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Influenza virus
- 1. INFLUENZA VIRUS PRESENTED BY SORAVSOROUT SAIYED SHOHZAB MOHAMMAD NOUR
- 2. INTRODUCTION • Influenza, commonlyreferred to as the flu, is an infectious viral disease caused by RNA viruses of the family ortho-myxoviridae (the influenza viruses),that affects birds and mammals. • Common symptoms are chills, fever, sore throat, muscle pains, severe headache, coughing, fatigue and general discomfort. • Although confused with other influenza-like illnesses,
- 3. DEFINITION •WHO : Influenzais a viral infection that affects mainly the nose, throat, bronchi and, occasionally, lungs. 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.
- 4. HISTORY • Influenza canbe traced as far back as 400 BC • In Hippocrates’ Of the Epidemics, he describes a cough outbreak that occurred in 412 BC in modern-day Turkey at the turn of the autumn season • 17th century:- • Between 1781-1782, an influenza epidemic infected 2/3 of Rome’s population and ¾ of Britain’s population. Later, disease spread to North America, West Indies, and South America. Spread of pandemic culminated in New England, New York, and Nova Scotia in 1789. • 1781 marked the beginning of the of influenza epidemics and
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- 6. AGENT • Influenza virusesare classified within the family of Ortho-myxoviridae. • There are three viral sub–types, namely influenza type A, type B and type C. • These three viruses are antigenically distinct. There is no cross–immunity between them. • Of importance are the influenza A and B viruses which are responsible for epidemics of disease throughout the world.
- 7. I. Both influenzaA and B viruses have two Hemoglutinin (H) and 9 distinct surface antigens – the Neuraminidase (N) antigens. II. The H antigen initiates infection following attachment of the virus to susceptible cells. The N antigen is responsible for the release of the virus from the infected cell.
- 8. I. The influenzaA virus is unique among the viruses because it is frequently subject virus to antigenic variation, both major and minor. I. When there is a sudden, complete or major change, it is called a shift, and when the antigenic change is gradual, over a period of time, it is called a drift..
- 9. •Antigenic shift appearsto result from genetic recombination of human with animal or avian virus, providing a major antigenic change. •This can cause a major epidemic or pandemic involving most or all age groups.
- 10. •Since the isolationof the virus A in 1933, major antigenic changes have occurred twice – once in 1957 (H2N2) and then again in 1968 (H3N2). • •Strains occurring between 1946 and 1957 have been called H1N1 strains. The shift in 1968 involved only the H antigen. • In 1977, a new antigenic type appeared in China and the USSR and the virus was identified as A (H1N1). Within a year, it had been isolated in countries all over the world.
- 11. • Curiously, thiswas an earlier virus which has appeared after a lapse of over 20 years. • In the past, the emergence of a new, influenza A sub–type led to the prompt disappearance of the previously prevalent sub–type. In the 1977 episode, however, this did not happen.
- 12. The prevailing A(H3N2) was not displaced. Dual infection with both viruses were reported. As of now, three types of influenza viruses – A (H1N1),A (H3N2) and B exist. Influenza viruses of the H1N1 sub–type have caused epidemics of the disease in two periods of this century – from about 1946 up until 1957, and from 1977 until the present
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- 15. RESERVOIR OF INFECTION •It has become increasingly evident that a major reservoir of influenza virus exists in animals and birds. • Many influenza viruses have been isolated from a wide variety of animals and birds (e.g. swine, horses, dogs, cats, domestic poultry, wild birds, etc.)
- 16. •Some of theseinclude the major H and N antigens related to human strains. •There is increasing evidence that the animal reservoir provides new strains of the influenza virus by recombination between the influenza viruses of man, animals and birds
- 17. SOURCE OF INFECTION •Thesource of infection usually is a case or sub– clinical case. • During epidemics, a large number of mild and asymptomatic infections occur, which play an important role in the spread of infection. • The secretions of the respiratory tract are infective.
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- 19. AGE AND SEX •Influenza affects all ages and people of both sexes. In general, the attack rate is lower among adults. Children constitute an important link in the transmission chain. • The highest mortality rate during an epidemic occurs among certain high–risk groups in the population such as old people (generally over 65 years of age), infants under 18 months, and persons with diabetes or chronic heart disease, kidney and respiratory ailments.
- 20. IMMUNITY • Antibodies appearin about seven days after an attack and reach a maximum level in about two weeks. After about 8 to 12 months, antibody levels drop to pre–infection levels. • The antibody to H neutralizes the virus while the antibody to N modifies the infection
- 21. CONTD .. • tractafter infection Secondary antibodies develop in the respiratory and consist predominantly of lgG. • Antibodies must be present in sufficient concentrations at the superficial cells (the site of virus invasion) of the respiratory tract.
- 22. ENVIRONMENTAL FACTORS OFINFLUENZA • Season The seasonal incidence is striking, epidemics usually occur in the winter months in the northern hemisphere. In India, however, epidemics have often occurred in summer • Overcrowding Overcrowding enhances transmission of the infection. The attack rates are high in closed population groups e.g. schools, institutions, ships, etc
- 23. INCUBATION PERIOD FORINFLUENZA • The incubation period is about 18 to 72 hours.
- 24. PATHOGENESIS • The virusenters the respiratory tract and causes inflammation and necrosis of the superficial epithelium of the tracheal and bronchial mucosa, followed by secondary bacterial invasion. • There is no viraemia.
- 25. SIGNS AND SYMPTOMS •Symptoms begin 1-4 days after infection. The following symptoms of the flu can vary depending on the type of virus, a person’s age and overall health: • Sudden onset of chills and fever (101 – 103 F) • Sore throat, dry cough • Fatigue, malaise • Terrible muscle aches, headaches • Diarrhea • Dizziness
- 26. COMPLICATIONS IN CHILDREN •Studies show a link between the development of Reye’s syndrome and the use of aspirin for relieving fevers caused by the influenza virus. • The disease involves the CNS and the liver and children exhibit symptoms of drowsiness, persistent vomiting and change in personality
- 28. RAPID INFLUENZA TESTS •These tests are 70% accurate for determining if the patient has been infected with the influenza virus and 90% accurate for determining the type of influenza pathogen. • Examples of rapid influenza tests: Directigen Flu A, Directigen Flu A + B, Flu OIA, Quick Vue, and Zstat flu. • Rapid influenza tests provide results in 24 hours and can be performed in the physician’s office.
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- 30. • The onlyproven method for preventing influenza is a yearly vaccination approximately 2 weeks before the “flu season” begins. • Since the influenza virus is subject to genetic mutations with the HA and NA proteins, new vaccines that consist of different influenza strains need to be developed each year. • Vaccine is trivalent, meaning that it provides resistance to three strains of influenza viruses. The vaccine consists of 2 influenza A virus pathogens and 1 influenza B pathogen.
- 31. KILLED VACCINES • Mostinfluenza vaccination programs make use of inactivated vaccines. • Subcutaneous route. A single inoculation (0.5ml) is usually given. However, in persons with no previous immunological experience two doses of the vaccine, separated by an interval of three to four weeks are considered necessary to induce satisfactory antibody levels
- 32. LIVE ATTENUATED VACCINES •Live attenuated vaccines based on temperature–sensitive (ts) mutants have been extensively used in the USSR. They may be administered as “Nose drops” into the respiratory tract. • They stimulate local as well as systemic immunity. The frequent antigenic mutations of the influenza virus present difficulties in the production of effective vaccines, particularly live vaccines.
- 33. •NEWER VACCINES Split–virus VaccineIt is also known as the sub–virion vaccine. It is a highly purified vaccine, producing fewer side effects than the “Whole virus” vaccine. Due to its lower antigenicity, it requires several injections instead of a single one. It is recommended for children
- 34. NEURAMINIDASE–SPECIFIC VACCINE • NEURAMINIDASE–SPECIFICVACCINE It is a sub–unit vaccine containing only the N antigen, which induces antibodies only to the neuraminidase antigen of the prevailing influenza virus. The antibody to neuraminidase reduces both the amount of virus replicating in the respiratory tract and the ability to transmit virus to contacts.
- 35. RECOMBINANT VACCINE • RECOMBINANTVACCINE By recombinant techniques, the desirable antigenic properties of a virulent strain can be transferred to another strain known to be of low virulence. Efforts to improve the influenza vaccine have been continuing.
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