Assignment

Viral Infection:    INFLUENZA

Influenza, commonly referred to as the flu, It is a wide spread human disease, caused by RNA viruses of the family Orthomyxoviridae (the influenza viruses), that affects birds and mammals. Infection with these viruses leads to a self-limiting illness usually characterized by fever, muscle aches, fatigue, and upper respiratory infection and inflammation. Although it is often confused with other influenza-like illnesses, especially the common cold, influenza is a more severe disease than the common cold and is caused by a different type of virus. Influenza may produce nausea and vomiting, particularly in children, but these symptoms are more common in the unrelated gastroenteritis, which is sometimes called inaccurately "stomach flu." Flu can occasionally cause either direct viral pneumonia or secondary bacterial pneumonia.

Transmition of Influenza :

Typically, influenza is transmitted through the air by coughs or sneezes, creating aerosols containing the virus. Influenza can also be transmitted by direct contact with bird droppings or nasal secretions, or through contact with contaminated surfaces.

Influenza viruses can be inactivated by sunlight, disinfectants and detergents. As the

virus can be inactivated by soap, frequent hand washing reduces the risk of infection.

Classification

Types of virus:  In virus classification influenza viruses are RNA viruses that make up three of the five genera of the family Orthomyxoviridae:

·        Influenzavirus A

·        Influenzavirus B

·        Influenzavirus C

Influenzavirus A:

Type A causes epidemic influenza, in which large numbers of people become infected during a short period of time. Flu epidemics caused by Type A viruses infect both humans and animals and usually originate in the Far East, where a large population of ducks and swine incubate the virus and pass it to humans. The Far East also has a very large human population that provides a fertile ground for viral replication.  The illness it caused was severe, and sometimes fatal. Although it was strongly believed that humans could not get the disease from eating properly cooked chicken.

Influenzavirus B:

 Influenza B almost exclusively infects humans and is less common than influenza A. The only other animals known to be susceptible to influenza B infection are the seal and the ferret.

Influenzavirus C:

This genus has one species, influenza C virus, which infects humans, dogs and pigs, sometimes causing both severe illnesses. However, influenza C is less common than the other types and usually only causes mild disease in children.

Structure and  properties: Influenza viruses A, B and C are very similar in overall structure. The virus particle is 80–120 nanometres in diameter and usually roughly spherical, although filamentous forms can occur. These filamentous forms are more common in influenza C, which can form cordlike structures up to 500 micrometres long on the surfaces of infected cells. However, despite these varied shapes, the viral particles of all influenza viruses are similar in composition.

STRUCTURE: These are made of a viral envelope containing two main types of glycoproteins, wrapped around a central core. The central core contains the viral RNA genome and other viral proteins that package and protect this RNA. RNA tends to be single stranded but in special cases it is double. Unusually for a virus, its genome is not a single piece of nucleic acid; instead, it contains seven or eight pieces of segmented negative-sense RNA, each piece of RNA containing either one or two genes. For example, the influenza A genome contains 11 genes on eight pieces of RNA, encoding for 11 proteins: hemagglutinin (HA), neuraminidase (NA), nucleoprotein (NP), M1, M2, NS1, NS2 (NEP: nuclear export protein), PA, PB1 (polymerase basic 1), PB1-F2 and PB2.

Entry into the Cell:

The influenza virus enters the cell by receptor mediated endocytosis through the clathrin-coated pits. After internalization, the virus containing the coated vesicle, uncoats and fuses with the endosome having acidic pH. The HA: hemagglutinin mediates fusion of the endosome membrane and viral membrane and all the viral RNA enters the cytosol where it replicates and expresses viral proteins.

Replication:

Viruses can replicate only in living cells. Influenza infection and replication is a multi-step process.

Process by which a virus enters a host cell and infects it by reproducing its own genetic material and assembling into virus particles.

The influenza virus is a class of viruses containing RNA as its hereditary material.
It replicates by entering a host cell and using this cell's resources to produce hundreds of copies of the viral RNA.

The virus attaches to the outside of the host cell and its RNA enters into the cell. The viral genes are transcribed and translated by the cell's enzymes and ribosomes. In this way, the virus takes over the cell's productivity. Now, instead of producing only new cellular material, the cell produces hundreds of new virus particles. The new virus particles are eventually released from the cell and drift off, and some may land on a host cell of their own to pirate.

Signs and symptoms:

Symptoms of influenza can start quite suddenly one to two days after infection. Usually the first symptoms are chills or a chilly sensation, but fever is also common early in the infection, with body temperatures ranging from 38-39 °C (approximately 100-103 °F). Many people are so ill that they are confined to bed for several days, with aches and pains throughout their bodies, which are worse in their backs and legs.^[Symptoms of influenza may include:

• Fever and extreme coldness (chills shivering, shaking (rigor)
• Cough
• Nasal congestion
• Body aches, especially joints and throat
• Fatigue
• Headache
• Irritated, watering eyes
• Reddened eyes, skin (especially face), mouth, throat and nose
• In children, gastrointestinal symptoms such as diarrhea and abdomin pain (may be severe in children with influenza B).

Prevention

Vaccination against influenza with an influenza vaccine is often recommended for high-risk groups, such as children and the elderly, or in people who have asthma, diabetes and heart disease.

Infection control:

Reasonably effective ways to reduce the transmission of influenza include good personal health and hygiene habits such as: not touching your eyes, nose or mouth; frequent hand washing (with soap and water, or with alcohol-based hand rubs); covering coughs and sneezes; avoiding close contact with sick people; and staying home yourself if you are sick. Avoiding spitting is also recommended. Although face masks might help prevent transmission when caring for the sick, there is mixed evidence on beneficial effects in the community. Smoking raises the risk of contracting influenza, as well as producing more severe disease symptoms.