Yellow fever is a disease that is mainly endemic to Africa and South America. Its rare appearances in North America and Europe at the beginning of the 20th century disrupted the economy and development, decimating entire populations.
The symptoms of yellow fever
If you are bitten by an infected mosquito, there is an incubation period of 3 to 6 days before the disease manifests. The infection remains asymptomatic in many people, but when symptoms appear, the most common ones are:
- muscular pains in the back
- loss of appetite
These symptoms (if they appear) disappear after 2 to 4 days. During this initial phase, yellow fever is not life threatening, although bacterial infections can quickly take hold in addition to the disease.
However, certain people do not fully recover from this initial phase. 24 hours after the person appears to be in remission, patients enter into a second, far more toxic phase:
- yellowing of the skin and eyes starts to appear (which is where the name “yellow fever” comes from)
- the urine becomes dark
- abdominal pain and vomiting starts
- bleeding in the mouth, nose, eyes or around the stomach can be observed
Half of affected people who go into the toxic phase die within 7 to 10 days
How is yellow fever spread, and what causes it?
Yellow fever is a virus that is transmitted by mosquitoes (you can have a look a our article on 7 plants that keep mosquitoes at bay). They can live and reproduce as easily in the middle of the Amazonian jungle as they do in residential areas.
Due to their various habitats, the virus has developed in three distinct transmission cycles:
- In the jungle: The virus is passed from mosquitoes to monkeys. A contaminated animal then spreads the virus to the rest of his group. Occasionally, yellow fever is also passed on to humans who may be studying the forest or local tribes.
- Intermediate yellow fever: the species of mosquitoes at the origin of this cycle can live as easily in the jungle as in urban areas. They can therefore infect humans and monkeys alike. In this way, it is not rare for a single group of mosquitoes to be responsible for an outbreak of the virus in an entire region. This is the most common cycle in Africa.
- In cities: Mosquitoes generally don’t live in cities, or at least very few do, with the exception of a few species. The majority of the time, it is someone who has already been contaminated by the disease that introduces it into a city. The high population density then means that the virus spreads extremely quickly and easily.
Treatment of yellow fever
If you have already contracted the disease, rapid administration of symptomatic treatment in the hospital increases survival rates. Unfortunately there is no specific medication for the yellow fever virus. However, specific treatments for dehydration, liver failure, renal failure and fever improve the outcome of the disease in patients. Antibiotics can treat any bacterial infections that followed the virus.
There is however a vaccine that immunises against yellow fever. It is mainly administered by organisation such as the WHO, UNICEF or Gavi. In order to prevent outbreaks of yellow fever, it is estimated that a minimum of 80% of a population need to be vaccinated.
Yellow fever is still a major threat
In 2016, there were two major outbreaks in Africa – one in Kinshasa (Democratic Republic of Congo) and another in Luanda (Angola). Even if these outbreaks were contained, the strain in Angola had the time to reach China, and caused local panic. It has been well proven that this virus is still extremely dangerous even for populations that are not familiar with it.
Because of this, a programme for elimination of the disease has been developed: the EYE programme. It aims mainly to contain the outbreaks. It should be noted that unlike smallpox, it would be extremely difficult to eradicate yellow fever. In order to eradicate it completely, we would have to succeed in killing all the infected mosquitoes in the world, or make them all immune to yellow fever.