Wednesday 26 February 2014

Dromedary camels are a host of MERS-CoV...

Yes. Not a "MERS-CoV-like" virus or "something very closely related to but slightly different" from MERS-CoV. Camels. Are. A. Host. 

There was already plenty of evidence to suggest this (see some of my previous posts on this linked below), and none to really dissuade me from thinking otherwise. And yesterday we saw a new paper by Ian Lipkin and his collaborating crew from King Saud University in Saudi Arabia that make this issue more obvious than ever. 

So let's stop messing around. There is an elephant in the MERS-room...and its a camel! 

The Middle East respiratory syndrome coronavirus, does in fact look to be a camel virus that causes few symptoms in that host, is acquired by young camels and has been for at least 22-years, and then people somehow get infected, probably from proximity to camels or due to habits involving camels. the keeping of camels or at gatherings in which grumpy slavering camels are congregating. 

Yes, there is little evidence for any contact with camels among the 186 human cases as Dr Ziad Memish, deputy health minister of the Kingdom of Saudi Arabia (KSA) points out, but as Prof Marion Koopmans noted to NPR"few people [with MERS] have had the kind of follow-up you would want". So we take denial of any contact with a grain of salt.

There is definitely some contact however; some that is pretty solid. For example, the owner of a camel in Jeddah (4) that both tested positive for MERS-CoV or the Qatari farm camels and owner and an employee that were all MERS-CoV positive (5,7). 

And there is far less evidence against camels as a source of  some/many/most human cases and for anything else. 

So in the new paper in mBio published online 25-Feb, we read of the most comprehensive KSA camel study to date. Camels from 2013 were sampled and camel sera collected and frozen since 1992-2010 were tested and many were found to be MERS-CoV antibody positive. From the more recent dromedary camels, nasal swabs were also found to be viral RNA positive; RNA that is definitely from MERS-CoV.

Some key findings...

  • No sheep or goats were MERS-CoV antibody or RNA positive; a routine finding now. Bovine CoV antibody reactivity was identified in these animals however, and in 17% of camels
  • Antibody was detected using infected cells and also using a method that employs a specific portion of a MERS-CoV protein (part of the nucleoprotein)
  • 150/203 (74%) of camels from all over the KSA had MERS-CoV antibodies in a pattern reminiscent of any endemic human respiratory virus
    • 95% in camels older then 2-years (adults)
    • 55% in those ≤2-years (juveniles)
    • The south west had the lowest proportion of positive camels (5%)
    • Higher proportions were found in central KSA (Riyadh)
  • 3 rectal swabs were positive for MERS-CoV RNA using real-time reverse transcriptase polymerase chain reaction (RT-rtPCR). 2/3 camels were also nasal swab POS
    • 36/104 juvenile camels were nasal swab POS
    • 15/98 adult camels were POS
    • 66% of samples from the west (Taif) were POS but none from the south west
    • no RNA was detected in a sampling of camel blood/sera and so the archived samples from earlier years could not be sequenced to verify that they had MERS-CoV sequences in them
  • Amplification and sequencing of a 1,044nt portion of the Spike gene, 2,004nt ORF1ab region found that less than 1% difference from previous published MERS-CoV sequences and the nucleocapsid gene region was identical. Great to see a move away from recent reliance on complete genome sequences and a more practical and rapid subgenomic, multi-target molecular epidemiology approach used. 
    • 11/13 higher viral load samples could be amplified and sequenced
It was interesting hear the TWiV (this week in virology) podcast interview with Prof Lipkin [IL] and Assoc. Prof Thomas Briese (TB) in which they noted:

  • MERS-CoV is a "puny" virus causing little overt disease on camels [IL]
  • The MERS-CoV genome seems to be fairly stable; its not influenza virus and does not seem likely to evolve rapidly
  • Baboons[!], dogs, cats, rodents are on the list to test when the team return to KSA
  • There has been a previous report on limited human antibody levels to MERS-CoV in at least the east of the KSA
Sources and previous posts on camels and MERS-CoV...

  1. mBio paper by Alagaili and colleagues
  2. NPR's Richard Knox: excellent story
  3. CIDRAP Story
  4. Camels owner in Jeddah
  5. Two Eurosurveillance studies reporting MERS-CoV antibodies in camels
  6. MERS-CoV antibodies in 10-year old UAE camel sera
  7. More on the Qatari camels and some MERS-CoV sequencing and social media chatting
  8. MERS-CoV antibodies in camels from the Canary islands and Oman
  9. Early cautionary thoughts from the WHO
  10. Thoughts about MERS-CoV acquisition
  11. Querying whether there is a better possible source for human cases
  12. Summing up the first 100-days of (human) MERS-CoV infections
  13. MERS-CoV antibodies in camel sera dating back to 2005 in the UAE
  14. Gatherings and acquisition/transmission of MERS-CoV between animals and humans
  15. Qatari camels clear the MERS-CoV from their systems
  16. TWiV podcast

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