There are many diseases that exist and have existed in the world throughout history. Some of them, such as the Black Death, were a plague that wiped out a large percentage of the world’s population. And the existence of serious diseases capable of causing pandemics is not only a thing of the past: there are still many diseases with no known cure and with the potential to kill.
One of them has been generating outbreaks and epidemics in African and South American countries for centuries. It is the yellow fever , which we will talk about throughout this article.
Yellow fever: description and symptoms
Yellow fever is one of the diseases classified as hemorrhagic fevers which has caused and continues to cause hundreds of thousands of deaths each year. It is an endemic disease present mainly in African or South American areas, and even today can lead to the appearance of important epidemics .
Yellow fever, also known as black vomit disease, Siamese disease or Barbados disease (where the first case was recorded), is named after one of its most characteristic symptoms, jaundice caused by alteration of the liver and pancreas.
But this is not his only symptom : it is also common to have bleeding through the mouth, ears or eyes, internal haemorrhages, very high fevers, headaches, arrhythmias, hypoglycaemia and if it reaches phases of intoxication in addition to the above, there can be convulsions, liver and kidney failure, even more severe bleeding, black vomit due to expulsion of clotted blood, bradycardia, dehydration, delirium or coma. In severe cases it has a high potential to cause death, and does so in a high number of cases.
In other cases, the milder ones, the disease is self-limiting and does not enter its most severe phase with the potential for death.
Phases of infection
Yellow fever is a dangerous disease. Infection involves going through a series of stages in which the symptoms and severity of the condition vary, although not everyone goes through the last stage. We can identify a total of three phases , to which we could add a previous one in the form of an incubation period.
Phase 0: Incubation period
From the moment the bite that transmits the virus that causes it occurs until the first symptoms appear, usually between three and six days. During these days the virus is spreading through the body , without any symptoms appearing at the moment.
Phase 1: Acute phase
Several days after the sting, a series of symptoms typical of an infection usually appear: high fevers, nausea and vomiting, photophobia, headache , redness of soft tissues, hot flushes, lack of appetite and jaundice.
Phase 2. Referral
As a rule, after several days of suffering from the symptoms described above, these usually end up disappearing gradually. In many cases the disease can be stopped at this stage, and the subject recovers . However, in other cases the person may suffer a relapse and worsen about a day later, entering the intoxication phase.
Phase 3: Intoxication
After several days of remission, some of those affected by yellow fever enter a phase of intoxication in which the symptoms reappear with great virulence . This is the most severe phase of the disease.
During this phase, the fever reappears and symptoms such as bleeding from the mouth, nose and eyes may also occur. Problems or even kidney or liver failure are also common . In fact it is in this phase of the disease that jaundice most often appears, giving the skin the yellowish colour that gives the disease its name. Pain in the abdomen, nausea and vomiting are also common.
It is also not uncommon for arrhythmias or bradycardia to occur. In addition to fever, hallucinations and delusions, states of confusion and brain dysfunction may occur. It is also possible for the subject to have convulsions or enter a coma. In short, there are usually multiorgan failures and major bleeding .
Unfortunately, about a quarter to sixty percent of people who enter this phase (in a window that ranges from 25% to 60%) fail to overcome the disease and die.
Causes of this disease
Yellow fever is a viral disease caused by the infection of the yellow fever virus, which like diseases such as dengue fever belongs to the genus Flavivirus.
This virus reaches humans through the bite of infected mosquitoes , usually of the genera Aedes or Haemagogus. The virus can be transmitted between monkeys and from monkey to human by mosquitoes in what is known as the jungle ecological cycle or between people in the urban ecological cycle.
There is also a combined cycle of the two previous ones, that of the sheet, in which infected mosquitoes after biting apes transmit the disease to a human and then after other mosquitoes bite the human they transmit it to other people.
Yellow fever is not spread by contact with an infected person , nor with their secretions.
Is there a treatment?
Yellow fever is a disease for which there is still no specific curative treatment. In the event of infection, the intervention involves supportive treatments. It is essential to monitor and maintain vital signs , to perform dialysis in case of renal failure and to administer fluids to maintain hydration and electrolyte balance. In addition, the use of antipyretics to lower fever and antibiotics (not for the virus but for possible bacterial infections that may appear during the virus) can be very useful.
Although there is no cure per se, we do have an effective vaccine against yellow fever, and in principle only one dose is needed for lifelong protection. This is why the best way to treat yellow fever is to prevent it, and it is necessary to establish vaccination programmes in countries where the condition is endemic and to be vaccinated if you travel to these countries. Another measure is based on controlling the mosquito population, a measure that has been shown to be effective in several countries.
However, the vaccine may be contraindicated or require medical evaluation prior to its application in some sectors of the population: pregnant women (except in high-risk situations), children under 9 months and over 60 years of age (also unless there is a high risk) and subjects who are immunosuppressed or allergic to eggs and their derivatives.
There are currently several initiatives to control yellow fever, such as the EYE programme organized by the World Health Organization, UNICEF and Gavi-alliance for vaccines. This programme aims to protect, prevent and control possible outbreaks of fever through participation in vaccination campaigns, research, health promotion and interaction with institutions and local administrations.
- World Health Organization. (2014). Yellow fever. Small bites big threats.
- Soteras, E. (n.d.). Yellow fever. World Health Organization [Online]. Available at: http://www.who.int/es/news-room/fact-sheets/detail/yellow-fever.