Illera is a peculiar planet—a nearly-frozen ball of rock shrouded from its black sun by a tear in space—but it has also had many guests. Although the Pesenese rock-spiders are usually thought of as the first colonists there, it is now widely accepted that early plane-hoppers from Earth were in fact the planet's first visitors. The only evidence that remains to mark their passing is the plague pathogen, called múreplú by the Lilitai, which is a parasite comprised of immortalized human cells, found only around thermal vents in caverns.

Múreplú, or death sand, colonizes the lymph nodes, eventually causing autoimmune dysfunction. Other symptoms include rapid weight loss, fever, extreme hunger, and loss of energy, ultimately culminating in an etiology similar to trypanosomiasis (sleeping sickness.) Unlike sleeping sickness, however, these symptoms can take years or even decades to play out, and though the disease is infectious it is not airborne, leading to a relatively slow spread. This painstakingly gradual rate of infection and fatality is the primary reason why the Lilitai did not quarantine or abandon the infected. By the time the disease was cured, 78% of the Lilitai living on Illera had perished (33,765), and it was estimated that as many as 65% (~40,000) of the total Lilitu population (~62,000) were infected when inoculations finally began in 827.

Múreplú was found growing in a cave not far from Koitra during a geological survey. It was initially mistaken for a peculiar sedimentary silt due to its grainy, blackish appearance, and as no evidence of Illera's sparse algae had ever been found growing underground, the possibility of a living organism was initially discounted. Many such samples were collected during 770–785.

The disease and its source was identified by Súa Gleméanivía as infectious in late 781, a few months after the first cases were seen. Following this, transit between the fleet and Illera—or any visitation of Makta—was strictly forbidden to prevent the spread of contamination. 70% of the total Lilitu population had moved to Illera when they arrived, leaving about 18,500 in orbit aboard their ships. As a result of the no-transit policy and earlier trade disputes, Makta had no permanent Lilitu residents after 765 until the second colony, millennia later, and the early history of diplomatic relations between the two worlds was forgotten.

Based on a new analysis of (nomadic-era) religious doctrines among the Darika cults, which exploded in number during the Illeran sedentary period but were then very poorly documented, it has been speculated that the high reproductive success of Múreplú, which had a relatively low rate of infection, might have been the result of deliberate apocalypticism on the part of one or more of these cults. This has not been definitively proven, however, and the extreme length of the pandemic, which lasted some 26 standard Terran years.