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Covid 19 virus

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Cerebus:

--- Quote from: DrG on March 16, 2020, 04:14:23 pm ---
--- Quote from: Cerebus on March 16, 2020, 02:58:24 pm ---
--- Quote from: SiliconWizard on March 16, 2020, 12:11:04 pm ---I don't know what would differ exactly from humans as to how the virus can propagate, so I'd be interested in more details. Maybe it just doesn't infect/ and thus get through their respiratory system at all?

--- End quote ---

Firstly there's a assumption here that the animal had exactly the same strain that is infecting humans as opposed to a closely related but 'dog targetting' variant of the species.

Viruses are incredibly specific to their host species. If a host cell doesn't express some cell surface antigen that the virus needs to get into the cell, it won't. If a host cell doesn't have the right variant of some enzyme involved in manufacturing or assembling new virions then the virus won't reproduce.

The response to viruses is also highly variable within species. For most people Epstein-Barr virus causes the disease Mononucleosis/Glandular Fever, but in some people (particularly in Sino-Asian populations) it causes a type of leukaemia.

All it takes for a virus to cause/not cause disease, or be infectious/no infectious can be as little as a single gene variation in the host species.

--- End quote ---

I don't know why you would say that when we have so much well-documented viral zoonoses. Maybe I am just not understanding.

--- End quote ---

For a virus to pass from say, birds, to people it needs to be able to infect both. Sometimes this is the case, most often it is not. Sometimes it happens because a strain randomly mutates so that it would infect another species (mutation in viruses happens all the time) and encounters a new species of host at the same time. Most of the time it doesn't encounter the new species and dies out. Crossing species is the exception not the rule. Vets don't catch Parvo from dogs, vets don't get immune deficiency by catching FIV from cats.

Viral zoonoses are comparatively rare. Bacteria zoonoses are not (e.g. Psittacosis). Bacteria and viruses are worlds apart, viruses need a fully working cell that is compatible with their biochemistry to reproduce, bacteria just generally need warmth, wet and food. You can grow a bacteria on an agar plate, viruses require tissue culture in a compatible species cells. Look at all the diseases that are commonly transmitted between humans and other animals - the vast majority are bacterial or parasitic. The rare viral ones typically require very specific hosts on both sides.

Some viruses only require very evolutionarily primitive cell biology, using cell biology that is common to whole sections of the evolutionary tree. Rabies is one - it'll infect most mammals -  but it's still limited in what it can infect, you won't find a lizard with rabies.


--- Quote ---"Firstly there's a assumption here that the animal had exactly the same strain that is infecting humans as opposed to a closely related but 'dog targetting' variant of the species."

OK, take herpes B for example. There are clearly documented cases of infection to humans after exposure (scratch or bite) to macaques. Indeed, the macaque is barely symptomatic other than shedding...the human, unfortunately can develop encephalitis in a couple of days. The infected human can also infect other humans.

Same virus. same infection albeit dramatically different effects. What am I missing?

--- End quote ---

A macaque is, like you and me, a primate. There's a much smaller difference between species of primate than there is between primates and dogs.

Look at it another way. The SARS-Covid-2 virus has a genome with about 30,000 base pairs, that means (crudely) it can only code 10,000 amino acid sequences, quite a few of which are overhead. Compare that to a computer virus with 30,000 bytes assembler instructions and 10,000 actual instructions. That little genetic material has to code for the structure of the virus, how it gets into a host cell, how it gets that host cell to manufacture more virions and so on. The part that says "how to get into a cell to reproduce" has to have a mechanism for doing so, usually this is by 'recognising' a surface protein on the cell and using that to leverage the cell's active transport mechanisms to get into the interior of the cell. If that protein isn't there, or it's a slightly different shape because it's the dog variant rather than the human variant, then the virion never gets to deliver its genetic payload to the cell, so no infection happens.

Lets go back to the computer analogy. If part of that 30,000 instructions is "how to infect a computer" and the virus was targetting Windows then it would fail to infect MacOS because MacOS doesn't expose the same interfaces on the outside that Windows does. They're both x86 operating systems so they have similar mechanisms for, say, networking but the exact details of the networking interfaces of Windows that might allow a virus to get its payload through are different on MacOS and so the virus fails to 'infect' its host.

maginnovision:
https://www.news.com.au/lifestyle/health/health-problems/coronavirus-australia-queensland-researchers-find-cure-want-drug-trial/news-story/93e7656da0cff4fc4d2c5e51706accb5

Probably not a cheap solution but at least here in the US most insurers are saying they'll cover all associated treatment for the virus.

Cerebus:

--- Quote from: maginnovision on March 16, 2020, 05:39:40 pm ---https://www.news.com.au/lifestyle/health/health-problems/coronavirus-australia-queensland-researchers-find-cure-want-drug-trial/news-story/93e7656da0cff4fc4d2c5e51706accb5

Probably not a cheap solution but at least here in the US most insurers are saying they'll cover all associated treatment for the virus.

--- End quote ---

From that article:

--- Quote ---University of Queensland Centre for Clinical Research director Professor David Paterson told news.com.au today they have seen two drugs used to treat other conditions wipe out the virus in test tubes.

--- End quote ---

In vitro and in vivo are two very different things. It could easily fall at the first hurdle. Just because the drugs work in a test tube is no guarantee that they will have any effect in a real living host. The good news is that they are both active, approved drugs with known safety profiles - it would seem there is no significant barrier to going ahead with a clinical trial with extreme speed. Who knows, they may get lucky.

Oh, and the named one of the two drugs, chloroquine, is as cheap as chips (unless you're in the US where all drugs cost many more times more than they do in the rest of the world).

rgarito:

--- Quote from: edavid on March 16, 2020, 04:04:52 pm ---
--- Quote from: not1xor1 on March 16, 2020, 09:23:05 am ---
--- Quote from: SiliconWizard on March 16, 2020, 02:15:03 am ---Yeah, since big malls and amusement parks are closing, people are trying the outdoors, which is not a bad thing in itself. They'll have to try wild nature though, because typical crowded outdoors such as beaches will be temporarily banned too.

Even wild nature may be a problem soon. Does anyone know if the virus can be transmitted to any other species?

--- End quote ---

so far I read about a dog in Hong Kong that tested positive, but there is no report of pet-human transmission
BTW significant viral load was found in dogs during Ebola epidemic but they didn't find any evidence of transmission to humans

--- End quote ---

I think the most likely explanation is that dogs don't shed enough virus to cause infection.  That could be pretty hard to measure in the midst of a crisis.

Does anyone know if the PCR tests being commonly done by public health services are quantitative?  How about the antibody tests?  I've read articles that mentioned both viral load and detected/not detected results.

--- End quote ---

At least in the USA, the PCR tests are pass/fail tests.  The test basically slices and dices the sample RNA, making copies each time, matching on 3 different sample patterns found in the virus.  Each one is tagged with a dye which is then measured (after each copy iteration).  This will generate a curve of the fluorescence at a specific wavelength.  They plot this on a graph and if all 3 different dye tags cross a specific threshold within a specific # of replications, its a positive test.

Cerebus:

--- Quote from: rgarito on March 16, 2020, 05:47:34 pm ---At least in the USA, the PCR tests are pass/fail tests.  The test basically slices and dices the sample RNA, making copies each time, matching on 3 different sample patterns found in the virus.  Each one is tagged with a dye which is then measured (after each copy iteration).  This will generate a curve of the fluorescence at a specific wavelength.  They plot this on a graph and if all 3 different dye tags cross a specific threshold within a specific # of replications, its a positive test.

--- End quote ---

Or to put it in terms that most people will be familiar with it's a "DNA fingerprint" (really an RNA fingerprint). It'll tell you the virus is there, but not in what quantity. The PCR bit is Polymerase Chain Reaction and refers to amplifying the RNA found into a detectable quantity by making very many copies of it.

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