3.1 Clinical examination and laboratory testing
On D16, all cats and were found bright, alert and responsive, with no cardiorespiratory signs (including upper respiratory signs) and normal temperature. According to the owner, their clinical condition remained unaltered throughout the observation period. Hematology and serum biochemistry findings were unremarkable (Table 1) and testing results for FIV and FeLV were negative for all 3 cats. Testing results of all oropharyngeal and fecal swabs obtained from C1 between D7 and D17 were negative via both SARS-CoV-2-specific real-time RT-PCR methods. However, positive results against both targets were obtained by testing of the other two cats (C2 and C3), and specifically, from the first sampling time-point (D7), and up to D13.
Daily monitoring of viral load in oropharyngeal and fecal swabs of the two SARS-CoV-2-positive cats are summarized in Figure 1. High virus titers (Ct values < 30) were observed in the pharynx of both C2 and C3 on the first sampling time-point (D7). For C2, 7.03 Log10 RNA copies/swab were determined on D7. A considerably lower virus titer (3.94 Log10 RNA copies/swab) was measured on D10. During the subsequent 3 days, a slightly increasing viral load was measured (4.61, 4.83 and 5.48 Log10 RNA copies/swab, respectively) in this animal’s pharynx, and it finally tested negative on D14. The oropharyngeal swab obtained from C3 on D7 was also characterized by a high viral load (8.42 Log10 RNA copies/swab). However, differences were observed in the kinetics of SARS-CoV-2 presence in the upper respiratory tract of this animal, since steadily declining virus titers were measured between D10 and D13 (7.55, 6.72, 4.13 and 4.07 Log10 RNA copies/swab, respectively). All subsequently collected swabs tested negative.
Fecal swabs obtained from C2 tested positive on the first day of sampling (D7, 5.31 Log10 RNA copies/swab) and up to D11 with progressively declining virus titers (3.89 Log10RNA copies/swab). Fecal swabs collected on D12 (i.e. 5 days after the first real-time RT-PCR-positive fecal swab) tested negative. Regarding C3, the kinetics of viral RNA concentrations in the fecal swabs was similar to that in its pharynx, although characterized by a time lag (Figure 1). A virus titer of 4.05 Log10 RNA copies/swab was measured on D7. Subsequently, a peak was observed on D9 (6.63 Log10 RNA copies/swab), followed by a progressive decline on D10, D11 and D13 (5.69, 4.23 and 3.89 Log10RNA copies/swab, respectively). Fecal swabs collected on D15 (i.e. 8 days after the first real-time RT-PCR-positive fecal swab) tested negative.
All sera obtained from C1 and C2 tested negative for SARS-CoV-2-specific antibodies. On the contrary, serological testing of C3 on D17 (i.e. 10 days after the first real-time RT-PCR-positive oropharyngeal swab) yielded a positive result (S/P% = 197.3%). Re-testing on D26 indicated an even stronger positive result (S/P% = 256.7%), with the respective OD value having reached a plateau (2.934 AU). On D70 an S/P% of 217.6% was observed, indicating a decline in the respective serum antibody titer.