Sunday, 28 July 2013

MERS-CoV & SARS-CoV zoonoses....what about the endemic human CoVs?

Hat tip to Crawford Kilian's story...

Arab News carries a piece entitled "Unpredictable MERS ‘deadlier than SARS’" noting a comment along this line by senior author, Prof Ziad Memish, on the recent Lancet large MERS-CoV case-study. Prof Memish is also senior infectious diseases consultant at King Fahad Medical City, Professor at Alfaisal Univeristy and King Saud University, President of the Saudi Association of Public Health, Adjunct Professor at Emory University, and Ministry of Health's Assistant Deputy Minister of Health for Preventative Medicine in the Kingdom of Saudi Arabia (KSA).

What strikes me as strange is a comment from the news article...
"MERS coronavirus appears to be more deadly, with 60 percent of patients with co-existing chronic illnesses dying, compared with the one-percent toll of SARS"
In the Lancet article, Prof Memish notes that only 1-2% of fatal SARS-CoV cases had comorbidities as opposed to 60% of MERS-CoV fatal cases.

  Some things to think about here.
  1. According to a 2004 paper "SARS: the new challenge to international health and travel medicine" by Venkatesh  and Memish, published  in the Eastern Mediterranean Health journal, the severe acute respiratory syndrome (SARS) disease (caused by another coronavirus), did not enter the KSA. This means we cannot necessarily extrapolate the impact in patient populations in other parts of the world, to what would happen in the KSA if SARS-CoV infection had taken hold.
  2. The 2004 article also noted that it banned entry to KSA of pilgrims from "the 5 SARS-stricken South East Asian countries-China, Hong Kong, Taiwan, Singapore and Viet Nam". That process has not been repeated by any countries outside the KSA, which has most MERS-CoV cases, for Umrah or the Hajj. And the WHO does not support travel restrictions in their latest advisory. Another sign that MERS ain't SARS.
  3. The MERS-CoV has its highest toll in the elderly, a disproportionate effect in this relatively small percentage of the KSA's population (see demographics I described on Friday). The impact is most severe among those with underlying disease...or comorbidities...96% of MERS-CoV cases already had something affecting their health which could have adversely affected the course of their infection compared to healthy people.
So, we don't really know that SARS-CoV wouldn't have displayed the exact same pattern as the MERS-CoV in the KSA but we do know that it is a particular sliver of the population that is affected most by this new coronavirus. Most deaths (>60%) are in males and those aged >50-years.

Could this be used as a clue to the animal host/source? 
Is there something specific that the over-50s do that exposes them to risk or are the worse outcomes because this group is already more ill? 

Is this group's risk increased because they have contact with the natural host animal or areas infested by that animal? Is there any information on common social behaviours among this age/sex group in the KSA? Does this demographic sit around date palms in the evening (fruit bat "hang-outs"?)? Eat certain foods, drink particular drinks? Prepare food or drink a certain way? Do things that they won't talk about because its a taboo subject - that could be putting them at risk? Keep certain animals as pets (a secondary host-intermediate vector?). Kill or have close contact with certain animal?

When you look at MERS-CoV as a virus that mostly causes death in a specific segment of the population, the next question might be, what do the endemic human coronaviruses (HCoV) 229E, OC43, NL63 and HKU1 do to people in the same age and comorbidity-laden populations? 

Stay tuned.