The organism toxoplasma gondii is well known to do almost exactly what you are wondering about. This is not fiction—it is actually a scientific fact on Earth now (except the organism is not considered to be of extraterrestrial origin.) Its most notable characteristics are
So far no concrete evidence has been found that t. gondii effects human behavior, even though half of the world's population is thought to be infected, up to 95% in certain populations. However, there is speculation it could effect human behavior, perhaps even causing schizophrenia and other mental illnesses.
I feel this type of organism could very well already be doing what you are asking about: BDSM, extreme sports, suicide bombings, schizophrenia, bipolar, etc., as well as unwillingness to agree to peace in the Middle East.
There are a few organisms, some microscopic, some macroscopic, that cause real zombie behavior:
1. Ophiocordyceps unilateralis
When a spore of Ophiocordyceps unilateralis meets an ant, things get very weird and very bad for the ant very quickly. The spore germinates and enters the ant’s body through holes in its exoskeleton. The fungus then starts to grow inside the ant’s body, absorbing soft tissue while leaving vital organs intact, for the ant must remain alive and fully functional for a while longer to be of real use to the fungus.
When O. unilateralis reaches the autumn of its short life and is ready to sporulate and make way for a new generation, its long, branching filaments grow into the ant’s brain. The fungus produces chemicals that poison the ant’s brain and cause it to become transportation to the fungus’ birthing ground—and its own hearse. The ant, no longer in control of its own body, leaves its colony, climbs a plant, and clamps its mandibles around a leaf at the top, fastening it to its grave. There, new life springs into the world, right out of the ant’s head. Now out in the open, the fruiting bodies of the fungus mature and burst, releasing clusters of spore capsules into the air. As they descend, these capsules explode, spreading spores like confetti over the ground. The spores infect other ants, continuing the fungus’ bizarre life cycle. The whole ordeal, from one infection to the next, can take as little as two weeks.
2. Hymenoepimecis argyraphaga
Normally, the web of an orb weaver spider is where bugs meet their untimely death and become spider snacks. Using an arsenal of toxins and mind-altering chemicals, though, the parasitic wasp Hymenoepimecis argyraphaga turns the spider into a slave and a meal, and its web into a safe haven. The female wasp paralyzes the spider with a sting and then lays her egg on its abdomen. When the egg hatches, the larva lives on the spider and sucks hemolymph (kind of the arthropod version of blood) from its body for nourishment.
A few weeks later, the larva is ready to move on to the next stage of its life cycle, and injects the spider with a chemical (as yet unidentified) that alters its behavior. The next time the zombie spider builds a web, it repeats the first few steps over and over again instead of going through all the regular steps, resulting in a web that’s just a few heavily-reinforced anchor threads and a small center section. Then the spider crawls to the center of the web and sits there complacently. The larva molts, kills the only companion it has ever known, sucks any remaining useful bits out from its corpse, and discards it. Then it builds its cocoon on a web custom-built for the job. A few weeks later, the adult wasp emerges and flies away, and the cycle starts over.
3. Jewel Wasp
Like H. Argyaphaga, the Emerald Cockroach (or Jewel) Wasp is free-living as an adult, but starts life inside a host. As their name suggests, these wasps use cockroaches as living nurseries for their little bundles of joy. When a female wasp is ready to lay her eggs, she swoops in, lands on a roach’s back and plunges her stinger into its midsection. The roach’s legs buckle and it tumbles to the ground, unable to flee or fight back for a short while. This buys the wasp time to play brain surgeon. She slides her stinger through the roach’s head and into its brain, slowly probing until she hits just the right spot. The venom she releases this time doesn’t paralyze the roach; it can move its legs again, but not of its own accord. When the momma wasp grasps its antennae and starts moving, it follows her like an obedient puppy. She leads the roach to her burrow, where she lays her egg on its abdomen and then leaves. All the roach can do is sit and wait. Soon the egg hatches and the larva emerges. It chews into the roach’s abdomen and wriggles inside, where it lives for a week, devouring the roach’s organs the whole while. It forms a pupa and emerges as a full-grown adult a few weeks later, bursting forth from the roach and leaving it buried in the burrow.
4. Glyptapanteles Wasps
The females of the genus Glyptapanteles lay scores of eggs inside caterpillars, and the larva squirm out a short time later to spin their cocoons. It seems like the caterpillar gets off a little easier than those poor roaches and spiders, but its work isn’t done yet. A few of the larva actually stay behind inside the caterpillar and give up their chance to pupate and mature, for the good of their siblings. They take control of their host’s body, and force it to stand guard over the cocoons. The caterpillar waits motionless, unless a potential predator comes too close to the pupae, in which case it thrashes violently at the visitor to drive it away. By the time the adult wasps emerge, the caterpillar, which hasn’t eaten during its guard duty, dies from starvation.
5. The parasitic hairworm
The parasitic hairworm grows up on land—specifically, inside a grasshopper or a cricket—but is aquatic as an adult. To make the transition to water, it forces its host to take it for a swim. The worm pumps the insect full of proteins (which may mimic ones that the host produces on its own) that sabotage its central nervous system and compels it to leap into the nearest body of water. The host drowns and the adult worm, three to four times longer than the corpse it once called home, wriggles out and swims away in search of a mate. The babies they make will infest the water until they're guzzled down by a host they can call their own.
Since these real-life parasitic organisms have the ability to control both the host's consciousness and physiology, even in complex ways, I think it is very plausible another organism could do so to the extent you describe.