Vampires on the leading edge

November 18, 2005

"Rabid vampire bats attack Brazilian children" may sound like something out of the tabloid Weekly World News, but the headline actually comes from the respected magazine New Scientist. Even weirder - it's true.

Vampire bats have indeed been attacking Brazilian children. In fact, they've bitten over 1,300 people since September and 23 of their victims have died from rabies. But beneath the sensational and bizarre story is more hopeful news about the emerging field of conservation medicine.

Conservation medicine is a relatively new discipline referring to the convergence of ecology, which looks at species and ecosystems, and health science, which looks at human, plant and animal health. It's a natural connection because the health of individual plants, animals, and people is intimately connected to the health of the ecosystems in which they are embedded.

What does this have to do with bats? Well, the reason for the recent increase in vampire bat attacks in Brazil is deforestation. The Amazon forests are being cleared for industry and agriculture - especially grazing animals. With their homes gone, the bats are roosting closer to humans and they have a new, plentiful supply of slow moving, warm-blooded prey - cattle. This has led to larger colonies in smaller areas, ideal breeding grounds for rabies, which makes the bats more aggressive and no longer fear humans.

And rabies isn't the only disease recently transferred to humans from bats. Bats are also a natural reservoir for SARS, the respiratory virus that caused panic in Toronto and tore through Southeast Asia two years ago. Originally, scientists thought civet cats were the reservoir for SARS, but they now believe the civets were infected by bats. Bats often don't eat all of their meals. Fruit bats, for example, chew fruit to extract the sugars and then spit out the pulp - which is eaten by foraging animals below.

Scientists now believe that this is how the Nipah virus was spread through pig farms in Malaysia five years ago, when farms began displacing forests and bats began roosting in barns. Authorities there had to kill one million pigs and over 100 farm workers died from the virus. More recently, in Bangladesh, the Nipah virus was spread directly to humans when children picked and sold fruit that had been contaminated with partially digested bat dinners. Researchers also believe fruit dropped by bats may have spread the Hendra virus in Australia and the Ebola virus among primates in Africa.

But before we get out the pitchforks and torches to hunt down these winged terrors, consider what ecologist Andrew Dobson wrote in an analysis in the journal Science: "Assuming we can control these diseases by simply controlling bats is both naïve and short sighted. Instead, we must recognize that increased spillover-mediated pathogen transmission from bats to humans may simply reflect an increase in their contact through anthropogenic modification of the bat's natural environment."

In other words, as humans continue to modify and destroy bat habitat, we will continue to run into these problems. To solve them, we must focus on conservation and learning more about bat ecology and immunology - about which we currently know very little. Ultimately, minimizing the conditions that lead to disease outbreak is much more effective than dealing with the problem after it has already occurred.

In nature, everything is connected. And while people tend to think that human society is somehow excluded from nature, like some sort of observer, we are in fact deeply embedded in the natural world. Because of this, our actions can have profound, unforeseen and mysterious repercussions. The new field of conservation medicine can help unlock those mysteries and help us build a healthier world.