Jun 23, 2018 influenza virus are remarkable because of the frequent antigenic change that occurs in ha hemagglutinin or na neuraminidase. One of these pandemics occurred in 2009, when an outbreak of a swine. Antigenic shift in influenza virus major changes in the viral genome as a result of reassortment. 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. The reservoirs of influenza a viruses aquatic birds are the. Differences between antigenic shift and antigenic drift. 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.
Review on influenza virus and its prevention and control. 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. Antigenic shift occurs when a radical and abrupt change in influenza type a virus hemagglutinins occurs. Antigenic drift occurs in all types of influenza including influenza a, influenza b and influenza c. Current annual vaccines contain two type a strains and one type b strain and are capable of inducing strong antibody responses. Mutations in the genes coding for the proteins na and ha result in minor changes to surface proteins. Influenza virus can mutate rapidly, resulting in both antigenic drift. 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. 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. Feb 26, 2019 antigenic shift is the molecular alteration of an antigen so that the human immune system can no longer recognize it.
Antigenic drift may also allow a virus to cross the species barrier to a new host. Shift can result in a new influenza a subtype in humans. Influenza virus are remarkable because of the frequent antigenic change that. Antigenic drift is a kind of genetic variation in viruses, arising by the accumulation of mutations in the.
Jul 27, 2017 seasonal and immediate mutations that enable influenza virus to escape immunity. Based on historical patterns, influenza pandemics can be expected to occur, on average, 3 to 4 times each century. Confusion can arise with two very similar terms, antigenic shift and genetic drift. Shift results in a new influenza a subtype or a virus with a h or a h and n. Publications of the world health organization can be obtained from who press, world health organization, 20. One way shift can happen is when an influenza virus from an animal population gains the ability to infect humans. Learn how type b influenza virus has genetic drift, whereas type a influenza virus has genetic drift and shift. 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. Influenza vaccine outmaneuvering antigenic shift and drift. 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. Refers to small changes in influenza viruses that happen continually over time.
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. This change is classified in antigenic drift and shift. Antigenic drift produces new virus strains that may not be recognized by the bodys immune system. 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. While antigenic drift occurs continuously, antigenic shift occurs infrequently. Antigenic drift of hemagglutinin and neuraminidase in. 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. Clinically it presents as fatigue, rhinorrhea runny nose, myalgia muscle.
These videos do not provide medical advice and are for informational purposes only. Influenza has ability to antigenic changes through antigenic drift and antigenic shift. When the flu strain mutates, our immune system recognizes it as a new virus. In some cases, a 50% change occurs in the hemagglutinin structure. See figure i for influenza virus replication immune evasion and the concepts of antigenic drift and shift. Made for the science ambassador scholarship category. 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. Antigenic shift, which is seen only with influenza a viruses, results from. 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. 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 flu viruses can change in two different ways. Despite efforts to vaccinate, the who estimates that. Influenza virus infections cause seasonal epidemics and occasional pandemics, when novel viruses are introduced into humans 1, 2. Antigenic shift is the molecular alteration of an antigen so that the human immune system can no longer recognize it. Drift and shift influenza viruses can change in two different ways.
Evasion of the immune response by influenza viruses in the human population has resulted in a heavy healthcare burden and substantial mortality 1, 2. Influenza type a viruses go through two kinds of changes. Influenza or flu is a respiratory illness,that is caused by a virus influenza virus. Small changes to the genetic makeup of influenza strains are referred to as antigenic drift, while a major change is called antigenic shift. 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. How the flu virus can change influenza viruses can change in two different waysantigenic drift and antigenic shift. Antigenic shift definition of antigenic shift by medical. 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. Influenza viruses undergo constant genetic variation. Viruses free fulltext substantial antigenic drift in the. May 09, 20 antigenic drift involves amino acid changes in antigenic regions of influenza proteins, facilitating escape from existing immunity.
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. Birds are the natural hosts for the flu, so they are infected first before infecting any other animals. The antibodies created in response to having the flu in the past are unable to. Periodically, the viruses undergo major evolutionary change by acquiring a new genome segment from another influenza virus antigenic shift, effectively becoming a new subtype. Antigenic shift, however, occurs only in influenza a because it infects more than just humans. The pandemics of 1908, 1957, 1968, and 2009 were caused by new viruses emerging as a result of antigenic shift. Antigenic shift occurs because influenza a viruses have a large animal reservoir, consisting primarily of wild aquatic birds e. Since antibodies against ha and neuraminidase na contribute independently to protection against disease, antigenic changes in na may allow ah1n1pdm09 viruses to escape from. The videos are not intended to be a substitute for professional medical advice, diagnosis or treatment.
It is a quick change of genes and is more complicated. Compare and contrast antigenic shift and antigenic drift in influenza virus. Antigenic shift, however, occurs only in influenzavirus a because it infects more than just humans. Antigenic shift and drift article pdf available in science teacher normal, ill. One way shift can happen is when an influenza virus from an animal. When antigenic shift does occur, a large proportion, or even all, of the worlds population has no antibody against the new virus.
Antigenic drift influenza viruses are changing by antigenic drift all the time. In this study, we induced antigenic drift in an ah1n1pdm09 virus in the ferret model. Influenza a appears in pandemics which occur after an antigenic shift. Antigenic shift is the reason that influenza can cause pandemics. Between the years of antigenic shift, the variable extent and severity of influenza. The influenza virus genes are made of rna and are more prone to mutations than genes made of dna. Due to the high mutation rate of the virus, a particular influenza vaccine usually confers protection for no more than a few years. World health organization 2011 all rights reserved. Influenza a h1n1, a h3n2, and influenza b viruses are included in each years influenza vaccine. Antigenic drift of h1n1 influenza a virus in pigs with and. During that season, antigenic drift of influenza virus ah3n2 occurred causing higher rates of ah3n2 infections. Understanding how flu viruses change nieman foundation.
The hallmark of influenzaviruses is antigenic variation, which comes in two forms. This means that individuals who have previously been infected can become re. The mechanism of antigenic drift in influenza viruses. These are small changes in the virus that happen continually over time. Antigenic shift has been studied most extensively in influenza type a viruses, which experience this change about once every 10 years. Antigenic drift occurs in both influenza a and influenza b viruses.
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. Antigenic variants of mem171 h3n2 were selected after a single passage of the virus in chick embryos in the presence of monoclonal antibody. Dec 11, 2017 watch and learn the story of antigenic drift and shift, and why they make preventing influenza a outbreaks so difficult. Dec 09, 2010 influenza a h1n1, a h3n2, and influenza b viruses are included in each years influenza vaccine. 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. Pneumonia is diagnosed by the presence of fluid dark shadows in an xray image in the alveoli. 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. The other type of change is a sudden change in the hemagglutinin and or the neuraminidase proteins.
Rishi is a pediatric infectious disease physician and works at khan academy. Scientists propose new explanation for flu virus antigenic drift. Influenza virus infections cause seasonal epidemics and occasional pandemics, when novel viruses are introduced into humans 1,2. Mar 11, 2020 influenza strains are constantly mutating. It can change its antigenic character abruptly and extensively antigenic shift, at 1020 year intervals, and also gradually from year to year antigenic drift. Antigenic drift and antigenic shift, the primary mechanisms behind the antigenic variation of the in.
The mechanisms that the virus uses to change its antigenic sites are called drift and shift. Antigenic drift of ah3n2virus and circulation of influenza. The accumulation of random mutations antigenic drift in ha and na, and new combinations of sequences from two or more. The other type of change is a sudden change in the hemagglutinin andor the neuraminidase proteins. This accounts for annual flu seasons and periodic pandemics. Jan 30, 2008 influenza is an rna virus that causes mild to severe respiratory symptoms in humans and other hosts. 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. Emergence of an influenza b virus with antigenic change. Seasonal and immediate mutations that enable influenza virus to escape immunity. Antigenic drift of the pandemic 2009 ah1n1 influenza virus. 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.
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. If the novel influenza a virus causes disease and is efficiently transmitted among. Natural and directed antigenic drift of the h1 influenza. 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. Antigenic characterization of novel h1 influenza a viruses in. Affected species include other mammals and birds, giving influenza a the opportunity for a major reorganization of surface antigens.
Influenza virus antigenic variation, host antibody production. Influenza virus is an example of a genetically labile virus. Although the influenza virus has been recognized for a long time, it is frequently reported in the news as an emerging virus when new outbreaks and even pandemics occur in humans, poultry, horses, or dogs. How do antigenic shifts and drifts contribute to the need for annual vaccinations to prevent influenza. Influenza virus influenza viruses are classified based on their membrane glycoproteins, hemagglutinin h and neuraminidase n. 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.
Scientists propose new explanation for flu virus antigenic. The significance of antigenic shift rapid change in circulating flu viruses is known as antigenic shift. Antigenic drift causes less extensive and severe outbreaks. Antigenic shift and drift of influenza virus biology essay. 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. Host protective immune responses against influenza a virus. Antigenic drift of the pandemic 2009 ah1n1 influenza. 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. The resulting change in viral protein structure results in high levels of susceptibility among populations. 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. 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.
In either case, the human immune system perceives the strain as. Watch and learn the story of antigenic drift and shift, and why they make preventing influenza a outbreaks so difficult. Influenza should not be confused with the bacteria haemophilus influenza aka h flu. Influenza is constantly changing in order to avoid immune detection. 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. Oct 15, 2019 the other type of change is called antigenic shift. Occurs as a result of the accumulation of point mutations in the gene. The two surface antigens of influenza undergo antigenic variation independent of each other. The influenza virus causes a very common acute respiratory tract infection.
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. One is a sequence of mutations that occur over time and causes a slow development of the virus. Antigenic drift occurs in all types of influenza including influenza virus a, influenza b and influenza c. 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. 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. 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. 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. 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, 2009 influenza is an infectious disease and can lead to lifethreatening complications like pneumonia. 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. The other type of change is called antigenic shift.
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