Increased Presence of Circulating Cell-Free, Fragmented, Host DNA in Pigs Infected with Virulent African Swine Fever Virus

Assessing Virus Survival in African Swine Fever Virus-Contaminated Materials-Implications for Indirect Virus Transmission

Introduction of African swine fever virus (ASFV) into pig herds can occur via virus-contaminated feed or other objects. Knowledge about ASFV survival in different matrices and under different conditions is required to understand indirect virus transmission. Maintenance of ASFV infectivity can occur for extended periods outside pigs. Current assays detecting ASFV have inherent disadvantages. Cell culture-based assays are labor-intensive and sensitive to contaminants while methods using qPCR detect ASFV DNA with high sensitivity and specificity, but this may not correspond to infectious virus. Here, we have combined the use of these assays to assess the replication of ASFV within cells and determined the effect of pig feces, straw, wood shavings, and mixed feed on ASFV infectivity. In porcine serum, infectious ASFV survived for at least 60 days at 4 °C, 22 °C, and 37 °C; for two days at 50 °C; one day at 60 °C; and ≤5 min at 70 °C. In the presence of feed, straw, or wood shavings, the survival of the virus wasmarkedly shortened. Samples remained positive in the qPCR assay despite the loss of virus infectivity. Thus, it was possible to distinguish between the presence of ASFV DNA and the survival of the infectious virus.

Evaluation of β-Actin and Mitochondrial DNA Levels in Determining the Age of Suidae Remains

African Swine Fever (ASF) is an infectious disease affecting pigs and wild boars, causing significant economic losses. Epidemiological surveillance plays an important role in minimizing its impact. The aim of this study was to evaluate the usefulness of β-actin DNA and mitochondrial DNA (mtDNA) levels in determining the age of animal remains from the Suidae family, which could be helpful in epidemiological investigations. The study included selected tissues and internal organs of Sus scrofa domesticus, exposed to natural environmental conditions or kept in stable 4 °C conditions, to assess the levels of β-actin and mtDNA over a period of 18 months. The levels of both tested parameters exhibited the expected decreasing trend over time. However, in most tissues, some discrepancies from this general pattern were observed. The results obtained for bone marrow showed a consistent downward trend and a strong correlation between mtDNA and β-actin, with long-term detectability (up to the 13th month of the study). Therefore, bone marrow could be considered a matrix of choice for age assessment. However, due to various influencing factors, further studies are required.

A Deep Sequencing Strategy for Investigation of Virus Variants within African Swine Fever Virus-Infected Pigs

African swine fever virus (ASFV) is the causative agent of African swine fever, an economically important disease of pigs, often with a high case fatality rate. ASFV has demonstrated low genetic diversity among isolates collected within Eurasia. To explore the influence of viral variants on clinical outcomes and infection dynamics in pigs experimentally infected with ASFV, we have designed a deep sequencing strategy. The variant analysis revealed unique SNPs at <10% frequency in several infected pigs as well as some SNPs that were found in more than one pig. In addition, a deletion of 10,487 bp (resulting in the complete loss of 21 genes) was present at a nearly 100% frequency in the ASFV DNA from one pig at position 6362-16849. This deletion was also found to be present at low levels in the virus inoculum and in two other infected pigs. The current methodology can be used for the currently circulating Eurasian ASFVs and also adapted to other ASFV strains and genotypes. Comprehensive deep sequencing is critical for following ASFV molecular evolution, especially for the identification of modifications that affect virus virulence.