Recomendados
Mais conteúdo relacionado
Mais procurados
Mais procurados (20)
Destaque
Destaque (20)
Semelhante a Influenza epidemiology
Semelhante a Influenza epidemiology (20)
Mais de Ashraf ElAdawy
Mais de Ashraf ElAdawy (20)
Último
Último (20)
Influenza epidemiology
- 4. 4 Infectious diseases in a globalized world
- 6. 6
- 7. ● RNA, enveloped ● Viral family: Orthomyxoviridae ● Size: 80-200nm or .08 – 0.12 μm (micron) in diameter ● Three types ● A, B, C ● Surface antigens ● H (haemaglutinin) ● N (neuraminidase) Influenza Virus
- 8. 8 Influenza viruses are divided scientifically into three types designated A, B, and C. Influenza A viruses are further classified into different subtypes according to combinations of various virus surface proteins or antigens : hemagglutinin (HA) & neuraminidase (NA) . There are 16 known H subtypes and 9 known N subtypes.
- 9. 9 Hemagglutinin (HA)–16 subtypes Neuraminidase (NA)–9 subtypes Influenza A Virus is subtyped by surface proteins
- 10. 10 Many different combinations of HA and NA proteins are possible, all of which have been found in wild birds, which are the natural reservoir of influenza A viruses. Among many subtypes of influenza A viruses,only influenza A(H1N1) and A(H3N2) are currently circulating among humans as seasonal Influenza strains. •
- 11. Wild birds are “natural” reservoir for all influenza A subtypes
- 12. H1 N1 H2 N2 H3 N3 H4 N4 H5 N5 H6 N6 H7 N7 H8 N8 H9 N9 H10 H11 H12 H13 H14 H15 H16 Haemagglutinin subtype Neuraminidase subtype
- 13. Avian Influenza AAvian Influenza A virusesviruses H1 - H16 N1 - N9 H1 - H3 N1 –N2 Human Influenza A Viruses Natural Reservoir for New Human Influenza A Virus Subtypes: Waterfowl (Aquatic Ducks, Geese)
- 14. All subtypes of influenza A are maintained in aquatic birds In human H1, H2, H3 N1, N2 The current subtypes of influenza A viruses found in people are A (H1N1) and A (H3N2).
- 15. 15 Influenza viruses ●Influenza A is subtyped by surface proteins . ● The subtypes of influenza A virus demonstrate species specificity and those, which infect animals do not usually cause infection in humans . ● Influenza B and C viruses are not divided into subtypes.
- 16. 16 Influenza viruses ● Influenza A Virus Wild birds are “natural” reservoir for all influenza A subtypes Epidemics and pandemics Animals and humans Can infect many animals – ducks, chickens, pigs, whales, horses and seals. Accounts for >80% of influenza infections of human each year - All ages.
- 17. 17 Influenza viruses ● Type B Milder epidemics Humans only Primarily affects children ● Type C Causes mild disease humans are natural hosts but isolates also found in pigs does not cause epidemics
- 18. Influenza Types – A and B Type A (Seasonal, avian, swine influenza,….) Type B (Seasonal influenza) Can cause significant disease Generally causes milder disease but may also cause severe disease Infects humans and other species (e.g., birds; H5N1) Limited to humans Can cause epidemics and pandemics (worldwide epidemics) Generally causes milder epidemics
- 19. 19 Seasonal influenza viruses cause annual epidemics that peak during winter in temperate regions Influenza A and influenza B are responsible for most clinical illness, can cause seasonal influenza epidemics in humans. Influenza type C usually causes either a very mild respiratory illness or no symptoms at all; it does not cause epidemics and does not have the severe public health impact of influenza types A and B.
- 20. How does influenza virus change? Type A viruses tend to undergo changes (from time to time) in their surface antigens or proteins ●Minor changes Antigenic drift ●Major changes Antigenic shift
- 21. 21 Antigenic Drift Yearly epidemics occur because of a process called antigenic drift.. Because of imperfect manufacturing, in other words genetic mutations, of progeny viruses in the “cellular factory,” small changes occur in the hemagglutinin and/or neuraminidase of circulating strains. These changes can prevent the antibodies generated by the body’s immune system, either from past infection or vaccination, from efficiently neutralizing the virus. . . In that setting, reinfection with a mutant virus can occur.
- 22. How do yearly epidemics occur? Answer: A process called antigenic DRIFT. Imperfect “manufacturing” of virus – Small changes in H and N – Partial immunity in population o Incomplete protection; still get sick o Need new flu vaccine every year H3N2 H3N2 Immune System: “Do I know you? You look vaguely familiar!”
- 23. 23 Antigenic Drift This term denotes MINOR changes in hemagglutinin and neuraminidase of influenza virus. This results from mutation in the RNA segments coding for either the HA or NA This involves no change in serotype; there is merely an alteration in amino acid sequence of HA or NA leading to change in antigenicity (point mutation(.
- 24. Children’s Healthcare of Atlanta
- 25. 25 Antigenic Drift Is a mechanism for variation in viruses that involves the accumulation of mutations within the genes that code for antibody-binding sites. This results in a new strain of virus particles which cannot be inhibited as effectively by the antibodies that were originally targeted against previous strains, making it easier for the virus to spread throughout a partially immune population. Antigenic drift occurs in both influenza A and influenza B viruses.
- 26. 26 Antigenic Drift Point mutations in the antigenic sites reduce or inhibit the binding of neutralising antibodies, thereby allowing a new strain to spread within a non-immune population. This phenomenon is called antigenic drift. The mutations that cause the antigenic drift are the molecular explanation for the seasonal influenza epidemics during winter time in temperate climatic zones.
- 27. 27 Antigenic Drift Antigenic drift is the reason that 1 or 2 of the three virus strains in the vaccine are updated every year based on what’s been circulating around the world. This necessitates the creation of a new flu vaccine every year. .
- 29. Antigenic Shift
- 30. Antigenic shift occurs only in Type A Occurs due to genetic exchange or reassortment The genetic content of influenza viruses is segmented into eight genes , this facilitates reassortment , in which genetic material is exchanged between human & avian viruses during co-infection of a human or pig (known as mixing vessel) . Antigenic shift
- 32. Reassortment (in human) Avian virus + Human virus Migratory water birds Pandemic potential
- 33. New subtype influenza REASSORTMENT : Pigs
- 35. What drives the occurrence of a pandemic? Answer: Instead of antigenic DRIFT occurring, an antigenic… …happens. Immune System: “Oh my gosh…I don’t know you at all!” H?N?
- 36. What is a Pandemic?
- 37. A new influenza virus emerges to which the general population has little/no immunity The new virus must be able to replicate in humans and cause disease The new virus must be efficiently transmitted from one human to another Prerequisites for pandemic influenza
- 38. Pandemic influenza in the 20th Century 1920 1940 1960 1980 2000 H1N1 H2N2 H3N2 1918 “Spanish Flu” 1957 “Asian Flu” 1968 “Hong Kong Flu” 20-40 million deaths 1 million deaths 1 million deaths
- 40. The influenza pandemic of 1918 killed more humans than any other disease in a period of similar duration in the history of the world. Alfred W. Crosby, historian & author America’s Forgotten Pandemic: The Influenza of 1918 The “Forgotten Pandemic”
- 42. History of pandemic influenzaHistory of pandemic influenza History of pandemic influenza
- 43. MOST FATAL EVENT IN HUMAN HISTORY WORLDWIDE FATALITIES: 20-40 MILLION US FATALITIES: 675,000 U.S. LIFE EXPECTANCY AT BIRTH 35 40 45 50 55 60 65 70 1900 1906 1912 1918 1924 1930 1936 1942 1948 1954 1960 Date Age
- 45. Emergency hospital, Camp Funston, Kansas 1918 Courtesy of National Museum of Health and Medicine
- 46. SCHOOLS FACE TOUGH PANDEMIC QUESTIONS
- 48. Antigenic Shift Novel HA or NA Reassortment of the segment genome from two different subtypes Antigenic Drift Point mutation in HA New strains of the same subtype Seasonal epidemics Requirement for a new vaccine each year PANADEMIC
- 50. 50 Seasonal influenza is characterized by a sudden onset of high fever, cough (usually dry), headache, muscle and joint pain, severe malaise (feeling unwell), sore throat and runny nose. Most people recover from fever and other symptoms within a week without requiring medical attention. But influenza can cause severe illness or death especially in people at high risk . The clinical burden of Seasonal influenza
- 51. 51 Seasonal influenza epidemics can cause febrile illnesses that range in severity from mild to debilitating and can lead in some instances to hospitalization and even cause death, mainly among high-risk groups. Seasonal influenza is a serious public health problem, it has been estimated that in developed countries, annual influenza epidemics infect about 10–20% of the population each season. Is Flu Serious ?
- 52. 52 Worldwide, annual influenza epidemics are estimated to result in ~1 billion cases of flu, ~3–5 million cases of severe illness and 300 000–500 000 deaths annually. Yearly influenza epidemics can seriously affect all populations, but the highest risk of complications occur among children younger than age 2 years, adults aged 65 years or older, pregnant women, and people of any age with certain chronic medical conditions , or weakened immune systems . Is Flu Serious ?
- 53. 53 When animal influenza viruses infect their natural animal host, they are named for that host , as in avian influenza viruses , swine influenza viruses , equine influenza viruses, etc. As such, the term “swine flu” refers to swine influenza viruses infecting swine, and is never used when such viruses infect people. Zoonotic Influenza ?
- 55. 55 Avian influenza (AI), commonly called bird flu, is an infectious viral disease of birds. Most avian influenza viruses do not infect humans; however some, such as A (H5N1) and A (H7N9) , Highly pathogenic avian influenza viruses , cross the species barrier have caused serious infections in people.
- 56. 56 Avian influenza viruses are divided into 2 groups based on their ability to cause disease in poultry 1)Highly pathogenic viruses result in high death rates (up to 100% mortality within 48 hours) in some poultry species. 2)Low pathogenicity viruses also cause outbreaks in poultry but are not generally associated with severe disease.
- 57. 57 Human infections with avian and zoonotic influenza viruses have been reported. Human infections are primarily acquired through direct contact with infected animals or contaminated environments, but do not result in efficient transmission of these viruses between people.
- 58. 58 Avian and other zoonotic influenza infections in humans may cause disease ranging from mild conjunctivitis to severe pneumonia and even death. The majority of human cases of A(H5N1) and A(H7N9) infection have been associated with direct or indirect contact with infected live or dead poultry. Controlling the disease in the animal source is critical to decrease risk to humans .
- 59. A new influenza virus emerges to which the general population has little/no immunity The new virus must be able to replicate in humans and cause disease The new virus must be efficiently transmitted from one human to another The A(H5N1) and A(H7N9) AI viruses remain two of the avian influenza viruses with pandemic potential NOT TO DATE
- 60. 60
Notas do Editor
- The internal antigens (M1 and NP proteins) are the type-specific proteins (type-specific antigens) used to determine if a particular virus is A, B or C. The M1 proteins of all members of each type show cross reactivity. The NP proteins of all members of each type also show cross reactivity. The external antigens (HA and NA) show more variation and are the subtype and strain-specific antigens. These are used to determine the particular strain of influenza A responsible for an outbreak Flu strains are named after their types of hemagglutinin and neuraminidase surface proteins, so they will be called, for example, H3N2 for type-3 hemagglutinin and type-2 neuraminidase. If two different strains of influenza infect the same cell simultaneously, their protein capsids and lipid envelopes are removed, exposing their RNA, which is then transcribed to mRNA. The host cell then forms new viruses that combine antigens; for example, H3N2 and H5N1 can form H5N2 this way. Because the human immune system has difficulty recognizing the new influenza strain, it may be highly dangerous.
- Influenza A viruses are found in many different animals, including ducks, chickens, pigs, whales, horses, and seals. There are 16 different haemaglutinin subtypes and 9 different neuraminidase subtypes, all of which have been found among influenza A viruses in wild birds. Wild birds are the primary natural reservoir for all subtypes of influenza A viruses and are thought to be the source of influenza A viruses in all other animals. Most influenza viruses cause asymptomatic or mild infection in birds; however, the range of symptoms in birds varies greatly depending on the strain of virus. Infection with certain avian influenza A viruses (for example, some strains of H5 and H7 viruses) can cause widespread disease and death among some species of wild and especially domestic birds such as chickens and turkeys. Pigs can be infected with both human and avian influenza viruses in addition to swine influenza viruses. Infected pigs get symptoms similar to humans, such as cough, fever, and runny nose. Because pigs are susceptible to avian, human and swine influenza viruses, they potentially may be infected with influenza viruses from different species (e.g., ducks and humans) at the same time. If this happens, it is possible for the genes of these viruses to mix and create a new virus.
- While there are three types of influenza viruses—A, B, and C—only two cause significant disease in humans (A and B). Type B influenza viruses are limited to humans, whereas Type A viruses can cause severe disease in humans and affect more species. Influenza Type A Type A influenza is considered to cause the most serious disease among the influenza viruses, although not all strains cause clinical disease. Influenza A can cause severe epidemics (as well as severe worldwide epidemics; or pandemics) among all ages. Influenza type A infects multiple species including people, birds, pigs, horses, and other animals. Wild birds are the natural hosts for these viruses. Influenza Type B Influenza B viruses are usually found only in humans. Influenza B viruses can cause some morbidity and mortality among humans, but in general are associated with less severe epidemics (chiefly among children) than influenza A viruses. Although influenza type B viruses can cause human epidemics, they have not caused pandemics. Because avian influenza and all pandemic viruses are of the Type A variety, we will focus this session on Type A influenza viruses.
- Yearly epidemics occur because of a process called antigenic drift. The viral H and N components are sometimes called antigens by scientists. Because of imperfect manufacturing, in other words genetic mutations, of progeny viruses in the “cellular factory,” small changes occur in the hemagglutinin and/or neuraminidase of circulating strains. These changes can prevent the antibodies generated by the body’s immune system, either from past infection or vaccination, from efficiently neutralizing the virus. In that setting, reinfection with a mutant virus can occur. Antigenic drift is the reason that 1 or 2 of the three virus strains in the vaccine are updated every year based on what’s been circulating around the world. This necessitates the creation of a new flu vaccine every year.
- a pandemic is an epidemic occurring worldwide or over a very wide area, crossing international boundaries and usually affecting large numbers of people. The new virus affects only birds and animals at first, but gradually changes to affect people as well. A pandemic begins when this new virus is passed easily from person to person.
- 2 of the 3 prerequisites for a human pandemic have been met A novel influenza virus has emerged and the general population has demonstrated little or no immunity And the new virus has been able to replicate in humans The main questions that remains are: Will the virus will develop into a form that is efficiently transmitted from one human to another? (thus meeting the criteria for a pandemic) If so, where, when, how quickly, and how severely?
- Earlier, you saw computer modeling of a future pandemic, this shows what happened in 1918.
- 2 of the 3 prerequisites for a human pandemic have been met A novel influenza virus has emerged and the general population has demonstrated little or no immunity And the new virus has been able to replicate in humans The main questions that remains are: Will the virus will develop into a form that is efficiently transmitted from one human to another? (thus meeting the criteria for a pandemic) If so, where, when, how quickly, and how severely?