On the hunt for a mystery virus

Viral threat

Bats are the leading suspect in the investigation of MERS illness that killed 40 people last year because they are a reservoir of SARS and carry other coronaviruses with genetic similarities to the MERS virus, writes Denise Grady.

As the scientists peered into the darkness, their headlamps revealed an eerie sight. Hundreds of eyes glinted back at them from the walls and ceiling. They had discovered, in a crumbling, long-abandoned village half-buried in sand near a remote town in southwestern Saudi Arabia, a roosting spot for bats. It was an ideal place to set up traps. The search for bats is part of an investigation into a deadly new viral disease that has drawn scientists from around the world to Saudi Arabia. The virus, first detected there last year, is known to have infected at least 77 people, killing 40 of them, in eight countries. The illness, called MERS, for Middle Eastern respiratory syndrome, is caused by a coronavirus, a relative of the virus that caused SARS (severe acute respiratory syndrome), which originated in China and caused an international outbreak in 2003 that infected at least 8,000 people and killed nearly 800.

As the case count climbs, critical questions about MERS remain unanswered. Scientists do not know where it came from, where the virus exists in nature, why it has appeared now, how people are being exposed to it, or whether it is becoming more contagious and could erupt into a much larger outbreak, as SARS did.

The disease almost certainly originated with one or more people contracting the virus from animals, probably bats, but scientists do not know how many times that kind of spillover to humans has occurred, or how likely it is to keep happening. Half the known cases have been fatal, though the real death rate is probably lower, because there almost certainly have been mild cases that have gone undetected. But the virus still worries health experts, because it can cause such severe disease and has shown an alarming ability to spread among patients in a hospital. It causes flulike symptoms that can progress to severe pneumonia.

The disease is a chilling example of what health experts call emerging infections, caused by viruses or other organisms that suddenly find their way into humans. Many of those diseases are “zoonotic,” meaning they are normally harboured by animals, but somehow manage to jump species. “As the population continues to grow, we’re bumping up against wildlife, and they happen to carry some nasty viruses we’ve never seen before,” said Peter Daszak, a disease ecologist and the president of EcoHealth Alliance, a scientific group that studies links between human health, the health of wild and domestic animals, and the environment.

Saudi Arabia has had the most patients so far (62), but cases have also originated in Jordan, Qatar and the United Arab Emirates. Travelers from the Arabian Peninsula have taken the disease to Britain, France, Italy and Tunisia, and have infected a few people in those countries. Health experts are also worried about the Hajj, the Muslim pilgrimage that will draw millions of visitors to Saudi Arabia in October. MERS has not reached the United States, but health officials have told doctors to be on the lookout for patients who get sick soon after visiting the Middle East.

In May, Saudi health officials asked an international team of doctors to help investigate the hospital cluster. One concern was that a number of cases were in patients at a dialysis clinic, and doctors feared that dialysis machines or solutions might be spreading the disease. “It was pretty easy to figure out that couldn’t have been the case,” said a member of the team, Dr Connie S Price, the chief of infectious diseases at Denver Health Medical Center. The patients’ records did not point to dialysis as the culprit, she said, and there were clear cases of transmission in other parts of the hospital that had no connection to dialysis. Why, then, the outbreak among dialysis patients?

The answer seems to be that they were older, chronically ill and often diabetic; diabetes can suppress the immune system’s ability to fight off infections. So, when one dialysis patient contracted MERS, others who happened to be in the clinic at the same time were easy targets for the virus. “Introducing it into a dialysis center gives it the perfect environment to spread among vulnerable patients sitting in open bays for many hours,” Price said.

Finding out where in the environment the disease is coming from might make it possible to tell people how to avoid it. Bats are the leading suspect, because they are a reservoir of SARS and carry other coronaviruses with genetic similarities to the MERS virus. Bats could be transmitting the disease directly to people, or they might be spreading it to some other animal that then infects humans.

But what kind of bat? There are 1,200 species; 20 to 30 have been identified in Saudi Arabia. Last October, to test the theory, a team of scientists from the Saudi Ministry of Health, Columbia University and EcoHealth Alliance began scouring Saudi towns near where cases of MERS had been reported, showing people pictures of bats and asking if they had seen any. They struck pay dirt when one man led them to an abandoned village in the southwest, said to be hundreds of years old. It was there, in the inky darkness, that they found a small room that had become the roost of about 500 bats.

The scientists set up nets to catch them when they flew out at dusk to hunt insects, then spent the night testing them for the MERS virus. The bats were let go after the testing.The animals can weigh as little as 4 grams, and a bat that size may have an eight-inch wingspan. It takes about 15 minutes to weigh and measure it, collect saliva, feces, blood and skin samples. The specimens were then frozen and sent to the laboratory of Dr W Ian Lipkin, a leading expert on viruses at Columbia. Hundreds of bats have been tested, he said, but it is too soon to disclose the results.