August 9, 2013
Camels Discovered To Carry MERS Coronavirus Antibodies
Lawrence LeBlond for redOrbit.com - Your Universe Online
As MERS Coronavirus continues to unleash its wrath in the Middle East, so far sickening 94 people and killing 46, researchers have struggled to find a source of infection. Once tying the SARS-like infections to pipistrelle bats, which carry a similar strain of the coronavirus, researchers now believe dromedary (one-humped) camels may be to blame.
A team of researchers, led by Chantal Reusken of the National Institute for Public Health and the Environment (RIVM) in The Netherlands, tested blood samples from a range of domestic animals including goats, sheep and cattle to find a more plausible source of infection. The reason bats were inevitably given a clear light was due to the animal's shy and nocturnal nature. With the new blood tests, the team was still not finding the answers they were looking for, that is, until they took samples from camels.
The vast majority of the MERS coronavirus cases have occurred and remained in the Middle East, with only a few cases of un-sustained human-to-human transmission within and beyond the country's borders. With this knowledge in hand, it was easy to assume that the path had led to some particular animal source. Researchers first surmised camels could be a source of infection back in May, but it was not until the study team conducted blood tests that a clear identification was made, at least initially.
In the preliminary study, published Friday in the journal Lancet Infectious Disease, the European team of scientists found traces of antibodies against MERS in dromedary camels, but not the virus itself. The antibodies make it clear that the camels did at one time have MERS or a similar virus and were able to fight off the infection.
"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," explained senior study author Prof Marion Koopmans, of RIVM and Erasmus University, to the BBC’s Rebecca Morrelle.
Although this is a significant discovery, the researchers note that more research is needed to confirm the findings.
In the study, the team found low levels of antibodies in 15 of 105 camels tested from the Canary Islands and high levels in each of 50 camels tested in Oman. This evidence suggests the virus has been circulating very recently in at least the Oman area.
"Antibodies point to exposure at some time in the life of those animals," Prof Koopmans explained.
However, no human cases of MERS have been reported in either Oman or the Canary Islands. The researchers said more testing is needed in other areas to see if the virus is present in other camel populations, especially those in Saudi Arabia where the bulk of infections have been reported.
"Finding the (MERS) virus is like finding a needle in a haystack, but finding the antibodies at least gives you an indication of where to look," Koopmans told Maria Cheng of The Associated Press (AP). "What this tells us is that there's something circulating in camels that looks darned similar to MERS."
Koopmans expects blood tests in other camel populations will show similar results.
"We can't say this proves camels are a reservoir for MERS but it does show there is something going on with camels that may be relevant for people," Koopmans noted.
Because camels are widely used and relied on in the Middle East, such as for their milk or for racing, it would make sense that MERS in humans is stemming from these even-toed ungulates (hooved animals).
MERS is part of the coronavirus family that can cause the common cold. The virus is very similar to the SARS virus that sparked a global outbreak in 2003, killing more than 770 people, and sickening thousands more. Saudi Arabian health officials just this week reported that seven new cases of MERS have been found in health workers.
While scientists believe that some animal is the definitive source of human infections, some speculate pipistrelle bats could still be the primary source. It is possible that the flying mammals passed infection on to other mammals before making a transition to human infection. MERS can cause fever, cough, breathing problems, pneumonia and kidney failure. Currently there is no known treatment or cure.
Some experts think more testing on other animal populations is needed before a clear winner is deduced.
"Camels may be involved in (MERS) transmission but there could also be cows, goats, or something else involved," Vincent Munster, a virologist at the National Institutes of Health, who co-wrote an accompanying commentary, told AP.
There are now tests being conducted on camel populations in the Middle East, as well as dates – which some experts believe are being infected by bat droppings before being consumed by people.
The camel findings are an “important development,” according to the WHO, despite many infected patients not having any contact with animals prior to diagnosis.
"There must be some other step somewhere that results in human infections," WHO spokesman Gregory Hartl told AP, adding that it is still unclear what kind of animal contact is needed for MERS to take hold in humans.
"Even if we know where the virus is, we don't know exactly how it's jumping into humans," Hartl said. "This is another piece of the puzzle, but there are still a lot of holes that need to be filled in."
As for the Oman camels, the scientists believe the MERS virus may have varied slightly, making it more transmissible between camels there. Or perhaps, they note, camels in the Canaries may have been kept in circumstances that prevented camel transmission on a widespread scale. They do believe it is possible that one of the three oldest Canary Island camels may have carried the virus when it arrived from Morocco more than 18 years ago.
"We cannot rule out that the population might have once had an outbreak but that by the time of sampling, antibody titres had waned and no new introductions of the virus had occurred," the researchers wrote, as cited by The Guardian’s Sarah Boseley. "The camels have contact with wild rodents, pigeons, and other doves, and possibly also bats. Seven insectivorous bat species, including three pipistrellus [species], are native to the Canary Islands, while Egyptian fruit bats (Rousettus aegyptiacus) have been introduced."
Boseley reports that the MERS infection may have arrived in the Middle East from African imported camels, where bats carrying a virus similar to MERS are found.
"In the Middle East, huge numbers of camels are imported from Africa to meet the demand for meat," wrote the researchers. "The top five camel breeding countries are all African, and Saudi Arabia and United Arab Emirates are in the top five camel-meat producing countries."
While this is also an important find, Munster, also of NIAID Rocky Mountain Laboratories in Montana, pointed out to Boseley that there had not been any reports of camels falling ill as a result of this or any other virus.
"This fact begs the question of whether the detection of MERS-CoV neutralizing antibodies in camels from both Spain and Oman is a result of unrelated cross-species transmission events or whether the virus has been circulating in camels for a long time. Regardless, a change in the ecology of MERS-CoV must have occurred to enable emergence in people," said Munster.
He remarked that it is very likely that the virus or some change in the environment or in agricultural practices enabled the virus to make the transition from animal to human. Whichever the case, there remains an "urgent need for an integrated, one health approach by public and veterinary health stakeholders in all involved countries, combined with the rapid dissemination of data," he added.
Health experts say confirming where this virus comes from is an important step in finding a treatment, cure and possible vaccine for MERS.
Data on this virus has suggested that it is not yet infectious enough to become a global health threat. Luckily, most experts concur, the virus is currently in a stage where researchers can still find and halt the disease from spreading, potentially preventing a worldwide pandemic.