The Pathogenesis Of The Resilient Measles Virus Biology Essay

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Pathogenesis is the mechanism or mechanisms to create structural and functional abnormalities within a cell by a particular disease to produce sickness which we can read as symptoms and allowing us to identify as a particular disease. After becoming infected with a virus there are three main outcomes, these are the death of a cell, the cell proliferation and a latent infection. The measles is a highly contagious disease caused by the morbillivirus which is a paramyxovirus which tells us that it is a single stranded RNA virus (second edition Alan Stevens and James Lowe (2000)). Viruses are parasitic organisms, which they cannot survive on their own. They require a host cell to generate more identical copies or clones of itself. It is known that only human cells can develop the measles. For other viruses do not differentiate between human or bacterial cells. As long as they have a host cell to infect they will take over that cells replication machinery and proliferate within the cytoplasm before lysing or budding off the cell. Budding has a more advantageous outcome as some viruses can exploit the cellular membrane they are rupturing from and actually take a layer of the host membrane and cover itself, essentially hiding from the body's immune system. ssRNA of the virus is replicated by the infected host cell. Once the virus has been expelled it can then spread to other cells and infect them in the same manner.

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The only way a person can become infected with the virus is if the person is in direct contact with the virus. The measles virus can survive outside the body of an infected person in aerosol droplet form for about two hours, this shows that it is a very resilient virus and is not to be taken lightly once it enters and infects a host organism.

The virus enters the body through the upper respiratory tract or the conjunctiva. This is known as the primary infection site from this point the virus moves to the lymphatic system, infecting the lymph nodes which is an intricate part of the immune system and non specific response. It infects the cells by injecting its single stranded RNA into the cell, once the RNA is within the cytoplasm a replication cascade occurs as the viral genome integrates into the host cell's DNA structure resulting in the expression and proliferation of viral proteins.. The virus produced bud off the infected cell and into the adjacent unaffected cell then the similar cycle continues this allows the virus to spread around the body, the virus uses energy out of the host cell to allow movement around the internal and external zones of the cell.

The latent period for someone with an infection is between ten to fifteen days after which the person becomes aware of the symptoms. After the secondary infection of the lymphatic system the virus binds to the epithelia cells in the lungs. They release buds of virus containing cells which are carried in aerosol form when the infect person breaths out the droplet containing the virus is sent out of the body. This allows the virus to infect other people in the same cycle. The secondary infection area being infected by the virus leads to the immune system being suppressed and it has been recorded that the Measles virus can leave the immune system suppressed for up to a couple of weeks but the suppression is usually not that long. There are a number of mechanisms that have been known to be affected by the measles virus one such mechanisms that is affected is regarding the dendritic cell. These cells are responsible for antigen presentation to the lymphatic system and initialising the antigenic response, if infected, interleukin 12 which is the hormone that is responsible for the initial response of the lymphatic tissue of more specifically the CD4 T cell response which are responsible for the election of the appropriate the Th response. These are T memory cells which are responsible for carrying the antigenic response that antibodies copy and use in order to destroy foreign pathogens. The suppression of interleukin 12 interrupts the overall production of the antigenic response allow opportunistic infections to set in. They come in many forms such as viral or bacterial which can lead to further more severe complications and possibly even death.

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What are symptoms? As stated before symptoms come about from the change in structural and functional systems to cause abnormal functions by the infected cells. When it comes to the measles virus there are some "classic" symptoms these would be runny nose, conjunctivitis (pink eye/ red eye), coughing, and a rash that is visible all over the skin it will first appear characteristically behind the ear or along the hairline of the infected patient during the latent period of the infection before covering the body, often the first classic symptoms are confused with common cold but the rash is usually the defining point in order to determine the measles disease. Another defining symptom that appears around the end of the latent period is the "koplik's spots" like the rash on discovery of these an easy diagnosis is possible. The kopliks spots are little white deposits that look like salt that are found in the back of the mouth.

The runny nose (coryza) comes about from the inflammation of the cilia epithelial cells in the nose causing an over production of mucosa lining which is a part of the non specific physical barrier in the prevention of infections. Conjunctivitis is when the measles virus initially lands, in aerosol droplet form, on the conjunctiva on the eye which is the outer lining of the eye and begins the process of infection. The measles virus would then cause inflammation of the conjunctiva which would cause irritation, this would make the eye more specifically the sclera to go really red and blood shot which is where it gets the name pink eye. In bacterial infections irritation and inflammation can cause the eye to produce a cloudy substance, this can be used to differentiate between bacterial and viral infections. From the eye the virus can easily spread throughout the body and attack the lymphatic systems as conjunctivitis is one of the first symptoms due to it being a primary infection site. Coughing is caused by an inflammation of the ciliated epithelial cells in the oesophagus causing them to secrete mucus which in turn causes the patient to begin coughing. The rash is caused by the virus infecting the Th1 T cells which attack the infected endothelial cells in the blood capillaries causing inflammation that in turn causes the capillaries to rupture or burst causing the skin to look red and in a rash this symptom often starts at the head before working its way to the rest of the body as I have previously stated. Koplik spots are formed from lesions of the ulcerated mucosal that are marked white by the death of the cell, the surrounding cells of the white spots are inflamed and appear red. The cells that are killed are killed in the same matter as the endothelial cells when the rash is formed, the Th1 T cells attack and destroy the infected cells via apoptosis.

What is a vaccine? A vaccine is a substance given to people to allow them to build immunity's to diseases. In this case a weaker form of the disease would be given so that the person can build immunity without the symptoms showing, in some cases the symptoms have been known to show in a small percentage of cases but it is not as severe as being infected with the real virus. The vaccine for measles is the MMR, this is a mixture of virus' containing mumps measles and rubella. Each of the virus' are prepared in different ways in order for them to be in a weaken form allowing the vaccination not to do damage to the receiving patient who is often infants at the age of around one. There is a second vaccination but this is not a booster and it often given before the child starts school. This is to make sure that the small percentage of children that may not have developed the immunity with the first vaccination develop one now due to the innate immunity which the mother transports to the child. The vaccine was first developed by David Edmonston who managed to extract a live virus from a young child. To weakened the strain to make it a viable vaccine he mixed it in a chick embryo and then extracted it, the strain that was a vaccine in 1954 was known as Edmonston A but this strain was still too strong to be used as a vaccine it was put back in the embryo to make it weaker again the resulting strain was still considered too strong for vaccination purposes and the same process was repeated giving three separate strain which where the basis of all the commercial vaccines that are used in worldwide today.

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Sub-acute sclerosing panencephalitis (SSPE) comes about due to a complication while infected by the measles virus. This complication affects the central nervous system and is a constantly growing disease that will eventually lead to death. This disease mainly affects those affected by the measles virus about fifteen years previously. As this disease is progressive it tends to more severe as time goes on starting with cognitive loss, certain things like reading may become difficult when this happens also memory loss may occur. The next stage is cognitive dysfunction, this usually means that thought processes are no longer available to the patient. After that the patient usually becomes paralyzed in movements in parts of the body or complete paralyzes as all motor function is lost as the diseases develops over time. Once the disease progresses the patient can suffer from seizures and eventually suffer from a total system crash with multiple organ failure. This is how people with this complication disease die. Predominately the neurons in the central nervous system that is infected, it is also known that children are much more likely to develop this disease that adults, in later periods of development of the disease there are more types of cells infected for example epithelial cells and oligodendrocytes. Within the neurons there is no budding but there are inclusion body's that spread through the central nervous system spreading the infection causing inflamation