The study used a very specific piece of the MERS-CoV Spike (S) protein. S is the bit of a CoV that sticks out and gives it the characteristic crown-like appearance under electron microscopy. The small piece of S acts as bait to detect the antibodies in serum samples and this interaction is identified by a fluorescent signal in the protein microarray system they used.
These antibodies were found in the sera of 50 of 50 retired racing dromedary camels from Oman and from 1 in 7 Spanish (14 of 105) dromedary camels from the Canary islands.
No antibodies were found in 80 cattle, 40 sheep, 40 goats or 34 other camelids.
The antibodies retained an ability to stop MERS-CoV infection in test that diluted the sera between 1:320-1:2560 for the Omani camels, and 1:20-1:320 for the Spanish camels
Camels also had some signs of antibody reactivity to bovine coronavirus (BCoV), but the authors, after additional testing, concluded that the MERS-CoV reactivity was specific to that virus and not to BCoV. Sera from 2 human cases of infection by with the BCoV relative (both betacoronaviruses), HC0V-OC43, did not stop MERS-CoV from infecting cells - infection was not neutralized by the patient's HCoV-OC43 antibodies.
Camels were implicated earlier during the outbreak, in the death from MERS-CoV (then the "novel coronavirus" or nCoV) of a 73-year old male from Abu Dhabi, capital of the United Arab Emirates.
"The patient owned racing camels. One of them got ill and was very weak; the patient was in close contact with that camel, and on the evening the camel got very sick, the patient developed flu-like symptoms. Three days later, he was in a medical unit in Abu Dhabi. There is another family member who also had close contact with the camel; he also got ill, but we could not follow up with that gentleman."
So this article points a finger at camels as some sort of host, possibly as an intermediate host between Pipistrellus spp and Rousettus aegypticus bats and humans. Perhaps the MERS-CoV story is akin to the Hendra virus story - bats contaminate horses and from there, close contact with horses can, on occasion result in disease in humans.
At the very least - there may be other animals involved yet and we still don't have viral RNA or a viral isolate from within a camel - we now have a specific animal contact to track and trace for each human case. Perhaps specific risk avoidance measures can also be implemented, and the hotzones can communicate to their populations that close, perhaps any, contact with camels carries with it some risk of MERS-CoV infection especially to be if you are in a category that places you at higher risk of severe outcomes from a MERS-CoV infection-older male, underlying conditions.
Housing camels away from bats and areas known to be bat flyovers or frequented by feeding or birthing bats, or keeping camels under cover may all be helpful reduce transmission of the virus between these animals.
Jennifer Yang and Helen Branswell have breakdowns of this story as well.