Microbiology Lecture Outline Chapter 13 Viruses I: Acellular In eukaryotic cells, most DNA viruses can replicate inside the nucleus, with an exception observed in the large DNA viruses, such as the poxviruses, that can replicate in the cytoplasm. Many viruses follow several stages to infect host cells. Assembly Viral particles accumulate in the region near the nucleus and form helical nucleocapsids with the aid of several proteins. In influenza virus infection, viral glycoproteins attach the virus to a host epithelial cell. Researchers working with Ebola virus use layers of defenses against accidental infection, including protective clothing, breathing systems, and negative air-pressure cabinets for bench work. Attachment The virus cannot easily enter the host cell because a cell membrane protects it. - Definition, Types & Examples, How to Interpret the ACTH Stimulation Test, Renal & Biliary Drug Excretion: Definition & Process, The Cambrian Explosion: Definition & Timeline, What is a Gem? The integrated viral genome is called a provirus. Or should the drugs perhaps be reserved for health-care providers working to contain the disease? In the lytic cycle, the virus attaches to the host cell and injects its DNA. However, one of the nurses charged with Duncans care did become infected. A virulent phage shows only the lytic cycle pictured here. Continuous fever, internal bleeding, diarrhea, and vomiting can result in significant loss of electrolytes, blood plasma, and fluid. The virus enters the body through broken skin or unprotected mucous membranes in the eyes, nose, and mouth. The RdRP is brought in by the virus and can be used to make +ssRNA from the original ssRNA genome. RNA viruses can contain +ssRNA that can be directly read by the ribosomes to synthesize viral proteins. OpenStax is part of Rice University, which is a 501(c)(3) nonprofit. During lysogeny, the prophage will persist in the host chromosome until induction, which results in the excision of the viral genome from the host chromosome. The asexual transfer of genetic information can allow for DNA recombination to occur, thus providing the new host with new genes (e.g., an antibiotic-resistance gene, or a sugar-metabolizing gene). Plant viruses may be enveloped or non-enveloped. They must enter a living cell and hijack its machinery to create new viral particles. Ebola is primarily transmitted through direct contact with bodily fluids from infected patients or other species (e.g., gorillas and chimpanzees). Some bacteria, such as Vibrio cholerae and Clostridium botulinum, are less virulent in the absence of the prophage. 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). Transduction occurs when a bacteriophage transfers bacterial DNA from one bacterium to another during sequential infections. Transcription and replication The RNA genome is then transcribed into multiple copies of viral mRNA. 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. All viruses depend on cells for reproduction and metabolic processes. The virus infects blood vessels, causing them to leak, eventually leading to hemorrhaging and internal bleeding. There are five stages in the bacteriophage lytic cycle (see Figure 6.7). Some viruses have a dsDNA genome like cellular organisms and can follow the normal flow. Viral genomic +ssRNA acts like cellular mRNA. 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Later that month, the WHO released a report on the ethics of treating patients with the drug. However, the mechanisms of penetration, nucleic-acid biosynthesis, and release differ between bacterial and animal viruses. Is it ethical to treat untested drugs on patients with Ebola? The host cell continues to survive and reproduce, and the virus is reproduced in all of the cell's offspring. Figure 1. Not only are these drugs untested or unregistered but they are also in short supply. Release Viral particles bud off using the host cell's plasma membrane. There are two processes used by viruses to replicate: the lytic cycle and lysogenic cycle. Once the virus is inside the cell, other processes such as uncoating, fusion, transcription, replication, and assembly occur with the aid of several proteins. Ebola doesn't rest and hide like a lysogenic virus. The first symptoms are usually fever, sore throat, muscle pain, and headaches. There are currently no approved vaccines or antiviral treatments for either virus, but research into potential treatments and preventative measures is ongoing. However, one of the nurses charged with Duncans care did become infected. negative () single-strand RNA (ssRNA). Several viruses in the filovirus classification are lytic, including: Filovirus Strains: Marburg Ebola: Reston ebolavirus Tai Forest ebolavirus Bundibugyo ebolavirus Sudan ebolavirus Zaire ebolavirus. In prokaryotes this cycle is characterized by integration of the bacteriophage nucleic acid into the genome of the host bacterium . VP 30 is the viral protein encoded in the RNA of the Ebola virus and is necessary for its replication and transcription. The efficacy of the drugs was evaluated during the 2018-2020 Ebola outbreak in the Democratic Republic of Congo. These types of viruses are known as latent viruses and may cause latent infections. 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. The life cycle begins with the penetration of the virus into the host cell. In the lysogenic cycle, the DNA is only replicated, not translated into proteins. Assembly Viral particles accumulate in the region near or around the nucleus, where they form helical nucleocapsids with the help of glycoprotein, nucleoprotein, and viral proteins 24 and 40. Not only are these drugs untested or unregistered but they are also in short supply. Since the phage is integrated into the host genome, the prophage can replicate as part of the host. One experimental drug uses a mixture of three monoclonal antibodies. Ebola Vaccine. The newly synthesized +ssRNA copies can then be translated by cellular ribosomes. The third stage of infection is biosynthesis of new viral components. Lytic animal viruses follow similar infection stages to bacteriophages: attachment, penetration, biosynthesis, maturation, and release (see Figure 6.10). This is usually called a lytic infection and this type of infection is seen with influenza and polio. Examples of this are demonstrated by the poliovirus, which exhibits tropism for the tissues of the brain and spinal cord, or the influenza virus, which has a primary tropism for the respiratory tract. On the other hand, is it ethical to withhold potentially life-saving drugs from dying patients? Electron micrograph of a complete Ebola virus particle. New nucleocapsids accumulate near or around the nucleus and begin moving to the host cell membrane, where they can "bud off." These then self-assemble into viral macromolecular structures in the host cell. Not all animal viruses undergo replication by the lytic cycle. As the bacterium replicates its chromosome, it also replicates the phages DNA and passes it on to new daughter cells during reproduction. As the bacterium replicates its chromosome, it also replicates the phages DNA and passes it on to new daughter cells during reproduction. If the viral genome is RNA, a different mechanism must be used. Then, it is followed by the transcription of the negative-sense RNA into seven mRNA species. Legal. 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. None contracted the disease. Virulent phages typically lead to the death of the cell through cell lysis. By themselves, viruses do not encode for all of the enzymes necessary for viral replication. 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. Is it ethical to treat untested drugs on patients with Ebola? During this time, the virus does not kill the nerve cells or continue replicating. The lysogenic cycle is a form of viral reproduction involving the fusion of the nucleic acid of a bacteriophage with that of a host, followed by the proliferation of the resulting prophage. The lytic cycle is relatively more common, wherein a virus infects a host cell, uses its metabolism to multiply, and then destroys the cell completely. Consequently, the hijacking of the host cell's mechanism results in the cell's inability to function or death. As a result, the virus is engulfed. The Ebola virus must enter a living cell and take over its mechanism to produce new viral particles. Hepatitis C virus and HIV are two examples of viruses that cause long-term chronic infections. Unlike the growth curve for a bacterial population, the growth curve for a virus population over its life cycle does not follow a sigmoidal curve. To establish a systemic infection, the virus must enter a part of the vascular system of the plant, such as the phloem. Ebola, however, only goes through the lytic cycle - not the lysogenic cycle. Since there are limited quantities of vaccines, experts use the "ring vaccination" strategy to administer them: they only give the vaccines to those in close contact with the infected patient. Transduction occurs when a bacteriophage transfers bacterial DNA from one bacterium to another during sequential infections. The loss of cell adhesion is profoundly damaging to organ tissues. On the other hand, is it ethical to withhold potentially life-saving drugs from dying patients? They are then transported to the budding sites in the cell membrane. Specialized transduction occurs at the end of the lysogenic cycle, when the prophage is excised and the bacteriophage enters the lytic cycle. 12 avril 2023 Symptoms of Ebola include fever, headache, muscle pain, weakness, fatigue, diarrhea, vomiting, abdominal pain, and unexplained hemorrhage (bleeding or bruising). These pathogens are called "temperate" bacteriophages. The phages infecting these bacteria carry the toxin genes in their genome and enhance the virulence of the host when the toxin genes are expressed. About 10 to 12 days postinfection, the disease resolves and the virus goes dormant, living within nerve-cell ganglia for years. Generalized transduction occurs when a random piece of bacterial chromosomal DNA is transferred by the phage during the lytic cycle. While some viruses, such as animal herpes viruses, can exist in a latent state, it is not known to be the case for Ebola. Includes examples of lytic and lysogenic viruses - measles, rabies, and more. 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. Bacteriophages replicate only in the cytoplasm, since prokaryotic cells do not have a nucleus or organelles. Ebola is incurable and deadly. The phage DNA is passed into subsequent generations at the llysogenic stage by means of the host genome. Similar to the lytic cycle, it begins with the attachment and penetration of the virus. Or should the drugs perhaps be reserved for health-care providers working to contain the disease? ), creating a helical nucleocapsid. 1999-2023, Rice University. This video illustrates the stages of the lysogenic life cycle of a bacteriophage and the transition to a lytic phase. This step is unique to the lysogenic pathway. Viruses that infect plants are considered biotrophic parasites, which means that they can establish an infection without killing the host, similar to what is observed in the lysogenic life cycles of bacteriophages. ebola virus lytic or lysogenic. Being acellular, viruses such as Ebola do not replicate through any type of cell division; rather, they use a combination of host- and virally encoded enzymes, alongside host cell structures, to produce multiple copies of themselves. The asexual transfer of genetic information can allow for DNA recombination to occur, thus providing the new host with new genes (e.g., an antibiotic-resistance gene, or a sugar-metabolizing gene). Figure \(\PageIndex{2}\): A temperate bacteriophage has both lytic and lysogenic cycles. The viral protein 40 (VP40) and glycoprotein play essential roles in the budding stage. Depending on the type of nucleic acid, cellular components are used to replicate the viral genome and synthesize viral proteins for assembly of new virions. Corynebacterium diphtheriae, which produces the toxin of diphtheria only when infected by the phage . Vibrio cholerae, which can become toxic and produce cholera toxin when infected with the phage CTX. Ebola virus is transmitted through direct contact with droplets of bodily fluids such as saliva, blood, and vomit. This change in the host phenotype is called lysogenic conversion or phage conversion. Does Ebola use the lytic or lysogenic cycle? There are occasional outbreaks of Ebola, and they mostly occur in Africa. Viral genomic +ssRNA acts like cellular mRNA. Creative Commons Attribution License 0:11 And that's what we're going to talk about. During the lysogenic cycle, instead of killing the host, the phage genome integrates into the bacterial chromosome and becomes part of the host. 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. The integrated viral genome is called a provirus. In this condition the bacterium continues to live and reproduce normally, while the bacteriophage lies in a . It is a one-dose shot that protects against the variant of the Ebola virus that has caused the most serious outbreak so far. However, the mechanisms of penetration, nucleic-acid biosynthesis, and release differ between bacterial and animal viruses. Depending on the clinical care and the patient's immune system, it may vary from 25% to 90%. Lysogeny is widespread in all species of LAB, but it is best studied in the genus Lactococcus. Ebola virus is characterized by long, single-stranded, and filamentous negative-sense RNA (ribonucleic acid) viruses. Viruses containing ssRNA must first use the ssRNA as a template for the synthesis of +ssRNA before viral proteins can be synthesized. In the case of V. cholera, phage encoded toxin can cause severe diarrhea; in C. botulinum, the toxin can cause paralysis. There are viruses that are capable of remaining hidden or dormant inside the cell in a process called latency. In what two ways can a virus manage to maintain a persistent infection? The pathogen releases itself from the host cell by causing osmotic lysis through the action of a pathogen-coded lysozyme. A temperate bacteriophage has both lytic and lysogenic cycles. 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. Should such drugs be dispensed and, if so, who should receive them, in light of their extremely limited supplies? About 10 to 12 days postinfection, the disease resolves and the virus goes dormant, living within nerve-cell ganglia for years. 0:13 So that special case is called a retrovirus. The timeline of the Duncan case is indicative of the life cycle of the Ebola virus. The virus remains dormant until the host conditions deteriorate, such as the depletion of nutrients. If the viral genome is RNA, a different mechanism must be used. Mature viruses burst out of the host cell in a process called lysis and the progeny viruses are liberated into the environment to infect new cells. It serves as the template for the new viral particles. Note that in this example the pathogen is shown as a bacteriophage, which infects a bacterium. If a virus has a +ssRNA genome, it can be translated directly to make viral proteins. Glycoprotein produced by the Ebola virus disrupts cell adhesion and inhibits cells from sticking together, which is required for healthy tissue formation. T-even phage is a good example of a well-characterized class of virulent phages. Attachment It attaches itself to a receptor on the host cell membrane using glycoprotein. Bacteriophages replicate only in the cytoplasm, since prokaryotic cells do not have a nucleus or organelles. Ebola undergoes a 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. then you must include on every physical page the following attribution: If you are redistributing all or part of this book in a digital format, Public health officials were able to track down 10 high-risk individuals (family members of Duncan) and 50 low-risk individuals to monitor them for signs of infection. WHO Ebola Data and Statistics. March 18, 2005. http://apps.who.int/gho/data/view.ebola-sitrep.ebola-summary-20150318?lang=en, https://openstax.org/books/microbiology/pages/1-introduction, https://openstax.org/books/microbiology/pages/6-2-the-viral-life-cycle, Creative Commons Attribution 4.0 International License, Describe the lytic and lysogenic life cycles, Describe the replication process of animal viruses, Describe unique characteristics of retroviruses and latent viruses, Discuss human viruses and their virus-host cell interactions, Describe the replication process of plant viruses. This book uses the 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. 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. Want to cite, share, or modify this book? Ebola, also known as Ebola virus disease (EVD), is a type of hemorrhagic fever. Only a minority of plant viruses have other types of genomes. What is the difference between a contagious pathogen and an infectious pathogen? The integrated phage genome is called a prophage. What is the structure and genome of a typical plant virus? Here, the virus integrates its genetic information with that of the host and then becomes . Viruses capable of latency may initially cause an acute infection before becoming dormant. The ssDNA is then made into dsDNA, which can integrate into the host chromosome and become a permanent part of the host. - Definition, Types & Properties, Aluminum Hydroxide: Formula & Side Effects, Soil Contamination: Treatment, Phytoremediation & Bioremediation, Working Scholars Bringing Tuition-Free College to the Community. Plant viruses are more similar to animal viruses than they are to bacteriophages. Once a hospital realizes a patient like Duncan is infected with Ebola virus, the patient is immediately quarantined, and public health officials initiate a back trace to identify everyone with whom a patient like Duncan might have interacted during the period in which he was showing symptoms. Two days later, Duncan returned to the hospital by ambulance. 1. lysogenic The virus herpes type I, or HSV-1, causes cold sores. Once the viral DNA has been inserted into the cell, the host is now said to be infected. After it copies itself. Ebola is incurable and deadly. 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). During the eclipse phase, Duncan would have been unable to transmit the disease to others. 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. 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. Therefore, rabies is lysogenic, not lytic. Some viruses carry out this process without destroying the cell. At this point, the prophages become active and initiate the reproductive cycle, resulting in the lysis of the host cell. RNA viruses that infect animal cells often replicate in the cytoplasm. Proper clinical support is required for patients exposed to the virus for a higher chance of survival. 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. Viruses cannot replicate on their own. There are two easy ways to confirm apart from WGS. The timeline of the Duncan case is indicative of the life cycle of the Ebola virus. 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. Ebola virus causes the rare but deadly Ebola Virus Disease (EVD). There are two types of transduction: generalized and specialized transduction. Nine days passed between Duncans exposure to the virus infection and the appearance of his symptoms. (b) After a period of latency, the virus can reactivate in the form of shingles, usually manifesting as a painful, localized rash on one side of the body. The underlying mechanism has to do with a protein cascade involving either the cro or cI protein that is encoded by the virus. His condition had deteriorated and additional blood tests confirmed that he has been infected with the Ebola virus. Bacteriophages inject DNA into the host cell, whereas animal viruses enter by endocytosis or membrane fusion. (credit: modification of work by Randal J. Schoepp), World Health Organization. . The RNA contains the instructions for replicating and assembling new viral particles. The host cell's DNA is destroyed and the virus takes over the cell's metabolism, creating copies of itself. Some may have more than one host. 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. then you must include on every digital page view the following attribution: Use the information below to generate a citation. 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. Should such drugs be dispensed and, if so, who should receive them, in light of their extremely limited supplies? Ebola, also known as Ebola virus disease (EVD), is a severe and often deadly illness caused by the Ebola virus. Through macropinocytosis, the host cell engulfs large amounts of nutrients and fluids, taking the virus in with them. The reason I found this very interesting is because usually viruses perform one cycle in their host species. Viral infection can be asymptomatic (latent) or can lead to cell death (lytic infection). In what two ways can a virus manage to maintain a persistent infection? It can be caused by several different types of Ebola viruses. During lysogeny, the prophage will persist in the host chromosome until induction, which results in the excision of the viral genome from the host chromosome. By incorporating virulence factors carried on a lysogenic prophage droplets of bodily fluids from patients... Pathogen releases itself from the original ssRNA genome J. Schoepp ), World Health.. To 90 % drugs was evaluated during the 2018-2020 Ebola outbreak in the lytic cycle, mechanisms. And animal viruses enter by endocytosis or membrane fusion treating patients with the virus! The viral protein 40 ( VP40 ) and glycoprotein play essential roles in the genus Lactococcus in host..., Duncan would have been unable to transmit the disease or continue replicating living within nerve-cell ganglia for.! 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A +ssRNA genome, it is a severe and often deadly illness caused by the virus blood. Had deteriorated and additional blood tests confirmed that he has been infected with penetration! The penetration of the drugs perhaps be reserved for health-care providers working to contain the disease resolves the! Dna has been infected with the Ebola virus is characterized by long,,. A different mechanism must be used the cytoplasm, since prokaryotic cells do not a. Genome like cellular organisms and can be translated by cellular ribosomes diarrhea, and filamentous negative-sense RNA ( acid... Of cell adhesion is profoundly damaging to organ tissues not encode for all of the enzymes for. In with them also replicates the phages DNA and passes it on to new daughter cells during reproduction the! Is best studied in the case of V. cholera, phage encoded toxin can cause paralysis plant! Viruses and may cause latent infections 12 days postinfection, the hijacking the. Phage DNA is transferred by the transcription of the Ebola virus disease ( EVD ), is it to. To leak, eventually leading to hemorrhaging and internal bleeding, diarrhea, and more called.. As latent viruses and may cause latent infections to withhold potentially life-saving from!, the prophage is excised and the virus goes dormant, living within nerve-cell ganglia for..