Dynamics of African swine fever virus (ASFV) infection in domestic pigs infected with virulent, moderate virulent and attenuated genotype II ASFV European isolates.

Abstract

This study aimed to compare the infection dynamics of three genotype II African swine fever viruses (ASFV) circulating in Europe. Eighteen domestic pigs divided into three groups were infected intramuscularly or by direct contact with two haemadsorbent ASFVs (HAD) from Poland (Pol16/DP/ OUT21) and Estonia (Est16/WB/Viru8), and with the Latvian non-HAD ASFV (Lv17/WB/Rie1). Parameters such as symptoms, pathogenicity, and distribution of the virus in tissues, humoral immune response, and dissemination of the virus by blood, oropharyngeal and rectal routes were investigated. The Polish ASFV caused a case of rapidly developing fatal acute disease, while the Estonian ASFV caused acute to subacute infections in the presence of surviving animals. In contrast, animals infected with the ASFV from Latvia developed a more subtle, mild, or even subclinical disease. Oral excretion was sporadic or even absent in the attenuated group, whereas in animals that developed an acute or subacute form of ASF, oral excretion began at the same time as in the blood, or even 3 days earlier, and persisted up to 22 days. Regardless of virulence, blood was the main route of transmission of ASFV and infectious virus was isolated from persistently infected animals for at least 19 days in the attenuated group and up to 44 days in the group of moderate virulence. Rectal excretion was limited to the acute phase of infection. In terms of diagnostics, the ASFV genome was detected in contact pigs from oropharyngeal samples earlier than in blood, independently of virulence and, together with blood, both samples could cover a longer range to detect ASFV infection. The results presented here provide quantitative data on the spread and excretion of ASFV strains of different virulence among domestic pigs that can help to better focus surveillance activities and thus increase the ability to detect ASF introductions earlier.

Development and validation of a fast quantitative real-time PCR assay for the detection of African swine fever virus

“…The average time of ASF symptom onset after exposure to ASFV was about 5 to 13 days and death of the infected pigs began to occur at 8-15 days after exposure (11,22). The time period from the onset of the disease to death of the animal is relatively short and the morbidity and mortality rate is almost 100% (2)(3)(4).…”

“…Eight serotypes are also known based on viral hemagglutinin CD2-like protein (CD2v) and C-type lectin (2,5,6). Among these, genotype II stain is highly virulent and is prevalent in Europe, Russia, China, and Southeast Asia (7)(8)(9)(10)(11)(12).…”

A practical guide for strategic and efficient sampling in African swine fever‐affected pig farms

“…This in turn usually leads to low mortality on farms in the early phase, usually within 2 to 3 weeks after virus introduction, though after this period most of the animals in the same pen will be infected. To date, all ASF viruses detected in domestic pigs and the majority of wild boar in Latvia were virulent strains despite the finding of an attenuated strain in a hunted wild boar in 2017 (Gallardo, Soler, et al., 2019; Gallardo et al., 2021). Taking into account that the dominant ASFV genotype II strains currently circulating are causing a case‐fatality rate of >90%, seropositive healthy pigs are rarely found as majority of pigs do not survive the acute phase (Blome et al., 2020).…”

Estimating transmission dynamics of African swine fever virus from experimental studies

“…Quantitative data, such as symptoms, pathogenicity and virus distribution in tissue, have been presented for different strains of the ASFV genotype II currently circulating in Europe (Gallardo et al., 2021). That study aimed at expanding current knowledge of ASFV transmission through inoculation and direct transmission experiments using three different strains (from Estonia, Latvia and Poland).…”

“…The results indicated that the different strains had different virulence, with the Polish strain causing rapid and fatal disease. The Estonian variant caused subacute infections, whereas the Latvian variant induced milder clinical symptoms (Gallardo et al., 2021).…”