stages of a viral infection

But sometimes these largely present entities cause trouble in human body. There are four stages of Infection: Incubation period- This period is starts from invasion of microorganisms into the body until the appearance of first sign of symptoms. A virus must use cell processes to replicate. Viral pathogenesis comprises of several stages, including (1) transmission and entry of the virus into the host, (2) spread in the host, (3) tropism, (4) virulence, (5) patterns of viral infection and disease, (6) host factors, (7) and host defense. These changes, called cytopathic effects, can change cell functions or even destroy the cell. These drugs, including the reverse transcriptase inhibitor AZT, inhibit HIV replication by reducing the activity of the enzyme without affecting the host’s metabolism. Many animal viruses, such as HIV (human immunodeficiency virus), leave the infected cells of the immune system by a process known as budding, where virions leave the cell individually. … The specificity of this interaction determines the host (and the cells within the host) that can be infected by a particular virus. Lytic animal viruses follow similar infection stages to bacteriophages: attachment, penetration, biosynthesis, maturation, and release (see Figure 4). Lytic animal viruses follow similar infection stages to bacteriophages: attachment, penetration, biosynthesis, maturation, and release (see Figure 6.2. Some infected cells, such as those infected by the common cold virus known as rhinovirus, die through lysis (bursting) or apoptosis (programmed cell death or “cell suicide”), releasing all progeny virions at once. Click here to let us know! Penetration or Entry. This can be illustrated by thinking of several keys and several locks where each key will fit only one specific lock. RNA viruses usually use the RNA core as a template for synthesis of viral genomic RNA and mRNA. RNA and proteins are then made and assembled into new virions. Of course, there are exceptions to this pattern. In the WHO classification, this is stage 2 (mild symptoms) and stage 3 (advanced symptoms). The third stage of infection is biosynthesis of new viral components. Unless otherwise noted, LibreTexts content is licensed by CC BY-NC-SA 3.0. There is no cure for HIV, but treatment with HIV medicines (called antiretroviral therapy or ART) can slow or … If a host cell does not provide the enzymes necessary for viral replication, viral genes supply the information to direct synthesis of the missing proteins. In other words, the virus continues to reproduce in the person’s liver for several months or years after infection. In addition, symptoms due to a bacterial infection often last more than 10 days without improvement. During release, the newly-created viruses are released from the host cell, either by causing the cell to break apart, waiting for the cell to die, or by budding off through the cell membrane. In some viruses uncoating is done by lysosomal enzymes of the host cell which degrade protein coat and make the nucleic acid free in cytoplasm. Opportunistic infections that the immune system is normally able to fight off may begin to occur. Stage I: The early infection or viral response phase during which symptoms of upper respiratory tract infection dominate. How A Virus Invades Your Body. In a typical infectious disease, the incubation period signifies the period taken by the multiplying organism to reach a threshold necessary to produce symptoms in the host. http://cnx.org/contents/185cbf87-c72e-48f5-b51e-f14f21b5eabd@10.8, http://cnx.org/contents/e42bd376-624b-4c0f-972f-e0c57998e765@4.4, List the steps of replication and explain what occurs at each step. The Stages of Viral Infection: How HPV and Shingles Play a Long Game. For many virus families the The viral replication cycle can produce dramatic biochemical and structural changes in the host cell, which may cause cell damage. This process is not fully understood. Flu Attack! The last stage of viral replication is the release of the new virions produced in the host organism, where they are able to infect adjacent cells and repeat the replication cycle. In a few cases, a bacterial infection may develop on top of a viral cold, in which case symptoms may get better and then worse again. Some infected cells, such as those infected by the common cold virus known as rhinovirus, die through lysis (bursting) or apoptosis (programmed cell death or “cell suicide”), releasing all progeny virions at once. In some cases of viral pneumonia, a doctor may prescribe antiviral medication to reduce viral activity. The induction of necroptosis also requires late stages of reovirus infection. The influenza reproductive cycle. In this video, Dr. Offit introduces the different types of viral infections and how some viruses remain in our systems after first contact. The specificity of this interaction determines the host—and the cells within the host—that can be infected by a particular virus. After entering the host cell, the virus synthesizes virus-encoded endonucleases to degrade the bacterial chromosome. Specifically, efficient synthesis of double-stranded RNA (dsRNA) within infected cells is required for necroptosis. Entry into the Body. A viral sinus infection will usually start to improve after five to seven days. Stage III: The hyperinflammation phase when patients develop acute respiratory distress syndrome (ARDS), sepsis, and kidney and other organ failures. This can increase the risk of liver damage and liver cancer. During this period microorganisms multiply to cause infection. During uncoating, replication, and assembly, the viral DNA or RNA incorporates itself into the host cell’s genetic material and induces it to replicate the viral genome. Risk of transmission is thought to be the greatestat this stage. To convert RNA into DNA, retroviruses must contain genes that encode the virus-specific enzyme reverse transcriptase, which transcribes an RNA template to DNA. The initial infection often occurs before adulthood and may be confused with a cold or the flu. The chances of the infection being missed at the beginning stage are very high because the symptoms of the earlier stages are not typical and mimic other common health conditions. However, the mechanisms of penetration, nucleic-acid biosynthesis, and release differ between bacterial and animal viruses. Viruses are present in almost every ecosystem on earth. Learn more about upper respiratory infections here. Pneumonia may be caused by viral infections, bacterial infections, or fungi; less frequently by other causes. Of course, there are exceptions to this pattern. As you’ve learned, some viruses are released when the host cell dies, and other viruses can leave infected cells by budding through the membrane without directly killing the cell. This includes fevers, dry coughs, and a lack of physical energy. The nucleic acid of bacteriophages enters the host cell naked, leaving the capsid outside the cell. It is a process of separation of viral nucleic acid from the protein coat. For more information contact us at info@libretexts.org or check out our status page at https://status.libretexts.org. But for infants, older adults and people with compromised immu… The viral mRNA directs the host cell to synthesize viral enzymes and capsid proteins, and assemble new virions. Most productive viral infections follow similar steps in the virus replication cycle: attachment, penetration, uncoating, replication, assembly, and release (Figure 1). Most productive viral infections follow similar steps in the virus replication cycle: attachment, penetration, uncoating, replication, assembly, and release. However, the damage to the cells that the virus infects may make it impossible for the cells to function normally, even though the cells remain alive for a period of time. Pneumonia is a lung disease characterized by inflammation of the airspaces in the lungs, most commonly due to an infection. Adopted a LibreTexts for your class? It can affect various parts of the human body. Viral replication involves six steps: attachment, penetration, uncoating, replication, assembly, and release. Incubation period is the time elapsed between exposure to a pathogenic organism, a chemical, or radiation, and when symptoms and signs are first apparent. However, the mechanisms of penetration, nucleic-acid biosynthesis, and release differ between bacterial and animal viruses. A virus attaches to a specific receptor site on the host cell membrane through attachment proteins in the capsid or via glycoproteins embedded in the viral envelope. We’d love your input. During attachment and penetration, the virus attaches itself to a host cell and injects its genetic material into it. Use a cough suppressant if you find it difficult to sleep. Your smile is one-sided, and your eye on that side resists closing.Bell's palsy, also known as facial palsy, can occur at any age. Viral infection involves the incorporation of viral DNA into a host cell, replication of that material, and the release of the new viruses. The viral replication cycle can produce dramatic biochemical and structural changes in the host cell, which may cause cell damage. In poxviruses, the viral DNA synthesizes a specific protein after infection. If a host cell does not provide the enzymes necessary for viral replication, viral genes supply the information to direct synthesis of the missing proteins. In the CDC system, it corresponds with stage 2 (a CD4 count between 200 and 500). An upper respiratory infection is an illness that affects the nose and throat, causing symptoms such as sneezing and coughing. Experimentally manipulating HDF timing and abundance enables probing of additional aspects of viral replication, while, at the same time, minimizing the bias towards early stages of infection. The fact that HIV produces some of its own enzymes not found in the host has allowed researchers to develop drugs that inhibit these enzymes. Did you have an idea for improving this content? If you're otherwise healthy, you'll likely recover without complications. Plant and animal viruses can enter through endocytosis (as you may recall, the cell membrane surrounds and engulfs the entire virus). The basic process of viral infection and virus replication occurs in 6 main steps. However, the damage to the cells that the virus infects may make it impossible for the cells to function normally, even though the cells remain alive for a period of time. Many animal viruses, such as HIV (Human Immunodeficiency Virus), leave the infected cells of the immune system by a process known as budding, where virions leave the cell individually. Viral Genome Replication - viral genome replicates using the host's cellular machinery. Entry of the viruses into the body is the first step of viral infections. Adsorption - virus binds to the host cell. They are then able to infect adjacent cells and repeat the replication cycle. DNA viruses usually use host cell proteins and enzymes to make additional DNA that is transcribed to messenger RNA (mRNA), which is then used to direct protein synthesis. Retroviruses, such as HIV (group VI of the Baltimore classification scheme), have an RNA genome that must be reverse transcribed into DNA, which then is incorporated into the host cell genome. This treatment tends to be most effective when the virus is in the early stage of infection. Penetration - virus injects its genome into host cell. The second stage (day 2-3), is characterized by white and red blood cells and damaged cellular debris clogging the airways and air-sacs (alveoli) and an increase in bacteria. Once inside the cell, the viral capsid degrades, and then the viral nucleic acid is released and becomes available for replication and transcription. During the budding process, the cell does not undergo lysis and is not immediately killed. The order of the stages of viral replication that follow the uncoating of the genome varies for different virus classes. In simple parlance, a disease that is/can be caused by different types of virus is known as Viral Infection. Some enveloped viruses enter the cell when the viral envelope fuses directly with the cell membrane. Viruses initiate infection and may cause disease through many defined stages. The replication mechanism depends on the viral genome. Once inside the cell, the viral capsid is degraded and the viral nucleic acid is released, which then becomes available for replication and transcription. A chronic hepatitis B infection means that the immune system is not able to get rid of the virus within six months after infection. Steps of Virus Infections. Modification of the virus replication cycle. RNA viruses usually use the RNA core as a template for synthesis of viral genomic RNA and mRNA. Assembly - viral components and enzymes are produced and begin to assemble. Legal. Plant and animal viruses can enter through endocytosis, in which the cell membrane surrounds and engulfs the entire virus. The viral mRNA directs the host cell to synthesize viral enzymes and capsid proteins, and to assemble new virions. During the budding process, the cell does not undergo lysis and is not immediately killed. Watch this video on viruses, identifying structures, modes of transmission, replication, and more: The following activity will show you just how the flu virus can infect your body. During attachment and penetration, the virus attaches itself to a host cell and injects its genetic material into it. Viruses may enter a host cell either with or without the viral capsid. Retroviruses, such as HIV, have an RNA genome that must be reverse transcribed into DNA, which then is incorporated into the host cell genome. The most common bacterial type that causes pneumonia is Streptococcus pneumoniae. The exact cause is unknown. These data indicate that viral RNA interfaces with host components at two different stages of infection … Because a P.C.R. test is more sensitive to low viral loads, it may be able to detect a coronavirus infection very early on. A virus must use its host-cell processes to replicate. The nucleic acid of bacteriophages enters the host cell “naked,” leaving the capsid outside the cell. Bell's palsy causes sudden, temporary weakness in your facial muscles. Following this, the virus is engulfed. In influenza virus infection, glycoproteins on the capsid attach to a host epithelial cell. To find out more, read the accompanying article in … The three stages of HIV infection are (1) acute HIV infection, (2) chronic HIV infection, and (3) acquired immunodeficiency syndrome (AIDS). Virus Multiplication: After infection, the virus particle disappears from view. The last stage of viral replication is the release of the new virions produced in the host organism. The fact that HIV produces some of its own enzymes not found in the host has allowed researchers to develop drugs that inhibit these enzymes without affecting the host’s metabolism. These changes, called cytopathic (causing cell damage) effects, can change cell functions or even destroy the cell. A bacterial sinus infection will often persist for seven to 10 days or … It's believed to be the result of swelling and inflammation of the nerve that controls the muscles on one side of your face. The symptoms of viral diseases result both from such cell damage caused by the virus and from the immune response to the virus, which attempts to control and eliminate the virus from the body. In the first stage, which occurs within 24 hours of infection, the lung has increased blood flow and swelling to the airways, but only a few bacteria or white blood cells to fight infection are present. Stages of Viral Infections Stages of Viral Infections. This approach has led to the development of a variety of drugs used to treat HIV and has been effective at reducing the number of infectious virions (copies of viral RNA) in the blood to non-detectable levels in many HIV-infected individuals. Stage II: The pulmonary phase when the patients develop full-blown pneumonia with all its associated symptoms. A virus attaches to a specific receptor site on the host cell membrane through attachment proteins in the capsid or via glycoproteins embedded in the viral envelope. Chronic Hepatitis B Virus Infection. Some enveloped viruses enter the cell when the viral envelope fuses directly with the cell membrane. In the second step of viral infection, the virus releases its … As you have learned, some viruses are released when the host cell dies, while other viruses can leave infected cells by budding through the membrane without directly killing the cell. They are marked as the most abundant biological entity on this planet. It is observed that some viruses are in the intestine, while many are in lungs and airwa… Attachment. But the diagnostic test can also pick up … [ "article:topic", "authorname:boundless", "showtoc:no" ], https://bio.libretexts.org/@app/auth/3/login?returnto=https%3A%2F%2Fbio.libretexts.org%2FBookshelves%2FIntroductory_and_General_Biology%2FBook%253A_General_Biology_(Boundless)%2F21%253A_Viruses%2F21.2%253A_Virus_Infections_and_Hosts%2F21.2A%253A_Steps_of_Virus_Infections, 21.2B: The Lytic and Lysogenic Cycles of Bacteriophages, List the steps of viral replication and explain what occurs at each step. We also acknowledge previous National Science Foundation support under grant numbers 1246120, 1525057, and 1413739. Reverse transcription never occurs in uninfected host cells; the needed enzyme, reverse transcriptase, is only derived from the expression of viral genes within the infected host cells. The replication mechanism depends on the viral genome. Figure 1. A viral disease is any condition that’s caused by a virus. Click here for a text-only version of the activity. This approach has led to the development of a variety of drugs used to treat HIV and has been effective at reducing the number of infectious virions (copies of viral RNA) in the blood to non-detectable levels in many HIV-infected individuals. Entry (Penetration and Uncoating) Replication and Assembly. Viral replication involves six steps: attachment, penetration, uncoating, replication, assembly, and release. This is a viral infection and an antibiotic will not help. Have questions or comments? 4). To convert RNA into DNA, retroviruses must contain genes that encode the virus-specific enzyme reverse transcriptase that transcribes an RNA template to DNA. The LibreTexts libraries are Powered by MindTouch® and are supported by the Department of Education Open Textbook Pilot Project, the UC Davis Office of the Provost, the UC Davis Library, the California State University Affordable Learning Solutions Program, and Merlot. Learn vocabulary, terms, and more with flashcards, games, and other study tools. This makes half of your face appear to droop. Start studying Unit 4: Steps of Viral Infection. It ceases to exist as an … Viral gastroenteritis is an intestinal infection marked by watery diarrhea, abdominal cramps, nausea or vomiting, and sometimes fever.The most common way to develop viral gastroenteritis — often called stomach flu —is through contact with an infected person or by ingesting contaminated food or water. There are several types of viral disease, depending on the underlying virus. The earlier the HIV infection is diagnosed, the better is the prognosis and the quality of life the person enjoys. In fact, it could make things worse. 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