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Unit 2 of 2 · B.Sc MLS Sem 6

Unit 2: Medical virology

Parasitology and Virology notes · PTU syllabus (BMLS604-18)

3 min read7 topics9 exam questions
On this page
  1. Unit summary
  2. Introduction to medical virology
  3. Classification of viruses
  4. Medically important viruses
  5. Collection, transport and storage of samples
  6. Staining techniques in virology
  7. Egg inoculation
  8. Tissue (cell) culture
  9. Key terms
  10. Quick revision
  11. Important questions

Unit summary

Viruses cause diseases from the common cold to HIV and need special diagnostic methods. This unit covers the introduction to medical virology, classification of viruses, medically important viruses, collection, transport and storage of samples, staining in virology, and sample processing by egg inoculation and tissue culture.

After this unit you can

  • Describe the properties and classification of viruses
  • Identify medically important viruses
  • Collect, transport and store samples for virology
  • Explain staining, egg inoculation and tissue culture

PTU syllabus topics

  • Introduction to medical virology
  • classification of viruses
  • medically important viruses
  • collection/transportation/storage of samples for viral diagnosis
  • staining techniques used in virology
  • sample processing for viral diagnosis (egg inoculation and tissue culture)
ProcessSample processing for viral diagnosis
  1. 1Collect early in illness

    Swab, blood, CSF

  2. 2Viral transport medium

    Keep cold

  3. 3Process quickly
  4. 4Detect

    Culture (eggs, cell lines), antigen, PCR, serology

  5. 5Report
1

Topic 1

Introduction to medical virology

  • Viruses: obligate intracellular parasites (20–300 nm) with DNA or RNA, a protein capsid, sometimes a lipid envelope; they lack ribosomes and enzymes for independent metabolism and multiply only in living cells.
ProcessViral replication
  1. 1

    Attachment to receptors

  2. 2

    Penetration

  3. 3

    Uncoating

  4. 4

    Synthesis of nucleic acid and proteins

  5. 5

    Assembly

  6. 6

    Release by lysis or budding

2

Topic 2

Classification of viruses

ComparisonClassification
Basis
Examples

DNA viruses

Double-stranded mostly

Herpesviruses (HSV, VZV, CMV, EBV), adenovirus, hepatitis B, poxviruses, papillomavirus

RNA viruses

Single-stranded mostly

Influenza, measles, mumps, polio, dengue, hepatitis A, C, E, rabies, rotavirus (dsRNA), coronaviruses

Retroviruses

RNA with reverse transcriptase

HIV

Symmetry

Icosahedral, helical, complex

Adenovirus, influenza, poxvirus

Envelope

Enveloped or naked

Enveloped viruses are destroyed by ether and detergents

  • Baltimore classification groups viruses by genome type and how they make mRNA.
3

Topic 3

Medically important viruses

ComparisonViral diseases and tests
Disease
Laboratory diagnosis

HIV

AIDS

ELISA or rapid tests (three-test strategy in India), viral load, CD4 count

Hepatitis B and C

Chronic hepatitis, cirrhosis

HBsAg, anti-HCV, PCR viral load

Dengue

Dengue fever and severe dengue

NS1 antigen (days 1–5), IgM ELISA, platelet count

Influenza and SARS-CoV-2

Respiratory infections

RT-PCR of nasopharyngeal swabs, antigen tests

Rabies

Fatal encephalitis

Antigen in brain or skin biopsy (IF), RT-PCR

Measles, mumps, rubella

Childhood rash and fevers

IgM ELISA

Herpes simplex and varicella

Vesicles

Tzanck smear (giant cells), PCR

Polio and enteroviruses

Paralysis

Stool for culture and PCR (AFP surveillance)

Rotavirus

Infant diarrhoea

Stool antigen

4

Topic 4

Collection, transport and storage of samples

Key termsVirology sample handling
Timing
Early in illness, when virus shedding is highest
Samples
Nasopharyngeal and throat swabs, vesicle fluid, CSF, blood, stool, urine, tissue
Swabs
Synthetic (flocked or Dacron) — not cotton or calcium alginate
Transport medium
Viral transport medium (VTM) with protein and antibiotics
Temperature
2–8 °C if tested within 48 hours; otherwise −70 °C; avoid repeated freeze–thaw
Packaging
Triple packaging; biosafety for high-risk agents
  • Paired sera: acute and convalescent (10–14 days apart) — a fourfold rise in antibody confirms recent infection.
5

Topic 5

Staining techniques in virology

Key termsStains and microscopy
Inclusion bodies
Negri bodies (rabies) with Seller's stain; Guarnieri bodies (vaccinia); owl's-eye inclusions (CMV)
Tzanck smear (Giemsa)
Multinucleated giant cells in herpes
Immunofluorescence
Viral antigens in cells with fluorescent antibodies (respiratory viruses, rabies)
Electron microscopy
Negative staining (phosphotungstic acid) — rotavirus in stool
Cytopathic effect
Unstained or stained cell cultures
6

Topic 6

Egg inoculation

ComparisonRoutes of egg inoculation (8–12-day embryonated hen's eggs)
Site
Viruses

Chorioallantoic membrane

Pocks (white lesions)

Variola, vaccinia, herpes simplex

Amniotic cavity

Primary isolation

Influenza, mumps

Allantoic cavity

Large yields

Influenza (vaccine production), Newcastle disease

Yolk sac

Embryo

Chlamydia, rickettsiae, some arboviruses

  • Procedure: candle the egg to locate the embryo and air sac, disinfect the shell, drill and inoculate aseptically, seal and incubate; detect growth by death, pocks or haemagglutination of harvested fluids.
7

Topic 7

Tissue (cell) culture

ComparisonTypes of cell culture
Description
Examples

Primary cell culture

Directly from tissue; limited divisions

Monkey kidney cells

Diploid cell strains

Normal cells; about 50 divisions

Human fibroblasts (WI-38, MRC-5)

Continuous cell lines

Transformed; divide indefinitely

HeLa, Vero, HEp-2

Key termsDetecting viral growth
Cytopathic effect (CPE)
Rounding, giant cells (syncytia), inclusions, cell death
Haemadsorption
Red cells stick to infected cells (influenza)
Interference
Virus blocks another's CPE (rubella)
Immunofluorescence or PCR
Identifies the virus
  • Shell vial culture (centrifugation enhanced, detected by IF in 1–2 days) speeds diagnosis. Today molecular methods (PCR, RT-PCR) are the mainstay of viral diagnosis.

Key terms

Capsid
Protein coat of a virus
Envelope
Lipid membrane around some viruses
Viral transport medium
Medium preserving viruses in transit
Cytopathic effect
Visible damage to cells caused by virus growth
Inclusion body
Aggregate of virus or viral proteins in infected cells

Quick revision

  • Virus structure; replication steps.
  • DNA, RNA, retroviruses; symmetry; envelopes; Baltimore.
  • Important viruses and tests.
  • Sample timing, swabs, VTM, temperature, paired sera.
  • Inclusion bodies, Tzanck, IF, EM; egg routes; primary, diploid, continuous cell cultures; CPE, haemadsorption; PCR.

Important exam questions

Practice questions written to the PTU exam pattern for this unit's syllabus: short answers (Section A style) and long answers (Sections B and C style).

Short-answer questions

  1. Q1.Why are viruses called obligate intracellular parasites?
  2. Q2.Give two DNA and two RNA viruses.
  3. Q3.Which swab is preferred for viral samples?
  4. Q4.What are Negri bodies?
  5. Q5.Name the routes of egg inoculation.
  6. Q6.What is cytopathic effect?

Long-answer questions

  1. Q1.Describe the general properties and classification of viruses.
  2. Q2.Describe the collection, transport and storage of samples for viral diagnosis.
  3. Q3.Describe egg inoculation and tissue culture for virus isolation.

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