Speaking about human viral disease, it is impossible not to mention that viruses are the tiniest and simplest of microbes. The term "virus" is referred to the particles infecting both single-celled and multi-celled organisms. Topically they carry a small amount of DNA or RNA (not both of them). Viruses have played an important role in shaping the history of our planet. They shuffled and redistributed genes among organisms and caused diseases in plants and animals. Thus, the human viral disease is apparently caused by the human body's response to a particular kind of virus infection. Among the common virus-caused disorders of the human immune system are immune reactions to the virus-infected cells, circulation in the human body of various virus-antibody complexes, and release of inflammatory substances by infected cells. There are several viral families able to cause human viral disease. Each of them can be discussed based on those family members, which are likely to cause the disease. According to modern medical practice there are 19 families of viruses. They are known to be defined by chemical type of nucleic acid, physical type of nucleic acid, presence or absence of an envelope, capsid symmetry, number of capsomeres and quantity of genes. One of the well-known viral families has the name "Family Papovaviridae (papovaviruses)". This name has been taken from the human viral disease caused bythe group members (for example, such small DNA containing viruses as Vacuolating, Polyoma and Papilloma). JC virus also belongs to this family and is considered to be the etiological agent of progressive multifocal leukencephalopathy. The second most complex viral family is called "Family Herpesviridae (herpesviruses)". Each virus species has about 160 genes. Here are the most common examples of herpes viruses: Epstein-Barr virus (causes infectious mononucleosis), herpes simplex virus (causes genital herpes infections and cold sores), varicella-zoster virus (causes shingles and chickenpox). Varicella-zoster virus is known to be spread in the air through sneezes, coughs or direct close contact with fluid from the chickenpox blisters. Thus, viruses of the Family Herpesviridae include the agents of different kinds of herpes, gingival stomatitis, chickenpox or varicella, shingles and other ones. Speaking about this viral group it's necessary to pay high attention to the illness called chickenpox caused by the varicella-zoster virus (or VZV). It is considered to be one of the highly contagious and common viral infections which causes itching and rash. According to recent scientific researches, more than 90% of the world population becomes infected with this disease at some stage of their lives unless they have received a special chickenpox vaccine. It occurs most often in late winter or early spring. Be aware that any human viral disease requires appropriate control and treatment. For this purpose it is important to consult your health specialist as soon as possible.