Influenza Virus

[Guest guest]

Department

of Microbiology <http://microbiology.mtsinai.on.ca> Toronto

Medical

Laboratories <http://www.torontomedicallabs.com> Mount Sinai

Hospital

<http://www.mtsinai.on.ca>

Influenza

Virus

 

The Disease

 

What is

it?

How do

you get it?

Clinical

Symptoms

Laboratory

Diagnosis

Treatment/Recovery

 

 

What is

it?

Influenza

is an acute contagious respiratory illness caused by influenza viruses. It is

one of the oldest and most common diseases known to man.

It can

also be one of the deadliest. Influenza was first described by

Hippocrates

in 412 BC at Perinthus in North Greece, and the first well-described pandemic

of influenza-like disease occurred in 1580.

Since

that time, 31 influenza pandemics have been documented, with three occurring in

this century : in 1918; 1957 and 1968. There is evidence that the virus which

caused these epidemics originated from animals or birds (1918-swine, 1957 and

1968 - birds). In 1976, a new influenza virus from pigs caused human infections

and severe illness and in 1998, an H5N1 poultry strain of influenza also caused

human disease.

 

Each

year, tens of thousands of Canadians become ill with influenza, and

1000-7000

die from its complications.

 

How do

you get it?

The

influenza virus invades the respiratory mucosal cells of the upper and lower

respiratory track. Viral reproduction begins within 4-6 hours, after which

infectious virus is releasedd to infect nearby cells. Whe the infected person

coughs, sneezes, or talks, virus laden particles are sprayed into the air.

 

 

ONCE

THE VIRUS IS INHALED IT ENTERS THE LINING OF THE NASOPHARYNX AND/OR THE

BRONCHIAL TREE. THERE, IT TARGETS COLUMNAR EPITHELIAL CELLS.

The

steps in the infectious cycle are:

 

Haemagglutinin

on the viral surface binds to sialic acid coating the cell surface.

 

This

complex triggers the cell to engulf the virus, forming an endosome within the

cell.

 

The

viral M2 protein acidifies the endosome, breaking down both the virus and

endosome membranes, and releasing viral RNA

 

Viral

RNA enters the cell nucleus and initiates viral replication.

 

New

viral particles are packaged within the cell, and transported through the cell

membrane.

 

Neuraminidase

on the surface of new viruses cleaves molecules of sialic acid, allowing release

of virus. Viral replication initiates the process of cell death, which occurs

several hours after release of the virus.

 

Clinical

Symptoms

During

the 48-hour incubation period after infection, virus replication in the

respiratory tract and transient asymptomatic viremia may occur.

In mild

cases (in resistant or partially immune hosts), the symptoms are like those of

a common cold. In more severe cases, symptoms typically start suddenly with

chills and fever (up to 39 to 39.5ºC) prostration and generalized aches and

pain (most pronounced in the back and legs).

Headache

may be is prominent, often with photophobia and retrobulbar aching. Respiratory

tract symptoms may be mild at first, with scratchy sore throat, substernal

burning, non productive cough, and some times coryza. Later, the lower

respiratory illness becomes dominant; cough can be persistent and productive. In

severe cases, sputum may be bloody.

Nausea

and vomiting may occur in children. After 2 to 3 days, acute symptoms subside

and fever usually resolves

 

Abnormal

lung clearance and altered bronchiolar air flow can be demonstrated, and, in

asthmatics, attacks are frequently precipitated by weakness and fatigue.

Fulminant pneumonia is rare, but when it occurs, death may ensue in as little

as 48 hours.

 

Secondary

bacterial infection of the bronchi and lungs, most commonly pneumococcal or

staphylococcal, is suggested by persistence or recurrence of fever, cough and

other respiratory symptoms in the 2nd week. When pneumonia develops,

cough and fever worsen, purulent or bloody sputum may be produced, and

pleuritic chest pain may occur.

 

Encephalitis,

myocarditis, and myoglobinuria are infrequent complications of influenza and,

if present, usually occur during convalescence. Virus is rarely recovered from

organs outside the respiratory tract, and a specific role in the pathogenesis

of the extra- pulmonary diseases cannot be positively established. However, an increased

incidence of such disease regularly follows influenza A

pandemics.

Reye's syndrome, characterized by encephalopathy, fatty liver, hypoglycemia and

lipidemia, has been prominently associated with epidemics of influenza B,

particularly in children who have ingested aspirin.

 

Laboratory

Diagnosis

Influenza

infection can be diagnosed by serology using haemagglutinin-inhibition tests to

detect antibodies that develop during acute infections; however, such antibodies

require 10-14 days to develop. More immediate diagnosis may be achieved by the

direct detection of viral antigens in nasal secretions by immunofluorescence, polymerase

chain reaction (PCR) or ELISA, using monoclonal antibody to the nucleoprotein.

Culture of the influenza viruses is required for

subtyping

of strains, which is essential for the detection of newly evolved strains, and

thus for the selection of new vaccine, and the detection of pandemics.

 

Treatment/Recovery

Once a

person has Influenza, treatment usually consists of rest, drinking plenty of

fluids.

 

Antibiotics

are not effective against influenza viruses.

 

©

Copyright 1999-2005 Microbiology Department, Mount Sinai Hospital,

Toronto,

Canada. All rights reserved.

 

 

Radiating

UNCONDITIONAL LOVE & Truth

To

ALL who share our circle – our universe, our love, our trust.

May

I always be found worthy.

A

key for life:

Gratitude

& Thankfulness to All of Us

ASoaringHawk

(I

never met a virus, bacteria or fungus that lived in the presence of pure

silver.)

 

Look at everything as

though you were seeing it either for the first or last time. Then your time on

earth will be filled with joy & glory.

 

 

Thank you for YOU!