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
- Suckling mice (> 48 hrs old) → toga and coxsackievirus
- 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
- 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.
- 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
- 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
- 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