Filatov S. Peculiarities of African swine fever spread in Ukraine and risks for the biological transmission of the virus

This thesis is devoted to the study of the epizootological role of a soft tick Ornithodoros verrucosus and to the risk assessment for the tick-vector involvement into African swine fever virus (ASFV) circulation in Ukraine. It has been established that the species occurs sporadically in the Kherson and Mykolaiv regions of Ukraine and its distribution is related exclusively to specific natural habitats. Anthropogenic activities appear to be a limiting factor for the tick populations however, local use of limestone for building and renovation purposes creates a stable risk for introduction of O. verrucosus into peridomestic habitats, which means their contacts with domestic animals cannot be excluded completely. For the first time in Ukraine, a laboratory colony of the species has been established. The colony is an important resource for subsequent fundamental studies in vector biology as well as for development of new methods for vector surveillance. Experiments to assess vector competence of O. verrucosus for ASFV genotype II have been conducted. The results revealed that the ticks were able to transmit the ASFV trans-stadially, preserved infectious virus for at least two months, and excreted it with feces and coxal fluid. Feeding of a group of 30 ticks was not sufficient to transmit ASFV to susceptible animals however, the result was notably similar to that obtained with an established vector species — O. erraticus. Using a multidisciplinary approach that combines epizootological, virological, parasitological methods and statistical modeling, local peculiarities of ASFV circulation have been revealed. This led to definition of geographical zones in southern Ukraine where the existence of potential biological vectors and reservoirs for ASFV cannot be presently excluded. Keywords: arthropod vectors of diseases, Argasidae, African swine fever, GIS, epizootology, modeling, risk analysis.