Like Zika virus or malaria, yellow fever is a potentially fatal illness spread by mosquitos.
While it's typically found in sub-Saharan Africa, South America and parts of the Caribbean, there are concerns over it becoming a "global health emergency".
Earlier this week, two academics made headlines after calling on the World Health Organisation (WHO) to hold an emergency meeting about the issue.
Daniel Lucey and Lawrence Gostin, from Georgetown University, explained that the ongoing spread, and potential future spread, of yellow fever combined with a limited vaccine supply should compel the WHO to act immediately.
"Prior delays by the WHO in convening emergency committees for the Ebola virus, and possibly the on-going Zika epidemic, cost lives and should not be repeated," they wrote.
The Independent reported that nearly a billion people are at risk from the disease in Africa and Latin America. Additionally, there's danger of an outbreak in Asia.
While there's nothing in Europe as of yet, scientists are concerned that as the climate gradually gets warmer, the mosquito could flourish here too.
What are the symptoms of yellow fever?
Yellow fever is a very serious virus which is passed to humans through mosquito bites and cannot be transmitted via human-to-human close contact.
Mosquitos infected with the fever are often found in sub-Saharan Africa, South America and parts of the Caribbean.
Symptoms appear in two stages, according to the NHS. The first symptoms develop three to six days after infection and last for roughly three to four days. These are:
- High temperature
- Headache
- Nausea or vomiting
- Muscle pain, including back ache
- Loss of appetite
The second stage of the illness is far more serious and roughly 15% of people with yellow fever will go on to develop symptoms including:
- Jaundice (yellowing of the skin and whites of the eyes)
- Kidney failure
- Bleeding from the mouth, nose, eyes or stomach - the latter of which causes blood to appear in vomit and stools.
Up to half of those who experience the second stage of symptoms will die.
How is yellow fever treated?
If you think you might have yellow fever, it is essential to see a doctor as soon as possible - even if you are abroad.
Unfortunately there is no specific treatment for the illness, but the symptoms can be treated while the body fights off the virus.
Painkillers are used to combat headache, high temperature and muscle pain, and sufferers are advised to drink lots of water to avoid dehydration.
How can it be prevented?
Thankfully, a vaccination against yellow fever is available which protects over 95% of those who have it.
According to the NHS, the vaccine - which comes in the form of a single injection - should be taken at least 10 days before travelling to a known infected area.
This then enables your body to develop protection against the virus.
In addition to the vaccine, the virus can be prevented by wearing long-sleeved clothing and using mosquito nets abroad.
You should also use an insect repellent containing 50% DEET on exposed skin.
