Virus

Viruses are classified based on their genetic composition, in modern taxonomy - DNA and RNA viruses.

Differences in the type of DNA and RNA composition and structure help to further categorize them into:

dsDNA - virus with a double stranded (ds) DNA.
ss DNA - virus with single stranded (ss) DNA.
+ssRNA - virus with a positive sense RNA [ this type of RNA is like the mRNA that can be directly read to be translated into proteins]
-ssRNA - virus with a negative sense RNA [type of RNA must be converted to positive sense like the mRNA and then can be used to for translation into proteins]

Recollect the central dogma of life. Remember, virus either has RNA or DNA and never both. It also lacks ribosomes that help in translate of mRNA into proteins, which is why, they must enter a living cell to use the host's ribosomes and enzymes to decode its own DNA or RNA into proteins that will form a new viral particle. We will learn the details in Viral Life Cycle (Next exam module).

Central dogma of life

Table 1: Common Pathogenic Viruses
Genome	Family	Example Virus	Clinical Features
dsDNA, enveloped	Poxviridae	Orthopoxvirus	Skin papules, pustules, lesions
	Poxviridae	Parapoxvirus	Skin lesions
	Herpesviridae	Simplexvirus	Cold sores, genital herpes, sexually transmitted disease
dsDNA, naked	Adenoviridae	Atadenovirus	Respiratory infection (common cold)
	Papillomaviridae	Papillomavirus	Genital warts, cervical, vulvar, or vaginal cancer
	Reoviridae	Reovirus	Gastroenteritis severe diarrhea (stomach flu)
ssDNA, naked	Parvoviridae	Adeno-associated dependoparvovirus A	Respiratory tract infection
ssDNA, naked	Parvoviridae	Adeno-associated dependoparvovirus B	Respiratory tract infection
dsRNA, naked	Reoviridae	Rotavirus	Gastroenteritis
+ssRNA, naked	Picornaviridae	Enterovirus C	Poliomyelitis
	Picornaviridae	Rhinovirus	Upper respiratory tract infection (common cold)
	Picornaviridae	Hepatovirus	Hepatitis
+ssRNA, enveloped	Togaviridae	Alphavirus	Encephalitis, hemorrhagic fever
	Togaviridae	Rubivirus	Rubella
	Retroviridae	Lentivirus	Acquired immune deficiency syndrome (AIDS)
−ssRNA, enveloped	Filoviridae	Zaire Ebolavirus	Hemorrhagic fever
	Orthomyxoviridae	Influenzavirus A, B, C	Flu
	Rhabdoviridae	Lyssavirus	Rabies

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Table 1Links to an external site. CC BY 4.0 SA is modified to add more information by Shreya Patel from original table licensed under CC BY 4.0Links to an external site.

Table Reference: D: Taxonomy of Clinically Relevant Microorganisms.; Microbiology OpenStax 2022. Link to Textbook