golden syrian hamsters are highly susceptible to coronavirus that causes COVID-19, a new study shows.
While the species is popular with pet owners, the results, published April 20 on bioRxiv, are not a cause for panic, says Anne Balkema-Buschmann, a veterinarian at the Friedrich-Loeffler-Institut in Riems, Germany. “The message of this article is not that hamsters are ticking time bombs that can no longer be kept in homes.” But determining how sensitive animals are to SARS-CoV-2 may help researchers refine experiments using hamsters to test potential treatments for COVID-19.
Rodents made headlines in January when a cluster of COVID-19 cases in people emerged around pet stores in Hong Kong. In accordance with its “COVID-zero” strategy, the government slaughtered more than 2,000 animals. A viral genetic analysis eventually revealed that infected hamsters had transmitted the delta variant of the virus to humans twice, leading to at least one additional person-to-person transmission. Apart from a case of mink-to-human transmission in Denmark and a possible case of white-tailed deer to human transmission in Canada, this is the only documented example of the virus passing from animals to humans.
hamsters can transmit the virus to their uninfected siblings and show symptoms of pneumonia similar to humans. So, since the early days of the pandemic, rodents, including golden Syrians (Mesocricetus auratus), emerged as a useful animal model for the investigation of drugs and vaccines against COVID-19.
To better design their own COVID-19 vaccine and drug studies, the Balkema-Buschmann team tried to determine how much SARS-CoV-2 virus actually makes animals sick and kills them. The researchers found that the minimum infectious dose for hamsters is 1/5000 of some preliminary estimates and 1/100,000 of the minimum infectious dose for humans, which is perhaps not too surprising given that hamsters are much smaller than humans.
At this minimal dose, the virus infected the animals’ lungs and replicated in their noses and throats. When that minimum dose was increased by a factor of 100, the animals’ rapid oral swab tests came back positive, and the animals developed pneumonia and lost weight. There was also a delay of a few days before the animals began to shed the virus and show symptoms of illness, which could cause hamster cases to go undetected. Other hamster species that can contract the virus may be at similar risk, and even at low doses, the animals can shed enough virus to infect humans.
For the researchers, the results provide a better timeline of disease progression in hamsters and may mean lowering the dose levels of the hamster virus in drug and vaccine studies to better reflect what happens in humans. For pet owners, takeout is use proper hygiene around hamsters if a human in the household tests positive for the virus and consult a veterinarian. Taking a swab from your pet hamster’s mouth may also tell you if he might be infected.
“We do not believe from these results that hamsters play a role in the dynamics of the pandemic. It’s just that the virus could ping-pong inside the home if an infected person has close contact with a hamster,” says Balkema-Buschmann.
The biggest danger, says Leo Poon, a virologist at the University of Hong Kong who studied the pet shop group, is from hamsters in breeding or pet trade settings. “With such high susceptibility to SARS-CoV-2, introducing an infectious hamster to a hamster farm or hamster flock could cause a population outbreak,” says Poon. “Worse, it could be spreading silently.”
The new hamster study also examined two genetic versions of the virus from hamsters given high and low doses, respectively. None contained significant mutations. Anytime a virus moves from one species to another, there is concern that it could mutate and become more infectious or dangerous (as we’ve seen in humans), but Poon points out that one would need to see multiple rounds of infection to say anything about the virus. mutation risk in these rodents.