Viral infections
The oral cavity can be targeted by a variety of viral pathogens (Tyring, 2006). While these viral infections are variable in severity, they are more virulent in individuals with compromised immune systems (Regezi, 2016).
Viruses are biologically different than bacteria or fungi in that viruses are not capable of replication and proliferation by themselves.
A virus particle, or virion, consists of a protective protein coat called a capsid that contains the viral genome.
The viral genome is encoded with either deoxyribonucleic acids (DNA) or ribonucleic acids (RNA), depending on the viral species.
The capsid includes proteins that target specific cell types in specific species as well as mechanisms for entering into the target cell types.
The host cell’s own protein machinery then replicates the virus’s genetic material and produces the viral proteins required for capsid formation encoded by the virus’s genome. This replicates the virus, allowing more copies to be released to infect more cells.
1. Herpes Viral Infections
Herpesviridae is the largest viral family, encompassing over 300 species of the herpes virus that can infect animal cells, although only a small number of them are capable of causing maxillofacial or oral infections in humans (Slots, 2009). Besides the herpes viruses, the viruses that cause influenza and the common cold are the only viral species more common in humans.
All herpesviruses share a latency behavior, which means that the virus remains dormant within infected cells for a certain length of time, which in some species can last decades. Herpes viruses are grouped into subfamilies based on the cell types in which they lay dormant.
The varicella-zoster virus and the herpes simplex virus (HSV) 1 and 2 are in the Alphaherpesvirinae subfamily that exhibits latency in neuronal cells.
The Epstein-Barr virus (human herpesvirus 4) is a member of the Gammaherpesvirinae subfamily and remains latent within B-lymphocytes.
Cytomegalovirus (human herpesvirus 5) is a Betaherpesvirinae subfamily member and is latent within immune monocytes and lymphocytes (Akhter, 2017).
2. Papillomavirus
Papillomavirus is another large family of viruses that can infect or cause complications in oral and maxillofacial tissues (Graham, 2017).
A typical presentation of papillomavirus infection on the face or mouth includes venereal and oral warts and squamous papillomas. Human papillomaviruses infect epithelial cells and most commonly affect epithelial tissue in anogenital, urethral, epidermal, laryngeal, tracheal, bronchial, and mucosal tissue types.
In addition, several papillomavirus subtypes have been shown to cause cancers in certain tissues, including oropharyngeal squamous cell carcinoma (Hobbs et al., 2006).
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