Distinct mutation in the feline coronavirus spike protein cleavage activation site in a cat with feline infectious peritonitis-associated meningoencephalomyelitis

André, Nicole M; Cossic, Brieuc; Davies, Emma; Miller, Andrew D; Whittaker, Gary R

Histologic examination revealed lesions typical of FCoV infection within the CNS. In the spinal cord, the leptomeninges were diffusely expanded by moderate numbers of predominantly plasma cells, admixed with fewer lymphocytes and macrophages, and surrounded by a moderate amount of edema. The underlying white matter was multifocally vacuolated with numerous dilated myelin sheaths, digestion chambers and rare spheroids (Figure 1a) . At the level of the lateral aperture, the choroid plexus was expanded by large numbers of plasma cells, lymphocytes and macrophages (Figure 1b) . The ependyma lining the ventricular system was effaced by a similar inflammatory population, admixed with fibrin, edema and was also forming thick perivascular cuffs often disrupting the sub-ependymal parenchyma (Figure 1c) . Immunohistochemistry revealed strong intracytoplasmic immunoreactivity within macrophages (Figure 1d ). No FIPassociated lesions were present in other organs. Non-FCoV comorbid histologic findings were chronic enteritis with mid-mucosal fibrosis and mesenteric lymphoid hyperplasia. Molecular analysis of the viral spike protein was performed at several time points during the study. Fecal samples were collected at 5 months of age (feces #1) and at 8 months of age (feces #2). Following euthanasia (at 10 months of age) tissue samples were collected, along with a fecal sample (feces #3). A central 156 base pair region of the spike protein gene, including the critical S1/S2 activation site of the virus, was PCR amplified and sequenced as described in Licitra et al, 17 with the following modifications: 25 μl reverse transcription PCRs were performed with qScript XLT 1-Step RT PCR kit (Quantbio). PCR conditions were 20 mins at 50°C, 3 mins at 95°C and 40 cycles of 10 s at 95°C, 20 s at 55°C, 40 s at 72°C, then 10 mins at 72°C. PCR products were purified using Diffinity RapidTips (Diffinity Genomics).