Taking Advantage of Viruses

Image of Flu Virus via Wikipedia

Did You Know... that we can take advantage of the high mutation rate of viruses?

The Details: I'm sure that all of you, at one point or another, have had a vaccine at some point. The basic idea of a vaccine is that it lets your immune system "see" a pathogen in a harmless way so that, if you encounter that pathogen again, your body will remember it and attack it again. If our bodies encounter a pathogen that they have never seen before, they just don't know what to do - not for a bit, at least. Remember the flu pandemic of 1918?



Now, the problem with viruses is that, because they replicate (and therefore mutate) so quickly, we can't entirely keep up with them. Take the flu: the predominant strains change every year, and we have to do year-round surveillance of which strains appear to be circulating and most likely to cause disease. Many people infected with HIV stop responding to drugs because the virus mutates so quickly* that one virus particle resistant to the drug is bound to turn up quickly; it then replicates, and makes more of itself... I'm sure you get the picture. That's why drug combination therapy is suggested for treatment: a strain that becomes resistant to one drug may make itself vulnerable to another.

*HIV can replicate to about 10^10 virions per day, and its mutation rate is about 3 x 10^-5 per cycle - that's a lot of mutations.

 Now, since viruses mutate so much, that can make strains that don't usually infect one organism all of a sudden capable of doing so. Swine H1N1, for example, usually infects swine, and infects humans very rarely.* Canine parvovirus evolved from feline panleukopenia virus - the former now no longer infects cats, only dogs. The new virus came about from two mutations that resulted in two amino acid changes in the viral capsid, which allowed the virus to attach to dog cells and infect them**.

Albert Sabin

*The pandemic of 2009 came from a new strain that appeared to be a reassortment of several different flu viruses
** Future blog post: virus entry into cells. I promise. :p

Great, so viruses mutate a lot. How can this be helpful to us?

Well, we can do something called serial passage.Basically, you incubate the virus in a host (or cell line), then infect another host with those viruses, on and on. With each passage, the virus tends to become better adapted to that host. Let's illustrate with an historical example: the live-attenuated polio vaccine, created by Albert Sabin in the 1950s. Basically, by passing the virus through non-human cells, the viruses mutated to a form that was wasn't harmful to humans, but would still induce an immune response. Cool, right?

So, why am I bringing this up?

Thanks again, Wikipedia

Well, a lab at Erasmus Medical Center in the Netherlands has managed to create a strain of H5N1 that passes easily between mammals. This is scary because humans are usually dead-end hosts if they become infected with that strain of influenza - an individual can contract the flu, but they won't pass it on to anyone else. With this newly mutated strain, a lot of people fear that a pandemic could be triggered if the virus "escapes" the lab somehow, in the pocket of a careless scientist or (potentially) a bioterrorist.

There are pros, though: first, we can now study which mutations make the virus transmissible between mammals; and second, we can now start trying to develop vaccines and antivirals against this particular strain, just in case.

I think that this is a really fascinating study, and I look forward to seeing how the response develops - especially public reaction to it.

What are your thoughts? Are we playing with fire, or lighting a match to develop an extinguisher?