The influenza parainfluenza viruses
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The Influenza & Parainfluenza viruses. Orthomyxoviridae & Paramyxoviridae. Classification. ORTHOMYXOVIRIDAE. Influenza viruses. Type A. Type B. Type C. Family:. Genus:. Types:. “ myxo ” refers to interaction with mucins (glycoproteins)

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The Influenza & Parainfluenza viruses

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The influenza parainfluenza viruses

The Influenza &Parainfluenza viruses

The influenza parainfluenza viruses







Influenza viruses

Type A

Type B

Type C




The influenza parainfluenza viruses

  • “myxo” refers to interaction with mucins (glycoproteins)

  • Different from paramyxoviruses : -segmented genome

  • - smaller (average 110 nm in diameter against 150 nm).

An enveloped viruse helical symmetry capsid segmented linear rna genome

An envelopedviruse, helicalsymmetrycapsid, segmentedlinear RNA genome


Nucleoprotein (7 or 8 RNA segments)



Matrix protein (M)

Lipid bilayer

Haemaglutinin (HA)



Neuraminidase (NA)

80 to 120 nm

The influenza parainfluenza viruses

Each hemagglutinin spike is made up of three entwined molecules while each neuraminidase is comprised of four entwined molecules.

On the surface of the virus are M2 proteins. Inside the lipid envelope, there are eight RNA gene segments called RNPs(RNA molecule+ Nucleoprotein+ Polymerases).

Ball shaped M1 proteins: as cushions for the RNPs inside.

Surface glycoproteins

Surface glycoproteins


H or HA

responsible for pathogenicity of the virus

allows virus to adhere to endothelial cells in the respiratory tract

main determinant of immunity


N or NA

allows release of newly formed viruses within host

determinant of disease severity

The influenza parainfluenza viruses

Antibody against the hemagglutininneutralizes the infectivity of the virus and prevents disease. Ab against neuraminidase only reduces disease.

Influenza subgroups

Influenza subgroups

Influenza A

highly infective

infects many species

causes widespread epidemics

Influenza B

found only in humans

capable of producing severe disease

causes regional epidemics

Influenza C

causes mild disease

humans are natural hosts, but isolates also found in pigs

does not cause epidemics

The influenza parainfluenza viruses

  • Reassortment of segments of the genome RNA

  • Influenza viruses, especially type A show changes in the antigenicity of their hemagglutinin and neuraminidase proteins.  epidemics.

  • Influenza viruses antigenes

  • Group-specific (internal ribonucleoprotein) antigenes.

  • Type-specific (surface N and H) antigens.

The influenza parainfluenza viruses

Many species of animal (eg. Birds, swine, and hourses) have their own influenza A viruses.

These animal viruses are probably the source of the new antigenic types.

Antigenic shift: Major changes based on reassortment of genome pieces. Occurs every 10-11 years

Antigenic drift: Minor changes based on mutation occurs every year.

The influenza parainfluenza viruses

  • Antigenic shift appears to result from genetic recombination of human with animal or bird ,providing major antigenic change.This can cause a major epidemic or pandemic involving most or all age groups.

The influenza parainfluenza viruses

Epidemics and pandemics occur when the antigenicity of the virus has changed sufficiently that the preexisting immunity of many people is no longer effective.

The influenza parainfluenza viruses

Various combinations of RNA segments can result in a new subtype of virus (known as antigenic shift

It is even possible to include RNA strands from birds, swine, and human influenza viruses into one virus if a cell becomes infected with all three types of influenza.

Occurrence of influenza a viruses

Occurrence of influenza A viruses

Influenza A viruses16 HA types

9 NA types

Species affectedhumans, pigs, horses, birds, marine mammals

In humans3 HA types (H1, H2, H3)

3 NA types (N1, N2, N8)

In birdsall HA types

all NA types

Influenza viruses nomenclature

Influenza viruses nomenclature

For example:

A / Beijing / 32 / 92 (H3N2)

Avirus type, here A

Beijingplace where the strain was isolated

32strain number

92year of first isolation

H3N2subtypes H3 and N2 virus sub type, here H3N2

Electron microsope image of h1n1 influenza virus


The influenza parainfluenza viruses


After the virus is inhaled, the neuraminidase degrades the protective mucus layer, allowing the virus to gain access to the cells of the upper and lower respiratory tract.

Viremia rarely occurs, but there is necrosis of the superficial layers of respiratory epithelium.

The influenza parainfluenza viruses


Circulating IgG against the virus occurs after infection, but offers little protection. Secretory IgA in the respiratory tract is protective.

Symptoms of swine flu in humans


The influenza parainfluenza viruses

  • Clinical findings

  • Incubation period: 24-48 hours

  • Symptoms: fever, myalgias, headache, cough develop suddenly.

  • The symptoms resolve spontaneously in 4-7 days but sometimes is complicated with secondary infections.

  • Rey’s syndrome (Encephalopathy and liver degeneration life-threatening complication in children) following some viral infections, particularly influenza B and chikenpox, if they have been given Asprin to reduce the fever.



  • Pneumonia

  • Respiratory failure

  • Convulsion (muscles contract and relax rapidly and repeatedly, resulting in an uncontrolled shaking of the body)

When to seek emergency medical care

When to Seek Emergency Medical Care

  • has difficulty breathing or chest pain

  • has purple or blue discoloration of the lips

  • is vomiting and unable to keep liquids down

  • has signs of dehydration such as dizziness when standing, absence of urination, or in infants, a lack of tears when they cry

  • has seizures (for example, uncontrolled convulsions)

  • is less responsive than normal

Risk groups


  • Persons with certain chronic medical condition

  • School children

  • Travelers to some high risk places

  • Border workers

  • Health care workers or public health workers



  • Prevention in swine or other animal hosts.

  • Prevention of transmission to humans.

  • Prevention of its spread among humans.

Prevention of its spread among humans

Frequent washing of hands with soap and water

Prevention of its spread among humans.

The influenza parainfluenza viruses

Use of face masks

The influenza parainfluenza viruses

Use of

towel while sneezing

The influenza parainfluenza viruses

Use of alcohol based sanitisers.

The influenza parainfluenza viruses

Lab diagnosis

  • Virus isolation (by throat washing) with cell culture. Then flurescent-antibody staining of the infected cells by using antisera to influenza A and B.

  • A rise in antibody titer of at least 4-fold in serum samples using hemmagglutination inhibition or complement fixation.

  • PCR reactions



  • supportive care is required. Bed Rest

  • Keep the sick person in a room separate from the common areas of the house.

  • Antibiotics (to treat this disease, do help prevent bacterial pneumonia and other secondary infections.)

  • Viral agent is used in severe infections.

    (Zanamivir orTamiflu is recommended by C.D.C.)



  • The current trivalent influenza vaccine is likely to provide protection against the new 2009 H1N1 strain.

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