Influenza, or flu is one of the most common infectious diseases that affects mainly the upper respiratory system. The infection usually lasts for about a week, and is characterized by sudden onset of high fever, aching muscles, headache and severe malaise, non-productive cough, sore throat and rhinitis.

Several viruses can cause Influenza. The virus is transmitted easily from person to person via droplets and small particles produced when infected people cough or sneeze. The virus can also spread by direct contact with infected individuals or with contaminated objects from them such as toys, doorknobs. Influenza tends to spread rapidly in seasonal epidemics.

Most infected people recover from influenza within one to two weeks without requiring medical treatment. However, with some people - such as young children, elderly, and chronically ill patients - influenza can lead to severe complications and may eventually be fetal. The epidemics caused by the influenza virus are estimated by world health organization to cause about 3 to 5 million cases of severe illness, and up to 500 thousand deaths every year worldwide.

A yearly flu vaccine is considered as the first and most important step in protecting against flu viruses. While there are many different flu viruses, a flu vaccine protects against the viruses that research suggests will be most common that year. October and November are best time to take the vaccine; i.e. before the season in which influenza becomes widespread, particularly cold months, in many countries.

Influenza, commonly known as “flu", is a highly contagious viral infection that affects mainly the nose, throat, bronchi and, occasionally, lungs. Influenza affects all age groups, though kids tend to get it more often than adults. The infection occurs most often in the late fall, winter, and early spring. Influenza can cause mild to severe illness. It causes significant loss of workdays, human suffering, and mortality.

• Type A influenza. Influenza A viruses cause most human and all avian influenza infections. The virus is considered the most pathogenic human influenza virus. The emergence of a new and very different influenza A virus to infect people can cause an influenza pandemic.
• Type B influenza. B viruses are another cause of seasonal epidemics of influenza, but with less severity than type A. Type B influenza is found only in humans and do not cause pandemics. Both Type A and B are targeted in the yearly flu vaccine.
• Type C influenza. This Type occur much less frequently than A and B. That is why it is not included in flu vaccine. It generally causes a mild respiratory illness and are not thought to cause epidemics or pandemics.
• Type D Influenza. D viruses that cause influenza primarily affect cattle and are not known to infect or cause illness in people. These viruses that have been detected recently, shares common ancestry with known influenza viruses, but are distinct enough to be classified into a different group.

Influenza is an acute infection caused by an influenza virus that circulate in all parts of the world. There are 3 types of seasonal influenza viruses that affect humans: A, B, and C. Most experts think that flu viruses are spread mainly by droplets made when people with flu cough, sneeze or talk. While coughing may produce several hundred droplets, a good sneeze can generate up to 20,000. These droplets can land in the mouths or noses of people who are nearby or possibly be inhaled into the lungs. Less often, a person might also get flu by touching a surface or object that has flu virus on it and then touching his own mouth or nose or even eyes.

Influenza virus consists of RNA core of 8 gene segments surrounded by a coat of 10 (influenza A) or 11 (influenza B) proteins. Immunologically, the most significant surface proteins include hemagglutinin (H) and neuraminidase (N). Hemagglutinin binds to respiratory epithelial cells, allowing cellular infection. Neuraminidase cleaves the bond that holds newly replicated viruses to the cell surface, permitting the infection to spread.

At first, the person is exposed to influenza virus that reach the airway. The main targets of the virus are the columnar epithelial cells of the respiratory tract. These cells may be susceptible to infection if the viral receptor is present and functional to bind with the surface of host cells. The defensive body mechanisms such as specific immune response may not work, so the virus start controlling the cells and using their qualifications to replicate and numerous viruses are produced within hours.

As essential as the binding of the influenza virus is its cleavage from the binding site at the host cell, as it allow for the virus to spread to infect other cells, which lead to disease development and progression. The infectious particles are released into the air way, which will trigger inflammation and symptoms.

Influenza is often confused with the common cold, because these two types of respiratory illnesses have similar symptoms. However, influenza symptoms usually start suddenly and are more severe than typical sneezing and stuffiness of a cold. The other symptoms of flu may include:

• High fever;
• Chills;
• Headache;
• Muscle aches;
• Cough, usually dry;
• Sore throat;
• Runny, or congested nose;
• General tiredness and weakness;
• Severe feeling of unwell;
• Loss of appetite;
• Vomiting and diarrhea, commonly in children.

Symptoms start 1 to 4 days after the virus enters the body, and diminish within a week. However, some have a lingering cough and still feel very tired for a further couple of weeks. Most infected adults are able to infect others beginning 1 day before symptoms develop and up to 5 to 7 days after becoming sick. Children may pass the virus for longer than 7 days.

The person is suspected to have influenza if he has flu symptoms. This suitability is further supported if there is a close contact with infected person, and happened during colder months of the year or periods of influenza epidemic. However, influenza can also occur outside of the typical flu season. In addition, other viruses can also cause respiratory illness similar to the flu. So, it is impossible to tell for sure if the person has flu based on symptoms and the season alone.

A number of flu tests are available to detect influenza viruses. The most common are called “rapid influenza diagnostic tests.” Unfortunately, the ability of these tests to detect the flu can vary greatly depending on the type of rapid test used, and on the type of flu viruses circulating. Therefore, most people with flu symptoms do not require testing because the test results usually do not change how you are treated.

Influenza is acute disease that usually pass after a week. The aim of the treatment is to control symptoms and prevent further complications, especially for high risk groups, such as elderly people, children, pregnant women, immunocompromised patients, and those affected with chronic illnesses, such as diabetes, asthma, and chronic heart.

• Home management: For most healthy adults, Symptoms can be managed at home without need to see the doctor. This can be achieved by:
  • Getting Rest, to help the body fight the virus and help feeling better;
  • Maintaining normal fluid intake to prevent dehydration and loose secretions;
  •  Drinking something soothing, such as warm water, lemon and honey drink;
  • Having Chicken soup, as it may help with symptoms of upper respiratory tract infections;
  • Humidifying the environment, as breathing moist air helps ease nasal congestion and sore throat;
  • Inhaling steam to help relieve a clogged nose;
  • Trying nasal irrigation with saline solution, to ease stuffiness and post-nasal drip;
  • Gargling with warm salty water and sucking a throat lozenge to soothe a sore throat;
  • Avoiding all kinds of smoke, as they can worsen the symptoms.
• Medications to treat symptoms: Even they cannot provide cure, many drugs are helpful to relieve influenza symptoms until the disease pass away. Based on the complaints, the patient can take some over the counter medications for influenza. However, he/she is encouraged to ask the doctor before start ingestion of drugs, such as:
  • Decongestants. These drugs are used to reduce swelling in the nasal passageways and come in oral or nasal spray forms. However, nasal spray decongestants should not be used for more than a few days because, if they are used too long and then stopped, they can cause rebound symptoms. Examples of decongestants are oxymetazoline, phenylephrine, and pseudoephedrine.
  • Antihistamines. Antihistamines are drugs that treat allergy symptoms by blocking the effect of the inflammatory mediator histamine, thus help relieve such annoying symptoms of flu as sneezing, itching, eye tearing, and runny nose. Examples include chlorpheniramine, loratadine, cetirizine, and azelastine.
  • Analgesics. Some medications may help relieve pain and discomfort associated with influenza. These drugs include NSAIDS – such as ibuprofen and naproxen – and Acetaminophen. The last one can help both decrease pain and fever. Aspirin can be only used for adults, as it may carry a risk for children and adolescents.
• Antiviral medications: Antiviral drugs are a second line of defense to treat influenza. They work by stopping the flu virus from multiplying in the body. Antiviral won't cure flu, but they may help slightly reduce the length of the illness and relieve some of the symptoms and may reduce severe complications and deaths in the people at-risk groups. Ideally, these drugs need to be administered early (within 48 hours of onset of symptoms) in the disease. Some influenza viruses develop resistance to the antiviral medications, limiting the effectiveness of treatment. There are 2 classes of such medications:
  • Adamantanes1(amantadine and rimantadine). Whilst relatively inexpensive, these drugs are effective only against type A influenza, and may be associated with severe adverse effects, including delirium and seizures that occur mostly in elderly persons on higher doses.
  • Inhibitors of influenza neuraminidase (oseltamivir and zanamivir; as well as peramivir and laninamivir). Considered a new class of antiviral drugs, the neuraminidase inhibitors have fewer adverse side effects and the virus less often develops resistance. However, these drugs are expensive and currently not available in many countries.
• Additional care: In severe influenza, admission to hospital may be required. The patient may need breathing support and sometimes send for intensive care, particularly if the condition has developed into more devastating outcomes, or caused worsening of the existed disease, such as diabetes and chronic respiratory diseases. Although antibiotics have nothing to do with flu as they are for bacteria not for virus, antibiotic therapy may be used for some risky patients to prevent secondary infection.

Most people can get ride from influenza without repercussions, but people in high-risk groups have greater chance to develop some Complications, such as:

• Chest infections. The most common complication of influenza is a bacterial chest infection, such as bronchitis. Occasionally, this can become serious and develop into pneumonia, which can become life-threatening for these people.
• Worsening of the existing conditions. In some people with long-term health conditions, getting flu can make their condition worse. For example, people with asthma may find that their symptoms become more severe when they get the flu. Diabetic patients may potentially face hyperglycemia.
• Pregnancy complications. Flu may cause the pregnant to go into premature labour (before 37 weeks of pregnancy), or it may result in a baby with a low birth weight. Occasionally, getting flu during pregnancy can result in a miscarriage or stillbirth.
• Other infections. In less common circumstances, flu viruses can either spread to other area, or pave the way for bacteria to cause another infection. This may result in tonsillitis, otitis media, sinusitis, and meningitis.

• Flu vaccine: The most effective way to prevent influenza and/or severe outcomes from the illness is vaccination. Among healthy adults, influenza vaccine can provide reasonable protection. However, the efficacy decreases with age. Influenza viruses are constantly changing, for that the vaccine is updated each year. Influenza vaccination is most effective when circulating viruses are well-matched with vaccine viruses. The ability of influenza vaccine to prevent flu illness can range widely between seasons and persons. According to Centrals of disease control and prevention, USA, recent studies show vaccine reduces the risk of flu illness by about 50% to 60% among the overall population during seasons when most circulating flu viruses are like the vaccine viruses. Vaccination is especially important for individuals at higher risk of serious influenza complications, and for people who live with or care for these individuals. World health organization recommends annual vaccination for:
  • pregnant women at any stage of pregnancy;
  • children aged 6 months to 5 years;
  • elderly individuals (≥65 years of age);
  • individuals with chronic medical conditions;
  • health-care workers.

Flu vaccination can reduce flu illnesses, doctors’ visits, and missed work and school due to flu, as well as prevent flu-related hospitalizations. Flu vaccination also may make the illness milder if you do get sick. The vaccine is available in two main forms: injectable influenza vaccines, and nasal spray flu vaccine. The last one is not recommended to be used during 2016-2017 as an indicator that it has low efficacy.

• Preventive acts: Everyone can take the lead in protecting himself and the others from influenza by adhering to good practices that reduce the risk of influenza virus transmission. It is advised to:
  • Avoid close contact with infected people. If the person is sick, he has to keep distance from others to protect them from getting sick too;
  • Stay home from work, school, and errands if the person is sick. This will help prevent spreading your illness to others;
  • Cover mouth and nose with a tissue when coughing or sneezing. This will prevent strewing of virus in the surroundings;
  • Wash hands often, to help protect from germs. If soap and water are not available, the person can use an alcohol-based hand rub;
  • Avoid touching eyes, nose or mouth as the virus often spreads with handle these parts after touching something contaminated with germs;
  • Clean and disinfect frequently touched surfaces at home, work or school, especially when someone is ill;
  • Improve immunity through getting plenty of sleep, being physically active, managing stress, drinking plenty of fluids, and eat nutritious food.

Most people recover from influenza symptoms within a week without requiring medical attention, although full recovery may take 2 weeks. However, influenza can cause severe illness or death especially in the very young, the elderly and people suffering from medical conditions such as lung diseases, diabetes, cancer, kidney or heart problems people. Taking antiviral medications may reduce the severity of symptoms and the duration of illness. Other flu drugs and home remedies may relieve symptoms but without affecting the duration of illness.

Influenza occurs worldwide and spreads very quickly in populations, especially in crowded circumstances. In annual influenza epidemics 5-15% of the population are affected with upper respiratory tract infections. Hospitalization and deaths mainly occur in high-risk groups. Although difficult to assess, these annual epidemics are thought to result in between three and five million cases of severe illness and between 250,000 and 500,000 deaths every year around the world.

Most deaths currently associated with influenza in industrialized countries occur among people over 65 years of age. Much less is known about the impact of influenza in the developing world. However, influenza outbreaks in the tropics tend to have high attack and case-fatality rates. Seasonal epidemics of the virus occur mainly during the winter time, compared to tropical regions where it may occur throughout the year, resulting in much more irregular outbreaks.

Pandemic influenza is a global spread of a new influenza strain to which the general population is not immune. Example of the drastic effect of Pandemic influenza is the Spanish influenza that killed at least 40 million people in 1918. The pandemic repeated two times more in the 20th century, particularly in 1957 and 1968, with Asian and Hong Kong influenzas, respectively. With the speed of air travel today, public health experts believe an influenza pandemic could spread much more quickly.