Yellow Fever: Symptoms, Transmission, Vaccination

Yellow fever (caused by yellow fever virus from the family Flaviviridae, RNA arboviruses) is a serious illness that presents with sudden fever, head and spinal pain, yellowing of tzhe skin and sometimes bleeding from the nose and mucous membranes.

It is currently found in Africa, Central and South America. This situation may not be stable. In some countries, the disease is being contained, while in others it may flare up.

The World Health Organization therefore publishes an updated list of countries where the risk of infection is possible and probable every year.

There are 33 endemic countries in Africa and 9 endemic countries in South America, where between 15° north and 10° south of the equator and on some Caribbean islands, Bolivia, Brazil, Colombia, Ecuador and Peru are considered to be at high risk of acquired infection.

A traveller who becomes infected during a stay in one of these countries may become ill in Slovakia. However, the conditions for the spread of the disease are not present here.

Some sufferers get the disease easily, but the mortality rate is as high as 60% for travellers who get infected while travelling to the countries of outbreak.

Yellow fever is caused by a virus that is transmitted from person to person by mosquitoes. Mosquitoes become infected from reservoir animals, most commonly monkeys. The disease is a natural outbreak.

The virus causes not only febrile states but also haemorrhagic syndrome, i.e. bleeding during the course of the disease.

The virus in the body most commonly attacks the liver, bone marrow and kidneys and can take two forms, the urban cycle and the jungle cycle. These forms are distinguished by the causative agent and the vector of the disease.

The incubation time of the disease is short, 3 - 6 days.

If a person infected with yellow fever virus returns from forested to urban areas, he or she may be bitten by an Aedes aegypti mosquito, which further spreads the virus among the urban population.

Vaccination is therefore mainly recommended for people who intend to visit high-risk areas for mosquitoes or for people who live in high-risk areas.

The highest mosquito activity, and therefore the highest risk of yellow fever virus transmission, is from December to July.

The most common cases of jungle-type yellow fever occur when a person becomes infected while visiting forested areas or after contact with infected monkeys in such areas.

In this form, transmission is caused by the Aedes africanus mosquito or the Haemagogus mosquito.

The causative agent of the disease is the mosquito, which transmits the disease from monkeys to humans, but also from humans to humans. This virus multiplies in the human body and causes the symptoms of the disease.

This viral disease belongs to the Flaviviruses and occurs in the liver, bone marrow and kidneys.

It is an arbovirus that can be vaccinated against with a vaccine that lasts up to 10 years, but there is no effective treatment for yellow fever yet.

Yellow fever has an incubation period of roughly 3-6 days, with the disease itself occurring in two stages.

The first stage is called red and is characterized by fever, pain in the loins, chills, chills, general flushing of the patient and restlessness.

Slowing of the heart may also occur. This stage usually lasts 3 to 4 days, usually starting within a week of infection, which is the maximum incubation period, but many times shorter.

After the first stage comes the more serious second stage of yellow fever, which develops in about 15% of infected patients.

At this stage, cyanosis or pallor are already present, there is a deterioration of the state of health, and bleeding from the mucous membranes occurs. The person also vomits, and in the vomit, digested blood is also present.

The bleeding becomes progressively heavier, the person bleeds from the digestive tract, skin, eyes, ears, nose or even genitals.

If there is more damage to the liver, the skin will turn yellow. If the liver is damaged, it also becomes enlarged and painful to the touch.

Table: symptoms of yellow fever

Other symptoms include:

• head spinning
• Malaise
• chills
• shivers
• vomiting of blood (haematemesis)
• disgust
• enlargement of the liver (hepatomegaly)
• restlessness

The disease is diagnosed on the basis of symptoms, especially during the second phase, but if a rapid diagnosis is necessary, blood is taken and laboratory diagnosis of antibodies or the virus in the blood is carried out.

Other laboratory tests will show decreased white blood cell count (leukocytes), protein in the urine (proteinuria), increased liver function test (AST, ALT, bilirubin - bile dye).

Based on the medical history, we learn about the presence of risk factors, for example, staying in a high-risk area if it is imported yellow fever in tourists.

Since the treatment is symptomatic, early diagnosis plays an important and large role in the speed of treatment.

How can I protect myself against the disease?

Yellow fever vaccination is the only effective means of preventing infection. The vaccine is a live vaccine that is prepared on chicken embryos. It is administered subcutaneously. It is highly effective, almost 100%. 

Who is the vaccination for?

Vaccination is recommended for all persons living in a yellow fever endemic area. 

Yellow fever vaccination is mandatory for travelers to certain countries and recommended for travelers to countries with yellow fever (yellow fever occurs in Africa and South America). 

Is yellow fever vaccination before travelling abroad compulsory?

Yellow fever vaccination is the only mandatory vaccination before travelling abroad. It is required by some countries in Central and South America and equatorial Africa.

Other countries, such as India, require it for those travelers who come to India from areas where yellow fever occurs.

Every year, the World Health Organization publishes an up-to-date list of countries where vaccination is mandatory and recommended.

Is this vaccination safe?

In general, the administration of this vaccine is safe, but rarely serious neurotropic and viscerotropic disease can occur (2.4 - 1 / 100 000 doses administered).

Side effects after vaccination are very mild and rare.

People with:

• a serious immune deficiency,
• symptoms of HIV infection,
• with hereditary fructose intolerance of HIV infection,
• with egg white allergy
• pregnant women and
• children under 6 months of age

... are NOT recommended to get vaccinated!

In children aged 6-8 months, yellow fever vaccination is administered only if there is a high risk during an epidemic. 

As this is a live vaccine, the risk and benefit of vaccination should be carefully weighed in pregnant and breastfeeding women. 

When do I need to be vaccinated?

If the trip is planned well in advance, it is ideal to be vaccinated 1 month before the trip, but at least 10 days, because the antibodies that are formed after vaccination reach an effective protective level on the 10th day after vaccination, and this is also the time when minor reactions after vaccination completely disappear.

Vaccinations are compulsory for some countries, which means that upon arrival in such a country, the traveller may be required to present an international vaccination card, in which these vaccinations must be recorded, 10 days prior to travel.

Some countries, particularly those where the disease is not currently present but the conditions for its spread are present, require vaccination only of persons arriving there from outbreak countries.

The vaccination protects the vaccinated person for 10 years. After that, the vaccination must be repeated.

Is it necessary to consult vaccination?

During the consultation at the travel medicine clinic, they will try to weigh up the benefits and risks of vaccination on an individual basis, taking into account the plan and length of your trip, your health and your age.

When staying in areas with a low risk of yellow fever transmission, vaccination will generally be considered on the basis of:

• length of stay,
• risk of significant exposure to mosquito bites,
• other paths in the future and
• the immune status of the traveller. 

Do you need a vaccination and a accination card?

One dose of yellow fever will provide lifelong immunity against yellow fever. Its administration is recorded on the International Vaccination Card. It becomes valid 10 days before travel. 

Vaccination is not necessary. 

If you cannot be vaccinated against yellow fever for medical reasons, you will be issued with a vaccination contraindication document, which is valid for the trip and is accepted in most countries.

At the same time, it is necessary to take precautions against mosquito bites. 

How to prepare for vaccination?

Come to the vaccination completely healthy.

After vaccination, we recommend avoiding heavy physical activity for 1 week. 

The price of the yellow fever vaccine (Stamaril) is 60 euros, including administration.

Recommendations

Public Health Offices recommend the following for travellers to the affected areas:

• Vaccination is recommended for travelers to high-risk areas.
• Vaccination is recommended at least 10 days before travel to build up sufficient antibody levels.
• Vaccinations are to be recorded in writing.
• Vaccination is carried out by foreign diseases departments.
• Vaccination is done with a single dose of yellow fever vaccine.
• Vaccination is recommended in the following areas of Brazil.

Precautions against insect bites:

• Use of repellents.
• Wearing lightweight long clothing made of natural material preferably light in colour.
• Use mosquito nets in areas where mosquitoes are most active.

Upon return:

• Check your health (especially high temperature, chills, vomiting).
• Contact your doctor in case of health problems and inform him/her about staying in risky areas.