Symptoms of the illness may be mild, such as muscle aches, fever, or headache, or they may become severe, such as meningoencephalitis or meningitis. V. Varicella Zoster Virus – This is the virus that causes chickenpox in children and causes shingles in adults.. Measles – The measles virus is the cause of the disease measles. The virus only infects humans and is spread through respiratory secretions. Complications may occur and can include pneumonia, encephalitis, and even death. Mumps – The mumps virus causes the disease mumps in people.