In early July, scientists at the National Institute of Health in Maryland, USA, discovered a stash of vials containing the deadly (and thankfully all but extinct) disease smallpox. They had been sitting, forgotten in a storage room since the 1950s. So, if the smallpox in the vial was infected with another microbe, could the mix result in a new infectious disease?
Thankfully, the short answer is no. Viruses change in two main ways. The first way is mutation. It sounds like the stuff of an X-Men movie, but mutations happen all the time – although they cause change relatively slowly. The second way is called “recombination”. This occurs when two separate, but related, viruses infect the same cell. During the process of multiplying within the host, the genetic coding from both viruses can get mixed together, making a new virus. This wouldn’t necessarily make it a “superbug”, but it could give it new abilities. It may mean that people who were previously immune are now vulnerable, or the virus could become more contagious.
To multiply and spread, most viruses hijack the infected person’s cells’ own replication machinery inside the cell nucleus. Smallpox works a little bit differently – it has its own copying apparatus and so can replicate outside the nucleus. (Even so, it still needs to infect a cell – but just doesn’t need to burrow into the central nucleus of the cell.) The upshot is that just mixing two viruses in a test tube, away from any living cells, won’t produce anything new. Without something to infect, a virus can do nothing. Therefore smallpox virus would have to get out into the world and start infecting people before it would have any chance of combining with other viruses. Even then, recombination is unlikely because the smallpox would have to infect somebody at the same time as another virus similar enough to recombine with it.
Fortunately, there’s not much chance of the virus escaping out into the wide world, as the Centers for Disease Control and Prevention (CDC) pledged to destroy the sample once they’ve run a few tests. That still leaves samples of smallpox in two labs: one at CDC HQ in Atlanta and one in Moscow. Debate continues over whether to destroy these final two samples, potentially making smallpox extinct once and for all, or continue using them for research, with the risk of the virus breaking free and sweeping through the world once again.
Answer by Simon Makin. Question sent via Twitter: If smallpox in that vial was infected with another microbe could it mutate […] in 50 years?
Footnote: Interestingly, the tool that was instrumental in eradicating smallpox was a virus of the same poxvirus family, vaccinia. This has the same “antigen” (the part that triggers an immune response) as smallpox, but it’s a fairly minor infection, so it could be used as a “live” vaccine, conferring immunity to smallpox without doing much harm. Researchers are still using vaccinia today, by using recombination to create vaccines with the antigens of the virus the vaccine is made for, but which cause mild infections. It’s also being used in gene therapy, but that’s a story for another day…
Image credit: Vincent Racaniello on flickr