Six-year surveillance of African Swine Fever in pigs and wild boars in an outbreak-origin region of Romania.

Importance: African Swine Fever (ASF) is a highly contagious and fatal disease severely affecting Romania's pig industry and wild boar populations. This study provides insights into the prevalence of ASF in Constanța County, where wetlands like the Danube Delta and Danube River, home to dense wild boar populations, facilitate the spread of the virus to domestic pigs.

Objective: The study examined the incidence of ASF in pig and wild boar populations over six years (2018-2023) in Constanța County, Romania's second outbreak origin in 2018.

Methods: The real-time polymerase chain reaction data from 3,187 samples (2,204 pigs and 983 wild boars) collected between 2018 and 2023 were analyzed. A 251 bp fragment of the African Swine Fever virus (ASFV) B646L gene (positions 105,320-105,570; GenBank MN194591.1), encoding the capsid protein p72, was amplified using a TaqMan assay, sequenced in 10 ASFV-positive samples, and subjected to phylogenetic analysis against ASFV GenBank references.

Results: Analysis revealed a decline in ASF outbreaks in Constanța County, from 93 in 2018 to only two in 2022. Despite this, 2023 saw a resurgence, with 38 cases and 21 outbreaks in pigs from nearby private households, likely due to poor biosecurity. Phylogenetic analysis of 10 ASFV isolates and GenBank sequences from Europe, Asia, and Africa confirmed 100% similarity to strain II. ELISA testing identified ASFV antibodies in 23 of 144 pigs (15.9%) and 28 of 559 wild boars (5.0%), indicating that some animals survived ASFV infection.

Conclusions and relevance: The results revealed a steady decline in ASF outbreaks and cases in Constanța County, attributed to eradication measures. The detection of ASFV antibodies in 51 animals highlights post-infection survival in both domestic pigs and wild boars, offering valuable insight for future research on the genetic basis of acquired immunity.