This study analysed spatial and temporal patterns of FMD occurrence in Turkey to explore factors associated with the disease's persistence and spread. Annual records of FMD distribution in Turkish provinces throughout 1990-2002, grouped by serotype (O, A and Asia 1), were analysed using geostatistical techniques to explore their spatial and temporal patterns. A meta-population model was used to test how disease status, expressed in terms of presence/absence, extinction, and colonization, and measured at the province level throughout the periods 1990-1996 and 1997 2002, could be predicted using province-level data on: ruminant livestock numbers; meat production-demand discrepancy (as a surrogate measure of animal and animal products marketing, i.e. long-distance contagion through the traffic of mainly live animals to urban centres); and the disease prevalence distribution as recorded for the previous year. A drastic overall reduction in FMD occurrence was observed from the period 1990-1996 to 1997-2002 when the disease was shown to retract into persistence islands. FMD occurrence was associated with host abundance, short distance contagion from adjacent provinces, and meat production-demand discrepancies. With FMD retracting into identified provinces, a shift in predictors of FMD occurrence was observed with a lower contribution of short-distance contagion, and a relatively higher association with meat production-demand discrepancies leading to live animal transport over long distances, and hence presenting opportunities for identifying critical-control points. The pattern of persistence differed according to serotype groups and is discussed in relation to their differential affinity to cattle and small ruminant hosts.