Influenza Virus Essay

Influenza, an innocent little virus that annually comes and goes, has always been a part of people’s lives. Knowing this, one would not believe that it has caused not one, not two, but three pandemics and is on its way to causing a fourth! The Spanish flu of 1918, the Asian flu of 1957, and the Hong Kong

Influenza remains as a significant global threat to public health. In United States alone, a typical influenza epidemic results in over 25 million infections, 300,000 hospitalizations and 13,000 deaths every year (1). The virus evolves antigenically from one year to the next, requiring annual reformulation of the vaccine and leading to variable vaccine efficacy. Exacerbating this natural antigenic evolution, adaptation to the chicken eggs may occur during the manufacture of virus used to produce the inactivated vaccine (2). This year such adaptation has reduced the vaccine efficacy against H3N2 strain (3). Low vaccine efficacy is expected to generate higher attack rates, as has already occured in Australia (3, 4). Compounding the effects of low vaccine efficacy, public perception following the widespread media attention may depress vaccine uptake for a given year. The combination of low vaccine efficacy and low coverage has the potential to reduce herd immunity, putting the population at risk of elevated infection incidence and ultimately high rates of infections and mortality. Consequently, optimizing epidemiological effectiveness of vaccination given vaccine efficacy is imperative to minimize the annual mortality and morbidity of influenza.

Avian influenza is a disease that has been wreaking havoc on human populations since the 16th century. With the recent outbreak in 1997 of a new H5N1 avian flu subtype, the world has begun preparing for a pandemic by looking upon its past affects. In the 20th Century, the world witnessed three pandemics in the years of 1918, 1957, and 1968. In 1918 no vaccine, antibiotic, or clear recognition of the disease was known. Killing over 40 million in less than a year, the H1N1 strain ingrained a deep and lasting fear of the virus throughout the world. Though 1957 and 1968 brought on milder pandemics, they still killed an estimated 3 million people and presented a new

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)

It is believed that humans first contracted the disease when animals were first domesticated. The term “influenza” was originally coined in 1357 AD from an Italian word meaning “influence”. The first true report of the disease was in 1694. It was not until 1933 that influenza was identified as a virus (Taubenberger, Reid, and Fanning 30). The first documented pandemic was in 1580, where it spread throughout the Asia Minor, North Africa, and Italy (White). Since the first influenza pandemic, there have been six major influenza pandemics. These major pandemics began in the years 1889, 1918, 1957, 1968, 1997, and 2009 (Gibbs and Soares

Influenza A virus is extremely virulent and is known for being the most severe type of influenza. This type of virus generally resides in aquatic birds, which act as hosts for the virus. However, influenza A is capable of being transmitted to other species which

Influenza is a life threatening illness caused by influenza virus. It is a contagious disease of the respiratory tract causes serious infections and death around the globe usually in winter season. There are three types of influenza viruses infect humans, type A, B and C. Influenza A and B cause severe disease and major outbreaks and can be prevented through influenza vaccination. Influenza C causes common cold like illness among children. Influenza A is responsible for influenza pandemics. Influenza A and B viruses have two main proteins on the outside of virus, the haemaglutinin (H) and the neuraminidase (N) proteins and are referred as antigens as they are the structures to which our immune system responds. New strains of influenza A and B continually form because the H and N antigens change.

Influenza type A viruses are divided into subtypes based on two proteins on the surface of the virus. These proteins are called hemagglutinin (HA) and neuraminidase (NA). There are 15 different HA subtypes and 9 different NA subtypes. There are three prominent subtypes of influenza A that are known to infect both birds and people. The first one is influenza A H5; there are nine known subtypes of H5 viruses (H5N1, H5N2, H5N3, H5N4, H5N5, H5N6, H5N7, H5N8, and H5N9). Most H5 viruses identified worldwide in wild birds and poultry are low pathogenic viruses, but occasionally highly pathogenic viruses have been detected. Sporadic H5 virus infection of humans, such as with Asian-origin highly pathogenic avian influenza A (H5N1) viruses currently circulating among poultry in Asia and the Middle East have been reported in 16 countries, often resulting in severe pneumonia with approximately 60% mortality worldwide. The second one is influenza A H7; there are nine known subtypes of H7 viruses (H7N1, H7N2, H7N3, H7N4, H7N5, H7N6, H7N7, H7N8, and H7N9). Most H7 viruses identified worldwide in wild birds and poultry are LPAI

Influenza is one of the most important human respiratory infections and its seasonal recurrence is a major contributor to human morbidity and mortality. Seasonal influenza has an estimated annual attack rate of 10-20%, leading to 3-5 million cases of severe illness and 250,000 to 500,000 deaths each year [1]. Throughout history, influenza A has also been the greatest contributor of human pandemics. During the last century, four influenza A pandemics (1918, 1957, 1968 and 2009) caused over 50 million deaths globally, created significant social and economic impact on the human society, and shaped future research and public health policies.

The flu (influenza) is a highly contagious virus that attacks the respiratory system. The flu has three strains, H1N1 strain, H3N2 strain and influenza B strain. The first known case according to UXL Encyclopedia of Diseases and Disorders “The first influenza pandemic that is known to have been global in scale took place in 1850; it started in China and spread across central Asia to Africa and then to Europe where it nearly wiped out the populations of several major cities in southern Italy and Spain”. The number of cases in the U.S. and worldwide is according to www.cdc.gov “There has been 11,965 laboratory-confirmed flu-related hospitalizations.” The number of cases in the US and world wide per year is 3-5 million.

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

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

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 odds of detecting, controlling, and perhaps preventing the spread of an influenza virus with pandemic potential have improved dramatically since 1918, and they continue to increase with expanding knowledge of influenza viruses and the threat they present to human and animal health. Today, international programs permit the characterization of thousands of viral isolates each year and support worldwide surveillance and communications networks. These efforts are informed by research on viral molecular biology and evolution, and bolstered by simultaneous preparations against the threat of bioterrorism. Yet major challenges to pandemic preparedness remain to be overcome. The world's growing—and increasingly urbanized—population and the speed

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”