Diagnostic approach to swinepox virus infection in a German 2-site swine production unit

In 2008, nearly 50% of weaned piglets at a German 2-site production unit in Saxony-Anhalt had skin lesions 1-2 wk after relocation into the nursery. First clinical signs were maculae, followed by papules, pustules, and finally crusts, distributed over the dorsal and lateral body flank. Tentative clinical diagnosis was an infection with swinepox virus (SWPV; family Poxviridae, taxon species Suipoxvirus swinepox). Electron microscopy confirmed within one hour that the causal agent was a brick-shaped poxvirus, and routine PCR validated the poxvirus detection; PCR for Orthopoxvirus was negative. Phylogenetic analysis of the thymidine kinase genes from different poxviruses and from our SWPV isolates, 3 isolates from Germany, and 1 isolate from Austria, provided a good picture of evolutionary relationships of poxvirus genera, which was also consistent with phylogenetic analysis of poxviruses based on other genes. The German and Austrian isolates from domestic pigs were 99.8-100% identical to previously isolated German SWPV from wild boar and domestic pigs. All isolates belonged to the North American/European lineage. In a second step, SWPV assembly in naturally infected domestic pigs was analyzed by ultrathin sectioning. The virus assembly resembled that of other poxviruses and completed gaps in the SWPV morphogenesis model described in prior publications. Because there is no specific therapy, recommended interventions were improvements in biosecurity measures, especially hygiene management and disinfection procedures at the farm and within the transporters between the farrowing unit and the nursery. No further infections with SWPV were seen 5-6 wk after commencement of the hygiene interventions.