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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slide2

Orthomyxoviridae

&

Paramyxoviridae

classification
Classification

ORTHOMYXOVIRIDAE

Influenza viruses

Type A

Type B

Type C

Family:

Genus:

Types:

slide4

“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

Nucleocapsid:

Nucleoprotein (7 or 8 RNA segments)

Internal

antigens

Matrix protein (M)

Lipid bilayer

Haemaglutinin (HA)

Surface

antigens

Neuraminidase (NA)

80 to 120 nm

slide6

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

Haemagglutinin

H or HA

responsible for pathogenicity of the virus

allows virus to adhere to endothelial cells in the respiratory tract

main determinant of immunity

Neuraminidase

N or NA

allows release of newly formed viruses within host

determinant of disease severity

slide9

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

slide11

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.
slide12

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.

slide13
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.
slide14

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

slide16
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 viruses 16 HA types

9 NA types

Species affected humans, pigs, horses, birds, marine mammals

In humans 3 HA types (H1, H2, H3)

3 NA types (N1, N2, N8)

In birds all HA types

all NA types

influenza viruses nomenclature
Influenza viruses nomenclature

For example:

A / Beijing / 32 / 92 (H3N2)

A virus type, here A

Beijing place where the strain was isolated

32 strain number

92 year of first isolation

H3N2 subtypes H3 and N2 virus sub type, here H3N2

slide21

Pathogenesis

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.

slide22

Immunity

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

slide24

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.
complications
COMPLICATIONS
  • 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
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
PREVENTION
  • Prevention in swine or other animal hosts.
  • Prevention of transmission to humans.
  • Prevention of its spread among humans.
slide31
Use of

towel while sneezing

slide33

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
treatment
TREATMENT
  • 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.)

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