Viruses are non-cellular obligate intracellular parasites, requiring a living host cell in order to reproduce. A developed viral particle (virion) lacks the metabolic machinery of cells, containing just a single type of nucleic acid (DNA or RNA) encased in a protein coat or capsid. Viruses can be distinguished by their structure and by the nature of their genetic material (single or double stranded DNA or RNA). Viruses that affect humans are more difficult to study because they require living animals, embryos, or cell cultures in order to replicate.
The particular host range of a virus is determined by the virus’s requirements for attaching to the host cell and the availability, within the host, of the cellular factors needed for viral multiplication. In some viruses, the capsid is covered by an envelope, which protects the virus from the host’s nuclease enzymes. Spikes on the envelope provide a binding site for attachment to the host. Influenza virus is an enveloped virus with many glycoprotein spikes. Viruses are larger than prions and many times smaller than bacteria. They range in size from 30 to 300 nm. Cause:
The causes of the flu are from three types of influenza viruses: A, B and C. Human influenza A and B viruses cause seasonal epidemics of disease almost every winter. Influenza type C infections cause a mild respiratory illness and are not thought to cause epidemics. Influenza A viruses are divided into subtypes based on two proteins on the surface of the virus, the hemagglutinin (H) and the neuraminidase (N). There are 18 different hemagglutinin subtypes and 11 different neuraminidase subtypes. Influenza A viruses can be further broken down into different strains.
Current subtypes of influenza A viruses found in people are influenza A (H1N1) and influenza A (H3N2) viruses. Influenza B viruses are not divided into subtypes, but can be further broken down into different strains. Type A flu viruses are found in many different animals, including ducks, chickens, pigs, and horses. Influenza B viruses circulate widely only among humans. How it is transmitted: The transmission of the influenza virus can be either direct or indirect: Direct contact: The virus can be spread in droplet nuclei produced by aerosolisation, e.g. when coughing or sneezing.
The viral particles are inhaled through the nose and mouth. Or when there is direct contact with an infected person’s secretion. E. g. kissing, touching, sharing food utensils. Indirect contact: Serving as a secondary reservoir of infection, viral particles can settle on surfaces. E. g. the infected person touches their respiratory tract and then something else, such as a door handle. A second person touches the door handle soon afterwards and then places their hand on their nose or mouth.
Influenza has envelope with attachment spikes or fibres. 1. Attachment, when a viral particle encounters the outer surface of a body cell, it attaches to the receptor sites of proteins on the cell’s plasma membrane. 2. Penetration, once the viral particle is attached, the host cell begins to engulf the virus by endocytosis. This is the cell’s usual response to foreign particles. Virus is enclosed in a membrane. 3. Uncoating, the nucleic acid core is uncoated and the synthesis of new viral particles begins.
After maturing, these are released to infect other cells. Digestion of the capsid releases the viral DNA, which is replicated in the host cell’s nucleaus using viral enzymes. Viral proteins are synthesised in the cytoplasm using the host’s enzymes. 1. Virus attaches to host cell and injects nucleic acid into host cell 2. Cell makes copies of virus DNA 3. Cell makes virus proteins 4. Cell produces the structures of the virus 5. New viruses are assembled 6. Cell bursts and releases new viruses Host response in reducing infection:
The immune response is initiated by the presence of the virus in the body. This produces antibodies and other immune-response cells specific for the particular strain or influenza virus that has infected the body. The immune response is responsible for destroying the viral particles that have invaded the body. Strain-specific antibody responses are induced, which exert selective pressure on circulating influenza viruses and which drive antigenic drift of seasonal influenza viruses, especially in the hemagglutinin molecule.
This antigenic drift necessitates updating of seasonal influenza vaccines regularly in order to match the circulating strains. Upon infection also virus-specific T cell responses are induced, including CD4+ T helper cells and CD8+ cytotoxic T cells. These cells are mainly directed to conserved proteins and therefore display cross-reactivity with a variety of influenza A viruses of different subtypes. T cell mediated immunity therefore may contribute to so-called heterosubtypic immunity and may afford protection against antigenically distinct, potentially pandemic influenza viruses.
Major symptoms of the disease: Flue symptoms develop one to three days after infection and include: High fever(38. 5 degrees Celsius) , chills and sweating Sore throat Weakness/fatigue Headache General muscles and joint pains (mainly legs and back) (myalgia) Dry cough that can later become more severe and develop mucous Flu symptoms will usually be at their worst after 2–3 days and will generally last for 5–8 days. However, some of the symptoms of flu such as tiredness and coughing can last for about 2–3 weeks. The flu is more severe than a bad cold because:
Cold symptoms last from two to a few days, while the flu can last up to a week The flu causes a high fever, whereas a cold sometimes causes only a mild fever Muscular pains and shivering attacks occur with the flu, but not with a cold Colds cause a runny nose, while the flu usually starts with a dry sensation in the nose and throat. Treatment: There are now specific antiviral medications available, but they need to be given early (within 48 hours of the onset of symptoms) in the illness and might only reduce the symptoms rather than prevent them.
Influenza is caused by a virus and therefore there is no treatment that will cure it. The main method of treatment is to relieve the symptoms, get plenty of bed rest and drink extra fluids. Bed rest allows the body and immune system to fight the disease and then recover. Aspirin or paracetamol can be given to help alleviate headaches, sore throat and muscle pain and to reduce fever. Antibiotics are ineffective in the treatment of viral diseases but can be used if secondary bacterial infections develop. Prevention including vaccination: The primary method of prevention of influenza involves the use of influenza vaccines.
New vaccines are produced each year and are derived from the influenza A and B viruses that circulated during the previous influenza season. As the influenza virus is constantly changing by mutation, the vaccines have to be constantly updated. Other strategies include wearing protective masks, avoiding crowded areas and ensuring you get adequate nutrition and sleep. Good hygiene practices like regularly washing hands, and sneezing or coughing into a tissue.
The flu vaccine is recommended for: anyone older than 6 months who would like to be vaccinated children aged 6 months to 5 years pregnant women (at any stage of pregnancy) and women planning a pregnancy or breastfeeding Aboriginal and Torres Strait Islander people aged 15 years and older anyone older than 6 months with a long-term medical condition including those with heart, lung or kidney disease, diabetes, or nervous system disorders that may affect breathing children older than 6 months who need long-term aspirin treatment people with Down syndrome people who are obese (i. e. a body mass index [BMI] ? 30 kg/m2) people who have a weakened immune system (e. g.due to HIV infection or medicines that suppress the immune system).
Older people who live in aged care facilities homeless people people who are 65 years and older health workers, and people who care for children or older people, or who provide essential services People travelling to countries where it is winter. Help prevent the spread of flu and other infections by: washing your hands regularly with soap and running water, particularly before preparing and eating food and after blowing your nose coughing and sneezing into a tissue then throwing it away covering your mouth when sneezing or coughing keeping your hands away from your eyes, nose and mouth avoiding sharing cups, glasses and cutlery when eating or drinking keeping your household surfaces clean.
Control: To reduce the spread of the disease through the population a number of strategies could be employed. These include: Implementing immunisation programs along with education programs to encourage at-risk individuals to be vaccinated Isolating infected individuals to reduce the spread of influenza throughout the population, this would include infected individuals remaining at home to stop the spread of the virus to their work or school colleagues.
Following quarantine procedures to prevent the spread of the disease from one country to another. Since influenza spreads through both aerosols and contact with contaminated surfaces, surface sanitizing may help prevent some infections. Alcohol is an effective sanitizer against influenza viruses, while quaternary ammonium compounds can be used with alcohol so that the sanitizing effect lasts for longer. In hospitals, quaternary ammonium compounds and bleach are used to sanitize rooms or equipment that have been occupied by patients with influenza symptoms. At home, this can be done effectively with a diluted chlorine bleach.
History: Flu pandemics have occurred throughout history. There have been four since 1918: 1918-1919 The Spanish flu, people who caught it did not die from it but often died from complications caused by bacteria, such as pneumonia. An estimate 50 million people died. 1957-1958 In February 1957, a new flu virus was identified in the Far East. To prepare, health officials closely monitored flu outbreaks. Vaccine production began in late May 1957 and was available in limited supply by August 1957. In the summer of 1957, the virus came to the United States quietly with a series of small outbreaks.
When children returned to school in the fall, they spread the disease in classrooms and brought it home to their families. Infection rates peaked among school children, young adults, and pregnant women in October 1957. By December 1957, the worst seemed to be over. However, another wave of illness came in January and February of 1958. Most influenza and pneumonia related deaths occurred between September 1957 and March 1958. Although the 1957 pandemic was not as devastating as the 1918 pandemic, about 69,800 people in the United States died. The elderly had the highest rates of death. 1968-1969.
In early 1968, a new flu virus was detected in Hong Kong. The first cases in the United States were detected as early as September 1968. Illness was not widespread in the United States until December 1968. Deaths from this virus peaked in December 1968 and January 1969. Those over the age of 65 were most likely to die. The number of deaths between September 1968 and March 1969 was 33,800, making it the mildest flu pandemic in the 20th century. The same virus returned in 1970 and 1972. 2009-2010 In the spring of 2009, a new flu virus spread quickly across the United States and the world.
The first U. S. case of H1N1 (swine flu) was diagnosed on April 15, 2009. By April 21, the Centers for Disease Control and Prevention (CDC) was working to develop a vaccine for this new virus. On April 26, the U. S. government declared H1N1 a public health emergency. By June, 18,000 cases of H1N1 had been reported in the United States. A total of 74 countries were affected by the pandemic. By November 2009, over 61 million vaccine doses were ready. Reports of flu activity began to decline in parts of the country, which gave the medical community a chance to vaccinate more people. 80 million people were vaccinated against H1N1, which minimized the impact of the illness.
The CDC estimates that 43 million to 89 million people had H1N1 between April 2009 and April 2010. They estimate between 8,870 and 18,300 H1N1 related deaths. Hippocrates made the first accurate description The first person to give a clear and an accurate description of the symptoms of influenza was Hippocrates. In his works, the Greek philosopher, Hippocrates, described various types of diseases from the medical perspective and influenza was one of them.
For his pioneering work, he is considered as the “Father of Modern Medicine”. He was born in 460 BC and died in 370 BC. Discovery of the Influenza Virus The association of the influenza virus with the disease was first discovered in 1933. Christopher Andrewes, Wilson Smith, and Patrick Laidlaw, three prominent physicians of that time made this discovery. They were researching on an appropriate host for the propagation when the discovered and identified the virus that causes influenza in human beings. The influenza disease on animals and the virus responsible for them were also discovered at about the same time.
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