Another deadly virus is poised to go global

An outbreak of yellow fever that's been hitting the Democratic Republic of Congo and Angola hard, killing more than 400 people and sickening even more, is poised to spread beyond central Africa. It's already the region's largest outbreak in decades.

Yellow fever is transmitted by the same mosquito as the Zika virus. The symptoms can be anything from just a general fever to jaundice (that's where the "yellow" comes in) and a severe liver disease with bleeding. While the more severe symptoms are relatively rare, the virus kills about half of those who develop them.

There's no treatment once you get yellow fever. There is a vaccine that protects against it, but a current vaccine shortage has some groups worried that there won't be enough doses to contain the most recent outbreak.

"There is no known cure for yellow fever and it could go global," Save the Children's country director for the Democratic Republic of Congo, Heather Kerr, said in a statement.

On Tuesday, the World Health Organization launched a vaccination campaign with the hope to vaccinate more than 14 million people in affected areas. The organization is working with limited supplies of the vaccine, and it takes a minimum of 6 months to manufacture more vaccines. To make up for that, the WHO plans to use just a fifth of a vaccine dose per person, which will spread the limited supply to a wider population but give those people protection only for about a year.

"We've got to urgently reach as many children and families as we can with the supplies that are left, and this is the only way we are able to do that right now," Kerr said in the statement.

There are currently 10 million people at risk of getting yellow fever in DRC's capital Kinshasa. Scientific American's Emily Baumgaertner, reporting from the DRC, found that there was another problem facing prevention efforts: hospitals weren't testing patients to see whether they had yellow fever. She reported that it had been more than a month since a yellow fever diagnostic test was run in the country.

The vaccination campaign will have until the start of the rainy season in October to tackle the problem before the mosquitoes that carry the disease have a chance to breed and infecting more people.