Tuesday, 20 May 2014

Camels at the centre, aerosol all around...

v2 12JUN2015
A droplet (and perhaps airborne)-centric view of how the camel could be a source of sporadic human infection by MERS-CoV, a virus that is genetically very similar whether found in camels or humans.

The inner ring (orange) is more about bigger wetter droplets and aerosols-if you must differentiate on size. 

These are potential routes by which a human in contact with, or near to, camels might acquire virus from them, when those camels are actively infected. Keep this in context though- because of a number of large hospital-based outbreaks, most cases of MERS seem to have occurred by virus transmission between humans and their environments rather than from camels to humans.

Camels are not all infected all the time. This is probably why there wasn't a rash of camel herdsmen coming down with MERS after the YouTube camel-kissing outbreak...at least as far as we know there wasn't.

Camels have been found to be actively infected more often when young, but adult camels have also been found actively infected by MERS-CoV as well so there is risk of exposure to camels at any age, when they are infected.

Sometimes camels do not show signs of illness (e.g. no runny nose) but other times they do, so illness alone cannot be used as a warning sign.

There are also some data to suggest adult camels can be reinfected. This makes sense if you remember that MERS-CoV is well entrenched among camels spread over large areas of the Arabian Peninsula and Africa. The virus would disappear if there were no susceptible hosts left among the adults to maintain it in the herds between camel breeding seasons. Plus, there is nothing to physically stop a new infection anyway. That's a conversation about whether that infection leads to notable or debilitating disease or not.

The outer (Blue) ring in the picture above is more about consumption of camel products. As you can see in the inner ring, some of these activities could also generate aerosols and it is important to think about, and recognize, that avoiding consuming of camel products may still be about reducing your risk of exposure to virus that you can breathe in during the process of preparing the camel products to consume, when the camel is infected.

We don't yet have any evidence that the virus can infect after eating/drinking material contaminated with it. Or whether many camel products are contaminated with it. I tend to think that if eating/drinking were a route to acquiring MERS, then a lot more people would be infected by such a deliberate process of viral delivery. Plus. the disease almost always shows up as a respiratory tract illness with gut issues thrown in sometimes, not the other way around. And the physiology underpinning a virus being ingested, disseminating systemically and mostly showing up as pneumonia? Plus the few exported cases that have forward transmitted probably weren't consuming camel products at their destinations. Meh. Droplets. Respiratory

So we still need to find out which bits of the camel actually have virus in them. No milk testing has been done yet but nasal swabs and faeces have been positive for MERS-CoV RNA and have had infectious virus grown from them.

On cleaning this blight from the camels, I'd like to see more talk about quarantine and isolation processes now. Can camel herds be kept separated for long enough that the virus is "burned out" of each herd by limiting its ability to infect new herds? It would be a huge job but it may be a way to rid areas, countries and perhaps the Peninsula of MERS-CoV while routine animal testing can be put in place for imported camels. Just a thought. In the meantime, finding ways to perhaps do this on a small scale for the incoming pilgrims so that they could still visit with "safe" camels, might be a matter of priority.

Make no mistake, camels host this virus and they have done so for at least 20-years.

That's not the end of the story - but it's one chapter of it and it's written in stone.

Version history.

  • v2-changed some use of the term 'airborne' as my understanding of the word has mutated over the past year