( CNN ) -- Evidence is mounting against camels as leading suspects in a deadly mystery that 's claimed more than 100 lives in the Middle East . The biological supervillain is the virus causing MERS-coV , short for Middle East Respiratory Syndrome , a type of coronavirus . Since the first documented cases in spring 2012 , MERS has sickened at least 339 people in Saudi Arabia alone and killed nearly a third of them , according to the country 's Ministry of Health . A recent surge in reported cases -- including 26 new ones this past weekend -- has fanned concern the outbreak might be shifting into a more dangerous phase . With any newly recognized virus , disease detectives start with a few key questions . What kind of illness does it cause ? How is it spread ? And where does it come from ? With regard to that last question , a new paper leaves little doubt that at least one answer is camels . Researchers from Columbia University , King Saud University and the New York-based EcoHealth Alliance managed to isolate live MERS virus from two single-humped camels , known as dromedaries . Should I be concerned about new virus ? A genetic analysis found numerous substrains in the camel viruses , including one that perfectly matches a substrain isolated from a human patient . The findings are published in mBio , the open-access journal of the American Society for Microbiology . The attention on camels is n't new ; in February , the same group published a finding that nearly three-quarters of camels in Saudi Arabia tested positive for past exposure to the MERS coronavirus . The new paper still leaves many questions unanswered : For example , what other animals might harbor the virus ? Could it be bats , as some have suggested ? `` There might be another animal , but we do n't know , '' says Dr. Ian Lipkin , who organized the research as director of the Center for Infection and Immunity at Columbia 's Mailman School of Public Health . `` We need more in terms of surveillance . '' Does the virus make camels sick ? Researchers do n't know , says Peter Daszak , another study author and president of the EcoHealth Alliance , which researches links between animal health and human disease . Perhaps most urgent : Has something recently changed to make MERS-coV more dangerous ? Here , some of the evidence is reassuring . Any avid mystery reader knows that a watchdog who does n't bark can be an important clue . With MERS , there is a lack of alarm bells from the laboratory ; so far there is no evidence that the virus is changing to attack people more aggressively or to spread more easily . There is n't enough evidence to draw a firm conclusion , says Dr. Mark Denison , a leading expert on coronaviruses and a professor of pediatrics at Vanderbilt University . It also remains to be seen whether humans are being infected by more than one of the substrains found in camels . `` There 's a lot more work that would need to be done '' to prove it , he says . Those who study MERS-coV says it 's crucial to pin down just how the virus is transmitted . `` We need to know what people are most at risk , '' Daszak says . `` We do n't know if they 're involved in camel racing , camel breeding , camel slaughter -- that 's really critical right now . '' Lipkin says the virus likely spreads in a variety of ways , but he 'd like to see more aggressive steps taken to prevent the possibility of people being infected by eating camel meat or drinking raw , unpasteurized camel milk -- both of which are common in Saudi Arabia . He says the Saudis will face special concerns again this fall when millions descend on the holy cities of Mecca and Medina for the Hajj pilgrimage . As part of the ritual , animals are sacrificed , and their meat shipped all over the world to help feed the hungry . Saudis : More deaths from respiratory syndrome . `` The butchery will begin in three or four months ' time , and we have to have measures in place to ensure that the animals are n't infected , '' Lipkin says . For example , he says , officials could decide to forbid the slaughter of young camels for food since younger animals are more likely to carry the MERS virus . Dr. David Swerdlow , who heads the team responsible for tracking MERS at the U.S. Centers for Disease Control and Prevention , says the Saudi government took steps to discourage the spread of the virus during last year 's Hajj , including posting warnings to discourage people older than 65 , pregnant women or those who were immune-compromised from making the pilgrimage . Health authorities have not yet decided what steps to take this year , Swerdlow says , but the United States is watching the situation closely . `` Any time you have an emerging infection that has a high case fatality rate , that 's been around for over a year , that has caused illness in multiple countries , that 's caused illness in travelers and health care workers , and for which there is no treatment or vaccine , we 're concerned . We 've been concerned for a year and a half , and we remain concerned . ''
The MERS coronavirus has sickened more than 500 people in Saudi Arabia . Twenty - two new cases were reported last year . Researchers have found the live virus in camels .