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Virology Short Notes

The topic ‘ Virology  Short Notes for MCQs’  will serve as a capsule for candidates who are participating in posts for medical lab technician,  medical lab technologist, and such related fields.

General Characteristics of Virus

• Viruses are obligate intracellular parasites.
• Viruses lack the metabolite machinery of their own to generate energy or synthesize proteins.
• Size 20-400 nm ( largest – poxvirus, smallest – picornavirus)

Morphology of Virus

• Nucleic acid core surrounded by a protein coat (capsid)
• The capsid is made of capsomers ( morphological subunits). Capsomers in turn made of protomers
• Whole virus particles may be cubic or helical – cubical are icosahedral ( 20 triangle facets and 12 vertices)
• The envelope consists of the lipid bilayer ( derived from host cell membrane) and glycoprotein viral coded, also called peplomer.

Prion:  Proteiaceous infection particles ( no nucleic acid, only protein coat) called a slow virus.

Disease caused: -Kuru, Creutzfeld-Jacob disease

Viroid: Only nucleic Acid but not protein coat

Important points

• Except for Reovirus and Rotavirus, all RNA viruses are single-stranded.
• Except for the parvo virus, all DNA viruses is double-stranded
• The time period during which no virus is recovered from cells is called the ” Eclipse period”
• The time period from infection until lysis  of cell is called ‘ latent period’

1 . Culture  of animal virus

1. Suckling mice (> 48 hrs old) → toga and coxsackievirus
2. Chick embryo ( 7- 12 days old)

1. chorioallantoic membrane -Pox virus

2. Allontic cavity – influenza and rabies for vaccine production.

3. Amniotic fluid – influenza ( primary isolation)

4. Yolk sac – virus as well as bacteria ( Chlamydia and Rickettsia)

2.  Cell culture

1. Primary cell culture :

Obtain from the fresh organ, undergo mitosis only limited growth, used for vaccine production and primary isolation. eg. monkey kidney cell

2. Diploid ( semi-continuous)

Undergo up to 50 serial subculture

Used for some fastidious virus and vaccine production

Fibroblast derived from’ human embryo lung strains’ is used.

3. Continuous culture

These are cells of a single type capable of infinite growth in vitro

Not used for vaccine production

e.g. Hela cell, Hep 2, KB, etc.

1. RNA virus

1. Single-stranded

• Orthomyxoviruses → ( influenza)
• Paramyxoviruses → ( measles, mumps, parainfluenza)
• Rhabdovirus → Rabies ( bullet-shaped)
• Retrovirus → AIDS  and related disorders
• Enterovirus → poliomyelitis
• Coxsackievirus → myocarditis, pericarditis
• Rhinovirus → common cold
• Toga virus → rubella, yellow fever, Japanese encephalitis
• Hepatitis A, C, D and E → Hepatitis

2. Double-stranded RNA

• Rheoviruses → gastroenteritis
• Rotavirus → infantile diarrhea
• Orbivirus

2. DNA virus

1.  Single-stranded

Parvovirus ( defective virus ) cannot replicate autonomously cause aplastic crisis in sickle cell disease.

2. Double-stranded

• Poxvirus ( largest virus brick-shaped) → smallpox and vaccine
• Adenovirus → Respiratory infection
• Herpes simplex virus → chickenpox, shingles
• Varicella-zoster virus -1 → ( HSV-1)  and  conjunctivitis, gingivostomatitis
• HSV -2→ Genital disease
• Epstein Barr virus ( EBV) → infectious mononucleosis, Burkett’s  lymphoma
• Hepatitis -B virus → Hepatitis
• Polyomavirus → Popiloma, mart
• Cytomegalovirus (CMV) → CMV mononucleosis

Oncogenic virus ( cancer-causing virus)

RNA virus

HTLV-I and II (Human  T cell leukemia virus) → leukemia

Hepatitis C virus → Hepatocellular Carcinoma

DNA virus

EB virus → Burkitt lymphoma

HSV-2 → B- cell lymphoma, carcinoma

Hepatitis B virus → Hepatocellular carcinoma

Human papillomavirus→ cervical, penile cancer

Inclusion Body

1. Intracytoplasmic

Guarneri body → Smallpox

Negri body→ Rabies

Councilman body → Yellow fever

Bolling body → Fowlpox

2. Intranuclear 

Cowdry ‘A’ body → Herpes, yellow fever

Cowdry ‘B’ body → Poliovirus, Adenovirus

Contd…