The yellow fever virus causes the disease known as yellow fever. The yellow fever virus is basically an RNA belonging to the family flaviviridae. The yellow fever virus is transmitted by the yellow fever mosquito. This particular mosquito which belongs to the Aedes Aegypti family is found mainly in the tropical and sub tropical areas of South America and Africa. These mosquitoes are not found in Asia. The virus can stay alive only in the primate humans and several species of mosquitoes. In other animals, it exists but is not termed as alive or active. It remains dormant in other species of animals.
The disease has several symptoms and the most common of all symptoms are fever, nausea and pain. The symptoms usually disappear after several days. It has been observed in some patients that a toxic phase follows the disappearance of these symptoms and then liver damage occurs which leads to the death.
There is an increased tendency for bleeding in yellow fever patients and therefore it belongs to the group of hemorrhagic fevers. According to the estimates made by the WHO, almost 200,000 cases of yellow fever are reported every year and it leads to the death of almost 30,000 individuals annually worldwide. Out of all these cases, around 90% of cases are reported in Africa.
There is usually an incubation period of 3 to 6 days after the infection after which the yellow fever begins suddenly. Most of the cases are only reported to cause mild infection along with fever, chills, head ache, back pain, loss of appetite, nausea and vomiting. Most of these cases last for only 3 to 4 days and only 15 % of the reported cases enter the second phase which is toxic. The toxic phase of yellow fever shows symptoms like recurring fever, this time also accompanied by jaundice because of the damaged liver.
Abdominal pain is also reported in these cases. There is internal bleeding in the mouth, gastrointestinal tract and the eyes which subsequently causes vomits containing blood. This toxic case is reported to be fatal in almost 20 % of the reported cases.
The virus, as mentioned earlier, belongs to the flaviviridae family. The length of the positive e sense single stranded RNA is approximately 11 nucleotides long. The virus has a single open reading frame which encodes a poly protein. The viruses infect monocytes, macrophages and dendritic cells. Specific receptors enable the virus to attach itself to the cell surface, which is then taken up by an endosomal vesicle in the host cell. The virus then begins its complex activity within the cell and replicates itself along with the normal course of cell division. During this course the symptoms of the first phase occur and manifest themselves on the human body.
The attenuated live vaccine was developed to provide immunity from yellow fever. The vaccine is also known as “stem 17 D” among medical professionals and researchers. This vaccination was developed in the year 1937 by Max Theiler. Upon providing these vaccinations, mild flu like symptoms can develop which lasts for a couple of days. Sometimes, in very rare cases, as rare as 1 in 200,000 to 300,000 cases where vaccination cannot be conducted for some reason, dispensation is possible and permitted.
In these cases an exemption certificate which can be issued by any WHO approved vaccination center is required. There are 44 countries where yellow fever is known to occur endemically. But only 32 of these countries have the vaccination program in place. Even among these countries, only about 50 % of the people are vaccinated. All this stems from reports generated by the WHO from time to time.
Knowing about a disease in detail often prevents one from getting infected by it. The causes and the vectors which aid in spreading such a disease must be carefully noted and any exposure to that must be immediately followed by a thorough checkup to nip the spread of the disease in the bud itself. However, if the symptoms show themselves, without the person being aware of being infected, it must be treated immediately by any qualified medical professional.
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