<p>Feline coronavirus is common in domestic cats worldwide, and while most infected animals show no symptoms, viral mutations in a subset of cases can trigger feline infectious peritonitis, a fatal systemic disease that appears in either effusive or non-effusive forms. Two substitutions in the viral spike gene, M1058L and S1060A, have been proposed as possible markers of systemic viral dissemination in feline infectious peritonitis, but their diagnostic significance remains debated. A new open-access study in BMC Veterinary Research, published 24 October 2026, reports the detection of feline coronavirus RNA in blood, effusion, and combined blood-effusion samples from cats suspected of having the disease, along with phylogenetic and mutational analysis of a partial spike gene fragment from Iranian isolates.</p><p>The research team, led by Viana Javaheri Nasr with colleagues including Naser Sadri, Shahram Jamshidi, Iradj Ashrafi Tamai and Hesameddin Akbarein, collected a total of 100 samples from cats suspected of feline infectious peritonitis: 40 blood samples, 40 effusion samples, and 20 combined blood-effusion samples. All samples were examined by RT-PCR to screen for the feline coronavirus genome. The screening proceeded in two steps. First, PCR was performed targeting the 3' untranslated region of the viral genome to detect feline coronavirus. Second, a nested PCR was used t