Las Plagas were first discovered by a religious group in Europe known as "Los Illuminados" (The Enlightened Ones) in an unknown, rural region of Spain. The cult used the Plagas as a means of recruiting new members. However, the first castellan of the Salazar family opposed the cult and sealed off access to the parasites in his castle.
Centuries later, Ramon Salazar, the eighth Salazar castellan, was convinced by Osmund Saddler, the new leader of Los Illuminados, to join Los Illuminados and open the seal that concealed Plagas. The two hired the local villagers as miners to extract the parasites.
Due to years of confinement, the Plagas parasites seemed dead. Some were later found fossilized (which takes hundreds of thousands of years at least, implying that Las Plagas has existed for a very long time indeed) in the rocks below Salazar's castle. However, despite this, the Plagas were still alive at the microscopic level in spores within the fossils. The miners that were excavating the site accidentally inhaled the spores which after many years gave birth to the parasites within their bodies. Since then, Saddler was able to recreate the parasites wholly, injecting them in egg form into potential hosts.
Albert Wesker, controlling what was left of the Umbrella Corporation had tasked Ada Wong with retrieving a sample of the Plagas in order to help re-establish Umbrella after learning of the creatures via intercepted messages sent by Luis Sera. He had previously employed rogue US Special Forces operative Jack Krauser to infiltrate Saddler's inner circle but decided that Ada could achieve his aims via more direct action after it appeared that Saddler was not going to entrust Krauser in his confidence. Krauser kidnaps the daughter of the US President and Leon S. Kennedy is sent to rescue her, and is reunited with Ada and Krauser. He also cooperates with Luis Sera, who was being held captive for betraying Saddler. Leon kills Ramon Salazar, and looks for Ashley on an unknown island.
Saddler kills Sera and Krauser fights Leon, but is defeated by Ada. Leon finds Ashley and proceeds to kill Saddler and recover the Master Plaga, but it is taken from him by Ada at gunpoint. Leon and Ashley then escape the self-destructing island via Jet-ski.
Ada betrayed Wesker and gave him a fake Master Plaga, delivering the real sample to "The Organization". Wesker was not fooled by the fake however, and he was expecting the Agency to betray him. Although it delayed Wesker's plans, it wasn't long until Las Plagas began to appear in the black market. Although he never obtained a master plaga sample, Wesker and Tricell were eventually able to obtain regular Plaga and Control Plaga samples, possibly by Ricardo Irving.
Five years later, within the African country of Kijuju, Chris Redfield and Sheva Alomar soon encountered Plaga-infected villagers. These plaga were modified through intensive research to enhance their performance and make more effective B.O.W.s.
Las Plagas are a type of parasite which alters its host's behavior by attaching itself internally to the nervous system. The undeveloped parasite is found between the lungs, beneath the heart, where it can tap into the host's spinal cord, as a link to the rest of the nervous system. Unlike other parasites, the Plagas are a social organism, meaning that they live together in social harmony. Luis Sera postulates that they have a collective intelligence akin to a hivemind, possibly communicating via ultra high frequency sound waves.
As a Plaga grows inside a host, the host can suffer from a number of symptoms (in addition to the influence of the parasite on the host's behavior). These include, but are likely not limited to: coughing up of blood, blood flowing from the eyes, convulsions, sudden unconsciousness, hallucinations, swelling and discoloration of blood vessels, and discoloration of the iris – usually to a reddish color. The eyes of an infected person can be seen to glow in dark conditions.
The parasites also have a high adaptability rate, as they can possess other kinds of organisms besides humans. (Ramon Salazar uses Plagas-infected wolves as guard dogs in his castle.) In addition to the Ganados, Saddler and his men also created several kinds of mutant creatures such as El Gigante, the Regenerators, Novistadors, and the U3 as a result of genetic experimentation with the parasites and human specimens.
All of the members of Los Illuminados, including Saddler himself, have Plaga parasites implanted into their bodies. However, the ones used by him and his top underlings (Bitores Mendez, Krauser and Salazar) are superior to the regular Plagas being able to exert influence over the lesser Ganados while allowing their host a greater amount of independence.
Except for manifesting when sufficient trauma is induced on a host, Plagas have no true mutagenic effect on their hosts' body. While the Plaga infecting the Ganados and Colmillos can manifest and mutilate the body of their host, they do not actually induce any significant mutation or physiological change like Umbrella's myriad viruses do. However, certain feats by enemies in the game (such as lifting Leon into the air with one hand) suggest that the parasites can increase their hosts' strength. It is this attribute that hosts exhibit no outward sign of infestation besides discolored irises which make the Plagas such a dangerous threat, as they are much more subtle and invasive than Umbrella's viruses. The Plaga parasite does not stop their hosts from feeling pain however, unlike the T-Virus zombies, since the hosts have still retained their nervous system. Rather, they give their hosts better resilience against bullet wounds.
Also of note, according to a note written by Saddler, the subject's mindset does seem to be important when choosing a host ("the Plaga reflects the conscience of the hosts") suggesting that a Plaga's control over the host can be resisted, even overcome entirely. This seems to be a reference to Sera who was a host himself before managing to remove his Plaga. This might also explain the need to kill those who refused the Plaga, as they were obviously judged to be "incompatible".
Another side effect viewed in those infested with plagas is an apparent biological instability. That is, they disintegrate into a black or yellow goo when killed. This is common with nearly all Plaga infested individuals, both Majini and Ganados. However, certain individuals, such as the first group of Ganados that Leon encounters, Dr Salvador, J.J., Chainsaw Majini, and a particular El Gigante, do not disintegrate when killed. Plagas themselves also suffer the same fate upon death.
In the game, Las Plagas of the Ganados, zealots, and milita only appear where the head is. Once a Plaga is exposed, the enemy will no longer sprint towards the victim.
The Majini located within Kijuju are infected with a different type of Plaga, created through extensive research. Majini have been shown to develop strange mutations, such as tentacles within their mouths, as well as the ability to fully open their mouth/jaw to expose tendrils to attack others. It has also been shown that the Plaga within Kijuju appear to already be fully awakened, and enter via the mouth or throat, already hatched, they seem to grown inside the host of another plaga wich will later put it in another possible host, eliminating the need to inject the egg. These Plaga also do not appear to be harmed by sunlight, as they appear within brightly lit areas. Some strains have also been shown to fly after leaving the host body. Despite these new modifications, they are still vulnerable to bright flashes by flash grenades (i.e. UV light).
Las Plagas formsEdit
There are several forms of Las Plagas that appear in the game. Some may be different stages of the same organism, others are very clearly different 'species'.
- Blade Plagas- These Plagas are the first form of Las Plagas Leon will encounter. These Plagas are most commonly found in villagers and Saddler's militia. These Plagas wield a scythe like blade on the end of a long tentacle which they will use to slash at the player at some range. They are however the weakest of the Plagas.Template:Verify They control the weaker Armadura suits.Template:Verify
- Tentacle Plagas- This form of plaga can be found in Colmillos. As with the Blade Plagas, if the host receives enough damage, the plaga will erupt from the spine of the dog, as a swarm of tentacles that can whip Leon possibly to death.Template:Verify
- Centipede Plagas- These Plagas are the second form of Las Plagas Leon will encounter infesting human hosts. These Plagas are often found inside the lower ranking zealots, and are the second type which control Armaduras. These Plagas are short ranged but can cause instant death by biting the players head off at close range. Due to graphic resource issues related to the Gamecube version coming on two discs, they are never seen after Salazar's castle is finished.Template:Verify
- Crab Plagas- This form of The Plagas only appears within Garradores. Since they cannot attack and are visible at all times, they serve as the Garradors weak spot. This is one of the few Plagas that do not possess a form of self-defense.Template:Verify
- Spider Plagas- These Plagas (which somewhat resemble 'Facehuggers' from the Alien franchise) mostly inhabit the higher ranking zealots and militia. They are the most durable, can spit acid over some distance and detach themselves from their host following death. They are roughly equal to Blade Plagas in terms of threat while attached, and are relatively weak when detached. While detached, they have a leaping grapple which lacks an animation for attacking from the side or rear, much like the Colmillos, meaning they can only use it when directly in front of Leon. Curiously, several are encountered in the game without hosts at all. When without a host, a Spider Plaga will eventually die even if it has taken no damage whatsoever. As they can't climb ladders, simply moving outside their immediate area is an effective means of defeating them.
- Leech Plagas- This type of Plaga is exclusive to two closely related creatures: the Regenerators and Iron Maidens. They are not visible externally, being entirely contained inside the host's body, and are only visible with an infrared scope. These Plagas rebuild organic matter and must all be terminated in order to kill a Regenerator or Iron Maiden. These Plagas cannot attack the player directly.Template:Verify
- El Gigante Plaga- This gigantic Plaga, resembling a giant version of the Centipede Plaga located between the host's shoulder blades, will only emerge after sufficient amounts of damage have been inflicted on its host. It serves as the monster El Gigante's only weak point. This is another Plaga form that cannot attack Leon directly. The same type of Plaga can be found in the Gigante variant known as Ndesu, though that creature has numerous smaller versions of this Plaga located throughout its body.Template:Verify
- Del Lago Plaga- The plaga-infested salamander Del Lago hosted Plaga parasites similar to those found in Colmillos, filling its mouth with flailing tentacles, bloating its body and grossly increasing its size. This mutation also left its body relatively soft and weak, however.Template:Verify
- Control Plagas- These are more complex types of Plagas. They are more than mindless puppets of the Master, and can make more individual actions. There were only four people infected with the Control Plagas: Bitores Mendez, Ramon Salazar, the Merchant, and Ricardo Irving. Notably, this type of Plaga can create extremely powerful individuals, while having almost no detrimental effect on the host's mental capacity; something Umbrella's top virologists failed to succeed in doing. The prime example is Mendez, as he exhibited characteristics of a Tyrant whilst retaining his loyalty and intelligence even after transforming.Template:Verify
- Master Plaga- There are only two samples of the Master Plaga, and one is already injected into Saddler's body. This Plaga gives control over all those who are hosts of Las Plagas, with the possible exception of those with Control Plagas. This occurs regardless of whether the egg has hatched or not, though it is possible to resist this control if the parasite has yet to take full control of the host. Saddler described the second sample as "our life blood". The Master Plaga has no form on its own, but gives a very powerful mutation due to the power it controls; it also allows for partial transformations, as with the rather infamous trouser-tentacle Saddler uses to kill Luis, also sporting a huge yellow eye inside his throat and super-human strength, speed and resistance to firearms.Template:Verify