The real bat-man story

Bats have been getting a bad rap.

Last fall, a team of scientists tied bats to the deadly SARS outbreaks. Bats in China, they said, are likely where the virus hides between human outbreaks. Then, in December, another group of researchers suggested that bats in Africa serve as a reservoir for the vicious virus for Ebola hemorrhagic fever, which causes its human victims to bleed to death. Bats have also been definitively tied to two other recently discovered viruses that are lethal to humans: Nipah and Hendra.

But as researchers have worked to uncover the mysterious links between bats and these emerging viruses, they say they have stumbled upon an even wilier culprit working behind the scenes: humans. It now seems that these outbreaks, and likely many others, were set off when people encroached on rain forests, expanded wild animal markets, or made other changes that removed the natural barriers that keep diseases at bay.

''This is not a wildlife problem, it is a human problem," said Jonathan Epstein, an American researcher who spoke by phone from Bangladesh, where he has been investigating the causes of Nipah outbreaks.

The insights that are coming from these outbreaks are feeding an emerging discipline that seeks to redefine the very meaning of health. Epstein and other proponents of this thinking, which they have dubbed ''conservation medicine," argue that it is impossible to divorce human health from that of the environment. Emerging viruses like the one that causes SARS are symptoms of the drastic, large-scale changes humans are making in the life of the planet.

At a time of intense concern about avian flu, it is hardly controversial to argue that human health is linked to animal health. But the field challenges traditional academic divisions, especially the cultural divide between doctors and veterinarians. Epstein is a senior research scientist at the New York-based Consortium for Conservation Medicine at Wildlife Trust, which organizes projects that cross the old disciplinary boundaries. The consortium includes the Cummings School of Veterinary Medicine at Tufts University, the Johns Hopkins Bloomberg School of Public Health, and the United States Geological Survey National Wildlife Health Center.

There are other centers of activity, such as the Harvard Medical School Center for Health and the Global Environment, as well as more ad hoc teams of researchers working on projects that bring together biologists, public health specialists, doctors, and others. The focus of this work is varied, from the health impact of climate change to a program organized by Tufts to use volunteers around New England to monitor the health of seabirds -- a kind of biological early-warning system on our coast.

As researchers do their detective work around the world, they are finding connections between human society and disease. Global warming could push mosquito-borne diseases like malaria and encephalitis into more northern countries. One new bat-borne disease, the Nipah virus, was tied to the expansion of pig farming in Malaysia. Outbreaks of avian flu have been tied to farms, and the disease's spread has been helped by farmers reluctant to come forward with sick birds.

The researchers hope that by studying these connections, they will discover the means to prevent future epidemics.

After the 2003 outbreaks of SARS, which attacks the respiratory system, scientists initially identified an animal known as a civet as the disease's reservoir, the place where the virus sustains itself between outbreaks in humans. But further testing found that civets were not widely infected. In a paper published online by the journal Science last September, a team that included Epstein and scientists from China and Australia named a new suspect: cave-dwelling horseshoe bats. These bats, they reported, carry a family of viruses very similar to the one that causes SARS.

It is likely, the study found, that one of these ''SARS-like" viruses evolved into the SARS virus at an exotic animal marketplace, where it infected civets, which, in turn, infected humans, according to Michael Farzan, a Harvard Medical School assistant professor who was not involved in the research.

But why did this happen when it did? One intriguing possibility is that it is linked to China's economic boom, according to Peter Daszak, a co-author of the SARS paper who is executive director of the Consortium for Conservation Medicine. With the newfound wealth there, he said, animal markets have grown as more people can afford fresh animal meat. As the markets grow, so grow the chances that a virus will jump from one species to the next.

In December, a different group of researchers linked fruit bats to the dreaded Ebola virus. Outbreaks of the disease in humans have been associated with dramatic outbreaks among chimpanzees and gorillas. The team, working in Gabon and the Republic of Congo, captured various animals near the bodies of chimpanzees and gorillas. They then looked for signs of Ebola virus.

From this, the team found three different species of bats with antibodies to the virus, according to a paper in the journal Nature. Bats are now the leading suspect as the Ebola virus reservoir, but the case against them remains controversial, according to Jens Kuhn, an Ebola specialist at Harvard Medical School. It is thought that changes in human activity are behind the Ebola outbreaks -- such as new mining operations deep in forests and the eating of primate meat -- Kuhn said, but nobody knows the true origin.

The ties between bats and disease have raised fears in the conservation community that the winged creatures, long maligned and misunderstood, will become the targets of calls for elimination. This would be a mistake, researchers said, because bats play important environmental roles, such as eating pests -- and killing off bats would be very difficult in any case. There are about 1,000 species of bats, making up a fifth of all mammal species.

One study, published in December in the journal Emerging Infectious Diseases, found that bats are involved in fewer of the world's emerging viruses than other groups of animals. But with their role becoming clear in several particularly nasty viruses, scientists have been pushing to better understand bats and their role in carrying disease.

At Boston University, Thomas H. Kunz, a professor of biology and longtime bat specialist, is involved in an ambitious study in the United States of bats and the virus that causes rabies. This study, he said, should shed new light on rabies, but it could also yield clues into the interactions between bats, viruses, and the environment.

For example, he said, his team wants to measure the dynamics of the virus during the year. It may turn out that the ebbs and flows of the virus can be tied to factors like migration, when the animals are under more stress. If the team finds patterns, then researchers could look for similar patterns in the bats that carry other viruses, like Nipah.

Kunz and his collaborators are also working on experiments on the immune systems of bats. There could be reasons why bats carry particular viruses, and there also may be reasons why some bats are able to fend off viruses that kill humans. All of this could help in the fight against disease, he said -- once someone figures out the answers.

The key, he and other researchers said, will be to understand the bat as a part of a larger web of life that also includes humans. And before we blame the bat, or any other animal, for our diseases, we need to look closely at ourselves.

Gareth Cook can be reached at cook@globe.com.