Experimental Infection and Genetic Characterization of Two Different Capripox Virus Isolates in Small Ruminants

Abstract

Capripox viruses, with their members “lumpy skin disease virus (LSDV)”, “goatpox virus (GTPV)” and “sheeppox virus (SPPV)”, are described as the most serious pox diseases of production animals. A GTPV isolate and a SPPV isolate were sequenced in a combined approach using nanopore MinION sequencing to obtain long reads and Illumina high throughput sequencing for short precise reads to gain full-length high-quality genome sequences. Concomitantly, sheep and goats were inoculated with SPPV and GTPV strains, respectively. During the animal trial, varying infection routes were compared: a combined intravenous and subcutaneous infection, an only intranasal infection, and the contact infection between naïve and inoculated animals. Sheep inoculated with SPPV showed no clinical signs, only a very small number of genome-positive samples and a low-level antibody reaction. In contrast, all GTPV inoculated or in-contact goats developed severe clinical signs with high viral genome loads observed in all tested matrices. Furthermore, seroconversion was detected in nearly all goats and no differences concerning the severity of the disease depending on the inoculation route were observed. Conclusively, the employed SPPV strain has the properties of an attenuated vaccine strain, consistent with the genetic data, whereas the GTPV strain represents a highly virulent field strain.

Establishment of a Challenge Model for Sheeppox Virus Infection

“…Since the utilized clinical score system successfully used for characterization of lumpy skin disease virus (LSDV) infections in cattle [ 33 , 41 ] and GTPV in goats [ 25 ] was insufficient for examination of SPPV in sheep, we developed a new modified version ( Table 3 ). The newly established score system is based on both the clinical scoring for LSDV in cattle of Carn and Kitching (1995) [ 34 ] and our previously modified version [ 33 ], considering the experiences obtained in the present study.…”

“…Initially, organ samples were homogenized in serum-free medium using the TissueLyser II tissue homogenizer (QIAGEN, Hilden, Germany). For DNA extraction of all sample matrices (EDTA blood, serum, nasal swabs, oral swabs and homogenized organs), the NucleoMag Vet Kit (Macherey–Nagel, Düren, Germany) was used according to the manufacturer’s instructions and with previously described modifications of certain volumes [ 25 ] employing the KingFisher Flex System (Thermo Scientific, Darmstadt, Germany). For control of successful DNA extraction, an internal control DNA (IC2-DNA) [ 35 ] was added to each sample during the extraction process.…”

“…Sequencing was done as previously described [ 25 ]. Briefly, an approach combining short high-quality reads gained by Illumina sequencing and long reads by MinION Nanopore sequencing, respectively, was applied.…”

“…Whereas the Illumina platform provides short, high quality reads, the MinION platform allows real-time sequencing and produces longer reads. This hybrid sequencing approach has been successfully employed for capripox viruses [ 25 ] and other large DNA viruses, e.g., African swine fever virus [ 26 ].…”

“…The present study examines the pathogenesis in sheep after experimental infection with two different SPPV isolates from Surankote, India (2013) and Egypt (2018), respectively. As performed in a recent animal study [ 25 ], three inoculation routes were compared: Intravenous and intranasal inoculation as well as contact transmission between experimentally inoculated and naïve animals. Furthermore, diagnostic tools for sheeppox virus infections were validated and the suitability of both virus isolates as challenge models in future vaccine studies was analyzed.…”