Signs are increasing that camels are involved in spreading a deadly new virus that surfaced in the Middle East last year. The World Health Organization (WHO) announced today that researchers had detected Middle East respiratory syndrome (MERS) coronavirus in a herd of camels in Qatar linked to two recent human cases. "This is a very important piece of the puzzle," says Mike Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota, Twin Cities. So far, the virus has sickened 160 people and killed 68.

The finding was part of an investigation into two patients from Qatar who both contracted MERS but survived. Qatari officials took samples from the environment and numerous animals at the farm where the two worked. Researchers in the Netherlands detected MERS coronavirus RNA in nose swabs from three of the 14 camels tested. The scientists confirmed the result by sequencing a fragment of the virus. "Based on the length of the sequence we are absolutely certain that this is MERS," says Marion Koopmans, chief of virology at the National Institute for Public Health and the Environment in the Netherlands, who was involved in the work.

Scientists suspect bats as the ultimate source of the new virus, but human interactions with bats are limited so another animal species may act as a bridge. In August, Koopmans and other scientists reported that they had found antibodies against MERS coronavirus in 50 out of 50 camels from Oman. They also tested sheep, goats, and cows but found no antibodies. Whether the camels really were infected with MERS remained unclear, however. Earlier this month, Saudi officials announced that a camel owned by a MERS patient had tested positive for MERS as well but they have not presented any sequence data to date.

The result from the Qatari camels does not prove that the virus is transmitted from camels to humans. Infected humans could also have transmitted it to the camels, and other animals may also be involved. "We have to be careful about assuming that this is just in camels," Osterholm says. "If camels can be infected then it's very likely that other domestic animals can be infected as well." Virologist Ab Osterhaus, who was involved in the work, confirmed to ScienceInsider that other animals including pigeons, chickens, and sheep were being tested as well, but did not want to discuss preliminary findings. Researchers were also trying to piece together the whole viral sequence found in the camel samples, he said.

Even if they succeed and the link to camels is confirmed, many questions about the outbreak remain open. It is not clear, for instance, how many of the observed cases are linked to human-to-human transmissions and how many were animal-to-human. Osterholm also points out that many mild cases in humans may be being missed. Saudi Arabia has been looking for the virus only in patients in intensive care, he says. "That is like the drunk looking for his lost keys only under the street light because that is where there is light."

Osterholm praises Qatar for its efforts. "The public health officials in Qatar deserve a great deal of credit for their aggressive actions in investigating this situation and involving the relevant international laboratory partners," he says. "This could have been done in Saudi Arabia months ago."