Limitations of using feline coronavirus spike protein gene mutations to diagnose feline infectious peritonitis

Barker, Emily N.; Stranieri, Angelica; Helps, Chris R.; Porter, Emily L.; Davidson, Andrew D.; Day, Michael J.; Knowles, Toby; Kipar, Anja; Tasker, Séverine

In one cat (#94) CSF was collected from both lumbar and cisternal sites, and was FCoV RT-qPCR-positive for the cisternal sample (relative FCoV copy number 104) and negative for the lumbar sample. Brain or spinal cord from this cat was not available for histological examination. One FCoV RT-qPCR-positive sample (#100, pleural fluid) was lost from further analysis. Of the remaining FCoV RT-qPCR-positive samples five (12.8%) failed target gene sequencing. One of these samples (#98, pericardial fluid), collected from a cat with mutated FCoV detected in tissue samples, had a very low relative FCoV copy number (see Table 3 ). Four were abdominal fluids from four cats (#82, #145, #146 and #147) that had relative FCoV copy numbers (≥ 27; see Table 3 ) that were expected to be successful for sequencing; further analysis revealed the presence of serotype 2 FCoV. These four cats also had serotype 2 FCoV detected in tissue samples.