General Virology- RNA viruses

General Virology and
Overview of Viral Infections

GENERAL PROPERTIES OF
VIRUSES
2

Essentials of Medical Microbiology by Apurba S Sastry © Jaypee Brothers Medical Publishers
GENERAL PROPERTIES OF VIRUSES
3
▰ Smallest unicellular organisms that are obligate intracellular.
▰ Viruses are the most primitive microorganisms infecting man.

Viruses differ from bacteria as:
4
▰ Obligate intracellular
▰ Possess either DNA (deoxyribonucleic acid) or RNA (ribonucleic acid), but
never both
▰ Smaller than bacteria, can be passed through the bacterial filters
▰ Cannot be grown on artificial cell free media (grow in animals, embryonated
eggs or tissue culture)

Viruses differ from bacteria as (Cont..):
5
▰ Multiply by a complex method (not by binary fission).
▰ Do not have a proper cellular organisation.
▰ Do not have cell wall or cell membrane or cellular organelles including
ribosomes
▰ Lack the enzymes necessary for protein and nucleic acid synthesis.
▰ Not susceptible to antibacterial antibiotics

MORPHOLOGY OF VIRUS
7
▰ The entire virus particle called as virion, comprises of a nucleic acid (DNA or
RNA) surrounded by a protein coat called as capsid, together known as the
nucleocapsid.
▰ Some viruses also have an outer envelope.

Nucleic Acid
8
▰ Viruses have only one type of nucleic acid, either DNA or RNA.
▰ They are classified as DNA viruses and RNA viruses.
▰ Nucleic acid - single or double stranded, circular or linear, segmented or
unsegmented.

Nucleic Acid (Cont..)
9
▰ Most DNA viruses possess dsDNA, except parvoviruses, which have ssDNA.
RNA viruses possess ssRNA, except:
 Reoviruses (e.g. rotaviurs)–possess dsRNA
 Retrovirsues–possess two copies of ssRNA

Capsid
10
▰ Composed of a number of repeated protein subunits (polypeptides) called
capsomeres.
▰ Functions:
 Protects the nucleic acid core from the external environment
 In non-enveloped viruses - initiates the first step of viral replication.
 Antigenic and specific for each virus.

Symmetry
11
▰ Based on arrangement of capsomeres:
Type of symmetry Explanation Examples
Icosahedral (cubical) symmetry  Capsomeres are arranged
as if they lay on the faces
of an icosahedron
 20 triangular facets and 12
corners or vertices
 Rigid structure.
 All DNA viruses
(except poxviruses)
 Most of the RNA
viruses have
icosahedral
symmetry

Symmetry (Cont..)
12
Helical symmetry  Capsomeres are coiled
surrounding the nucleic
acid in the form of a helix
or spiral.
 Flexible structure.
RNA viruses such as-
myxoviruses,
rhabdoviruses,
filoviruses, bunyaviruses,
etc.

Symmetry (Cont..)
13
Complex symmetry  Do not have either of the
above symmetry.
Poxviruses

Envelope
14
▰ Envelope surrounding the nucleocapsid.
▰ Lipoprotein in nature.
 Lipid part is derived from host cell membrane
 Protein part is virus coded, made up of
subunits called peplomers.
 Peplomers - project as spikes on the surface of
the envelope.

Envelope (Cont..)
15
Most Viruses are Enveloped Except:
▰ Non-enveloped DNA viruses - parvovirus, adenovirus and papovavirus
▰ Non-enveloped RNA viruses - picornavirus, reovirus, calicivirus, hepatitis A
virus and hepatitis E virus.

Size of the Viruses
16
▰ Size vary from 20-300nm in size.
▰ Smallest virus - parvovirus(20 nm)
▰ Largest - poxvirus (300nm).
▰ Because of the small size, viruses can pass through bacterial filters and they
cannot be visualized under light microscope.

Size of the Viruses (Cont..)
17

Shapes of the Viruses
18
Most of the animal viruses are roughly spherical with some exceptions:
▰ Rabies virus: Bullet shaped
▰ Ebola virus: Filamentous
▰ Poxvirus: Brick shaped
▰ Adenovirus: Space vehicle shaped
▰ Rotavirus: wheel shaped
▰ Tobacco mosaic virus: Rod shaped

NOMENCLATURE AND
CLASSIFICATION
19

NOMENCLATURE AND CLASSIFICATION
20
Family DNA type Envelope Symmetry Size (nm) Representative Viruses
DNA viruses DNA
Herpesviridae ds,linear Yes Icosahedron 150-200 Herpes simplex virus - 1
Herpes simplex virus- 2
Varicella-zoster virus
Epstein-Barr virus
Cytomegalovirus
Human herpes virus 6,7 & 8
Hepadnaviridae ds, circular,
incomplete
Yes Icosahedron 40–48 Hepatitis B virus
Parvoviridae ss, linear Absent Icosahedron 18–26 Parvovirus B19

NOMENCLATURE AND CLASSIFICATION (Cont..)
21
DNA viruses DNA
Papovaviridae ds, circular Absent Icosahedron 45-55 Human papillomaviruses
JC virus and BK virus
Poxviridae ds, linear Yes Complex 230 x 400 Variola (smallpox)
Molluscum contagiosum virus
Adenoviridae ds, linear Absent Icosahedron 70–90 Human adenoviruses

22
RNA viruses RNA
Picornaviridae ss, +ve sense Absent Icosahedral 28–30 Poliovirus
Coxsackievirus
Echovirus
Enterovirus
Rhinovirus
Hepatitis A virus
Caliciviridae ss, +ve sense Absent Icosahedral 27-40 Norwalk agent
Hepatitis E virus
Togaviridae ss, +ve sense Yes Icosahedral 50-70 Rubella virus
Eastern equine encephalitis virus
Western equine encephalitis virus

23
RNA viruses RNA
Flaviviridae ss, +ve sense Yes Icosahedral (?) 40-60 Yellow fever virus
Dengue virus
St. Louis encephalitis virus
West Nile virus
Hepatitis C virus
Coronaviridae ss, +ve sense Yes Helical 120-160 Coronaviruses
Rhabdoviridae ss, -ve sense Yes Helical 75x180 Rabies virus
Vesicular stomatitis virus
Filoviridae ss, -ve sense Yes Helical 80 x 1000 Marburg virus
Ebola virus

24
RNA viruses RNA
Paramyxoviridae ss, -ve sense Yes Helical 150–300 Parainfluenza virus
Mumps virus
Measles virus
Respiratory syncytial virus
Newcastle disease virus
Metapneumovirus
Orthomyxoviridae ss, -ve sense, 8
segments
Yes Helical 80–120 Influenza viruses- A, B, and C
Bunyaviridae ss, -ve sense,
3 circular
segments
Yes Helical 80–120 Hantavirus
California encephalitis virus
Sandfly fever virus

25
RNA viruses RNA
Arenaviridae ss, -ve sense,
RNA,2 circular
segments
Yes Helical (?) 50-300 Lymphocytic choriomeningitis virus
Lassa fever virus
South American hemorrhagic fever
virus
Reoviridae ds, 10–12
segments
Absent Icosahedral 60-80 Rotavirus
Reovirus
Colorado tick fever virus
Retroviridae 2 identical copies
of +ve sense ss
RNA
Yes Icosahedral
(spherical)
80-110 HTLV (Human T Lymphotropic virus)
HIV (Human immunodeficiency
virus)

VIRAL REPLICATION
27
▰ Viruses undergo a complex way of cell division.
▰ Replication of viruses passes through six sequential steps:
▰ Attachment →Penetration → Uncoating→ Biosynthesis→ Maturation →
Release

28

PATHOGENESIS OF VIRAL
INFECTIONS
29

PATHOGENESIS OF VIRAL INFECTIONS
30
▰ Transmission (entry into the body)
▰ Primary site replication
▰ Spread to secondary site
▰ Manifestations of the disease

Transmission and spread of viruses
31
Mode of transmission Produce Local infection at the portal of entry Spread to distant sites from the portal of entry
Respiratory route
(probably the most common
route)
Produce Respiratory infection-
1. Influenza virus
2. Parainfluenzavirus
3. Respiratory syncytial virus
4. Rhinovirus
5. Adenovirus
6. Coronavirus such as SARS-COV2
7. Herpes simplex virus
Measles virus
Mumps virus
Rubella virus
Varicella-zoster virus
Cytomegalovirus
Parvovirus
Small pox virus
Oral route Produce gastroenteritis
1. Rotavirus
2. Adenovirus-40,41
3. Calicivirus
4. Astrovirus
Poliovirus
Coxsackie virus
Hepatitis Virus – A & E
Cytomegalovirus
Epstein-Barr virus (EBV)

Transmission and spread of viruses (Cont..)
32
Cutaneous route Produce skin lesions
Herpes simplex virus
Human papilloma virus
Molluscumcontagiosum virus
Vector bite - Arboviruses such as-
1. Dengue virus (Aedes)
2. Chikungunya virus(Aedes)
3. Japanese encephalitis virus (Culex)
4. Yellow fever and Zika virus(Aedes)
5. Kyasanur Forest disease virus (Tick)
Animal bite - 1. Rabies virus

33
Sexual route Produce genital lesions-
2. Human papilloma virus
Hepatitis B, C& rarely D
HIV
Blood transfusion - 1. Hepatitis B, C & rarely D
2. HIV
3. Parvovirus
Injection - Hepatitis B, C & rarely D
HIV

34
Transplacental
route
Produce congenital manifestations in fetus
1. Rubella virus
2. Cytomegalovirus (CMV)
4. Varicella-zoster virus
5. Parvovirus
Transmitted through placenta to fetus, without
congenital manifestations
1. Measles virus
2. Mumps virus
3. Hepatitis B virus
4. Hepatitis C virus
5. Hepatitis D virus
6. HIV
Conjunctival route 1. Adenovirus
2. Enterovirus70
3. Coxsackie virus A-24

Virus Shedding
35
Stages Explanation Examples
Portal of entry For those viruses that produce
local infection.
Influenza virus is shed in
respiratory secretions
Blood Viruses that spread through
vector bite or blood transfusion or
needle pricks
Arboviruses, hepatitis B
Near the target tissue /organ Skin, salivary gland and kidney Varicella zoster, mumps,
cytomegalovirus
No shedding Humans are the dead end for
certain viruses infecting CNS,
such as
Rabies.

Manifestations of Viral Infections (Cont..)
36
Clinical Manifestations (Cont..):
▰ Respiratory viruses such as influenza and coronaviruses produce upper and
lower respiratory tract infections
▰ Gastroenteritis may be produced by viruses such as rotavirus and norovirus
▰ Hemorrhagic fever may be a manifestation of viruses such as dengue, Ebola
virus etc
▰ Neurotropic viruses can produce meningitis (enteroviruses) or encephalitis
(rabies, Japanese encephalitis)

Morphological Changes in the Host Cells
37
▰ Certain viruses induce characteristic changes in the host cells (e.g. inclusion
body), which can be detected by histopathological staining.

Inclusion body
38
▰ Aggregates of virions or viral proteins & other products of viral replication that
confer altered staining property to the host cell.
▰ Characteristic of specific viral infections.
▰ They have distinct size, shape, location and staining properties by which they
can be demonstrated in virus infected cells under the light microscope.

Inclusion body (Cont..)
39
Intracytoplasmic inclusion bodies
Negri bodies – seen in Rabies virus
Paschen body- seen in Variola virus
Guarnieri bodies - seen in Vaccinia virus
Bollinger bodies - seen in Fowl pox virus
Molluscum bodies - seen in Molluscum contagiosum virus
Perinuclear cytoplasmic body- seen in Reovirus

Inclusion body (Cont..)
40
Intranuclear inclusion bodies
A)Cowdry type A inclusions
Torres body- seen in Yellow fever
Lipschultz body - seen in Herpes simplex
B)Cowdry type B inclusions - seen in
Poliovirus
Adenovirus
Intracytoplasmic & intranuclear inclusion bodies
Owl’s eye appearance- seen in Cytomegalovirus
Measles

LABORATORY DIAGNOSIS OF
VIRAL DISEASES
41

LABORATORY DIAGNOSIS OF VIRAL DISEASES
(Cont..)
42
Direct Demonstration of Virus
Electron microscopy
Immunoelectron microscopy
Fluorescent microscopy
Light microscopy
Detection of Viral Antigens
By various formats such as ELISA, direct IF, ICT, flow through assays.

(Cont..)
43
Detection of Specific Antibodies
Conventional techniques such as HAI, neutralization test and CFT
Newer diagnostic formats such as ELISA, ICT, flow through assays.
Molecular Methods to Detect Viral Genes
Nucleic acid probe—for detection of DNA or RNA by hybridization
PCR—for DNA detection by amplification
Reverse transcriptase-PCR—for RNA detection
Real time PCR—for DNA quantification
Real time RT-PCR—for RNA quantification.

(Cont..)
44
Isolation of Virus by
Animal inoculation
Embryonated egg inoculation
Tissue cultures: Organ culture, explant culture, cell line culture (primary, secondary and
continuous cell lines).

TREATMENT OF VIRAL
DISEASES
45

TREATMENT OF VIRAL DISEASES
46
Anti-Viral drugs Mechanism of action Active against
Anti-herpesvirus drugs
Acyclovir , Valacyclovir, Penciclovir Inhibit Viral DNA polymerase HSV1>HSV2>VZV&EBV
Famciclovir Inhibit Viral DNA polymerase HSV,VZV,HBV
Ganciclovir Inhibit Viral DNA polymerase CMV,EBV, HSV, VZV
Cidofovir Inhibit Viral DNA polymerase HSV,CMV
Foscarnet Inhibit Viral DNA polymerase HSV& CMV
Fomivirsen Inhibit mRNA of CMV CMV(including resistant strains)
Docosanol (topical) Inhibit the fusion of the human host cell
with envelope of herpes virus
HSV (recurrent herpes labialis)
Trifluridine (topical) Inhibits viral DNA polymerase Herpes keratitis (eye drops)

TREATMENT OF VIRAL DISEASES (Cont..)
47
Anti- Influenza virus drugs
Oseltamivir,
Zanamivir
Neuraminidase Inhibitor H1N1flu
Avian flu
Seasonal flu
Amantadine,
Rimantadine
Matrix protein inhibitor Seasonal flu

TREATMENT OF VIRAL DISEASES (Cont..)
48
Anti-Hepatitis drugs
Telbivudine, tenofovir, lamivudine,
adefovir, entecavir
Nucleoside analogues Primarily for Hepatitis B
Interferon alfa Indirectly inhibits viral protein
synthesis
For hepatitis B and C infection
Grazoprevir Paritaprevir ,
Simeprevir
NS3/4A inhibitors (proteases) For hepatitis C infection
Dasabuvir, Sofosbuvir NS5B inhibitors (polymerases) For hepatitis C infection
Daclatasvir, Ledipasvir, Velpatasvir NS5A inhibitors For hepatitis C infection
Ribavirin Nucleoside inhibitor For For hepatitis C infection

IMMUNOPROPHYLAXIS FOR
VIRAL DISEASES
49

Viral Vaccines (Active Immunization)
50
▰ Since viral antigens are potent immunogens, viral vaccines confer prolonged
and effective immunity.
▰ Vaccines for viral infections may be available either in live, killed or in subunit
forms.

Killed Viral Vaccines
51
▰ Preparation: By inactivating viruses with heat, phenol, formalin or beta
propiolactone. Ultraviolet irradiation is not recommended because of the risk
of multiplicity reactivation. E.g., Rabies vaccine .
▰ Advantages- They are more stable and are safely when given in
immunodeficiency or in pregnancy.
▰ Disadvantages- Killed vaccines are associated with more adverse side effects
due to reactogenicity, which can be reduced to some extent by purification of
viruses.

Subunit Vaccines
52
▰ Only a particular antigen of the virus is incorporated in the subunit vaccine.
▰ Preparation - DNA recombinant technology. The gene coding for the desired
antigen is integrated into bacteria or yeast chromosome. Replication of the
bacteria or yeast yields a large quantity of desired antigens, e.g. Hepatitis B
vaccine
▰ Unlike killed vaccines, there is no local side effects associated with subunit
vaccines

Live Vaccines
53
▰ Preparation- Most of the live vaccines are prepared by attenuation by serial
passages. (Exception is small pox vaccinewhere the naturally occurring
vaccinia viruses were used for vaccination).
▰ Advantage- Live vaccines provide a stronger and long lasting immunity,
mimickingimmunity produced after natural infection. They are administered
as a single dose (except OPV).
▰ Disadvantages- Live vaccines are risky in immunodeficiency or pregnancy.
They are less stable than killed vaccines

Passive Immunization (Immunoglobulin)
54
▰ Passive immunization is indicated when an individual is immunodeficient or
when an early protection is needed (i.e. for post-exposure prophylaxis).
However, as there is no
▰ Passive immunization has no role in prevention of subsequent infections.
▰ Human immunoglobulins are available for many viral infections such as
mumps, measles, hepatitis B, rabies and varicella-zoster.

Combined Immunization
55
▰ Simultaneous administration of vaccine and immunoglobulin in post exposure
prophylaxis is extremely useful. It is recommended for-
 Hepatitis B (neonates born to HBsAg positive mothers or for unvaccinated
people following exposure )
 Rabies (for exposures to severe class III bites)

MYXOVIRUSES
56
▰ Group of viruses that bind to mucin receptors on the surface of RBCs.
▰ They are divided into two families:
 Orthomyxoviridae - They possess segmented RNA; e.g. influenza virus
 Paramyxoviridae - They possess non-segmented RNA; e.g. parainfluenza
virus, mumps, measles, nipah, and respiratory syncytial virus.

Influenza Virus
57
▰ Major cause of morbidity and mortality.
▰ Responsible for several epidemics and pandemics of respiratory diseases in
the last two centuries, caused by various serotypes; of which the latest
pandemic was caused by H1N1 serotype in 2009.

Influenza Virus (Cont..)
58
Types:
▰ Based on hemagglutinin (HA) and neuraminidase (NA) antigen,
▰ Influenza comprises of four types (A to D).
▰ Influenza type A is further divided into various subtypes.

59
Seasonal flu:
▰ Currently circulating strains causing seasonal flu are influenza A/H1N1,
A/H3N2 and influenza B.
Clinical manifestations:
▰ Majority of individuals develop mild flu-like symptoms such as chills,
headache, and dry cough, followed by high-grade fever, myalgia and anorexia.

60
▰ Laboratory diagnosis - detection of viral RNA in nasopharyngeal swabs by
real-time reverse transcriptase PCR.
▰ Treatment: Neuraminidase inhibitors (e.g. oseltamivir) or matrix protein M2
inhibitor (e.g. amantadine).
▰ Vaccine: Both live attenuated and injectable vaccines are available for
influenza.

Parainfluenza Viruses
61
▰ Major cause of respiratory tract disease in young children; producing various
infections such as mild common cold syndrome, croup
(laryngotracheobronchitis), pneumonia or bronchiolitis.

Mumps Virus
62
▰ Most common cause of parotid gland enlargement in children.
▰ In severe cases, it can also cause orchitis and aseptic meningitis.
▰ Transmitted through the respiratory route via droplets, saliva, and fomites.
▰ Live attenuated vaccine is available for the prevention of mumps.

Measles Virus
63
▰ Acute, highly contagious childhood disease, characterized by fever and
respiratory symptoms, followed by, appearance of Koplik’s spots on buccal
mucosa and maculopapular rash.
▰ Rarely, post measles complications may occur such as giant cell pneumonitis,
subacute sclerosing panencephalitis (SSPE).
▰ Prevented by administration of a live attenuated vaccine, given at nine months
of birth.

Nipah and Hendra Viruses
64
▰ Cause an emerging viral infection (encephalitis).
▰ Transmitted to humans after direct contact with infected bats, pigs, or
persons.
▰ Latest outbreak of Nipah encephalitis occurred in Kerala, India in 2018.

Respiratory Syncytial Virus
65
▰ Major respiratory pathogen of young children and is the most common cause
of bronchiolitis in infants.

RUBELLA VIRUS
67
▰ Rubella - important agent of childhood exanthema.
▰ In addition, it is highly teratogenic and can cause congenital malformations
affecting organs such as eye, ear and heart in fetus (congenital rubella
syndrome).
▰ Live attenuated vaccine - available for rubella; recommended for children and
young women.

PICORNAVIRUSES
69
▰ Include two major groups of human pathogens: enteroviruses and
rhinoviruses.
▰ Enteroviruses are transmitted by feco-oral route - include polioviruses,
coxsackieviruses and others.
▰ Rhinoviruses are transmitted by respiratory route and cause common cold.

Poliovirus
70
▰ Causative agent of polio (also known as poliomyelitis).
▰ Pathogenesis - transmitted by feco-oral route and then spreads to CNS/spinal
cord by hematogenous route.
▰ Clinical manifestation - Majority of infections are asymptomatic; rarely
progresses to aseptic meningitis and paralytic poliomyelitis.

Poliovirus (Cont..)
71
▰ Vaccine - Killed injectable and live oral polio vaccines are available.
▰ Eradication - Poliomyelitis is now at the verge of eradication. This is attributed
to the extensive immunization program being conducted globally.

Coxsackievirus
72
Produce a variety of clinical illnesses in humans, such as
▰ Aseptic meningitis,
▰ Hand-foot-and mouth disease,
▰ Conjunctivitis,
▰ Myocarditis,
▰ Pericarditis and
▰ Pancreatitis.

ARBOVIRUSES
74
▰ Arboviruses (arthropod-borne viruses) are diverse group of RNA viruses that
are transmitted by blood sucking arthropods (insect vectors) from one
vertebrate host to another.

ARBOVIRUSES (Cont..)
75
India: The following are the important arboviruses prevalent in India.
▰ Dengue virus
▰ Chikungunya virus
▰ Kyasunar forest disease (KFD) virus
▰ Japanese B encephalitis

RABIES VIRUS
77
▰ Causes a rapidly progressive, acute infectious disease of the central nervous
system in humans and animals.
▰ Transmission - transmitted from another infected animal bite (most common
being dog).
▰ Clinical manifestation - From the site of bite, it spreads to CNS via neuronal
route - produces an acute neurologic phase, which may be either encephalitic
or paralytic type.

RABIES VIRUS (Cont..)
78
Laboratory diagnosis:
▰ Detection of rabies viral antigen from hair follicles at nape of the neck by
direct IF test.
▰ Antibody detection
▰ Viral RNA detection by RT PCR.
▰ Postmortem diagnosis - detection of characteristic inclusion bodies (Negri
bodies) in histopathological staining of brain tissue.

RABIES VIRUS (Cont..)
79
Management:
▰ Post-exposure prophylaxis can be provided by local wound care and
administration of antirabies immunoglobulin and vaccine.

HUMAN IMMUNODEFICIENCY
VIRUS (HIV)
80

HUMAN IMMUNODEFICIENCY VIRUS (HIV)
81
▰ Etiologic agent of acquired immunodeficiency syndrome (AIDS); the biggest
threat to mankind in last three decades.
Transmission:
▰ Sexual route (most commonly)
▰ vertical (mother to fetus),
▰ parenteral (blood transfusion)
▰ percutaneous (needle prick injury).

HUMAN IMMUNODEFICIENCY VIRUS (HIV) (Cont..)
82
Pathogenesis:
▰ Following transmission, HIV infects CD4 T cells and where the unique viral
enzyme ‘reverse transcriptase’ converts viral RNA to DNA, which then
integrates with host DNA and undergoes latency.

83
Clinical manifestations:
▰ Typical course of HIV infection includes following stages -
▰ Acute retroviral syndrome, followed by asymptomatic stage (clinical latency),
then progresses into persistent generalized lymphadenopathy, and
symptomatic HIV infection.
▰ Finally, the patients move towards the advanced end stage called AIDS.

84
Laboratory diagnosis:
▰ Detection of antibodies (by rapid tests or ELISA or western blot),
▰ p24 antigen (by ELISA), or
▰ viral RNA (by RT-PCR).
▰ In India, the strategy recommended by national AIDS control organization
(NACO) is used for HIV diagnosis.

85
Treatment:
▰ Antiretroviral Therapy (ART) is advocated for treatment of HIV infected
patients.
▰ The NACO recommended first-line ART regimen in adults includes
combination of tenofovir, lamivudine and efavirenz (TLE regimen).

CORONAVIRUSES
87
▰ Widespread and produce mild upper respiratory tract infection.
▰ Two exceptions are SARS-CoV (severe acute respiratory syndrome
coronavirus), and MERS-CoV (Middle East respiratory syndrome coronavirus);
which are geographically restricted - transmitted from man to man and have
produced outbreaks of severe respiratory disease with higher mortality.

COVID-19
88
▰ SARS-CoV-2 has emerged in 2019-2020 in China and then rapidly spread to
other part of the World causing a catastrophic global pandemic known as
COVID-19 (coronavirus disease-2019).
▰ Epidemiology: Till June 2020, 1 crore cases have been reported worldwide
with 5 Lakh deaths. Although >200 countries were effected, the worst
affected are USA, Brazil, Russia and India.

COVID-19 (Cont..)
89
▰ Diagnosis: real time RT-PCR in throat swab or nasopharyngeal swab
▰ Treatment: No effective drug or vaccine has been developed yet, although
intense research is ongoing.
▰ Control measures: control measures such as social distancing, lockdown,
hand hygiene and use of mask.

HEPATITIS VIRUSES
91
▰ Heterogeneous group of viruses that are taxonomically diverse (belong to
different families) but all are hepatotropic; and produce similar clinical illness
such as fever, nausea, vomiting, and jaundice.
▰ There are five important hepatitis viruses (A to E).
▰ All are RNA viruses except HBV which is a DNA virus.
▰ They can be divided into two groups based on the route of transmission.

HEPATITIS VIRUSES (Cont..)
92
Hepatitis A and E viruses:
▰ Transmitted by feco-oral route.
▰ The clinical course has an abrupt onset.
▰ Disease is self-limiting with good prognosis.
▰ They do not have carrier stage, or chronicity or oncogenic potential. .

93
Hepatitis B, C and D viruses:
▰ Transmitted by percutaneous, sexual or vertical routes.
▰ The clinical course has an insidious onset and variable prognosis.
▰ The disease may progress to carrier stage, chronic hepatitis, cirrhosis or
hepatocellular carcinoma.

94
Laboratory diagnosis of viral hepatitis includes detection of various viral markers
such as:
▰ Detection of viral antigens (e.g. HBsAg for HBV) or
▰ Detection of antibodies [anti-HAV, anti-HBc and anti-HBs (for HBV), anti-HCV
and anti-HEV] or
▰ Detection of viral nucleic acid (by PCR).

95
Treatment:
▰ HAV and HEV infections are self-limiting, do not require specific treatment.
▰ Antiviral drugs are available for HBV and HCV infections; for example,
 Tenofovir and telbivudine - for HBV
 Interferon, ribavirin for - HCV
▰ Vaccine: Vaccines - available for HAV and HBV.

Rodent-borne Viruses
97
▰ Transmitted from rodents to man by contact with infected body fluids or
excretions.
▰ Major rodent-borne viruses include:
 Hantaviruses - cause two categories of manifestations - hemorrhagic
fever with renal syndrome and hantavirus pulmonary syndrome.
 Arenaviruses - cause various diseases such as South American
hemorrhagic fever.

Filoviruses
98
▰ Long filamentous viruses; example include Ebola virus and Marburg virus.
▰ They cause hemorrhagic fever, associated with very high mortality.
▰ Transmitted by close contact with blood or other body fluids or secretions of
infected animals or man.

Slow Viruses and Prions
99
▰ Group of neurodegenerative conditions affecting both humans and animals.
▰ Characterized by: long incubation period, predilection for CNS and a strong
genetic predisposition.

Slow Viruses and Prions (Cont..)
100
▰ Conventional slow viruses: Examples include - subacute sclerosing pan
encephalitis, progressive multifocal leukoencephalopathy.
▰ Unconventional transmissible slow viruses - termed as ‘prion disease’,
characterized by spongiform encephalopathies due to deposition of abnormal
prion proteins in neural tissues.

Questions:
101
▰ Q1. Which of the following virus is enveloped:
a. Poliovirus
b. Adenovirus
c. Herpesvirus
d. Parvovirus B19

Questions:
102
▰ Q2. All of the following viruses are transmitted by respiratory route, except:
a. Influenza virus
b. Rotavirus
c. RSV
d. Rhinovirus

Questions:
103
▰ Q3. Which of the following vaccine is a killed vaccine:
a. Mumps vaccine
b. Measles vaccine
c. Rubella vaccine
d. IPV

Questions:
104
▰ Q4. The largest virus in size is:
a. Herpes simplex virus
b. Hepatitis B virus
c. Poxvirus
d. Adenovirus

Questions:
105
▰ Q5. Which of the following DNA virus is single stranded:
a. Parvovirus
b. Hepatitis B virus
c. Poxvirus
d. Adenovirus

Questions:
106
▰ Q6. Human fibroblast cell line is used for cultivation of:
a. Measles
b. CMV
c. Poliovirus
d. Adenovirus

General Virology- RNA viruses

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