.

1. Dr Abhishek Kumar Jain
Assistant Professor
Department of Microbiology
RVRS Govt Medical College Bhilwara
1

2. Over view
• Special features of viruses
• Identify major human viral illnesses
• Identification of viral diseases
• Treatment options
• Prevention
• Vaccination
• Safety measures
2

3. Introduction
Figure 1- On the left is a scale that ranges
from the size of an atom to the size of a
child (one meter).
From this, we can see how tiny viruses are
relative to bacteria, as well as how small
bacteria are relative to parasites and fungi.
From the microscope images on the right,
we can see how diverse pathogens are
structurally.
This diversity originally made
microorganisms very difficult to classify.
Today, they are primarily classified by
differences in their genetic material (DNA
vs. RNA), as well as morphological
features.
3
nm
nm
μm
mm

4. Properties of Viruses
• Very small, infectious, obligate intracellular non living parasite
• Size= 0.02 to 0.3 μ m.
• Have either RNA or DNA core
• Have outer cover of Protein or lipid (capsid)
• They contain enzymes needed by themselves unless they get
susceptible and permissive cellular host.
• All viruses must make mRNA that can be translated by host
ribosomes.
4

5. Basic Virus Structure
Nucleocapsid
Host derived Lipid Membrane
Glycoprotein
5
Capsomere
Non enveloped
virus
Nucleic acid

6. Classification of viruses
• Viruses are classified principally according
• To the nature and structure of their genome and
• Their method of replication,
• Not according to the diseases they cause.
• Thus there are DNA viruses and RNA viruses.
• Each type may have single or double strands of genetic
material.
6

7. Classification of viruses
• RNA virus- Single Stranded (ss) RNA viruses are further divided into
• Positive (+) sense RNA and
• Negative (-) sense RNA.
• DNA viruses typically replicate in the host cell nucleus, and
• RNA viruses typically replicate in the cytoplasm.
• If the infected cell belongs to the germ line, the integrated provirus can
become established as an endogenous retrovirus that is transmitted to
offspring.
7

8. Retrovirus
• Certain ss, (+) sense RNA viruses termed retroviruses use a very
different method of replication.
• Reverse transcription is accomplished using the enzyme reverse
transcriptase, which the virus carries inside its shell.
• Because RNA transcription does not involve the same error- checking
mechanisms as DNA transcription, RNA viruses, particularly
retroviruses, are prone to mutation.
• 1% of the human genome consists of endogenous retroviral sequences,
representing past encounters with retroviruses during the course of
human evolution.
8

9. Overview-the Good-the Bad-the Ugly
• Viruses seem to exist solely to wreak havoc on society and suffering to
humanity. They are responsible for knocking out significant chunks of the
global population
• 1918 Influenza epidemic which killed 50 to 100 million people.
• Smallpox in the 20th century causes deaths of around 200 million.
• Swine flue in 2003 and the current SARS COVID-19 Pandemic is just one
in a series of ongoing and never- ending deadly viral assaults.
• But most of us are not aware of the Positive role viruses play in supporting
much of life on earth.
• Lately virologists are of the opinion that “Viruses keep us & the planet
alive, rather than kill us.”
9

10. The Good About Viruses…
• All the essential things viruses do in the world far outweigh the bad
things.
1. Some viruses maintain the health of fungi and plants.
2. They are the major predators of the bacterial world.
3. These viruses kill about 20% of all oceanic microbes, and about
50% of all oceanic bacteria, each day.
Which gives enough nutrients to oxygen-producing planktons with
high rates of photosynthesis.
Those planktons produce about half the oxygen on the planet- a
process enabled by viruses.
10

11. The Good About Viruses…
4. When populations become very abundant, viruses tend to
replicate very rapidly and knock that population down, creating
space for everything else to live “Kill The Winner”
5. Certain kind of grass has an increased heat tolerance due to
viruses.
11

12. Host Defence
• The body has a number of defences against viruses:
1. Physical barriers, such as the skin and mucous membranes which
discourage easy entry.
2. The body’s immune defences, which attack the virus.
When a virus enters the body, it triggers the body’s immune
defences. These defences begin with WBCs and lymphocytes, which
learn to attack and destroy the virus or the infected cells
3. Immunity can also be produced by getting a vaccine.
12

13. Virus infection
• The virus first attaches to the host cell at receptor molecules on the
cell surface.
• The viral DNA or RNA then enters the host cell and separates from
the outer cover (uncoating) and replicates inside the host cell with the
help of specific enzymes.
• The newly synthesized viral components assemble into a complete
virus particle.
• The host cell typically may or may not die, releasing new viruses
that infect other host cells.
13

14. Virus infection
• Each step of viral replication involves different enzymes and offers an
opportunity to interfere with the process of infection.
• Many viral infections are cleared by the body's defenses, but some
remain in a latent state, and some cause chronic disease
• In latent infection, viral RNA or DNA remains in host cells but does
not replicate or cause disease for a long time. Sometimes a trigger
(immunosuppression) causes reactivation.
14

15. Viral Replication
• Step 1: Attachment: The virus attaches itself to the target cell.
• Step 2: Penetration: The virus is brought into the target cell.
• Step 3: Uncoating and Replication: The enveloped virus loses its
envelope, and viral RNA is released into the nucleus to replicate.
• Step 4: Assembly: Viral proteins are assembled.
• Step 5: Egress (Release): New viral particles are released.
15

16. Viral Replication
• In the case of the flu, the target cell is not killed; however, other
viruses, like the T4 bacteriophage, cause cell death to release the
newly created copies of itself.
• Remember: The correct order of the different steps is as follows:
• "Attachment, penetration, uncoating and replication, assembly,
and egress (release)"
16

17. Viral Replication
As we’ve seen, viruses go through
as specific cycle as they replicate—
and they target and infect cells in
order to do so. Let’s look at the
process of a flu virus replicating:
1. Attachment
2. Penetration
3. Uncoating & Replicaion
4. Assembly
5. Egress (Release)
17

18. Infection by Virus
18

19. Difference between Bacterial & Viral
Infection
• Difference between bacterial and viral infection
• Clinically -We know- Virus infection will produce intense prodromal
symptoms like
• Low grade fever,
• Severe myalgia,
• Malaise, fatigue,
• Loss of appetite as against bacterial disease
• Epidemiology - usually outbreaks especially respiratory viruses.
• Season of the year is important in viral illnesses-
Ex- dengue in rainy season and Chickenpox in winter.
• Respiratory viruses dominate the viral illnesses
19

20. Bacteria Virus
What is it ? A bacteria is a living organism that has DNA &
RNA, and has a cell wall and cell membrane.
A virus is a small, infectious agent which has
either DNA or RNA but no cellular structure and
only lives inside the living cells of the organism
What it does ? They grow, live and metabolize to help fight
foreign substances by breaking down cells.
A virus invades and takes over cells. A virus
cannot exist without a living host.
Good or Bad Appx. 90% are good and 10 % are bad All bad
Number of cells One cell No cells , not living
Size Larger (1000 nm) Smaller (20-400 nm)
Spreads in body Reproduces using a form of a sexual reproduction Invades a host cell, takes over the cell and
reprograms the cell to make copies of the viral
DNA/RNA. It then destroys host cell, releasing
new virus DNA/RNA.
Infection Localized infection Systemic infection
Treatment Antibiotics or Antibacterials, immune system and
infection prevention
Vaccine or antivirals, immune system and
infection prevention. 20
Difference between Bacterial and Viral infection

21. Transmission
• Viruses exist worldwide, but their spread is limited by inborn resistance,
prior immunizing infections or vaccines, sanitary and other public health
measures (SMS), and prophylactic antiviral drugs.
Transmission occurs by various methods
1. Via respiratory and enteric secretions.
2. Sexually transmitted.
3. Transfer of blood (via transfusion, mucosal contact, or puncture by a
contaminated needle).
4. Via rodent or arthropod vectors, and bats.
5. GI tract (feco-oral).
6. Animal bites like Rabies infection .
21
* SMS- Soap & water, Mask, Social distancing >1 m

22. Types of Viral
Infections
22

23. Types of Viral Infections
• Respiratory infections: The most common are upper respiratory
infections, that produce sore throat, sinusitis and the common cold and
lower respiratory infections involving lung parenchyma.
• Viruses that are commonly seen-influenza, pneumonia and COVID 19
• In small children, viruses commonly cause croup or bronchiolitis
• Respiratory infections are more likely to cause severe symptoms in
infants, older people, and people with a lung or heart disorder.
• Gastrointestinal tract: gastroenteritis, by noroviruses and rotaviruses
• Liver: hepatitis A,B,C, D,E,
23

24. Types of Viral Infections
• Nervous System :Rabies and west Nile virus cause encephalitis,
meningitis
• Poliomyelitis is being eradicated.
• Skin: result in warts or other blemishes. Chickenpox cause a rash.
• Placenta and fetus: Some viruses, such as the Zika, the rubella virus,
and cytomegalovirus can infect the placenta and fetus in pregnant
women.
• Enteroviruses, coxsackie viruses typically affect many body systems.
• AND MANY MORE.........
24

25. Viruses and Cancer
• Some viruses are oncogenic and predispose to certain cancers:
• Human papillomavirus (HPV): Cervical carcinoma,
• Human T-lymphotropic Virus 1 (HTLV-1): human leukemia and
lymphoma
• Epstein-Barr virus: Nasopharyngeal carcinoma, Burkitt lymphoma,
Hodgkin lymphoma,
• Hepatitis B and hepatitis C viruses: Hepatocellular carcinoma
• Human herpes virus 8: Kaposi sarcoma, lymphomas, and ,
multicentric Castleman disease (a lymphoproliferative disorder)
25

26. Diagnosis
• Viral disorders can be diagnosed as follows:
• Clinically - by clinical syndromes - e.g. characteristic skin rash in measles,
rubella & chickenpox
• Epidemiologically - during epidemic outbreaks such as influenza and
mumps, Cholera.
• Definitive laboratory diagnosis is necessary mainly when specific
treatment may be helpful or when the agent may be a public health threat
(HIV).
• Typical hospital laboratories can test for some viruses, but for less common
disorders (e.g. rabies), specimens must be sent to National Virology
Institutes (NIV)
26

27. Specimen collection and transport
• Appropriate sample should be collected as per clinical manifestation
• Blood
• Nasopharyngeal or oropharyngeal swab collected in VTM.
• Biopsy Tissue
• Histopathological specimen
• Sample should be transported maintaining cold chain
27

28. Direct examination
• Direct examination by electron microscopy
• A sample of blood or other tissues is examined with an electron
microscope, which provides high magnification with clear resolution.
• Histopathology with electron (not light) microscopy
can sometimes help.
28

29. Culture
• It is gold standard for diagnosis.
• Not used for routine diagnosis
• Tedious and required special setup.
29

30. Serology
• Serologic examination during acute and convalescent stages can be
sensitive and specific, but slow; with some viruses, especially
flaviviruses, cross-reactions confound diagnosis.
• Blood may also be tested for antigens, or antibodies.
30

31. Molecular testing (NAAT)
• More rapid diagnosis can sometimes be made using polymerase chain
reaction(PCR), or viral antigen tests.
• PCR techniques make it easier for doctors to rapidly and accurately
identify the virus.
• These tests are quick, especially when the infection is a serious threat
to public health.
31

32. Infections
Microbes Microscopy Culture NAAT Antigen Antibody
Adenovirus √ √
BK virus √ √
COVID 19 (SARS-CoV-2) √ √
Cytomegalovirus (CMV) √ √ √ √
Enteroviruses √ √ √
Epstein-Barr Virus (EBV) √ √
Hepatitis A, B, C, D and E √ √
Herpes simplex virus √ √ √ √
Herpes virus 6 √ √
HIV √ √ √
Human papillomavirus (HPV) √ √
Influenza √ √ √ 32

33. Infections
Microbes Microscopy Culture NAAT Antigen Antibody
Lymphocytic choriomeningitis (LCMV) √ √
Measles √ √
Mumps √ √
Nor Virus √ √
Para influenza √ √
Parvovirus B19 √ √ √
Rabies √ √ √ √
Respiratory syncytial (RSV) √ √ √
Rubella √ √
St. Louis encephalitis √
Tick Borne encephalitis √
Varicella zoster √ √ √ √
West Nile Virus √ √
Zika virus √ √ 33

34. Treatment of Viral Infection
1. General measures
2. Antiviral drugs & Interferons
3. Vaccines
4. Immune globulins
34

35. General measures
• Personal protective measures
• People can help prevent many viral infections by common sense
measures to protect themselves and others. They vary depending on
the how the virus is spread.
• Frequently and thoroughly washing the hands with soap and water
• Consuming appropriately prepared food and liquids
• Avoiding contact with infected people and contaminated surfaces
• Cough etiquette (Sneezing and coughing into tissues (into the folded upper
arm), completely covering the mouth and nose)
• Using safe-sex practices
• Preventing bites by ticks, mosquitoes, and other arthropods.
35

36. Antiviral drugs
• Antiviral chemotherapy can be directed at various phases of viral replication.
• Mechanism of action:-
1. Interferes with viral particle attachment to host cell membranes or
uncoating of viral nucleic acids
2. Inhibits a cellular receptor required for viral replication
3. Blocks specific virus-coded enzymes and proteins that are produced in the
host cells and that are essential for viral replication but not for normal host
cell metabolism
• Antiviral drugs are most often used therapeutically in
1. Herpes viruses (including cytomegalovirus),
2. Respiratory viruses
3. HIV
4. Chronic Hepatitis B and C 37

37. Interferons
• Interferons- are compounds released from infected host cells in
response to viral or other foreign antigens having antiviral properties.
They act by:-
1. Blocking translation and transcription of viral RNA and
2. Stopping viral replication without disturbing normal host cell function.
• Interferons are sometimes given attached to polyethylene glycol
(pegylated formulations), allowing slow, sustained release of the
interferon.
38

38. Interferons
• Viral disorders sometimes treated with interferon therapy include
1. Chronic hepatitis B and C
2. Genital warts
3. Kaposi's sarcoma
4. COVID-19
• Adverse effects - include fever, chills, weakness, and myalgia,
typically starting 7 to 12 hours after the first injection and lasting up to
12 hours. Depression, hepatitis, and,
• When high doses are used, bone marrow suppression are also possible.
39

39. Vaccine Prevention-
• Vaccination is the primary method of controlling viral disease, which is
intended to prevent outbreaks by building immunity.
• Vaccines may be prepared using live viruses, killed viruses, or molecular
subunits of the virus.
• The killed viral vaccines and subunit viruses are both incapable of causing
disease.
• Vaccines work by stimulating immunity.
• Viral vaccines in general use include hepatitis A, hepatitis B, human
papillomavirus, influenza, Japanese encephalitis, measles, mumps,
poliomyelitis, rabies, rotavirus, rubella, tick-borne encephalitis, varicella,
and yellow fever.
40

40. Vaccine Prevention-
• Adenovirus and smallpox vaccines are available but used only in high-
risk groups (eg, military recruits).
• There is a vaccine for prevention of Zaire Ebola virus.
• Smallpox was eradicated in 1978,
• Cattle plague was eradicated in 2011.
• Measles has been almost eradicated Americas.
• COVID-19
41

41. Prevention- Vaccination
• Cattle plague (caused by a virus closely related to human measles
virus) was eradicated in 2011.
• Poliomyelitis has been eradicated from all but a few countries where
logistics and religious sentiment continue to impede vaccination.
• The prospects for eradication of other more intractable virus infections
(such as HIV) are presently uncertain.
42

42. Immunoglobulins
• Immunoglobulins are a sterilized solution of antibodies
collected from the blood of a group of people.
• They are available for passive immune prophylaxis in
limited situations.
• They can be used
 Pre-exposure (eg, for hepatitis A), OR
 Post-exposure(eg, for rabies or hepatitis, COVID-19)
OR
 Treating disease (eg, eczema vaccinatum).
43

43. Immunoglobulins
• The immunity provided by immune globulins lasts for only
a few days or weeks, until the body eliminates the injected
antibodies.
• When people are exposed to rabies or hepatitis B, they are
given both immune globulin (Passive) and a vaccine to
help prevent infection from developing or reduce the
severity of infection.
44

44. Immunoglobulins
• Immunoglobulins can be collected from the blood from
1. People who are generally healthy (pooled human immunoglobulin)
2. People who have been infected with the organism (hyperimmune
globulin)
3. Hyperimmune globulin is available for only a few infectious
diseases, such as hepatitis B, rabies, tetanus, and chickenpox. It is
usually given after people have been exposed to a microorganism
but before they get sick.
4. Immune globulins are given by IM /IV injection.
45

45. Take Home Message
• Identifying the viral infection is essential with common clinical guidelines
• Establishing the pathogen is often not needed in common illnesses like
common cold, Influenza in children diarrhea due to Rotavirus
• Diagnosis is imperative in many other viral diseases like types of viral
hepatitis, Dengue COVID-19 as these can pose public hazard and need to be
notified
• PCR techniques recognize the virus with good specificity and sensitivity.
• Antigen antibody assessment along with serology give good results
• General measures along with specific antiviral drug can cure the illness.
• Use of Interferons and Immunoglobulins is helpful.
• Prevention with vaccination can control the viral disease and eradicate it
like in a case of Poliomyelitis
46

46. THANK YOU
47