Additionally, certain bacteria can become virulent through lysogenic conversion with the virulence factors carried on the lysogenic prophage, but this is not known to occur with Ebola. 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 . 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). The Ebola virus begins. Temperate viruses, such as bacteriophages, can undergo both lysogenic and lytic cycles, while virulent viruses only replicate via the lytic cycle. 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. Not all animal viruses undergo replication by the lytic cycle. 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). Once inserted, the viral genome is known as a prophage. 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. 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. The LibreTexts libraries arePowered by NICE CXone Expertand 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. 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. None contracted the disease. Since Ebola can be serious, prevention is essential. Viruses capable of latency may initially cause an acute infection before becoming dormant. No approved treatments or vaccines for Ebola are available. 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. 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. 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. Later that month, the WHO released a report on the ethics of treating patients with the drug. In the lysogenic cycle, phage DNA is incorporated into the host genome, forming a prophage, which is passed on to subsequent generations of cells. 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. To liberate free phages, the bacterial cell wall is disrupted by phage proteins such as holin or lysozyme. In the lysogenic cycle, the DNA is only replicated, not translated into proteins. If the viral genome is RNA, a different mechanism must be used. This corresponds, in part, to the eclipse period in the growth of the virus population. As a result of its lytic cycle, the phage replicates and lyses the bacteria on host cells. 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. However, the host cell has a mechanism to allow nutrients to enter, which the Ebola virus uses to attach and enter the cell. Once the viral DNA has been inserted into the cell, the host is now said to be infected. Plant viruses may have a narrow or broad host range. As the bacterium replicates its chromosome, it also replicates the phages DNA and passes it on to new daughter cells during reproduction. To unlock this lesson you must be a Study.com Member. The immune system becomes overwhelmed and is unable to fight off the infection. Some bacteria, such as Vibrio cholerae and Clostridium botulinum, are less virulent in the absence of the prophage. 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). As an Amazon Associate we earn from qualifying purchases. Ebola virus causes the rare but deadly Ebola Virus Disease (EVD). The newly synthesized +ssRNA copies can then be translated by cellular ribosomes. The second stage of infection is entry or penetration. Most phages have a narrow host range and may infect one species of bacteria or one strain within a species. Once the Ebola virus enters the cell, unknown factors trigger the uncoating of the nucleocapsids enveloping the viral RNA. 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. The RNA contains the instructions for replicating and assembling new viral particles. Environmental stressors such as starvation or exposure to toxic chemicals may cause the prophage to be excised and enter the lytic cycle. 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. 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. 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. Bacteriophages inject DNA into the host cell, whereas animal viruses enter by endocytosis or membrane fusion. The underlying mechanism has to do with a protein cascade involving either the cro or cI protein that is encoded by the virus. The phage head and remaining components remain outside the bacteria. A chronic infection is a disease with symptoms that are recurrent or persistent over a long time. 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 virus life cycle is complete when it is transmitted from an infected plant to a healthy plant. After examination, an emergency department doctor diagnosed him with sinusitis, prescribed some antibiotics, and sent him home. They are then transported to the budding sites in the cell membrane. 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. Ebola, also known as Ebola virus disease (EVD), is a type of hemorrhagic fever. The incubation time for Ebola ranges from 2 days to 21 days. then you must include on every digital page view the following attribution: Use the information below to generate a citation. During the initial stage, an inoculum of virus causes 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. Legal. RNA viruses can contain +ssRNA that can be directly read by the ribosomes to synthesize viral proteins. The lysogenic cycle involves the incorporation of the viral genome into the host cell genome, infecting it from within. 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. Ebola virus is transmitted through direct contact with droplets of bodily fluids such as saliva, blood, and vomit. 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. Viruses capable of latency may initially cause an acute infection before becoming dormant. We will also explore the impact of the lytic replication cycle on the host cells and the severity of the disease. During the eclipse phase, Duncan would have been unable to transmit the disease to others. In the lysogenic cycle, the DNA is only replicated, not translated into proteins. The hospital continued to treat Duncan, but he died several days after being admitted. There are five stages in the bacteriophage lytic cycle (see Figure \(\PageIndex{1}\)). 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. This occurs through contraction of the tail sheath, which acts like a hypodermic needle to inject the viral genome through the cell wall and membrane. 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. 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). Assembly Viral particles accumulate in the region near the nucleus and form helical nucleocapsids with the aid of several proteins. Note that in this example the pathogen is shown as a bacteriophage, which infects a bacterium. One of the therapeutic targets considered is the use of small fragments of genetic material called small-interfering RNAs (siRNAs) to inhibit the virus replication process. Ebola, however, only goes through the lytic cycle - not the lysogenic cycle. Some viruses reproduce using both methods, while others only use the lytic cycle. However, most plant viruses do not have a DNA genome; the majority have a +ssRNA genome, which acts like messenger RNA (mRNA). Is a latent phage undetectable in a bacterium? 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 viral protein 30 (VP30) plays a significant role in initiating transcription at the nucleoprotein gene. The phage and host DNA from one end or both ends of the integration site are packaged within the capsid and are transferred to the new, infected host. 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. Lytic and Lysogenic Cycles of a bacteriophage: A temperate bacteriophage can go through both lytic and lysogenic cycles. This is usually called a lytic infection and this type of infection is seen with influenza and polio. Others become proviruses by integrating into the host genome. The outbreak in West Africa in 2014 was unprecedented, dwarfing other human Ebola epidemics in the level of mortality. In the eclipse phase, viruses bind and penetrate the cells with no virions detected in the medium. The regulation of gene expression in phages is all about how the lytic cycle gets switched to the lysogenic cycle and vice-versa. 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. After binding to host receptors, animal viruses enter through endocytosis (engulfment by the host cell) or through membrane fusion (viral envelope with the host cell membrane). 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. Figure 21.2 B. To establish a systemic infection, the virus must enter a part of the vascular system of the plant, such as the phloem. A patient may be unaware that he or she is carrying the virus unless a viral diagnostic test has been performed. 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). In a lysogenic cycle, the phage genome also enters the cell through attachment and penetration. Not only are these drugs untested or unregistered but they are also in short supply. 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. This situation is an example of compassionate use outside the well-established system of regulation and governance of therapies. She has been a science content writer and copywriter for over three years now. They must enter a living cell and hijack its machinery to create new viral particles. Filoviruses, including the Ebola virus, are transmitted through direct contact with bodily fluids from infected patients or other species (e.g., gorillas and chimpanzees). Similar to the lytic cycle, it begins with the attachment and penetration of the virus. Symptoms typically start anywhere between two days and three weeks after infection. Ebola - spread by blood and body fluids, reservoir unknown; . negative () single-strand RNA (ssRNA). OpenStax is part of Rice University, which is a 501(c)(3) nonprofit. The final stage is release. Virulent phages typically lead to the death of the cell through cell lysis. The virus is responsible for causing outbreaks in several African countries, with the most recent outbreak occurring in Uganda in 2022. Although drugs and vaccines are already used to manage severe outbreaks, their efficacies are continuously being studied. (credit: modification of work by NIAID, NIH), (a) Varicella-zoster, the virus that causes chickenpox, has an enveloped icosahedral capsid visible in this transmission electron micrograph. Persistent infection occurs when a virus is not completely cleared from the system of the host but stays in certain tissues or organs of the infected person. It can switch between the lytic cycle and the lysogenic cycle. 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, During the initial stage, an inoculum of virus causes infection. Since the phage is integrated into the host genome, the prophage can replicate as part of the host. While some drugs have shown potential in laboratory studies and animal models, they have not been tested in humans for safety and effectiveness. The newly synthesized +ssRNA copies can then be translated by cellular ribosomes. 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. Not only are these drugs untested or unregistered but they are also in short supply. 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. It is typical of temperate phages to be latent or inactive within the cell. Plant viruses are more similar to animal viruses than they are to bacteriophages. The Ebola virus life cycle is divided into several stages: Experts continue to study the different stages of the Ebola life cycle to understand its mechanisms and find viable therapeutic targets. Ebola is incurable and deadly. However, some viruses destroy host cells as a means of release. Entry The cell then engulfs the virus through the process called. During the lytic cycle of viral replication, the virus hijacks the host cell, degrades the host chromosome, and makes more viral genomes. The hospital continued to treat Duncan, but he died several days after being admitted. Plant viruses may be enveloped or non-enveloped. Phage microbiologists discovered decades ago that lysogenic phages . Transduction seems to play an important role in the evolutionary process of bacteria, giving them a mechanism for asexual exchange of genetic information. In the lytic cycle, the DNA is multiplied many times and proteins are formed using processes stolen from the bacteria. A virus in the. The timeline of the Duncan case is indicative of the life cycle of the Ebola virus. The Ebola virus causes the rare and deadly Ebola Virus Disease (EVD), which has an average case fatality of 50%. If you travel, be aware of CDC updates on Ebola outbreaks. While some drugs have shown potential in laboratory studies and animal models, they have not been tested in humans for safety and effectiveness. What aspect of the life cycle of a virus leads to the sudden increase in the growth curve? Typically, viruses can undergo two types of DNA replication: the lysogenic cycle or the lytic cycle. 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). Accessibility StatementFor more information contact us atinfo@libretexts.orgor check out our status page at https://status.libretexts.org. 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