Monday 19 October 2015

Can MERS-CoV be found in the upper and lower respiratory tract of infected camels? You bet your single hump it can!

Today's review is of a paper listed as published in Emerging Infectious Diseases in July 2015, authored by Khalafalla and colleagues from King Faisal University in the Kingdom of Saudi Arabia and from the CDC in the United States of America.[1]

Al Omran City (also Al Umran) city is located 
just adjacent to Al Hofuf on this map.
The introduction tells us that bats "seem to be the reservoir host" but are not the likely ongoing source of human Middle East respiratory syndrome (MERS) cases in the KSA. An assumption based on the finding of 1 small yet diagnostic MERS-CoV sequence in 1 bat from 1,003 samples, once.[5,6] It also reminds us that up to this point in time, camels were mostly sampled from the nose and eye during MERS-CoV investigations. We still didn't know whether other parts of the camel respiratory tract could test positive for MERS coronavirus (MERS-CoV). This is important knowledge as it pertains to virus transmission from camel-to-camel and camel-to-human.

This study focused on the dromedary camel (DC; Camelus dromedarius) collected samples
from around the Al-Ahsa area. These comprised two sample populations collected during a year (April 2013-May 2014):
  1. Tissue from at least lung lobe of camels slaughtered at the Al Omran Abattoir, Al Omran City. Animals were kept in groups of 10-15 for up to 4 days in stock markets prior to slaughter
    ..8 batches of samples were collected (a batch every 1-2 months) from 91 carcasses in total
    ..28 young animals (<4 years of age) and 63 adult animals (4 or more years old) were sampled
  2. Over the same period, age-matched nasal swab samples were collected from Al Omran abattoir, Al Ahsa livestock market and the King Faisal University veterinary hospital
    ..96 animals were swabbed; 36 young animals and 60 adults
    ..only 2/94 animals were visibly unwell - the 2 had nasal and lacrimal discharge
Samples were tested by a pancoronavirus conventional RT-PCR assay [4] as well as two real-time RT-PCR assays [2,3] No culture of virus was attempted so we must extrapolate from the RT-PCR findings to assume a positive finding of MERS-CoV RNA represents replicating virus-at some point during the infection anyway (a safe assumption).

The findings...
  • 84 of 187 DCs (44.9%) tested positive, most often during the cooler months (NOV2013-JAN2014) and more often from young camels than adults
  • 59 of 91 (61.5%) DC carcasses had MERS-CoV RNA detected
  • 28 of 86 (29.2%) nasal swabs were positive
  • 4 samples yielded a spike gene sequence-these differed from each other but clustered with other human and camel MERS-CoV spike gene sequence
The authors are clearly not exuberant that their findings have shed much new light on the camel>human debate and call for longitudinal studies to better understand how MERS-CoV spreads among DCs. A good suggestion indeed. 

Nonetheless, this study adds pieces to the story; DCs appear to be infected throughout their respiratory tract, not just at the openings usually swabbed. And if the seasonality of MERS-CoV in DCs hinted at by this study at this locale, does not overlap perfectly with human cases at the same time and place, that is most likely because camel>human infections are very rare. Also this mismatch is likely because most human infections are not due to camel/human interactions, but are acquired from human-to-human infections, thanks to errors in the management of a sick index case. That case's uncontrolled infection is what usually results in many other patients, healthcare workers and visitors becoming infected. 

That's the camel in the room that seems to be overlooked so frequently. 

Another thing that seem lost in translation - MERS itself is a relatively rare human disease and when you consider that camel>human transmission is only a fraction of that.... 

Some seem to think that lots of infected camels must equate to lots of infected humans if this crazy theory about camels being the source of human cases is to be believed. Sorry. Not the case (unless reported contacts are much more frequent than we are being told). 

There are definitely human MERS-CoV infections who only had DC, not infected human, exposures. Unarguably we do need to do better to try and catch transmission 'in the act' and show how it happened in order to dot the 'i' and cross the 't'. The same also applies to a lot of zoonoses. Until those breakthroughs though - we have a lot of data which can be used to better protect people from getting infected by MERS-CoV. 

Seems pretty dumb to wait on more convenient data while people still get infected, become sick and often die.
On balance, separating camels from humans, being better protected when in contact with camels, and improving infection prevention and control in hospitals may even obviate the need for vaccination. Gasp.

  1. MERS-CoV in Upper Respiratory Tract and Lungs of Dromedary Camels, Saudi Arabia, 2013–2014Abdelmalik I. Khalafalla, Xiaoyan Lu, Abdullah I.A. Al-Mubarak, Abdul Hafeed S. Dalab, Khalid A.S. Al-Busadah, and Dean D. Erdman

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