Dynamics of leukocyte populations, immune-regulatory cytokines, and biochemical parameters in wild boar and domestic pigs experimentally infected with a virulent African swine fever virus genotype II strain

Giulia Franzoni^1*Fabian Z. X. Lean²Emanuela Giaconi¹Giuseppe Tedde¹Susanna Zinellu¹Paola Nicolussi¹Mireille Le Dimna³Marie-Frédérique Le Potier³Elliot Steedman²Helen Rachel Crooke²Cecilia Righi⁴Stefano Petrini⁴Noemí Rayón⁵Dolores Gavier-Widen⁶Alejandro Nunez²Pedro Jose Sanchez-Cordon^7*

• ¹Experimental Zooprophylactic Institute of Sardinia (IZS), Sassari, Italy
• ²Animal and Plant Health Agency, Addlestone, United Kingdom
• ³Anses Laboratoire de Ploufragan-Plouzane, Ploufragan, France
• ⁴Istituto Zooprofilattico Sperimentale dell'Umbria e delle Marche Togo Rosati, Perugia, Italy
• ⁵Univesidad Alfonso X el Sabio Biblioteca, Madrid, Spain
• ⁶Statens Veterinarmedicinska Anstalt, Uppsala, Sweden
• ⁷Centro de Investigación en Sanidad Animal (CISA), Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA), Valdeolmos, 28130, Madrid, Spain

African Swine Fever Virus (ASFV) is the causative agent of devastating disease affecting domestic and wild pigs globally. A previous study of the intranasal inoculation of domestic pigs (DP) and wild boar (WB) with the ASFV genotype II strain "Armenia 2007" demonstrated distinct disease outcomes. This study aims to compare the leukocyte, cytokine and biochemical profiles in experimentally infected DP and WB. Blood and serum samples were collected before infection (day 0), from animals euthanized in groups of six (comprising 3 DP and 3 WB) on days 1, 2, 3 and 5 post infection (pi) and from animals that reached a humane endpoint. Both DP and WB developed severe lymphopenia, occurring earlier in WB. Inflammatory response occurred earlier in WB, as evident from day 3 pi by the increased levels of TNF, followed by IL-6 and, to a lesser extent, IL-1β. IL-8 concentrations only increased in some WB, but not in DP. No modulation of Th1-associated cytokines (IFN-γ, IL-12 and IL-18) was detected in DP, whereas WB had a moderate increase in IL-12 and IFN-γ levels from day 5 pi, which peaked at humane endpoint. C-reactive protein levels increased in concomitant with the release of pro-inflammatory cytokines, as early as day 5 pi in WB, reaching its maximum in both DP and WB at the humane endpoint. A delayed but significant increase in the levels of anti-inflammatory mediators IL-1Ra and IL-10 was observed in both groups, but earlier in some WB from day 5 pi. Biochemical analysis revealed potential perturbations of the liver function in both subspecies, characterized by changes in serum AST and triglycerides levels, in addition to renal alterations in DP evidenced by changes in creatinine and urea levels. These findings underscore earlier immune activation in WB, potentially contributing to the different subspecies-specific disease outcomes following ASFV inoculation.