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Could you create a system that continually filters viral particles out of a patient's blood like in the following diagram?

Corona virus particles are 100nm to 160nm, while the smallest blood cells are 2 to 3 microns. So they could be separated by an appropriate sized filter.

Reasonably high doses of UVC at 250nm will deactivate viruses.

Alternatively, or in combination, a second filter this time 50nm could be used to remove the virus particles from the flow.

Then the blood cells and the sterilized portion of the flow could be recombined and put back into the patient in a continuous flow.

Is this system viable, and could it help treat viral diseases like COVID-19? Cheers!

Cannula Outflow
       |
0.5 micron Osmosis
       |          \
Blood Cells   Viral Particles 
       |           |
       |      UVC 250nm Irradiation
       |          /
Recombination of Parts
       |
Cannula Inflow

Edit: There's a company called Aethlon Medical looking into this with their Hemopurifer device. They used a special filter in a dialysis machine to treat ebola successfully. Here's their statement on applying the technology to COVID-19. See answers for more context.

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    What tissue does the virus that causes covid19 live in? Apr 7 '20 at 14:40
  • I think it mostly reproduces in lung cells, but I was assuming it would be getting aroud in, and generally present in the blood stream. Maybe not? Apr 7 '20 at 14:56
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    Have you seen the swabs they use for testing? It's a pain to do and easy to screw up. If it was common in the blood it could be a simple blood draw. I know everyone is excited to try to engineer a cure but it's probably worth studying a bit more about the biology of a virus before wondering if you've come across something scientists haven't thought of. Apr 7 '20 at 15:02
  • Asking questions is a part of learning. Discouraging that is the opposite of the purpose of this site. Do you know the blood concentrations of the virus? Do you know the distribution of the virus in the body? If you do, maybe you could put them in an answer. Thanks for your advice. Apr 7 '20 at 15:12
  • @tobuslieven Bryan isn't discouraging questions. He's encouraging prior research, which we require here. You did some research on the size of the virus as compared to human cells, but you didn't ask yourself the question that he asked you. I recommend that you pursue that angle and add your findings to your question.
    – Carey Gregory
    Apr 7 '20 at 15:20
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The only viral diseases for which I found this method mentioned (in the popular pres) has been Ebola (in 2014), and that's an experimental treatment.

The device, called the Hemopurifier, was attached to the dialysis machine that was already filtering the patient’s blood. The specially designed filter is made of a protein that acts as glue for proteins found on the Ebola virus’s surface. Over a period of 6.5 hours, the filter extracted the virus from the blood that flows through. While most dialysis filters can pull out molecules that are less than 4 nanometers in diameter, the virus filter boasts a mesh that’s able to filter out larger viral particles that are less than 250 nanometers. That means only the virus is pulled out, and the immune cells remain in the blood, ready to fight off any remaining viral invaders.

“We had no [idea] about how much [virus] would be extracted, because this was the first patient, but I was very surprised because the drop in viral load was deeper than I expected,” says Geiger. Before the filtration began, the patient’s virus count was about 400,000 per mL blood. After the session it had dropped to 1,000 copies/mL. [...]

Freed from that viral burden, the patient soon began to improve rapidly. His own immune system began fighting off the remaining virus, and he no longer needs dialysis or a ventilator. The patient is walking and waiting to be released from the hospital.

Geiger stresses that it’s not clear yet whether the Hemopurifier alone was responsible for the patient’s recovery, since he was given other experimental therapies, but the amount of virus removed from his body and his rapid recovery after the filtration suggests that it at least played a role in helping him survive his infection.

While puling viruses out of infected individuals has never been tried before, Geiger believes it will be an important strategy for treating not just Ebola but other vial infections as well, including HIV, hepatitis and even influenza. “It’s a very interesting concept. The big advantage is that the plasma is filtered, and only the virus is removed and the other plasma components like immune cells go back to the patient. That’s important because with viral infections, the patient is in a reduced immune situation.”

The inventors mention influenza as a possible target too, but frankly I suspect that was way optimistic.

A search in pubmed for "Hemopurifier" only finds 3 articles (and the 2001 hit is a name coincidence for an unrelated device), none of which are even about Ebola (never mind influenza), but there is (a 2009) one about hepatitis C. You can look through the (37) Google Scholar citations of that 2009 paper for subsequent research.

(The 2nd real hit in pubmed for "Hemopurifier" was a more cited 2012 article on exosome removal in cancer patients. Unfortunately, most of the citations for the 2009 hep-C paper seem to also be about exosome removal...) There is one 2014 review about Ebola though that mentions the Hemopurifier as follows:

Recent discoveries have led to the development of specific extracorporeal sorbent techniques to reduce viral particle concentrations in blood. The application of a specific device called ‘Hemopurifier' has been advocated to reduce viral load in several acute viral infections [8]. Blood is circulated through a hollow fiber plasma filter that has a specific sorbent matrix stuffed in the compartment external to hollow fibers. Due to the fluid mechanics inside the device, plasma is produced from whole blood in the proximal part of the fibers and it is forced to flow through the sorbent bed. In the distal part of the device, plasma reenters the hollow fibers by a backfiltration mechanism. No plasma loss occurs since plasma never leaves the device (the plasma ports are left capped). According to the company's specifications (Aethlon Medical Inc., San Diego Calif., USA), the sorbent is highly specific for glycoproteins (GP) that viral envelopes. Viral particles are thereby captured and their concentration in blood is significantly reduced [9]. This process, called ‘Lectin Affinity Plasmapheresis', is based on the concept of affinity chromatography developed in the 1970s [10]. A unique lectin protein (Galanthus nivalis agglutinin, GNA) from Galanthus nivalis (the common snowdrop) has a high affinity to the mannose-rich GP that ubiquitously populate the surface of enveloped viruses [11,12] to inter alia mediate entry into host cells. This device has been used either alone or in series with a hemodialyzer and has displayed encouraging results both in vitro and in vivo on hepatitis C and HIV infected blood. Assuming a delicate equilibrium between the viral load and the immunological system, the eradication of a viral infection may be realized only by tipping the balance in favor of the innate immune response by lowering the circulating viral particle concentration in blood.

Unlike the Hemopurifier's invetors' own claims, this review doesn't mention respiratory viruses as a likely (useful) target. (It only mentioned Ebola, Hep C, and HIV.)

I found the (2015) scientific publication on the Eblola experiment now too; it mainly uses the generic name of the method "Lectin Affinity Plasmapheresis" (LAP), although Hemopurifier is mentioned in there. This paper is not indexed by pubmed; I think it's because it's a conference rather than a journal paper.

There's a more recent (2018) paper testing LAP (in vitro) on MERS, which is indexed in pubmed though. The fact that most of these papers appear in rather niche methods publications like the Blood Purif. journal should tell you something though.

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  • Wow, that is fascinating. It seems like a really impressive result against Ebola. 400,000 down to 1,000. I'm really surprised it hasn't had more widespread mention. Do you think the results are credible? Sorry for not quite getting it, but what does it mean that the papers are in niche method publications? Does that discredit them somewhat? Thanks for the awesome answer by the way. Faith restored. Apr 7 '20 at 21:19
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    @tobuslieven: it means that there don't seem to be randomized clinical trials (RCTs) going with these. In vitro research and case reports won't get this into an FDA approved treatment method for anything--except in extreme circumstances "compassionate use". (European agencies have similar treatment-approval standards.)
    – Fizz
    Apr 7 '20 at 21:23
  • That's weird. Find a cure for Ebola, and then not develop it. I don't get it. Still, interesting. Apr 7 '20 at 21:39
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Because viruses often infect a specific cell type, and the viral particles may not be common in the blood, filtering of the blood might not be an effective way to prevent the spread of a virus inside a patient.

Table 3 of this paper on the original outbreak of COVID-19 reports that 15% of patients had RNAaemia, which is their term for finding indications of the virus' RNA in the bloodstream. But that presence doesn't seem to correlate with prognosis. I.e. 15% of those patients who died tested positive for RNAaemia, and 14% of the patients who survived also tested positive for RNAaemia.

So maybe removing the virus from the bloodstream wouldn't make much difference anyway.

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  • This is exactly the kind of prior research we look for. You could have added the info from the paper to your question and had a pretty good question (you still could). I know you think we're being unreasonable, but you'll find that virtually all the science and academic sites have the same prior research requirement. Even stackoverflow does in that they require questions to demonstrate prior effort at solving programming problems.
    – Carey Gregory
    Apr 7 '20 at 17:25
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    This is an answer. Not something that should be added to the question. I have spent literally days researching this topic. But I am not an academic, and cannot spend my whole life researching before I dare to ask a question. This site is for all of us, and we should not be shamed for asking a question, least of all by academics. Help by contributing an answer if you can. If you cannot, or do not want to, then do not. We do not need further contributions that do not answer the question. Thank you. Apr 7 '20 at 17:35
  • +1 but I think you could have found the same answer for viral respiratory illnesses in general. Or SARS. I.e. it wasn't probable that Covid-19 would be all that different in this respect (blood infection).
    – Fizz
    Apr 7 '20 at 18:10
  • @Fizz I've never heard of even a blood borne virus being treated by filtering blood. I expect there are reasons, but I don't know what they are. HIV springs to mind as one that it might help with? Maybe the HIV virions are so quick at getting into the T cells that the viruses don't spend enough time in the blood for blood filtering to work. I think it's an interesting question though. Apr 7 '20 at 20:06
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    @tobuslieven: see my answer below for that.
    – Fizz
    Apr 7 '20 at 20:10

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