The Lancet: First case of a human being infected with COVID-19 by a pet

On March 11, a study published in the international medical journal The Lancet by scholars from the University of Hong Kong found that Syrian hamsters can be naturally infected with the Delta virus, which in turn infects humans. This is the first time in the world that pet Syrian hamsters have been confirmed to be able to transmit the new coronavirus to humans.

This is a very shocking study. It can be said to be the first case of a pet infecting a human. It also raises some new thoughts on our epidemic prevention.

For example, pet owners should take some protective measures for their pets and avoid letting their pets go out during the epidemic; for example, many children like to touch pets outside, so they should also pay proper attention; for another example, the pet trade is a large global mobile trade, and prevention needs to be strengthened.

Next, we discuss this article in detail.

01. Did the new coronavirus spread from humans to other animals, or from animals to humans?

Although the novel coronavirus has been widely transmitted between humans and animals, and many studies have found that pets also have the novel coronavirus, people have always believed that it was because the owner was infected with the novel coronavirus and spread it to the pet, but there have been no reports of pets spreading it to humans.

Recently, The Lancet published a study, "Transmission of SARS-CoV-2 delta variant (AY.127) from pet hamsters to humans, leading to onward human-to-human transmission: a case study"

In this study, pet hamsters transmitted the new coronavirus (SARS-CoV-2 delta variant (AY.127)) to their owners, which further led to human-to-human transmission.

In fact, there are many news reports about people bringing the new coronavirus to animals. For example, tigers and gorillas in zoos were infected with the new coronavirus, which was transmitted by humans.

But can animals transmit the new coronavirus to humans?

Although many researchers believe that animals have a lower load of COVID-19 and that COVID-19 is more likely to spread to humans, the evidence has been insufficient. Of course, farmed minks were previously thought to be able to be infected with COVID-19 and spread it to humans, so minks were slaughtered.

However, in fact, considering a basic fact: the new coronavirus first came from animals, so it is inevitable that it will spread from animals to humans.

However, there is a lack of evidence! In fact, more people believe that the new coronavirus spread from animals to humans through "contamination", which is similar to contact with frozen items containing the new coronavirus or transmission through contact with objects.

Therefore, this Lancet study is also quite representative, from animals to humans, and it is an infection.

02. COVID-19 outbreak in pet store

A pet shop in Hong Kong suddenly had an outbreak of COVID-19, with both pets and shop staff being infected.

However, it is strange that the virus that was prevalent in Hong Kong at that time was Omicron, but the virus that was infected in this pet store was Delta. So how do we explain the infection in this pet store?

So the researchers began a large-scale investigation of pet stores.

They tested pet store staff and pets in their warehouses and found that both humans and animals were infected with the new coronavirus. It must be emphasized here that it is infection, that is, the virus enters the body and begins to multiply, rather than accidentally being contaminated with the virus. They used oral, anal and blood tests at the same time to confirm this.

Among them, hamsters have the highest infection rate.

Eight of 16 Syrian hamsters (50%) and seven of 12 Syrian hamsters (58%) from the corresponding warehouse were positive for SARS-CoV-2 infection by RT-qPCR or serological testing.

However, other pets such as dwarf hamsters (n=75), rabbits (n=246), guinea pigs (n=66), chinchillas (n=116), and mice (n=2) were negative in the RT-qPCR test.

03. Is the virus transmitted from humans to rats or from rats to humans?

So, in this case, was the novel coronavirus transmitted from humans to hamsters or from hamsters to humans? The time of infection for humans is certain, but for hamsters, it is unknown because we cannot pry open their mouths to ask them when they were infected. Not to mention that they themselves do not know, and even if they can speak, it is hard to say whether hamsters have symptoms of novel coronavirus infection.

At this time, we can only rely on bioinformatics methods, that is: sequencing.

This is different from our nucleic acid test. Our nucleic acid test is determined to be positive as long as this fragment is detected.

Sequencing, on the other hand, is to find out the entire sequence of the virus from beginning to end, directly exposing the true appearance of the virus.

Therefore, the researchers used Illumina's ISeq sequencing platform to test the collected COVID-19 samples.

As expected.

1. Humans and hamsters are infected with the same new coronavirus

I believe that after this period of time, everyone has a deep understanding of the new coronavirus. For example, delta, omicron, etc., are all the same virus, but they have different genetic mutations, forming independent evolutionary branches. This time, hamsters and humans were infected with the basically identical delta mutant strain (AY.127).

2. This strain had not spread locally before.

Combined with local epidemiological surveys, it was found that the AY.127 mutant strain was completely new in the local area and had not appeared in the local area before. This means that the strain was in this store, either the clerk or the hamster.

3. The virus was transmitted to humans from hamsters

I guess many people are curious at this time, is there no solution? In fact, there is still a solution in bioinformatics. That is, phylogenetic analysis can be performed on its genome sequence to view the order of evolution (just like everyone sees that humans originated in Africa, which is the method used).

It was found that although hamsters and humans were infected with the same mutant strain, there were still specific differences

Further phylogenetic tree analysis

The results showed that, from a phylogenetic perspective, the virus in hamsters appeared first, and that in humans came later.

Specifically, the hamsters were infected around October 14, 2021 (95% CI is September 15 to November 9, 2021), and this batch of hamsters were imported from a long distance and arrived at the pet store on December 22, 2021, and humans were infected on January 4, 2022.

This can be said to be a very typical example, that is, the new coronavirus can be transmitted from pets to humans and cause further infection in the population.

04. The particularity and significance of this study

Many people are probably curious. It has been three years since the COVID-19 pandemic, and pets have come into contact with humans so much, and there have been many reported cases of pet infection. Why was this study the only one published in The Lancet? In fact, it is very difficult to prove that pets can infect humans.

First, most people have close contact with pets. It is difficult to determine whether it is a person who infects a pet or a pet who infects a person. For example, in a previous case of pet infection reported in Hong Kong, due to insufficient evidence, it can only be considered that a person infected a pet.

Secondly, most infections are often caused by the same strain, just like the current mainstream strain in the world is Omicron. In this case, you cannot determine where the strains of pets and humans come from.

The special thing about this Lancet study is that the strain that broke out in Hong Kong at the time was Omicron, but the one that appeared in this pet shop was delta, which means an independent source of infection, which is further worthy of attention.

Third, there must be a sufficient time difference to determine the order.

This point is similar to the first one, that is, the vast majority of infections are concentrated in one period and it is impossible to distinguish the order.

What is special about the Lancet case is that there is a clear timeline.

Around October 14, 2021, the hamster was infected with the new coronavirus.

On December 22, 2021, imported hamsters arrived at pet stores.

On January 4, 2022, a pet shop staff member was infected with the new coronavirus.

Sufficient time difference ensures that the order of infection can be determined.

From October to January of the following year, the new coronavirus strain also mutated, resulting in certain mutation differences between the strains of hamsters and pet workers, although they belonged to the same evolutionary branch, so they could be separated.

05. Conclusion and Tips

This is the first study to confirm transmission from pets to humans. I see that many people are dissatisfied with this study and even think that it should not be reported. I personally think it is unreasonable. In fact, whether you watch it or not, the new coronavirus is there, and it will not become invulnerable just because we have armed ourselves mentally.

In addition: The new coronavirus has been found to be infectious in a variety of non-human hosts:

For example, companion animals: dogs, cats, ferrets

Zoo: Cats and Gorillas

Breeding: Mink

Wild: White-tailed Deer

Experimental: Nonhuman primates, hamsters, ferrets, American minks, cats, dogs, raccoon dogs, North American deer mice, Egyptian fruit bats, Asian small-clawed otters, and white-tailed deer

In fact, this study also has some implications for our current epidemic prevention:

1. Considering the frequent cross-border trade of pets, it is recommended that relevant agencies such as customs pay attention to the issue of pets being infected with the new coronavirus.

2. Pet owners need to manage their pets to a certain extent, especially for those pets that live outdoors. During the epidemic, their activities should be restricted to a certain extent to prevent the virus from spreading back to their owners.

3. Children like to touch pets, so they need to be protected and disinfected.

As for the attacks on other pets mentioned by many people, I personally think that there is insufficient evidence at present.

Yen HL, Sit THC, Brackman CJ, Chuk SSY, Gu H, Tam KWS, Law PYT, Leung GM, Peiris M, Poon LLM; HKU-SPH study team. Transmission of SARS-CoV-2 delta variant (AY.127) from pet hamsters to humans, leading to onward human-to-human transmission: a case study. Lancet. 2022 Mar 12;399(10329):1070-1078. doi: 10.1016/S0140-6736(22)00326-9. PMID: 35279259; PMCID: PMC8912929.