This paper reports on a study which uses a ferret transmission model to assess the direct and indirect spread of SARS-CoV-2.
In the study four individually housed ferrets were inoculated intranasally with SARS-CoV-2 and six hours later a “direct contact” ferret was added to each of the cages. The next day, “indirect contact” ferrets were placed in adjacent cages, separated from the donor cages by two steel grids, 10 cm apart. Nasal, throat and rectal swabs were taken from each ferret every other day, the samples were examined for SARS-CoV-2 by qualitative PCR and virus titration.
SARS-CoV-2 RNA levels peaked at three days post-inoculation (dpu) and were detected up to 11 dpi in two animals and up to 15 and 19 dpi in the other two animals. All the direct contact ferrets showed evidence of viral RNA 1 – 3 days post exposure and was detected for 13 – 15 days post exposure. Viral RNA was also detected in three of the four indirect contact ferrets starting between day 3-7 and continuing until day 13-19 post exposure.
Higher levels of SARS-CoV-2 were detected in the throat swabs compared to nasal swabs, with RNA levels in rectal swabs being the lowest. However, despite the different method of infection (inoculation, direct contact and indirect contact) the pattern of viral shedding was similar in terms of duration and levels of viral RNA. All the ferrets that were found to have been positively infected with SARS-CoV-2 seroconverted 21 after inoculation or exposure and the antibody levels were similar in donor, direct contact and indirect recipient ferrets.
Although the researchers primarily saw this research in terms of providing additional evidence to inform decision making in human disease control it does provide some additional evidence about direct and indirect spread in a species that veterinary professionals may be asked to treat.