Suspected Type III Hypersensitivity Post-Inactivated Vaccination Leukocytoclastic Vasculitis in Two Sows

This case report describes the investigation of two cases of cutaneous vasculitis in sows following vaccination. The herd was porcine reproductive and respiratory syndrome virus (PRRSV)-stable, with routine PRRSV-1 and porcine circovirus type 2 (PCV2) sows' vaccination. Two sows developed red-to-purple macules on the udder, flanks, and hind limbs, occurring two and three days after vaccination, respectively. Diagnostic investigations included biochemistry, complete blood count, PCR, immunohistochemistry (IHC), serology, histopathology, Gram staining, and immunofluorescence (IF) to assess the involvement of type III hypersensitivity. Clinical examination and herd evaluation revealed no significant abnormalities. Both sows showed biochemistry results within the reference intervals. One sow had lymphocytosis. All PCR PCV2, PCV3 and PRRSV-1/2 on serum and IHC PCV2 conducted on skin biopsies were negative, although both animals were seropositive for PCV2. Histopathology revealed necrotizing leukocytoclastic vasculitis, and Gram staining detected no bacteria. IF failed to identify immune complex or complement deposition. However, type III hypersensitivity could not be excluded, as immune complexes are transient and biopsies were collected about 48 h after lesion onset. Overall, the findings support a vaccine-related adverse reaction. Vaccine adverse effects should therefore be considered in the differential diagnosis of cutaneous vasculitis in swine.