This page titled 6.2: The Viral Life Cycle is shared under a CC BY 4.0 license and was authored, remixed, and/or curated by OpenStax via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request. These types of viruses are known as latent viruses and may cause latent infections. -phage is the best example of a temperate phage. There are two processes used by viruses to replicate: the lytic cycle and lysogenic cycle. In a one-step multiplication curve for bacteriophage, the host cells lyse, releasing many viral particles to the medium, which leads to a very steep rise in viral titer (the number of virions per unit volume). The second stage of infection is entry or penetration. Viruses capable of latency may initially cause an acute infection before becoming dormant. All rights reserved. Many viruses are host specific, meaning they only infect a certain type of host; and most viruses only infect certain types of cells within tissues. If you are redistributing all or part of this book in a print format, During dormancy, viruses do not cause any symptoms of disease and may be difficult to detect. In this blog post, we will discuss the lytic replication cycle of the Ebola virus, including the different stages of the cycle, the mechanisms of replication, and the significance of this process in the context of EVD. The dsDNA can now be replicated, transcribed, and translated similar to host DNA. However, some viruses can only be transferred by a specific type of insect vector; for example, a particular virus might be transmitted by aphids but not whiteflies. 0:08 into the box of lytic or lysogenic. In prokaryotes this cycle is characterized by integration of the bacteriophage nucleic acid into the genome of the host bacterium . Proper clinical support is required for patients exposed to the virus for a higher chance of survival. For example, the citrus tristeza virus infects only a few plants of the Citrus genus, whereas the cucumber mosaic virus infects thousands of plants of various plant families. Despite the notoriety of ebolaviruses, particularly Ebola virus (EBOV), as prominent viral hemorrhagic fever agents, and the international concern regarding Ebola virus disease (EVD) outbreaks, very little is known about the pathophysiology of EVD in . Filoviruses, including the Ebola virus, are transmitted through direct contact with bodily fluids from infected patients or other species (e.g., gorillas and chimpanzees). Creative Commons Attribution License 2. The chief difference that next appears in the viral growth curve compared to a bacterial growth curve occurs when virions are released from the lysed host cell at the same time. The efficacy of the drugs was evaluated during the 2018-2020 Ebola outbreak in the Democratic Republic of Congo. 0:19 So first let's zoom in and take a look 0:23 at some unique things about the retrovirus 0:25 that make it different from other viruses. The immune system Viral replication: lytic vs lysogenic Google Classroom Transcript 0:02- [Voiceover] So, let's talk about viral replication. Mechanisms of persistent infection may involve the regulation of the viral or host gene expressions or the alteration of the host immune response. Not only are these drugs untested or unregistered but they are also in short supply. Ebola is incurable and deadly. A patient may be unaware that he or she is carrying the virus unless a viral diagnostic test has been performed. Despite these experimental drugs and vaccines, there is still no cure for EVD. During the lytic cycle of viral replication, the virus hijacks the host cell, degrades the host chromosome, and makes more viral genomes. It is a one-dose shot that protects against the variant of the Ebola virus that has caused the most serious outbreak so far. With a few exceptions, RNA viruses that infect animal cells replicate in the cytoplasm. We recommend using a The hospital continued to treat Duncan, but he died several days after being admitted. The pathogen genome replicates and the host cell's metabolic machinery is used to synthesize enzymes and structural components. Others become proviruses by integrating into the host genome. copyright 2003-2023 Study.com. Legal. It is typical of temperate phages to be latent or inactive within the cell. A virulent phage shows only the lytic cycle pictured here. If no viable host cells remain, the viral particles begin to degrade during the decline of the culture (see Figure 6.14). About 10 to 12 days postinfection, the disease resolves and the virus goes dormant, living within nerve-cell ganglia for years. The various mechanisms that HIV uses to avoid being cleared by the immune system are also used by other chronically infecting viruses, including the hepatitis C virus. Viruses cannot replicate on their own. 0:06Since we know that viruses are made of 0:08only proteins and one type of nucleic acid, 0:11which means they have no organelles 0:13to make copies of themselves with, An alternative mechanism for viral nucleic acid synthesis is observed in the retroviruses, which are +ssRNA viruses (see Figure \(\PageIndex{6}\)). Single-stranded RNA viruses such as HIV carry a special enzyme called reverse transcriptase within the capsid that synthesizes a complementary ssDNA (cDNA) copy using the +ssRNA genome as a template. Only a minority of plant viruses have other types of genomes. After induction has occurred the temperate phage can proceed through a lytic cycle and then undergo lysogeny in a newly infected cell (see Figure 6.8). Some viruses reproduce using both methods, while others only use the lytic cycle. To liberate free phages, the bacterial cell wall is disrupted by phage proteins such as holin or lysozyme. His condition had deteriorated and additional blood tests confirmed that he has been infected with the Ebola virus. In the lytic cycle, the phage replicates and lyses the host cell. The cI protein is a repressor, and it will prevent the lytic genes from being transcribed. Ebola, also known as Ebola virus disease (EVD), is a severe and often deadly illness caused by the Ebola virus. Which phage life cycle is associated with which forms of transduction? The Ebola virus must enter a living cell and take over its mechanism to produce new viral particles. Release Viral particles start to "bud off", where the plasma membrane wraps them until they protrude and pinch off from the cell surface. During the initial stage, an inoculum of virus causes infection. Depending on the clinical care and the patient's immune system, it may vary from 25% to 90%. This book uses the If a genome is ssDNA, host enzymes will be used to synthesize a second strand that is complementary to the genome strand, thus producing dsDNA. This is usually called a lytic infection and this type of infection is seen with influenza and polio. Further investigations revealed that Duncan had just returned from Liberia, one of the countries in the midst of a severe Ebola epidemic. The RdRP is also an important enzyme for the replication of dsRNA viruses, because it uses the negative strand of the double-stranded genome as a template to create +ssRNA. Such an occurrence is called a burst, and the number of virions per bacterium released is described as the burst size. Latent viruses may remain dormant by existing as circular viral genome molecules outside of the host chromosome. The RdRP is brought in by the virus and can be used to make +ssRNA from the original ssRNA genome. The lytic pathway kills the host cell when newly made bacteriophages are released. Some viruses carry out this process without destroying the cell. are licensed under a, Unique Characteristics of Prokaryotic Cells, Unique Characteristics of Eukaryotic Cells, Prokaryote Habitats, Relationships, and Microbiomes, Nonproteobacteria Gram-Negative Bacteria and Phototrophic Bacteria, Isolation, Culture, and Identification of Viruses, Using Biochemistry to Identify Microorganisms, Other Environmental Conditions that Affect Growth, Using Microbiology to Discover the Secrets of Life, Structure and Function of Cellular Genomes, How Asexual Prokaryotes Achieve Genetic Diversity, Modern Applications of Microbial Genetics, Microbes and the Tools of Genetic Engineering, Visualizing and Characterizing DNA, RNA, and Protein, Whole Genome Methods and Pharmaceutical Applications of Genetic Engineering, Using Physical Methods to Control Microorganisms, Using Chemicals to Control Microorganisms, Testing the Effectiveness of Antiseptics and Disinfectants, History of Chemotherapy and Antimicrobial Discovery, Fundamentals of Antimicrobial Chemotherapy, Testing the Effectiveness of Antimicrobials, Current Strategies for Antimicrobial Discovery, Virulence Factors of Bacterial and Viral Pathogens, Virulence Factors of Eukaryotic Pathogens, Major Histocompatibility Complexes and Antigen-Presenting Cells, Laboratory Analysis of the Immune Response, Polyclonal and Monoclonal Antibody Production, Anatomy and Normal Microbiota of the Skin and Eyes, Bacterial Infections of the Skin and Eyes, Protozoan and Helminthic Infections of the Skin and Eyes, Anatomy and Normal Microbiota of the Respiratory Tract, Bacterial Infections of the Respiratory Tract, Viral Infections of the Respiratory Tract, Anatomy and Normal Microbiota of the Urogenital Tract, Bacterial Infections of the Urinary System, Bacterial Infections of the Reproductive System, Viral Infections of the Reproductive System, Fungal Infections of the Reproductive System, Protozoan Infections of the Urogenital System, Anatomy and Normal Microbiota of the Digestive System, Microbial Diseases of the Mouth and Oral Cavity, Bacterial Infections of the Gastrointestinal Tract, Viral Infections of the Gastrointestinal Tract, Protozoan Infections of the Gastrointestinal Tract, Helminthic Infections of the Gastrointestinal Tract, Circulatory and Lymphatic System Infections, Anatomy of the Circulatory and Lymphatic Systems, Bacterial Infections of the Circulatory and Lymphatic Systems, Viral Infections of the Circulatory and Lymphatic Systems, Parasitic Infections of the Circulatory and Lymphatic Systems, Fungal and Parasitic Diseases of the Nervous System, Fundamentals of Physics and Chemistry Important to Microbiology, Taxonomy of Clinically Relevant Microorganisms. Ebola is a lytic virus - it reproduces due to the lytic cycle. Its like a teacher waved a magic wand and did the work for me. Once a person becomes infected with HIV, the virus can be detected in tissues continuously thereafter, but untreated patients often experience no symptoms for years. Ebola, also known as Ebola virus disease (EVD), is a type of hemorrhagic fever. Examples of viruses that cause latent infections include herpes simplex virus (oral and genital herpes), varicella-zoster virus (chickenpox and shingles), and Epstein-Barr virus (mononucleosis). A prime example of a phage with this type of life cycle is the lambda phage. 0:11 And that's what we're going to talk about. Since the phage is integrated into the host genome, the prophage can replicate as part of the host. (credit: modification of work by Randal J. Schoepp), World Health Organization. 1: Lytic versus lysogenic cycle: A temperate bacteriophage has both lytic and lysogenic cycles. Is it ethical to treat untested drugs on patients with Ebola? The integrated phage genome is called a prophage. citation tool such as, Authors: Nina Parker, Mark Schneegurt, Anh-Hue Thi Tu, Philip Lister, Brian M. Forster. A patient may be unaware that he or she is carrying the virus unless a viral diagnostic test has been performed. For further reading on the steps of the Lytic process, check out this article on Libretexts. Lysogenic conversion is a process in which a non-virulent bacteria becomes a highly virulent pathogen by incorporating virulence factors carried on a lysogenic prophage. A chronic infection is a disease with symptoms that are recurrent or persistent over a long time. Duncan could conceivably have transmitted the disease to others at any time after he began having symptoms, presumably some time before his arrival at the hospital in Dallas. None contracted the disease. Later that month, the WHO released a report on the ethics of treating patients with the drug. The role of viruses in disease For the following scenarios, determine if the virus causing the disease is generally in a lytic cycle or a lysogenic cycle. Does Ebola go through the lysogenic life cycle or lytic life cycle? This means that once it enters a host cell, it begins using the cell's energy and resources to make copies of itself, eventually causing the host cell to burst and release new virus particles. This corresponds, in part, to the eclipse period in the growth of the virus population. There are three types of RNA genome: dsRNA, positive (+) single-strand (+ssRNA) or negative () single-strand RNA (ssRNA). Here is where the main difference between the two cycles occurs. In a lysogenic cycle, the phage genome also enters the cell through attachment and penetration. Used by viruses to replicate: the lytic process, check out this article on Libretexts his condition had and... With Ebola viral or host gene expressions or the alteration of the nucleic! 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