There are many types of diseases. The diseases to humans are generally classified as avian and aquatic mode of transmission. However in certain cases they can be transmitted genetically too, radioactive diseases and blood sugar are some examples of such type. There is yet another kind or subdivision of diseases that are caused to humans due to constant exposure to animals or even a voluntary transmission. These kinds of diseases that are transmitted from an animal into humans are termed as "zoonotic" diseases.

Although there are various zoonotic diseases, the most common one is the rabies. This disease is caused by a "virus". Rabies infects the domestic animals mostly but in certain cases it can be seen in wild animals too. The animals that have the possibility to get infected from the rabies virus are called as rabid animals. Dog is one of the commonly known rabid animal. Surprisingly rabbits, wild animals from the dog family and monkeys too are rabid animals. However the transmission of this virus to humans occurs to a maximum extent due to dogs. Dogs alone contribute around 55,000 cases of rabies infection in a year.

The disease does not spread by a mere contact with the rabid animals, but due to contact with their infected saliva. When an animal is infected by rabies virus its saliva gets infected immediately as a consequence of the disease's take over in the animal's body. The peculiar reason as to why dogs are the major contributors to the spread of this disease to humans is that, when dogs get infected by the disease they develop a mental imbalance as a counter effect, which is not seen in other rabid animals. This mental imbalance causes them to be more aggressive towards the external world. As a result of this aggressive behavior they tend to bite or lick more, which causes us to come in contact with its infected saliva, Thereby spreading the disease to humans. This disease alone causes 95% of human mortality rate in Asia and Africa. Rabies virus causes encephalitis in the animal that gets infected, that is inflammation of the brain which triggers the aggressive nature.

The incubation period of rabies in humans varies from a week to a month depending on the person's immune system. It also widely depends upon the amount of time taken by the virus to reach the central nervous systems. The rabies virus travels through the brain via the peripheral nerves in humans. Once the disease reaches the central nervous system symptoms of the disease begin to show up one by one or even simultaneously in certain cases. At this point of time of the infection the disease is termed to be at its effective stage that is it has entered into an untreatable stage. From this point the fatality rate is almost 100 percent. Rabies generally affects the warm blooded animals which includes humans too. Although animal to human transmission of this virus have been proved, its human to human transmission is dormant and has less or no chance at all. However it is possible during organ or blood transplants.