Lysogenic cycle is a rarer method of viral reproduction and depends largely upon the lytic cycle. HIV is an example of a virus that produces a chronic infection, often after a long period of latency. No approved treatments or vaccines for Ebola are available. If no viable host cells remain, the viral particles begin to degrade during the decline of the culture (see Figure 6.14). The RdRP is brought in by the virus and can be used to make +ssRNA from the original ssRNA genome. However, the virus maintains chronic persistence through several mechanisms that interfere with immune function, including preventing expression of viral antigens on the surface of infected cells, altering immune cells themselves, restricting expression of viral genes, and rapidly changing viral antigens through mutation. Here are some pictures to show you what these Ebola-like viruses look like: Measles is also a lytic disease - it infects animal cells, not bacteria. Enrolling in a course lets you earn progress by passing quizzes and exams. - Definition, Structure & Function, Shapes of a Virus: Helical, Icosahedral, Prolate, Complex & Enveloped, Classification of Viruses: Viral Genome and Replication Scheme, The Life Cycle of a Virus: How Viruses Live, Attack & Replicate, Lytic Cycle of a Virus: Definition & Steps, Lysogenic Cycle of a Virus: Definition & Steps, Ebola Virus Life Cycle: Definition & Stages, How Viruses Mutate: Antigenic Drift and Antigenic Shift, Prentice Hall Biology: Online Textbook Help, Praxis Family and Consumer Sciences (5122) Prep, College Chemistry: Homework Help Resource, SAT Subject Test Chemistry: Practice and Study Guide, ILTS Science - Environmental Science (112): Test Practice and Study Guide, Human Anatomy & Physiology: Help and Review, FTCE Middle Grades General Science 5-9 (004) Prep, Environmental Science 101: Environment and Humanity, Potassium Bromide: Formula & Side Effects, What is a Benign Tumor? 12 avril 2023 On September 15, nine days before he showed up at the hospital in Dallas, Duncan had helped transport an Ebola-stricken neighbor to a hospital in Liberia. The two primary categories of persistent infections are latent infection and chronic infection. The cI protein is a repressor, and it will prevent the lytic genes from being transcribed. 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). Finally, the new Ebola viruses are ready to travel throughout the body and infect new cells. Infection in the immune system's dendritic cells also means that the T lymphocytes do not signal the body of the infection, allowing the Ebola virus to replicate rapidly. Environmental stressors such as starvation or . Is RNA-dependent RNA polymerase made from a viral gene or a host gene? What aspect of the life cycle of a virus leads to the sudden increase in the growth curve? Medications for infections and management of blood pressure, fever, diarrhea, vomiting, and pain are also administered. In what two ways can a virus manage to maintain a persistent infection? Since Ebola can be serious, prevention is essential. Latent viruses may remain dormant by existing as circular viral genome molecules outside of the host chromosome. VP 30 is the viral protein encoded in the RNA of the Ebola virus and is necessary for its replication and transcription. Not all animal viruses undergo replication by the lytic cycle. If a virus has a +ssRNA genome, it can be translated directly to make viral proteins. The Zaire ebolavirus, more commonly known as the Ebola virus, was linked to severe EVD outbreaks such as the 1976 viral hemorrhagic fever outbreak in Sudan and Congo. The virulence genes can be carried within prophages as autonomous genetic elements called morons, which confers an advantage to the bacteria and indirectly benefits the virus through enhanced lysogen survival. The pathogen genome replicates and the host cell's metabolic machinery is used to synthesize enzymes and structural components. T-even phage is a good example of a well-characterized class of virulent phages. They are then transported to the budding sites in the cell membrane. The dsDNA can now be replicated, transcribed, and translated similar to host DNA. Ebola Vaccine. This unique recognition can be exploited for targeted treatment of bacterial infection by phage therapy or for phage typing to identify unique bacterial subspecies or strains. 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. - Definition, Types & Properties, Aluminum Hydroxide: Formula & Side Effects, Soil Contamination: Treatment, Phytoremediation & Bioremediation, Working Scholars Bringing Tuition-Free College to the Community. Filoviruses such as Ebola and Marburg only use the lytic cycle for replication, targeting and destroying epithelial cells, which contributes to the severity of the disease. No approved treatments or vaccines for Ebola are available. The lysogenic cycle is a viral replication cycle in which the viral DNA or RNA enters a host cell and incorporates itself into the host DNA as a new set of genes known as prophage. The first symptoms are usually fever, sore throat, muscle pain, and headaches. However, some conditions (e.g., ultraviolet light exposure or chemical exposure) stimulate the prophage to undergo induction, causing the phage to excise from the genome, enter the lytic cycle, and produce new phages to leave host cells. The combined damage of the Ebola virus may result in organ failure, septic shock, and death. The lysogenic cycle involves the incorporation of the viral genome into the host cell genome, infecting it from within. Later that month, the WHO released a report on the ethics of treating patients with the drug. Most phages have a narrow host range and may infect one species of bacteria or one strain within a species. There are currently no approved vaccines or antiviral treatments for either virus, but research into potential treatments and preventative measures is ongoing. In the lytic cycle, the phage replicates and causes the host cell to lyse, meaning the host cell dies. Uncoating and fusion The viral membrane fuses with the host cell's vesicle membrane, and the nucleocapsid is released into the cell's cytoplasm. Viral infection can be asymptomatic (latent) or can lead to cell death (lytic infection). Lytic animal viruses follow similar infection stages to bacteriophages: attachment, penetration, biosynthesis, maturation, and release (see Figure 6.10). However, if a virus contains a ssRNA genome, the host ribosomes cannot translate it until the ssRNA is replicated into +ssRNA by viral RNA-dependent RNA polymerase (RdRP) (see Figure 6.11). Ebola virus is one of the species within the genus Ebolavirus and family Filoviridae, characterized by the long, single-stranded, and filamentous negative-sense RNA (ribonucleic acid) viruses. In August 2014, two infected US aid workers and a Spanish priest were treated with ZMapp, an unregistered drug that had been tested in monkeys but not in humans. Electron micrograph of a complete Ebola virus particle. Which phage life cycle is associated with which forms of transduction? If you travel, be aware of CDC updates on Ebola outbreaks. Viruses cannot replicate on their own. (credit a: modification of work by Erskine Palmer and B.G. 1. lysogenic The virus herpes type I, or HSV-1, causes cold sores. 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. 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. After induction has occurred the temperate phage can proceed through a lytic cycle and then undergo lysogeny in a newly infected cell (see Figure \(\PageIndex{2}\)). Whereas chickenpox affects many areas throughout the body, shingles is a nerve cell-specific disease emerging from the ganglia in which the virus was dormant. The process in which a bacterium is infected by a temperate phage is called lysogeny. Since the DNA transferred by the phage is not randomly packaged but is instead a specific piece of DNA near the site of integration, this mechanism of gene transfer is referred to as specialized transduction (see Figure 6.9). 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. Polymerase genes are usually expressed early in the cycle, while capsid and tail proteins are expressed later. Legal. During the eclipse phase, Duncan would have been unable to transmit the disease to others. One of the interesting things about the Ebola virus is its ability to replicate through the lytic cycle, a mechanism of virus replication that uses the host cell to produce new copies of viral particles and destroy the host cell's DNA. During this time, the virus does not kill the nerve cells or continue replicating. To establish a systemic infection, the virus must enter a part of the vascular system of the plant, such as the phloem. An important exception that will be highlighted later is Influenza virus. A patient may be unaware that he or she is carrying the virus unless a viral diagnostic test has been performed. The presence of the phage may alter the phenotype of the bacterium, since it can bring in extra genes (e.g., toxin genes that can increase bacterial virulence). She is a licensed teacher and has taught Grade 10 Physics for three years. However, some viruses destroy host cells as a means of release. The lysogenic cycle, or non-virulent infection, involves the virus assimilating its genome with the host cell's genome to achieve replication without killing the host. Some may have more than one host. She has been a science content writer and copywriter for over three years now. . 1999-2023, Rice University. The genus Ebolavirus consists of six species, but only four have been known to cause human disease: Zaire ebolavirus, Sudan ebolavirus, Tai Forest ebolavirus, and Bundibugyo ebolavirus. This is called lysis and provides the name of the 'lytic cycle'. Mechanisms of persistent infection may involve the regulation of the viral or host gene expressions or the alteration of the host immune response. His condition had deteriorated and additional blood tests confirmed that he has been infected with the Ebola virus. In the lysogenic cycle, phage DNA is incorporated into the host genome, forming a prophage, which is passed on to subsequent generations of cells. Its like a teacher waved a magic wand and did the work for me. The phage head and remaining components remain outside the bacteria. The provirus stage is similar to the prophage stage in a bacterial infection during the lysogenic cycle. In this minireview we consider the diversity of phage types as based on potential infection strategies, particularly productive or lysogenic along with lytic release versus chronic release, with emphasis on what major variants should be called (see Table 1 for glossary of terms). Except where otherwise noted, textbooks on this site All rights reserved. Attachment It attaches itself to a receptor on the host cell membrane using glycoprotein. For further reading on the steps of the Lytic process, check out this article on Libretexts. In the lytic cycle, the phage replicates and lyses the host cell. Virulent phages typically lead to the death of the cell through cell lysis. The lytic cycle, or virulent infection, involves a virus taking control of a host cell and using it to produce its viral progeny, killing the host in the process. On the other hand, is it ethical to withhold potentially life-saving drugs from dying patients? 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. then you must include on every digital page view the following attribution: Use the information below to generate a citation. Despite these experimental drugs and vaccines, there is still no cure for EVD. The underlying mechanism has to do with a protein cascade involving either the cro or cI protein that is encoded by the virus. Only a minority of plant viruses have other types of genomes. The one-step multiplication curve for a bacteriophage population follows three steps: 1) inoculation, during which the virions attach to host cells; 2) eclipse, during which entry of the viral genome occurs; and 3) burst, when sufficient numbers of new virions are produced and emerge from the host cell. Viruses of the Ebolavirus genus cause sporadic epidemics of severe and systemic febrile disease that are fueled by human-to-human transmission. Virulent phages typically lead to the death of the cell through cell lysis. After examination, an emergency department doctor diagnosed him with sinusitis, prescribed some antibiotics, and sent him home. 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