Want to clear a room quickly? Just casually mention you’ve recently encountered anthrax. Turns out the mere whisper of the word, to most Americans, conjures up a mental image of white powder falling like snow from an envelope sent by terrorists, followed by a gruesome and highly exaggerated death scene. Indeed anthrax in high doses can be extremely lethal and many a government has even considered it for biological warfare.
My experience with anthrax, though, has been more organic, because it is actually caused by a naturally occurring bacterium that lives in the soil. Spores that cause anthrax are known for being hardy—they can lay dormant for decades or even centuries, survive all over the world, and withstand extreme heat, cold and drought. In Tanzania, where I work, and throughout much of Africa, anthrax outbreaks occur occasionally—when an unsuspecting cow, wildebeest or hippo consumes or inhales spores while grazing. And anthrax has a little trick for attracting unsuspecting, hungry ungulates: its spores encourage plant growth, literally making the grass greener where it is present.
Now I’ll let you in on a little secret: I didn’t go to Tanzania to study anthrax. I’ve learned about (and probably even been exposed to) a number of maladies, not because of my love for disease ecology itself, but rather because I study a species that eats diseases, along with a bit of carrion, for breakfast—the white-backed vulture. My passion for African vultures has found me counting, watching, trapping and tracking these birds for the last nine years, primarily in Kenya and Tanzania. Unlike me, the vultures have the advantage of being resistant to a whole host of horrific diseases such as rabies, tuberculosis and brucellosis. In the case of anthrax, we suspect that they can digest the microbes into oblivion with their incredibly acidic gut, and this maybe one of the few ways to remove bacteria from the environment during an outbreak.
During a recent trip to Ruaha National Park, Tanzania, we had the unique opportunity to study the spread of anthrax using vultures. I was back in the field as part of my job with North Carolina Zoo, working with Wildlife Conservation Society biologists, to satellite-tag white-backed vultures. Things did not go according to plan. After 14 days of attempting to trap vultures with our own bait—a dead goat—we saw almost no interest from the birds. We knew about the anthrax outbreak, but were unaware of the scale or the effect it would have on the birds’ behavior. However, this was not our first rodeo. We had actually tagged 10 vultures in the previous year and could see from daily downloads of their whereabouts that something was up.
This particular outbreak had started with, and was still mostly infecting, hippos. The common hippopotamus, a species I love dearly and had studied in Ruaha many years back, is highly susceptible to anthrax for a number of reasons. First, hippopotamuses come into contact with spores when out munching grass at night. Second, they aggregate, especially as waterholes shrink during the dry season. The terrible effect was obvious as blood gushed from the eyes and mouth of one dead hippo slowly filling the pond—still occupied with its live compatriots—with anthrax spores. Third, and we actually witnessed this, hippos are cannibalistic. That’s right, they eat each other. Not often, but when there are lots of dead around, as in the case of this outbreak, these supposed herbivores get to consuming one another, which probably further spreads the infection.
Not too surprisingly, the vultures had been spending a lot of time along the river. But as we began investigating the data more closely, interesting patterns emerged. Because multiple birds either aggregate in one place, or a single individual devotes extended periods of time to a location when it finds a carcass, we could establish the location and timing of where and when hippos were dying along the river from our tagged flock.
In essence, we could determine when the outbreak started, how it had spread from pool to pool along the river, when new mortalities occurred in a given pool, and how long it was going to continue—a unique dataset about the disease dynamics of anthrax. In this situation, our tagged vultures were not only going to do their important job by digesting and therefore reducing the spread of anthrax, but were going to teach us something new about how the disease operated in real time. Such information could prove useful for understanding and potentially even containing future outbreaks, not just here but around the world, lending a whole new value to the vulture, nature’s ultimate garbage disposer.
This post was written by a graduate of the online course Share Your Science: Blogging for Magazines, Newspapers and More, offered by Scientific American and the Alan Alda Center for Communicating Science at Stony Brook University, with sponsorship from the Kavli Foundation.