Researchers yesterday pointed to the Arabian camel as a possible host of the deadly human Mers virus plaguing the Middle East.
The exact origin of the virus is a riddle scientists have been working hard to solve to halt its spread, especially in the lead-up to the annual haj pilgrimage to Saudi Arabia in October.
Now an international team says blood tests are positive for antibodies in camels from Oman, meaning they were at some point infected with Middle East Respiratory Syndrome coronavirus, or a closely related virus.
The findings suggest Arabian or dromedary camels "may be one reservoir of the virus that is causing Mers in humans", said a note with a study published in The Lancet Infectious Diseases journal.
Mers has killed 46 of the 94 people confirmed infected since last September, according to the World Health Organisation.
Concerns about the virus, for which there is no vaccine, have led Saudi Arabia to restrict visas for this year's haj, which sees millions of Muslims flock to the holy sites of Mecca and Medina.
Scientists had long suspected that like its cousin virus Sars (severe acute respiratory syndrome) - which killed 774 people worldwide, including 299 in Hong Kong - Mers may originate in bats. But it is unlikely these shy, nocturnal creatures are passing the virus on to humans, and the involvement of an intermediary "reservoir" animal is suspected, with anecdotal evidence of patients having been in contact with camels or goats.
The team took blood from 50 dromedary camels from across Oman and 105 in the Canary Islands. They found Mers-like antibodies in all of the Omani camels and lower levels in 15 of those from the Canary Islands.
Yuen Kwok-yung, professor of microbiology at the University of Hong Kong, said many scientists in the city and elsewhere had guessed that the Mers coronavirus probably originated in bats but needed an intermediate host before passing to humans.
"It turns out that the camel may be one because of the high prevalence of Mers antibodies in the camels of Oman," he said.
"Though no virus can be found in these camels, it is likely that they have been exposed to Mers or a Mers-like virus. Further searches for other animal hosts are necessary to get the full picture of the disease transmission."
Dromedary camels are popular in the Middle East and North Africa, used for transport, meat and milk, as well as racing.
A respiratory virus that causes fever and pneumonia, Mers has claimed lives in Jordan, Qatar, the United Arab Emirates, Saudi Arabia, France, Germany, Italy, Britain and Tunisia. Everyone who fell ill outside the Arabian peninsula had either visited one of the Middle Eastern countries or was infected by a person thought to have come from there.
"This looks like the big break that public health workers needed in the fight against Mers," said University of Reading microbiologist Benjamin Neuman.
Additional reporting by Emily Tsang