¶ … ordinal list of the causes of death in the US. It has been reported that the disease causes more havoc in developing countries. During a flu epidemic, up to 20% of Americans are infected by the virus. Of this figure, approximately 36 000 people might die of the infection. It is reported that over 200 000 of those infected are infected in various hospital facilities across the country. Indeed, few viruses have inflicted as much damage and endured as the influenza virus. Respiratory ailments blamed on influenza are documented in records that trace the infection back to Greece and Rome of the ancient world. The word influenza when viewed from its original Greek form: influentia points to the popular belief that the epidemics that people suffered were a result of the influence of stars. Indeed, people including medical experts refer to the infection of influenza as flu, yet most of these are not (Specter, 2005. Orthomyxovirus which occurs in three forms is the cause of influenza. The three are termed as A, B, and C. The virus strains referred to as B. and C. have the capacity to infect humans and make them fall sick. This strain is fairly rare and indeed less commonly serious when it happens. It is the type A virus that we are always worried about. Each of the viruses of influenza is home to hundreds of spikes that are microscopic and they rise from the surface of the virus. These spikes are usually made of a protein referred to as hemagglutinin. These spikes latch and attach on cells that the virus intends to infect. The other spikes are commonly known as neuraminidase. This is the enzyme that gives the virus its fire power. The two proteins are the reason behind the naming of the flu virus I labeled as type N and type H. The type A influenza is known to be the most mutating virus and thus the most successful in causing damage. It can alter or swap any of its eight genes with the others of variant strains (Specter, 2005).

The Nature of Influenza Micro-Organism

Its genome is encased in a capsid made of proteins. The one of influenza A contains neuraminidase (NA) and glycoproteins hemaglutinin (HA) which are antigenic. Hundreds of molecules are required from each of the protein capsids. These are the parts of the virus which noted as foreign material by the immune system of the host body. Owing to the fact that there are many varying types of influenza A neuramidase and hemagglutinin proteins the immune system of the human species is often compromised because of the challenge of eliciting an appropriate immune response. Apart from the human body, other organisms are known to host the virus and act as a reservoir for the influenza virus. Indeed, influenza outbreaks have been noted among poultry, pigs, camels, seals and horses. Details of the origin, strain number, isolation year and NA/HA proteins are normally included when a strain is named (Clancy, 2008).

The influenza A genome has eight genes which encode 11 different types of proteins and has the NA/HA genes. The proteins contain 3 RNA polymerases that work together in a complex formula that is needed by reproduce its RNA genome. It is worth noting that the polymerases have been observed to contain a high error rate because of the fact that they do not have proofreading ability. This causes a high rate of mutation in the viral genomes that have been replicated. The end result is a high rate of evolution for the viruses. The genome of influenza also encodes extra structural proteins required to constitute the capsid, the NS1, NS2 proteins whose purpose is still under research and nucleoprotein. Other proteins that are encoded by the genone include M1 AND M2. These are needed for export of nuclear and a range of other functions, and NA/HA which influence the attachment and release of the virus on host cells (Clancy, 2008).

Owing to the segmented patterns of the genome of influenza where the sequence of coding is located within individual RNA strands, there is ready shuffling of the genomes within the cells of the host with a variety of flu viruses. Furthermore, owing to the fact that there are at least 16 varying hemagglutinin sub types and a total of nine neuraminidase categories, it is possible to have many combinations of capsid proteins. Out of these sub types, 3 of them, i.e. H1 to H3, and two neuraminidase subtypes, i.e. N1 and N2 have led to epidemics that have sustained for years among the

All influenza A is known to find home in the bodies of birds and these act as the reservoir from which the subtypes of HA infiltrate the human body (Clancy, 2008).
Mode of Transmission

It is believed that the infection spreads through airborne means in which very small nuclei in droplets are inhaled but there is little evidence to support such hypothesis. It has been argued theoretically that minute nuclei droplets that contain the virus leave from the respiratory tract of those infected and due to their small size and lightness hang around in the sir for a long time. Once they are inhaled by a fresh victim, the virus enters the respiratory tract of the host and attaches itself to the specific receptor cells or antigens on epithelial cells surface which form the lining of the trachea and the pharynx. These in turn replicate to constitute a large mass of new particles of virus which spread out to attach other body cells or even leave to infect fresh victims. The transmission for type A influenza has been shown to spread faster. It has also been shown that the virus spreads faster in enclosures such as residential places, hospitals and nursing homes. This tendency has led to the speculation that the virus is spread during the prodromal stage before its symptoms show in the victim (Gould, 2011).

Pathology

Influenza virus replicates within the epithelial cells along the stretch of the respiratory spread. The virus can be recovered from both upper and lower respiratory tracts of those infected. It is not sufficient to make histotologic diagnosis since histologic changes are not specific. Proper diagnosis requires specific tests such as isolation of the virus, RT-PCR tests, serologic analysis autopsy or biopsy tissue section which should be confirmed by immunohistochemical and in situ hybridization techniques. Influenza infections that are non fatal commonly involve the upper part of the respiratory tract and the trachea. The fatal incidences of influenza have shown evidence of pneumonia. This review is focused on the lower respiratory tract pathology (Taubenberger and Morens, 2008).

Infection Cycle

There must be several steps to facilitate infections to occur. Such stages are commonly referred to as the infection cycle. Each of the stages must happen if the infection is to occur. The control of infection is based on the reality that transmission of infectious diseases will be forestalled when any level in the cycle is interrupted or broken (Lindh et al., 2013).

The steps include

1. The agent of infection

These are microorganism that can be lumped into five categories, i.e. rickettsia, fungi, parasites, bacteria and viruses. An agent must be present for an infection to occur. When an infectious disease is identified, on the basis of the organism that causes the disease, the infection of that disease could be stopped by use of an anti infective medicine or other infection control strategy (Lindh et al., 2013).

2. Reservoir

The main reservoir of human influenza A virus. The reservoir of influenza A virus among the avian group is the wild birds group. There is suspicion that some animals act as reservoirs to some new human infection subtypes. The influenza A virus is commonly isolated in such animals as horses and pigs. It has also been noted that swine have special receptors for human and avian influenza virus. There seems to be a chance that there will be a re-assortment with antigenic characteristics that will infect humans even as the human immune system remains naive (Public Health Agency of Canada, 2011).

3. Portal of Exit

When the agent migrates from the reservoir, there is a high chance that an infection will occur. They include secretions and excretions, respiratory tract, gastrointestinal tract and mucous membranes (Basarkar, S., 2016).

1. Means of transmission

Transmission can occur through aerosols and droplets via the respiratory tract. It may also occur through contact with infected surfaces. Transmission has also been noted to occur rapidly through encloses spaces of human habitation and activity. Transmission from generous donors of the virus can take place and evolve into actual infection within 8 hours through surfaces made of stainless steel and for a couple of minutes via tissue paper (Public Health Agency of Canada, 2011).

2. Postal of entry

The ocular surface is a potential virus infection site for the respiratory tract and a replication venue. Nevertheless, properties governing influenza virus ocular tropism, virus spread mechanisms for evolution from ocular to respiratory tissue, the possible differences in respiratory disease acquired from various infection channels are still…