Hamsters Cause a COVID Outbreak?

Hamsters Cause COVID Outbreak


Did hamsters cause a COVID outbreak? That is what a new pre-print case study implies. It’s a pre-print, and while everyone has run with preprints during this pandemic, it’s good practice to keep in mind that they have yet to be peer-reviewed. But we can still talk about the study, because it’s about hamsters. And we like hamsters.

Where did this happen? 

A pet store in Hong Kong. Hong Kong pursued a “zero-COVID” strategy, meaning they were extremely strict with restrictions. There were no locally acquired infections with the Delta variant since October 9’21. Most came from outside travelers identified at the airport or while in quarantine. Then the “pet shop” case popped up.

What exactly happened? 

A COVID-19 case was identified in a 23-year-old female pet shop worker on 15 Jan’22. The pet shop sold hamsters, rabbits and chinchillas. She was fully vaccinated with Comirnaty and had no known contact with any infected individuals. In addition, a mother and daughter who previously purchased a hamster from the pet shop returned to the shop on 8 Jan’22 to discuss “hamster issues” with the 23-year-old worker. On 12 Jan’22, the mother developed upper respiratory symptoms which was confirmed to be COVID a few days later. Her husband, daughter and son also were infected with COVID. All were fully vaccinated, either with Comirnaty or Coronavac. Given the “zero-COVID” policy, this puzzled investigators. How did the 23-year-old get infected? That’s when they decided to swab the pet store animals.

Investigators collected 125 swab specimens from hamsters (n=69), rabbits (n=42) and Guinea pigs (n=14). 7 of the hamster swabs were confirmed positive for COVID-19, but no others from any of the other animals. Next the wholesale warehouse that supplied the pet-store chain was investigated on 18 January’22. 511 swabs were collected from 137 hamsters, 204 rabbits, 52 Guinea pigs, 116 chinchillas and 2 mice. One Syrian hamster swab was positive for COVID-19. Given the pet-store swabs and the warehouse swabs, investigators asked themselves if the cute lil’ hamsters caused a COVID outbreak. More work needed to be done.

In mid-January, they proceeded in a more detailed sampling of hamsters from the pet shop. They took swabs and serum from the Syrian and dwarf hamsters. 43.8% of the Syrian hamsters (Golden Hamsters) were confirmed to be COVID positive. 31% had antibodies to COVID, meaning they had a prior infection and recovered. None of the 20 cages housing dwarf hamsters were positive for COVID or antibodies to COVID. Investigators also tested other pet stores in Hong Kong that the warehouse supplied. 2 of 49 swabs from hamsters in one of the pet shops tested positive for COVID-19.

Were the hamsters visibly ill? 

No, there were no visible symptoms of illness in the pet-store hamsters or the warehouse hamsters.

Where did the hamsters come from? 

The Netherlands imported the affected hamsters to the warehouse that then distributed the hamsters to various pet stores in Hong Kong. They arrived in 2 batches, one on 22 Dec’21 and one on 7 Jan’22. The December arrivals were imported by Qatar Airways, changed airplanes in Doha, Qatar, with a total transit time of 15 hours. Water was provided for the hamsters but no food. The January arrivals were transported by KLM with a stop in Bangkok and no change of aircraft or additional water or food was provided. The transport cages had a mesh covering, which could or could not be a source of contamination.

Specimen Collection

Specimens from the first 3 human cases, positive hamster cases at the pet store and positive hamster cases at the warehouse underwent full viral genome sequencing. All sequencing showed up as Delta AY.127. (By this time, Delta had not been detected in Hong Kong for 3 months.) The sequences indicated that the viruses had the same origin. Interestingly, the sequences from humans and the sequences from hamsters were not identical. They differed by 1 to 13 nucleotides, which suggests that transmission (and mutations) has been going on for a while.

Take-Home Points for “Hamsters Cause a COVID outbreak”:  

First, don’t panic and kill your pet hamster. This is about hamsters in a pet store that interacted with lots of other hamsters and were handled by multiple people and countries. Also, it was only the Syrian hamster found to be infected. Although that said, the Syrian (Golden) hamster, sometimes called the Teddy bear hamster because they’re so cute, is the most common pet hamster in the US.

As first mentioned, this is a pre-print so we should wait till peer review completes to run with it. But assuming it passes peer review, it would be the first study to show hamster to human jump of COVID-19 and then onward to human-to-human spread. Not all hamsters, of course, just the Syrian hamster. It would also be the first study to show hamster to hamster spread of COVID. It would be the first to show spread via the international pet trade. Of course, there is the possibility that undetected local human-to-human spread led to a human infecting a hamster, though given the evidence thus far, this seems unlikely.

We’ve seen other examples of viral spillover from one species to species. Recently, I interviewed a Penn State University Researcher about his work showing that COVID jumped from humans to deer. You can listen to the podcast here. The deer seemed to be able to spread it to other deer, but symptoms didn’t appear severe. Dogs and cats have tested positive for COVID, but I haven’t heard of any cases of them spreading it to humans. Zoonotic viruses can jump from one species to another. What that means for the trajectory of an infectious disease is difficult to determine. If a virus has multiple hosts and can mutate in multiple hosts, what does that mean for vaccination campaigns? What does it mean for ending an infectious disease pandemic? My research internship at public health school involved modelling and predicting emerging infectious diseases and how the way humans interact with animals and our environment can propagate new viruses. You can read more about that here, if you are interested.

In conclusion, did hamsters cause a COVID outbreak? Maybe. There is strong preliminary evidence for it. We might find more evidence of animal to human transmission (and human to animal transmission) as time goes on. Again, the big questions are: What does species-to-species jumping of the virus mean for the trajectory of the virus? What does it mean for human vaccination campaigns and/or animal vaccination campaigns?


Thanks for reading, guys.

Definitely check out my Causes or Cures podcast! I’ve uploaded 3 more and have recorded 3 more that I will post soon. One is about a new way to address obesity; the other is with a neuroscientist who discusses why animal research may be more cruel than beneficial (and she suggests alternatives to using animal models) and the other is with a doctor/researcher in Australia who published a great study on how drug companies/industry interfere with the drug approval process in Australian hospitals. It’s quite interesting and can’t wait to post.

Talk soon- Eeks

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2 Responses to “Hamsters Cause a COVID Outbreak?”

  1. A little basic hamsterology. The most commonly kept hamster is the the Syrian or golden hamster, Mesocricetus auratus, and they are the species implicated in the Hong Kong outbreak. Pet shop golden hamsters are extremely inbred – they all have the same mitochondrial DNA, and random pairs of hamsters are often histocompatible.

    There were “dwarf hamsters” in the pet shop also, and they didn’t get infected. Dwarf hamsters are more recently introduced in the pet trade – I’ve never seen one – three closely related species in the genus Phodopus, all three species are in the pet trade. Nor did guinea pigs, which other than being rodents are completely unrelated.

    There are several other rodents called hamsters, some of which are used in scientific research.

  2. Hamsterology. Ha! Thank for the lesson, Dr. Richmond! 🙂 Eeks

    (Also…how do you know so much about hamsters?)

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