Comparison of Genotype II African Swine Fever Virus Strain SY18 Challenge Models

Abstract

African swine fever (ASF) is a viral haemorrhagic disease found in domestic and wild boars caused by the African swine fever virus (ASFV). A highly virulent strain was used to evaluate the efficacy of newly developed vaccine candidates. The ASFV strain SY18 was isolated from the first ASF case in China and is virulent in pigs of all ages. To evaluate the pathogenesis of ASFV SY18 following intraoral (IO) and intranasal (IN) infections, a challenge trial was conducted in landrace pigs, with intramuscular (IM) injection as a control. The results showed that the incubation period of IN administration with 40–1000 50 % tissue culture infective dose (TCID50) was 5–8 days, which was not significantly different from that of IM inoculation with 200 TCID50. A significantly longer incubation period, 11–15 days, was observed in IO administration with 40–5000 TCID50. Clinical features were similar among all infected animals. Symptoms, including high fever (≥40.5 °C), anorexia, depression, and recumbency, were observed. No significant differences were detected in the duration of viral shedding during fever. There was no significant difference in disease outcome, and all animals succumbed to death. This trial showed that IN and IO infections could be used for the efficacy evaluation of an ASF vaccine. The IO infection model, similar to that of natural infection, is highly recommended, especially for the primary screening of candidate vaccine strains or vaccines with relatively weak immune efficacy, such as live vector vaccines and subunit vaccines.

Disease Course of Korean African Swine Fever Virus in Domestic Pigs Exposed Intraorally, Intranasally, Intramuscularly, and by Direct Contact with Infected Pigs

“…This implies that alternative challenge routes should be developed to assess the efficacy of ASFV vaccines precisely. Additionally, the IM route, an unnatural route of infection, can cause the virus to enter blood vessels that are closely intertwined within skeletal muscle tissues and directly and quickly contact target cells, leading to the rapid progression of clinical disease [ 35 , 45 ]. As IM inoculation is appropriate for studying the late stage of ASFV infection, it should be avoided when mimicking the natural course of the disease, including research on the pathogenesis mechanism, especially in the early stage of the disease course.…”

“…With 10 6 HAD 50 of highly virulent ASFV-Malawi strain (Malawi-Lil-20/1), IO and IN groups composed of farm-raised pigs had a comparable disease course [ 35 ], which was similar to the result of this animal experiment. On the other hands, SPF pigs challenged with 200 and 1000 TCID 50 of highly virulent ASFV-Chinese strain (SY-18) via the IN route demonstrated more rapid clinical course of infection than the IO route [ 45 ]. In this study, 10 3 times of virus titers for IO or IN route were necessary to induce similar disease progression by IM route.…”