Scarcely a week goes by without some public discussion of superbugs, new contagions, or disease outbreaks. Humans fear the insidious threats we cannot see. But we are not the only species to experience devastation at the hands of an infectious foe. Here are four horrifying animal diseases:

Hendra Virus: In Australia, it's hard to find a veterinarian who doesn't subtly wince at the word "Hendra." Harmless enough on paper and fragile outside a host, Hendra virus is anything but harmless in horses. A slight wobble in an equine's step coupled with listlessness in its demeanor are the initial signs of infection, followed by rapid deterioration and death. Hendra kills 80 percent of horses it infects, and can even rarely cross over into humans, where it kills with similar efficiency. It's for this reason that many veterinarians will not treat a horse with symptoms of Hendra if the animal has not been previously vaccinated.





Chytridiomycosis: According to at least one group of scientists, it's “the worst infectious disease ever recorded among vertebrates in terms of the number of species impacted, and its propensity to drive them to extinction." Chytridiomycosis is caused by two types of chytrid fungi, and it has infected about 30% of all amphibian species in the entire world. Three percent of all frog species have gone extinct because of it. Chytridiomycosis affects the skin of amphibians, often causing it to thicken. Having "thick skin" may be seen as beneficial to humans, but to amphibians, it's deadly, as many species absorb nutrients, release toxins, and even breathe through their skin.

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White-Nose Syndrome: A dusty cap of white fungus resembling a dab of powdered sugar is the hallmark sign of of this syndrome, which began infecting North American bats back in 2006. Since then, white-nose syndrome has laid waste to bat populations in 33 U.S. states and seven Canadian provinces, sweeping mechanically and menacingly across the continent from where it originated in New York. The aptly named Pseudogymnoascus destructans is the architect of the deadly disease. The fungus erodes the skin of bats, particularly on the wings, leaving the little critters with open wounds. Infection eventually results in weight loss, dehydration, electrolyte imbalances, and death. At least 5.7 million bats have died as of 2012. That number has surely elevated into the tens of millions by now.

Marek's Disease: Named for the Hungarian veterinarian who discovered it, Marek's disease is caused by a hearty herpesvirus capable of persisting in the environment for more than a year. The virus' preferred home is in the feather follicle of chickens, and it is here that it spreads by hitching a ride on flaky dander and also seeps in to the animal's body. Initial infection is marked by some paralysis, which quickly subsides as the virus progresses over the ensuing weeks. Finally, the full-blown disease roars with gray tumors covering birds' internal organs as well as the skin, along with paralysis of the legs, wing, and neck. Flocks infected with Marek's disease lose between 10 and 70 percent of their populations.