short note on influenza
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Answer:
Explanation:
Influenza, commonly known as "the flu", is an infectious disease caused by an influenza virus.[1] Symptoms can be mild to severe.[5] The most common symptoms include: high fever, runny nose, sore throat, muscle and joint pain, headache, coughing, and feeling tired.[1] These symptoms typically begin two days after exposure to the virus and most last less than a week.[1] The cough, however, may last for more than two weeks.[1] In children, there may be diarrhea and vomiting, but these are not common in adults.[6] Diarrhea and vomiting occur more commonly in gastroenteritis, which is an unrelated disease and sometimes inaccurately referred to as "stomach flu" or the "24-hour flu".[6] Complications of influenza may include viral pneumonia, secondary bacterial pneumonia, sinus infections, and worsening of previous health problems such as asthma or heart failure.[2][5]
Three of the four types of influenza viruses affect humans: Type A, Type B, and Type C.[2][7] Type D has not been known to infect humans, but is believed to have the potential to do so.[7][8] Usually, the virus is spread through the air from coughs or sneezes.[1] This is believed to occur mostly over relatively short distances.[9] It can also be spread by touching surfaces contaminated by the virus and then touching the mouth or eyes.[5][9] A person may be infectious to others both before and during the time they are showing symptoms.[5] The infection may be confirmed by testing the throat, sputum, or nose for the virus.[2] A number of rapid tests are available; however, people may still have the infection even if the results are negative.[2] A type of polymerase chain reaction that detects the virus's RNA is more accurate.[2]
Frequent hand washing reduces the risk of viral spread.[3] Wearing a surgical mask is also useful.[3] Yearly vaccinations against influenza are recommended by the World Health Organization (WHO) for those at high risk,[1] and by the Centers for Disease Control and Prevention (CDC) for those six months of age and older.[10] The vaccine is usually effective against three or four types of influenza.[1] It is usually well-tolerated.[11] A vaccine made for one year may not be useful in the following year, since the virus evolves rapidly.[1] Antiviral drugs such as the neuraminidase inhibitor oseltamivir, among others, have been used to treat influenza.[1] The benefit of antiviral drugs in those who are otherwise healthy do not appear to be greater than their risks.[12] No benefit has been found in those with other health problems.[12][13]
Influenza spreads around the world in yearly outbreaks, resulting in about three to five million cases of severe illness and about 290,000 to 650,000 deaths.[4][1] About 20% of unvaccinated children and 10% of unvaccinated adults are infected each year.[14] In the northern and southern parts of the world, outbreaks occur mainly in the winter, while around the equator, outbreaks may occur at any time of the year.[11] Death occurs mostly in high risk groups—the young, the old, and those with other health problems.[1] Larger outbreaks known as pandemics are less frequent.[2] In the 20th century, three influenza pandemics occurred: Spanish influenza in 1918 (40–50 million deaths), Asian influenza in 1957 (two million deaths), and Hong Kong influenza in 1968 (one million deaths).[15] The World Health Organization declared an outbreak of a new type of influenza A/H1N1 to be a pandemic in June 2009.[16] Influenza may also affect other animals, including pigs, horses, and birds.[17]