Prevention, Control and Replication of Influenza Virus

Treatment

• Some actions that can take at home is such as getting plenty of rest, drinking plenty of liquids, avoiding alcohol and tobacco use, and taking medication to relieve the symptoms of flu.
• Aspirin should never be used to treat flu-like symptoms in children.
• Using aspirin or ibuprofen can also help to treat the fever, headaches and muscle aches associated with the flu.
• Antiviral drugs may also be prescribed for treating the flu, depending on the duration of illness, severity of symptoms, and your medical history.
• Amantadine and Rimantadine are effective in the treatment of influenza illness during the first 24-248 hrs of onset of illness. These agents prevent viral penetration of target cell or uncoating.

Prevention and control by vaccine

• The most important step in flu prevention is getting vaccinated each year with a flu shot.
• In certain situations, antiviral drugs can be used to prevent seasonal influenza.
• Avoid close contact with people who are sick, stay home when you are sick, cover your mouth and nose when you a cough or sneeze, wash your hands, avoid touching your eyes, nose or mouth, get plenty of sleep, and drink plenty of fluids.
• Artificial immunization is the primary means of penetration of influenza; its efficacy is about 70%.
• The vaccine is typically available as an injection or as a nasal spray.
• The Centers for Disease Control and Prevention recommends annual flu vaccination for everyone over the age of 6 months.
• Each year's seasonal flu vaccine contains protection from the three or four influenza viruses.

Controlling the spread of infection

The influenza vaccine isn't only effective and able to control it, so some important measures should be taken to reduce the spread of infection such as:

Hand washing:

• Frequent hand-washing is an effective way to prevent many common infections.
• Or use alcohol-based hand sanitizers if soap and water aren't readily available.

Contain your coughs and sneezes:

• To avoid contaminating your hands, cough or sneeze into a tissue or into the inner crook of your elbow.
• Cover your mouth and nose when you sneeze or a cough.

Avoid crowds:

• Flu spreads easily wherever people are in group places such as in child care centers, schools, office buildings, auditoriums and public transportation.
• By avoiding crowds during peak flu season, can reduces a chance of infection.

Fundamental Elements to Prevent Influenza Transmission

Multi-faceted approach within healthcare settings is required for preventing transmission of influenza virus and other infectious agents. The spread of influenza virus can occur among patients, HCP, and visitors, community. The core prevention strategies include:

• administration of influenza vaccine
• appropriate management of ill HCP
• implementation of respiratory hygiene
• adherence to infection control precautions for all patient-care activities
• control of aerosol-generating procedures
• applying environmental and engineering infection control measures.

Clear administrative policies and organizational leadership that promotes to these recommendations among the various people is required for proper implementation of these approaches. Furthermore, this guidance should be implemented in the context of a comprehensive infection prevention program to prevent transmission of all infectious agents among patients and HCP.

Composition of vaccine

Type A and B are grown in the allantoic cavity of an embryo and inactivated by formalin.thr vaccine include B prevalent strains of Type A. The vaccine is parentally administrative in a single dose.

Prevention by hygienic practice

• Using a mask to prevent spread by aerosols.
• Hand transmission can be prevented by hand washing with soap and water.
• Avoiding close contact with an infected person and staying home if you are sick.

Replication of influenza virus

Influenza infection and replication is the multistep process. First, the virus has to bind and enter the cell, then deliver its genome to a site where it can produce new copies of viral proteins and RNA. Assemble those components into new viral particle and exit the host cell. Influenza virus bind through hemagglutinin onto sialic acid sugars on the surfaces of epithelial cells typically in the nose, throat, and lungs of mammals and intestines of birds (STAGE 1). After the hemagglutinin is cleaved by the protease, the cell imports the virus by endocytosis.

• The low PH within the endosome is required for virus-mediated membrane fusion that releases viral RNA, RNA-dependent RNA polymerase, and core proteins into the cytoplasm (STEP 2).
• These core proteins and viral RNA from a complex that is transported into the cell nucleus, where the RNA-dependent RNA polymerase begins transcribing complementary positive sense viral RNA (STEP 3a and 3b).
• The viral RNA either is exposed into the cytoplasm and translated (STEP 4) or remains in the nucleus.
• Newly synthesizes viral proteins are either secreted through the Golgi apparatus onto the cell surface (STEP 5 b) or transported back into the nucleus to bind viral RNA and form new viral genome particles (STEP 5a).
• Negative-sense viral RNA that from the genome of future viruses RNA-dependent RNA polymerase and other viral proteins is assembled into a virion. HA and NA molecules cluster into a bulge in the cell membrane. The viral RNA and viral core proteins leave the nucleus and enter this membrane protrusion (STEP 6).
• The mature virus buds off from the cell membrane acquiring HA and NA with their membrane coat (STEP 7). The mature viruses detach one and their NA has cleaved sialic acid residue from the host cell. After the release of new influenza virus, the host cell dies.

Epidemiology

Transmission

Influenza virus transmits from person to person by airborne droplets or by contact with a contaminated surface.

Incidence

• Influenza virus occurs worldwide and causes annual outbreaks of variable intensity. It is estimated that annual epidemics of seasonal influenza cause 3-5 million cases of severe illness and 25000-50000 death worldwide.
• The 3 types of influenza vary in their epidemiological patterns influenza C is least significant. It causes mild sporadic respiratory disease but not epidemic influenza. Influenza B sometimes causes epidemics but influenza C may cause pandemics.
• The incidence of influenza peak during the winter. In the US, an influenza epidemic usually occurs from January to April.
• In 1918, pandemic of influenza, 21 million people died worldwide mostly as a result of secondary bacterial pneumonia.
• Influenza virus shows remarkable ability to undergo antigenic variation due to frequent changes in antigenecity of HA and NA. The variation is highest in type A and less in type B while none in type C.
• The period between epidemic waves of influenza A tends to be 2-3 years. Every 10-40 years, when a new subtype of influenza A appears, a pandemic results. This happened in 1918(H2N1), 1957 (H2N2) and 1968 (H3N2). The H1N2 subtype emerged in 1977. A Nobel swine-origin H1N1 virus appeared in early 2009 and reached pandemic spread.
• In 1997 in Hongkong, the first documented infection of humans by influenza A virus H5N1 occurred. The source was domestic birds had expanded to induce many countries in Asia, Africa, Europe and the middle East.

REFERENCE

Cheesbrough, M.Medical Laboratory Manual for Tropical Countries. Vol 2. ELBS London, 2007.

Tille, P.Diagnostic Microbiology.13th. Elsevier, 2014.

D Grenwood, Slack RCB, and Peutherer J.Medical Microbiology.Dunclude Livingstone: ELBS, 2001.