Prospective Cohort, Ecological, Other
Study population and setting
The study describes an experimental infection of fourteen raccoon dogs (Nyctereutes procyonoides) from a commercial fur farm with SARS-CoV-2. Nine animals (three males, six females) were inoculated intranasally with 10^5 median tissue culture infectious dose (TCID50). Three contact animals (all females) were added in adjacent cages 24 hours after inoculation of the nine other animals. Two other animals (one male, one female) were used as controls to assess pathological changes in infected animals. Swabs from the upper respiratory tract and rectum and fecal samples were taken to test for viral shedding (via RT-PCR), and blood was taken to test for antibodies (reactive and neutralizing) regularly for 28 days post infection. To check for pathological signs in infected tissues, two inoculated animals each were sacrificed on day 4, 8, and 12, and the remaining inoculated animals and direct contact animals were sacrificed on day 28 and subject to autopsy.
Summary of Main Findings
Six of the nine inoculated animals became infected and shed infectious virus, detectable in nasal and oropharyngeal swabs starting at 2 days post infection (dpi). Shedding was detectable up to 16 dpi in nasal swabs, to 12 dpi in oropharyngeal swabs, and to 4 dpi in rectal swabs. Two of three direct contact animals became infected while the third did not become infected because its inoculated neighbors never shed virus. Viral shedding was detected at 8 dpi (7 days post contact, dpc) and lasted until 16 dpi (15 dpc), mainly in nasal secretions. Antibodies against SARS-CoV-2 (reactive and neutralizing) were found in all inoculated animals at 8 dpi and infected contact animals at 12 dpi. Antibody titers increased up to 28 dpi. The only clinical signs of infection were reduced activity in three animals at 4 dpi and mild tissue pathology (rhinitis) at 4, 8, and 12 dpi. There was no change in body temperature or weight loss.
The authors tested for the presence of neutralizing antibodies (not just reactive antibodies), performed assays that detected shedding of live virus and isolated viruses, and confirmed that no viral evolution had occurred in the animals by sequencing isolated viruses and comparing to the original virus inoculum.
Only one inoculation route was tested (intranasal). Other routes may result in a higher or lower likelihood of infection and potentially different clinical manifestations. The lack of pulmonary signs in infected animals indicates that this species would not be a good animal model for pulmonary symptoms of COVID-19 in human patients.
This is the first study to confirm raccoon dogs as potential hosts of SARS-CoV-2. These findings are important because this species was found naturally infected with SARS-CoV in 2003 and may have been an intermediate host in that pandemic. China has a large fur industry for raccoon dogs (millions of animals), so there may be a risk for outbreaks of the virus on fur farms similar to outbreaks seen on mink farms in Europe and the US. Additionally, this species is invasive in Europe, presenting a possible risk of reverse zoonotic transmission from humans into wild populations.
This review was posted on: 13 October 2020