Rabies is due to:

Explanation

Rabies is caused by a virus (Lyssavirus), which infects nerve cells and travels to the brain, leading to fatal neurological symptoms. It is not bacterial, since antibiotics don't work and bacteria cause different infections. It is not fungal, as fungi affect skin or lungs, not nerves. It is also not a protozoan, because protozoa cause diseases like malaria, not rabies, and respond to antiparasitic drugs, not vaccines.