Wednesday, April 1, 2020

A latent infection Essays

A latent infection Essays A latent infection Essay A latent infection Essay A latent infection refers to an infective agent, in this instance a virus, staying in an inactive or hibernating province [ I ] . This can happen in both DNA and RNA viruses, including Herpes Simplex virus and HIV. The virus life rhythm includes two parts, the lytic and lysogenic rhythm. Latent infections come under the lysogenic rhythm. This latent phase is utile in hedging an immune response so the virus lasts for a longer clip within the host cell. The lytic rhythm is the chief rhythm where reproduction occurs and is shown below in diagram 1. The first phase is attachment where the virus attaches to the host cell via a receptor. The viral nucleic acid is either injected into the cell through incursion or the whole virus atom is taken up by endocytosis. If the virus was taken up in this manner it now needs to be uncoated so the viral nucleic acid is exposed in the cytol of the host cell. The following phase is cistron look and the control of cistron look determines the overall class of a virus infection ( acute, chronic, relentless or latent ) ( Principles of Molecular Virology, 4th edition, Alan J. Cann, 2005 ) . Depending on the type of nucleic acid, DNA or RNA, look and reproduction of the cistron can take topographic point in the cytol or the karyon of the host cell. Assembly so takes topographic point to acquire all the constituents necessary to do a new virion together and they are packaged into membranes and envelopes. This is known as the ripening procedure and is the point when the virus becomes infective. Replication occurs rapidly and so many mature virions are made, that they are released from the host cell through lysis of the cell wall. The virions can now reiterate this procedure on another host cell to distribute the infection. Diagram 1 the lytic and lysogenic rhythms: Viral DNA/RNA is incorporated into the host genome in the lysogenic rhythm besides shown in diagram 1. The host genome is now termed a prophage and the viral nucleic acid replicates as a portion of the host cell and can be passed onto girl cells. No new virions are made in this rhythm and there are no symptoms from the infection. The viral nucleic acid can stay in the lysogenic rhythm for a long clip but if the prophage is triggered by emphasis or UV visible radiation, the rhythm can return back to the lytic rhythm where new viral offspring is formed. Viral latency is portion of the lysogenic component of the virus life rhythm. Gene look is down regulated so, in this latent province, the virus is non being replicated ( Janeway s Immunobiology, 7th edition, Murphy et Al, 2008 ) . The viral nucleic acid is integrated into the host genome and replicates with the host genome but no new viral proteins are being made. This happens at a point after the initial infection with the virus. There is no disease nowadays in this phase but the virus has non been eradicated. The virus can be reactivated from a latent province to a lytic province due to a figure of factors. These include emphasis, sunlight or hormonal alterations. A reversion to the lytic phase of the life rhythm consequences in viral proteins being made and the infection returning, but perchance in a different look compared to the initial infection. The latent province is maintained by the written text of certain cistrons, either maintaining the virus in the latent province or returning it back to the lytic. The forms of the latent phase can be studied utilizing bacteriophage lambda as it does non do disease. Diagram 2 below shows in graph signifier how the virus can travel in and out of a latent province over clip. Diagram 2 latency graph demoing viral burden vs. clip The virus in the latent phase does non bring forth any proteins, which makes it undetectable to the immune system as there are no sensing markers. The virus can besides conceal in cells that do non split, for illustration in some cells of the immune system. The virus does non acquire broken down or engulfed by macrophages as it has become portion of the host cell. The latent phase is a good manner of lasting in a host cell in order to reinfect the host subsequently on. It can so besides spread to other host cells, advancing drawn-out endurance and perennial infection. In a productive infection, the lytic rhythm is activated and viral proteins are made. This is different to the latent phase. The virus would merely last for a certain period of clip in a productive infection until it was eliminated from the host. Herpesviruses do latent infections in many different carnal species ( Introduction to Modern Virology, 6th edition, Dimmock et Al, 2007 ) . Herpesviruses can do different sorts of diseases, for illustration, poulet syphilis, the Herpes Simplex Virus and the Epstein-Barr virus. The Herpes Simplex Virus or HSV has many types, which include Type 1, associated with cold sores around the oral cavity and Type 2 with venereal herpes. Once infected with the HSV virus, it infects the mucose membranes around the oral cavity. The viral DNA of HSV1 so integrates into the host genome in nervus cells called nervous ganglion [ two ] . Viral look is restricted during the latent phase, so no viral offspring is formed. The virus can be in the latent phase and remain in the organic structure for the remainder of its life, perchance repeating at different phases. If the virus is reactivated from the latent phase, it goes into the lytic phase and replicates to organize new viral offspring, which reinfects the mucose membranes of the oral cavity. The new infection can besides look as a signifier of herpes zosters after reactivation. The latent phase of HSV1 has no effects on the host and no symptoms are produced from it unless reactivated into the lytic rhythm. Factors that affect the reactivation of HSV1 include other unwellnesss, for illustration a cold, sing nerve-racking state of affairss either emotionally or physically an d hurts. Within the nervous cells, in the latent phase, RNA sequences are expressed called Latency-associated Transcripts ( LATs ) . There are tonss of LATs and they modify procedures within the host cell so it is non removed by the immune system. This is the merely active portion of the virus during the latent phase and they help keep latency within the cell. LATs are besides required for reactivation. The Epstein-Barr virus or HHV-4 virus is besides portion of the herpes virus household. Peoples infected with the Epstein-Barr virus are frequently symptomless for most of their lives. If the infection arises in a kid, there is an acute infection. However, if the infection arises in an grownup, it can do glandular febrility. Symptoms include a sore pharynx, conceited secretory organs and a febrility [ three ] . The infection starts in the salivary secretory organ and can hence be dispersed direct contact with the septic spit, for illustration, through caressing. It lasts for around 2-3 hebdomads but after that clip, there are no longer symptoms and the virus remains latent in resting, memory B lymphocytes [ four ] . When the B cells are infected with EBV, they proliferate and T cells are recruited to acquire rid of septic B cells. Reactivation of the EBV virus frequently causes a subclinical infection but can besides do malignant neoplastic diseases, like Burkitt s lymphoma, largely found in Africa or B cell lymphoma. When the virus is in a latent province the cistrons are expressed in the round signifier of an episome, instead than a additive signifier in the lytic province. Upto nine viral proteins are expressed in the latent province which is a little sum compared to the viral proteins produced in the lytic province. These specific proteins help to keep the latent province. These include six Epstein-Barr atomic antigens ( EBNAs ) and three latent membrane proteins ( LMPs ) [ 5 ] . EBNA-1 is the lone one of these proteins which is necessary for DNA reproduction and the others are used in cell procedures like cell signalling. EBNA-1 is besides the lone antigen nowadays in Burkitt s lymphoma and T cells ca nt adhere with it, so ca nt acquire rid of the septic cell. Human Immunodeficiency virus ( HIV ) is a RNA retrovirus, which causes AIDS. AIDS is a status where the immune system has been degraded so much that it can no longer contend against infection. HIV contains 2 RNA strands and is covered by a protein coat. When HIV infects a cell, rearward RNA polymerase is used to change over its RNA into DNA so that reproduction can happen within the host. After infection, the virus either replicates quickly to infect other cells or goes into the latent province in CD4+ T lymphocytes. HIV is known as a slow virus which means it takes a long clip to bring forth symptoms, frequently taking to a late diagnosing of the disease. An infection with HIV causes flu like symptoms at first, before going symptomless and traveling into a clinically latent stage. In this stage there is still reproduction of the HIV virus in some cells but some of the virus has gone into a latent province, which means some of the virus is active and some is inactive. The clinical la tency phase varies in length from hebdomads to old ages and the virus can still be passed on to other people as the retroflexing virus is besides present. CD8 T cells are responsible for the diminution of the virus but they can non extinguish the virus. Peoples with the HIV virus carry the disease for the remainder of their lives. Anti-retroviral drugs and chemotherapy can non acquire rid of the virus from the latent phase, so even if the activated virus was eliminated, the virus can still re-emerge. The latent virus can be reactivated but the specific grounds for this happening are non known. Reactivation of the virus from the latent phase, consequences in more serious symptoms developing and leads to the oncoming of AIDS. To reason, latent infections are another manner that certain viruses can hedge the immune responses of the host. The virus can either conceal in cells in certain tissues like the Herpes Simplex Virus or conceal in B cells of the immune system like the Epstein-Barr virus. HIV is a RNA virus that prolongs the life of the virus by concealing in CD4+ cells. All these viruses can be reactivated to do a ulterior infection. Often the reverting infection is acute but sometimes more serious infections arise for illustration malignant neoplastic diseases like Burkitt s lymphoma upon reactivation of the EBV virus. The latency phase is a clever technique of the virus to remain in the host for a longer period of clip. hypertext transfer protocol: // Latent Viruss and Diseases from World of Microbiology and Immunology. Â ©2005-2006 hypertext transfer protocol: // Introduction to Modern Virology, 6th edition, Dimmock et Al, 2007 hypertext transfer protocol: //

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