Virus, Infection : Preventing and Treatment
A virus is a microscopic parasite that infects cells of biological organisms. Viruses are obligate parasites, it is because the virus can only reproduce in living material to invade and take advantage of living cells because the virus does not have the cellular equipment to reproduce itself. Usually contain small amounts of viral nucleic acid (DNA or RNA, but not a combination of both) are shrouded in a kind of protective material consisting of proteins, lipids, glycoproteins, or a combination of all three. Virus genome will be expressed both proteins are used to contain genetic material or proteins required in the life cycle.
The term virus usually refers to particles that infect cells of eukaryotes (multicellular organisms and many types of single cell organisms), while the term bakteriofage or phage used for this type of attack the cell types of prokaryotes (bacteria and other organisms that are not nucleated cells) .
Viruses often debated status as living beings because he is unable to perform its biological function independently if not in the host cell. Because of its distinctive characteristics of these viruses are always associated with specific diseases, both in humans (eg influenza virus and HIV), animals (eg bird flu virus), or plants (eg tobacco mosaic virus / TMV).
History of Discovery
* The virus has infected since the days before BC, it is proved by the discoveries of several reports of viral infections in the hieroglyphics in Memphis, the capital of ancient Egypt (1400SM) showing Adana poliomyelitis disease, in addition, King Pharaoh Ramses V died in 1196 years BC and is believed died of smallpox virus.
* In the BC era, a fairly well-known viruses endemic smallpox is a virus that attacks the people of China in the year 1000. But in the year 1798, Edward Jenner discovered that some of the dairy farmer has immunity against pox viruses. This is presumably because Pox Virus found in cattle, protecting humans from Pox. The findings are understandable and is a pioneer the use of vaccines.
* In 1880, Louis Pasteur and Robert Koch put forward a "germ theory" is that a disease-causing microorganisms. At that time also famous Koch's postulates are very popular so far are:
1. Disease agent must be present in every case of disease
2. Agent must be isolated from the host and can be grown in vitro
3. When the culture was inoculated into the agent muri healthy susceptible host cells it can cause illness
4. The same agent can be taken and re-isolated from the infected host is
* Research on the virus began with research on mosaic disease of tobacco plants inhibits growth and make the leaves of these plants have spots. In 1883, Adolf Mayer, a German scientist, discovered that the disease can be transmitted when the plant became ill after he was thoroughly sprayed with the sap of diseased plants. Unable to find microbes in the plant sap, Mayer concluded that the disease is caused by bacteria that are smaller than normal and can not be seen with a microscope.
* In 1892, Dimitri Ivanowsky from Russia found that the sap of tobacco leaves that have been filtered by the filter bacteria can still cause mosaic disease. Ivanowsky then deduce two possibilities, namely that the shape of the bacteria causing the disease is so small that can still pass through the filter, or the bacteria release toxins that can pass through the sieve. The second possibility was discarded in 1897 after the Dutch Martinus Beijerinck found that infectious agents in the resin that has been filtered is able to reproduce because of its ability to cause disease did not diminish after several times transferred between plants. pathogen tobacco mosaic summed up as not bacteria, but is contagium vivum fluidum, which is a kind of living disease-carrying fluid.
* After that, in 1898, Loeffler and Frosch reported that the cause of bovine foot and mouth disease can pass through a filter that can not be bypassed bacteria. Nevertheless, they concluded that the pathogen is a bacteria that is very small.
* Opinions new Beijerinck proved in 1935, after Wendell Meredith Stanley of the United States managed to crystallize the particles causes mosaic disease now known as tobacco mosaic virus. The virus is also a virus which was first visualized by electron microscopy in 1939 by scientists German GA Kausche, E. Pfankuch, and H. Ruska.
* In 1911, Peyton Rous discovered the healthy if the chicken induced by tumor cells from sick chickens, then on a healthy chicken will also be affected by cancer. In addition, also tried melisis Rous tumor cells from sick chickens and then filter sari-sari with pores that can not be traversed by the bacteria, then the juices are injected in chicken cells are healthy and apparently it can also cause cancer. concluded that cancers caused by Rous virus cells in the tumor cells of chicken illness that infects cells of healthy chickens. The discovery is the first discovery of an oncogenic virus, the virus that can cause tumors. Virus found by Rous Rous Sarcoma Virus called (RSV).
* In 1933, Shope papilloma virus, or cottontail rabbit papillomavirus (CRPV) were found by Dr. Richard E Shope is the first human cancer models yag caused by a virus. Dr. Shope has been experimenting with taking the filtrate from tumors in animals and then injected on a healthy domestic rabbits, and it arises the tumors in rabbits.
* Wendell Stanley was the first to successfully crystallize the virus in 1935. The virus is a crystallized Tobacco Mosaic Virus (TMV). Stanley suggests that the virus can remain active even after crystallization.
* Martha Chase and Alfred Hershey in 1952 managed to find bakteriofage. Bakterofage is a virus that has a host of bacteria that can only replicate inside bacterial cells.
Structure and Anatomy of the Virus
Viruses are organisms that subcellular because its size is very small, only visible using electron microscopy. Its size is smaller than bacteria, so the virus can not be filtered by filter bacteria. Virus The smallest diameter of only 20 nm (smaller than a ribosome), whereas even the largest of the virus hard to see with light microscope.
Viral genome can be either DNA or RNA. The genome of a virus may consist of double-stranded DNA, single-stranded DNA, double-stranded RNA, or single-stranded RNA. In addition, the viral genome nucleic acid can form a single linear or circular. The number of viral genes varies from four for the smallest up to several hundred for the largest. most of the viral genetic material of animals and humans in the form of DNA, and in most plant viruses is a single-stranded RNA.
Viral genetic material enclosed by a protective layer. The protein is a protective layer called a capsid. Depending on the type of virus, the capsid can be round (spherical), helical, polihedral, or form a more complex and consists of proteins encoded by the genome of the virus. capsid is made up of many protein subunits called capsomeres.
For helical viruses, the capsid protein (usually called the nucleocapsid protein) bound directly to the viral genome. For example, the measles virus, nucleocapsid protein each connected with six bases along the RNA to form a helix of about 1.3 micrometers. The composition of the complex proteins and nucleic acids is called the nucleocapsid. In measles virus, nucleocapsid is enveloped by a lipid layer obtained from the host cell, and the glycoprotein encoded by the viral lipid envelope is attached. These passages function in binding to and entry into host cells early in infection.
Spherical virus capsid surrounds the virus genome as a whole and not too bind to the viral nucleic acid such as helices. This structure can vary from size of 20 nanometers to 400 nanometers and consist of viral proteins arranged in the form of icosahedral symmetry. The amount of protein required to form a spherical virus capsid is determined by the coefficient T, which is about 60t of protein. For example, hepatitis B virus has a number T = 4, need 240 to form a capsid protein. As the form of a helical virus, the capsid part types spherical enveloped viruses can be lipid layer, but usually the capsid protein itself directly involved in cell infection.
Some types of viruses have an additional element that helped infect inang.Virus in animals have viral envelope, the membrane surrounding the capsid. The sheath contains phospholipids and proteins from the host cell, but also contains proteins and glycoproteins derived from viruses. In addition to the protein envelope and capsid protein, the virus also carries several enzyme molecules in the capsid. There are also several types of bacteriophage tail protein that has attached to "head" of the capsid. Tail fibers are used by the phage to attach to a bacterium. a complete virus particle is called a virion. Virion gene serves as a means of transportation, while the envelope and capsid components in the mechanism responsible infection host cells.
Various kinds of viral infections
The virus can infect its host and cause a variety due to its host. there is a danger, but also there that can be handled by the immune cells in the body so that the result produced is not too large.
1. Acute Infection
Acute infections are infections that take place within a period of fast but can also be fatal. As a result of acute infection are:
* Recover without damage (Heal total)
* Heal the damage / defect, for example: polio
* Continues to chronic infection
* Death
2. Chronic infection
Chronic infection is a prolonged viral infection, so there is a risk of disease symptoms reappear. Examples of chronic infection are:
* Silent lifelong subclinical infection, eg cytomegalovirus (CMV)
* Long silent period before the emergence of diseases, eg HIV
* Reactivation of which cause acute infections, eg shingles
* Chronic recurrent disease (relapse), eg HBV, HCV
* Cancer example: HTLV-1, HPV, HBV, HCV, HHV.
Viral Replication
Viral replication consists of several stages of virus attachment, penetration, release coat, genome replication and gene expression, assembly, maturation, and release.
Virus Attachment
Virus attachment is a process of initial interactions between virus particles with receptor molecules on the surface of host cells. At this stage, specific binding occurs between the antireseptor cellular receptor molecules on the virus. Some types of viruses require other molecules for the attachment of co-receptors .
Molecules that target receptors on the cell surface can be shaped proteins (usually glycoproteins) or carbohydrate residues found on glycoproteins or glycolipids.
Some complex viruses such as poxviruses and herpesviruses have more than one receptor so as to have multiple routes to bind to the cell.
Virus receptor has several different classes:
* Molecules immunoglobulin-like superfamily
* Associated membrane receptors
* Channels and transmembrane transporters
Some examples of virus and its receptor are owned by:
* Human Rhinovirus (HRV)
Human Rhinovirus have receptors ICAM-1 (Intracelluler adhesion molecule-1). This molecule is an adhesion molecule that is normally functions to bind cells to the substrate. the structure of ICAM-1 is similar to the immunoglobulin molecule with the domain C and V so that supefamily classified as immunoglobulin proteins
The structure of ICAM-1 has five Ig-like domains to bind to LFA-1 (Leukocite function antigen-1), Mac-1 (Macrofage antigen-1), Rhinovirus (HRV), fibrinogen, and PFIE (malaria infected erythocytes).
10 serotypes of HRV using the ICAM-1 as a receptor, ten other serotypes using protein related by LDL receptors.
* Poliovirus
has the form of the virus receptors are integral membrane proteins are also members of the immunoglobulin superfamily molecules. This receptor has three domains: one form of variable and two constant.
* The influenza virus
This virus has two types of spike glycoproteins on the surface of virus particles is hemagglutinin (HA) and neuraminidase. HA binds to receptors in the form of the influenza virus sialat acid (N-acetyl neuraminic acid).
This virus binds to the negative charge of the existing sialat acid moieties on oligosaccharide chains covalently bind to glycoproteins on the cell surface.
sialat acid in the presence of almost all types of influenza viruses can cause cells bind to many cell types.
Penetration
Penetration occurs in a very short time after the virus attachment to receptors on the cell membrane. This process requires energy Three mechanisms are involved:
* Translocation of viral particles
Translocation process is relatively rare among viruses and the mechanisms are fully understood correctly belom, possibly mediated by proteins in the virus capsid and specific membrane receptors
* Endocytosis virus into intracellular vacuoles
endocytosis process is a very common mechanism for virus entry into cells. Not required except specific viral proteins that have been used for receptor binding.
* Fusion of the envelope with the cell membrane (for viruses that berenvelope)
Berenvelop viral fusion process with the cell membrane either directly or with the cell surface or following endocytosis in the cytoplasm. requires the existence of specific fusion proteins in the envelop viruses, eg influenza HA and the transmembrane glycoprotein (TM) Rhinovirus.
The Release Coat
This stage occurs after viral capsid penetration process in which either wholly or partially transferred into the host cell cytoplasm. At this stage of the viral genome is exposed in the form of nucleoprotein complexes. In some cases, this stage was quite modest and occur during the fusion the viral membrane with the plasma membrane. for other viruses, this stage is a multistep process that involves endocytosis pathway and the nuclear membrane.
Genome Replication and Gene Expression
Strategy replication of several viruses depend on the natural genetic material of the virus. In this case, the virus is divided into 7 groups as the grouping of [[David Baltimore]. The process of gene expression will determine all the processes of virus infection (acute, chronic , persistent, or latent).
* Class I: DNA Double Thread
The group was divided into two groups:
1. Replication occurs in the nucleus and are relatively dependent on cellular factors (Adenoviridae, Polyomaviridae, Herpesviridae)
2. Replication occurs in the cytoplasm (Poxviridae). viruses involves all the factors that are important for transcription and replication of the genome, and most do not depend on the replication of its host
* Class II: DNA Single Thread
Replication occurs in the nucleus, involving multiple pieces of intermediate forms as templates for the synthesis of single pieces of DNA derivatives (Parvoviridae)
* Class III: RNA Doubles Thread
The virus has a segmented genome. each segment separately transcribed to produce mRNA monosistronik individual. example: Reoviridae
* Class IV: Single Thread RNA (+)
Viruses with a polycistronic mRNA in which this class of genomic RNA to form mRNA is translated to form a polyprotein which is broken down to form a mature protein. Example: Picornaviridae
* Class V: Single Thread RNA (-)
Genome in this class is divided into two types:
1. Genome is not segmented (Rhabdoviridae), the first step in replication is transcription of the RNA genome Thread (-) by the virion RNA-dependent RNA polymerase to produce mRNA monosistronik well as templates for genome replication.
2. Segmented genome (Orthomixoviridae), replication occurs in the nucleus where monosistronik mRNA for each gene the virus produced by virus transcriptase.
* Class VI: Single Thread RNA (+) with DNA Intermediate
Single thread Retrovirus RNA genome (+) are diploid and not used directly as mRNA, but as a template for reverse transcriptase into DNA.
* Class VII: Multiple threads of DNA with RNA Intermediate
Viruses of this group depend on reverse transcriptase, but in contrast to retroviruses, the process occurs in the virus particles during maturation (Hepadnaviridae).
Assembling
Assembly is the process of gathering the components of the virion in a special section in the cell. During this process, the formation of the structure of viral particles. This process is dependent on the replication process within the cell and the places where viruses escape from cells. the mechanism of assembly varies for different viruses. Example: the assembly process picornavirus, poxvirus, and Reovirus occurs in the cytoplasm, while assembly process Adenovirus, poliovirus, and parvovirus occur in the nucleus.
Maturation
Maturation is the stage of viral life cycle where the virus is infectious. at this stage there is a change in the structure of viral particles produced by the breakdown of the possibility of specific capsid protein to produce a mature product. viral proteases and other cellular enzymes normally involved in this process.
Release
All plant viruses unless the virus escape from host cells through a mechanism he:
* For lytic virus (all non-envelope viruses), the release is a simple process, where the open-infected cells and viruses out.
* For enveloped viruses, lipid membranes are needed when a virus out of cells through the membrane, a process known as budding.
The process of release of viral particles might damage the cells (paramyxovirus, Rhabdovirus, and Togavirus), and likely some will not damage the cells (Retroviruses).
Classification of viruses
Viruses can be classified according to morphology, tropism and dissemination, and functional genomics.
* The classification of viruses based on morphology
Based on morphology, divided by type of viral nucleic acid and outer membrane proteins (envelope) into 4 groups, namely:
1. Virus DNA
2. RNA Viruses
3. Enveloped viruses
4. Non-envelope viruses
* Classification based on virus tropism and spread of
Based on the tropism and the way the spread, the virus is divided into:
1. Enteric Viruses
2. Respiratory Virus
3. Arbovirus
4. Oncogenic virus
5. Hepatitis virus
* The classification of viruses based on functional genomics
Viruses in the classification into 7 groups based on the flow of genome function. This classification is also called the Baltimore classification as follows:
1. Virus Type I = DNA Double Thread
2. Virus Type II = DNA Single Thread
3. Virus Type III = RNA Doubles Thread
4. Type IV = RNA viruses Single Thread (+)
5. RNA Virus Type V = Single Thread (-)
6. RNA Virus Type VI = Single Thread (+) with a DNA intermediate
7. Virus Type VII = Multiple threads of DNA with RNA intermediate
The role of viruses in the Life
Some viruses exist that can be used in recombination genetics. Through gene therapy, gene evil (the cause of infection) found in the virus transformed into either gene (healer). More recently David Sanders, a professor of biology at Purdue's School of Science have discovered how to use the virus in the health world. In finding published in the Journal of Virology, December 15, 2002 Edition, David Sanders managed to tame the outer shell of the Ebola virus so that it can be used as carriers of genes to diseased cells (lung ). However, most viruses are harmful to human life, animals, and plants.
The virus is known to cause infectious disease in humans, animals, and plants. So far there are no living beings that are resistant to the virus. Any virus specifically to attack certain cells of its host. Viruses that cause flu attacks the respiratory tract, measles virus infects the skin, hepatitis virus infects the liver, and rabies virus attacks the nerve cells. The same thing occurs in the disease AIDS (acquired immune deficiency syndrome), which is a disease that resulted in a decreased immune disease is caused by the HIV virus that specifically attacks the white blood cells. The following table sets out some kind of disease caused by the virus.
Besides humans, the virus also causes suffering to animals and plants. Not a few others who suffered losses due to cattle ranchers or farmers who are sick or who reduced their yields.
Animal diseases caused by viruses
Newcastle disease, the type of disease affecting the poultry, especially chickens. The reason is the new castle disease virus (NCDV). hoof and mouth disease, the type of disease affecting cattle and buffalo. The disease of cancer in chickens by Rous sarcoma virus (RSV). The disease rabies, ie type of disease affecting dogs, cats, and monkeys, caused by rabies virus.
Plant diseases caused by viruses
Mosaic disease, ie type of disease that attacks tobacco plants. The cause is tobacco mosaic virus (TMV) tungro disease, ie type of disease that attacks rice plants. The cause is a virus Tungro. Disease vessel degeneration in an orange filter . The cause is a virus Citrus vein phloem degeneration (CVPD).
Human diseases caused by viruses
The most common examples of diseases caused by viruses are colds (which could have been caused by one or several viruses at once), smallpox, AIDS (caused by the HIV virus), herpes and fever (caused by herpes simplex virus). neck cancer the uterus is also thought to be caused partly by papillomavirus (which causes papillomas, or warts), which shows examples of cases in humans that showed an association between cancer and agents infektan. Also there is some controversy over whether Borna virus, previously suspected as the cause neurological disease in horses, is also responsible for psychiatric diseases in humans.
The potential of the virus to cause outbreaks in humans raises concerns the use of viruses as biological weapons. Suspicions increased with the discovery of a way of creation of new virus variants in the laboratory.
Concerns also occurred against the spread of the virus re-type smallpox, which has caused the biggest epidemic in human history, and able to cause the extinction of a nation. Some Indian tribes have become extinct due to epidemics, particularly smallpox, brought by European colonists. While undoubtedly true in the exact number, it is believed the death had occurred in large numbers. This disease has indirectly helped the dominance of Europeans in the new world of America.
Which is considered one of the most dangerous viruses are filovirus. The group consists of filovirus Marburg, first discovered in 1967 in Marburg, Germany, and ebola. filovirus is a long-shaped viruses such as worms, which look like large amounts of plate mi. In April 2005, the Marburg virus attracted press attention with the spread in Angola. From October 2004 to 2005, this incident became the worst epidemic in human life.
Diagnosis in the laboratory
Detection, isolation, until the analysis of a virus is usually through a difficult and expensive process. Therefore, the study of viral diseases requires large and expensive facilities, as well as expensive equipment and experts from various fields, such as technicians, molecular biologists , and virus expert. Usually this process is carried out by a state agency or done in cooperation with other nations through world institutions like the World Health Organization (WHO).
Prevention and Treatment
Because usually manipulate the mechanisms of stem cells to reproduce, the virus is very difficult to kill. The method of treatment that is considered by far the most effective is the vaccine, to stimulate the body's natural immunity against the infection process, and drugs that treat symptoms caused by viral infection.
Cure diseases caused by virus infection is usually misconstrued anticipated with the use of antibiotics, which does not have an influence on the life of the virus. The side effects of antibiotic use is the resistance of bacteria to antibiotics. For this reason further investigation is needed to determine whether a disease caused by bacteria or viruses.
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