More GOOFing
"On reading," by Simon Wain-Hobson, is a weekly discussion of scientific papers and news articles around gain of function research in virology.
Since January 2024, Dr. Wain-Hobson has written weekly essays for Biosafety Now discussing risky research in virology. You can read his entire series here.
Canine distemper virus (CDV) infection is often fatal with a mortality rate of 50% in adult dogs and 80% in puppies. Increased susceptibility to distemper in juveniles results in more wildlife cases in the spring and summer when babies are being born. However, there are cases all the year round. It is a respiratory infection with transmission occurring mainly through sneezing, coughing, or barking.
CDV can infect a number of other species. It killed approximately 20% of giant pandas and can infect Japanese macaques. That said it is widely considered not infect humans. There is just a single report of a man getting the infection. At such a low level, this could reflect some underlying immune system defect.
There is a dog vaccine for CDV and the American Animal Hospital Association considers it a core vaccine and recommended for all dogs regardless of geographical location.
CDV belongs to the measles group of viruses. Indeed, some consider that it was derived from measles virus introduced into South America dogs by European settlers. The virus went its own way and CDV today is clearly distinct from measles. To get into the cell CDV uses a protein on the dog cell surface called CD150. Measles virus uses the human lookalike.
The authors of this paper consider that When the goal of measles eradication may be achieved, and when measles vaccination will be stopped, CDV might eventually cross the species barrier to humans and emerge as a new human pathogen.
First, vaccine coverage is far from adequate even in advanced economies with regular outbreaks, in part due to vaccine hesitancy and anti-vax propaganda. In Africa two dose coverage is barely 50%. Accordingly, such post-measles scenario is currently science fiction and way down the line.
Second, where is the data supporting the idea that a niche might open following measles eradication? The last case of smallpox was described in 1976 and nothing moved to take its place. Yes, the recent monkeypox outbreak is worrying but huge swaths of world’s population have been immunologically naïve to smallpox for decades. This niche hypothesis is flimsy at best.
In order to get an impression how fast such alterations may occur, alterations being mutations in the virus allowing it to grow on human cells, they infected a human cell line expressing the human CD150 protein with CDV. In as little as three successive virus amplifications (passages), they recovered a mutant that grew well. Indeed, It is astonishing how quickly the adaptation occurred (3 passages), although we started from a cloned recombinant virus with a defined sequence…
The second and equally big surprise was that a single mutation in the hemagglutinin, or H protein, accounted for this adaptation. This makes intrinsic sense to the virologist as H recognizes and sticks to the target cell allowing the virus getting inside the cell.
Three passages and a single mutation, hmm.
What can be said about the experiment? The strain of CDV used has been around for ages and is well adapted to growth on canine cells under lab conditions. It’s not what we call a primary isolate, one that has undergone little manipulation in the lab. The cell line used has been around for years and like so many cell lines, it is anything but ‘normal’. That said, this is very much par for the course for much of virology. They could have tested this human adapted CDV on human tissue, to be sure that their result was physiologically meaningful, but they didn’t. Like many in virology.
We find ourselves in a more unsatisfying situation vis-Ã -vis the avian H5N1 flu work where the virus transmission was at least tested in an animal model. Prudence and precaution indicate we should regard this CDV-derivative as a novel human pathogen. What is its potential?
Measles virus kills around 0.1% of those infected in developed nations to up to 8% in some contexts, like refugee camps. As mentioned above CDV kills over 50% of animals. Obviously, we cannot know what this human adapted virus would do if it ever infected Sapiens. Even if it was on a par with Spanish flu, only 2% of those infected would succumb. Spanish flu was mightily feared and is the Big One in terms of past human pandemics.
Once again, nobody has the slightest idea as to how lethal the virus would be if it got out. Sure, there may be a little protection for those who have been vaccinated against measles yet remember half of Africa is not vaccinated. More than a billion people might be susceptible. The cynic may note, once again, that the poor will be shafted.
The paper has been highly cited; indeed, Google Scholar shows 101 citations which is very respectable. Nearly all of them use the paper in the context of papers and review articles about viruses jumping species. None comment on the fact that, suddenly, there is a new human virus among us, sitting in a freezer and lurking on the cloud.
Why was it done? No doubt because it was an easy experiment to do, although the outcome could not have been foreseen. Perhaps it was done out of simple curiosity and with the result in hand the paper was written backwards with the hollow justification that CDV might move to fill the measles virus niche once eradicated.
No thought was given to the DURC dimensions of this work, which is not on the radar of most virologists anyway, something that showed up in a previous essay (Virus Research of Concern). Most virologists are unaware of the dangers while few seem to care. That said, some element of awareness is to be found at the end of the paper, Taken together, there is obviously no high hurdle for CDV to adapt and utilize human entry receptors. However, in spite of this swift adaptation, these data should not lead to the misunderstanding that other human target cells or humans will be infected so easily.
Even so, nothing is mentioned about the biosafety containment level used for this experiment which is less reassuring. BSL-2 safety levels are required for work on CDV which is understandable as CDV doesn’t infect humans. For measles virus BSL-2 labs are required. On reading imagines it was performed in a BSL-2 lab.
Takeaways
• For years the NIH was focused on select agents, aka the starting point of a GOF/DURC experiment as the key criterion. This example shows that it is the endpoint, not the starting point of the experiment that matters. Accordingly, during the review process when deciding whether an experiment runs the risk of being classified as GOF/DURC, possible or probable end points must be borne in mind. If the intent, aim if you prefer a milder word, of the researchers is to adapt any microbe to growth on human cells then the proposal should be flagged.
• That a single mutation can morph an agent that is of no danger to man into a bona fide human virus. It shows how easy it is for a DURC situation to arise. ALSO, the astute lay science observer, may remark that this mutation will be present in any stock of CDV. Correct. All the more surprising that CDV spillovers to humans has numbered but one case. This mutation has not been documented before.
• That the authors didn’t seem too concerned by what they had done for they didn’t even report the BSL status under which the experiment was performed.
• On reading’s opinion is that experiments like this are so easy to perform, you wouldn’t write a grant proposal, you’d do it and see what happens. It would go under the grant review radar until submitted for publication. This emphasizes the need for microbiologists to be far more aware of the DURC dimensions of their work. They are the front line, the eyes and the ears of society as the police say. Yet as we saw in a previous essay (Virus Research of Concern), most are oblivious to the other dimension of their work – malevolent exploitation of their findings. In short, they need help.
• As researchers tend to overestimate the benefits of their work and underestimate the hazards, they are part of the risk. It’s an old conundrum, experts being part of the problem yet charged with finding the solution.
Virology is so broad that precise rules, which have the merit of being clear, will not cover every possibility. We need to adopt a general rule that any attempts to adapt any microbe to growth on human cells or mammals that imply human adaptation, such as the ferret for aerosol transmission of bird flu viruses, must be flagged up before being undertaken. Concerns must be shared up front and the pros and cons articulated and discussed with others. Faits accomplis are no longer acceptable.
Aside 1
Others have performed analogous experiments around the same time.
Aside 2
For completeness, a novel measles-like virus from Jamaican fruit bats was reported in 2023 and found to grow well on human cells in the lab. Although it’s another virus to keep tabs on the authors are of the opinion that We conclude that although zoonotic spillover into humans may theoretically be plausible, MBaMV replication would likely be controlled by the human immune system.
Complex, which is why discussion is needed to find ways of understanding what is out there and how this research can be done.
