Now a tiger has also been caught in a zoo in the Bronx district of New York: Nadia, a four-year-old Malayan big cat, tested positive for Sars-CoV-2 in the zoo's own laboratory. First things first: she is fine, also three other tigers and three lions, all of whom have no fever, but according to the zoo with Covid – 19 – typical symptoms such as dry cough, loss of appetite and, in part, difficulty breathing were noticed.
The first question that arises: How to do a throat swab with a big cat? A protective mask is not enough, anesthesia is necessary, which is why only a tiger was tested. The second question is one that – like so many things these days – cannot be answered unambiguously: If tigers and lions can catch the new corona virus, are domestic cats also infectable? And can the lap animals possibly even spread the virus, i.e. infect people?
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Cats can be infected, ferrets also, but dogs probably not
The veterinarian and virologist Klaus Osterrieder from the Free University of Berlin wants to know more and now offers cats and dogs to get tested for the virus. “The evidence is growing that both cats and ferrets can be infected by humans,” Osterrieder told Tagesspiegel. With the offer to have his cat or dog tested, his laboratory wants to get an overview of whether the virus can affect cats and to what extent. “Our primary concern is to find out how careful veterinarians have to be when they have cats in their practice.”
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In fact, initial, preliminary studies indicate that the new coronavirus is able to penetrate into cells from animals of the Felidae group, the feline species. The gateway that the viruses use is apparently very similar in humans and cats. It is a molecule in the cell membrane, ACE-2. For this lock to the cell, the new corona virus (and also the 2002 and 2003 circulating Sars virus) apparently the right key: a sting protein (“spike”) in the virus envelope.
This is also indicated by the first, if not yet independently evaluated, experiments by a research group led by Hualan Chen and Bu Zhigao from the Harbin Veterinary Research Institute at the Chinese Academy of Sciences. Accordingly, Sars-CoV-2 can infect cats and the fairly closely related ferrets, but not dogs, pigs, chickens or ducks. However, the researchers had smeared large amounts of viruses directly into the nasal mucosa of the animals, including five cats.
Six days later, the researchers found both viral genetic material and mature, infectious viruses in the upper respiratory tract of cats – but only in ferrets and cats. When they locked three of these infected cats in cages next to not yet infected cats, however, they were only able to find virus genes in one of three later. According to the researchers, she must have been infected by droplet infection, otherwise it would have had no contact. Cats should be monitored to ensure that the animals are not a reservoir for the viruses from which humans or other animals could be infected.
Cats are infected, but probably not sick
The experiment shows even more. Because the animals were given much higher virus amounts than naturally, it is obvious that dogs should not be infectable under normal conditions. And it shows that even with such high doses of virus, cats rarely infect other species and do not become sick themselves: Because none of the infected animals showed symptoms. Osterrieder is also skeptical about the reported symptoms of zoo tigers in the Bronx as to whether they were actually triggered by the detected corona viruses. According to the media reports, the tiger was probably infected by an infected carer.
Background information on the coronavirus:
- Interactive map: All confirmed coronavirus infections by counties and Federal states
- Senate decides contact restrictions: What is still allowed in Berlin now
- Closures, hotlines, contact points: you have to know, you can get it here in Berlin Help
- Sick of the corona virus or just a cold? What you know about the symptoms
Day by day: on our interactive map you can see how the virus has spread globally
So there is every reason to believe that the viruses in the cats reproduce tolerably, but hardly enough to endanger their peers or even humans will. This is probably due to the fact that the “spike” key of the virus fits well, but not perfectly. And that perhaps other important proteins of the virus are better adapted to humans than to other animals – such as dogs.
Therefore reports from Hong Kong, where small amounts of virus genome were detected in two dogs, are ultimately misleading: Of course, sooner or later infected viruses will also be found on intimately cuddled and kissed lap dogs be – however, this alone is not proof of an infection of the animal. If Sars-CoV-2 does not get into dog cells or does not get enough of it, it cannot multiply and remains harmless to the animal.
And it is not enough either just get into the cell. The virus must also be able to hijack the cell's machinery to such an extent that it can multiply, and in as large an amount as possible. Only then can it attack other cells quickly enough – namely faster than the host's respective immune system could react – and multiply so much that a sufficiently large amount of virus can be coughed up and another individual can be infected.
Antibodies against Sars-CoV-2 in the blood of the cats are an indication that this works at least a little in cats and ferrets. “Namely neutralizing antibodies that can checkmate the virus,” says Osterrieder. These antibodies were found in domestic cats in Wuhan as well as in stray cats there.
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So if Sars-CoV-2 Can infect cat cells so strongly that even the animal's immune system becomes aware, these cats can then infect humans again – for example, if they are from a covid – 19 – Mistress nibbles at the neighbors food and pats? Osterrieder cannot rule it out with certainty either, because the data on it is still lacking, but “so far it always seems that humans have infected the cat” – not the other way around. So far, there has been no report that a human has been infected by a cat with Sars-CoV-2. Also during the Sars epidemic 2002 / 2003 such cases were not known, cats definitely did not play a role in the epidemic.
No reason to enter your own pet Risk to see
Ten swab samples from dogs and cats, sent by veterinarians in veterinary clinics and medical practices, have already been examined by Osterrieder's laboratory, coming on Monday 50 added. And since ferrets are also sometimes kept as pets, samples should also be taken here – provided that the owners agree. “We are at the very beginning.”
The fact that his laboratory is now testing cats, dogs and ferrets for the corona virus should by no means be understood as alarmism. There is no reason to see your own pet as a danger or risk of infection. “We just want to know whether cats and dogs brought to veterinary practices carry the virus.”
Pathogen detection for cats and dogs at the Institute of Virology at the Free University Berlin only by prior appointment: 030 / 838 – 51822