A new research suggests that dromedary camels could be responsible for passing to humans the deadly MERS coronavirus that emerged last year.
Tests have shown the MERS (Middle East Respiratory Syndrome) virus, or one that is very closely related, has been circulating in the animals, offering a potential route for the spread.
The study is published in the journal Lancet Infectious Diseases.
But the scientists say more research is needed to confirm the findings.
The MERS coronavirus first emerged in the Middle East last year. So far, there have been 94 confirmed cases and 46 deaths.
While there has been evidence of the virus spreading between humans, most cases are thought to have been caused by contact with an animal. But until now, scientists have struggled to work out which one.
To investigate, an international team looked at blood samples taken from livestock animals, including camels, sheep, goats and cows, from a number of different countries.
Dromedary camels could be responsible for passing to humans the deadly MERS coronavirus
They tested them for antibodies – the proteins produced to fight infections – which can remain in the blood long after a virus has gone.
Professor Marion Koopmans, from the National Institute of Public Health and the Environment and Erasmus University in The Netherlands, said: “We did find antibodies that we think are specific for the MERS coronavirus or a virus that looks very similar to the MERS coronavirus in dromedary camels.”
The team found low levels of antibodies in 15 out of 105 camels from the Canary Islands and high levels in each of the 50 camels tested in Oman, suggesting the virus was circulating more recently.
“Antibodies point to exposure at some time in the life of those animals,” Prof. Marion Koopmans explained.
No human cases of the MERS virus have been reported in Oman or the Canary Islands, and the researchers say they now need to test more widely to see if the infection is present elsewhere.
This would include taking samples from camels in Saudi Arabia, the country where the virus is the most prevalent.
Prof. Marion Koopmans said: “It is a smoking gun, but it is not definitive proof.”
Health officials say confirming where the virus comes from is important, but then understanding how humans get infected is a priority.
Gregory Hartl, from the World Health Organization, said: “Only if we know what actions and interactions by humans lead to infection, can we work to prevent these infections.”
Data suggests that it is not yet infectious enough to pose a global threat and is still at a stage where its spread could be halted.
The new Middle East Respiratory Syndrome (MERS) virus, which has killed half of those infected, is “unlikely” to reach the same scale as SARS, ministers in Saudi Arabia say.
Most of the 90 MERS cases reported so far have been in Saudi Arabia.
MERS is from the same group of viruses as the common cold and SARS, which killed 774 people.
However, a detailed analysis of the Saudi cases, published in Lancet Infectious Diseases, did warn of “major gaps” in understanding of the virus.
The MERS coronavirus emerged in 2012 and has infected 90 people worldwide, 45 of them have died.
MERS is from the same group of viruses as the common cold and SARS, which killed 774 people
The global concern is that cases could spread much further, echoing the SARS outbreak.
Cases have been centered on the Middle East – with patients in Jordan, Qatar, Saudi Arabia and the United Arab Emirates. Additional cases in France, Germany, Italy, Tunisia and the UK have all been linked to travel to the Middle East.
Researchers in Saudi Arabia have published details of the 47 cases reported in the country.
They suggest a pattern of mostly older men being infected. Most cases were also in people with other medical problems, more than two-thirds of the reported cases also had diabetes.
The lead researcher and Deputy Minister for Public Health, Prof. Ziad Memish, said: “Despite sharing some clinical similarities with SARS, there are also some important differences.
“In contrast to SARS, which was much more infectious especially in healthcare settings and affected the healthier and the younger age group, MERS appears to be more deadly, with 60% of patients with co-existing chronic illnesses dying, compared with the 1% toll of SARS.
“Although this high mortality rate with MERS is probably spurious due to the fact that we are only picking up severe cases and missing a significant number of milder or asymptomatic cases.
“So far there is little to indicate that MERS will follow a similar path to SARS.”
However, the latest Saudi investigation both highlighted the need to find where the virus was coming from.
Prof. Ziad Memish’s report said: “Reducing the rate of introduction of MERS coronavirus into human beings is unpredictable because the source of the virus is not yet known.
“We are searching vigorously for the source.”
According to the World Health Organization (WHO), it appears likely that the new coronavirus (NCoV) can be passed between people in close contact.
This comes after the French health ministry confirmed a second man had contracted the virus in a possible case of human-to-human transmission.
Two more people in Saudi Arabia are also reported to have died from the virus, according to health officials.
NCoV is known to cause pneumonia and sometimes kidney failure.
WHO officials have expressed concern over the clusters of cases of the new coronavirus strain and the potential for it to spread.
Since 2012, there have been 33 confirmed cases across Europe and the Middle East, with 18 deaths, according to a recent WHO update.
Cases have been detected in Saudi Arabia and Jordan and have spread to Germany, the UK and France.
“Of most concern… is the fact that the different clusters seen in multiple countries increasingly support the hypothesis that when there is close contact this novel coronavirus can transmit from person to person,” the WHO said on Sunday.
French health ministry confirmed a second man contracted the new coronavirus in a possible case of human-to-human transmission
“This pattern of person-to-person transmission has remained limited to some small clusters and so far, there is no evidence to suggest the virus has the capacity to sustain generalized transmission in communities,” the statement adds.
France’s second confirmed case was a 50-year-old man who had shared a hospital room in Valenciennes, northern France, with a 65-year-old who fell ill with the virus after returning from Dubai.
“Positive results [for the virus] have been confirmed for both patients,” the French health ministry said, adding that both men were being treated in isolation wards.
Meanwhile, the Saudi deputy minister of health said on Sunday that two more people had died from the coronavirus, bringing the number of fatalities to nine in the al-Ahsa governorate in the east of Saudi Arabia, Reuters news agency reports.
WHO officials have not yet confirmed the latest deaths.
In February, a patient died in a hospital in Birmingham, England, after three members of the same family became infected.
It is thought a family member had picked up the virus while travelling to the Middle East and Pakistan.
Novel coronavirus is from the same family of viruses as the one that caused an outbreak of Severe Acute Respiratory Syndrome (SARS) that emerged in Asia in 2003.
However, NCoV and SARS are distinct from each other, the WHO said in its statement on Sunday.
Coronavirus is known to cause respiratory infections in both humans and animals.
But it is not yet clear whether it is a mutation of an existing virus or an infection in animals that has made the jump to humans.