Experimental study of soft tick vector competence for African Swine Fever in Europe

African swine fever (ASF) is a lethal viral disease that has spread to Europe and Asia. Infected tick bite is one of the known routes of ASF virus (ASFV) transmission. Some species in the Ornithodoros genus are competent vector for ASFV. However, their role in transmission and maintenance of ASFV currently circulating in Europe remains to be determined. Three Ornithodoros species were selected for transmissions trials: O. moubata (known vector in Africa), O. erraticus (reported vector in Portugal) and O. verrucosus (suspected vector in Ukraine). Four ASFV strains were selected (Liv13/33, OurT88/1, Georgia2007/1 and Ukr12/Zapo) and matched to tick species, which yielded five pairs for vector competence testing: O. moubata-Liv13/33 (OmL), O. moubata-Georgia2007/1 (OmG), O. erraticus-OurT88/1 (OeO), O. erraticus-Georgia2007/1 (OeG) and O. verrucosus-Zapo (OvZ). Tick infection was attempted by feeding on viraemic pigs then re-feeding two to eight months later on healthy pigs to test for virus transmission ability. Only O. moubata was able to transmit ASFV. For other pairs, ticks were crushed and the homogenate of supernatant was injected in naïve pigs. All inoculated pigs developed clinical signs and viremia within a week, confirming ASFV was infectious in these tick-virus pairs. For the first time, the vectorial competence of O. erraticus and O. verrucosus for European strains was tested under experimental conditions and showed the ability of these both ticks to keep the virus infectious after feeding on viraemic pig. These experiments reinforce the importance of studying underlying mechanisms of soft tick vector competence for ASFV