Virus classification

Question 1

How does the classification in viruses work?

Answer 1

• it is hierarchial
• order, family (all families have suffix viridae), genus (split into strain/type and species); genera have the suffix virus

Question 2

6 classes of classification

Answer 2

1) MORPHOLOGY (size, shape, enveloped/non-enveloped -naked)
2) PHYSIOCHEMICAL PROPERTIES (molecular mass, thermal and ionic stability)
3) GENOME (RNA/DNA)
4) MACROMOLECULES (protein composition and function)
5) Antigenic properties
6) Biological properties (host range)

Question 3

Classification of the genome

Answer 3

• BALTIMORE CLASSIFICATION
• USED BY THE INTERNATIONAL COMMITTEE ON TAXONOMY OF VIRUSES
• classification is based on the structure of the viral and distinguishes between 6 groups
• group 1: double stranded DNA
• group 2: single stranded DNA
• group 3: double stranded RNA
• groups 4 and 5: single stranded RNA
• group 6: single stranded RNA
• group 7: double stranded DNA
• subviral agents: satellites, viroids spongiform encephalopthies(eg: vCJD)

Question 4

dsDNA viruses

Answer 4

• ADENOVIRUSES: UPPER RESPIRATORY TRACT INFECTION
• POXVIRUSES: VARIOLE -SMALLPOX VIRUS-; VACCINIA-DERIVED FROM COWPOX VIRUS, IMMUNE AGAINST SMALL POX
• HERPES VIRUSES: HERPES SIMPLEX (HSV1-COLD SORES- HSV2-GENITAL HERPES); CYTOMEGALOVIRUS (unborn baby during pregnancy, people who work with children, immunocompromised patients, organ transplant recipients)
• PAPILLOMAVIRUS (CERVICAL CANCER)

Question 5

PARVOVIRUSES- ssDNA viruses

Answer 5

• PARVOVIRUS B-19- FIFTH DISEASE SLAPPED CHILD DISEASE
• SYMTPTOMS: low grade fever,headache, cold0like symptoms (runny or stuffy nose) ; then a few days later:bright red, mild rash on face, particularly on cheeks
• incubation time:4-21 days
• transmission:respiratory secretions (saliva, mucus)
• problems: complications may arise during pregnancy and with immunocompromised patients

Question 6

ds RNA viruses

Answer 6

• rotaviruses

- group A: severe gastroenteritis in infants and young children

Question 7

ssRNA viruses

Answer 7

• TOGAVIRUSES: RUBELLA-congenital rubella infection (CRI), intrauterine rubella infection, miscariage, stillbirth, abortion
• ORTHOMYXOVIRUSES (INFLUENZA A,B,C)
• RHINOVIRUSES (COMMON COLD 50%)
• PARAMYXOVIRUSES (MUMPS VIRUS)
• PICORNAVIRUSES (HEPATITIS A)

Question 8

RETROVIRUSES

Answer 8

• RETROVIRUSES (Group 6:single stranded RNA) e.g:HIV
• Hepadnaviruses (Group 7: Double stranded DNA) e.ghepatitis B
• These are called reverse transcriptase virusesas there is a RNA immediate before viral proteins can be manufactured
• group 7 can first transcribe their DNA into RNA then transcribe it back to DNA (using reverse transcriptase) before it’s inserted into the host DNA

Question 9

Reverse transcriptase enzymes

Answer 9

• encoded in retroviruses viral genome
• the enzyme is responsible for the transcription of viral RNA to produce a dsDNA that can be inserted into the host genome