Reproductive Ratio for the Local Spread of African Swine Fever in Wild Boars in the Russian Federation.

Abstract

African swine fever (ASF) has caused the swine industry of the Russian Federation substantial economic losses over the last 7years, and the disease spread from there to a number of neighbouring countries. Wild boar has been involved in the spread of the disease both at local and at transboundary levels. Understanding ASF dynamics in wild boars is prerequisite to preventing the spread and to designing and applying effective surveillance and control plans. The reproductive ratio (R0 ) is an epidemiological indicator commonly used to quantify the extent of disease spread. Here, it was estimated in nine spatio-temporal clusters of ASF in wild boar cases in the Russian Federation (2007-2013). Clusters were defined by exploring the maximum distance of association of ASF cases using K Ripley analysis and spatio-temporal scan statistics. A maximum spatial association of 133km in wild boar cases was identified which is within de the conventional radius of surveillance zone (100-150km). The mean range value of R0 =1.58 (1.13-3.77) was lower compared to values previously estimated for ASF transmission within farms but similar to early estimates between farm (R0 =2-3), in domestic pigs using notification data in the Russian Federation. Results obtained provide quantitative knowledge on the epidemiology of ASF in wild boars in the Russian Federation. They identify the ASF transmission rate value in affected natural wild populations, for the first time, which could provide basis for modelling ASF transmission and suggest that current surveillance radius should be reviewed to make surveillance in wild nature more targeted and effective.