GREVID-2185 outbreak "Green Leech plague"
Disease:	Green Leech virus disease 2185 (GREVID-2185)
Virus strain:	Green Leech-1
Location:	Gozu District, Omega
First outbreak:	Solar Electronics store, south Gozu
Date:	13 July - 11 August 2185 CE (4 weeks and 1 day)
Source:	Maw's Blood Pack
Patient zero:	Doston Velisa
Confirmed cases:	13,750
Recovered:	6,353
Deaths:	7,395
Fatality rate:	92%

"Advanced design. Suspected Collectors before you mentioned them. One of few species with technology necessary to design it. Purpose seems experimental. Destroys respiratory systems with harmful genetic mutations. Makes sense to avoid humans. Unnecessary to force mutation on human genetic structure for sake of variance."

— Mordin Solus describing the plague to Commander Shepard in August 2185 CE.

The GREVID-2185 outbreak, also known as the Green Leech epidemic, the GREVID-2185 epidemic, the Gozu plague or simply the plague amongst Omega's residents, was an epidemic of the "Green Leech" virus that occurred within the Gozu District on Omega in late July to early August 2185 CE and lasted a month. The virus was designed as a bioweapon by the Collectors for use in their abduction of human colonies with the goal of expanding their operations to target multispecies populations in addition to pan-human colonies: the idea was that they could design a weapon that would be harmless to humans, but would eradicate a local alien population, allowing a Collector cruiser to then arrive and abduct the human population and leave no witnesses. The eventual plan for the virus was that it would evolve into an instantaneous kill for those afflicted it, able to be deployed, spread across a wide area, and prove instantly lethal to its victims, allowing a covert pickup of human victims to be made before any alien authorities could react in time. The virus, dubbed the "Green Leech" later by Omega citizens due to the leeching effect it had on its victims, violently assaulted a host's respiratory systems, destroying them in a ruthless attack that was hoped to eventually be capable of killing them in only a few seconds, spreading with terrifying speed throughout the body and making any attempt to treat it impossible, and leaving no trace of its presence in the victims' system, making it impossible to develop an inoculation for it. The virus was designed for a 100% mortality rate, and could spread across nearly every organic species, with only two exceptions: the vorcha, who were immune to disease, and humans, which the virus was designed not to target.

Having developed an experimental prototype of the virus, the Collectors enlisted the help of a third party in order to spread it, choosing the Gozu District of Omega as a control group. Seeing as vorcha were perfect carriers for such a virus due to their immunity to disease, the Collectors reached out to a pack of vorcha in the Omega chapter of the Blood Pack, giving them the virus to use as a weapon against the Blue Suns-occupied Gozu District, promising them it would destroy the Blue Suns and allow them a simple and easy conquest of the district, granting them the tools to then overthrow their krogan taskmasters. The vorcha, who were easily manipulated, accepted the plan and the glory promised to them, with the Collectors providing them vials of the virus to spread into the Gozu District's water supply. Starting in early July of 2185 CE, this group of vorcha, led by Maw, executed this plan, and the virus very quickly ravaged the Gozu District, creating a devastating outbreak. Within days hundreds of citizens were afflicted with the virus and died, with the Blue Suns hit especially hard, with the dent in their forces allowing the vorcha to launch a devastating conquest of the district, overrunning the Blue Suns forces in rapid succession. As the Gozu Mercenary War raged, the virus continued to claim victims, and when Aria T'Loak received word of the outbreak, she ordered her syndicate to quarantine the entire district, locking it down and stopping anyone from getting in or out. As planned, the humans of the district were unafflicted, leading to paranoia from non-human residents that the humans had spread the virus, something which led to severe reprisals from what remained of the Blue Suns forces, even against their own human members. The virus would ultimately claim hundreds of lives, with many seeking refuge at the clinic run by Doctor Mordin Solus, who quickly identified the virus as bioengineered and of Collector origin due to its perfect mortality rate and vicious spread. Within three weeks however, after the virus and the ongoing mercenary war had claimed hundreds more victims, the salarian finally developed a cure, able to do so as the virus had not yet been perfected. At this time, Commander Shepard and his Normandy Squad were allowed to enter the district to find Mordin, and they helped him spread the cure through the district's ventilation system, capturing the facility from the vorcha occupiers using it to spread the virus. The rapid spread of the cure inoculated those not yet infected and cured those who were: this brought an official end to the outbreak.

With a cure to their virus developed and its existence now exposed, the Collectors postponed their plan to expand their operations and continued with abducting human colonies: remaining incubated in-development samples of the virus were destroyed with the Collector Base two months later in October of that same year, neutralizing the virus entirely and removing any possibility of a future outbreak. Mordin would hand over all research documents and details regarding his research into the virus and the eventual cure he developed to the Special Tasks Group when he reenlisted in December of that year. The Gozu District would take months to recover from the effects of the outbreak, and the Blue Suns forces in the area were permanently weakened, leading to them being easily and permanently evicted by forces of the Dread Battalion and the Blood Pack during the early stages of the First War for Omega.