mosquito yellow fever
Aedes mosquitoes carry the virus responsible for yellow fever.Getty Images

Since the month of December 2015, Angola has been struggling with a deadly outbreak of yellow fever. The country had not faced an outbreak of this scale in 20 years.

On Friday 26 February, the country has announced that 125 people had already died from the virus. In total, more 664 suspected cases have been reported. The worst affected area is the capital Luanda with 92 deaths.

An immunization campaign has been launched at the beginning of February, targeting more than 1.5 million people.

What is yellow fever?

Yellow fever is an acute viral haemorrhagic disease transmitted by the aedes and Haemogogus mosquitoes. It is not always easy to diagnose, especially at the beginning, since its symptoms can often be confused with those of malaria, dengue fever, or other haemorrhagic fever. However, some patients will suffer from a jaundice specific to the disease, which explains why the term "yellow" is used.

The virus incubates for 3 to 6 days before the first symptoms are observed. The infection can occur in one or two phases. The first one is called the "acute phase". It is characterized by fever, muscle pains, nausea and vomiting, or headaches. After 3 or 4 days a majority of patients recovers.

However, 15% of them fall even sicker, less than 24 hours after their recovery and enter the second phase of the infection. It is in this phase that the jaundice appears. Vomiting, abdominal pains and bleeding are also seen, and kidney function deteriorates. The patient can die, and half of those who reach the second phase of the infection eventually do.

The infection is diagnosed with a blood test which can detect either the antibodies produced by the body to fight off the infection or actual traces of the virus.

Who is affected by the disease?

World Health organization estimates suggest close to 200 000 cases of yellow fever occur each year worldwide, leading to around 30 000 death. Like with the recent Angola outbreak, most of the cases, up to 90% occur in the African continent.

There, 31 countries are considered "endemic", with 508 million people at risk of contracting the virus. The other big region affected by yellow fever is Latin America, with 13 countries there described as "endemic".

What can be done against yellow fever?

To date, there is no treatment against yellow fever. Water and medicines can be given to target the symptoms, such as fever or dehydration.

Vaccination is the best option to prevent outbreaks of the disease and to protect people against it. The vaccine has been proved to be both safe and effective, providing 99% immunity after only 30 days. A single dose can protect a person throughout her life.

However, for outbreaks to stop coverage must reach between 60 and 80% minimum of the population, in an endemic region. In many cases, vaccination coverage remains too low, especially in Africa.

Other strategies to combat the disease include mosquito population control, with the large scale use of pesticides and mosquito nets, as well as the treatment of stagnant water sources.

Recommendations for UK travellers

People who travel to endemic countries like Angola must be vaccinated, under WHO regulations. They will be asked to show a vaccination certificate in order to go to the country.

The traveller should be vaccinated at least 10 days before the departure, to allow the body some time to develop the necessary protection.

The vaccine was to offer a 10 years protection, but recently the WHO has found that a single dose can be enough to protect for a life time and as from June 2016, receiving booster doses after 10 years will not be necessary.

The nearest centre offering yellow fever vaccination can be found on the National Travel Health network website, and the list of countries where vaccination is needed on the WHO's website.