Hamsters Hong Kong

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Hamsters Hong Kong

Published 1 February 2022 | updated 13 February 2022

There have been multiple reports in the news of hamsters from a pet shop in Hong Kong being culled, and that other pet shops selling hamsters must suspend business, over fears of the spread of COVID.

While it has been known for some time that hamsters can be experimentally infected with SARS-CoV-2 and spread the virus to other hamsters, to date there have not been any reports of natural infection or any evidence that they can transmit the virus to other species.

The Agriculture, Fisheries and Conservation Department (AFCD) in Hong Kong have released the following statement, which reports that 11 hamsters have so far given preliminary positive tests for SARS-CoV-2, while all other animals tested have tested negative.


Government of  the Hong Kong Special Administrative Region: Agriculture, Fisheries and Conservation Department (2022) Press release: hamster samples preliminarily test positive for COVID-19 virus [online] . Available at: https://www.afcd.gov.hk/english/publications/publications_press/pr2516.html    [Accessed 29 January 2022]

Yen, H.L. (2022) Transmission of SARS-CoV-2 (variant Delta) from pet hamsters to humans and onward human propagation of the adapted strain: a case study.  Preprints with The Lancet  https://dx.doi.org/10.2139/ssrn.4017393

This paper, currently in preprint, reports on the investigation of SARS-CoV-2 infection in hamsters at a pet shop in Hong Kong and provides some preliminary evidence of transmission of infection from hamsters to humans.

The first human case was a 23-year-old female vaccinated pet shop worker (Patient 1), presented with sore throat and cough, confirmed to be infection with COVID (VOC Delta -AY127 virus lineage). She has no known contact with infected humans.

A mother (patient 2) and her daughter who visited the pet shop and purchased a hamster, also tested positive for SARS-CoV-2 on PCR tests. Subsequently two other members of the household were also confirmed to be infected.

Initial screening of the animals in the pet shop, hamsters (n=69), rabbits (n=42) and Guinea pigs (n=14) returned seven (10.2%) positive swabs from hamsters while none of those from other animals tested positive by RT-PCR. The wholesale warehouse supplying this pet-shop chain was then investigated, with 511 swabs collected from hamsters (n=137), rabbits (n=204), Guinea pigs (n=52), chinchilla (n=116) and mice (n=2) housed there. Here one Syrian hamster swab was RT-PCR positive for SARS-CoV-2.

Since the initial screening suggested that hamsters were infected at both the warehouse and the pet shop, a more detailed sampling was carried out at both sites with swabs and serum being collected from the Syrian and dwarf hamsters.

At the pet shop 8 (50%) of 16 Syrian hamsters had evidence of infection, either by serology or confirmed RT-PCR, with 4 animals testing positive by both serology and RT-PCR, 3 animals tested positive by RT-PCR alone and 1 animal tested positive by serology alone. A total of 3 cages housing Syrian hamsters were sampled and two (66.7%) had animals with confirmed RT-PCR or serology results. In contrast, none of 20 cages housing dwarf hamsters were positive in either RT-PCR or antibody assays.

At the warehouse twelve Syrian hamsters and 55 dwarf hamsters were sampled. Two (16.7%) of the swabs were RT-PCR positive and seven (58.3%) of the sera from Syrian hamsters, had evidence of antibody. The authors interpreted the detection of 5 animals with antibodies but without viral RNA to suggest that infection may have occurred at an earlier date.

Investigation into the source of the infected hamsters suggested that they were imported from Netherlands to Hong Kong in two different batches (arrival dates: 22-December-2021 and 7-January-2022) and that some hamsters arriving on the 7-January-2022 were transferred to pet shop A on the day of arrival.

The virus sequenced from the hamsters were genetically closely related to recent AY.127 viruses detected in multiple European countries. By contrast, none of the AY.127 sequences previously detected from returning travellers in Hong Kong is genetically similar to the sequences detected in this outbreak. This further supports the hypothesis that this outbreak was caused by a recent introduction of AY.127 virus from Europe.

Specimens from the first 3 human cases (Patients 1-3) and positive hamster samples collected in pet shop A (n=11) and the warehouse (n=1) were subjected to full viral genome sequence analysis. The viral genomes all belong to the Delta AY.127 viral lineage.

While the sequences from these human and hamster cases were highly similar, they were not identical. The divergent date of this cluster of human and hamster viruses is estimated to be on 21-November-2021 (; 95% CI range: 18-October-2021 to 16- December-2021). Interestingly, the viral genome of the pet shop worker (patient 1) was phylogenetically distinct (5 nucleotides different) from those of the mother (patient 2) and her husband (patient 3), which were identical.

The authors considered that these results suggest that Patient 1 and Patient 2 acquired the infection independently from hamsters at the pet shop rather than from each other. As Patient 3 did not visit the pet shop, these findings further suggest that the SARS-CoV-2 virus circulating in hamsters allowed at least 1 human-to-human transmission.

The authors conclude that pet hamsters can acquire SARS-CoV-2 infection in real-life settings and can transmit the virus back to humans.

Please note this paper has been published as a preprint and has not been subject to peer review.

Further information

For anyone looking for further details of the pathogenesis and signs of SARS-CoV-2 in hamsters, the following two papers may be of interest.

Sia, S.F. et al (2020) Pathogenesis and transmission of SARS-CoV-2 in golden hamsters. Nature, 583 (7818), pp. 834-838. https://doi.org/10.1038/s41586-020-2342-5

This paper reports on the presence of viral antigens in nasal mucosa, bronchial epithelial cells and areas of lung consolidation on days 2 and 5 after inoculation with SARS-CoV-2, followed by rapid viral clearance at 7 days after inoculation. They also detected viral antigens in epithelial cells of the duodenum and detected viral RNA in faeces.

It was found that SARS-CoV-2 was transmitted efficiently from inoculated hamsters to naive hamsters by direct contact and via aerosols. However, transmission via fomites in soiled cages was not as efficient.

Although viral RNA was continuously detected in the nasal washes of inoculated hamsters for 14 days, the communicable period was short and correlated with the detection of infectious virus but not viral RNA.

Osterrieder, N. et al (2020) Age-dependent progression of SARS-CoV-2 infection in Syrian hamsters. Viruses, 12 (7), p. 779. https://doi.org/10.3390/v12070779

This paper shows that, as in humans, hamsters appear to show an age dependent response to infection with SARS-CoV-2, with young hamsters launching earlier and stronger immune response and older hamsters showing a more pronounced and consistent weight loss.

In providing advice for those who own or handle hamsters the following resources may be helpful

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