By Julie Steenhuysen
CHICAGO (Reuters) - Fewer than half of Saudi Arabian patients in a study passed the Middle East Respiratory Syndrome virus to household members, and many of those who developed secondary infections contracted mild cases of MERS, global researchers reported on Wednesday.
The study, published in the New England Journal of Medicine, confirmed observations that the virus can cause mild disease, but overall transmission rates are low.
"If less than half of infected patients transmit the virus to contacts, such as in this study, we can be pretty sure that this virus will not be able to start an epidemic in humans," co-author Christian Drosten of the Institute of Virology at the University of Bonn Medical Center said in an email.
MERS, thought to originate in camels, causes coughing, fever and pneumonia, and kills about a third of its victims.
The study confirms that the virus is extremely lethal, "suggesting that up to 30 percent of first-generation cases will die," Drosten said.
Understanding how Middle East Respiratory Syndrome (MERS) is transmitted has been a quest for doctors trying to quell the outbreak that emerged in the Middle East in 2012 and has infected more than 850 people and killed 333 worldwide.
The paper was co-written by Ziad Memish, former deputy health minister of Saudi Arabia, who was sacked over his handling of the outbreak.
Based on the findings, Drosten said, the focus of research should be on containing animal-to-human transmission, perhaps by vaccinating dromedary camels.
The study involved testing 280 family members and close contacts of 26 MERS patients. The researchers used sensitive diagnostic tests to detect silent or mild infections. They identified 12 probable cases, suggesting a secondary transmission rate of about 4 percent.
"These viruses can cause serious human-to-human transmission chains, but they don´t in normal situations such as household contacts as investigated here," said Drosten. He noted that human-to-human transmission did occur in a hospital in Jeddah, where hospital workers likely transmitted the infection to patients.
Dr Amesh Adalja, an infectious disease expert at the University of Pittsburgh Medical Center, said the study makes clear that mild MERS infections "do occur and make control a little more difficult" because people with silent infections can harbor the virus and transmit it to others.
There are no drugs to treat MERS and no vaccines capable of preventing it. The virus is closely related to Severe Acute Respiratory Syndrome or SARS, which killed around 800 people worldwide after it appeared in China in 2002.
(Reporting by Julie Steenhuysen; editing by Sharon Begley and David Gregorio)