Officially, chupakabras are coyotes or other canine animals infected with a mange-like parasite which leaves the animals hairless with sunken, shrivelled bodies the size of a small bear and a pronounced spinal ridge. The animals are reported to attack and drink the blood of livestock, leaving puncture wounds in the neck corresponding to the canine's teeth. They are extremely territorial with keen senses of smell. Their long legs easily outpace police dogs and are capable of hunting down a human with relative ease.
If the parasite is transmitted to humans, such as through a bite or other open wound, and the human survives, a mutualistic, rather than parasitic, relationship develops. The organism infects the brain, adrenal glands, and bone marrow, becoming obligatory for the host's survival. The human meanwhile takes on characteristics of insanity which in centuries past would have been described as rabies. They lust for blood rather than flesh, an insatiable desire to alleviate their bone-marrow deprived anemia. The changes to their adrenal glands produce excess adrenaline which infuses them with extraordinary strength, speed, and paranoia. While their constant anemia induces a sunken, dehydrated face with a prominent bony structure while receeded gumlines leaves their teeth resembling fangs.
The canine-infected chupakabra have been noted in the americas, Russia, and the Phillipines. News has also emerged from central Russia, Ukraine, and Belarus of a beast which kills fowl, livestock, chickens, and other herded animals and drinks their blood. Meanwhile, more subtle evidence of attacks emerge from Moscow itself: that of birds and rats found bloodless and bearing strange incisions, likely from a population of human-infections.