Yellow fever

yellow fever summary

Yellow fever is a disease caused by a virus and is transmitted by the bite of a mosquito, being endemic to tropical regions. In urban areas, the disease is transmitted by the bite of the Aedes aegypti mosquito ; in wild and rural regions, the transmitting mosquito is of the genus Haemagogus and Sabethes. In Brazil, the last recorded case of urban yellow fever was in 1942.
Initial symptoms include fever, body aches, diarrhea , nausea, vomitingand jaundice. Some patients progress to a severe form of the disease, with internal bleeding, kidney, liver and heart failure. A portion of patients progress to a very severe form, known as the toxic phase. At this stage, mortality is high and can reach 50% of cases. Patients present with various hemorrhages, organ failure, delirium, jaundice and coma.

Treatment is symptomatic and aims to reduce symptoms, using antipyretics and electrolyte and platelet replenishers to ease the severity of the disease.

Medicinal plants such as passion fruit, lemongrass and angelicó can help combat symptoms such as fever .

Prevention is done by combating transmitting mosquitoes, vaccination and education of the population.


Yellow fever is an infectious disease caused by a virus from the flavivirus family, with an RNA genome, transmitted by a mosquito bite.

It is a type of hemorrhagic fever transmitted by a species of mosquito and endemic to Africa, Asia and South America.

Mosquitoes become infected when they bite primates that have the virus.1.


Approximately 200,000 people worldwide are infected with yellow fever each year2 . This disease causes approximately 30,000 deaths per year. Most of these cases and deaths (about 90%) occur in Africa.

United States  
The United States has not experienced a yellow fever epidemic since 1905.

Causes & Transmission

Yellow fever is caused by a virus of the flavivirus family, with a single positive-sense RNA genome. In English, this virus is called the Yellow Fever Virus (YFV).
In this same family of viruses, which cause yellow fever, there are other viruses such as  dengue , Zika and West Nile fever . All of these viruses are transmitted to humans by mosquitoes (eg Aedes aegypti ).

Transmission (mosquito bites)
Transmission of the yellow fever virus can occur in urban, wild or rural areas, and in Brazil, the last recorded case of transmission in an urban region was in 1942, in Acre, according to data from the Ministry of Health.
In wild and rural areas, the virus is transmitted by the bite of a mosquito, mainly of the genus Haemagogus and also of the genus Sabethes (to a lesser extent). In these areas, mosquitoes acquire the virus by biting an infected monkey (the main host of the yellow fever virus) and transmit it to their eggs. An unimmunized person, who eventually goes to an endemic area and is bitten by a mosquito contaminated with the virus, can move to an urban area and become a source of infection for the Aedes aegypti mosquito .(the same dengue transmitter ) and Aedes albopictus. The latter has not yet been definitively identified as a transmitter of yellow fever.

The Aedes aegypti mosquito , after having bitten a person infected with the yellow fever virus, transmits the virus after 9 to 12 days. This mosquito (as well as Aedes albopictus ) has diurnal habits (they usually bite during the day) and reproduce in clean, still water, accumulated in gutters, plant pots, bromeliads, tires, bottles, barrels, swimming pools, etc.

As with other diseases caused by flaviviruses (such as dengue ), transmission during pregnancy can occur through the placenta, although this is not common.

Is yellow fever contagious?
You cannot directly transmit yellow fever to another person if you have the disease. For example, you don’t transmit it by coughing or kissing. However, if you have this infection and a mosquito bites you and then it bites someone else, it could infect that other person.

Groups of risk

In Brazil, with the reintroduction of Aedes aegypti, all regions have risk areas (rural areas, forests, cerrados, etc.). Risk groups include non-immunized (vaccinated) tourists who travel to disease-endemic regions and travel to urban regions. These individuals are reservoirs of the virus and can transmit it to other people through the bite of the Aedes aegypti mosquito. In addition, people who live in endemic regions and are not vaccinated against the disease are also a potential risk group.


– The virus spreads through the blood causing the first nonspecific symptoms: fever , headache , chills, nausea , body aches, vomiting, jaundice (skin, eyes and mucous membranes turn yellow), diarrhea and hemorrhages (gums, nose, urinary tract , gastrointestinal system).
No symptoms
Some individuals are asymptomatic, and these cases occur mainly in endemic areas. In Brazil, it is estimated that in most cases yellow fever has no symptoms.
– The symptoms that call the most attention are fever and back pain . After approximately 3 to 4 days of disease evolution, most patients improve and the symptoms disappear.
Severe symptoms
– However, in about 15% of patients, the disease progresses to a worsening, known as the toxic phase of the disease. In this phase, the fever rises again, the patient has diarrhea with a bad smell, abdominal pain, bleeding in the gums, skin, nose, internal bleeding with disseminated vascular coagulation, causing infarction in several organs. In this phase, renal and hepatic functions are compromised, in addition to a decrease in cardiac function. Fulminant hepatitis often occurs due to the shock caused by multiple internal hemorrhages. Impaired liver function increases the circulation of bilirubin, which gives the skin and mucous membranes a yellow color. The mortality rate in the “toxic phase” of the disease is around 50% and these patients die after 7 to 10 days3.

period The incubation period is 3 to 7 days after the bite of the infected mosquito (in exceptional cases, up to 15 days). That is, after infection with the virus, the initial symptoms appear 3 to 7 days later.

Risk of death in the absence of vaccination:
In symptomatic individuals infected with the yellow fever virus and not vaccinated, the risk of death is approximately 30%, as shown by the Brazilian study carried out by the University of São Paulo (USP) and published in May 2019 in the scientific journal The Lancet Infectious Diseases . This study carried out in 2018 showed that of the 231 patients admitted to the Hospital das Clínicas in São Paulo (Brazil), about 30% of patients with symptoms died. All patients were adults.


The diagnosis of the disease is essentially clinical, made by observing the symptoms and clinical history of the patient (travel, vaccination status, symptoms presented, etc.). In addition, virological tests, such as PCR, MAC-ELISA or culture isolation, can also be used, especially in the first cases of disease in a region.


About 15% of patients evolve, within 24 hours, to a very severe phase of the disease, known as the toxic phase. At this stage, a series of events, such as internal bleeding and disseminated coagulation, lead to the failure of multiple organs, especially the kidney (the patient has a deficit in urine production, known as anuria), liver (fulminant hepatitis and liver failure) and heart.

In this phase, the patient presents blood elimination through vomiting (hematemesis) and feces (melena), in addition to liver and kidney failure, jaundice, delirium and coma. Mortality is high, reaching up to 50% of patients, most of whom are elderly and children. Normal yellow fever has a mortality of about 5%.


Yellow fever has no specific treatment to eliminate the virus from the body, and the drugs administered are aimed at reducing symptoms such as fever, muscle aches, headaches, diarrhea, etc. Antipyretics are introduced with the purpose of reducing the patient’s fever, as well as replacing fluids lost through diarrhea.

If yellow fever is suspected, the patient should avoid medications that contain acetylsalicylic acid in their composition, as these products increase the risk of bleeding due to their anti-platelet aggregation action.

Severe forms of the disease require specific treatment, which may include platelet transfusion and dialysis procedures. During the initial phase of the disease, it is recommended that the patient be protected by mosquito nets, so that he does not become a focus of infection by the Aedes aegypti mosquito.

Vaccination against yellow fever appears as an alternative to prevent the disease. With the re-emergence of sylvatic yellow fever in regions outside the Amazon and with the appearance of outbreaks from 1999 onwards, constant work has been carried out so that more people can be vaccinated. Read more about vaccination below, in the Prevention section


For the prevention of yellow fever contamination, some tips are useful:

– In case of suspicion of the disease (if the patient has traveled to an endemic region), seek medical attention immediately;

– Do not leave standing water in places where it can accumulate;

– Keep water tanks, barrels, cisterns, wells always clean and closed;

– Use mosquito repellents containing DEET (N,N-Diethyl-m-toluamide);

– Use screens to prevent mosquitoes from entering;

– Before traveling to an endemic location, look for a health center and get the vaccine.


Prevention of yellow fever can be done in the following ways:

Yellow fever vaccination

Vaccination is considered by the World Health Organization (WHO) to be the main and most effective way to fight yellow fever.

The yellow fever vaccine consists of the attenuated virus. In Brazil, the vaccine against yellow fever is manufactured with attenuated live virus. WHO says immunity is acquired within 30 days in 99% of those vaccinated.
According to the Brazilian newspaper Folha de S.Paulo (in an article dated January 13, 2017) it is estimated that in Brazil the effectiveness of the yellow fever vaccine is around 90%.

A single vaccination
– The duration of immunization against yellow fever is lifetime (according to WHO studies published in 2013), before May 2013, it was estimated that immunization should be repeated 10 years after the first injection. Today, a single vaccination against yellow fever is sufficient. In Brazil, since April 2017 a single dose of yellow fever vaccine is also recommended.

Split vaccine The split
vaccine is 0.1 ml and the normal vaccine is 0.5 ml. That is, the fractionated vaccine has a fifth of the volume of the normal vaccine. So far, studies have shown that the protection of the fractional dose, of 0.1 ml, is the same as that of the standard or normal dose, of 0.5 ml. The first protects the person for up to eight years, and the second, for life. In Brazil, in 2018, the strategy of using the fractionated vaccine is an emergency and has the support of the World Health Organization.

Why the split vaccine?
The fractionation of the vaccine as an option is used when there is a risk of yellow fever expanding in cities with a high population rate and that had not previously recommended vaccination.

Side effects of the yellow fever vaccine: in some cases there is mild muscle pain in the area of ​​injection or fever within 48 hours of vaccination. Body aches and headaches are also possible. These very mild side effects affect about 2 to 5% of vaccinees.
A very serious but very rare side effect of the vaccine (about 1 person in 400,000 people vaccinated) is the development of an often fatal illness called viscerotropic disease. This disorder can lead to shock and multiple organ failure. According to the Brazilian Ministry of Health, quoted in an article in Folha de S.Paulo on January 13, 2017, authorities counted 8 cases of this disease with 7 deaths between 1999 and 2007.
Encephalitis is another serious side effect of the vaccine, but it is also very rare.
For a full list of side effects, ask your doctor or pharmacist, read the package leaflet.

Contraindications for the yellow fever vaccine (unless your doctor recommends otherwise): the vaccine is contraindicated for pregnant women, people allergic to eggs (if the vaccine is based on eggs or derivatives), people with the flu or fever, children under the age of 6, people who are immunocompromised (with illnesses such as AIDS or cancer), people who take immunosuppressant drugs, and people who have radiotherapy. People with autoimmune conditions such as lupus or rheumatoid arthritis should talk to their doctor to see if vaccination is recommended.
In some countries, it is estimated that yellow fever vaccination is considered safe in people aged 9 months to 60 years. In persons younger than 9 months or older than 60 years, please seek advice from a physician. Ask your doctor or pharmacist for more information.

In Brazil, the vaccine is not indicated for pregnant women, women breastfeeding children aged up to 6 months and immunosuppressed people, such as patients undergoing chemotherapy, radiotherapy or high-dose corticosteroids ( Lupus patients , for example). In case of doubt, it is important to consult the doctor.

Where to find the vaccine?
In Brazil, the vaccine is free and available at any time of the year, at ANVISA posts and health posts. If you are over 60 years old or younger than 9 months, contact a doctor. In Brazil, the vaccine is also available in private clinics (values ​​around R$250 in January 2018).

In case of travel
Yellow fever vaccination must be carried out at least 10 days before travel (to ensure its effectiveness upon arrival in the risk area).

fight against mosquito

As with dengue , combating the transmitting mosquito is essential for preventing the disease. Combat measures include:

– Do not leave clean, stagnant water in plant pots, gutters, barrels, bottles, old tires or any other container that can accumulate water.

– Keep water tanks, barrels, cisterns, etc. covered.

– Water plants with water treated with chlorine (40 drops of bleach to 2.5 liters of water).

– Use mosquito nets and screens to prevent mosquitoes from entering the home.

Education of the population

The education of the population is an important step, as it alerts people to prevent and avoid the disease. Campaigns by the Ministry of Health guide the population to avoid the accumulation of clean, stagnant water and to maintain adequate conditions of cleanliness and hygiene.

World Health Organization (WHO), Ministry of Health (Brazil), Folha de S.Paulo,, Secretariat for Green and Environment (SVMA) in São Paulo (SP), Government of Brazil (with information Ministry of  Health  and  Fiocruz ), Princeton University .

Jeanne Kenney
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I’m a stylist trainer, a content creator, and an entrepreneur passion. Virgo sign and Pisces ascendant, I move easily between my dreams, the crazy world I want, and my feet on the ground to carry out my projects.

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