Intranasal inoculation with African swine fever virus genotype II reveals dose-dependent infectivity, pathogenesis and diagnostic challenges in pigs

The African swine fever virus (ASFV) surveillance strategies, including the early diagnosis, are key for prevention and control of African swine fever (ASF). This work studies the effects of different doses of ASFV Georgia strain: high dose (10⁴ HAU); moderate dose (10^2.5 HAU) and low dose (10 HAU), inoculated intranasally in three groups with 20 pigs each. The qPCR was used to follow the infection dynamics in a wide sample panel (clinical, tissues, non-invasive and environmental), together with LAMP, serological tests and cytokine detection. After inoculation, the Georgia strain was lethal for all animals that resulted infected, including those in the low-dose group, where such low ASFV doses, as used in this study, have rarely been tested before. However, in the low dose group only one pig developed the ASF, while the rest remained negative despite being in contact with the infected one. Here, blood was confirmed as the gold standard sample but other matrices such as serum, spleen, tonsils, bone marrow, ear tip and tongue could be useful for the early ASFV diagnosis. We also showed the air and non-invasive samples as helpful monitoring tools for ASFV. No ASFV-specific antibodies were detected in most of the animals. Our data support the relevance of both molecular and serological diagnostic strategies for ASF control. The rapid detection together with strict biosecurity measures can efficiently minimize the ASFV dissemination.