Lumpy skin disease II. Data collection and analysis
The spatial and temporal patterns of lumpy skin disease (LSD) epidemics were analysed based on the data collected from affected and at-risk countries in southeastern Europe in 2016 and 2017. The reported outbreaks decreased from 7,483 in 2016 to 385 in 2017. Those were reported mainly in Albania in areas where vaccination was not completed. Only two and four outbreaks were reported in Greece and in the former Yugoslav Republic of Macedonia in 2017, respectively, where the herd immunity achieved by vaccination significantly reduced the further spread of the disease. However, this showed that the virus was still circulating and may re-emerge in not fully immunised animals. No further outbreaks were reported in the other countries that were affected in 2016, thus providing field evidence about the effectiveness of the regional vaccination campaign. The mathematical model fit to the Albanian data showed that the LSD spread is mostly up to 4 km with some longer distance transmission. The inclusion of relative vector abundance improves the model fit and supports that the abundance of potential LSD vectors is one of the major risk factors for LSD spread. This should be confirmed by field surveys on potential LSD vectors. The vaccination effectiveness in Albania, Bulgaria and Greece was estimated by survival analysis and Cox regression model to be 62%, 96% and 84%, respectively, and these results were validated by the mathematical model. This highlighted that the high coverage vaccination with the live homologous vaccine is the most effective measure for reducing lumpy skin disease virus (LSDV) spread. The housing type of animals was explored as risk factor in Greece, and the risk in farms with outdoor access was six times higher than in farms where animals are kept indoors, independently of vaccination status.