Influenza Virus Evolution

According to Center for Disease Control (CDC), influenza viruses are divided into three types, designated as A, B, and C. Influenza type C usually only causes either very mild symptoms or no symptoms at all. Types A and B, however, are responsible for epidemics of respiratory illnesses that can result in hospitalization, or even death. Influenza is constantly changing over time by mutations. This continual change allows the virus to evade the antibodies that were meant to kill it. A host infected with influenza virus develops antibodies against that virus; as the virus changes, the "first" antibody no longer recognizes the "newer" virus and infection can occur because the host does not recognize the new flu virus as a problem until the infection is well under way. The first antibody developed may, in some instances, provide partial protection against infection with a new influenza virus. According to Medicine Net.com, In 2009, almost all individuals had no antibodies that could recognize the novel H1N1 virus immediately. It quickly spread throughout the world so fast that the WHO declared this new flu strain (termed novel H1N1 influenza A swine flu). There are currently four main strains of influenza circulating worldwide. Three of the viruses are type A, and one is type B. Type A viruses are divided into subtypes based on the differences in two viral proteins called hemagglutinin (H) and neuraminidase (N). The three subtypes of influenza A are A(H1N1), A(H3N2), and A(H5N1). The reason for several strands of type A are because of the two kinds of change influenza A

Every year, millions of people start talking about the influenza virus and getting their vaccines as the flu season approaches, which starts around the October-November period and reaches its peak between December and March. Therefore, public health officials around the world- and in the U.S in particular- are constantly challenged by properly preparing for the annual influenza dilemma, given that this viruses, and other respiratory viruses, are a serious health threat to the U.S population and the world as a whole. Furthermore, what makes the influenza virus even more challenging to control is that it can mutate rapidly and reassort to form new strains, having the ability to reside in multiple animal hosts. In fact, many scientists and researchers have been doing in-depth intensive research so as to understand the mechanism behind this unique characteristic of the virus, try to find new ways to control it, and explore different areas of protection and vaccination.

According to the CDC there was a breakout in “1918-19 Flu pandemic, which killed as many as 50 million people worldwide”causing the biggest breakout for Influenza (Reconstruction of 1918 Influenza Pandemic Virus). Influenza originated from Asia and the Middle East. Virtually all mammalian species have influenza. Influenza is a contagious respiratory illness caused by the Influenza virus. There are three types of Influenza: type A, type B, and type C. Influenza has numerous symptoms, vaccinations, and is unlikely to kill it’s host.

There are there types of influenza A and C or the most severe types and B which is the most common, Luckily not the to severe. The virus works by first attaching to the outside of a host cell. It injects its RNA into the cell. Unfortunately our cells treat the RNA like they should. It translates the viral genes using the cell’s ribosomes and enzymes. Now the virus can take the cell over and use it to reproduce more viruses. Sooner or later it releases the new nauseating viruses and they search for another cell to raid.

Influenza is a highly contagious viral infection of the respiratory passages that causes severe body aches, high fever, and can sometimes lead to death. To be protected, you must be immunized every year. “A new study found that the influenza vaccine prevents type A and type B in only 1.5 out of every 100 vaccinated adults, but the media portrays these statistics as this meaning the vaccination is 60 percent effective” (Medline Plus). Unfortunately, this does not mean 60 out of 100 people who receive the flu shot leads to protection against influenza. Researchers can confirm that most strains of influenza are harmless against healthy individuals; however, the virus has an ability to mutate into different strains which can cause an extensive

There are two important proteins used in the determination of the type of influenza; haemagglutinin (HA) and neuraminidase (NA). There are 18 known variations of the haemagglutinin protein and 11 of the neuraminidase protein, giving hundreds of possible variations in the subtypes of the virus . These subtypes are further divided into different strains that have a divergent molecular makeup, giving rise to viruses that differ in virulence, ease of transmission and severity of symptoms. Not all strains of influenza can cause disease in humans; influenza D subtypes cannot infect humans and influenza C infections are rare and usually very minor. Influenza A and B are the subtypes that are responsible for the common infections and the epidemics and pandemics that occur periodically, with influenza A causing the majority of these infections. The virus is transmitted through the inhalation of droplets which are expelled when an infected person coughs or sneezes, through contact with a contaminated surface and through the exchange of saliva . The infected person becomes infectious to others around 12 hours after first contact with the virus and remains contagious for around the next five days; this can vary as the immunocompromised can take longer to subdue the virus and children tend to be more infectious than adults . The virus incubates in the respiratory tract by invading cells through the cleavage of the viral protein haemagglutinin by human proteases . The pathogenicity of a certain strain is determined by the spread of proteases in the respiratory tract that can cleave the proteins of the virus; a strain is typically milder if the proteases that reside in the lungs and throat are the only ones capable of cleaving the virus, causing an upper respiratory tract (URT)

IAV is a virus classified as part of the orthomyxoviridae and one of the causative agents of influenza or “the flu”. (Edinger, Pohl & Stertz, 2014) Its natural reservoir is primarily wild aquatic fowl where it is mostly nonpathogenic, though zoonotic infections can occur in mammals and domestic fowl. (Klenk, Matrosovich & Stech, 2008) The jump between species often results in the establishment of highly pathogenic variants that can have devastating effects, as was the case of the “Spanish” influenza pandemic of 1918. (Taubenberger, 2006) The infection across special barriers is dependent on changes to the structure of glycoproteins on the viral envelope, particularly haemagglutinin (HA). The different subtypes of HA and neuraminidase (NA) serve to classify different viral lineages. These changes in the structure can result in proteolytic activation; that when coupled to changes of receptor binding specificity allow for interspecies transmission. (Klenk, Matrosovich & Stech, 2008) The modifications can affect the pathogenicity of the virus even within the same species, which can allow for infection of new cell types, or even systemic disease. (Steinhauer, 1999) These mutations accumulate through successive replications or genetic re-assortment during confection. The resulting structural changes account for the observed antigenic drift that causes loss of immunity despite prior exposures to the virus. This evolutionary process drives the consistent

The influenza virus usually has a round shape; it can be elongated or even have an irregular shape at times. In addition, it has a layer of spikes on its exterior. Note that there are two different types of these spikes. Each spike has its own protein, one is the hemagglutinin (HA) protein and the other is the neuraminidase (NA) protein. The HA protein lets the virus to attach to a cell, so it can enter into a host cell and start the infection process (every virus must enter cells in order to make more copies of themselves). The NA protein is needed for the virus to leave the host cell, so that new viruses that were made inside the host cell can infect more cells. Because these proteins are present on the surface of the virus, they are visible to the human immune system. Inside the layer of spikes, are eight pieces of RNA that contain the genetic information for making new copies of the virus. Each segment contains instructions to make one or more proteins of the virus.

Influenza virus has caused serious respiratory illness and death over the past centuries. Epidemics and pandemics due to Influenza virus were known to cause morbidity and mortality in humans and other animals. Pandemics have been documented since the 16th century (WHO, 2005) and in the last 400 years, at least 31 pandemics have been recorded (Lazzari and Stohr, 2004). Influenza virus belongs to the family Orthomyxoviridae, which is characterized by a segmented, minus-stranded RNA genome. Influenza viruses are irregular, spherical (80-120 nm diameter) or filamentous structures and their surfaces are studded with rod-shaped hemagglutinin (HA) and neuraminidase (NA) spikes (Betts, 1995). Influenza viruses are of three types A, B, and C. The typing

The virus has been studied in detail during 2009-2010. Being a complex virus, it is important to study the current scenario and the trends of the circulating virus. During 2015, the incidence of pandemic H1N1 2009 influenza virus among patients presenting with ILI, diagnosed in our tertiary care hospital during the study period was 18.6%. In the 2012-2013 the incidence of pandemic H1N1 2009 influenza virus among patients presenting with ILI, was 8.20% indicating a sharp increase in the number of cases. 9 After 2010, the 2009 pandemic H1N1 influenza A reappeared in several northern and western states of the country during the winter months of 2012-2013. The presently ongoing resurgence since December 2014 however appears to be worse than the previous one, leading to over 30,000 cases and 2000 deaths countrywide (as of 28th March,2015) as compared to 5044 cases and 405 deaths in 2012 and 5250 cases and 692 deaths in 2013.10 The resurgent waves lead to more number of hospitalizations and deaths due to pdmH1N1 as compared to the rest part of the year and appear at an interval of 1.5-2

Influenza pandemics are caused by type A virus. Influenza A viruses have two specific antigens Hemagglutinin (HA) and neuraminidase (NA) on their surfaces. Various influenza strains are identified by the combination of their HA and NA antigens. HA protein antigens allow

The Influenza virus replication cycle starts with HA binding to the sialic acid receptor on the respiratory epithelial cell surface permitting the entry of influenza virus into the cell via endocytosis [17]. Aided by the acidic environment of the endosomes, the virus fuses its envelope with the endosomal membrane and releases the virus nucleocapsid making its way to the host nucleus.

Influenza virus can mutate in two ways, Antigenic shift and Antigenic drift. The genome is in 8 segments of RNA. Each of those 8 segments must be packaged within the viral particle in order for it to be viable. Influenza virus uses an RNA polymerase enzyme that doesn’t proofread. This allows for point mutations, incorrect bases are inserted into the genome which causes minor changes in 1 to 2 amino acids. Mutations cause slight variations in the shapes of the hemagglutinin and neuraminidase. This prevents neutralizing antibodies from binding. If a person were exposed to the new mutant strain, their immune system won’t be able to protect them. This is called antigenic drift and may happen anytime the virus replicates. Point mutations are most

Influenza viruses belong to the Orthomyxoviridae family of families, and has a single-stranded RNA genome segments. Basis of influenza virus core protein on into A, B and C. ( WHO 2014)

With a huge number of victims, 80 to 100 million, since 1918, the influenza is considered as one of the most pandemic diseases ever. There are three types of influenza virus: influenza virus A, influenza virus B, and influenza virus c. These are a subtypes of the virus family orthomyx-oviride. The types B and C do not cause pandemic diseases while type A does. The type A classified into three main subtype H1.N1, H1.N2, and H3.N2. The (H.N) refers to the two kinds of proteins on the surface of the virus (hemagglutinin and neuraminidase). The difference in numbers is due to the difference in protein variability. A H1.N1 virus which is widely known as Spanish flu is the only type that can transmit from human to human. The H5.N1, or “bird flu”