Influenza

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Influenza , commonly known as " flu ", is an infectious disease caused by influenza virus. Symptoms can be mild to severe. The most common symptoms include: high fever, runny nose, sore throat, muscle aches, headache, cough, and feel tired. These symptoms usually begin two days after exposure to the virus and most recently less than a week. However, the cough may last more than two weeks. In children, there may be nausea and vomiting, but this is not common in adults. Nausea and vomiting are more common in unrelated infection gastroenteritis, which is sometimes inaccurately referred to as "stomach flu" or "24 hour flu". Influenza complications may include viral pneumonia, secondary bacterial pneumonia, sinus infections, and worsening of previous health problems such as asthma or heart failure.

Three types of influenza virus affect people, called Type A, Type B, and Type C. Usually, the virus spreads through the air from coughing or sneezing. This is believed to occur over a relatively short distance. It can also spread by touching surfaces contaminated by the virus and then touching the mouth or eyes. A person can be transmitted to others both before and during which time they show symptoms. Infection can be confirmed by testing the throat, sputum, or nose for the virus. A number of quick tests are available; However, people may still have an infection if the outcome is negative. The type of polymerase chain reaction that detects viral RNA is more accurate.

Frequent hand washing reduces the risk of spreading the virus. Wearing a surgical mask is also useful. Annual vaccination against influenza is recommended by the World Health Organization for those at high risk. Vaccines are usually effective against three or four types of influenza. Usually well tolerated. Vaccines made for a year may be useless the following year, as the virus evolves quickly. Antiviral drugs such as oseltamivir neuraminidase inhibitors, among others, have been used to treat influenza. Their benefit to those who are healthy does not seem greater than their risk. No benefits are found in those with other health problems.

Influenza spreads throughout the world in an annual outbreak, which accounts for about three to five million cases of serious illness and about 250,000 to 500,000 deaths. In the Northern and Southern parts of the world, outbreaks occur mainly in winter while in areas around the equatorial plague can occur at any time of the year. Death occurs mainly in young people, the elderly and those with other health problems. Large outbreaks known as pandemics are less common. In the 20th century, three influenza pandemics occurred: Spanish influenza in 1918 (~ 50 million deaths), Asian influenza in 1957 (two million deaths), and Hong Kong influenza in 1968 (one million deaths). The World Health Organization declared a new outbreak of influenza A/H1N1 into a pandemic in June 2009. Influenza can also affect other animals, including pigs, horses, and birds.

Video Influenza

Signs and symptoms

About 33% of people with influenza have no symptoms.

Symptoms of influenza can start quite suddenly one to two days after infection. Usually the first symptoms are chills and body pain, but fever is also common in early infections, with body temperature ranging from 38 to 39 ° C (about 100 to 103 ° F). Many people are so sick that they are confined to bed for a few days, with pain and pain all over their bodies, which is worse on their backs and feet.

Symptoms of influenza

• Fever and chills
• Cough
• nasal congestion
• Nose runny
• Sneeze
• Sore throat
• Serious Sound
• Ear pressure
• Ear Pain
• Muscle aches
• Fatigue
• Headaches
• Eyes irritated and watery
• Red eyes, skin (especially face), mouth, throat and nose
• Petekie rash
• In children, gastrointestinal symptoms such as diarrhea, vomiting, and abdominal pain (probably severe in children with influenza B)

It is difficult to distinguish between colds and influenza in the early stages of this infection. Influenza is a mixture of common cold symptoms and pneumonia, body aches, headaches, and fatigue. Diarrhea is usually not a sign of influenza in adults, although it has been seen in some cases of H5N1 "bird flu" and can be a symptom in children. The most obvious symptoms seen in influenza are shown in adjacent tables.

Because antiviral drugs are effective in treating influenza if given early (see the treatment section, below), it is important to identify earlier cases. From the symptoms listed above, combinations of fever with cough, sore throat and/or nasal congestion may improve diagnostic accuracy. Two decision analysis studies have shown that during influenza outbreaks the prevalence will be more than 70%, and thus patients with one of these symptom combinations can be treated with a neuraminidase inhibitor without testing. Even in the absence of local outbreaks, treatment may be justified in the elderly during the influenza season during prevalence above 15%.

Laboratory tests available for influenza continue to improve. The United States Centers for Disease Control and Prevention (CDC) maintains the latest summary of available laboratory tests. According to the CDC, rapid diagnostic tests have a 50-75% sensitivity and 90-95% specificity when compared with viral culture.

Occasionally, influenza can cause severe illness including primary viral pneumonia or secondary bacterial pneumonia. The obvious symptoms are difficulty breathing. In addition, if a child (or perhaps an adult) appears to be better and then recurs with a high fever, it is a danger sign because this recurrence can become bacterial pneumonia.

Occasionally, influenza may have abnormal presentation, such as confusion in the elderly and sepsis syndrome in children. Fluid encephalitis is rare but unheard of. One patient and his sibling had a fever, severe diarrhea, and lowered consciousness, followed by seizures and coma and finally death without respiratory illness. An aging man is confused, slowly lowering the Glasgow Coma Scale, and immediately coma. He survived, but he has residual neurological symptoms such as paraplegia and urinary incontinence.

Emergency alert

• Shortness of breath
• Chest pain
• Dizzy
• Confusion
• Extreme vomiting
• Flu symptoms are improved but then recur with high fever and severe cough (can bacterial pneumonia)
• Cyanosis
• Fever and rash.
• Not drinking liquids

Signs of dehydration

• (in infants) Much less wet nappy than regularly
• Can not hold liquids
• (in baby) There is no tears when crying.

Maps Influenza

Virology

Virus type

In the classification of the influenza virus virus is the RNA virus that forms three of the five genes of the Orthomyxoviridae family:

• Influenzavirus A
• Influenzavirus B
• Influenzavirus C

These viruses are only remotely linked to the human parainfluenza virus, which is an RNA virus belonging to the paramyxovirus family which is a common cause of respiratory infections in children like croup, but can also cause inflammatory diseases similar to those in adults.

The fourth family of influenza viruses has been proposed - influenza D. The species species for this family are the first Bovine Influenza D virus isolated in 2012.

Influenzavirus A

This genus has one species, influenza A virus. Wild water birds are a natural host for a wide range of influenza A. Sometimes, the virus is transmitted to other species and can then cause severe outbreaks in domestic poultry or cause a human influenza pandemic. Type A virus is the most virulent human pathogen among the three types of influenza and causes the most severe disease. Influenza A virus can be divided into different serotypes based on the antibody response to these viruses. The confirmed serotypes in humans, commanded by the number of known human pandemic deaths, are:

• H1N1, which caused the Spanish Flu in 1918, and Swine Flu of 2009
• H2N2, which caused the Asian Flu in 1957
• H3N2, which caused Hong Kong Flu in 1968
• H5N1, which caused Avian Influenza in 2004
• H7N7, which has an unusual zoonotic potential
• H1N2, endemic to humans, pigs and birds
• H9N2
• H7N2
• H7N3
• H10N7
• H7N9
• H6N1, which only infects one person, who recovers

Influenzavirus B

This genus has one species, the influenza B virus. 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 seals and ferrets. This type of influenza mutates at levels 2-3 times slower than type A and consequently less genetically diverse, with only one influenza B serotype. As a result of the lack of antigenic diversity, the level of immunity to influenza B is usually obtained at an early age. However, influenza B is sufficiently mutated so that long-lasting immunity is not possible. This reduces the rate of antigenic changes, combined with a limited range of hosts (inhibiting the shift of anthropic antigens), ensuring that influenza B pandemic does not occur.

Influenzavirus C

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

Structure, property, and subtype nomenclature

Influenzavirus A, B and C are very similar in overall structure. The viral particles are 80-120 nanometers in diameter and are usually roughly round, although filamentous forms may occur. These filamentous forms are more common in influenza C, which can form cable-like structures up to 500 micrometers long on the surface of infected cells. However, although the shape varies, viral particles of all influenza viruses have the same composition. It is made of a viral envelope containing two main types of glycoproteins, wrapped around a central core. The central nucleus contains viral RNA genomes and other viral proteins that pack and protect this RNA. RNA tends to be single wrapped but in special cases it doubles. Unusual for viruses, the genome is not a part of nucleic acid; instead, it contains seven or eight negative-sense RNA parts, each RNA section containing one or two genes, which code for the gene product (protein). For example, the genome of influenza A contains 11 genes in eight parts of RNA, encoding for 11 proteins: hemagglutinin (HA), neuraminidase (NA), nucleoprotein (NP), M1, M2, NS1, NS2 (NEP: nuclear export protein), PA , PB1 (base polymerase 1), PB1-F2 and PB2.

Hemagglutinin (HA) and neuraminidase (NA) are two large glycoproteins outside the viral particles. HA is a lectin that mediates the binding of viruses to target cells and the entry of viral genomes into target cells, while NA is involved in the release of virus progeny from infected cells, by cleaving sugar that binds mature viral particles. Thus, this protein is the target for antiviral drugs. Furthermore, they are antigens that antibodies can be raised. Influenza A viruses are classified into subtypes based on antibody responses to HA and NA. These different types of HA and NA form the basis of the distinctions H and N , for example, H5N1 . There are known subtypes of 16 H and 9 N, but only H 1, 2 and 3, and N 1 and 2 are commonly found in humans.

Replication

Viruses can replicate only in living cells. Influenza infection and replication is a multi-step process: First, the virus must bind and enter the cell, then deliver its genome to a site where it can produce copies of new virus and RNA proteins, assembling these components into new viral particles. , and, lastly, out of the host cell.

Influenza virus binds through hemagglutinin to sialic acid sugar on the surface of epithelial cells, usually in the nose, throat, and lungs of mammals, and the bird's intestine (Stage 1 on image infection). After the hemagglutinin is cleaved by protease, it imports the virus with endocytosis.

Intracellular details are still being described. It is known that the virions converge to the organizing center of microtubules, interact with the acid endosomes and eventually enter the target endosomes for genome release.

Once inside the cell, the acidic condition in the endosome causes two events to occur: First, part of the hemagglutinin protein unifies the viral membrane with the vacuole membrane, the M2 ion channel allows the proton to move through the viral envelope and acidify the virus core, causing the nucleus to dismantle and releasing viral RNA and core protein. RNA molecules (vRNAs), accessory proteins and dependent RNA polymerase RNA are then released into the cytoplasm (Stage 2). M2 ion channels are blocked by amantadine drugs, preventing infection.

These core proteins and vRNAs form complexes transported into cell nuclei, where RNA-dependent RNA polymerases begin to transcend complementary positive-sense vRNAs (Steps 3a and b). VRNAs are either exported to the cytoplasm and translated (step 4) or remain in the nucleus. Newly synthesized viral proteins are secreted through the Golgi apparatus to the cell surface (in the case of neuraminidase and hemagglutinin, step 5b) or transported back to the nucleus to bind vRNAs and form new viral genome particles (step 5a). Other viral proteins have many actions in host cells, including lowering cellular mRNA and using nucleotides released for synthesis of vRNA and also inhibiting the translation of host cell mRNA.

The negative VRNA that forms the future viral genome, RNA-dependent RNA polymerase, and other viral proteins are assembled into virions. The hemagglutinin and neuraminidase molecules clump together into bulge in the cell membrane. VRNA and viral core proteins leave the nucleus and enter these membrane protrusions (step 6). The adult virus shoots off of the cells within the scope of the host's phospholipid membrane, obtaining hemagglutinin and neuraminidase with this membrane layer (step 7). As before, viruses attach to cells through hemagglutinin; adult virus releases once their neuraminidase has cleaved the sialic acid residue from the host cell. After the release of a new influenza virus, the host cell dies.

In the absence of RNA-rectifying RNA polymerase enzymes, RNA-dependent RNA polymerase makes a mistake of approximately 10,000 nucleotides, which is a long estimate of influenza vRNA. Therefore, the majority of newly produced influenza viruses are mutants; this causes antigenic drift, which is a slow change in the antigen on the surface of the virus over time. Separation of the genome into eight separate segments of vRNA allows mixing or reassortment of vRNA if more than one type of influenza virus infects a single cell. Rapid changes generated in viral genetics produce antigenic changes, which are sudden changes from one antigen to another. This sudden large change allows the virus to infect new host species and quickly resolve protective immunity. This is important in the emergence of a pandemic, as discussed below in the section on Epidemiology.

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Mechanism

Transmission

When an infected person sneezes or coughs over half a million virus particles can spread to nearby people. In healthy adults, the shedding of the influenza virus (the time at which a person may be transmitted to someone else) increases sharply one and a half to one day after infection, peak on day 2 and continues for an average total duration of 5 days - but can persist for 9 days. In those who developed symptoms of experimental infection (only 67% of healthy experimental infected individuals), symptoms and release of the virus showed the same pattern, but with viral shedding of the disease previously by one day. Children are much more infectious than adults and release the virus from just before they develop symptoms for up to two weeks after infection. In people with immune disorders, the release of the virus may continue for more than two weeks.

Influenza can spread in three main ways: by direct transmission (when an infected person sneezes directly into the eyes, nose or mouth of another person); air routes (when a person inhales an aerosol produced by an infected person coughing, sneezing or spitting) and through hand-to-eye, hand-to-nose, or hand-to-mouth transmission, either from a contaminated surface or from a direct person contact like a handshake. The relative importance of these three transmission modes is unclear, and they all contribute to the spread of the virus. On air routes, droplets small enough to be inhaled by humans are 0.5 to 5 Âμm in diameter and inhalation only one drip may be enough to cause infection. Although a single sneeze releases up to 40,000 droplets, most of these droplets are quite large and will rapidly precipitate from the air. How long influenza survives in the air droplet appears to be affected by moisture and UV radiation, with low humidity and lack of sunlight in the winter to help its survival.

Because influenza viruses can survive outside the body, the virus can also be transmitted through contaminated surfaces such as banknotes, door handles, light switches, and other household items. The length of time the virus will survive on the surface varies, with the virus lasting for one to two days on a hard and non-porous surface such as plastic or metal, for about fifteen minutes of dry tissue paper, and just five minutes on the skin.. However, if the virus is present in the mucus, it can protect it for longer periods (up to 17 days on paper money). Avi influenza virus can survive indefinitely when frozen. They are inactivated by heating to a temperature of 56Ã, Â ° C (133Ã, Â ° F) for at least 60 minutes, as well as by acids (at pH & lt; 2).

Pathophysiology

The mechanism by which influenza infection causes symptoms in humans has been studied intensively. One mechanism is believed to be the inhibition of the adrenocorticotropic hormone (ACTH), which lowers cortisol levels. Knowing which genes are carried by a particular strain can help predict how well the gene will infect humans and how severe the infection is (that is, predict the pathophysiology of the strain).

For example, part of a process that enables influenza viruses to attack cells is the cleavage of a viral hemagglutinin protein by one of several human proteases. In mild and avirulent viruses, the hemagglutinin structure means that it can only be cleaved by proteases found in the throat and lungs, so the virus can not infect other tissues. However, in very malignant strains, such as H5N1, hemagglutinin can be broken down by various proteases, allowing the virus to spread throughout the body.

Viral hemagglutinin proteins are responsible for determining which species can infect and where in the human respiratory tract, the strain of influenza will be bound. The easily transmitted strains between people have hemagglutinin proteins that bind receptors at the top of the respiratory tract, such as in the nose, throat and mouth. In contrast, the highly lethal H5N1 strain binds to receptors that are mostly found deep within the lungs. This difference in the site of infection may be part of the reason why the H5N1 strain causes severe viral pneumonia in the lungs, but is not easily transmitted by people who cough and sneeze.

Common symptoms of flu such as fever, headache, and fatigue are the result of a large number of proinflammatory cytokines and chemokines (such as interferon or tumor necrosis factor) generated from influenza-infected cells. Unlike rhinoviruses that cause common colds, influenza does cause tissue damage, so the symptoms are not entirely due to inflammatory responses. This immense immune response can produce life-threatening storm cytokines. This effect has been proposed to be an unusual cause of death from H5N1 bird flu, and the pandemic strain of 1918. However, another possibility is that this large amount of cytokines is simply the result of the enormous viral replication produced by this strain, and the immune response is not themselves contribute to the disease.

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Prevention

Vaccinations

The influenza vaccine is recommended by the World Health Organization and the US Centers for Disease Control and Prevention for high-risk groups, such as children, elderly, health care workers, and people with chronic diseases such as asthma, diabetes, heart disease, or compromise immuno among others. In healthy adults it is very effective in reducing the number of influenza-like symptoms in a population. Evidence supports decreasing levels of influenza in children over two years of age. In those with chronic obstructive pulmonary disease vaccination reducing exacerbations, it is unclear whether it reduces the exacerbation of asthma. Evidence supports a lower rate of influenza-like illness in many groups that have immune system disorders such as those with: HIV/AIDS, cancer, and post organ transplantation. In those at high risk immunization may reduce the risk of heart disease. Whether immunization of health care workers affect patient outcomes is controversial with some reviews finding insufficient evidence and others finding transient evidence.

Due to high levels of viral mutation, certain influenza vaccines usually provide protection no more than a few years. Each year, the World Health Organization predicts which virus types are most likely to circulate in the next year (see Annual historical reform of influenza vaccine), which allows pharmaceutical companies to develop vaccines that will provide the best immunity to this strain. The vaccine is reformulated every season for certain types of flu but does not include all the strains that are active in the world during that season. It takes about six months for producers to formulate and generate the millions of doses needed to deal with seasonal epidemics; sometimes, new or neglected strains become prominent during that time. It is also possible to become infected before vaccination and become ill with strains that should prevent the vaccine, since the vaccine takes about two weeks to become effective.

Vaccines can cause the immune system to react as if the body is really infected, and the symptoms of a common infection (many symptoms of colds and flu just general symptoms of infection) may appear, although these symptoms are usually not as severe or lasting as influenza.. The most dangerous side effects are severe allergic reactions either to the viral material itself or to the residue of a chicken egg used to cultivate influenza; However, this reaction is very rare.

The cost effectiveness of seasonal influenza vaccinations has been widely evaluated for different groups and in different settings. In general, there have been found cost-effective interventions, especially in children and the elderly, but the results of the economic evaluation of influenza vaccination are often found to depend on key assumptions.

Infection control

This is the main way influenza spreads

• with direct transmission (when an infected person sneezes directly into the eyes, nose or mouth of another person);
• air routes (when a person inhales aerosols produced by an infected person coughing, sneezing or spitting);
• via hand-to-eye, hand-to-nose, or hand-to-mouth transmission, either from contaminated surfaces or from direct personal contacts such as shaking hands.

Effective ways to reduce influenza transmission include good personal hygiene and hygiene habits such as: not touching eyes, nose or mouth; frequently washing hands (with soap and water, or with alcohol-based alcohol); covering coughing and sneezing; avoiding close contact with sick people; and stay at home if you are sick. Avoiding spit is also recommended. Although facial masks may help prevent transmission when treating the sick, there is mixed evidence of beneficial effects in the community. Smoking increases the risk of contracting influenza, as well as producing more severe disease symptoms.

Because influenza is spread through aerosols and in contact with contaminated surfaces, surface sanitation may help prevent some infections. Alcohol is an effective cleanser against influenza viruses, while quaternary ammonium compounds can be used with alcohol so that the sanitizing effect lasts longer. In hospitals, quaternary ammonium compounds and bleaches are used to clean rooms or appliances that have been occupied by patients with influenza symptoms. At home, this can be done effectively with diluted chlorine bleach.

Social distance strategies used during past pandemics, such as closing schools, churches and theaters, slowed the spread of the virus but did not have a major effect on overall mortality. It is uncertain whether reducing public meetings, such as closing schools and workplaces, will reduce transmission because people with influenza may be moved from one area to another; such actions will also be difficult to enforce and may be unpopular. When a small number of people are infected, isolating the sick can reduce the risk of transmission.

Some patients like young and old people may have abnormal symptoms. Parents may have confusion, white babies may have sepsis syndrome.

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Diagnosis

There are a number of quick tests for flu. One is called Rapid Molecular Assay, when the upper respiratory tract specimen (mucus) is taken using a nasal swab or nasopharyngeal swab. This should be done within 3-4 days of symptom onset, as upper respiratory viral outflow takes a downward spiral afterwards.

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Treatment

People with flu are advised to get plenty of rest, drink plenty of fluids, avoid using alcohol and tobacco and, if necessary, take medications such as acetaminophen (paracetamol) to relieve flu-related fevers and muscle pains. They are also advised to avoid close contact with others to prevent the spread of infection. Children and adolescents with flu-like symptoms (especially fever) should avoid taking aspirin during influenza infection (especially type B influenza), since it may lead to Reye's syndrome, a rare but potentially fatal liver disease. Because influenza is caused by a virus, antibiotics have no effect on infection; unless prescribed for secondary infections such as bacterial pneumonia. Antiviral drugs may be effective, if given earlier (within 48 hours for the first symptoms), but some influenza strains may show resistance to standard antiviral drugs and there is concern about the quality of the study. High-risk individuals such as young children, pregnant women, the elderly, and those with compromised immune systems should visit a doctor for antiviral medications. Those with an emergency alert should immediately visit the emergency room.

Antiviral

Two classes of antiviral drugs used against influenza are neuraminidase inhibitors (oseltamivir, zanamivir, laninamivir and peramivir) and M2 protein inhibitors (adamantane derivatives).

Neuraminidase inhibitors

Overall the benefit of neuraminidase inhibitors in those who are healthy does not appear to outweigh the risks. There seems to be no benefit to those who have other health problems. In those suspected of having the flu, they reduce the length of time symptoms appear less than a day but do not appear to affect the risk of complications such as needing hospitalization or pneumonia. Prior to 2013 the benefits were not clear because the manufacturer (Roche) refused to release trial data for independent analysis. The more resistance to neuraminidase inhibitors has led researchers to seek alternative antiviral drugs with different mechanisms of action.

M2 inhibitors

Amantadine and rimantadine antiviral drugs inhibit viral ion channels (M2 proteins), thus inhibiting the replication of influenza A viruses. These drugs are sometimes effective against influenza A if given early in the infection but are ineffective against influenza B viruses, which have no targeted drug M2. The measured resistance to amantadine and rimantadine in the American isolate H3N2 has increased by 91% in 2005. This high level of resistance may be due to the availability of easy amantadines as part of over-the-counter cold medicines in countries such as China and Russia. , and its use to prevent outbreaks of influenza in poultry farms. CDC recommends against the use of M2 inhibitors during the 2005-06 influenza season due to high drug resistance levels.

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Prognosis

The effects of Influenza are much more severe and last longer than the common cold. Most people will fully recover about one to two weeks, but others will develop life-threatening complications (such as pneumonia). Thus, influenza can be lethal, especially for the weak, young and old, those who have a weakened immune system, or who are chronically ill. People with weakened immune systems, such as people with advanced HIV infection or transplant patients (whose immune systems are medically suppressed to prevent transplant organ rejection), suffer from severe illness. Pregnant women and young children are also at high risk for complications.

Flu can worsen chronic health problems. Patients with emphysema, chronic bronchitis or asthma can experience shortness of breath when they have flu, and influenza can cause worsening of coronary heart disease or congestive heart failure. Smoking is another risk factor associated with more serious illness and increased deaths from influenza.

According to the World Health Organization: "Every winter, tens of millions of people are exposed to the flu Most are sick and do not work for a week, but parents are at a higher risk of death from disease We know the world The number of deaths exceeded several hundred thousand people per year, but even in developed countries the numbers are uncertain, as medical authorities usually do not verify who actually died of influenza and who die of flu-like illness. "Even healthy people can be affected, and serious problems with influenza can occur at age whatever. People over 65, pregnant women, very young children and people of all ages with chronic medical conditions are more likely to get complications from influenza, such as pneumonia, bronchitis, sinus, and ear infections.

In some cases, an autoimmune response to influenza infection may contribute to the development of Guillain-Barrà ©  © syndrome. However, since many other infections can increase the risk of this disease, influenza may only be an important cause during the epidemic. This syndrome is also believed to be a rare side effect of the influenza vaccine. One review provides an incidence of about one case per million vaccinations. Infected by influenza itself increases the risk of death (up to 1 in 10,000) and increases the risk of developing GBS to a much higher level than the highest level of suspected vaccine involvement (about 10 times higher by recent estimates).

According to cdc.gov, "Children of all ages with neurological conditions are more likely than other children to be very sick if they catch the flu.Cluid complications may vary and for some children, it can include pneumonia and even death.

Neurological conditions may include:

• Brain and spinal dysfunction
• Cerebral palsy
• Epilepsy (seizure disorder)
• Stroke
• Intellectual disability
• There's a severe development delay
• Muscular dystrophy
• spinal cord injury

This condition can disrupt coughing, swallowing, clearing the airways, and in the worst cases, breathing. Therefore, they worsen the flu symptoms.

Encephalitis is rare but unheard of, and can occur in the elderly and present as confusion and slurred speech.

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Epidemiology

Season variations

Influenza achieves peak prevalence in the winter, and since the Northern Hemisphere and the South have winter at different times throughout the year, there are actually two different flu seasons each year. This is why the World Health Organization (assisted by the National Influenza Center) makes recommendations for two different vaccine formulations each year; one for the North, and one for the Southern Hemisphere.

A long-standing puzzle why flu epidemics occur seasonally rather than uniforms throughout the year. One possible explanation is that, because people are in the house more often during the winter, they are more often in close contact, and this encourages the transmission from person to person. Increased travel due to winter holiday season in the northern hemisphere may also play a role. Another factor is that cold temperatures cause drier air, which can drain mucus particles. The dried particles are lighter and thus can remain in the air for longer periods. The virus also lasts longer on the surface at colder temperatures and transmits the highest aerosol virus in cold environments (less than 5 Â ° C) with relatively low humidity. Lower air humidity in winter appears to be a major cause of seasonal influenza transmission in temperate climates.

However, seasonal changes in infection rates also occur in the tropics, and in some countries the peak of the infection is especially noticeable during the rainy season. Seasonal changes in the contact rates of school terminology, which are a major factor in other childhood illnesses such as measles and pertussis, may also play a role in the flu. The combination of these small seasonal effects can be reinforced by dynamic resonance with endogenous disease cycles. H5N1 showcases seasonally on humans and birds.

An alternative hypothesis to explain seasonally in influenza infection is the effect of vitamin D levels on immunity to the virus. This idea was first proposed by Robert Edgar Hope-Simpson in 1965. He proposed that the causes of influenza epidemics during the winter can be attributed to seasonal fluctuations of vitamin D, which are produced in the skin under the influence of solar (or artificial) UV radiation. This could explain why influenza occurs mainly in winter and during the tropical rainy season, when people stay indoors, away from the sun, and their vitamin D levels fall.

Epidemic and pandemic outbreaks

Because influenza is caused by various species and virus strains, in certain years some strains may die while others create epidemics, while other strains can cause a pandemic. Normally, within a normal year of two flu seasons (one per side), there are between three and five million cases of severe illness and around 500,000 deaths worldwide, which by some definitions are an annual influenza epidemic. Although the incidence of influenza can vary greatly between years, approximately 36,000 deaths and over 200,000 hospitalizations are directly linked to influenza each year in the United States. One method of calculating the deaths of influenza produced an estimated 41,400 average deaths per year in the United States between 1979 and 2001. Different methods in 2010 by the Centers for Disease Control and Prevention (CDC) reported a range of the lowest of approximately 3,300 deaths of 49,000 per year.

Approximately three times per century, a pandemic occurs, which infects most of the world's population and can kill tens of millions of people (see pandemic section). One study estimates that if a strain of the same virulence as 1918 influenza appears today, it could kill between 50 and 80 million people.

New influenza viruses continue to evolve with mutations or by reassortment. Mutations can cause small changes in the hemagglutinin and neuraminidase antigens on the surface of the virus. This is called antigenic drift, which gradually creates a variety of strains that continue to increase until an evolution that can infect people who are immune to pre-existing strains. This new variant then replaces the older strain as it rapidly sweeps the human population, often causing epidemics. However, since the strains produced by drift will still be quite similar to the older strains, some people will still be immune to them. Conversely, when influenza viruses do reassort, they acquire new antigens - for example by reassortment between strains of birds and human strains; this is called antigenic shift. If human influenza viruses are produced that have new antigens, everyone will be vulnerable, and new influenza will spread uncontrollably, causing a pandemic. In contrast to this pandemic model based on antigenic drift and shift, alternative approaches have been proposed where a periodic pandemic is produced by the interaction of a fixed set of viral strains with a human population with a continuous series of immunities for different strains of the virus..

From a public health standpoint, the flu epidemic is spreading rapidly and is very difficult to control. Most strains of the influenza virus are not highly contagious and every infected individual will only infect one or two other individuals (the number of basic reproductions for influenza is generally around 1.4). However, the generation time for influenza is very short: the time of a person becomes infected when he infects the next person for just two days. Short generation time means that the epidemic of influenza generally peaks around 2 months and burns down after 3 months: the decision to intervene in the influenza epidemic should therefore be taken earlier, and the decision is therefore often made behind incomplete data. Another problem is that individuals become infected before they become symptoms, which means putting people in quarantine after they get sick is not an effective public health intervention. For the average person, viral shedding tends to peak on the second day while symptoms peak on the third day.

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History

Etymology

The word influenza comes from Italian which means "influence" and refers to the cause of the disease; initially, a disease that is thought to have originated from this unfavorable influence of astrology. It was introduced into English in the mid-eighteenth century during the pan-European epidemic. Ancient terms for influenza include epidemic catarrh , la grippe (from France, first used by Molyneaux in 1694), sweaty disease , and Spanish fever (especially for the 1918 flu pandemic strain).

Pandemic

The symptoms of human influenza were clearly described by Hippocrates about 2,400 years ago. Although the virus appears to have caused epidemics throughout human history, historical data on influenza are difficult to interpret, because the symptoms can be similar to other respiratory diseases. This disease may have spread from Europe to America at the beginning of European colonization in America; because almost all of the indigenous population of the Antilles were killed by an outbreak that resembled influenza that broke out in 1493, after the arrival of Christopher Columbus.

The first convincing recording of an influenza pandemic was an outbreak in 1580, which began in Russia and spread to Europe through Africa. In Rome, more than 8,000 people were killed, and several towns in Spain were almost destroyed. The pandemic continued sporadically throughout the 17th and 18th centuries, with the pandemic from 1830 to 1833 becoming very widespread; it infects about a quarter of the people exposed.

The most famous and deadly plague was the 1918 flu pandemic (the Spanish flu pandemic) (influenza type A, H1N1 subtype), lasting from 1918 to 1919. It is not known exactly how many were killed, but estimates range from 50 to 100 million. people. This pandemic has been described as "the largest medical massacre in history" and may have killed many people like the Black Death. This enormous casualty is caused by a very high infection rate of up to 50% and the severity of extreme symptoms, thought to be caused by cytokine storms. Symptoms in 1918 were so unusual that initially influenza was misdiagnosed as dengue fever, cholera, or typhoid. An observer writes, "One of the most striking of the complications is bleeding from the mucous membranes, especially from the nose, stomach, and intestines.Bleeding from the ear and petechal bleeding in the skin also occur." The majority of deaths come from bacterial pneumonia, secondary infections caused by influenza, but the virus also kills people directly, causing massive bleeding and edema in the lungs.

The 1918 flu pandemic is truly global, spreading even to the arctic and remote Pacific islands. Severe illness kills between two and twenty percent of those infected, compared with a normal epidemic death rate of over 0.1%. Another unusual feature of this pandemic is that most kills young adults, with 99% of pandemic influenza deaths occurring in people under 65, and over half in young adults 20 to 40 years old. This is unusual because influenza is usually the most lethal for very young (under age 2) and very old (over the age of 70). The total pandemic death of 1918-1919 is unknown, but it is estimated that 2.5% to 5% of the world's population is killed. A total of 25 million may have been killed in the first 25 weeks; on the contrary, HIV/AIDS has killed 25 million in the first 25 years.

Then the flu pandemic is not so damaging. They include the 1957 Asian Flu (type A, H2N2 strain) and Hong Kong 1968 flu (type A, H3N2 strain), but even these smaller outbreaks kill millions of people. Later, pandemic antibiotics are available to control secondary infections and this may have helped reduce deaths compared with the Spanish Flu of 1918.

The first isolated influenza virus came from poultry, when in 1901 the agent causing a disease called "poultry fowl" was passed through Chamberland filter, which had pores that were too small to pass by bacteria. The cause of the etiology of influenza, the family of the Orthomyxoviridae virus, was first discovered in pigs by Richard Shope in 1931. This discovery was soon followed by isolation of the virus from humans by a group led by Patrick Laidlaw at the Medical Research Council of the United. Kingdom in 1933. However, it was not until Wendell Stanley first crystallized the tobacco mosaic virus in 1935 so the viral non-cellular properties were appreciated.

A significant first step to prevent influenza was the development in 1944 of the viral vaccine dying to influenza by Thomas Francis, Jr. It was built on a work by Frank Macfarlane Burnet Australia, which shows that the virus lost its virulence when cultured on chicken fertilization. egg. The application of this observation by Francis allowed a group of researchers at the University of Michigan to develop the first influenza vaccine, with support from the US Army. The army was heavily involved in this research because of the influenza experience in World War I, when thousands of troops were killed by viruses in a matter of months. Compared with the vaccine, the development of anti-influenza drugs was slower, with amantadine being licensed in 1966 and, almost thirty years later, subsequent class of drugs (neuraminidase inhibitors) developed.

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Society and culture

Influenza produces direct costs due to lost productivity and related medical care, as well as indirect costs of preventive measures. In the United States, influenza is responsible for a total cost of more than $ 10 billion per year, while it is estimated that future pandemics can lead to hundreds of billions of dollars in direct and indirect costs. However, the economic impact of the past pandemic has not been studied intensively, and some authors suggest that Spanish influenza actually has a positive long-term effect on per capita income growth, despite a large decline in the working and short-term population. term depressive effects. Other studies have attempted to predict the cost of a pandemic just as serious as the 1918 Spanish flu in the US economy, where 30% of all workers fell ill, and 2.5% were killed. 30% disease rate and three week disease will decrease gross domestic product by 5%. Additional costs will come from medical care from 18 million to 45 million people, and the total cost of the economy will be around $ 700 billion.

Prevention costs are also high. Governments around the world have spent billions of dollars preparing and planning the potential for the H5N1 avian influenza pandemic, at the expense of purchasing drugs and vaccines and developing disaster drills and strategies to improve border control. On November 1, 2005, United States President George W. Bush launched a National Strategy to Protect Against Pandemic Influenza Danger backed by a request to Congress of $ 7.1 billion to begin implementing the plan. Internationally, on January 18, 2006, donor countries pledged US $ 2 billion to combat bird flu at the two-day International Conference of Delivery on Avian and Human Influenza held in China.

In the 2009 H1N1 pandemic assessment in certain countries in the southern hemisphere, data indicate that all countries experience some socioeconomic effects that are time-limited and/or geographically isolated and a temporary decline in tourism is likely due to fear of H1N1 disease in 2009. It is still too early to determine whether the H1N1 pandemic has caused long-term economic impact.

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Research

Research on influenza includes studies of molecular virology, how viruses produce disease (pathogenesis), host immune responses, viral genomes, and how the virus spreads (epidemiologically). These studies assist in developing influenza mitigation; for example, a better understanding of the immune system response helps the development of vaccines, and a detailed picture of how influenza attacks cells helps the development of antiviral drugs. One of the most important basic research programs is the Genome Influenza Sequencing Project, which creates a series of influenza libraries; this library should help clarify which factors make one strain more deadly than another, which genes most affect immunogenicity, and how the virus evolves over time.

Research on new vaccines is very important, because the vaccine is currently very slow and expensive to produce and must be reformulated every year. Influenza genome sequencing and recombinant DNA technology can accelerate the generation of new vaccine strains by allowing scientists to replace new antigens into previously developed vaccine strains. New technologies are also being developed to grow viruses in cell cultures, which promise higher yields, lower costs, better quality and surge capacity. Research on universal influenza A vaccine, targeted to the external domain of M2 virus transmembrane virus (M2e), is being conducted at Ghent University by Walter Fiers, Xavier Saelens and their team and has now successfully completed Phase I clinical trials. There have been several successful studies on " universal flu vaccine "that produces antibodies to proteins in the mutated virus layer that are less rapid, and thus one shot potentially provides more durable protection.

A number of biologics, therapeutic vaccines and immunobiologists are also being investigated for the treatment of viral infections. Therapeutic biology is designed to activate the immune response against viruses or antigens. Usually, biology does not target metabolic pathways such as anti-viral drugs, but stimulates immune cells such as lymphocytes, macrophages, and/or antigen-presenting cells, in an attempt to induce an immune response to cytotoxic effects on the virus. Influenza models, such as murine influenza, are an easy-to-use model for testing the effects of prophylactic and therapeutic biology. For example, T-Cell Immune Modulator lymphocytes inhibit viral growth in murine influenza models.

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Other animals

Influenza infects many animal species, and transfer of inter-species virus strains may occur. Birds are considered to be the primary animal reservoir of influenza virus. Sixteen forms of hemagglutinin and nine forms of neuraminidase have been identified. All known subtypes (HxNy) are found in birds, but many subtypes are endemic to humans, dogs, horses, and pigs; populations of camels, weasels, cats, seals, minks, and whales also show evidence of previous infection or influenza exposure. Variants of flu viruses are sometimes named based on species whose strains are endemic or adapted. The main variants called using this convention are: bird flu, human flu, swine flu, horse flu and dog flu. (Flu cats generally refer to cat viral rhinitis or feline calicivirus and not infection from influenza virus.) In pigs, horses and dogs, influenza-like symptoms are similar to humans, with cough, fever, and loss of appetite. The frequency of animal diseases was not well studied as human infections, but the outbreak of influenza in port seals caused about 500 mortality seals off the coast of New England in 1979-1980. However, outbreaks in pigs are common and do not cause severe deaths. Vaccines have also been developed to protect birds from avian influenza. This vaccine can be effective against several strains and is used either as part of a prevention strategy, or combined with annihilation in an attempt to eradicate the outbreak.

Bird flu

Symptoms of flu in birds are varied and not specific. The following symptoms of infection with low pathogenic avian influenza may be as light as feathers fall, a small decrease in egg production, or weight loss combined with mild respiratory illness. Because these mild symptoms can make the diagnosis in the field difficult, tracking the spread of avian influenza requires laboratory testing of samples from infected poultry. Some strains like Asian H9N2 are highly virulent to poultry and can cause more extreme symptoms and significant deaths. In the most pathogenic form, influenza in chickens and turkeys results in the appearance of sudden symptoms and almost 100% mortality within two days. When the virus spreads rapidly in the crowded conditions seen in intensive chicken and turkey farms, this epidemic can cause huge economic losses for poultry farmers.

A highly pathogenic and highly pathogenic strain of H5N1 (called HPAI A (H5N1), for "highly pathogenic avian influenza type A subtype H5N1") causes the H5N1 flu, commonly known as "bird flu" or "bird flu" only, and endemic in many bird populations, especially in Southeast Asia. The Asian lineage strains from HPAI A (H5N1) are spreading globally. Epizootic (epidemic in non-humans) and panzootic (a disease that affects animals of many species, especially in large areas), killing tens of millions of birds and spurring the destruction of hundreds of millions of other birds in an effort to control its spread. Most of the references in the media for "bird flu" and most references to H5N1 are about this particular strain.

Currently, HPAI A (H5N1) is a disease of poultry, and there is no evidence to suggest human-to-human efficient transmission of HPAI A (H5N1). In almost all cases, those who are infected have extensive physical contact with infected birds. In the future, H5N1 can mutate or reassort into strains capable of efficient human-to-human transmission. The exact changes that are needed for this to happen are not well understood. However, due to the high mortality and virulence of H5N1, its endemic presence, and its large and increasing biological reservoir, the H5N1 virus is the world pandemic threat in the 2006-07 flu season, and billions of dollars are raised and spent. examine H5N1 and prepare for potential influenza pandemic.

In March 2013, the Chinese government reported three cases of H7N9 influenza infection in humans. Two of them have died and the third is critically ill. Although this strain of the virus was not thought to spread efficiently among humans, by mid-April, at least 82 people had fallen ill with H7N9, of whom 17 had died. These cases include three small family groups in Shanghai and one group between neighboring girls and boys in Beijing, raising at least the possibility of human-to-human transmission. WHO indicates that one cluster does not have two cases confirmed by the laboratory and furthermore, as basic information, that some viruses can cause human-to-human transmission is limited in close contact conditions but can not be transmitted. enough to cause a large community outbreak.

Swine flu

In swine influenza pigs produce fever, lethargy, sneezing, coughing, difficulty breathing, and decreased appetite. In some cases, the infection may cause an abortion. Although mortality is usually low, the virus can produce weight loss and poor growth, causing economic losses for farmers. Infected pigs can lose up to 12 pounds of weight over a 3 to 4 week period. Direct transmission of influenza viruses from pigs to humans is sometimes possible (this is called zoonotic swine flu). Overall, 50 human cases have been known since the virus was identified in the mid-20th century, which has resulted in six deaths.

In 2009, the H1N1 strain of the pig virus originally referred to as the "swine flu" caused the 2009 flu pandemic, but there is no evidence that it is endemic to pigs (ie swine flu) or transmission from pigs to humans, whereas the virus spreads from person to person person. This strain is a reassortment of several H1N1 strains normally found separately, in humans, birds, and pigs.

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References

src: www.crick.ac.uk

Further reading

src: vet.osu.edu

External links

• Influenza in Curlie (based on DMOZ)
• Seasonal Influenza at the Health Protection Center in Hong Kong
• Info on influenza at CDC
• Fact Sheet Overview of influenza at the World Health Organization
• How to avoid the spread of flu from the Smithsonian Institution

Source of the article : Wikipedia