[melaniejs (OP)]

Andy is concerned about the rapid spread of the virus in Italy, despite the lockdown measures and wonders:

Is there some environmental or animal vector causing the continued spread? Direct contact with wildlife seems unlikely, so possibly domestic pets are involved?

Anyone have any idea?

[RD]

Demographics is a factor. In Italy a greater proportion of the population are elderly than in the UK ...

In 2017 29.4% of the population of Italy was over 60 years old ...
In 2017 25.3% of the population of United Kingdom was over 60 years old ...

https://en.wikipedia.org/wiki/Ageing_of_Europe

The virus kills disproportionately more elderly people ...

According to figures from the Chinese Centers for Disease Control and Prevention, those aged 10-39 have a 0.2% mortality rate, while those in their 60s have a mortality rate of 3.6%. For those aged 80 and older this rises to almost 15%.

https://www.theguardian.com/world/2020/mar/13/how-many-will-die-of-coronavirus-in-the-uk-a-closer-look-at-the-numbers


The high-frequency of cheek-kissing isn't going to help ...

[4ndy]

I am Andy and it was me that raised the question on the NS website.

I accept that the explanations offered are valid points and explain variations in infection rate and outcomes. However I don’t think they explain the still exponential increase in cases despite a police enforced lockdown.

Media footage shows entirely empty streets (apart from dog walkers). NS Dr Chris Smith has spoken several times about how Covid-19 is an animal virus and it should be no surprise that it has already been detected in a tested dog. So I think there is still something in the hypothesis.

Has anyone else got an explanation?

[chris]

Hello Andy; thanks for the question and thanks for joining in here.

The Covid-19 coronavirus is what we call a zoonotic infection - it's a virus that has jumped the species barrier from animals into humans.

Based on reading the genetic code of the virus, it appears to be a bat coronavirus that also contains some sequences from a pangolin coronavirus. Thus it appears to be a hybrid of two viruses. The components from the pangolin grant the virus its access to human cells by enabling it to bind onto a molecule called ACE2 present on certain types of cells in the human body.

At the moment, we are comfortable that there is no animal reservoir for this (other than from the initial animal source), because it has not circulated before.

The question of whether it can infect - and begin to spread among - other animals species is an open one that is currently being investigated. It's an important issue to address because it has implications for the likely future spread and dynamics of the outbreak.

There is presently one case report, to my knowledge, that documents a pet dog testing positive for the virus following the diagnosis being made in the owner. The dog remained test-positive over a period of days, although the amount of virus detected, we are told, was low and it's not clear if that constitutes an infectious dose.

Therefore, at this time, we do not regard pets as either at risk or a risk. This may change as we gather more data.

[evan_au]

animal vector causing the continued spread?

This outbreak was unusual in that the Chinese scientists published the RNA code of the virus almost as soon as the Chinese government was prepared to admit that the virus existed.

Since then, the virus genome has been decoded and published many times - first in China, and then in other countries as it started to appear there, too.

Just like ancestry.com* can help you build a family tree from your genes, scientists have been able to build a family tree for this new coronavirus.
- Every time the virus infects a new person, it has a few small mutations compared to the previous person - but it also has all the mutations of the previous patient.
- Genetic statisticians can tell "this person was infected with the virus that came from that earlier patient"
- They can only afford to sequence a small fraction of infected people, but it is still enough to draw a family tree
- And even estimate how long ago was the common ancestor of the virus in 2 different people.
- This has left them to conclude that there was a single jump from animals into humans, around mid-November 2019, in Wuhan China
- And IIRC, the outbreak in Washington state USA was caused by a single individual who arrived in January 2020, and infected many people before the first cases were recognized by the hospital system
- In contrast, the outbreak in Milan Italy was caused by a number of people bringing the virus to that city

It is true that the original animal host of the virus still exists in the wild - perhaps Chinese horseshoe bats.
- But these bats don't have a big geographic range - they won't transmit it around the world
- And bringing together 3 quite different species in close proximity only happens rarely - which is why these jumps from species to species are relatively rare
- New zoonotic diseases are increasingly likely as habitat destruction continues unabated

So I'm afraid that there was only 1 jump of this particular virus into humans; the rest of it we have done to ourselves!

*Other DNA testing providers are available...

[evan_au]

possibly domestic pets are involved?

To have the exponential growth we have observed, the virus needs to be passed from person to person.

Each new person gets infected by one or a couple of virus particles, but they produce trillions of virus particles, amplifying the amount of virus in the community.

The typical indoor or backyard pet would interact with no other pets directly.
- A cat has its own territory, which it marks with scent, and defends from other cats in their neighbourhood. Outside mating season, cats don't interact much with other cats.
- Some responsible dog-owners take their dogs to the dog park, where they interact with a number of other dogs. But there are an equal number of humans interacting.

The human(s) in these same households will typically interact with perhaps 100 other people on a typical day, whether on public transport, work, school, shopping, the gym, etc. If you work at a supermarket checkout, you may interact more directly with even more people.
- When you include the contacts of these 100 people (and then their contacts), you can see where the idea came from that you are separated from any other person in your country by just "6 degrees of separation".
- So the virus is able to spread quite rapidly through human-to-human contact, and not very possible through pet-to-pet contact.
- It is more likely that an infected pet owner will shed trillions of virus particles, some of which will land on their dog, without actually infecting the dog.

In fact, rather than infecting 100 other people, a typical infected person infects perhaps 2 to 3 other people. This means that a country like the UK (current population 66 million) rather than 6 degrees of separation for people you know, it is more like 26 degrees of separation for this virus.
- If you become infectious after 7 days, that means it could reach everyone in the UK in 6 months.
- Unless social distancing is applied vigorously, in which case it might take a year or so to reach pretty much everyone in the UK.
- Hopefully, by then we might have a vaccine?

See: https://en.wikipedia.org/wiki/Six_degrees_of_separation

[Bored chemist]

"Does the Covid-19 coronavirus have an animal reservoir or vector?"
Yes, and unfortunately the animal concerned invented air travel and cities.

[4ndy]

I would like to revisit my original question in light of reports, from the BBC and other respected news sources, that a tiger has tested positive at Bronx zoo. Other tigers are apparently showing symptoms, with the source suspected to be the zookeeper.

At least here in the UK cats, (though not social to other cats), tend to be very sociable to multiple households and it is easy to see how domestic cats would be able to carry an infection from one household to another. This would undermine the most draconian lockdown.

I have no knowledge of differences in cat ownership in say north Italy versus say South Korea and
I realise that there are a few intellectual jumps here, but I wonder if this changes people’s thoughts. This could have great significance in fighting the pandemic.

[chris]

Hi @4ndy - you raise a tremendously important point and one that many of us have been worrying about for a little while.

If dogs and cats can catch this - and are infectious when they do - they could constitute an important reservoir of infection. Moreover, they could be efficient vectors, transmitting infection to other animals and other owners!

This is definitely a serious area for study; we need to establish the route of infection in the animals (e.g. aerosol, or faecal oral), incubation periods and duration of infectivity, and likelihood of transmission to other animals and also humans.

[4ndy]

Thank you for the reply @chris . I have no scientific background, but I can see the enormous potential repercussions of having such a reservoir or vector in our pet population, or indeed in the agricultural or wildlife populations.

You mentioned ongoing research and I have no idea how that is progressing, but if there is any concern, shouldn’t we be taking some precautionary measures in the mean time? Maybe keeping pets indoors as a minimum?

This should ideally be in a directive from the Government of course, but I fear that they are selective in the experts they choose to listen to and may need to be forced to confront this. The Potential human loss is too great to ignore this risk.

I am aware of what happened with the 5g conspiracy, and would not like to be responsible for alarm or panic. 

[4ndy]

Article by Victoria Gill just posted on BBC website.

Not allowed to post link but president on British Veterinary Association advises keep cats indoors to prevent coronavirus infection.

Suggest you search in Science and Environment section for article unless mods can post link for me.