Disease! is a (hopefully) weekly series of diaries about a category of overlooked epidemics -- plant and animal diseases. While they rarely make the news, these epidemics, often caused by invasive pathogens, have had and continue to have enormous ecological and economic impact. And in a world with changing climate and blending borders, we can only expect more to come.
A horrible plague sweeps across eastern North America. Few are spared. Mortality rates are almost incomprehensibly to modern Americans. 50%. 90%. 95%. 100%. What were once thriving communities are left as little more than collections of the dead. Recovery -- what they call recovery, anyway -- takes decades, if not longer. But calling it a recovery rings hollow; things will never be the same. And for smaller, more vulnerable groups, there can be no recovery at all.
It sounds like something out of an overblown drama. But in the 16th and 17th centuries (further west, into the 18th), it was the reality of smallpox among Native Americans. Whole cultures, like the Gaunches of the Canary Islands, were extinguished. By any metric, the loss is virtually impossible to measure. It was one of the worst pandemics in human history, rivaled only by the great plagues of European antiquity: the Antonine Plague, the Plague of Justinian, the Black Death.
It is a tragic chapter of human history, and worthy of further examination ... but not here. Because this diary series isn't about human tragedy. Eastern North America is again bearing witness to a horrible plague, from the Canadian provinces of Ontario and Quebec, down to the American Upland South -- so far. As before, the mortality rates are almost so high as to be unbelievable. 90%. 95%. 100%. Communities of thousands have been wiped out in a single season. For less populous groups, the specter of complete elimination looms.
But this plague has not become the news story to end all news stories, or an impetus for widespread panic. It has only barely entered the media's attention at all. Because this isn't a human pandemic.
It is killing bats.
Some of this diary is "self-plagiarized" from my May 2010 work on this topic.
In February 2006, a a caver in Schoharie County, New York noticed a white fungus on some hibernating bats. A few were dead. But bat ecology was poorly researched, and no one realized anything significant was wrong. The next winter, the dead bats numbered in the hundreds, and had spread to caves in two counties in New York. It was now a topic of interest for the New York Department of Environmental Conservation and a handful of bat biologists. But it was a curiosity of science, not a problem.
A year later, the reports of dead and dying bats, infected with this "white-nose syndrome," ballooned. From just south of the Canadian border to just north of the New Jersey one, there were now nine New York counties with the strange disease known. Pathogens don't have much regard for political borders, either, and neighboring states were not immune. Vermont, Massachusets, Connecticut. At this point, it was hard to ignore that something was very, very wrong. In the middle of winter, people were starting to call local wildlife departments to report sickly bats dropping flying in mid-day. Or crawling, dying onto their lawns. Now the United States Fish and Wildlife Service's Northeast Region was involved. Researchers rushed to hibernacula -- caves that serve as the wintering communities of bats -- and found scenes out of a horror film. Mortality rates started at 70% in infected caves, and only went up. In some, there were no living bats at all, only a carpet of animal corpses covering the ground at the cavern entrance.
The researchers found only questions. Fungal diseases are known in some animals; the global amphibian die-off caused by chytridiomycosis will be a topic of a later installment of Disease!, but they are rare in mammals. Was the fungus an opportunistic infection, with another disease as the root cause? Parasites? Pesticides? Bats were necropsied at laboratories throughout the northeast. But bat research has been a poorly-funded fringe topic. The baseline research in healthy populations that was needed for comparison had never been done.
Winter 2008-2009 came, and no answers were forthcoming. Epidemics don't wait for science to find answers, though. There had never been a bat-banding program like the one in widespread use for migratory birds. We learned about the details of bat migration patterns by watching where the bats began to die. New Jersey. Pennsylvania. West Virginia. Virginia. The fungus was identified, its genetics sequenced. It was new to science, and got a name. Geomyces destructans. But naming a disease isn't enough to stop its spread, and there was still no understanding of how the disease killed, much less what to do about it. In three years, white nose syndrome had killed a half million animals. The Fish and Wildlife Service was blunt in its conclusion: "If we cannot find how to eradicate WNS, we face the real possibility of losing entire bat species." Use restrictions were placed on caves, hoping to hold WNS, if not east of the Appalachians, then east of the Mississippi, and away from the huge bat populations of Tennessee, Kentucky, Georgia, and Alabama.
Last winter, the spread accelerated, as the fungus moved into populations connected to longer-distance bat migration flyways. In the north, it became an international issue, infecting animals in Ontario and Quebec. It jumped the Appalachians into western New York and Pennsylvania. And it moved south -- not only in small, measured expansions into Delaware and Maryland, but in huge leaps. Four counties in Tennessee. Two in Missouri. And all the way to Woodward County, in western Oklahoma. Hopes of holding the epidemic at the Mississippi River, or out of the South, were dashed in a single season. Beginning in France, European bats were found that tested positive for the fungus, but seem, so far, not to develop the lethal disease. Does this mean white nose syndrome is an invasive pathogen, with origins in Europe? If so, how did it arrive here via a rarely-visited cave in rural central New York? There are no answers yet, but a European origin is looking increasingly likely.
The warm seasons of 2010 saw some good news, and more bad. Congress authorized emergency funding to research and combat the condition. Widespread cave closures ensured that human activity would not assist in the spread of disease-causing spores. And a causal mechanism that connected fungal infection to death was finally determined. Although the powdery fungal coating on the bats' muzzles is the distinctive symptom, it is microscopic damage to wing membranes that kills them, disrupting their ability to retain heat and water, and interfering with oxygen exchange across the ultra-thin skin. The fungus's growth conditions were better defined, too. It is psychrophilic -- cold-loving -- and it is the very drop in body temperature that makes hibernation possible which allows a mammal to fall prey to a type of illness never thought to affect them in this manner before. Unfortunately, however, a captive breeding program failed catastrophically. And evidence began to accumulate that spores can remain dormant in caves, making reintroduction without resistance futile.
So far this winter, WNS has spread to North Carolina and Indiana. Illinois, Kentucky, and Ohio are now largely just a matter of time.
As things stand right now, the fungus is present in 16 states and 2 provinces. It has killed well over a million bats; better numbers are impossible because no comprehensive population surveys were taken beforehand. All cave-dwelling, hibernating bats seem vulnerable. Nine species are known to be affected so far, including the endangered Indiana and gray bats. WNS has resulted in the death of over 10% of the Indiana bat population. Eight hibernacula support 95% of the population of the gray bat, five of which are in states where the disease is already known. But with mortality rates exceeding 90%, even the widespread little brown bat is in danger. Mated pairs of bats produce only a single pup each year, so this scale of catastrophic loss can drop the population below sustainable levels even where there are survivors.
Bats are a long way from charismatic megafauna that attract people's attention and sympathy. But in addition to the ecological disaster, this threatens to be an economic nightmare. Despite popular belief, mosquitoes are not the preferred prey of insectivorous bats. The insects that are, however, include several economically important crop pests. Based on the die-off figures that were available in 2009, estimates were that WNS resulted in 2.4 million pounds of bugs going uneaten. Because bats are such efficient niche predators, no other animal is available to fill the role of nocturnal insectivore in their place. Insecticide use across New England has already increased. If WNS destroys the millions-strong bat populations of the Deep South, the cost to agriculture there will be substantial. The Fish and Wildlife Service has asked that the public suspend operations in caves that host, or might host, hibernating bat populations during the winter months. Many states on the borders of the infected region, or with significant bat populations, have passed emergency laws and regulations restricting cave use, as a last-ditch effort to hold a quarantine line against a disease whose mode of transmission is not yet even understood.
Last week's installment of Disease! ended with the deaths of 4 billion trees, the death of a major industry in southern Appalachia, and a permanent change in the makeup of the eastern hardwood forests. Where does the WNS end? It's too soon to know. There may be climate, genetic, or migratory pattern barriers that will contain the epidemic's spread. The fungus is vulnerable to known anti-fungal agents, and a means to combat it in the wild may be developed. But our first-order quarantine lines have failed. I'll let the researchers' comments speak for themselves here. This is "the most precipitous wildlife decline in the past century in North America." The observed mortality "far exceeds the rate and magnitude of any previously known natural or anthropogenic mortality events in bats, and possibly in any mammalian group." Or, as a National Park Service researcher put it more succinctly, WNS "threaten[s] extinction."
You can follow the spread of the disease and scientists' efforts to understand at combat it at the Fish and Wildlife Service's WNS page, which has become something of a de facto clearinghouse for WNS updates on the web. Also, many of the major papers on this topic have been made open-access to facilitate research and education. You can read the paper that officially described and named the fungus (pdf), a study of the fungus in Europe, and the paper describing how the disease kills bats. I encourage interested Kossacks to read them; the research done on this topic has been excellent, and has been written with an eye towards accessibility.
Next week on Disease!: A story with a happy ending, I promise.
Previously on Disease!:
Four billion dead, the story of the chestnut blight