Epidemiology, etiology and gene analysis of spike S protein of porcine epidemic diarrhea virus infection in Ukraine during 2016-2017

Abstract

The spread of PEDV of pigs continues in various countries and regions of the world. PED was first registered in several areas of Ukraine in 2014. At present, there is a limited number of publications on the characteristics of the spread of the virus infection in Ukraine. Moreover, obtained research data do not clarify the epizootic situation as a whole. Having regard to the state of pig farm industry and permanent growth of losses caused with PEDV infection, the study of PED in Ukraine is relevant and important. Therefore, the goal of the work was to clarify the epizootic situation of PED in various areas of Ukraine. We studied the epizootic state of PED with a typical course in pig farms and the made a primary assessment of the relation of genetic groups between identified pathogens from distinct regions of the country where the highest intensity of the epizootic process was determined. The work was carried out in the Biosafety Center (Ukraine). To determine the epizootic situation of PED during 2016-2017 we collected samples of the blood serum and biological materials from pigs from 105 agricultural enterprises that are located in 85 administrative regions of Ukraine. In total we tested 543 serum samples and 591 samples of pathological tissues. The detection of PEDV was performed by PCR-RT. Serological diagnostics were tested with ELISA. Sequence analysis was performed according to Sanger. The results of sequences were analyzed in the FinchTV / Chromas program. The analysis of the epizootic features of PED in different areas of Ukraine for 2016-2017 established that PEDV is the main causative agent of the infection. An infection circulates among sensitive animals in pig farms and induces PED, which is difficult to control and weakly managed as a particularly dangerous emergent infectious disease of pigs. In 2016, 6.5\% of administrative districts located in 12 of the 25 regions of Ukraine were included in the study, and in 2017, 10.8\% of administrative districts located in the 14 regions of the 25 regions of the country were investigated. In general, during 2016 and 2017 1134 samples of blood serum and animal tissue were collected from 105 agricultural enterprises from 17.3\% of the administrative regions of Ukraine. The obtained results showed that in 2016 PED was registered in 7 administrative districts from 4 regions of Ukraine, and in 2017 the infection was registered in 2 regions. The results of RNA sequence analysis of the PED virus identified the characteristics of the PEDV genes which reflect a high degree of homology with the Chinese strain BJ-2011-1. The analysis of the obtained results revealled the relation of PEDV circulating in Ukraine to the strains identified in the USA. Moreover, the samples of PEDV from Ukrainian pig farms have the sequences that belong to the North American clade II from the group of 2 strains of the PED virus. However, the PEDV observed in Ukraine is different from them by at least one nucleotide replacement of the gene which codes a protein of the S domain. Based on the obtained results, it can be assumed that in Ukraine the PED virus could have spread from East Asia.