The novel coronavirus originating from the Middle East has now been re-named MERS-CoV (Middle Eastern Respiratory Syndrome-Coronavirus). A better name may have been Middle Eastern Respiratory Disease Entity, or MERDE-CoV. This acronym may more accurately reflect the trouble we would be in if this virus were to take hold. However for whatever reason, the powers that be have stayed away from this definition. I cannot think why…
All the correspondence I am getting in my mailbox regarding H7N9 and MERS-CoV is very much pertaining to the former, making me worry that the MERS-CoV is being somewhat neglected. My personal opinion is that H7N9 is going to disappear from our conciousness in the next few months. The graphs suggest that the prevalence of H7N9 is now declining significantly. However I hope that the legacy of H7N9 will be that it puts an end once and for all to the “live bird markets” and the risks that they carry.
MERS-CoV is a different proposition altogether. Far from disappearing, it seems to be cropping up in clusters in various places. Click here for the latest CDC updates on this virus. It has a very high mortality rate, and has clear evidence of human to human transmission. The one saving grace is that it has now been around for several months so propagation throughout populations at the moment seems to be sluggish.
I would urge that people start to switch their attention somewhat from H7N9 (without completely ignoring it) and start to really focus on this MERS-CoV, both on a local and international scale. This virus might just have the potential to create a genuine global health problem. Time will tell….
H7N9 Influenza seems to have settled somewhat for the time being…..(famous last words)
Novel CoronaVirus (NCoV) infection is continuing to cause problems with recent evidence of human to human spread. Click here for an update. See below for a bit about how coronavirus replicates.
These emerging infections made me ask myself a couple of questions. Why are they usually viruses and why do they sometimes just go away as quickly as they came…?
Almost all emerging viruses come from an animal (zoonotic) reservoir (for H7N9 this is birds and for NCoV probably bats). Mutations (NCoV) or genetic reassortments (H7N9) will occasionally produce a virus that is capable of jumping the species barrier from animal to human. The new “human” virus has no natural immunity so is often very pathogenic (H7N9 and NCoV), but is not used to jumping from human to human so transmissability is often low (H7N9 and NCoV), particularly in the early stages.
This is not always the case however. In contrast the H1N1 2009 pandemic managed to produce a virus that was of low pathogenicity but of high transmissability (the random odds of genetic reassortment…).
When the virus first starts replicating in humans it then undergoes a period of adaptation to it’s new host, with further selection of mutant strains etc. This is a very difficult period to predict exactly how the virus is going to change and how its behaviour will be affected. Both H7N9 and NCoV are probably still in this phase so it is a bit of a guessing game as to the eventual role of these viruses in the human host (hence the need for very close surveillance). In some cases the virus simply decides it doesn’t much like humans as a host and disappears.
So why is it viruses and not usually bacteria that cause emergent diseases?
I don’t know if I really know the answer to this one, but I suspect the solution lies in the relative complexity of bacteria compared to viruses. Because viruses are genetically more simple micro-organisms a single mutation or genetic reassortment is more likely to have a more dramatic effect on behaviour with the potential of creating a change that is able to facilitate that species jump. On an evolutionary timescale, bacteria are probably a bit lazier, finding a comfortable niche within a certain species and reluctant to go anywhere on the basis of spontaneous mutations alone.
It’s a complex area, and one I would not claim to have any degree of expertise in. However I do think that it is important for us as microbiologists to have at least a basic understanding of the different factors at play. It also makes following the progress of NCoV and H7N9 just that little bit more interesting…
I have been keeping half an eye on the current situation with the H7N9 avian influenza strain currently infecting humans in Eastern China. For more details on this click here.
The current Outbreak made me ask myself two questions:
- If the 1919-20 pandemic Influenza strain (Spanish Flu) emerged in today’s world, would it have the same devastating impact that it had back in 1919?
- Is there a chance we could have in the future a pandemic of equal (or greater) severity as the Spanish Flu?
My personal answers to these questions are No and Yes respectively.
The world has changed a lot since 1919. In 1919 there was massive displacement of population following WW1, there was great poverty and there were no antibiotics to deal with post influenza bacterial pneumonia. Nor was there any Influenza vaccines. For these reasons I don’t think the 1919 pandemic strain would have had nearly the same impact today.
But yes, I do think we could potentially have another pandemic as severe as 1919. It would just take a more pathogenic Influenza virus to do this, and we know that antigenic shift and mixing of Influenza strains from different species certainly have the potential of creating very pathogenic viruses. Fortunately most of these strains turn out to have low transmissability between humans.
We have had at least four recognised Influenza pandemics in the past century (Spanish Flu 1919-20, Asian Flu 1957-58, Hong Kong Flu 1968-69, Swine Flu 2009-10). The next one will not be a matter of “If”, but “When”. Fortunately the 2009 H1N1 Influenza pandemic, although very transmissable, was no more pathogenic than the usual seasonal strains.
None of us particularly enjoy putting in a lot of work to plan for something which may or may not happen during our working lifetimes. But this is what needs to happen. I am not saying it is easy either. To try and draft a policy to prepare for an Influenza pandemic of totally unpredictable size and severity is one of the hardest things I have had to do as a microbiologist. Some might say that drafting such a policy is close to impossible. But we need to try, in an attempt to at least reduce the inevitable panic that ensues….
Even though the “Swine Flu” pandemic was relatively mild in pandemic terms, hopefully we will use this recent experience to hone our policies for when the next pandemic strikes.