1. Introduction
African swine fever (ASF) is a high-consequence transboundary disease of domestic and wild swine that typically presents as a fatal hemorrhagic fever, often with high case mortality in domestic populations. Due to its potential high mortality rate, ASF has serious implications for international trade, the socio-economic welfare of swine producers, and the health and management of domestic and wild swine populations. African swine fever virus (ASFV) is the causative agent of ASF and is an enveloped, double-stranded DNA virus with a genome size of approximately 175,000-195,000 base pairs. Over twenty genotypes have been described in the last 70 years based on characterization of the p72 (B646L ) gene C-terminal region (Bastos et al., 2003).
ASF was first discovered in Kenya in 1921 (Sánchez-Vizcaíno et al., 2019). The first international outbreak of ASF occurred in 1957, affecting Portugal, and a second outbreak occurred in 1960, which impacted Europe, Brazil, Cuba, the Dominican Republic, and Haiti for the next several decades (Sánchez-Vizcaíno et al., 2019). Following these outbreaks, ASF was eradicated in the affected countries outside of Africa, except on the island of Sardinia, Italy (Mur et al., 2016). A third international outbreak of ASFV occurred in Georgia during June 2007, involving a p72 genotype II strain. Since 2007, p72 genotype II ASFV strains have been the most widely circulating ASFV isolates globally (Dixon et al., 2019). The 2007 Georgia outbreak affected Russia and subsequently Eastern and Central Europe in 2012-2018. China reported its first outbreak in 2018, with subsequent outbreaks reported in Southeast Asia. Here, we describe a recently identified outbreak of a p72 genotype II ASFV strain in the Dominican Republic (DR) first detected in samples dating to May 2021.
In the current investigation of the DR ASF outbreak, the National Veterinary Services Laboratories’ Foreign Animal Disease Diagnostic Laboratory (USDA NVSL FADDL) initially received a batch of samples on July 26, 2021. The samples were obtained through a surveillance project initiated in 2018 between the United States Department of Agriculture (USDA) and the Dirección General de Ganadería (DIGEGA) to support early detection of ASF through surveillance for ASF and classical swine fever (CSF) in the DR. The initial shipment received at USDA NVSL FADDL included specimens collected from February through July 2021. PCR testing at USDA NVSL FADDL confirmed several samples positive for ASFV, the earliest of which was collected on May 13, 2021; and on July 29, 2021, the Dominican Republic reported ASFV detections and an outbreak in four provinces. To investigate the molecular epidemiology and characterize the genetic diversity of ASFV in the DR, the PCR-positive samples were subjected to whole genome sequencing. USDA NVSL FADDL continued to sequence samples collected by the DR through October 2021. This report details the analysis of the whole genome sequencing data and the molecular epidemiology of the DR 2021 ASFV outbreak that had been previously reported (Gonzales et al., 2021).