World health organization 2011 all rights reserved. Influenza virus is an example of a genetically labile virus. Antigenic drift occurs in both influenza a and influenza b viruses. The disease is caused by three types of rna viruses called influenza types a, b and c, each consisting of eight negative singlestranded rnasegments encoding 11 proteins. Shift can result in a new influenza a subtype in humans.
Pneumonia is diagnosed by the presence of fluid dark shadows in an xray image in the alveoli. Influenza virus antigenic variation, host antibody production. Influenza viruses can change through antigenic drift, which is a process in which mutations to the virus genome produce changes in the viral h or n. The mechanisms that the virus uses to change its antigenic sites are called drift and shift. Review on influenza virus and its prevention and control. Differences between antigenic shift and antigenic drift. Watch and learn the story of antigenic drift and shift, and why they make preventing influenza a outbreaks so difficult. Current annual vaccines contain two type a strains and one type b strain and are capable of inducing strong antibody responses. The two surface antigens of influenza undergo antigenic variation independent of each other. The other type of change is a sudden change in the hemagglutinin and or the neuraminidase proteins.
The influenza virus genes are made of rna and are more prone to mutations than genes made of dna. The other type of change is called antigenic shift. Antigenic shift, which is seen only with influenza a viruses, results from. Rishi is a pediatric infectious disease physician and works at khan academy. A gradual minor point mutation in the genes responsible for encoding ha and na proteins on the surface of the influenza virus, called antigenic drift, may occur. However, as surveillance activities on swiav have increased, more isolates have been characterized, revealing a high level of genetic and antigenic differences even within the same swiav lineage. Antigenic drift of the pandemic 2009 ah1n1 influenza. See figure i for influenza virus replication immune evasion and the concepts of antigenic drift and shift. Drift mutations most commonly occur in the gene encoding the ha surface glycoprotein, which is the major target of neutralizing antibodies elicited as a result of vaccination and or natural infection. Since antibodies against ha and neuraminidase na contribute independently to protection against disease, antigenic changes in na may allow ah1n1pdm09 viruses to escape from. Oct 29, 2009 the findings in mice, using a strain of seasonal influenza virus first isolated in 1934, also suggest that antigenic drift might be slowed by increasing the number of children vaccinated against. Mar, 2009 influenza is an infectious disease and can lead to lifethreatening complications like pneumonia. On occasion, antigenic shift occurs when an influenza a virus with an ha or an hana combination that has not recently infected humans is transmitted and causes disease see figure 171.
Clinically it presents as fatigue, rhinorrhea runny nose, myalgia muscle. The findings in mice, using a strain of seasonal influenza virus first isolated in 1934, also suggest that antigenic drift might be slowed by increasing the number of children vaccinated against. How the flu virus can change influenza viruses can change in two different waysantigenic drift and antigenic shift. To date, the 2009 pandemic virus ah1n1pdm09 has not undergone significant antigenic drift, with the result that the vaccine remains wellmatched and should provide good protection to ah1n1pdm09 circulating viruses. Jun 23, 2018 influenza virus are remarkable because of the frequent antigenic change that occurs in ha hemagglutinin or na neuraminidase. The other type of change is a sudden change in the hemagglutinin andor the neuraminidase proteins.
The pandemics of 1908, 1957, 1968, and 2009 were caused by new viruses emerging as a result of antigenic shift. Scientists propose new explanation for flu virus antigenic. Drift and shift influenza viruses can change in two different ways. Antigenic variants of mem171 h3n2 were selected after a single passage of the virus in chick embryos in the presence of monoclonal antibody. Antigenic drift may also allow a virus to cross the species barrier to a new host. These are small changes in the virus that happen continually over time. The resulting change in viral protein structure results in high levels of susceptibility among populations. It can change its antigenic character abruptly and extensively antigenic shift, at 1020 year intervals, and also gradually from year to year antigenic drift. But this number is substantially larger in the case of pandemics, with the most dramatic instance being the 1918 spanish flu that killed more than.
Antigenic shifts can lead to serious diseases, and this quizworksheet combo will help you test your understanding of what an antigenic shift is and how an antigenic shift can lead to a dangerous. If the novel influenza a virus causes disease and is efficiently transmitted among. One way shift can happen is when an influenza virus from an animal population gains the ability to infect humans. This means that individuals who have previously been infected can become re. One of these pandemics occurred in 2009, when an outbreak of a swine. Periodically, the viruses undergo major evolutionary change by acquiring a new genome segment from another influenza virus antigenic shift, effectively becoming a new subtype. One is a sequence of mutations that occur over time and causes a slow development of the virus. This accounts for annual flu seasons and periodic pandemics. Host protective immune responses against influenza a virus. When antigenic shift does occur, a large proportion, or even all, of the worlds population has no antibody against the new virus.
Mutations in the genes coding for the proteins na and ha result in minor changes to surface proteins. The significance of antigenic shift rapid change in circulating flu viruses is known as antigenic shift. Oct 15, 2019 the other type of change is called antigenic shift. The hallmark of influenzaviruses is antigenic variation, which comes in two forms. Based on historical patterns, influenza pandemics can be expected to occur, on average, 3 to 4 times each century.
Made for the science ambassador scholarship category. Antigenic shift is an abrupt, major change in an influenza a virus, resulting in new ha andor new ha and na proteins in influenza viruses that infect humans. Antigenic shift and drift of influenza virus biology essay. The antigenic drift that routinely generates a new influenza virus every year is usually responsible for 35 million cases of severe illness worldwide and 250,000500,000 deaths. Natural and directed antigenic drift of the h1 influenza. An antigenic drift is a small change, but it is possible that the human antibodies do not recognize it and people become susceptible and get sick again. Influenza is constantly changing in order to avoid immune detection. Antigenic drift occurs in all types of influenza including influenza virus a, influenza b and influenza c. Flu is highly contagious and is usually spread by the cough and sneezes of aperson who is infected,flu viruses constantly change and mutate, flu viruses can change into two ways antigenic drift and antigenic shift. Antigenic drift of hemagglutinin and neuraminidase in. Dec 09, 2010 influenza a h1n1, a h3n2, and influenza b viruses are included in each years influenza vaccine. The videos are not intended to be a substitute for professional medical advice, diagnosis or treatment.
How do antigenic shifts and drifts contribute to the need for annual vaccinations to prevent influenza. The degree of antigenic drift in swine influenza a viruses swiav has historically been regarded as minimal compared to that of human influenza a virus strains. Mar 11, 2020 influenza strains are constantly mutating. Antigenic drift influenza viruses are changing by antigenic drift all the time. It also occurs because the rna genome of influenza a viruses is in the form of eight segments, which during viral replication are susceptible to a type of genetic exchange known as genetic reassortment. Antigenic drift occurs in all types of influenza including influenza a, influenza b and influenza c. Antigenic variants of apr834 hon1 influenza virus were selected after a single passage of the parent virus in embryonated chicken eggs in the presence of monoclonal antibodies to this virus. Antigenic drift of h1n1 influenza a virus in pigs with and. Since antibodies against ha and neuraminidase na contribute independently to protection against disease, antigenic changes in na may allow ah1n1pdm09 viruses to escape from vaccine. Mar 11, 2020 accumulation of amino acid substitutions in these antigenic sites antigenic drift, due to immune selection pressure, can allow the virus to escape the preexisting immunity antigenic variants or. Small changes to the genetic makeup of influenza strains are referred to as antigenic drift, while a major change is called antigenic shift.
Antigenic shift and drift article pdf available in science teacher normal, ill. Occurs as a result of the accumulation of point mutations in the gene. Influenza virus infections cause seasonal epidemics and occasional pandemics, when novel viruses are introduced into humans 1, 2. In this study, we induced antigenic drift in an ah1n1pdm09 virus in the ferret model. Jul 27, 2017 seasonal and immediate mutations that enable influenza virus to escape immunity. Antigenic shift has been studied most extensively in influenza type a viruses, which experience this change about once every 10 years.
Antigenic shift is the reason that influenza can cause pandemics. Influenza has glycoprotein spikes of hemagglutinin h and neuraminidase n antigenic shift reassorts the genes of different influenza strains, antigenic drift is a gradual accumulation of mutations influenza infection of the intestinal tract causes stomach flu vaccination provides lifelong protection against all. In some cases, a 50% change occurs in the hemagglutinin structure. Compare and contrast antigenic shift and antigenic drift in influenza virus. This change is classified in antigenic drift and shift. Antigenic shift, however, occurs only in influenza a because it infects more than just humans. One of these pandemics occurred in 2009, when an outbreak of a swineorigin novel h1n1 influenza a virus ph1n1 began in mexico, and was rapidly disseminated worldwide 3, 4. Feb 26, 2019 antigenic shift is the molecular alteration of an antigen so that the human immune system can no longer recognize it. Affected species include other mammals and birds, giving influenza a the opportunity for a major reorganization of surface antigens. Shift results in a new influenza a subtype or a virus with a h or a h and n. Antigenic shift of greater public health concern is the process of antigenic shift also called reassortment through which at least two different viruses combine, resulting in exchange of the ha for example h3 replaced by h5 and consequently the. Influenza viruses undergo constant genetic variation.
Antigenic drift is a kind of genetic variation in viruses, arising by the accumulation of mutations in the. Antigenic drift of ah3n2virus and circulation of influenza. Antigenic shift can be the result of a direct jump from an unknown animal strain to humans or a reassortment of two or more influenza viruses within the same cell. It is a quick change of genes and is more complicated. The accumulation of random mutations antigenic drift in ha and na, and new combinations of sequences from two or more. The reservoirs of influenza a viruses aquatic birds are the. Seasonal and immediate mutations that enable influenza virus to escape immunity. During that season, antigenic drift of influenza virus ah3n2 occurred causing higher rates of ah3n2 infections. Emergence of an influenza b virus with antigenic change. Influenza should not be confused with the bacteria haemophilus influenza aka h flu. May result in a strain that has never been witnessed by humans in terms of the ha and na, which could pose a huge problem for humanity feck. Antigenic shift, genetic alteration occurring in an infectious agent that causes a dramatic change in a protein called an antigen, which stimulates the production of antibodies by the immune systems of humans and other animals.
The effectiveness of influenza vaccines against circulating ah1n1pdm09 viruses was modest for several seasons despite the absence of antigenic drift of hemagglutinin ha, the primary vaccine component. Influenza vaccine outmaneuvering antigenic shift and drift. While antigenic drift occurs continuously, antigenic shift occurs infrequently. Influenza virus eludes the immune system through multiple processes, including seasonal mutations in the surface epitopes, termed antigenic drift, and gene segment reassortment from distinct strains generating a novel lineage, termed. Monoclonal antibodies to the hemagglutinin molecule of the hong kong variant, mem171 h3n2, influenza virus were used to study antigenic drift in the h3n2 subtype of influenza viruses. Influenza virus influenza viruses are classified based on their membrane glycoproteins, hemagglutinin h and neuraminidase n. Due to the high mutation rate of the virus, a particular influenza vaccine usually confers protection for no more than a few years. Refers to small changes in influenza viruses that happen continually over time. Jan 30, 2008 influenza is an rna virus that causes mild to severe respiratory symptoms in humans and other hosts. Antigenic characterization of novel h1 influenza a viruses in. Antigenic shift is the molecular alteration of an antigen so that the human immune system can no longer recognize it. Influenza virus can mutate rapidly, resulting in both antigenic drift. In addition to antigenic shift, a pandemic virus may arise by the process of adaptive mutation in, for example, a virus that has crossed the species barrier, such as avian influenza ah5n1 infections of human. One way shift can happen is when an influenza virus from an animal.
Between the years of antigenic shift, the variable extent and severity of influenza. Birds are the natural hosts for the flu, so they are infected first before infecting any other animals. Antigenic shift bird virus gets into a pig co infected with a human virus pigs have receptors on its cells for both rearrangement leads to deadly form that can now pass from human to human. Influenza type a viruses go through two kinds of changes. Dec 11, 2017 watch and learn the story of antigenic drift and shift, and why they make preventing influenza a outbreaks so difficult. Antigenic shift occurs at infrequent and unpredictable intervals, when the current influenza a virus disappears and is replaced by a new subtype with novel glycoproteins always a novel ha and often a novel na. The influenza virus causes a very common acute respiratory tract infection. Antigenic shift in influenza virus major changes in the viral genome as a result of reassortment.
Publications of the world health organization can be obtained from who press, world health organization, 20. Scientists propose new explanation for flu virus antigenic drift. Transmission of influenza viruses from animals to people influenza a viruses also are found in many different animals, including ducks, chickens, pigs, whales, horses and seals. Evasion of the immune response by influenza viruses in the human population has resulted in a heavy healthcare burden and substantial mortality 1, 2. The mechanism of antigenic drift in influenza viruses. Viruses free fulltext substantial antigenic drift in the. Antigenic shift occurs because influenza a viruses have a large animal reservoir, consisting primarily of wild aquatic birds e. Antigenic shift occurs when a radical and abrupt change in influenza type a virus hemagglutinins occurs. Antigenic drift and antigenic shift, the primary mechanisms behind the antigenic variation of the in.
Antigenic drift of the pandemic 2009 ah1n1 influenza virus. Antigenic shift is an abrupt, major change in the influenza a viruses, resulting in new h andor new h and n proteins in influenza viruses that infect humans. In contrast, antigenic shifts are responsible for much more serious pandemics, as exemplified by three widespread influenza outbreaks in 1918 h1n1, 1957 h2n2. Antigenic shift is contrasted with antigenic drift, which is the natural mutation over time of known strains of influenza or other things, in a more general sense which may lead to a loss of immunity, or in vaccine mismatch. Influenza virus infections cause seasonal epidemics and occasional pandemics, when novel viruses are introduced into humans 1,2. May 09, 20 antigenic drift involves amino acid changes in antigenic regions of influenza proteins, facilitating escape from existing immunity. Antigenic shift definition of antigenic shift by medical. Antigenic drift produces new virus strains that may not be recognized by the bodys immune system. In either case, the human immune system perceives the strain as. Antigenic drift causes less extensive and severe outbreaks. Confusion can arise with two very similar terms, antigenic shift and genetic drift. Learn how type b influenza virus has genetic drift, whereas type a influenza virus has genetic drift and shift. Antigenic drift involves minor changes in the hemagglutinin ha and neuraminidase na, whereas antigenic shift involves major changes in these molecules resulting from replacement of the gene segment. Influenza virus are remarkable because of the frequent antigenic change that.
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