Yellow fever is an acute and infectious viral disease that is caused by the virus belonging to the Flaviviridae family of the yellow Flavivirus genus. The adjective “yellow” refers to signs of jaundice that manifest in some patients.
At present, it can be prevented effectively by vaccination. However, it continues to represent a public health problem, since it causes around thirty thousand deaths per year.
At present, yellow fever has a notable incidence in areas such as: Africa, South America and the Caribbean. Most outbreaks occur in people who work in tropical rainforests, which is why it is considered an occupational disease.
Yellow fever is transmitted by the bite of female mosquitoes, mainly of the genus Aedes or Haemagogus, which abound in humid areas around stagnant water.
Two main transmission cycles are known: jungle and urban. In addition, an intermediate cycle is also distinguished in Africa
Jungle yellow fever
This type is transmitted from monkey to monkey , having as a vector the Aedes africanus , which inhabits central Africa. It also occurs in South America, but by the bite of Haemagogus mosquitoes . This form of transmission is rare in humans, since it only occurs when, for some reason, they enter the jungle.
Urban yellow fever
This is the most common type and is transmitted from person to person , through the bite of the mosquito, which abounds in humid areas around reservoirs of stagnant water and that only itches during the day.
Intermediate transmission cycle
This cycle of transmission occurs when the yellow fever virus is transmitted from the monkey to man and from man to man by the bite of mosquitoes Aedes simpsoni and Aedes bromeliae . They are common in the humid areas of the savannah of Central and Western Africa during the .
The incubation period of yellow fever lasts between 3 and 6 days until symptoms manifest. Its name refers to two of its main symptoms: fever and jaundice (yellowing of the skin). Depending on its development, we can say that the infection goes through three stages:
Most infected patients remain in stage one of yellow fever and, since the symptoms are similar to those of a flu syndrome , many overlook it. This phase lasts from 3 to 4 days and may include:
- Muscular and joint pains.
- Fever and hot flashes.
In general, patients recover when they reach this stage. However, some cases may get worse in a 24-hour period.
Half of the patients who reach this stage die within 7 to 10 days. If the infection gets to a higher level of severity, what is known as hemorrhagic fever occurs , compromising the , liver and kidney. Symptoms include: jaundice, high fevers, seizures, vomiting (of clotted blood), internal bleeding, coma and delirium.
The diagnosis of yellow fever is usually difficult , especially in the early stages, due to the similarity of its symptoms with the flu-like symptoms. More severe cases are often also confused with severe malaria, , and other flavivirus infections (such as dengue hemorrhagic fever).
For this reason, initially, the health professional will start with some clinical data , questioning the patient about possible trips to endemic areas of the disease, and if he has received the yellow fever vaccine.
The doctor will also suggest selected blood tests , which will be used to detect the virus and determine if there are liver and kidney complications. The tests include a complete hematology, in which a decrease in white blood cells (leukopenia) and an increase in hematocrit due to dehydration can be observed, indicating the presence of yellow fever.
At present, there is no specific antiviral treatment to cure yellow fever. That is why, initially, the most effective measure is its prevention through vaccination.
Unvaccinated people who contract the disease can only receive symptomatic treatment, which aims to reduce the severity of symptoms. The use of Do not use aspirin because of the risk of bleeding.
On the other hand, it is essential that the patient drink plenty of fluids to avoid dehydration. If associated bacterial infections occur, the doctor will suggest antibiotics to treat them. In case the disease reaches its most advanced stage, the treatment includes:
- Blood products for serious bleeding.
- Dialysis for kidney failure.
- Intravenous fluids (intravenous fluids).
If you are thinking of traveling to endemic areas of the disease, or if you live or work in any of them, it is essential to consult the doctor and request a yellow fever vaccine.
Centers for Disease Control and Prevention. Accessed January 22, 2016.
Kanzaria HK, Hsia RY. Mosquitoes and mosquito-borne diseases. In: Auerbach PS, ed. Wilderness Medicine. 6th ed. Philadelphia, PA: Elsevier Mosby; 2012: chap 48.
Thomas SJ, Endy TP, Rothman AL, Barrett AD. Flaviviruses (dengue, yellow fever, Japanese encephalitis, West Nile encephalitis, St. Louis encephalitis, tick-borne encephalitis, Kyasanur Forest disease, Alkhurma hemorrhagic fever, Zika). In: Bennett JE, Dolin R, Blaser MJ, eds. Mandell, Douglas, and Bennett’s Principles and Practice of Infectious Diseases. 8th ed. Philadelphia, PA: Elsevier Saunders; 2015: chap 155
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