Tuesday 12 November 2013

Camel cough, coronavirus caught? [UPDATED]

Are camels the main source of human infection
by the Middles East respiratory syndrome
coronavirus (MERS-CoV)?
I awoke to find the world has learned of a camel that tested positive using a Middle East respiratory syndrome coronavirus PCR. According to the Kingdom of Saudi Arabia's Ministry of Health announcement (on the Arabic language and not English language page), the camel was owned by by a recent case (43M from Jeddah, reported on 7th of Nov- FluTracker's #156) and was showing signs of disease. The fact that it was ill may suggest it was the source, but we don't yet know which illness came first, the camel or the man. We do know (from CIDRAP/WHO) that 43M became ill on Oct-27 and has been in hopsital since Nov-3.

This is in line with recent studies finding antibodies to a MERS-CoV-like virus. I've previously reported on that here and here.

The PCR positive has not yet been genotyped (had its DNA sequence determined, and by inference, any of its RNA genome - a way of measuring the similarity, or not, to known "human" MERS-CoV). That work is ongoing. Hopefully we won't have to wait until the entire genome is achieved as that can be a lengthy process.

For the record, if you are relying on Google translate, the Arabic for beauty (jamaal, الجمال)  is derived from the Arabic word for camel - so read "beauty" as meaning camel (h/t Mike Coston).

I found it interesting that 43M was a healthy adult and yet he was ill enough to require intensive care. He wasn't old and had no underlying comorbidities. Does this hint towards his acquisition of MERS-CoV being from an animal source rather than a secondary human exposure? The latter often seems to result in milder disease or asymptomatic detection (mostly based on contacts of known cases). It's as if passage to another healthy human is via a smaller dose (reduced viral load after growth in 1st human?) or is the virus changed by growth in a human rendering it less capable of severe disease (perhaps seen as less "foreign" by our immune system?)?

A model of possible MERS-CoV acquisition. Is the camel the
central player or a secondary host?
The KSA Ministry of Agriculture is helping to try and grow the virus. MERS-CoV is certainly culturable - and with a positive camel at hand, getting fresh samples should yield results quickly.

Its great to hear about this in real time. No waiting on the publication process. 43M was only reported 5-days ago (my time; not sure when he became symptomatic of course). Well done KSA MOH!

We don't need to find every camel to be MERS-CoV-positive
for them to be a likely source of infections. We know that cases have been sporadic and widespread and that genetically, a number of different introductions of MERS-CoV have occurred into the Arabian peninsula's human population.

Could this finding be used in a quick retrospective analysis? Among otherwise healthy MERS-CoV-positive humans, does evidence of contact with camels more often link to severe disease outcomes than if there has definitely been no contact at all? The corollary then is that milder disease results when acquisition is via a human-to-human route among the otherwise healthy. Keeping in mind a quote from Dr. House, M.D. "I don't ask why patients lie, I just assume they all do." Patients may not always want to own up to something, for whatever reason.

Some questions that remain from this finding:

  • Which diagnostic PCR was used? Presumably the well-validated version suggested by the WHO. We don't yet know if this assay cross reacts with any as-yet-unknown-but-very-closely-related CoVs such as one that may reside in camels. My bet is that it doesn't.
  • Is it MERS-CoV or a camel cousin to that virus?
  • Does this virus, MERS-CoV or very close relative, actually cause disease in camels? It's possible that 43M's ill camel was symptomatic due to another viral or bacterial infection.
  • Did the camel transmit virus to the human or did the human transmit the virus to the camel?
  • If acquired via camel-to-human (seems most likely), how did 43M acquire the infection from the camel? Airborne drops or aerosols, faecal-oral, scratch/broken skin, direct contact with secretions...?
  • Where did the camel get its infection from? Another camel (enzootic within the camel population?) or from a primary host or other secondary vector (bat, baboon...whatever?)
References for further reading
  1. PCR assay for MERS-CoV.
  2. KSA MOH report on camel MERS-CoV-assay. positive
  3. 43M report by KSA MOH.
  4. Helen Branswell's article.
  5. BBC health news article.
  6. MERS-CoV can grow in cell culture.
  7. Mike Coston's Avian FluDiary Post.http://afludiary.blogspot.com.au/2013/11/ksa-mers-investigationtesting-beast-not.html
  8. MERS-CoV-like antibodies in Omani and Spanish camels.
  9. Most MERS cases may not have met a camel.
  10. CIDRAP on camel case and WHO update.

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