Respiratory viral infection. Virus of flue (influenza)

RESPIRATORY VIRAL INFECTION
Respiratory infection means something that affects the lungs and airways (breathing passages)
Myxovirus

INFLUENZA
Influenza is a highly contagious viral infection of the nose, throat, and lungs that occurs most often in the late fall, winter, and early spring.
Incubation period is about 2 days but ranges from 1 - 4 days
There are 4 types (on the basis of variation in this nucleoprotein antigen) –
influenza A
Hemagglutinin(HA)
Neuraminidase(NA)
Influenza B
Influenza C
Influenza D

STRUCTURE
Shape - Spherical or filamentous
Envelope –
the outer layer - is a lipid membrane , Inserted with‘spikes’, which are proteins – glycoproteins ,H (hemagglutinin) and N (neuraminidase). These are the proteins that determine the subtype of influenza virus, Also embedded in the lipid membrane is the M2 protein(channel)
inner layer – made up of protein , M1(matrix protein)
Nucleocapsid – made up of protein
RNA – single stranded ,antisense

ANTIGEN
Two types of antigens:
Group-specific antigens - The ribonucleoprotein (RNP) antigen, or the “soluble” antigen, or the internal antigen is the group-specific antigen.
Type-specific antigens - surface antigen, or “viral” antigen, or “V antigen” is composed of two virus-encoded proteins, HA and NA, which are the type-specific antigens.

LABORATORY DIAGNOSIS
Direct antigen detection
Virus isolation
Detection of influenza-specific RNA by reverse transcriptase-polymerase chain reaction (RT-PCR).Laboratory confirmation of influenza virus

DIRECT ANTIGEN DETECTION
It works on the principle of immunofluorescent
In this antigen are placed at the base and then an antibody with enzyme attached at its base is added
At last substrate is added and if there is antigen – antibody reaction then there will be color change (i.e positive test)

VIRUS ISOLATION AND ANIMAL SUSCEPTIBILITY
Chick embryos. The influenza viruses grow in the allantoic and amniotic cavity of the chick embryos. After an incubation period of 3 days, the fluid is tested for hemagglutination activities of the viruses.
Cell culture. Cell lines are widely used for culture of influenza viruses. They can grow in several primary and continuous cell lines. Rhesus Monkey kidney cell lines (LLC-MK2) and Madin–Darby canine kidney (MDCK) are the continuous cell lines frequently used to isolate influenza viruses.
Laboratory animals. Human influenza virus causes experimental infections in a variety of animals. Intracerebral inoculation of mice by neurotrophic strains produces fatal encephalitis. It causes an acute respiratory disease on intranasal inoculation in ferrets.
Pathogenesis and Immunity. Influenza virus is transmitted from person to person primarily in droplets released by sneezing and coughing.

RT - PCR
It is same as PCR but it has an added step of reverse transcription of RNA to DNA
RT–PCR is used for those containing RNA that needs to be transcribed to DNA for amplification
It is performed in ‘real time’, which means results are visible almost immediately

TREATMENT
Old drugs
Amantadine and rimantadine are the specific antiviral agents available for treatment of influenza.
These drugs are effective against influenza A virus but not against influenza B virus.
These drugs when given within 1–2 days of the onset of illness, reduce severity of the disease and also hasten the disappearance of fever and other symptoms.
Latest drugs
Zanamivir (Relenza) and oseltamivir (Tamiflu) are newer drugs for treatment of influenza and are effective against both influenza A and B viruses.
These are the NA inhibitors, which act by inhibiting the release of viruses from infected cells.
These drugs also prevent the spread of virus from one cell to another.
Relenza is used in the form of nasal spray, whereas Tamiflu is given orally.

PREVENTION AND CONTROL
1. Immunoprophylaxis by vaccines
2. Chemoprophylaxis