Some human-to-human transmission isn't surprising in Wuhan

A couple of people have asked me lately if they should be worried about the novel Wuhan coronavirus. Which got me to thinking. Much of what we sciencey types chat about online can quickly get – or just start off as – too technical for the general public. And sometimes that may leave them with a sense that things are more worrying than we think they are. One thing that concerns folks, is how fast this emerging virus is spreading. So I put down a few thoughts which I hope are broadly understandable. If not – ask questions below.

To say that there is *no* human-to-humsn (h2h) transmission during the very early or discovery phase of an emerging disease is to use language that is too strong. It may lead to doubt in the narrator or the story because it doesn’t feel right or might develop a false sense of security.

It makes a kind of natural sense that a virus which infected a human after exposure to an animal source, would be able to infect a human if projected from a human source. It may not do that frequently but it is quite possible that it can do that under suitable circumstances.

If the virus replicates in the lower airways rather than the upper airways like a common cold virus (think of the larynx as a boundary line), it can be less easy for us to breath, cough, drip or sneeze it out for someone else to pick up. So spread is more limited. But spread is far from impossible.

As yet, we know ZERO about where in the human body this virus replicates. We also know just as little about where it might replicate within the market animal(s) it is presumed to have been in. Or in a possible reservoir animal that the virus may naturally occur in.

Routinely, when testing for respiratory viruses, we sample from the upper airways but lower airway samples are recommended by the World Health Organization for more serious cases of illness associated with the detection of this new coronavirus. And these were the types of samples that permitted Chinese researchers to first identify the novel virus.

Some have said (perhaps a little late) that we should not be surprised to see some h2h spread. That is because of those suitable circumstances I mentioned earlier. They include close contact through caring for the sick person, picking up the virus from contaminated surfaces and items in shared environments & infection after prolonged contact

These are three things which all occur among families and this is where we can see an otherwise poorly h2h transmitting virus jump between humans. And this fits in with the a suspected family-related instance of h2h transmission of the novel Wuhan coronavirus identified thus far. The same occurs with MERS (the disease) and MERS-CoV.

We can also see h2h transmission in healthcare facilities if the healthcare workers get exposed before instituting suitably protective protocols. Nurses and doctors have close and prolonged exposure to sick patients. One reason we may not have seen this in Wuhan could be a very good use of such protocols.

Infection by close contact or contact with contaminated surfaces is pretty self-explanatory. Prolonged exposure may occur through repeated exposure to small doses of a virus such that our immune system cannot contain the virus and an infection takes hold, becoming ill.

So should you be worried if you live somewhere other than Wuhan and visit a market containing live or freshly killed animals of all shapes and sizes or their component parts? Not at this stage based on the info we have to hand.

That isn’t a lot of info though and things may change.

What we know is that the virus isn’t causing widespread pneumonia. What little h2h transmission there has been, is not continuous. Could the virus be causing milder respiratory illnesses? It doesn’t seem like it is based on observations of the 760 contacts in Wuhan, China. 187 of them have already been released from quarantine without showing any symptoms for two weeks. That’s good news.

It seems like something delivered the virus to human airways probably from animals at the Huanan seafood (and other animals) market. That animal may be at one more other markets but remains unfound. The recently reported case in a traveller from Wuhan who arrived in Thailand had not visited the Huanan seafood market. This suggests the suspected animal source may have been sold at more than one market. There seems to be limited h2h transmission, even associated with close contact so the other option, h2h transmission in the community, seems less likely.

So now we wait for more information. That info will take time to get together. So more patience is required. But to be clear, China has put these findings together and reported on them in record time. Faster than I think most other countries would have.

Hits: 966

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.