VIRAL INFLUENZA

What is INFLUENZA ? INFLUENZA is an acute infectious disease of the respiratory tract . The causative agent of influenza is Influenza Virus. Three immunologic types of influenza viruses are known, designated A, B and C. The influenza viruses are a major determinant of mortality caused by respiratory disease.

MORPHOLOGY The influenza virus is typically spherical with a diameter of 80-120nm and are readily visible under the dark ground microscope. The virus core consists of ribonucleoprotein in helical symmetry. The nucleocapsid is surrounded by an envelope which has an inner membrane protein layer and an outer lipid layer.

TYPES OF INFLUENZA VIRUSES Influenza type A is antigenically highly variable and is responsible for most cases of epidemic influenza. Influenza type B may exhibit antigenic changes and sometimes causes epidemics. Influenza type C is antigenically stable and causes only mild illness in immuno competent individuals.

LABORATORY DIAGNOSIS Diagnosis of influenza relies on identification of viral antigens, isolation of the virus, or demonstration of a specific immunological response by the patient. Nasal washings, gargles, and throat swabs are the best specimens for diagnostic testing. 1. Polymerase chain reaction It is a test based on detection of influenza RNA in clinical specimens using Reverse transcription polymerase chain reaction.

2. Serology Antibodies to several viral proteins (hemagglutinin, neuraminidase, nucleoprotein, matrix) are produced during infection with influenza virus. Routine serodiagnostic tests in use are based on HI and enzyme linked immunosorbent assay (ELISA). The HI test reveals the strain of virus responsible for infection.

TREATMENT 1. ANTIVIRAL MEDICATIONS Using antiviral drugs- Adamantanes: Amantadine, Rimantadine Neuraminidase inhibitors: Zanamivir, Oseltamivir Antiviral treatment lasts for 3-5 days and must be started within the first 2 days of illness.

2. CONTROL BY VACCINES Inactivated viral vaccines are the primary means of prevention of influenza in the US. A live virus vaccine must be attenuated so as to induce the disease it is designed to prevent. Annual influenza vaccination is recommended for all children ages 6 months to 18 years and for high risk groups. 3. PREVENTION BY HAND HYGIENE Although transmission of influenza virus occurs primarily by aerosol spread, but transmission is also potentially important.