The Pathogenesis Of The Measles Virus Infection Biology Essay

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The paramyxovirus is a negative sense RNA virus which is single stranded and extremely stable due to the proteins contained within its envelope. The paramyxovirus family contains the morbillivirus genus, and it is this particular genus to which the measles virus belongs.(1) The measles are not to be confused with the German Measles which are better known as Rubella. The measles are scientifically referred to as Rubeola and sometimes called the "English Measles" to avoid confusion as the Rubella and Rubeola infections are in no way related.(2) The measles are an extremely contagious infection; however due to immunisation, reported cases are a lot less compared to the pre-vaccine years. Dr Rob Hicks discusses the measles on behalf of BBC Health, he comments "Worldwide, the highly contagious viral disease measles still kills about a million children a year. In the UK, vaccination has made it much rarer, but cases are at their highest level for 20 years."(3) The recent rise in cases of measles may be due to the increasing controversy over its usage.

The measles is one of the most infectious viruses in existence. The virus is contained in little droplets within the throat, mouth and nose cavities. The virus is highly infectious as sneezing and coughing produce a lot of droplets into the air making the virus airborne. When in the nose and throat the virus inhabits the mucus which provides the perfect living environment for the virus to strive and reproduce.(4) When the virus is expelled out into the air, the mucus is carried around it providing enough material for the virus to survive for a few hours in the air. The virus may stay in the air or rest on objects or other people. This makes the transfer to another body extremely easy, mostly by touching infected items such as handles of doors. Personal contact is a direct way for the virus to enter the body, close contact with an infected person e.g. kissing will result in transfer of the virus.(1) Any contact with the virus containing droplets will cause infection; however it is less likely if immunisation has occurred or a past case of the measles. This is due to the built up immunity against the virus, when the virus enters the body an automatic immune response occurs as soon as the virus is detected as a foreign body and the present antibodies will fight off the virus before any symptoms have time to develop. Those who have not received the immunisation will be more susceptible to the virus and therefore leading to the further spreading as they will go through a contagious period.(5) When the virus enters the body it needs to spread and multiply before the external symptoms appear. The multiplying stage is the most contagious period of infection as the sufferer is unaware of the virus being present. They continue with everyday life and remain in contact with others, so the virus is already beginning to spread through the air. When the virus enters the body it firstly inhabits the nose and throat as mentioned above. This is an easy passage straight into the immune system, if the virus invades the immune system the body will be unable to fight it off until the virus had run its course. The virus is always multiplying so as it leaves the respiratory tract for the immune system it leave lots of virus cells behind which continue to multiply and spread by being expelled out into the air. When the virus enters the immune system it targets and invades the monocytes. The monocytes travel all around the body and subsequently carry the virus around with them. As the virus spreads all around the body the organs begin to get infected and the virus begins to multiply within them. Finally the virus spreads to the skink and multiplies and infects the endothelial and epidermal cells, this is when the sufferer begins to notice the rash.(6)

The measles is commonly associated with a blotchy red rash; however when the rash appears, the most contagious period of the infection has passed but the sufferer is still contagious. The majority of symptoms can take seven to ten days to develop and most sufferers are recovering after fourteen days. The infection begins with basic flu like symptoms, fever, runny nose and itchy eyes. After this Koplik's spots present themselves in the mouth.(1, 4) These are small white spots which develop roughly a couple of days into the infection, due to their location they are extremely difficult to notice; however this is how many GP's diagnose the measles. The symptoms progress with a persistent cough, fatigue and bodily aches, most sufferers develop vomiting and diarrhoea.(4) Due to the vagueness of these symptoms, sufferers do not suspect measles. This is when the prominent rash begins to present itself; roughly four days after the fever began. The rash begins as a bumpy red coloured lumps (7) but as they begin to fade they do not disappear, the skin covered in the rash flakes of leaving a brown rash underneath. The red marks on the skin normally begin around the head and neck and take a couple of days to develop all over the body. The rash and fever begin to disappear after five days of illness and the sufferer begins to regain full health. During the infection the body produces the antibodies to fight off the virus in case it enters the body in the future. These antibodies ensure the sufferer is protected against measles for life.(5)

As the body is fighting the measles virus, there are gaps in the immune system which can lead to further complications. Other infections may get into the body due to the compromised immune system; however complications are more likely to appear in sufferers whose immune system was suppressed before contracting the measles. The sufferer may contract conjunctivitis or more common respiratory diseases like laryngitis; (4) however complications of the nervous system are very rare. Encephalitis more commonly known as swelling of the brain can occur in conjunction with development of the rash, this can lead to brain damage however this is rare and only one quarter of encephalitis sufferers develop brain damage. (1,2) Commonly one tenth of measles sufferers develop an ear infection, this can also be very dangerous as it can continue into the inner ear and cause mastoiditis. Antibiotics can resolve this; however if untreated sufferers may need to have part of their eardrum removed. Pregnant women who develop measles have a higher risk of consequences such as miscarriage, premature delivery and underweight babies. There is also a risk of the mother passing the infection to the foetus which can lead to serious problems when the child is born. This is a serious complication called Cognitive Rubella leading to the child being born with impaired hearing and sight or even cataracts. The child can also grow up with severe learning difficulties or problems with development of the heart.(8) Non-pregnancy related complications are usually present in people who have not been immunised. The immunisation is available as the MMR vaccine which is suggested to be given to babies around the age of one. A booster is available for primary one children. The vaccine is the only way to prevent contracting the infection and due to the prevalence of measles among young children, it is advisable to have children vaccinated.

Maurice Ralph Hilleman was the microbiologist who developed the vaccine to fight against the measles in 1963. The vaccine is called the MMR as it is a triple live, attenuated virus combination in a vaccine for fighting Measles, Mumps and Rubella.(10) The vaccines used to be available but not combined and nowhere as effective as the MMR. It is a two part vaccine as described above- the first dose at the age of one and the second dose around primary one age. If both doses are not received then a full immunity against measles, mumps and rubella is not provided.(3,4) Research has been on going over the years to determine negative effects of the vaccine. Links have been made between receiving the MMR vaccine and the development of Autism (5) or a more recent discovery of the development of Crohn's disease.(3) These links seem to be inconclusive as none of the vast information proves these links to be true and studies carried out show no proof. Most medical professionals will stand by the vaccine and promote its competent and dynamic result.

There are single replacement vaccines available in place of the MMR; however this is only available in special circumstances. If a child is allergic to certain aspects of the MMR vaccine then a single specific vaccine should be provided; however these single vaccines are not as readily available as the MMR. (1)

Most children will benefit from the MMR but consult from their GP would be advised as some children may be at risk if they have had on going nervous system trouble. Receiving the immunisation automatically provides a resistance to the measles virus. Due to worldwide vaccination the outbreaks of measles have been little in number; however due to parents abstaining from having their children immunised, measles are beginning to become more common again.(4) Although measles are more common in school aged children, anyone who is not immune can get infected by the measles virus which can cause an outbreak. This means if an outbreak occurs in a university or office situation, a large number of people will have to receive the vaccine again or for the first time to prevent spreading. (2)

An extremely rare complication of the measles virus is Subacute Sclerosing Panencephalitis (SSPE). (4) SSPE is a devastating progressive neurological disorder which is detrimental to the lives of children and young adults who have suffered from measles in their early childhood, most commonly before the age of two. SSPE is slow to develop with symptoms only developing six to eight years after contracting the measles virus. SSPE is caused by a defective version of the measles virus which targets the Central Nervous System.(11) The symptoms begin after the latent period and include irregular behavioural patterns and mild memory loss as the disorder is developing. With progression of the disorder, the sufferer begins to experience erratic movements of their extremities which are beyond their control. Blindness and seizures may also occur as symptoms; however these are less common. When SSPE accelerates, the muscles of the body tend to be more susceptible to tauten and cramp, this means the sufferer looses the ability to walk. The deterioration continues until the sufferer enters into a coma, which after a period of time leads to a constant vegetative state.(12) SSPE does cause death; however it is common to be caused indirectly by the body's inability to regulate its temperature so death is caused by high fevers. As the brain looses ability to control functions death can also be caused by heart and autonomic nervous system failure.