Viruses are known to cause a number of diseases in humans. These include influenza polio, herpes, and AIDS among others. Viruses depend on the host cell to reproduce (Bauer et al., 2013). Outside the host cell, viruses exist as capsid. In this form, the virus is inactive. It’s only after being inserted into a cell that it becomes active again and takes over the functions of the host cell (Bauer et al., 2013).. Prions are infectious pathogens that cause a number of neurodegenerative diseases. A prion is a small infectious particle made of abnormally folded proteins. Unlike virus, prions do not multiply in the organism that they infect (Pruisner, 1998). They affect the brain structure by converting normal proteins to fold abnormally. One of the most common diseases caused by prions is the mad cow disease.

Herpes viruses are a major cause of viral diseases. The viruses cause both overt diseases as well as diseases that remain inactive in the body for a long time before r, for instance, regaining activity shingles (Prevention Training Center, 1999). An infection by herpes virus remains in the body till death. Once one is infected with the virus, there occurs a period of latency, followed by reactivation.

The herpes virus structure has four parts. These are the envelope, the tegument, the capsid and the genome. Herpes viruses are normally enveloped. They emerge from an inner nuclear membrane which has been changed by adding herpes glycoproteins (Prevention Training Center, 1999). Later, it is these glycoproteins that determine the cell which the virus will infect. The envelope is lipid in nature and is sensitive to acids and detergents. Tegument is the space between the envelope and the capsid. It contains proteins that initiate replication. The capsid, on the other hand, is the doughnut shaped part of the virus. The genome part of the virus contains a double strand DNA. The size of the genome differs from one virus to the other. HSV-1 and HSV-2 are large viruses whose genome contains over 80 proteins. In these viruses, the genome has 11 glycoproteins which help in attachment and fusion of the virus membrane to the host cell. Hence, the structure facilitates the entry of the virus into the host cell.

Epidemiology

HSV-1 and HSV -2 infections last the whole of one’s lifetime. The virus is found on the lesions of the skin as well as in several other body fluids (Bauer et al., 2013). These include saliva and vaginal secretions. HSV-1 is spread by mouth to mouth kissing as well as by sharing dirty utensils. HSV-2 is spread sexually and is normally found in the anus, genital area and upper alimentary tract. HSV-1 is found in more than 90%of children, in the underdeveloped world. HSV-2 is most common in prostitutes at a rate of 80% globally (WHO, 2001).. Children can catch HSV-2 from genitally infected mothers. Anyone who comes in contact with infected fluid is also at risk.

How it causes disease

Herpes infects by its ability to infect lymphocytes. The virus then goes to a nucleated neurone where it stays until it is reactivated. HSV-1 and HSV-2 first infect mucoepithelia cells before infecting the neurones. Only humans show symptoms of the disease (WHO, 2001). HSV 1 and HSV 2 can cause severe disease in an infected person. One of these diseases is oral herpes. Oral herpes can be as a result of either HSV-1 or HSV-2 infection. Herpetic gingivostomatitis infection first begins on the lips then spreads to other areas of the mouth and pharynx. Genital herpes is mostly brought about by HSV-2. Here a painful lesion develops on shaft of penis or the vulva of the vagina.

Mode of action of prion

Prion diseases present themselves as genetic, infectious or sporadic disorders. One characteristic common in all prion diseases is modification of prion protein. Prion protein is a normal component of mammalian cells (Pruisner, 1998). Prion diseases manifest themselves as ataxic illnesses. Prions lack nucleic acid and are made of a modified isoform of prion protein. Mad cow disease is a neurological disorder of cattle caused by prion. The first instance of mad cow disease is said to have occurred in 1970’s. By 2010, more than 180, 000 cases of mad cow disease had been reported in United Kingdom alone (CDC, 2014). By early 2012, there were 23 reported cases of mad cow disease in North America. Mad cow disease is believed to have a close relation with a human prion disease called Creutzfedt-Jakob disease.