World Health Day encourages people to talk about health problems affecting countries around the world, including emerging diseases with the potential to harm millions.
The World Health Organization has identified the top 8 emerging diseases that are likely to cause severe outbreaks in the near future.
A group of scientist and health experts came together to prioritize the most concerning diseases that are expected to cause epidemics in the future, and for which few or no medical countermeasures exist.
The list provides a basis for working on research and development preparedness to try and control potential future outbreaks.
The list excludes diseases that already have sufficient R&D programs and funding, including HIV/AIDS, tuberculosis, and malaria.
Crimean-Congo haemorrhagic fever is a tick-borne virus primarily found in Africa, the Middle East and Asia. It causes death in up to 40% of cases and has no vaccine.
Filovirus diseases include Ebola, a virus that saw severe outbreaks in West Africa in 2014-2015 and is often fatal if untreated. There are currently no vaccines for Ebola, but two potential candidates have been identified.
Highly pathogenic emerging coronaviruses that affect humans include MERS CoV and SARS. These are respiratory syndromes caused by coronaviruses. The MERS CoV virus does not appear to pass between humans - camels are the suspected transmitter.
Lassa fever has a death rate of only 1%, with only 1 in 5 infections resulting in severe disease where the virus affects several organs. Around 80% of people who become infected with the virus have no symptoms.
The Nipah virus was first identified in 1998, and affects both humans and animals. There is no vaccine and treatment for humans is intensive supportive care.
Rift Valley fever primarily affects animals, but the disease has also been found in humans. The virus usually lasts up to seven days with the body fighting the virus without medical assistance. However a small number of people develop a more severe form which can lead to death.
The WHO team of scientists also identified the potential for a new unknown disease to cause a severe epidemic, and the importance of continued research and development to be undertaken to prepare for any potential new disease.
A further three diseases were included and listed as serious, requiring action as soon as possible.
Chikungunya, a viral disease transmitted by mosquitoes, causes fever and severe joint pain. There is no cure for the disease and treatment is focused on relieving symptoms. It has been identified in over 60 countries across the world.
An emerging fever was also identified by the team, severe fever with thrombocytopenia syndrome was first identified in rural China, and as of 2014 there had been around 2500 reported cases, with a death rate of 7%.
Zika was the final disease identified by the WHO. It was officially declared a public health emergency on 1 February 2016, following a WHO mission to Brazil where the disease began to spread.
The disease has been found in 61 countries, and is currently part of campaigns and research and development programmes to provide recommendations and potential diagnostics.