The Infected know the disease they carry can be dangerous. They limit their interactions as best they can, trying to keep themselves away from society so they don't endanger others. So they limit themselves to a short lunch, they spend as much time out in open areas as possible, trying to avoid others. Sometimes they thing they could have a chance to at least prevent the disease from taking over another person's life before the Infected dies.
Then the plants in their area start acting differently. Animals start to look different. Finally, the undead arrive, and they aren't looking for blood this time. The chimeras and zombies now own the playing field.
In mythology, the chimera was a monster with the head of a lioness, a snake for a tail, and the head of a goat located directly at the center of the spine. It was literally a creature born of chaos and monstrous natures, terrible to behold and dangerous to man. In more modern times, a chimera is an animal with the genes of two different zygotes, or rarely, a virus with the genetic characteristics of multiple creatures. To the Infected, they're just plainly monsters.
When the disease in an Infected individual starts to propagate in it's immediate area, plants and simpler forms of life are the first to feel the effects. Plants become more mobile, animals more predatory. Even normally calm or timid animals will gain a predatory gleam in their eye, watching out eagerly for their next meals. The changes do take time, but when the disease takes hold, it will never let go. What they hunt is ATP, and while any source will do, chimera focus especially on the ATP of the Infected, since it is apparently "supercharged" in a manner.
Some Infected have taken the view of a "scorched Earth" policy, taking fire to any infected animal or plant they find, ensuring the disease in contained. Others, however, have learned a trick to actually control small numbers of infected animals, others managing to "communicate" with plants in the thrall of the disease. How is still unclear, but some feel that there is a pheromone communication, using olfactory senses to guide the actions of the chimera.
Small efforts have been made to categorize the different "breeds" of chimera, with limited results.
Venus Traps are the plant species that become infected and become predatory. They quickly suck up the nutrients in the ground below them, killing the ground around them, and they soon become ambulatory, gaining the ability of uproot themselves and seek out newer grounds. However, even this quickly loses it's effectiveness, and the Traps soon start to develop primitive digestive systems. Often, wildflowers become like their flytrap cousins, their petals gaining movement, trapping any unfortunate insects that fly inside and digesting them to death. Larger plants, such as bushes, become thorny and thick, trapping animals and other wild animals, using their corpses to fertilize their ground. Barked plants such as trees are rarer than their smaller cousins, but these behemoths are able to soak up even the hardest of attacks, and while unable to truly consume other creatures, they are perfectly suited to spread the infection, using seeds and leaves to spread the infection to anything it touches.
Thankfully for the infected, the Venus Traps are easily destroyed, as anyone with a match and a can of gasoline can attest to.
Grazers are those animals that are turned from herbivores and other plant-eaters that become changed by the infection. The changes are slow at first; male deer gain sharper horns, while the teeth of such animals become pointed and harder. Their organs start to shift, their stomach acids become more intense, and their intestines start to become able to digest meat and bone along with their diet of plants. Their personalities then start to shift violently, usually docile animals becoming hostile and territorial. Hikers sometimes report attacks by grazing animals, friends speared or bitten soon before they too become infected. While not often dangerous, one infected individual can spread it to the entire population of an area, meaning that the local ecosystem can be thrown into total disarray.
Grazers prefer to attack en masse, weak while alone but powerful with their others. Anyone hunting them would be able to take them out without much trouble if they don't let themselves get sloppy.
Stalkers are predatory animals, changed little by their infection but still as dangerous. Their attitudes are little shifted due to the infection, but their bodies are. Teeth and claws grow quickly, even regenerating from damage. Muscles grow and thicken, hearing becomes sharper, smells more intense than their even normal abilities. Stalkers will tear apart their prey, but sometimes they just let a survivor limp back to their herd, a herd of Grazers the result. They also become bolder, attacking lone humans or even small groups. Over time, their regenerative abilities can increase, to the point where a full shotgun blast to the skull has small chance to taking them down.
Stalkers are usually solitary hunters, but aren't against working with others of their breed to take down prey. Whether pack hunters or lone, they present a challenging foe to anyone hunting them, and care must be taken to ensure that the creatures aren't able to turn the hunt on the hunters.
Crawlers are comprised of the many insects and bugs that cover the earth, affected by the predations of the disease. Interestingly, there are two types of crawlers.
Solitary Crawlers are bugs like spiders or beetles, creatures who have no social structure outside of mating or battling for mates/territory. With infection, these miniscule creatures become even more dangerous, often becoming more colorful to attract predators to consume them. However, they also become more aggressive, and will often attack if they feel threatened. Often, they can pass infection along with a bite, if they are a predatory insect.
Mass Crawlers are social insects, such as ants or bees, creatures that work together to accomplish what they need to do. Though they too become more noticeable to predators, they still remain with their colonies or hives. They become as predatory as their Solitary cousins, but they use their numbers to their advantage. They swarm larger animals, sometimes killing them, sometimes infecting them, and even more disgustingly, some use animals as mobile hives, able to transport large numbers of infected Mass Crawlers to any location the hive wants. Eventually, though, this mobile hive starts to decompose, and the Mass Crawlers spread out, ready to find fertile ground again.
Crawlers of all types are difficult foes for the Infected, because they're just small enough to easily escape notice. If an Infected is able to find an area filled with Crawlers, they would have to work long and hard to fully exterminate them.
The Infected need ATP regularly. It's what drives their survival, allows them to use such terrifying abilities however they choose. Without ATP, they would die. But there is a dark side to this need for energy. Sometimes, an Infected needs ATP when they don't, craves it like the most addicting drug. It calls to them, forces them to consume. Most Infected can rise above this, ignore the cravings. Some aren't as lucky.
ATP Zombies is the term given to the Infected unlucky enough to fully succumb to the ravages of the disease inside them, a being driven only by pure instinct; reproduce, consume, reproduce, consume. To paraphrase Jaws, "All it does is eat, and swim, and make little baby zombies".
There are primarily two ways the Infected find ATP zombies. The first is from an Infected completely gone over to their natures, the drive to spread the disease overriding any other rational thought. The other is an individual close to death or already dead, the disease managing to replicate their bodily functions in a facsimile of life in order to continue the spread. Their appearance can range from a still living individual to a corpse weeks old. As long as there are enough muscles and nerves to keep the body moving, the ATP zombie will continue working towards spreading the disease, until it is destroyed.
Again, like the chimera, some Infected have found ways to control the zombies. Most, however, frown on this sort of treatment, feeling it better to put the poor soul out of their misery (and perhaps consume the zombies' delicious ATP themselves!) before moving on to the next zombie infestation.