Plaga

Las Plagas (from Spanish, meaning The Plagues) are a breed of parasitic organisms and the central focus of the Resident Evil 4 storyline. Unlike the T-Virus, which turned its victims into mindless zombies, the victims of Las Plagas (such as the Ganados) become much stronger and nigh-immune to pain, while still working collectively to pursue their targets. Another side effect is the loss of higher reasoning except in select subjects (who still are unable to shake off the need to obey higher orders) and the full compliance to the master Plaga, as embodied by Lord Osmund Saddler.

History
Las Plagas were first discovered by a religious group in Europe known as "Los Illuminados" in an unknown 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 the Plagas. The two hired the local villagers as miners to extract the parasites.

Due to years of confinement, the Plagas parasites were already dead. Some were later found fossilized (which takes hundreds of thousands of years at least) 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 reestablish 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 achive his aims via more direct action after it appeared that Saddler was not going to entrust Krauser in his confidence. Ada betrayed Wesker as she gave him a fake Plaga, delivering the real sample to a group she refers to as "The Agency".

Characteristics
Las Plagas are a type of parasite which alters its host's behaviour 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 soundwaves.

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, 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, Novistador's, 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 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. Also of note, according to a note written by Saddler, the subjects's mindset does seem to be important when choosing a host ("the plaga reflects the concience 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 would suggest that many Ganados were fully aware of the consequences of impantation and yielded voluntarily. This might also explain the need to kill those who refused the Plaga, as they were obviously judged to be "incompatible". If the Plaga could force compliance from anyone, why kill them?

Las Plagas forms
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'.


 * Tentacle Plagas- These Plagas are the first form of Las Plagas Leon will encounter. These Plagas are most commonly found in villagers and also 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.
 * Worm Plagas- These Plagas are the second form of Las Plagas Leon will encounter. These Plagas are often found inside the lower ranking zealots. These Plagas are short ranged but can cause instant death by biting the players head off at close range.
 * Crab Plagas- This form of The Plagas only appears within Garradors. 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.
 * Spider Plagas- These Plagas (which somewhat resemble 'Face Huggers' from the Alien franchise) mostly inhabit the higher ranking zealots. They are the most durable, can spit acid over some distance and detach themselves from their host following death. These are the most dangerous Plagas the player must fight in the game.
 * Leech Plagas- This type of Plaga is exclusive to two closely related creatures: The Regenerators and Iron Maidens 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 do not attack the player at all.
 * El Gigante Plagas- This large plaga will only emerge after sufficient amounts of damage have been inflicted on it's host where it serves as El Gigante's only weak point. Again, this is another Plaga form that cannot attack.
 * Queen Plagas- These are more complex types of Plagas. They give control over the average Plaga-Infected and have brilliant mutation forms. In the game, there were only two people infected with the Queen Plagas, Bitores Mendez and Ramon Salazar.
 * 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 infected with Las Plagas, whether the egg has hatched or not(Though some can resist when the egg hasn't hatched yet.). Saddler described the Second Master Plaga Sample as "their life blood". They were planning to inject the Master Plaga into Ashley when they captured her. The Master Plaga has no form on its own, but gives a very powerful mutation due to the power it controls.

Countermeasures
If a person has been infected with the parasite, then the parasite can still be neutralized with medication before the egg hatches. However, once the Plaga has hatched, then the only way to terminate the parasite is for the host to undergo a special kind of radiation treatment (specialized pills can be used to suppress growth of the parasite until then). This extremely painful procedure has the possibility of impairing the host's consciousness, and may still kill the host if the Plaga has already matured into adulthood.

Luis Sera, a researcher who betrayed Saddler, built an operating machine which produced this kind of radiation after extensive research regarding how the Plagas might be removed. Leon and Ashley, who had Plagas implanted into their bodies, used the machine to eliminate the Plagas, both managing to survive the operation.

Las Plagas are also very vulnerable to bright lights. They will only emerge from their hosts at night (except in The Mercenaries), and can be instantly killed by throwing a Flash Grenade at them.

Also, a type of weapon that's called the Plagas Removal Laser 412 (P.R.L. 412), which is unlockable after completion of the Professional difficulty, can instantly kill any enemy infected with Las Plagas.