Influenza is a highly contagious disease which causes annually millions of infections around the world. From time to time, the influenza virus can mutate, responsible for major epidemics of flu, with the Spanish flu of 1918 or the recent swine flu 2009.
In this article we will talk about influenza in general, emphasizing called seasonal flu, also known as flu. We'll talk about the modes of transmission, symptoms, possible complications and the treatments available.
As stated in the introduction, the flu is a contagious disease of viral origin, caused by Influenza virus A, influenza B and influenza C. Its most common symptoms include fever, cough and body aches.
The type of greater clinical relevance is the Influenza A, because it is not only responsible for most symptomatic cases in humans, it is also the origin of major epidemics of the last century. Influenza C virus is causing less illness, and when it does, it is usually a flu with mild symptoms.
The influenza virus is what has more subtypes, can infect birds, humans and other mammals. In general, every time a strain of Influenza A mutates, it becomes more prone to cause epidemics because the population has no immunity against the new mutant strain. As the Influenza A is highly prone to mutations, almost every year there is a new strain circulating among the population. Therefore, every winter there is an increase in the number of cases of influenza. Who had flu 1 or 2 years, you can easily get a new infection since the influenza A circulating at that time may no longer be the same circulating today. Influenza B can also mutate, but he does so in a less intense pace.
From time to time, these changes generate an influenza more virulent, capable of infecting a large number of people. The 2009 swine flu pandemic occurred after a strain of the Influenza A (H1N1), natural pigs, mutate and become capable of infecting humans. Since this H1N1 strain existed only in pigs, when she made the jump to humans picked up the immune system of most people off guard. The 1918 Spanish flu, which killed over 60 million people worldwide was also caused by a mutant strain of Influenza A (H1N1), this even more aggressive than the H1N1 swine flu.
Other famous outbreaks of flu in the last century were:
1957: Influenza A (H2N2) - Asian Flu.
1968: Influenza A (H3N2) - Influenza in Hong Kong.
1977: Influenza A (H1N1) - Russian flu.
2004: Influenza A (H5N1) - Avian flu (also called Asian influenza).
2013: Influenza A (H7N9) - Avian influenza.
Currently seasonal flu have been caused by less virulent strains of Influenza A (H2N2), (H1N2) and (H3N2). Influenza A (H1N1) 2009 is still circulating among the population, but currently much people have immunity against it, either by prior infection or by vaccination against influenza. This H1N1 strain is no longer capable of causing an epidemic, currently being considered one of the various strains of seasonal flu.
It is important to note that, contrary to what many people think, the flu and the common cold are different infections. While influenza is caused only by influenza viruses and their subtypes, the cold is a respiratory infection that can be caused by many different viruses, such as rhinovirus, adenovirus, parainfluenza virus, coronavirus, respiratory syncytial virus and several others.
Large quantities of influenza virus are present in the respiratory secretions of those infected, causing sneezing and coughing are the major route of transmission. The influenza virus is usually present in large droplets of respiratory secretions. This means that after a cough or sneeze, the virus falls to the floor along with droplets heavier, not being suspended in the air. Therefore, the risk of transmission is higher for people who are close to the patient, less than 2 meters away. If during the sneeze you are more than 2 meters away, is low risk of heavier droplets manage to achieve it.
Another common form of transmission is through the hands. When the patient with flu sneezes or coughs toward the hands, they are full of viruses, favoring infecting other people. Clear nasal secretions with hands also has the same effect. If you greet this person who has hands infected, will have the influenza virus on their hands. Just then you scratch your eyes or touch your hand in the mouth to the virus infect you.
Objects handled by people with flu may also contain the virus, which is another possible source of contagion. In general, the Influenza virus survives 2 to 8 hours on inanimate objects, depending on weather conditions. Wash hands and objects contaminated with soap and water (or alcohol) are sufficient to prevent the transmission of influenza.
The influenza incubation period is 1 to 4 days (on average 2). The infection period begins on the day before onset of symptoms and lasts for about 5 to 10 days. In general, the patient fails to eliminate the virus by the respiratory secretions 1 to 2 days after the end of the symptoms, but small children infectivity this period may extend for several days.
One of the main characteristics of influenza, as opposed to cold, is how the symptoms begin. In the cold, the picture begins so bland and will progressively worsen within 48 to 72 hours. In flu symptoms appear sudden way and before the end of the day the patient is already clearly sick, down in bed. In some cases, the onset of symptoms is so abrupt that the patient can even say what time it was and what he was doing at the time when the flu appeared.
The severity of symptoms depends on the degree virulence of influenza strain and the ability of our immune system to deal with the virus. The flu can cause mild symptoms from almost unnoticeable to severe clinical symptoms, including pulmonary infection and risk of death. But the vast majority of cases, even in those who develop significant flu symptoms, the picture usually has a benign course with spontaneous resolution within 1 week.
In general, when the patient infected develop symptoms, the most common are:
Gastrointestinal symptoms such as vomiting and diarrhea may occur, particularly in children, but they are not common in adult influenza. Exceptionally, some strains can cause these symptoms in adults, as occurred in Influenza A epidemic (H1N1) 2009, when the frequency of gastrointestinal symptoms was higher than usual cases of flu.
As mentioned above, the flu is usually a benign disease in the vast majority of cases. However, it can lead to complications in some patients, especially in the elderly, infants and immunocompromised people.
Among the simplest complications, otitis media and sinusitis are the most common. In relation to more serious complications, pneumonia is the main. The infection of the lung may be caused directly by the Influenza virus or may have bacterial origin, which is facilitated by the patient's fact be weakened by the flu. Also in relation to the lung, acute bronchitis and asthma frames may also occur. These pulmonary complications are more frequent in elderly patients with earlier respiratory diseases such as COPD, bronchiectasis, or asthma.
Another relatively common complication of influenza is rhabdomyolysis, muscle injury caused directly by the virus.
Central nervous system injuries may also occur during an influenza framework, and viral encephalitis, the transverse myelitis, viral meningitis and Guillain-Barré syndrome the most common.
Heart part, heart attacks, pericarditis, myocarditis and worsening heart failure are common. As with pulmonary complications, cardiac complications are more common in elderly patients and patients with heart diseases previously.
In general, young and previously healthy patients take letter an influenza frame. Even when the symptoms are strong and leave the bed patient after 4 to 5 days it is fully recovered without sequelae or complication.
The same facility to deal with the influenza does not occur in people at extremes of age (babies and older) patients, or patients previously, mainly lung or heart diseases.
We consider risk group for complications of pneumonia people with the following characteristics:
Children younger than 5 years.
Adults over 65 years.
Pregnant.
Individuals with lung diseases, including asthma, bronchitis or emphysema.
Individuals with cardiovascular disease, especially failure or cardiac valvular disease.
Immunosuppressed, including AIDS patients and transplant organs
Malnourished.
Obese, especially those with a BMI greater than 35.
It is because of the complications that occur in this group of patients that flu epidemics often cause a lot of deaths. Despite the overall mortality of influenza is low, usually below 1% when the disease strikes millions of people short time, 1% of deaths mean thousands of deaths. In the Spanish flu of the early twentieth century, when modern medicine, with antibiotics and intensive care units, did not exist, the number of deaths from the flu reached 60 million.
The flu, so it is a disease that usually has benign, but not all innocuous. Patients with influenza who begin to exhibit the following signs and symptoms should be evaluated promptly by a physician, especially if they are part of the risk group:
In most cases you do not need any treatment to cure the flu. Rest, good hydration and patience usually sufficient. The usual trend of influenza is spontaneously improve after about 4 to 7 days.
Cold medicines, called common cold medicine, help alleviate the symptoms but do not act directly on influenza. Their use is optional and serve primarily to control fever, runny nose and body aches. Vitamin C has no proven effect against influenza.
In patients belonging to a risk group, the use of antivirals such as oseltamivir (Tamiflu) and zanamivir (Relenza), may be mentioned, as they decrease the chance of complications and reduce the duration of disease. But to be effective, antiviral drugs should be started within 48 hours of symptoms.
Months before the arrival of winter, a period with higher rate of cases of flu, the health ministries of several countries offer the flu vaccine, containing the influenza strains that most circulating in the environment. The vaccine is updated every year, so that more viruses causing flu in the previous year are covered. Since 2010, the H1N1 strain causing the swine flu call is part of the vaccine.
In Brazil, the vaccination campaign usually begin in April and its target audience is individuals with increased risk of complications, including people 60 and older, pregnant women, women in period of up to 45 days after birth, children between six months and five years of age, health professionals or anyone with chronic disease that falls within the risk group for complications from influenza.
The flu vaccine is made from killed or inactivated virus, so there is no risk of the patient developing flu after administration of the same. It is important to note that the vaccine does not protect against the viruses that cause colds, it is specific against certain strains of influenza.
The appearance of antibodies against influenza occurs between 2 to 3 weeks after vaccination, and has usually lasts 6 to 12 months, long enough to traverse the peak period of influenza.
As the flu vaccine does not confer permanent immunity and the virus Influenza has changes quite often, individuals risk group should be revaccinated annually.
