Rabies is an awful disease that affects mainly mammals — the kinds that bite, scratch and eat primarily meat. Although almost any mammal could get rabies, most of its victims are dogs, monkeys, foxes, raccoons and bats. And humans can also get rabies.

It isn’t easy to transmit rabies — you couldn’t get it from simply touching a diseased animal. In order to pass it, the saliva of the infected animal needs to contact the bloodstream of the victim. This typically happens via an open wound, a mucous membrane or a bite that breaks the skin.

The incubation period for rabies — that is, the time between exposure and the first sign of symptoms — is surprisingly variable. Typically, rabies takes two to three weeks to present itself, but sometimes it can take as long as two or three months.

Since the rabies virus journeys to the brain along the nerve networks, the further the bite or infection site is from the brain, the longer the incubation period. Once the virus reaches the brain, it then travels back along the nerves to the salivary glands, where it takes root and multiplies.

The symptoms we normally see with rabies stem from encephalitis, or inflammation of the brain. An early, subtle sign may be a detectable yet not quite explainable change in your dog’s behavior or personality. If your dog is normally quiet and friendly, he might suddenly become surly and aggressive. Another way rabies manifests itself is with a slight fever, accompanied by diarrhea and vomiting.

As rabies advances and multiplies throughout the body, the dog becomes increasingly aggressive, even furious. He might also become paralytic. If you recall that scene from To Kill a Mockingbird, you’ve seen the sad image of a dog who’s both furiously crazy and partly paralyzed, staggering down the street.

When a rabid dog reaches the stage in the disease, he exhibits what’s called “mad dog behavior.” The dog is vicious, violent and prone to biting anything in his path. At this point, the end is near. Sooner or later, he’ll suffer periodic convulsions that eventually increase in length and frequency. Paralysis will follow, and then death.

If paralysis manifests in a particular case of rabies, the dog will often suffer paralysis of the head. This will result in his mouth dropping open and his tongue hanging out. The dog won’t be able to swallow, will be desperately thirsty, and will drool and paw at his mouth. In the most advanced stages, paralysis will take over his entire body.

Once clinical symptoms for rabies appear, there is no cure, either in humans or pets. But it’s possible to stop the disease from developing if you get a series of shots immediately after being bitten by an infected animal. In the United States, an average of one person a year dies from rabies, a much lower number than in most countries. This low number is due to the fact that we aggressively vaccinate our dogs, cats and ferrets.