Infected (Cradle of Monsters)

The manga Cradle of Monsters centers around a group of Japanese teenagers on a cruise ship, the Ocean's Cradle as part of a class trip. Suddenly, the vessel capsizes, leaving it floating upside-down. At the same time, the students encounter a violent individual armed with a fire axe. The teacher tries to fight him with a metal pipe, but fails and is bitten by the man. After the teacher is infected, it is revealed that the man was no ordinary psychopath... The man with the fire axe and the teacher, as well as other infected, kill numerous people in the chaos that insues, though a few people survive, including couple groups of Japanese high school students, one consisting of the main characters, and the other a group of juvenile delinquents every bit as violent as the zombies. In addition, a group of American construction workers and a Filipino stewardess also survive the initial onslaught and are forced to fight their way through the zombies to the bottom (now the top) of the ship.

The zombies are later revealed to be the result of a parasite transmitted through blood contact- the zombies usually have blood in their mouths, allowing it to be transmitted by bites. The parasite attaches itself to the brain stem and lymph node, roughly where the back of the head meets the neck, and takes over the central nervous system. The infected are shown to be extremely violent in nature, but much more intelligent than zombies as typically portrayed. The infected are shown to wield melee weapons including knives and axes, and even set up elaborate traps, for instance, triggering a gas explosion or faking their own suicide- pretending to hang themselves, then attempting to electrocute a victim with two loose wires and a knife. The infected are not shown using firearms as no such weapons appear in the manga, though, given the elaborateness of the traps mentioned above, it would seem likely that they would be able to use gun if they got a hold of one.

In addition their intelligence, the infected are highly resiliant. The only sure ways to kill them are to sever the head or destroy the brain stem and/or the attached parasite. The only other way to destroy them is to totally destroy their body. Fire seems to be effective for this purpose. The infected can be slowed down temporarily by the loss of limbs, but seem to be able to regenerate by feeding on human flesh, or by grafting parts from a dead body onto their own. They can even move at superhuman speeds when crawling on their hands- after both legs have been severed.

It is later revealed that the parasite was part of an illegal experiment by an unspecified military- testing a biological weapon on the a civilian population. The sudden capsizing of the ship was in fact the result of missile strike intended to destroy the evidence of the atrocity.