Colorized scanning electron micrograph of filamentous Ebola virus particles (blue) budding from a chronically infected VERO E6 cell (yellow-green). NIAID

The outbreak of Ebola Virus Disease (EVD) in West Africa that started in late March has spread across four countries (Guinea, Sierra Leone, Liberia and Nigeria) at a rate that has shocked public health officials. As of July 27, 729 people had been felled by the highly contagious virus, and on Thursday, the U.S. Centers for Disease Control issued its highest-level travel warning for the region.

The 122 new cases reported this week have brought the total of those infected to 1,323, with Sierra Leone and Guinea the hardest hit. The map below shows the total number of cases per country. Explore the latest numbers by clicking on each country:

Quarantines are being enforced in Sierra Leone and Liberia by police and military after the countries declared a state of emergency. Yet the virus is dramatically gaining momentum in Sierra Leone. The following chart from Quartz shows just how quickly the pandemic is growing:

Where the ebola epidemic is gaining momentum. Source: World Health Organization Quartz

The numbers look grim for the West Africa nations. In Sierra Leone, which has the highest total number of cases and yet only one laboratory capable of testing for EVD, 36 percent of those polled say it is difficult to obtain medical treatment at a public clinic. In an effort to control the pandemic, the World Health Organization announced a $100 million Ebola Virus Disease Outbreak Response Plan, which calls for "several hundred more personnel" to be deployed to the region.

While the rapid spread of EVD has set off international alarm bells, it's another disease -- malaria-- that's by far the No. 1 killer in West Africa, accounting for 33,205 deaths in Sierra Leone, Guinea and Liberia in 2011 alone. And though the spread of drug-resistant malaria has stayed mostly in Southeast Asia, the emerging resistance is a bad sign for recent gains in malaria control.

Look at the chart below to see where EVD stands in the rankings of the top causes of death in West Africa: