The original SARS-CoV-2 virus reassuringly appeared to have a limited host range (see 2020's Susceptibility of Ferrets, Cats, Dogs & Other Domestic Animals to SARS-CoV-2), but over the past 3 years the virus has undergone numerous changes, and more species are now susceptible to infection.
This raises genuine concerns that if the virus establishes itself in a new host, it could take new evolutionary paths - creating unpredictable variants that could potentially `spill back' into humans (see WHO/FAO/OIE Joint Statement On Monitoring SARS-CoV-2 In Wildlife & Preventing Formation of Reservoirs).
A few (of many) past blogs on SARS-CoV-2 spillover to non-human species includes:
Companion animals and household pets are also at risk, and we've seen rare instances where transmission from companion animals to humans can be inferred, including EID Journal: Suspected Cat-to-Human Transmission of SARS-CoV-2 - Thailand and Hong Kong Detects COVID In Pet Store Hamsters - Suspends Sales & Orders Cull.
USDA/APHIS: White-Tailed Deer Exposed To SARS-CoV-2 Detected In 4 States
Until 18 months ago, mice were believed largely immune, but in March of 2021 in PrePrint: The B1.351 and P.1 Variants Extend SARS-CoV-2 Host Range to Mice, we learned hat some SARS variants had overcome that barrier.
All of which brings us to a preprint, published this week, which documents a case of human-to-rat transmission of SARS-CoV-2 in France.
SARS-CoV-2 infection in domestic rats after transmission from their infected ownerXavier Montagutelli, Berenice Decaudin, Maxime Beretta, Hugo Mouquet, Etienne Simon-Loriere
We report the transmission of SARS-CoV-2 Omicron variant from a COVID-19 symptomatic individual to two domestic rats, one of which developed severe symptoms. Omicron carries several mutations which permit rodent infection. This report demonstrates that pet, and likely wild, rodents could therefore contribute to SARS-CoV-2 spread and evolution.
In May 2022 (week 18), a resident of the Southern outskirts of Paris, France, without recent history of travel, developed flu-like symptoms with moderate fever, headache, coughing, shortness of breath and fatigue, which resolved after 8 days. A SARS-CoV-2 antigenic test was positive three days after the onset of symptoms (day 3) and was confirmed by a RT-qPCR test performed on day 5. On day 12, one of the owner's two pet rats (Rat 1), a 3-year-old male, developed prostration, respiratory distress (open-mouth breathing, cyanosis, chromodacryorrhea, pulmonary cracks) and anorexia.
This rat had a history of frequent sneezing which had worsened during the previous weeks. The two rats had been in close contact with their owner for cuddles. On day 12, Rat 1 was presented to a veterinarian who noted very severe symptoms (respiratory distress and lethargy) responsible for marked suffering. These symptoms worsened three days after admission, leading to the decision to euthanize the rat on D15. A blood sample was collected, but no other samples were available for further analysis. On day 26, the owner presented to the veterinarian Rat 2, a 6-month-old male, which was in good condition with only occasional sneezing. A blood sample was collected for serology.
Infection of the owner with a SARS-CoV-2 variant of the Omicron lineage was evidenced by the detection of the K417N mutation in the PCR test performed 5 days after symptoms offset (week 18 of 2022), and compatible with the 100% proportion of Omicron reported by Santé Publique France in the sequencing of randomly selected SARS-CoV-2 positive samples in France during week 17 and 18 of 2022. Data from the National Reference Center for the Northern part of France further indicate that Omicron BA.2 was dominant at this time in the Paris area.
The sera of both pet rats presented IgG and IgM titers against both Wuhan and Omicron spike antigens when assayed by ELISA as previously described (Montagutelli, 2021, Planchais, 2022), in parallel to control sera collected from two healthy rats (Rat 3 and Rat 4) bred under specific-pathogen-free condition (Figure 1). This result indicates that the pet rats had been recently exposed to SARS-CoV-2. While we cannot entirely exclude a more distant infection, considering that the two rats were kept in a cage inside the owner's home, away from other animals, their contamination can most likely be attributed to their close and frequent contacts with the infected owner in May 2022.
While the initial SARS-CoV-2 variants were shown to be unable to infect rodents, this changed with the evolution of the virus during the pandemic circulation in humans. In particular, multiple Variants of Concern have been shown to be able to infect rodents in experimental settings. This extension of the host range has been associated with changes in the spike protein such as the recurrent N501Y mutation (Montagutelli, 2021). Omicron variants have been shown to readily infect laboratory rodents, with varying disease severity, and this capacity and variations likely involve other changes in parallel to N501Y (Montagutelli, 2022).