How does antigenic shift occur in influenza viruses

Antigenic shift is a more major change in the influenza virus. This shift typically occurs when a human flu virus crosses with a flu virus that usually affects animals (such as birds or pigs). When the viruses mutate, they shift to create a new subtype that is different from any seen in humans before.

Why does antigenic shift only occur in influenza A?

Antigenic shift, however, occurs only in influenza A because it infects more than just humans. Affected species include other mammals and birds, giving influenza A the opportunity for a major reorganization of surface antigens.

What is the mechanism of transmission of the influenza virus?

The influenza viruses mainly are spread from person to person through droplets produced while coughing or sneezing. Droplets of an infected person are propelled by coughing, sneezing, and talking into the air and are deposited on the mouth or nose of people nearby.

What is the difference between antigenic drift and antigenic shift in the influenza virus?

Antigenic drift vs. shift. Antigenic drift creates influenza viruses with slightly modified antigens, while antigenic shift generates viruses with entirely new antigens (shown in red).

What contributes to antigenic shift in influenza viruses group of answer choices?

Antigenic shifts occur by reassortment and introduction of a novel HA, NA, or both gene segments from the aquatic bird reservoir into currently circulating human influenza viruses.

Where does antigenic drift occur?

Antigenic drift is a natural process whereby mutations (mistakes) occur during replication in the genes encoding antigens that produce alterations in the way they appear to the immune system (antigenic changes) (Figure 1).

How does antigenic variation occur?

Antigenic variation can occur by altering a variety of surface molecules including proteins and carbohydrates. Antigenic variation can result from gene conversion, site-specific DNA inversions, hypermutation, or recombination of sequence cassettes.

What is the role of hemagglutinin in influenza infections?

The hemagglutinin(HA) of influenza virus is a major glycoprotein and plays a crucial role in the early stage of virus infection: HA is responsible for binding of the virus to cell surface receptors, and it mediates liberation of the viral genome into the cytoplasm through membrane fusion.

What causes antigenic drift?

20 Antigenic drift is caused by point mutations in the HA and NA genes that are driven by immune pressure and the infidelity inherent in the replication of RNA genomes.

Is influenza airborne or droplet?

Influenza is thought to be transmitted primarily by droplets (particles ≥ 5 μm, and settling within 3-6 feet); however, the airborne route (particles < 5 μm remaining suspended in air) has been implicated in special situations, such as aerosol-generating procedures.

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What does the term antigenic drift refer to?

One way flu viruses change is called “antigenic drift.” Drift consists of small changes (or mutations) in the genes of influenza viruses that can lead to changes in the surface proteins of the virus, HA (hemagglutinin) and NA (neuraminidase).

What is airborne transmission?

How Airborne Transmission Works. Airborne diseases are bacteria or viruses that are most commonly transmitted through small respiratory droplets. These droplets are expelled when someone with the airborne disease sneezes, coughs, laughs, or otherwise exhales in some way.

Which of the following is a reservoir for the antigenic shift variants of influenza virus?

Antigenic shift occurs because influenza A viruses have a large animal reservoir, consisting primarily of wild aquatic birds (e.g., ducks).

What is the fate of the prophage during the lysogenic stage?

What is the fate of the prophage during the lysogenic stage? It is released from the cell by lysing the cell. It is copied every time the host DNA replicates. It is packaged into viral proteins and maintained until the host is exposed to an environmental stress.

Can a prophage pop out of the chromosome?

Under the right conditions, the prophage can become active and come back out of the bacterial chromosome, triggering the remaining steps of the lytic cycle (DNA copying and protein synthesis, phage assembly, and lysis). Prophage exits chromosome and becomes its own circularized DNA molecule.

What is antigenic variation in viruses?

Antigenic variation refers to the observation that different isolates of a single virus species may show variable cross-reactivity when tested with a standard serum.

Is drift or antigenic shift worse?

Because the genes in the resulting virus are dramatically different, this is called antigenic shift. Antigenic shift is more concerning than antigenic drift. Antigenic shift can produce a version of influenza virus that no person’s immune system has antibodies to protect against.

Which of the following viruses is known for its antigenic variation?

Examples of random antigenic variation are those that occur in viruses such as the influenza virus and the human immunodeficiency virus (HIV), which causes acquired immunodeficiency syndrome (AIDS). The major antigenic components of these viruses are glycoproteins that make up their viral coat.

Does antigenic drift occur in all viruses?

All influenza viruses experience some form of antigenic drift, but it is most pronounced in the influenza A virus. Antigenic drift should not be confused with antigenic shift, which refers to reassortment of the virus’ gene segments.

When does antigenic shift occur?

While antigenic drifts occur almost annually, antigenic shifts occur at intervals of 10 years or more. Antigenic shifting is largely responsible for the ability of influenza to produce epidemics even in populations of persons who have previously been infected or immunized with influenza.

How does a virus use the hemagglutinin gene?

The hemagglutinin glycoprotein of influenza virus has important functions in the initiation of infection: it mediates adsorption of the virus particles to cell surface receptors and is responsible for the subsequent uncoating of the virus by a process of fusion between viral and host membranes.

What is the structure of influenza virus?

The structure of the influenza virus (see Figure 1) is somewhat variable, but the virion particles are usually spherical or ovoid in shape and 80 to 120 nanometers in diameter. Sometimes filamentous forms of the virus occur as well, and are more common among some influenza strains than others.

What is the structure of hemagglutinin?

The hemagglutinin molecule is actually a combination of three identical proteins (shown here as gray, green, and purple) that are bound together to form an elongated cylindrical shape. Hemagglutinin consists of a globular head and a stem. The globular head consists of three chains, Chains A, C, and E.

Is influenza spread by droplet?

People with flu can spread it to others up to about 6 feet away. Most experts think that flu viruses spread mainly by droplets made when people with flu cough, sneeze or talk. These droplets can land in the mouths or noses of people who are nearby or possibly be inhaled into the lungs.

Is influenza A droplet precaution?

Droplet precautions should be implemented for patients with suspected or confirmed influenza for 7 days after illness onset or until 24 hours after the resolution of fever and respiratory symptoms, whichever is longer, while a patient is in a healthcare facility.

Does flu spread through air?

The flu is mainly spread by breathing in air from infected people when they cough, sneeze, or talk. People can also get the flu by touching a surface that has the virus on it and then touching their eyes, nose, or mouth.

What is a parenteral exposure?

Parenteral exposure is defined as subcutaneous, intramuscular or intravenous contact with blood or other body fluid of an HIV-1 infected individual, but not mucocutaneous contact.

How is a congenital infection contracted?

Congenital infections occur when a mother infects a fetus before its birth. Congenital infections occur via vertical transmission, meaning that the virus is spread from one generation to the next generation (Fig. 5.6).

How do respiratory droplets spread?

People release respiratory fluids during exhalation (e.g., quiet breathing, speaking, singing, exercise, coughing, sneezing) in the form of droplets across a spectrum of sizes. These droplets carry virus and transmit infection. The largest droplets settle out of the air rapidly, within seconds to minutes.

What is antigenic shift with example?

An example of a pandemic resulting from antigenic shift was the 1918-19 outbreak of Spanish Influenza. This strain was originally the H1N1 avian flu, however antigenic shift allowed the viral infection to jump from pigs to humans, resulting in a large pandemic which killed over 40 million people.

What factor may induce a prophage to enter the lytic cycle?

What factor may induce a prophage to enter the lytic cycle? Ultraviolet radiation is known to cause the induction of prophage into the lytic cycle. During the lysogenic cycle, it is possible for integrated phage genes to change the characteristics of the host cell.