Pet hamsters can transmit Covid to humans and are the likely source of a recent outbreak of the Delta variant in Hong Kong, data suggests.
The research confirms fears that a pet shop was the source of a recent Covid outbreak in the city, which has seen at least 50 people infected and led to the culling of more than 2,200 hamsters.
However, virologists emphasised that, although the pet trade could provide a route for viral spread, existing pet hamsters are unlikely to pose a threat to their owners and should not be harmed.
Many animals are susceptible to catching Covid from humans, but until now, only one – the mink – has proved capable of transmitting it in the opposite direction. Hamsters are particularly vulnerable to the virus – dwarf Roborovski hamsters can die from it – so have been widely used as a model for studying the disease.
Concerns that hamsters might also be capable of infecting humans first surfaced when a 23-year-old worker at the Little Boss pet shop in Hong Kong tested positive for Covid on 15 January – the city’s first Delta variant diagnosis for more than three months. A woman who visited the pet shop was also infected, and other members of her family tested positive in the days that followed.
In response, public-health officials swabbed hundreds of rodents at the pet shop and at the warehouse supplying it. Viral genetic material or antibodies were detected in 15 of the 28 Syrian hamsters, but in none of the dwarf hamsters, mice, guinea pigs, rabbits or chinchillas tested. None of the hamsters had overt symptoms.
After coronavirus was detected in the hamsters, Prof Leo Poon, a virologist at the University of Hong Kong, and his colleagues undertook further viral genome sequencing, which revealed that the hamsters were all infected with the Delta variant, and that their viruses were closely related. The nature of the mutations contained within these viruses suggested that transmission had been going on for some time – possibly since mid-November. The hamsters were imported from a supplier in the Netherlands during December and January.
Meanwhile, analysis of samples from the pet shop worker and infected customer suggested that their viruses were closely related to the hamster viruses, but that they were unlikely to have transmitted the infection to each other.
The study, which has not yet been peer-reviewed, is the first to provide “convincing evidence” that hamsters can become infected in real-life settings, and that they can pass the virus to humans, as well as to other hamsters.
“Both genetic and epidemiological results strongly suggest that there were two independent hamster-to-human transmission [events], and that such events can lead to onward human transmission,” Poon said. “Importation of infected hamsters was the most likely source of virus infection.”
Most surprisingly, the virus could still “transmit between humans quite effectively” even after replicating in hamsters, Poon told the journal Nature. Although his results point to the global pet trade as a route for viral spread, people are still much more likely to be infected by each other than by their pets, he added.
Even so, the findings highlight the possibility that the virus may be spilling over to other animal species without being detected, providing an opportunity for further mutation and potential spillover back to humans. They therefore “highlight the need for awareness, surveillance and for appropriate quarantine and control policies for the pet animal trade”, said Poon.