2. RNA viruses can be either double-
stranded (dsRNA) or single-stranded
(ssRNA)
• Although relatively few RNA viruses have
dsRNA genomes, dsRNA viruses are
known to infect animals, plants, fungi, and
at least one bacterial species.
• More common are the viruses with
ssRNA genomes.
3. • Some ssRNA genomes have a base
sequence that is identical to that of viral
mRNA, in which case the genomic RNA
strand is called the plus strand or
positive strand. In fact, plus strand
RNAs can direct protein synthesis
immediately after entering the cell.
• However, other viral RNA genomes are
complementary rather than identical to
viral mRNA, and are called minus or
negative strands.
9. Orthomyxoviridae
orthos, Greek for "straight";
myxa, Greek for "mucus")
– Orthomyxoviridae - are a family of RNA
viruses that includes five genera:
– Influenzavirus A,
– Influenzavirus B,
– Influenzavirus C,
– Isavirus
– and Thogotovirus.
10. Orthomyxoviridae
– Influenzavirus A, В, С - cause influenza in
vertebrates, including birds, humans, and
other mammals.
– Isaviruses infect salmon;
– Thogotoviruses infect vertebrates and
invertebrates, such as mosquitoes and sea
lice.
11. Infuenza
–- is an acute infectious disease of
the resperatory tract which
occurs in sporadic, epidemic and
pandemic forms.
12. WHAT IS INFLUENZA?
• Influenza, commonly
called "the flu," is an
illness caused by RNA
viruses of
the family Orthomyxo
viridae
14. Infuenza
– The modern history of the
disease may be considered to
date from the pandemic of 1889-
1990, during which Pfeiffer
isolated Haemophilus influenzae
and claimed that it was the
causative agent.
15. The three genera of Influenzavirus, which are
identified by antigenic differences in their
nucleoprotein and matrix protein infect
vertebrates as follows:
– Influenzavirus A infects humans, other
mammals, and birds, and causes all flu
pandemics
– Influenzavirus B infects humans and seals
– Influenzavirus C infects humans and pigs
16. Morphology
– The influenza virus is typically
spherical, with a diameter of 80-
120 nm but pleomorphism is
common.
17. Morphology
– Filamentous form, up to several
micrometres in length and readily
visible under the dark ground
microscope, are frequent in
freshly isolated strains.
18. – The virus core consists of
ribonucleoprotein in helical symmetry.
– The negative sense single-stranded RNA
genome is segmented and exist as eight
pieces.
– Also present is a viral RNA-dependent
RNA polymerase which is essential for
transcription of the viral RNA in infected
host cells.
19. – The nucleocapsid is surrounded by an
envelope, which has an inner membrane
protein layer and an outer lipid layer.
– The membrane protein is also known as
the matrix or «M-protein» composed of
two components, M1 and M2.
– The protein part of the envelope is virus
coded but the lipid layer is derived from
the modified host cell membrane, during
the process of replication by budding.
20. There are 2 distinct types of glycoprotein:
one with
• Hemagglutin (HA)
• Neuramidase (NA)
Anchoring this bases of each of these
spikes on the inside of viral lipid
bilayer are membrane proteins (M
proteins and NP proteins)
21. – Projecting from the envelope are two types
of spikes (peplomers): hemagglutinin
spikes which are triangular in cross-setion
ant the mushroom-shaped neuraminidase
peplomers which are less numerous.
– Both surface antigen show a marked
tendency for antigenic variation (drift).
23. Hemagglutinin
• -have 16 subtypes and can attach to host
sialic acid receptors are present on the
surface of erythrocytes, so viruses with HA
glycoproteins cause heme- glutination when
mixed with red blood cells.
• Host cell sialic acid receptors also exist
on upper respiratory tract cell membranes
and HA binding to theses receptors activates
fusion of the host cell membrane with the
virion membrane, resulting in dumping of
the viral genome into the host cell. So HA is
needed for adsorption.
24. Neuraminidase (NA)
• have 9 subtypes and is an
important component of mucin
the substance covering
mucosal epithelial cells and
forming an part of host upper
respiratory defense barrier.
Exposing the sialic acid and
binding sites beneath.
25. Antigenic drift
• is a mechanism for variation in viruses
that involves the accumulation of
mutations within the genes that code for
antibody binding sites.
• This results in a new strain of virus
particles which can’t be inhibited as
effectively by the antibodies that were
originally targeted against previous
strains, making it easier for the virus to
spread throughout a partially immune
population.
27. Antigenic ‘shift’
• The segmented viral genome allows for
formation of viral reassortants
(‘recombinants’) between different strains
or subtypes of virus. A doubly-infected
host can thus give rise to a ‘new’ virus.
Such a profound change in antigenic
make-up (‘shift’)
28.
29. Laboratory diagnosis of influenza
• Specimen: nasopharyngeal aspirate.
• Detect virus antigen by indirect
immunofluorescence: a very rapid
method of diagnosis.
• Serology: (widely used) Complement
fixation test: with the “S” or soluble
nucleoprotein antigen.
• Isolation: monkey kidney tissue cultures.
30. Laboratory diagnosis of influenza
• Observe: for hemagglutination with
human group O erythrocytes.
• Type virus: by complement fixation, strain
identification by haemagglutination-
inhibition in a reference laboratory. A
commercially available identification
technique is Directigen FLU-A (an
enzyme immunoassay [EIA] rapid test).
This test can detect influenza A virus in
clinical specimens in less than 15
minutes.
31. Treatment
• Treatment is mostly symptomatic.
• Amantadine and rimantadine are useful
• They reduce the average duration of the
disease and cause symptomatic improvement,
though virus shedding and antibody response
are not affected.
• Resistance to these drugs develops rapidly.
• Zanamivir and oseltamivir, new drugs designed
to block viral neuraminidase, have been found
effective in the treatment and prevention of
influenza, when admivistered as nasal spray
Treatment is mostly symptomatic.
32. Immunoprophylaxis
• The main difficulty in the
immunoprophylaxis of influenza is the
frequent change in the antigenic make up
of the virus
• Vaccines can’t be made in bulk and
stockpiled, as the appearance of a new
variant will make the old vaccine obsolete
33. Immunoprophylaxis
• In cold countries, where it is necessery to
protect old persons and other high-risk
individuals, the practice is to immunise
them with a vaccine containing the latest
strains of type A and B viruses
34. Immunoprophylaxis
• The inactivated vaccines used
throughout the world are purified egg-
grown virus killed by formalin or
bybpropriolactone.
• The use of live attenuated vaccine is
limited. Preparations containing detergent
split virus or isolated surface subunits (H
and N) are mostly used. The two latter
types of vaccine are claimed to give fewer
side-effects than whole virus vaccine.
35. Immunoprophylaxis
• Persons for whom clinical influenza would lead
to further deterioration of their underlying
condition are recommended as target groups
for routine vaccination.
• Generally, these are the elderly, those with
chronic illnesses in the heart, lungs and
airways, and those withmetabolic disorders or
immune deficiencies.
• Protective levels of anti-influenza antibody will
ensue 1–3 weeks postvaccination.
• Immunity to influenza will last for about a year
as the ever-changing virus will outdate acquired
immunity.
36. Paramyxoviridae
• from Greek para-, beyond, -myxo-,mucus
or slime
• are family of the negative-sense single
stranded RNA viruses responsible for a
number of human and animal diseases
that includes following genera:
Paramyxovirus (Humans: colds,
respiratory infections, mumps),
Pneumovirus (Humans: pneumonia,
common cold), Morbillivirus (Humans:
measles).
37. General features on
Paramyxoviridae family
• Viruses replicate in the cytoplasm.
• Viruses induce cell-cell fusion via F
protein, causing multinucleated giant
cells.
• Paramyxoviridae are transmitted in the
respiratory droplets and initiate infection
in the respiratory tract.
• Cell- medicated immunity causes many of
the symptoms but is essential for control
of the infection.
38. Paramyxoviridae family
• There are 4 paramyxoviridae that cause
human disease:
• parainfluenza virus,
• respiratory syncytial virus,
• mumps virus,
• and measles virus.
39. Parainfluenza virus
• The parainfluenza virus causes upper
respiratory infections in adults ranging
from cold symptoms such as rhinitis,
pharyngitis, and sinus congestion, to
bronchitis and flu-like illness.
• Children, elderly, and the
immunocompromised also suffer from
lower respiratory tract infections
(pneumonia).
40. Clinical features
• Parainfluenza viruses are responsible for
about 10 per cent of resperatory
infections in children needing
hospitalisation.
• In adults cause milder respiratory
infection in which sore throat and
hoerseness of the voice are common.
Rarely, they cause parotitis.
41. Laboratory diagnosis
• Speciment: throat and nasal swabs.
• Virus isolation: Throat and nasal swabs
are inoculated in primary monkey kidney
cell cultures, or continuous monkey
kidney cell lines with trypsin. Virus growth
is detectrd by hemadsorption. Typing is
by immunofluorescence, hemadsorption
inhibition or hemagglutination inhibition.
42. Laboratory diagnosis
• Serology: serological diagnosis is
hampered by wide antigenic cross-
reactions. Paired sera can be tested by
neutralisation, ELISA, HI
(hemagglutination inhibition assay) or CF
(complement fixation test) for rise in the
titre of antibodies.
• PCR: Molecular diagnosis using reverse
transcriptase PCR is gaining more
acceptance.
43. Mumps virus
• replicates in the upper respiratory tract
and in the regional lymph nodes and
spreads via the blood to distant organs.
Infections can occur in many organs, but
the most frequently involved is the parotid
gland.
44. Clinical features
• Infection is acquired by inhalation, and
probably also through the conjunctiva.
The virus replicates in the upper
respiratory tract and cervical lymph nodes
and is disseminated through the
boodstream to variouse organs.
• Incubation period: 12-25 days.
• Parotid swelling is usually the first sign of
illness, though it may sometimes be
preceded by prodromal malaise.
45. Clinical features
• Parotid swelling is unilateral to start with
but may become bilateral. It is
accompanied by fever, local pain and
tenderness but the skin over the gland is
not warm or erythematous.
• Parotitis is non-suppurative ans ussually
resolves within a week.
• However, involvement of extraparotid
sites may be seriouse and may
sometimes occur even in the absence of
paratitis.
46. Complications
• Epididymo-orchitis is a complication seen in
about a third of postpubertal male patients. The
testis becomes swollen and acutely painful,
with accopanying fever and chills.
• Orchitis is usually unilateral but when it is
bilatrral and followed by testicular atrophy,
sterility or low sperm counts may result.
• 10 per cent show symptoms of meningitis
• Mumps meningitis and meningoencephalitis
ussually resolve without sequelae but deafness
may sometimes result
47. Laboratory diagnosis
• A typical case of mumps needs no
laboratory confirmation but it may be
essential in atypical infection and where
meningitis or other systemic involment is
the sole manifestation.
• Speciment: The virus may be isolated
from salva (within 4-5 days), urine (up to
two weeks) or CSF (8-9 days after onset
of illness)
48. Laboratory diagnosis
• Virus isolation: The specimens must be
inoculated soon after collection virus is
labile. Virus growth can be detected by
hemadsorption and identified by
hemadsorption inhibition using specific
antiserum. Cytopathic changes are not
reliable. Isolation may take 1-2 weeks.
• More rapid results can be obtained by
immunofluorescence testing of infected
cell cultures. This may become possitive
as early as 2-3 days after inoculation.
49. Laboratory diagnosis
• Isolation can also be made by inoculation into
six-to-eight-day-old chick embryos by the
amniotic route and testing the amniotic fluid
after 5-6 days for hemagglutinins.
• The virus can be identified by
hemagglutination inhibition using specific
antisera.
• Egg inoculation is less sensitive than call
cultures for isolation.
• Direct antigenic detection by IFA is helpful in
early diagnostis.
50. Laboratory diagnosis
• Serology: Serological diagnosis
depends on demonstration of a rise in
the titre of antibodies in paired serum
samples.
• The CF (complement fixation test) and HI
(hemagglutination inhibition assay) tests
are commonly used but cross-reactions
with perainfluenza viruses cause
probleems.
51. Laboratory diagnosis
• IgM-ELISA is useful in this respect
because cross-reacting antibodies are
IgG and do not interfere with IgM-ELISA.
• A positive CF test for antibody to the S
antigen in the acute phase serum is
presumptive evidence of current
infection.
• PCR: Molecular diagnosis using reverse
transcriptase PCR is more rapid and
sensitive.
52. Vaccination
• An effective live virus vaccine is available
against mumps.
• The vaccine is given as a single
subcutaneouse injection, alone or in
combination - MMR vaccine (measles, mumps
and rubella vaccines).
• It provides effective protection for at least ten
years.
• The vaccine may not prevent the disease if
given after exposure to the infection but there
are no contraindications for its use in this
situation.
53. Respiratory Syncytial Virus
(RSV)
• is so-named because it causes
respiratory infections and contains an F-
protein that causes formation of
multinucleated giant cells (syncytial cells).
This virus differs from the rest of its kin by
lacking both the HA and NA
glycoproteins.
54. Clinical features
• Most RSV infections are symptomatic.
• The virus is hardly ever found in healthy
persons.
• Infection causes a broad range of
respiratory illnesses. In infants, the
disease may begin s febrile rhinorrhea,
with cought and wheezing, progressing in
25-40 per cent to lower respiratory
involvement, including tracheobronchitis,
bronchiolitis and pneumonia.
55. Laboratory diagnosis
• Speciment: nasopheryngeal swabs or
nasal washings.
• Virus isolation: Samples should be
inoculated in cell cultures immediately
after collection. Freezing of clinical
samples may destroy the virus. In
cultured cells, RSV caused characteristic
giant cell and syncytial formation but
cytopathic effects take about 10 days to
appear.
56. Laboratory diagnosis
• Earlier detection of viral growth in cell is
possible by immunofluorescence tests.
• Rapid diagnosis of RSV infection can be
made by the immunofluorescence test on
smears of nasapharyngeal swabs.
57. Laboratory diagnosis
• Serology: Serological diagnosis is by
demonstration of rising antibody titres in
paired serum samples by ELISA, CF
(complement fixation test), neutralisation
or immunofluorescence tests.
• PCR: Molecular diagnosis by reverse
transcriptase PCR is sensitive and
rapid.
58. Treatment and prophylaxis
• Management is primarily by supportive
care.
• Administration of ribovirin by continuous
aerosol has been found beneficial in
hospitalised patients, decreasing the
duration of illness and of virus shedding.
• No effective vaccine is available.
59. Measles (Rubeola)
• is a highly contagious skin disease that is
endemic throughout most of the world. It is a
negative strand, enveloped RNA virus, in the
genus Morbillivirus and the family
Paramyxoviridae.
• The measles virus is monotypic, but small
variations at the epitope level have been
described. The variations are based on genetic
variability in the virus genes.
• Such variations, however, have no effect on
protective function since a measles infection
still provides a lifelong immunity against
reinfection.
60. Clinical features
• It takes about 9-11 days from the time of
exposure to infection for the first signs of
clinical disease to appear. These consist
of prodromal malaise, fever, conjuctival
infection, cought and nasal discharge.
• After 3-4 days of prodromal illness, and
rash appears.
• A day or two before the rash begins,
Koplik’s spots develop on the buccal
mucosa and occasionally on the
conjunctiva and intestinal mucosa.
61. Clinical features
• The prodromal illness subsides within a
day or two of appearance of the rash.
• The red maculopapular rash of measles
typically appears on the forehead first and
spreads downwards, to disappear in the
same sequence 3-6 days later, leaving
behind a brownish discolouration and
finely granular desquamation.
62. Laboratory diagnosis
• In a typical case of measles, diagnosis is
self-evident. In atypical cases, and for
differentiation from rubella, laboratory
tests are useful.
• Speciment: nasal secretions, throat,
conjunctiva and blood can be used. CSF
(cerebrospinal fluid) is collected in SSPE
(subacute sclerosing panencephalitis).
• IFA: The measles virus antigen can be
detected in cells on nasal secretions by
immunofluorescence.
63. Laboratory diagnosis
• Virus isolation: The virus can be isolated
from the nose, throat, conjunctiva and
blood during the prodromal phase and up
to about two days after the appearance of
the rash. The virus may be obtained from
urine for a few more days.
• Primary human or monkey kidney and
amnion cell are most useful.
• Cytopathic changes may take up to a
week to develop, but earlier diagnosis of
viral growth is possible by
immunofluorescence.
64. Laboratory diagnosis
• Serological diagnosis: Specific
neutralisation, hemagglutination inhibition
(HAI) and complement fixing antibodies
(in CFT) develop early.
• A fourfold rise in titre is looked for using
paired sera collected during the acute
phase and 10-21 days after.
65. Laboratory diagnosis
• Demonstration of measles-specific IGM in
a single specimen of serum drawn
between one and two weeks after the
onset of the rash is confirmatory.
• False negaives may occur if the serum is
taken earlier than one week before or
later than two weeks after onset of the
rash.
66. Laboratory diagnosis
• Demonstration of high titre measles
antibody in the CSF (cerebrospinal fluid)
is diagnostic of SSPE (subacute
sclerosing panencephalitis).
• PCR: Reverse transcriptase PCR is a
sensitive and specific method of
diagnosis.
67. Prophylaxis
• Passive protection:
• Normal human gammaglobulin given
within six days of exposure can prevent
or modify the disease, depending on the
dose.
• This is useful in children with
immunodeficiency, pregnant women and
others at special risk/
68. Prophylaxis
Active immunisation:
• The recommended age for measles
vaccination in developing countries is
now nine month, while in the advanced
nationss it remains 15 months.
• A safe and effective live attenuated
measles vaccine is available.
• The vaccine given either by itself, or in
combination, as the MMR vaccine
(measles, mumps and rubella vaccines).
69. Prophylaxis
• A single subcutaneous injection of the
measles vaccine provides protection
beginning in about 12 days and lasting for
over 20 years.
• Contraindications are immunodeficiency,
untreated tuberculosis and pregnancy.
70. Prophylaxis
• A live attenuated vaccine has been
developed which can be given by
intranasal aerosol to young babies and
gives good protection irrespective of the
presence of maternal antibodies.
• Efforts are being made to eradicate
measles by vaccination.
• Considerable progress has been
achieved in the USA and some other
countries.
