The diagnosis of VS-FCV infections relies on clinical signs typical for virulent systemic disease including systemic infection and organ involvement, often the occurrence in multicat environments, high contagiousness of the virus and epizootic spread of the infection, a high mortality rate of the disease, and the isolation of the same FCV strain from the blood, oropharyngeal swabs or cutaneous scrapings from ulcerated lesions of several diseased cats assessed by sequencing hypervariable regions of the capsid gene.