Viral diseases are some of the most common infections that affect humans. Virus hangs freely on air, animal bodies or the ground. There are a considerable number of viruses that reside in human bodies but only harm the body when the immune system is weak. Some of the most common diseases caused by viruses include:

Rabie   Rabie: This disease is fatal and comes from infected animal bites. The most common animals that transfer rabies are dogs, and it is advisable that you seek medical attention as soon as possible after you got bitten by a stray animal. Some of the significant symptoms of this disease include a headache, fever, excessive saliva, partial paralysis, agitation, and hallucinations. In humans, the symptoms display after nine days and sometimes even after years in extreme cases.

   Measles: Also known as rubeola, measles can be fatal. The disease affects children who are below the age of 5 years. Some of the major symptoms include running nose, cough, fever, skin rash and inflammation of the eyes. In the United States, the last confirmed death caused by measles was in July 2015. Early vaccination prevents the spread of measles when there is an outbreak.

   Common cold: This is the most common viral disease among human beings. A sore throat, cough, and runny nose characterize this infection. This disease is airborne and associates with more than 200 different viruses.

   AIDS: This illness starts as Human Immunodeficiency Virus (HIV). Some of the symptoms may include a sore throat, fever, headache, rashes, genital and mouth ulcers, diarrhea, swollen lymph glands and weight loss. However, pretty often, the virus can manifest no symptoms at all for years. HIV develops into AIDS if the condition is not contained. Recent studies indicate that more than 1.2 million people living in the US are infected with HIV. One out of every eight of these people doesn't know that they are HIV-positive. In 2014 alone, more than 44,000 people tested positive for HIV in the US.

   Chickenpox: This infection affects millions of children all over the world annually. Within 48 hours, the virus causing chickenpox can spread from the infected person to another. Some major symptoms include blisters with red rashes, fever, loss of appetite and headaches.

   In fact, there are scores of viral diseases out there that are affecting human beings. The incubation period and fatality differ depending on the type of infection and the immune system of the infected person. Many of them can be prevented by vaccination. However, some dangerous viruses like HIV, for example, have still no vaccine despite all the efforts the scientists around the world make to develop one.