Experimental Infection of Domestic Pigs with an African Swine Fever Virus Field Strain Isolated in 2021 from the Dominican Republic

Abstract

African swine fever virus (ASFV) is the etiological agent of African swine fever (ASF), a disease of domestic and wild swine that has spread throughout a large geographical area including Central Europe, East and Southeast Asia, and Southern Africa. Typically, the clinical presentation of the disease in affected swine heavily depends on the virulence of the ASFV strain. Very recently, ASFV was detected in the Dominican Republic (DR) and Haiti, constituting the first diagnosis of ASFV in more than 40 years in the Western hemisphere. In this report, the clinical presentation of the disease in domestic pigs inoculated with an ASFV field strain isolated from samples collected in the DR (ASFV-DR21) was observed. Two groups of domestic pigs were inoculated either intramuscularly (IM) or oronasally (ON) with ASFV-DR21 (104 hemadsorbing dose-50% (HAD50)). A group of naïve pigs (designated as the contact group) was co-housed with the ASFV-DR21 IM-inoculated animals to evaluate ASFV transmission and disease manifestation. Animals inoculated IM with ASFV-DR21 developed an acute disease leading to humane euthanasia at approximately day 7 post-inoculation (pi). Interestingly, animals inoculated via the ON route with ASFV-DR21 developed a heterogeneous pattern of disease kinetics. One animal developed an acute form of the disease and was euthanized on day 7 pi, another animal experienced a protracted presentation of the disease with euthanasia by day 16 pi, and the remaining two animals presented a milder form of the disease, surviving through the 28-day observational period. The contact animals also presented with a heterogenous presentation of the disease. Three of the animals presented protracted but severe forms of the disease being euthanized at days 14, 15 and 21 pi. The other two animals presented with a milder form of the disease, surviving the entire observational period. In general, virus titers in the blood of animals in all study groups closely followed the clinical presentation of the disease, both in length and extent. Importantly, all animals presenting with a prolonged form of the disease, as well as those surviving throughout the observational period, developed a strong ASFV-specific antibody response. These results suggest that ASFV-DR21, unless inoculated parenterally, produces a spectrum of clinical disease, with some animals experiencing an acute fatal form while others presented with a mild transient disease accompanied by the induction of a strong antibody response. At the time of publication, this is the first report characterizing the virulent phenotype of an ASFV field strain isolated from samples collected in the DR during the 2021 outbreak and provides information that may be used in developing epidemiological management measures to control ASF on the island of Hispaniola.