What is yellow fever?
Yellow fever is an acute viral disease transmitted by the bite of infected mosquitoes, most often of the species Aedes aegypti, and the virus responsible is an arbovirus of the genus Flavivirus.
What is the incubation period?
The yellow fever incubation period (time between contagion and the onset of symptoms) is 3 to 6 days.
What are the initial symptoms?
The initial symptoms of yellow fever are:
- fever
- headaches
- muscle aches and pains
- lack of appetite
- general malaise or nausea
- Vomiting
- fatigue
- yellowish discoloration of the skin and/or mucous membranes of the eyes (jaundice)
The initial symptoms tend to disappear after 3 to 4 days. However, after these initial symptoms, 1 to 2 in 10 patients will develop a severe form of yellow fever.
What are the symptoms of severe disease?
Symptoms of severe disease are:
- high fever
- yellowish discoloration of the skin and/or mucous membranes of the eyes (jaundice)
- bleeding (hemorrhage) from the digestive tract, nose, and/or eyes
- multi-organ failure and shock
Mortality in patients with severe disease is very high, reaching up to 50%.
How is it transmitted?
Transmission occurs through mosquito bites and consequent inoculation with the yellow fever virus.
Which countries are at risk of transmission?
The yellow fever virus is endemic (always exists) in tropical and subtropical regions of Africa, Central America and South America. It does not exist in any country on the Asian or European continent.
Refer to the maps available from the World Health Organization: Africa and Americas.
How is the diagnosis made?
The clinical diagnosis of yellow fever can be difficult, particularly due to the similarity of the clinical manifestations with other diseases such as severe malaria, fulminant hepatitis or other viral hemorrhagic fevers.
There are complex medical tests for diagnosis, in the early stages of the disease, to identify the virus and, in later stages, to detect antibodies.
It is important to have health insurance, as it contributes to better access to diagnosis at the destination and/or eventual treatment.
What types of treatment are available?
There is no treatment specifically directed at yellow fever. However, supportive treatment at the hospital level may improve the survival rate. The best treatment is prevention.
How can I prevent it?
People travelling to countries where yellow fever is present should seek advice as part of a Traveller Consultation.
In order to prevent the circulation of yellow fever between different countries, it is possible that a yellow fever vaccination certificate may be required upon entry into some countries under the international health regulations. There are other countries that do not require the vaccine, but due to the risk of disease transmission it may be advisable to administer it.
You can consult the World Health Organization for list of countries at risk of yellow fever and requiring vaccination for entry.
Is there vaccination?
There is a vaccine against yellow fever, with many years of use and therefore safe, effective and from which a single dose confers lifelong immunity against this disease.
As it is a live attenuated vaccine, it has some contraindications to its administration, and is, as a rule, contraindicated in case of:
- allergy to any component of the vaccine
- Infants under the age of 6 months
- immunity problems or medication that reduces immunity
And it should be considered in the following cases:
- for babies between 6 and 9 months of age
- after the age of 60
- in pregnancy and breastfeeding
Where can I get vaccinated?
Due to the requirements associated with the issuance of the International Certificate of Vaccination, the vaccine is only available at the International Vaccination Centres.
What are the precautions I should take during pregnancy?
Pregnant women should avoid or postpone travel to areas where there is a risk of yellow fever. If travel cannot be avoided, a consultation with the doctor before departure is recommended.
If yellow fever vaccination is done during pregnancy, clinical problems are unlikely to arise for both the woman and the baby.
Learn more at guide for pregnant women.
How can I prevent mosquito bites?
The best way to avoid yellow fever is to avoid mosquito bites.
Mosquitoes can transmit:
- malaria
- black vomit
- dengue
- Japanese encephalitis
- Chikungunya
- West Nile fever
- among other diseases, depending on the regions
Insect bites can be painful, but they are usually asymptomatic. It is important to take action:
- Find out locally about mosquito-infested areas, especially if you're in rural areas and it's a long-term trip
- Wear comfortable and loose clothing, in order to cover as many areas of the body as possible, namely long-sleeved blouses, trousers, socks and closed shoes
- Use repellents or insecticides (such as permethrin) on clothing, as bites can occur through clothing
- Use repellents on the skin, on exposed areas of the body
- Whenever possible, use air conditioning and/or sleep under a mosquito net, preferably impregnated with insecticide, accessible in stores that sell camping or travel equipment
What kind of repellents are there?
Repellents are available in various formulations and in different concentrations. Most formulations contain diethyltoluamide (DEET 20-50%), icaridin or IR3535, which are effective substances in preventing insect bites.
There are formulations:
- spray
- cream
- roll-on lotion
- Stick
How should I use the repellent?
You should use the repellent:
- on exposed areas of the skin, namely the neck, wrists and ankles
- If you apply sunscreen, the repellent should be applied last
Spray, should not be sprayed directly on the face. Do not use the repellent:
- eyes
- mouth
- About Cuts
- wounds
- irritated skin
Read the repellent package leaflet carefully. If in doubt, contact your doctor.
The effectiveness and duration of protection of repellents varies considerably between products and between mosquito species. The effectiveness and duration of protection of repellents affect the following:
- Ambient temperature
- The level of activity
- Perspiration
- Exposure to water
- Abrasive removal
- among other factors
It is necessary to take into account the protection time indicated on the packaging as well as all exposure factors, and if necessary repeat the application of repellents more frequently.
What precautions should I take when using repellents on children?
Repellents should not be handled by children, as they can potentially be applied to the eyes. Protective measures should be reinforced with clothing, and repellent should be used in exposed areas. Repellents can be applied to children over the age of 2 months.
Sources: Portuguese Society of Travel Medicine (SPMV), Directorate-General for Health (DGS)