After getting ahold of the genetic blueprints for molecular weapons, relatively harmless bacteria transformed into one that can cause anthrax—in places and animals where the original anthrax bacteria doesn’t. And it’s wreaking havoc.

Using data collected over a 26-year period, researchers found that this strange version of anthrax is running rampant in tropical rainforest habitats of Sub-Saharan Africa, killing off broad swaths of mammals. In fact, researchers estimated this week in Nature that this "rainforest anthrax" could wipe out chimpanzee populations in the Côte d’Ivoire’s Taï National Park within the next 150 years. It’s currently associated with nearly 40 percent of all chimp deaths there. And researchers are just getting started on understanding risks to humans, which have so far been thought to be low.

Among the living

Figuring out the scale and prevalence of this rainforest anthrax will be “critical for mitigating against the detrimental effects” to wildlife and “assessing human infection risk,” the researchers, led by infectious disease expert Fabien Leendertz of the Robert Koch Institute in Germany, conclude.

Researchers have known about the existence of this alternative cause of anthrax for more than a decade. However, they’ve known little about its whereabouts and spread.

Classic anthrax is caused by Bacillus anthracis, which tends to strike ungulates (hoofed mammals) in seasonal outbreaks in arid locales, such as the African savannahs. The bacteria can cause infection in skin, lungs, or intestines. In humans, B. anthracis causes ghastly skin lesions, and severe respiratory and intestinal infections—which have mortality rates as high as 85 and 60 percent, respectively.

The alternative anthrax bacteria appear to cause an identical anthrax disease in animal models. But, those bacteria aren’t B. anthracis; they’re cousins, B. cereus, commonly found in soil and food. Usually, these are relatively harmless, with some strains known to cause a minor fraction of food poisoning cases. But the ones causing alternative anthrax are different. They just so happen to have gotten their grips on B. anthracis’ virulence plasmids—circular, shareable bits of DNA that contain the genetic code for their disease-causing gene products.

Researchers dubbed these alternative anthrax bacteria: B. cereus biovar anthracis, or Bcbva.

Spreading the disease

Researchers saw Bcbva in Taï National Park (TNP) in 2001. With carcasses piling up, Leendertz and colleagues started testing them in 2004—sampling 204 in total—as well as bones of 75 mammals, collected since 1989. In 2008, they started testing carrion flies, which can spread Bcbva, netting 1,634 fly samples. To assess Bcbva prevalence, they also gathered 1,089 fly samples and 136 bones from 16 sites in 11 other sub-Saharan countries.

From the TNP samples, they wound up with 178 whole genome-sequences of Bcbva from 80 of the carcasses (40 percent), 26 bones (35 percent of bone samples), and 80 flies (five percent). They found that the killer microbes were genetically diverse, suggesting that they had been active and spreading in the region for a while.

Regional sampling suggested Bcbva was widespread and indiscriminate. It showed up in 5 of 11 test locations and seemed to be present all the time, not just in seasonal bouts. It also didn’t just strike ungulates but a variety of animals: chimps, mongooses, porcupines, six monkey species, and duikers (a type of antelope).

But the chimps seemed to be hit particularly hard by the microbe. Based on population data and modeling on the already endangered chimp populations studied in TNP, the researchers estimate a high likelihood that Bcbva will wipe out these slow-reproducing primates within the next 150 years.

In an accompanying commentary, senior biology editor and ecologist Anna Armstrong noted that the dim projection doesn’t account for other problems. The risk "is only set to increase if chimp mortality from hunting and human-borne diseases continues to rise."

Nature, 2017. DOI: 10.1038/nature23309 (About DOIs).