A man wearing a mask looks on as he stands in front of camels at a camel market in the village of al-Thamama near Riyadh May 11, 2014. Saudi Arabia said people handling camels should wear masks and gloves to prevent spreading Middle East Respiratory Syndrome (MERS), (Faisal Al Nasser/Reuters)

A DISEASE outbreak has a source and a pathway for transmission, but both can be exceedingly difficult to discover. Middle East respiratory syndrome, or MERS, is surging anew in Saudi Arabia and raising familiar questions: Where is this coronavirus coming from and how is it spreading?

There is growing evidence that the natural reservoir of MERS, which first appeared in 2012, is dromedary camels, and last year’s peak in the spring seemed to coincide with the weaning period of camel calves. A new seasonal oscillation may be starting now. But there are worrisome and unexplained gaps in recent case reports. This month alone, the kingdom reported 57 new cases, and 21 deaths, and many had no known exposure to camels. A large number of the new cases are in Riyadh.

Since 2012, the virus has infected 1,042 people and killed 419. There is no known vaccine or cure. So far, there is not sustained human-to-human transmission, although the virus has spread among people in close contact and in hospitals.

The World Health Organization, slow to respond to the Ebola crisis, just sent a team of experts to Saudi Arabia. Their report was disturbing. While data collection and surveillance have improved in recent months, the team said, “critical gaps in knowledge remain,” and there are obstacles still to be overcome. “For example, how and why infections occur in the community is yet to be understood, and this is critical for stopping the outbreak.”

A third of the recent cases may have a hospital origin. But there is uncertainty about how and why, especially why infections appear to be spreading in some hospitals and not others. The leader of the WHO team, Keiji Fukuda, the WHO assistant director-general, said that when health-care workers are infected, they can spread the virus to all other patients in a facility, which he described as a “breach” that must be found — and repaired.

Saudi Arabia announced it has closed one private Riyadh hospital for laxity. But the kingdom has a long tradition of opacity and insularity, and it has not handled MERS with sufficient transparency. The European Centre for Disease Prevention and Control said in a report Feb. 23 that “The source of MERS-CoV infection and the mode of transmission have still not been confirmed.”

A “breach” in Saudi Arabia is of concern to the whole world. Air travel has made it easy for people to carry infectious diseases far and wide; recently, the Philippines, which sends many workers to Saudi Arabia, reported its first case of MERS. Last year, in the two-month period of May and June, flights from Saudi Arabia and the United Arab Emirates brought 30,680 travelers to New York, 24,514 to Washington, 14,567 to Atlanta and more to other U.S. cities. The MERS outbreak is a good place to begin to learn the lessons of Ebola and focus the world’s attention before it is too late.