The Influenza The Influenza &&

Parainfluenza virusesParainfluenza viruses

Orthomyxoviridae

&

Paramyxoviridae

Family:

Genus:

Types:

Classification

Type A Type B

Influenza viruses

Type C

ORTHOMYXOVIRIDAE

• “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

80 to 120 nm

Surfaceantigens

Internalantigens

Nucleocapsid:Nucleoprotein (7 or 8 RNA segments)

Matrix protein (M)

Lipid bilayer

Haemaglutinin (HA)

Neuraminidase (NA)

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

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

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

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

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 antigenes1.Group-specific (internal ribonucleoprotein) antigenes.2.Type-specific (surface N and H) antigens.

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.

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.

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

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

Influenza A viruses 16 HA types9 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 typesall NA types

For example:

Influenza viruses nomenclature

A virus type, here A

Beijing place where the strain was isolated

92 year of first isolation

32 strain number

H3N2 subtypes H3 and N2 virus sub type, here H3N2

A / Beijing / 32 / 92 (H3N2)

ELECTRON MICROSOPE IMAGE OF H1N1 INFLUENZA VIRUS

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.

ImmunityCirculating 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

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

PneumoniaRespiratory failureConvulsion (muscles contract and

relax rapidly and repeatedly, resulting in an uncontrolled shaking of the body)

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 childrenTravelers to some high risk placesBorder workers Health care workers or public health

workers

PREVENTION

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

Use of face masks

Use of

towel while sneezing

Use of alcohol based sanitisers.

Lab diagnosis1. Virus isolation (by throat washing)

with cell culture. Then flurescent-antibody staining of the infected cells by using antisera to influenza A and B.

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

1. PCR reactions

TREATMENT

supportive care is required. Bed RestKeep 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 or Tamiflu is recommended by

C.D.C.)

VACCINE

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