What is the clinical evidence from this study?

Study design: Other. Population: African swine fever (n=22). Intervention: Estonian ASFV strain. Primary outcome: Survival rate.

April 19, 2018Scientific Reports196 citationsOpen Access

Deletion at the 5’-end of Estonian ASFV strains associated with an attenuated phenotype

LZLaura Zani JFJan H. Forth LFLeonie F. Forth

Key Result

An Estonian ASFV variant with a 14,560 base pair deletion at the 5' end showed reduced virulence, allowing 75% of infected minipigs and 100% of domestic pigs to recover, whereas all wild boar died.

Structured PICO

Population

22 pigs, including 12 minipigs, 5 domestic pigs, and 5 wild boar, experimentally infected with an Estonian ASFV strain to assess virulence.

Intervention

Inoculation with an African swine fever virus (ASFV) isolate obtained from a survivor in Estonia

Outcome

Survival/recovery and genomic characterization

An ASFV variant found in Estonia with a 14560 base pair deletion at the 5' end showed reduced virulence in minipigs and domestic pigs, though it remained lethal to wild boar.

Limitations

The deaths of three minipigs were not clearly linked to ASFV infection and could be a consequence of high stress sensitivity.
The necessary immobilization of adult wild boar during the acute phase could have negatively influenced their survival.

Abstract

African swine fever (ASF) was introduced into the Eastern European Union in 2014 and led to considerable mortality among wild boar. In contrast, unexpected high antibody prevalence was reported in hunted wild boar in north-eastern Estonia. One of the causative virus strains was recently characterized. While it still showed rather high virulence in the majority of experimentally infected animals, one animal survived and recovered completely. Here, we report on the follow-up characterization of the isolate obtained from the survivor in the acute phase of infection. As a first step, three in vivo experiments were performed with different types of pigs: twelve minipigs (trial A), five domestic pigs (trial B), and five wild boar (trial C) were inoculated. 75% of the minipigs and all domestic pigs recovered after an acute course of disease. However, all wild boar succumbed to infection within 17 days. Representative samples were sequenced using NGS-technologies, and whole-genomes were compared to ASFV "Georgia 2007/1". The alignments indicated a deletion of 14560 base pairs at the 5' end, and genome reorganization by duplication. The characteristic deletion was confirmed in all trial samples and local field samples. In conclusion, an ASFV variant was found in Estonia that showed reduced virulence.

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