Past lives of influenza.

Influenza is a highly contagious seasonal influenza caused by influenza virus, which may have existed for thousands of years. Humans once thought that the epidemic was influenced by planets and stars, and later thought it was related to bacterial infection. It was not until 1933 that Willson Smith and Christopher Andrews isolated the influenza virus from patients and proved it with ferrets’ experiments that it was confirmed that it was a disease caused by virus infection.

Influenza virus can cause infections and diseases in humans, birds, pigs, horses, cows, bats and other animals. During the 19th and 20th centuries, influenza was a super killer of human beings. During 1889-1893, the so-called "Russian flu" killed about 1 million people all over Europe. In 1918, the most terrible Spanish flu in history killed about 50 million people, accounting for nearly 3% of the world population at that time. At that time, in the face of the virus, human beings were almost helpless and waiting for death. Until modern times, human means to deal with the flu are still limited. According to the data of the World Health Organization (WHO), the epidemic of influenza causes 3-5 million cases of serious diseases worldwide every year, and causes about 290,000-650,000 deaths. In the 20th century, there were more than three influenza pandemics in the world, namely, the Asian influenza caused by influenza A virus (H2N2) in 1957, the Hong Kong influenza caused by influenza A virus (H3N2) in 1968 and the Russian influenza caused by influenza A virus (H1N1) in 1977.

Influenza virus belongs to orthomyxoviridae, which is cold-resistant and dry-resistant. It is often active from November to April of the following year, with the peak in January and February every year. There are four types of influenza viruses: A, B, C and D. Type D mainly infects animals, but no infected people have been found. Type C is relatively rare, which can cause mild respiratory diseases, and children are mostly infected. It is generally not considered to cause epidemics. The main causes of human seasonal influenza epidemic are A and B, especially A is considered to be the main cause of worldwide influenza pandemic. Influenza A virus is further classified into subtypes according to the types of two antigens (hemagglutinin H and neuraminidase N) on the virus surface. For example, H1N1 refers to influenza A virus with hemagglutinin subtype 1 and neuraminidase subtype 1. There are 18 subtypes of hemagglutinin H and 11 subtypes of neuraminidase N, and the two antigens are arranged and combined in different ways to form different strains, among which H1N1, H2N2 and H3N2 mainly infect humans. In addition, there are also zoonotic virus strains that cause epidemics, such as human infection with highly pathogenic avian influenza and human infection with swine flu. Recently, the activity level of influenza virus in China has been significantly enhanced, with influenza A (H1N1) as the main epidemic strain and H3N2 subtype co-prevalent.

The flu is different from what people usually call a cold. The common cold is a common acute viral infectious disease of upper respiratory tract. There are many kinds of viruses that can cause common cold, such as rhinovirus, parainfluenza virus, respiratory syncytial virus, echovirus, Coxsackie virus, coronavirus and adenovirus. The common cold is generally characterized by nasal congestion, sneezing, runny nose, fever, cough, headache, etc. Generally, it has no systemic symptoms or mild symptoms, and it is self-limited. Generally, it can heal itself in about 1 week to 10 days.

The symptoms caused by influenza virus infection are similar to the common cold, such as cough, runny nose, headache, fever, etc. Some patients also have digestive tract symptoms such as vomiting and diarrhea. But generally speaking, the symptoms are generally more serious than the common cold, and it is more prone to high fever above 38 degrees Celsius, and the systemic symptoms such as headache, muscle pain and joint pain are more obvious. Influenza virus will specifically attack respiratory epithelial cells. People with weak constitution may be infected deeply into the lungs, leading to pneumonia, or invade other tissues, causing myocarditis, kidney injury, encephalitis and so on. The most common complication is secondary bacterial pneumonia, and serious complications include adult respiratory distress syndrome, toxic shock, cardiac and renal failure, etc., thus endangering life safety. The course of the flu is generally longer than the common cold, and it usually takes 2-3 weeks to recover, and even some symptoms will last for several months.

It is almost impossible to eradicate the influenza virus from the world. It has an incredible ability to mutate, which makes it a constantly developing virus. The genetic material of influenza virus is very unstable, and it undergoes some mutations rapidly every year, which will slightly change the characteristics of its H and N antigens, which we call mutation. Because of this characteristic, if people were infected with influenza virus or vaccinated with influenza vaccine in the last year, they gained immunity against a certain influenza subtype. In the second year, because of the change of epidemic strains, most people’s immune systems could not effectively recognize and generate correct immune responses again, resulting in infection. Since 2004 alone, more than 5,000 different influenza strains have been sequenced. Scientists also need to make unremitting efforts to predict the possible epidemic strains in advance when the next winter comes according to the data of influenza in the current year and last season, and adjust the global vaccine strategy in time.

Influenza is generally spread mainly by droplets such as sneezing and coughing, and can also cause direct or indirect contact infection through oral cavity, nasal cavity, eyes and other mucous membranes. In order to effectively prevent infection, influenza vaccination before the arrival of the epidemic season (usually around October each year) is still the most effective means to prevent influenza, which can significantly reduce the risk of influenza and serious complications. This year, due to factors such as prevention and control strategies and changes in people’s personal protective behavior habits, the influenza epidemic season has been postponed compared with previous years. Considering that effective antibodies can be produced about 2 weeks after vaccination, it is still not too late to vaccinate against influenza. Priority vaccination is recommended for key groups such as the elderly over 60 years old, children from 6 months to 5 years old, pregnant women, family members and caregivers of children under 6 months old, patients with chronic diseases and medical staff. In the flu season, it is necessary to have regular ventilation in the house; Maintain good personal hygiene habits, wash your hands frequently, and be careful not to touch your face, eyes, nose and mouth with your hands; Wear masks when going to crowded places or some high-risk places such as hospitals; Keep a certain distance and pay attention to cough etiquette when talking with people. If you find yourself infected, you should take the initiative to reduce contact with others and take the initiative to isolate yourself when possible.

The treatment of influenza is mainly to improve symptoms, and antibiotics are ineffective against influenza virus. Over-the-counter cold medicines available in pharmacies generally have the functions of reducing fever, relieving pain, relieving cough, reducing respiratory tract or nasal secretions, etc., and are not aimed at the virus itself. In recent years, neuraminidase inhibitors have good antiviral effect, and their main mechanism is to inhibit the release of virus from infected cells, thus reducing the spread of virus. These drugs have clear requirements on the timing of use, such as oseltamivir and zanamivir, which are required to be taken within 48 hours after onset. If the window period is exceeded, the effect will be greatly reduced. If the patient or family members have low immunity, they should take it as soon as possible on the premise of excluding contraindications. In the final analysis, the fight against influenza depends more on the body’s own immune system. Therefore, whether for prevention or treatment purposes, it is necessary to ensure adequate rest and sleep, and to ensure adequate calories, protein and vitamins in the diet. A large dose of vitamin C is considered to have an auxiliary effect on anti-virus, and its immunomodulatory effect is multi-channel, especially in the initial stage of the disease (within 12 hours). Of course, if you have the flu, you should never take it lightly. When the symptoms persist, worsen or recur, you should seek medical advice in time and seek professional help.