5. Yellow fever
Like dengue, yellow fever is a member of the Flavivirus family, and it spreads from one person to the next by mosquitos. The disease gets its name from a symptom experienced by a small percentage of infected patients: jaundice, or yellowing of the skin and eyes.
However, most people who contract the virus never develop jaundice or any other severe symptoms. The small percentage of patients who do develop such symptoms are those who enter a second, more toxic, phase of the disease that affects their body systems, including the liver and kidneys. Half of the patients who enter the toxic phase of yellow fever die within 7 to 10 days, according to the WHO.
Luckily for those living and traveling in one of the 47 countries in Central America, South America and Africa where yellow fever is endemic, there is a highly effective vaccine against the disease. That was not the case in the 17th century, when yellow fever was first transported to North America and Europe, where it caused huge outbreaks and, in some cases, decimated populations, according to the WHO.
6. Hantaviruses
Hantaviruses are spread to humans by rodents, particularly mice and rats. People can become infected with a hantavirus if they come into direct contact with the bodily secretions of these animals or if they breathe in virus-carrying particles from those secretions that have become aerosolized.
The Sin Nombre hantavirus was first identified in the U.S. in 1993 after a mysterious disease killed several young people in the Four Corners region of the Southwest. Half of the 24 patients initially infected with the Sin Nombre virus died from the disease — a severe respiratory infection known as hantavirus pulmonary syndrome, or HPS.
Outside of the U.S. — in Asia, Europe and some parts of Central and South America — hantaviruses can cause another severe illness, known as hemorrhagic fever with renal syndrome, or HFRS. The initial symptoms of this disease are similar to those of HPS and include fever, vomiting and dizziness; but HFRS can also cause hemorrhaging and kidney failure.