After examination, an emergency department doctor diagnosed him with sinusitis, prescribed some antibiotics, and sent him home. Typically, viruses can undergo two types of DNA replication: the lysogenic cycle or the lytic cycle. Accessibility StatementFor more information contact us atinfo@libretexts.orgor check out our status page at https://status.libretexts.org. During the lytic cycle of virulent phage, the bacteriophage takes over the cell, reproduces new phages, and destroys the cell. This flowchart illustrates the mechanism of specialized transduction. In the eclipse phase, viruses bind and penetrate the cells with no virions detected in the medium. Once released, this virion will then inject the former hosts DNA into a newly infected host. 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. 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. 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. Lytic and Lysogenic Cycles of a bacteriophage: A temperate bacteriophage can go through both lytic and lysogenic cycles. However, unlike prophage, the provirus does not undergo excision after splicing into the genome. Ebola is incurable and deadly. The newly synthesized +ssRNA copies can then be translated by cellular ribosomes. This process can be as quick. This situation is an example of compassionate use outside the well-established system of regulation and governance of therapies. By the end of this section, you will be able to: All viruses depend on cells for reproduction and metabolic processes. Virulent strains are lytic. This causes the host cell or cells to burst. Create an account to start this course today. (credit: modification of work by Randal J. Schoepp), World Health Organization. There are viruses that are capable of remaining hidden or dormant inside the cell in a process called latency. 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. 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. A bacterial host with a prophage is called a lysogen. This is usually called a lytic infection and this type of infection is seen with influenza and polio. These are usually followed by vomiting, diarrhoea, rash and . Does Ebola go through the lysogenic life cycle or lytic life cycle? 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). The two primary categories of persistent infections are latent infection and chronic infection. The process in which a bacterium is infected by a temperate phage is called lysogeny. Such an occurrence is called a burst, and the number of virions per bacterium released is described as the burst size. In the lysogenic cycle, phage DNA is incorporated into the host genome, forming a prophage, which is passed on to subsequent generations of cells. The RdRP is brought in by the virus and can be used to make +ssRNA from the original ssRNA genome. Ebola Vaccine. During dormancy, viruses do not cause any symptoms of disease and may be difficult to detect. Transduction occurs when a bacteriophage transfers bacterial DNA from one bacterium to another during sequential infections. 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. These pathogens are called "temperate" bacteriophages. This step is unique to the lysogenic pathway. Ebola is a lytic virus - it reproduces due to the lytic cycle. Environmental stressors such as starvation or exposure to toxic chemicals may cause the prophage to be excised and enter the lytic cycle. Lytic animal viruses follow similar infection stages to bacteriophages: attachment, penetration, biosynthesis, maturation, and release (see Figure 6.10). Viral genomic +ssRNA acts like cellular mRNA. What types of training can prepare health professionals to contain emerging epidemics like the Ebola outbreak of 2014? Polymerase genes are usually expressed early in the cycle, while capsid and tail proteins are expressed later. On September 24, 2014, Thomas Eric Duncan arrived at the Texas Health Presbyterian Hospital in Dallas complaining of a fever, headache, vomiting, and diarrheasymptoms commonly observed in patients with the cold or the flu. The RdRP is brought in by the virus and can be used to make +ssRNA from the original ssRNA genome. 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. All rights reserved. Given the great suffering and high mortality rates, it is fair to ask whether unregistered and untested medications are better than none at all. The timeline of the Duncan case is indicative of the life cycle of the Ebola virus. As the bacterium replicates its chromosome, it also replicates the phage's DNA and passes it on to new daughter cells during reproduction. The lytic cycle is known as the active cycle, whereas the lysogenic cycle is the dormant phase of the virus. The hospital continued to treat Duncan, but he died several days after being admitted. Causes of Ebola. Lytic animal viruses follow similar infection stages to bacteriophages: attachment, penetration, biosynthesis, maturation, and release (see Figure \(\PageIndex{4}\)). Symptoms of Ebola include fever, headache, muscle pain, weakness, fatigue, diarrhea, vomiting, abdominal pain, and unexplained hemorrhage (bleeding or bruising). The two American aid workers recovered, but the priest died. This situation is an example of compassionate use outside the well-established system of regulation and governance of therapies. 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. No approved treatments or vaccines for Ebola are available. 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. It is typical of temperate phages to be latent or inactive within the cell. Phage microbiologists discovered decades ago that lysogenic phages . If no viable host cells remain, the viral particles begin to degrade during the decline of the culture (see Figure 6.14). The virus life cycle is complete when it is transmitted from an infected plant to a healthy plant. During the initial stage, an inoculum of virus causes infection. It was later associated with Sudan and Zaire ebolavirus and resulted in more than 11,000 fatalities. The pathogen injects its genome into the host cell's cytoplasm through a hole in the cell wall or through a hollow organelle such as flagella or pili. The integrated viral genome is called a provirus. Only a minority of plant viruses have other types of genomes. The virus now can remain in the host for a long time to establish a chronic infection. The dsDNA can now be replicated, transcribed, and translated similar to host DNA. An example of a virus known to follow the lysogenic cycle is the phage lambda of E. coli. Instead of packaging viral DNA, it takes a random piece of host DNA and inserts it into the capsid. During the lytic cycle of viral replication, the virus hijacks the host cell, degrades the host chromosome, and makes more viral genomes. Our mission is to improve educational access and learning for everyone. Viruses capable of latency may initially cause an acute infection before becoming dormant. There are occasional outbreaks of Ebola, and they mostly occur in Africa. Is it ethical to treat untested drugs on patients with Ebola? The incubation time for Ebola ranges from 2 days to 21 days. No approved treatments or vaccines for Ebola are available. In the lysogenic cycle, phage DNA is incorporated into the host genome, forming a prophage, which is passed on to subsequent generations of cells. Ebola, also known as Ebola virus disease (EVD) and Ebola hemorrhagic fever (EHF), is a viral hemorrhagic fever in humans and other primates, caused by ebolaviruses. In some cases, viruses may also enter healthy plants through wounds, as might occur due to pruning or weather damage. Hepatitis C virus and HIV are two examples of viruses that cause long-term chronic infections. 2. The ssDNA is then made into dsDNA, which can integrate into the host chromosome and become a permanent part of the host. Ebola - spread by blood and body fluids, reservoir unknown; . In contrast, the lysogenic cycle allows the viral genome to integrate into the host's DNA and replicate along with it without immediately causing the host cell to lyse. Latent viruses may remain dormant by existing as circular viral genome molecules outside of the host chromosome. Continuous fever, internal bleeding, diarrhea, and vomiting can result in significant loss of electrolytes, blood plasma, and fluid. Plant viruses are more similar to animal viruses than they are to bacteriophages. 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). Entry The host cell engulfs and uptakes large amounts of nutrients, including the virus, through a wave-like or ruffling motion called. Ebola virus causes the rare but deadly Ebola Virus Disease (EVD). Once it finds a host, the virus has to make its way inside. 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. However, the host cell has a mechanism to allow nutrients to enter, which the Ebola virus uses to attach and enter the cell. 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). The virus is responsible for causing outbreaks in several African countries, with the most recent outbreak occurring in Uganda in 2022. However, unlike prophage, the provirus does not undergo excision after splicing into the genome. The integrated phage genome is called a prophage. The provirus stage is similar to the prophage stage in a bacterial infection during the lysogenic cycle. What triggers lysogenic cycle? Many viruses follow several stages to infect host cells. However, others may have ssDNA, dsRNA, or ssRNA genomes. 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). Glycoprotein produced by the Ebola virus disrupts cell adhesion and inhibits cells from sticking together, which is required for healthy tissue formation. It then hijacks the host cell to replicate, transcribe, and translate the necessary viral components (capsomeres, sheath, base plates, tail fibers, and viral enzymes) for the assembly of new viruses. Transduction seems to play an important role in the evolutionary process of bacteria, giving them a mechanism for asexual exchange of genetic information. The lytic cycle is the main cycle of viral replication in which the viral RNA enters the host cell, transcribes itself into the host cell's messenger RNAs, and uses them to direct the ribosomes. Is a latent phage undetectable in a bacterium? You can learn more about these viruses at this link. will also make copies of the viral genetic material/RNA. The Ebola virus is a long, single-stranded, and filamentous negative-sense RNA virus enclosed by nucleoprotein and other viral proteins in a helical nucleocapsid. The two primary categories of persistent infections are latent infection and chronic infection. This process of host cell lysis during release is more common with non-enveloped viruses, such as polioviruses. 0:29 So first of all, it is an enveloped, After entering the host cell, the virus synthesizes virus-encoded endonucleases to degrade the bacterial chromosome. Specialized transduction occurs at the end of the lysogenic cycle, when the prophage is excised and the bacteriophage enters the lytic cycle. They must enter a living cell and hijack its machinery to create new viral particles. Some bacteria, such as Vibrio cholerae and Clostridium botulinum, are less virulent in the absence of the prophage. Some kinds of bacteriophages even go through both cycles. During the lysogenic cycle, instead of killing the host, the phage genome integrates into the bacterial chromosome and becomes part of the host. 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. 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. What aspect of the life cycle of a virus leads to the sudden increase in the growth curve? There are currently no approved vaccines or antiviral treatments for either virus, but research into potential treatments and preventative measures is ongoing. Here is where the main difference between the two cycles occurs. 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. Some examples of lysogenic cycles in bacteria include Corynebacterium diphtheriae, Vibrio cholerae, and Clostridium botulinum. 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. 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. Bacteriophages inject DNA into the host cell, whereas animal viruses enter by endocytosis or membrane fusion. An alternative mechanism for viral nucleic acid synthesis is observed in the retroviruses, which are +ssRNA viruses (see Figure 6.12). Consequently, the hijacking of the host cell's mechanism leads to its death or inability to function correctly. Several viruses in the filovirus classification are lytic, including: Filovirus Strains: Marburg Ebola: Reston ebolavirus Tai Forest ebolavirus Bundibugyo ebolavirus Sudan ebolavirus Zaire ebolavirus. We recommend using a The timeline of the Duncan case is indicative of the life cycle of the Ebola virus. Although drugs and vaccines are already used to manage severe outbreaks, their efficacies are continuously being studied. Others become proviruses by integrating into the host genome. then you must include on every digital page view the following attribution: Use the information below to generate a citation. After induction has occurred the temperate phage can proceed through a lytic cycle and then undergo lysogeny in a newly infected cell (see Figure \(\PageIndex{2}\)). The outbreak in West Africa in 2014 was unprecedented, dwarfing other human Ebola epidemics in the level of mortality. This nucleocapsid serves as the foundation during viral particle assembly and as a template during transcription and replication. Additionally, Ebola can also be contracted through exposure to contaminated surfaces, needles or medical equipment. The reason I found this very interesting is because usually viruses perform one cycle in their host species. In lysogenic cycles, the spread of the viral DNA occurs through normal reproduction of the host, whereas in lytic cycles, many copies of the virus are created quickly and the host cell is destroyed. Is RNA-dependent RNA polymerase made from a viral gene or a host gene? In the lytic cycle, the phage replicates and causes the host cell to lyse, meaning the host cell dies. Since Ebola can be serious, prevention is essential. The lytic pathway kills the host cell when newly made bacteriophages are released. A vaccine for Ebola was approved by the Food and Drug Administration in December 2019. 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. These monoclonal antibodies act as natural antibodies and neutralize the glycoprotein, preventing the virus from entering the cell. Ebola virus is transmitted through direct contact with droplets of bodily fluids such as saliva, blood, and vomit. 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). Virus leads to its death or inability to function correctly the former hosts DNA into host. As circular viral genome molecules outside of the culture ( see Figure 6.14 ) virus has to +ssRNA. Two types of genomes 21 days phage lambda of E. coli copies can then be translated by ribosomes. 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