Wednesday, 29 January 2014

A date with Middle East respiratory syndrome coronavirus (MERS-CoV)..

Click on image to enlarge.
Do regions that host transient high concentrations
of MERS-CoV (or a related virus)-positive animals play a
key role in the sporadic and geographically widespread
human infections?
This article in the Saudi Gazette was referred to me by a kindly commenter to a recent MERS-CoV post I wrote 24-Jan here.

It notes that August (through to December - see Ref #5 below for a lot of info on dates) is the date-harvesting season. When I received this comment, new MERS-CoV case announcements had ceased; a lull which, as I also wrote on the 24-Jan, I could not understand given that there had been no publicized steps to interrupt any type of transmission chain. 

Now we are seeing some publicized cases again, but it's clearly out of sync with date picking season. Nonetheless, I thought it might be worth looking at regional activities that may gather potential animal sources/vectors and humans, together , possibly addressing links in my disease acquisition scheme above; in particular links between dates, bats, camels and humans. No baboons this time around (I'm expecting a Tweet).


Click on image to enlarge.
Buraidah is located slightly north of 
central Saudi Arabia.
Buraidah (Buraydah) hosts the world's largest date festival in August/September and the Qassim date markets are a feature of the region as is agricultural in general.

Buraidah (population >600,000) is the well connected capital of Qassim Region (see map to the left). Qassim region is described as having plentiful water and, clearly, lots of palm trees as well as other fruit trees and wheat. 

Something else Buraidah has going for it? The world's largest camel market. Those are the beauties that seem to frequently have antibodies to the MERS-CoV (or a very similar virus that probably isn't any known coronavirus but reacts really specifically in MERS-CoV antibody-detection assays designed to detect the MERS-CoV but mainly in animals localized to the Arabian peninsula where most human MERS-CoV cases have been documented). Antibodies indicate past (about 1-2 weeks or more usually) exposure to replicating virus, with or without overt signs of disease in the host.

Recently there was also the the "Palm and Tree Date Festival" in Riyadh (15-16 Jan) and the "King Abdulaziz Award for Camels Beauty Contest" (26-Nov to 4-Jan) in Hafar Al-Batin.

I've made brief mention of the possibility of dates having a role in transmission (ingestion, self-inoculation or perhaps aerosolizing virus off bat-contaminated dates during their preparation?) previously here and here.

While this is all speculative, these latter events coincide a little with a small uptick in noted, and "social media suggested", MERS-CoV human cases.

So here's a speculative story:
  • A nexus point, like Buraidah, with its central, well-connected location (transportation-wise) serves or once served as an "inoculation station" for susceptible camels exposed to infected bats
  • Bats may be more reproductively active or in greater numbers because of higher concentrations of flowering insect-attracting date palms and other fruiting orchards in this region/at certain overlapping times (not actually sure if there is overlap)
  • Camels are brought in, sold and then return to herds all over the region. 
  • During their time in the markets, some camels become infected with the bat MERS-CoV and go on to infect their herd
  • Rarely, humans in close contact with their camels also get infected (it does happen - Ref#7) 
  • Rarely, some infected humans infect other humans
  • Rarely/frequently (unknown proportion) infected humans become severely ill and "show up" as hospitalized cases who get tested for MERS-CoV. 
As I said, twice, its all speculative and as also I've said, infection events are pretty rare. If nothing else, that bulleted list may address the geographically widespread and rare nature of human case distribution to date.

End of speculation. For now.

Sources..
  1. Saudi Gazette story
    http://www.saudigazette.com.sa/index.cfm?method=home.regcon&contentid=20130819177328
  2. Date markets
    http://www.youtube.com/watch?v=QJDBDmziikY
  3. Tourist information
    http://sauditourism.sa/en/About/Pages/k-Cities.aspx
  4. Events and festivals
    http://sauditourism.sa/en/Events/Pages/default.aspx
  5. 2012 Al-Rasub article on date festival
    http://www.alrasub.com/ksa-qassim-hosts-worlds-largest-date-market/
  6. Many, many date details
    http://postharvest.ucdavis.edu/files/71533.pdf
  7. Clinical course and outcomes of critically ill patients with Middle East respiratory syndrome coronvirus infection
    http://annals.org/article.aspx?articleid=1817260