Golden Syrian hamsters are highly susceptible to the coronavirus that causes COVID-19, a new study shows.
Although the species is popular with pet owners, the findings, published April 20 in bioRxiv, are no cause for panic, says Anne Balkema-Buschmann, a veterinarian at the Friedrich-Loeffler-Institut in Riems, Germany. “The message of this document is not that hamsters are ticking time bombs that can no longer be kept indoors.” But pinpointing the animals’ sensitivity to SARS-CoV-2 may help researchers fine-tune experiments using hamsters to test potential treatments for COVID-19.
The rodents made headlines in January when a cluster of COVID-19 cases in people surfaced in Hong Kong pet stores. In accordance with its “zero-COVID” strategy, the government has culled over 2,000 animals. A viral genetic analysis eventually revealed that the infected hamsters had passed the delta variant of the virus to humans twice, leading to at least one further human-to-human transmission. Aside 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 pass the virus to their uninfected siblings and show similar pneumonia symptoms to humans. Hence, since the early days of the pandemic, rodents, including Golden Syrians (Mesocricetus auratus), has emerged as a useful animal model for research on COVID-19 drugs and vaccines.
To better design their COVID-19 vaccine and drug studies, Balkema-Buschmann’s team sought to determine how much of the SARS-CoV-2 virus actually makes animals sick and releases the virus. The researchers found that the minimum infectious dose for hamsters is 1/5000 of some previous estimates and 1 / 100,000 of the minimum infectious dose for humans, perhaps not too surprising given that hamsters are much smaller than humans.
With this minimal dose, the virus infected the animals’ lungs and replicated in the nose and throat. When that minimum dose was increased by a factor of 100, the animals’ rapid oral swab tests gave positive results and the animals developed pneumonia and lost weight. There was also a delay of a few days before the animals began shedding viruses and manifesting symptoms of disease, which could cause hamster cases to go unnoticed. Other hamster species that can harvest the virus may have a similar risk, and even at low doses, animals can shed enough virus to infect humans.
For the researchers, the findings provide a better history of disease progression in hamsters and could mean lowering hamster virus dosage levels in drug and vaccine studies to better reflect what happens in humans. For pet owners, takeout is using proper hygiene around hamsters if a human in the home tests positive for the virus and consulting a veterinarian. Dabbing your pet hamster’s mouth could also tell you if it might be infected.
“We don’t think from these findings that hamsters play a role in the dynamics of the pandemic. It’s just that the virus could ping-pong within the family if an infected person has close contact with a hamster, ”says Balkema-Buschmann.
The greatest danger, says Leo Poon, a virologist at the University of Hong Kong who has studied the cluster of pet shops, is hamsters on farms or in pet trade settings. “With such high susceptibility to SARS-CoV-2, introducing an infectious hamster to a hamster farm or batch of hamsters could cause an outbreak in the population,” says Poon. “Even worse, it could silently spread.”
The new hamster study also looked at two genetic versions of the hamster virus that received high and low doses, respectively. Neither contained significant mutations. Whenever a virus passes between species there is concern that it may mutate and become more infectious or dangerous (as we have seen in humans), but Poon notes that it would be necessary to see multiple rounds of infection to say something about the risk of mutation. in these rodents.