Rabies (ˈreɪbiːz. From , "madness") is a viral

Virus

A virus is a small infectious agent that can replicate only inside the living cells of organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea...

 disease that causes acute encephalitis

Encephalitis

Encephalitis is an acute inflammation of the brain. Encephalitis with meningitis is known as meningoencephalitis. Symptoms include headache, fever, confusion, drowsiness, and fatigue...

 (inflammation of the brain

Brain

The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...

) in warm-blooded animals. It is zoonotic (i.e., transmitted by animals), most commonly by a bite from an infected animal. For a human, rabies is almost invariably fatal if post-exposure prophylaxis

Post-exposure prophylaxis

Post-exposure prophylaxis is any prophylactic treatment started immediately after exposure to a pathogen , in order to prevent infection by the pathogen and the development of disease.-Rabies:...

 is not administered prior to the onset of severe symptoms. The rabies virus infects the central nervous system, ultimately causing disease in the brain and death.

The rabies virus

Rabies virus

The rabies virus is neurotropic virus that causes fatal disease in human and animals. Rabies transmission can occur through the saliva of animals....

 travels to the brain by following the peripheral nerves

Peripheral nervous system

The peripheral nervous system consists of the nerves and ganglia outside of the brain and spinal cord. The main function of the PNS is to connect the central nervous system to the limbs and organs. Unlike the CNS, the PNS is not protected by the bone of spine and skull, or by the blood–brain...

.