Three-quarters of dromedary camels in Saudi Arabia have been infected with the virus that causes Middle East respiratory syndrome, or MERS, according to the most thorough survey of the animals there. The finding adds to mounting evidence that camels are a source of the deadly infections in humans.
In September 2012, health experts isolated the first human case of MERS coronavirus, which was discovered in Saudi Arabia and is related to the SARS virus. Since then, the World Health Organization has reported 182 cases and 79 deaths while researchers have scrambled to identify a source of the infections. So far, scientists have found signs that camels and bats harbor the virus (SN Online: 8/8/13; SN: 9/21/13, p. 18), which causes severe pneumonia in humans.
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Of more than 200 Saudi Arabian camels surveyed in 2013, researchers found that 74 percent showed signs of previous infection and around 25 percent had signs of active infections. In more than 250 archived samples of camel blood dating back to 1992, researchers found high rates of MERS exposure in every year represented, spanning from 93 to 100 percent.
Several research teams have found evidence of MERS in Middle Eastern camels over the last year. But the new study, published February 25 in mBio, confirms that the virus is common in camels in Saudi Arabia, which appears to be the epicenter of disease. The study is also the first to find signs of the virus dating back to the 1990s.
This study doesn’t prove that camels passed the virus to humans, says epidemiologist W. Ian Lipkin of Columbia University. But, he says, it shows that there doesn’t need to be another animal source. Domesticated camels and camel meat are common throughout Saudi Arabia.
Lipkin and colleagues collected blood samples and nasal and rectal swabs from camels across the country during 2013. They found that 95 percent of adult animals showed signs of past MERS infections, based on antibodies in their blood, while only 55 percent of young camels had antibodies. But, Lipkin says, the researchers found that younger camels were more likely than adults to have fragments of viral genetic material in their noses, suggesting an active infection.
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The team speculates that MERS is like the chicken pox of camels, with most animals getting the virus while they’re young and then becoming immune. But the camels don’t seem to experience symptoms, says Lipkin, making the infection hard to spot.
“Every camel I’ve ever seen has a runny nose,” Lipkin says. “It’s very difficult to tell if it’s unusually runny.”
The finding that camel blood samples from the 1990s also showed signs of MERS is quite important, says coronavirus researcher Matthew Frieman of the University of Maryland School of Medicine in Baltimore. “It shows that this virus has been in camels for longer than we expected,” he says.
Virologist Chantal Reusken of Erasmus University Medical Center in Rotterdam, Netherlands, agrees, noting that the disease could also have infected people much earlier than the first confirmed case. That theory could be tested using archived samples of blood and nasal swabs from humans, she says, which could clarify how the virus evolved and spread to people.
If future studies confirm camels as the virus’ source, Lipkin says, the next step might be to develop a vaccine for camels that could curb the virus’ spread to humans.