Viruses are the smallest and most primitive microorganisms that can only replicate inside host cells. They do not have cells and cellular organelles like bacteria, consisting only of genetic material (DNA or RNA but not both) surrounded by a protein coat. Viruses infect humans through various routes and have a complex replication process rather than binary fission. They are classified based on properties like nucleic acid type, shape, presence of envelope, size, and antigens; and replicate through attachment, penetration, uncoating, biosynthesis, assembly, and release stages inside host cells.

1. PRESENTED BY
EKTA RANI
ASST. PROFESSOR
PCPS

2.  Viruses are the smallest unicellular organisms
 They are obligate intracellular.
 Viruses are the most primitive microorganisms infecting man.
 They possess either DNA (deoxyribonucleic acid) or RNA
(ribonucleic acid), bur never both.
 Filterable: They are smaller than bacteria, can be passed through the
bacterial filters.
 They cannot be grown on artificial cell free media (However, they
can grow in experimental animals, embryonated eggs or tissue
culture).
 They multiply by a complex method, bur not by binary fission as
seen in bacteria.
 Viruses do not have a proper cellular organization.
 They do not have cell wall or cell membrane or cellular organelles
including ribosomes.
 They are not susceptible to antibacterial antibiotics.

3.  Nucleic Acid- Viruses have only one type of
nucleic acid, either DNA or RNA bur never both.
 Capsid- Capsid is composed of a number of
repeated protein subunits (polypeptides) called
capsomeres.
 Symmetry- Depending upon the arrangement of
capsomeres surrounding the nucleic acid, three
types of symmetries are described.
1. Icosahedral (cubical) symmetry
2. Helical Symmetry
3. Complex Symmetry

4.  Envelope- Certain viruses possess an envelope
surrounding the nucleocapsid. Envelope is
lipoprotein in nature.

5. viruses are extremely small, vary from 20-400
nm in size. Smallest virus is parvovirus (20 nm)
and largest being poxvirus (400 nm).

6.  Most of the animal viruses are roughly spherical
with some exceptions.
 Shapes of the Viruses-
1. Rabies virus: Bullet shaped
2. Ebolavirus: Filamentous shaped
3. Poxvirus: Brick shaped
4. Adenovirus: Space vehicle shaped

7.  International committee on Taxonomy of Viruses (2000)
had proposed a classification for viruses
 Viruses are grouped into families (ending with suffix
'viridae') on the basis of morphology, genome structure,
and strategies of replication.
 Viruses infecting humans belong to 24 families
 Most of the families are further classified into genera
(ending with suffix -'virus') based on physiochemical or
serologic differences.
 Some families (Poxviridae, Herpesviridae, Parvoviridae
and Paramyxoviridae) have subfamilies, which in turn
consist of genera.

8. Classical virus classification schemes have been based on
the consideration of major properties of viruses:
1- The type of nucleic acid which is found in the virion
(RNA or DNA, single stranded or double stranded)
2-The symmetry and shape of the capsid (Cubic, helical,
complex).
3- The presence or absence of an envelope (enveloped,
naked)
4- The size of the virus particle.
5- Antigenic properties.
6- Biologic properties, including natural host range, mode
of transmission, vector relationship, pathogenicity, and
tissue tropism.

10.  Viruses do not undergo binary fission (seen in
bacteria), but undergo a complex way of cell
division.
 Replication of viruses passes through six
sequential steps:
Attachment - > Penetration -> Uncoating- >
Biosynthesis -> Assembly-> Maturation ->
Release

11. 1) Respiratory route (probably the most common
route)
2) Oral route
3) Cutaneous route
4) Vector bite
5) Animal bite
6) Sexual route
7) Blood transfusion
8) Injection
9) Transplacental route
10) Conjunctival route

12.  Specimens for virus isolation should be collected
within 4 days after onset of illness as virus shedding
decreases rapidly after that time. With only a rare
exception, virus cultures are not worthwhile for
specimens collected more than 7 days after the onset
of illness.
 ensure proper evaluation, the following information
should accompany the specimen:
(1) date of illness onset
(2) date and time specimen was collected
(3) admitting diagnosis
(4) source of specimen.

13. 1. Cleanse venepuncture site with 70% isopropyl
alcohol.
2. Starting at the site, swab concentrically with 2%
iodine tincture.
3. Allow the iodine to dry (≈ 1 min).
4. Do not palpate the vein at this point.
5. Collect 8-10 ml in an anticoagulant tube (viral
transport is not required).
6. After venepuncture, remove iodine from the skin
with alcohol.

14. Disinfect site with 2% iodine.
2. Insert a needle with stylet at L3-L4, L4-L5, or L5-S1
interspace.
3. On reaching the subarachnoid space, remove the stylet
and collect 2-5 ml in a sterile leakproof tube.
Cervical & vaginal swab
1. If lesions are present, swab vigorously.
2. If lesions are not present, remove mucus from the cervix
with a swab and discard the swab.
3. Firmly sample the endocervix (≈ 1 cm. into the cervical
canal) with a fresh swab by rotating the swab for 5
seconds.
4. Carry out a vulvar sweep using a second swab; place
both swabs in the same transport tube.

15. Pass directly into a clean, dry container.
2. 2-4 g of stool to sterile, leakproof container and
transport immediately to lab.
NASAL SWAB
1. Pass a flexible, fine shafted swab into the nostril.
2. Rotate slowly for 5 seconds to absorb secretions.
3. Repeat for other nostril using a fresh swab. Place
both swabs in the same transport tube.

16. Firmly sample base of lesion(s) with a swab.
2. Place swab in UTM (Universal Transport Medium).
THROAT SWAB
1. Using a tongue depressor, depress the tongue to
prevent contamination with saliva.
2. Firmly sample the posterior pharynx, tonsils, and
inflamed areas with a sterile swab.
3. Place swab in UTMa

17. Refer to specific guidelines for urine collection.
Collect 5 ml. of midstream clean, voided urine in a
sterile container (UTMa not required)
TISSUE
1. Obtain samples from areas directly adjacent to
affected tissue.
2. Place specimen in a sterile vial containing UTMa.

18. 1. Electron microscopy
2. lmmunoelectron microscopy
3. Fluorescent microscopy
4. Light microscopy
5. Histopathological staining: To demonstrate inclusion
bodies
6. lmmunoperoxidase staining
7. Detection of viral antigens By various formats such as
ELISA, direct IF, ICT, flow through assays.
8. Detection of the Specific Antibodies
• Conventional techniques- such as HAI, neutralization test and
CFT.
• Newer diagnostic formats such as ELISA, ICT, flow through
assays.

19. 9. Molecular Methods to Detect Viral Genes
a) Nucleic acid probe-for detection of DNA or RNA by
hybridization
b) PCR- for DNA detection by amplification
c) RT-PCR- for RNA detection
d) Real time PCR- for DNA quantification
e) Real time RT-PCR- for RNA quantification
10. Isolation of Virus by
1) Animal inoculation
2) Embryonated egg inoculation
3) Tissue cultures: Organ culture, explant culture,
cell line culture

21. THANK YOU