Golden Syrian hamsters are highly susceptible to coronavirus which causes COVID-19, a new study shows.
Although the species is popular with pet owners, the results, published on April 20 in bioRxiv, are not a cause for panic, said Ann Balkema-Bushman, a veterinarian at the Friedrich-Löfler Institute in Rome, Germany. “The message of this document is not that hamsters are time bombs that can no longer be kept in households. But determining how sensitive animals are to SARS-CoV-2 could help researchers refine experiments using hamsters to test potential treatments for COVID-19.
Rodents made headlines in January when a group of human COVID-19 cases surfaced around Hong Kong pet stores. In line with its “zero COVID” strategy, the government more than 2,000 animals destroyed. Viral genetic analysis eventually revealed that hamsters were infected has transmitted the delta variant of the virus to humans twicewhich leads to at least one subsequent person-to-person transmission. Except for one case of transmission from mink to man in Denmark and a possible transmission of white-tailed deer by man in Canada, this is the only documented example of the virus being transmitted from animals to humans.
Hamsters can transmit the virus to their uninfected counterparts and show similar symptoms of pneumonia as humans. So from the first days of the pandemic, rodents, including the Golden Syrians (Mesocricetus auratus) has emerged as a useful animal model for research into drugs and vaccines against COVID-19.
To better develop their own studies on vaccines and drugs against COVID-19, the Balkema-Buschmann team tried to determine how much SARS-CoV-2 virus actually infects animals and discards 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 infects the lungs of animals and multiplies in the nose and throat. When this minimum dose was increased by a factor of 100, rapid tests on oral swabs from the animals showed positive results and the animals developed pneumonia and lost weight. There was also a delay of several days before the animals began to shed the virus and show symptoms of a disease that could cause hamster cases to go unnoticed. Other types of hamsters that can catch the virus may have a similar risk, and even at low doses, animals can shed enough of the virus to infect humans.
For researchers, the results provide a better timeline for the progression of the disease in hamsters and may mean lowering the dosage levels of the hamster virus in drug and vaccine studies to better reflect what is happening in humans. For pet owners, home food is a must use proper hygiene around hamsters if a person in the household is positive for the virus and consult a veterinarian. Wiping your pet hamster’s mouth can also tell you if it may be contagious.
“From these results, we do not believe that hamsters play a role in the dynamics of the pandemic. It’s just that the virus can ping-pong in the household if an infected person has close contact with a hamster, “said Balkema-Bushman.
The bigger danger, says Leo Poon, a virologist at the University of Hong Kong who studies the cluster of pet stores, is hamsters in farm or pet trading conditions. “With such high susceptibility to SARS-CoV-2, introducing an infected hamster to a hamster farm or batch of hamsters could cause an outbreak in the population,” said Poon. “Even worse, it can spread silently.
The new study on hamsters also examined two genetic versions of the hamster virus that received high and low doses, respectively. None of them contained significant mutations. Every time a virus passes between species, there are fears that it may mutate and become more infectious or dangerous (as we have seen in humans), but Poone notes that one will have to see many rounds of infection in order to say something about the risk of mutation in these rodents.