In vitro phenotypic characterisation of two genotype I African swine fever viruses with genomic deletion isolated from Sardinian wild boars

TL;DR

This study examines two African swine fever viruses with genomic deletions found in Sardinian wild boars and finds they grow more slowly in lab tests, suggesting a less severe disease.

Contribution

The study identifies and characterizes two genotype I African swine fever viruses with a genomic deletion in Sardinia, revealing their attenuated phenotype.

Findings

The deleted viruses 7303WB/19 and 7212WB/19 showed lower growth kinetics in macrophages compared to a virulent isolate.

Both deleted viruses had reduced intracellular levels of early and late ASFV proteins.

Genomically deleted viruses were not found in Sardinian wild boars before 2019, suggesting a new emergence.

Abstract

African swine fever virus (ASFV) causes a devastating disease affecting domestic and wild pigs. ASF was first introduced in Sardinia in 1978 and until 2019 only genotype I isolates were identified. A remarkable genetic stability of Sardinian ASFV isolates was described, nevertheless in 2019 two wild boar isolates with a sustained genomic deletion (4342 base pairs) were identified (7303WB/19, 7212WB/19). In this study, we therefore performed in vitro experiments with monocyte-derived macrophages (moMФ) to unravel the phenotypic characteristics of these deleted viruses. Both 7303WB/19 and 7212WB/19 presented a lower growth kinetic in moMФ compared to virulent Sardinian 26544/OG10, using either a high (1) or a low (0.01) multiplicity of infection (MOI). In addition, flow cytometric analysis showed that both 7303WB/19 and 7212WB/19 presented lower intracellular levels of both early and late ASFV proteins. We subsequently investigated whether deleted virus variants were previously circulating in wild boars in Sardinia. In the four years preceding the last genotype I isolation (February 2015–January 2019), other eight wild boar isolates were collected, all belonging to p72 genotype I, B602L subgroup X, but none of them presented a sustained genomic deletion. Overall, we observed the deleted virus isolates in Sardinia only in 2019, at the end of a strong eradication campaign, and our data suggest that it might possess an attenuated phenotype in vivo. A better understanding of ASFV evolution in endemic territories might contribute to development of effective control measures against ASF.

The online version contains supplementary material available at 10.1186/s13567-024-01332-8.

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