Their study is distinguished from similarly themed reports because it uses camel serum samples which are not as diluted. The thinking is that these may yield better indications of weaker positives.
It also differs in that it has not undertaken all the various validation steps used in many of the antibody studies I've listed below, to convince the dubious reader that positive results are not due to some other coronavirus that may be yielding a cross-reactive and thus falsely negative result.
MERS-CoV RT-PCRs were negative on extracts of serum aliquots.
The authors could not determine where or how the camels may have been exposed to infection, other than it had been prior to the beginning of sampling in 2005. 6 camels from North America ("likely" originating from Australia) were antibody-negative reinforcing the fairly localised nature of MERS-CoV's (or it's close relative) likely origin.
So far we've read of antibodies in camels that are not convincingly present in other animals including sheep, goats, chickens, cattle, horses or camels from outside Europe, America of Australia. These antibodies react with, and sometimes neutralise the infectivity of, MERS-CoV (or a very close relative). This list now includes dromedary camels from:
- Oman (retired racing camels)
- The Canary Islands (mostly born on this Spanish archipelago)
- Saudi Arabia
- Qatar (also some RT-PCR positivity indicating viral RNA)
- United Arab Emirates (Dubai; 632/651 samples antibody positive, including from 2003)
- United Arab Emirates (this report; Dubai, 9/11 older camels positive)
With this much data behind us, camels currently sit at the top of the MERS-CoV (or some other novel CoV)-positive "animals-tested-to date" list.