Comparative Pathology of Domestic Pigs and Wild Boar Infected with the Moderately Virulent African Swine Fever Virus Strain “Estonia 2014”

Abstract

Endemically infected European wild boar are considered a major reservoir of African swine fever virus in Europe. While high lethality was observed in the majority of field cases, strains of moderate virulence occurred in the Baltic States. One of these, “Estonia 2014”, led to a higher number of clinically healthy, antibody-positive animals in the hunting bag of North-Eastern Estonia. Experimental characterization showed high virulence in wild boar but moderate virulence in domestic pigs. Putative pathogenic differences between wild boar and domestic pigs are unresolved and comparative pathological studies are limited. We here report on a kinetic experiment in both subspecies. Three animals each were euthanized at 4, 7, and 10 days post infection (dpi). Clinical data confirmed higher virulence in wild boar although macroscopy and viral genome load in blood and tissues were comparable in both subspecies. The percentage of viral antigen positive myeloid cells tested by flow cytometry did not differ significantly in most tissues. Only immunohistochemistry revealed consistently higher viral antigen loads in wild boar tissues in particular 7 dpi, whereas domestic pigs already eliminated the virus. The moderate virulence in domestic pigs could be explained by a more effective viral clearance.

Blood Counts, Biochemical Parameters, Inflammatory, and Immune Responses in Pigs Infected Experimentally with the African Swine Fever Virus Isolate Pol18_28298_O111

“…These results are in accordance to those presented by Sanchez-Cordon et al conducted with the application of genotype I of ASFV [ 32 ]. Histopathological changes found in the examined animals were consistent with the inflammation associated with the ASFV infection described previously by other authors [ 13 , 33 , 34 ]. Vascular changes and an increased number of activated macrophages in the lungs and liver were the most common observations, followed by lymphocytolysis in the spleen, tonsils, and lymph nodes, leading to lymphoid depletion.…”

African Swine Fever Laboratory Diagnosis—Lessons Learned from Recent Animal Trials

“…An explanation could be that the virus was not yet distributed to peripheral sites. However, this would not be in line with the antigen detection in popliteal lymph nodes in the same study [ 39 ] and thus, sampling error, i.e., inclusion of fatty or connective tissues of the inguinal region, cannot be completely excluded. Ocular fluid was difficult to sample and genome loads were low.…”

“…This genotype II strain originates from Estonian wild boar [ 50 ] and shows moderate virulence [ 51 ] with a tendency of more severe disease courses in wild boar. For this reason, the strain was chosen for a comparative study on clinical outcome and pathology that was recently published by Sehl et al [ 39 ]. Another aim of the study was generation of well-defined sample matrices for diagnostic test validation.…”

Understanding and combatting African Swine Fever

“…Minimal oedema may affect the bile duct and gall bladder wall in some cases, occasionally with petechiae appearing on the serosal and mucosal surfaces. Apart from moderate congestion observed in the meninges (Figure 4.9A) and choroid plexus, no other gross lesions are usually observed in the central nervous system (Galindo-Cardiel et al, 2013;Gallardo et al, 2015b;Kleiboeker, 2002;Moulton and Coggins, 1968;Sánchez-Vizcaíno et al, 2015;Sehl et al, 2020).…”

“…Within the endocrine system, the presence of haemorrhages is occasionally described in the inner cortical and medullary region of the adrenal gland. Extensive haemorrhages and necrotic areas in pancreas ( (Galindo-Cardiel et al, 2013;Gallardo et al, 2015b;Kleiboeker, 2002;Moulton and Coggins, 1968;Sánchez-Vizcaíno et al, 2015;Sehl et al, 2020).…”