Orthomyxovirus
Morphology of Influenza virus
The Influenza virus is usually spherical?with a diameter of 80-120 nm;however,while some stains show pleomorphism. The virus core consist of ribonucleoprotein in helical symmetry.
The negative-sense single stranded RNA genome is segmented into eight pieces/
Antigenic Variation
Antigenic Variation
A unique feature of the influenza virus is its abilityto undergo antigenic variation. This has an impact on the epidemiology of the disease. Antigenic variability is highest in influenza virus type A, is lesser in type B and has not been demonstrated in type C.
The internal RNP antigen and M protein antigen are stable but both surface antigens undergo independent antigenic variations
Antigenic structure of Paramyxoviruses
ANTIGENIC STRUCTURE OF
The nucleocapsid is surrounded by a lipid envelope which has the matrix (M) protein at its base and in two types of transmembrane glycoprotein spikes at the surface. The longer spike is hemagglutinin (H), which may also possess neuraminidase (N) activity and is hence known as the H or HN protein. It is responsible for the adsorption of the virus to the host cell surface.
The second spike is the F (fusion) protein, responsible for the fusion of the viral envelope with the plasma membrane of the host cell, which is the essential early step of infection. It also brings about cell-to-cell fusion, forming large giant cells or syncytia, which are he characteristic of paramyxovirus infections. The F protein also mediates the hemolytic activity of paramyxoviruses.
RESPIRATORY SYNCYTIAL VIRUS (RSV)
RESPIRATORY SYNCYTIAL VIRUS (
The virus causes cell fusion and the formation of
multinucleated syncytia in cell cultures, and so, is named respiratory syncytial virus (RSV). It is now recognised as the most common cause of lower respiratory tract infections in infants, particularly in the first few months of life. RSV is pleomorphic and has a size range of 150- 300 nm. The viral envelope has two glycoproteins- the G protein by which the virus attaches to cell surfaces, and the fusion (F) protein which brings about fusion between viral and host cell membranes. The F protein is also responsible for cell-to-cell fusion, which leads to the characteristic syncytial cytopathic changes in RSV infection.
RSV does not possess hemagglutinin activity, nor
does it possess neuraminidase or hemolytic properties, and thus differs from other paramyxoviruses. Another difference is that its nucleocapsid diameter (13 nm) is less than that of other paramyxoviruses (18 nm). It is propagated on heteroploid human cell cultures such as HeLa and HEp-2. It is highly labile and is inactivated rapidly at room temperature. It can be preserved by lyophilisation. It is antigenically stable and only one antigenic type exists. However, studies using monoclonal antibodies have identified two subtypes, A and B.
A virus can infect organisms from these kingdoms plant, animal, fungi, bacteria, and protist
true
Describe the classification and nomenclature system of the Influenza virus
The classification of influenza viruses into the three serotypes A, B and C is based on the antigenic nature of the 'internal' or ribonucleoprotein (RNP) and the matrix(M) protein antigens. These antigens are not cross-reactive amongst the three types.
Influenza virus type A is further divided into subtypes based on the HA and NA glycoproteins.
15 HA subtypes are H1-H15
9 NA subtypes N1-N9.
Human isolates belong to H1-H3, H5 and N1, N2
subtypes.
Antigenic drift
Antigenic drift The gradual sequential change in antigenic structure occurring regularly at frequent intervals is known as antigenic drift. Here, the new antigens, though different from the previous antigens, are still related to them, so they react with antisera to the predecessor virus strains to varying degrees.
Antigenic drift is due to mutation and selection, the process being influenced by the presence of antibodies to the predecessor strains in the host population. Antigenic drift accounts for the periodic epidemics of influenza.
Classification of Paramyxoviruses
The family Paramyxoviridae consists of large enveloped RNA viruses infecting mammals, birds, reptiles and fish. Many paramyxoviruses are host-specific and several, such as measles virus, mumps virus, Nipah virus, Hendra virus and several parainfluenza viruses, are pathogenic for humans.
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When a virus infects a bacterium, it injects viral nucleic acid
true
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Antigenic shift
Antigenic s Unlike antigenic drift, this is an abrupt, drastic and discontinuous variation in the antigenic structure, resulting in a novel virus strain, unrelated antigenically to the predecessor strains. Such changes may involve hemagglutinin, neuraminidase or both. Antibodies to the predecessor viruses do not neutralise the new variant and spread widely in the population, causing major epidemics or pandemics. The changes involved in antigenic shift are too extensive to be accounted for by mutation.
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What is provirus?
A provirus is the integrated form of a viral genome within a host cell's DNA. In simpler terms, it's a virus that has become a permanent resident within your cells. This integration allows the virus to remain dormant for extended periods, replicating alongside the host's DNA. ex:HIV
Proviruses are primarily formed by retroviruses, a family of viruses that have the unique ability to reverse-transcribe their RNA genome into DNA. This DNA copy then integrates itself into the host's genome, becoming a provirus.
Lets mix the numbers
18-81
81-18
Antigenic classification
Antigen Classification
The internal antigens of the influenza virus can be
classified into the following types:
RNP antigen
M protein antigen
V antigen or the surface antigen
Hemagglutinin is a glycoprotein composed of two
polypeptides, HA 1 and HA 2.
It is responsible for hemagglutination and hemadsorption.
Pathogenesis
Pathogenesis
The route of entry is the respiratory tract. Small doses by aerosols can cause infection. Larger doses are required when infection is by intranasal instillation.
The viral neuraminidase facilitates infection by reducing the viscosity of the mucus film lining the respiratory tract and exposing the cell surface receptors for virus adsorption. At this stage, the virus may get inactivated by mucosal
IgA or other non-specific inhibitors. The viruses that bypass this mechanism affect the ciliated cells. The ciliated cells of the respiratory tract are the main sites of viral infection. These cells are damaged and shed by the viral neuraminidase, laying bare the basal cells in the trachea and bronchi. This renders the respiratory tract highly vulnerable to bacterial invasion. Viral pneumonia is associated with hyperemia and thickening of the alveolar walls, interstitial infiltration with leucocytes, capillary thrombosis and leucocytic exudation. In some cases, a hyaline membrane is formed, occupying the alveolar ducts and alveoli. In the late stages, there is infiltration with macrophages which engulf and remove desquamated alveolar cells. The disease is confined to the respiratory tract
Clinical Features
Parainfluenza viral infection is confined to the respiratory tract, unlike mumps which is a systemic disease, with the virus disseminating through blood and multiplying in various organs and tissues. The causative viruses are responsible for about 10 per cent of respiratory infections in children needing hospitalisation.
All human parainfluenza types are strongly correlated with specific clinical syndromes, ages and times of the year. PI types 1 and 2 are the pathogens most commonly associated with croup, a serious clinical disease.
In this part of the host cell Influenza genome replication occurs?
In nucleus
Viruses can only replicate inside of a host cell
true
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Laboratory Diagnosis
Laboratory Diagnosis
1. Specimen collection
Throat garglings, nasal wash or throat swabs (alginate swabs) are collected using virus transport media or suitable buffered salt solution. If the specimen is not processed immediately, it should be stored at 4°C, or if the delay is long, at -70°C.
2. Demonstration of the virus antigen Rapid diagnosis
of influenza may be made by the demonstration of the virus antigen on the surface of the nasopharyngeal cells by immunofluorescence.
3. Isolation of the virus
Virus isolation is obtained readily during the first two or three days of the illness but less often in the later stages. The virus grows in primary monkey kidney cell cultures, as well as in some continuouscell lines. Cytopathic effects are not prominent and virus growth is detected by hemadsorption or demonstration of hemagglutinin in the culture fluid.
Isolation may also be made in eggs in the amniotic cavity of chick embryos.
4.Serology
5.PCR- based diagnosis
Laboratory diagnosis of Parainfluenza virus
Laboratory Diagnosis
1. Specimen Throat and nasal swabs are collected for laboratory investigations.
2. Virus isolation Throat and nasal swabs are inoculated in primary monkey kidney cell cultures or continuous monkey kidney cell lines (LLC-MK2) with trypsin.
Cytopathic changes are not readily apparent, except
with the type 2 virus. Isolation may take ten days or
more.
Virus growth is detected by hemadsorption. Typing is
by immunofluorescence, hemadsorption inhibition or
hemagglutination inhibition.
3. Serology Serological diagnosis is hampered by wide antigenic cross-reactions. Paired sera can be tested by neutralisation, ELISA, HAI or CF (complement fixation) for rise in the titre of antibodies.
4. PCR Molecular diagnosis using reverse transcriptase PCR is gaining acceptance as a more specific and rapid technique.
What is the difference between Orthomyxovirus and paramyxovirus?
Attribute Orthomyxovirus Paramyxovirus
Family Orthomyxoviridae Paramyxoviridae
Genome Segmented Non-segmented
Size 80-120 nm 150-300 nm
Replication In the nucleus In the cytoplasm
Diseases Influenza Measles, mumps, respiratory syncytial
virus (RSV)
Binary fission is the process in which two parents combine their genetic material to produce a new organism that differs from both parents
False