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What is yellow fever and how it is spread?

Also known as the black vomit disease or American plague, yellow fever is a viral disease transmitted by the bite of a mosquito, which causes jaundice and fever, sometimes with hemorrhages.

Yellow fever is also known as disease the black vomit or American pest, is an acute disease transmitted viral caused by the bite of an infected female mosquito, primarily of the genus Aedes or gender Haemagogus, which feeds blood and is more common in regions of the south of America (as the last cases appeared in Brazil) and Africa. It is characterized mainly by the fever that it produces, sometimes with bleeding, and jaundice, or yellowish coloration, that appears on the skin of those affected.

Although this pathology can be asymptomatic and go unnoticed or be confused with a flu picture, yellow fever can also cause serious complications such as liver or kidney failure, secondary bacterial infections, shock, coma, and even death of the patient.

Yellow fever epidemiology

According to the World Health Organization (WHO), an estimated 200,000 cases of yellow fever occur each year, causing around 30,000 deaths annually, and 90% of the cases occur in Sub-Saharan Africa among the non-population. Vaccinated.

The disease is endemic in several countries – or certain areas – in Africa, Central, and South America, so travelers must be vaccinated before visiting those places to avoid importing the disease to countries where there is no yellow fever.

The first records in history on yellow fever date from the Mayans’ time, who described a similar disease that they called “Xekik” and which translates as “black vomit.” Then, in the famous book Popol-Vuh, a pathology related to monkeys and, later, human beings, who developed a yellowish coloration of the skin.

How Yellow Fever Is Spread

From an epidemiological point of view, the infectious agent of yellow fever is the “yellow fever virus,” an arbovirus (viruses transmitted by arthropods –invertebrate animals, such as insects, spiders, and crustaceans–) of the genus Flavivirus, family Flaviviridae; the reservoir (living being that houses the germ of the disease) are humans in urban areas, and monkeys and some marsupials in jungle areas; and the vector (i.e., the agent that carries the virus from the reservoir to humans) are female mosquitoes, mainly of the genus Aedes or the genus Haemagogus.

Yellow fever has two different transmission cycles: jungle and urban. In Africa, there is also an intermediate cycle that combines the other two.

  • Jungle or jungle yellow fever: occurs when the virus is transmitted from monkey to monkey, mainly infected by the Aedes African mosquito, which lives in central Africa. This form also occurs in South America, but by the Haemagogus mosquito bite. This form of transmission produces very sporadic cases in humans who enter the jungle.
  • Urban yellow fever or urban ecological cycle: it occurs when the virus is transmitted from person to person through the bite of the Aedes aegypti mosquito, which has been infected at least two weeks before after biting a sick patient in the viremic phase (when the virus enters the bloodstream of the affected person and from there to the rest of the body) or viral multiplication in the blood. This mosquito abounds in humid areas around stagnant water reservoirs (vases, pond) and only bites during the day. This is the most frequent form of transmission in America and leads to a large number of cases.
  • Intermediate or savanna transmission cycle: it is the one that occurs when the virus is transmitted from monkey to man. It occurs in the humid areas of the savanna of Central and West Africa during the rainy season. Other Aedes species are vectors of the disease in West Africa, such as Aedes Aedes leptocephalus. It can sometimes cause a larger outbreak if a sick individual introduces the virus to a larger city. This type of transmission has not been observed in South America.

Symptoms of yellow fever

Yellow fever is named after two of the most common symptoms of the disease: fever and yellowing of the skin and eyes (jaundice). Some cases are asymptomatic, while in other people, after suffering a mosquito bite, the incubation period of between three and six days until symptoms appear. The infection can present itself in two ways:

In most patients, yellow fever can go unnoticed since the symptoms they experience. Which last three or four days and usually resolve spontaneously – are similar to those of a flu syndrome :

  • Muscle aches (especially back).
  • Nasal congestion.
  • Loss of appetite
  • Nausea or vomiting

The other type of manifestation of yellow fever, much more aggressive, occurs between 15% and 25% of patients 24-48 hours after the remission of the first phase and is called hemorrhagic fever. In addition to fever, chills, headache, and muscle aches, hemorrhagic fever is characterized by:

  • Internal hemorrhages, and also nasal, oral, or ocular sacred bleeding.
  • Vomiting of black clotted blood (hematemesis).
  • High fever.
  • Dark-colored urine.
  • Abdominal pain with vomiting
  • Kidney failure. The kidneys begin to fail, decreasing the elimination of toxic substances through the urine, and finally, a shock or collapse of the circulatory system occurs.
  • According to WHO estimates, 50% of patients who reach this stage of the disease die within seven to ten days, while the other 50% manage to recover.