Drafa was a deadly airborne neural virus that was both 100% contagious and 100% fatal. The incubation period of the disease can be several days to several weeks, but once the disease comes out of dormancy, death results within about 24 hours. First symptoms were dizziness and a sore throat. The patient quickly became weak, unable to stand. Numbness spread to the limbs and a strange sense of light euphoria occurred.
The disease worked by attacking specialized cells (called yellow cells) that create chemicals for the synaptic gap in the Markab nervous system. Without the chemicals functioning properly, the brain fails to relay message throughout the body, including to the heart and lungs.
The virus briefly jumped species, attacking the green cells of the pak'ma'ra. However, most species (including humans) do not have specialized cells to create the chemicals for the synaptic gap, so they were immune to the disease.
In ancient times, the plague first appeared on an island named Drafa, a place known for being highly immoral. Storms separated the island for almost a year, so by the time people from the mainland reached the island, no one was left alive to transmit it.
Over the centuries, the disease (named after the island) became a legend, a story used to frighten children. The Markabs believed it was punishment from the gods for the islanders' immorality.
In 2258, the disease resurfaced on the homeworld. The family of the first victim was so scandalized by it that they kept it a secret, and because they believed they were moral, they did not fear going out among the general population, spreading the disease. Each outbreak was accompanied by fear and silence. Even those in the government were swayed and (fearing a panic) ordered every doctor to remain silent.
About a year later, the disease had been carried to every colony and location of the Markabs. It began to spread more rapidly, particularly in areas (such as aboard Babylon 5) where the air was recycled.
Dr. Stephen Franklin, working with a Markab doctor, Lazarenn, was able to create a vaccine for the plague. It worked by boosting production of the targeted cells, allowing them time to build resistance to the plague. However, the discovery came too late for the Markab, and Lazarenn and all other Markabs were claimed by the disease. The vaccine was still of use, though, keeping the pak'ma'ra from becoming the next species to suffer.