Anyone traveling to South America or visiting some countries in Africa should get vaccinated against yellow fever in time. The yellow fever virus is transmitted by mosquitoes and can be fatal, but the vaccination provides reliable protection against the disease. Yellow fever is notifiable in Germany. You can find out everything important about the disease here.
Transmission of yellow fever
Primarily monkeys, but also snakes, birds and bats are among its actual victims. The small mosquito Aedes aegypti infects these animals with the yellow fever virus during its blood meal. But humans are also bitten and infected by the mosquito. It usually affects workers in the forested fringes of the jungle in a number of countries in tropical sub-Saharan Africa and tropical South America, such as the Amazon region. It is they who, on their return to the towns and villages, in turn transmit the virus to other mosquitoes of this genus. If the mosquito now bites other people, the yellow fever virus spreads epidemically in cities.
Yellow fever mosquito as a vector of the disease
Of the approximately 3,000 mosquito species known worldwide, about 200,000 yellow fever infections and, as a result, about 60,000 deaths annually are attributed to the yellow fever mosquito, according to the World Health Organization (WHO) (as of 2016). When they bite, the viruses quickly enter the bloodstream, where they attack the macrophages in the lymph nodes, spleen, liver and bone marrow. Here they multiply and enter the blood – for two to four days – and are then transmissible via bites.
Symptoms and course of yellow fever
Yellow fever virus belongs to the flavivirus family. The dengue virus and the hepatitis C virus also belong to this family. In it is the Latin word flavus – yellow, because there is also a yellowing (icterus) of the skin and eyes. The cause is an increase in the concentration of the blood breakdown product bilirubin in the body. It is formed during the breakdown of red blood cells, a process that constantly takes place in the spleen, bone marrow and liver. The incubation period lasts three to six days. Here, the following symptoms occur during the initial phase of illness, and may subside after three to four days:
- Fever
- Chills
- Headache and pain in the limbs
- Loss of appetite
- Nausea and vomiting
These symptoms resemble a “normal” infection and are not always taken seriously. This is followed, but only in about 15 percent of those infected, the second phase with high fever and internal and external bleeding, which ends fatally in 20 percent of those affected.
What is the prognosis for yellow fever?
Survival of the infectious disease, which usually heals without sequelae, results in lifelong immunity. The lethality (fatality) of clinically observed cases ranges from ten to 50 percent, with the age group between 20 and 30 years having the highest lethality.
Treatment of yellow fever
There is no drug against the virus. Only the symptoms can be alleviated. If the course is unfavorable, the patient usually dies within the second week. According to the Robert Koch Institute (RKI), the last known death in Germany was in 1999 – a man who had traveled to the Ivory Coast and was not vaccinated.
The origin of yellow fever
The first yellow fever outbreaks in the New World are documented from the Yucatan Peninsula (Mexico) and Havana (Cuba) in 1648. Since then, numerous epidemics have occurred in Central and South America. The name “Yellow Jack” for yellow fever also originated in England. Yellow fever patients have been provided with jackets marked yellow, and a yellow flag has also been raised over the quarantine area.
Vaccination against yellow fever
Although a highly effective vaccine against yellow fever has been available for decades, WHO has recorded an increasing number of infected people in Africa and South America. The vaccine was developed in 1937 by South African physician and scientist Max Theiler and is one of the best and safest vaccines. Theiler received the Nobel Prize for his research in 1951. The vaccine consists of attenuated yellow fever viruses capable of replication. 0.5 ml of the vaccine is injected under the skin – almost always into the upper arm. Vaccination is possible from the 6th month of life (according to WHO recommendation from the 9th month of life). Vaccination protection begins about ten days after vaccination and lasts for at least ten years.The WHO even assumes lifelong protection. The antibodies are detectable in 96 percent of those vaccinated.
Side effects of yellow fever vaccination
The yellow fever vaccine is well tolerated; only those allergic to chicken protein should inform the doctor before vaccination. Pregnant women and those infected with HIV, immunocompromised individuals, and patients who have just been vaccinated against other diseases should also seek medical advice. The risk of severe side effects is increased in people over 60 years of age. The RKI has evaluations of yellow fever tolerance over a period of more than 35 years; after administration of more than 2.3 million vaccine doses, a total of only 20 vaccine complications have been described. According to the WHO, damage to the liver, kidneys, or nervous system occurs on average in 0.4 to 0.8 per 100,000 vaccinated persons. The RKI recommends abstaining from alcohol for one week after the yellow fever vaccination and avoiding major physical exertion as well as visits to saunas and solariums. Typical vaccination reactions such as fatigue, exhaustion, a slight rise in temperature and redness at the injection site have been described in five to ten percent of those vaccinated.
Don’t forget your vaccination card
The vaccination is entered in the vaccination certificate – this is important for entry or transit in the countries affected by yellow fever. In South America, for example, these are Bolivia, Brazil, Ecuador, Colombia and Peru; in Africa, they include Burkina Faso, Ghana, Kenya and Nigeria. It is essential to find out about the current regulations of the respective country in good time before starting your journey. Yellow fever vaccination is one of the international travel vaccinations; it is only available at vaccination centers or from certain vaccinators and is strongly recommended for the affected areas.