In the story I have been writing and asking questions for, the main conflict is parasites. What I have so far is that the parasite lives dormant inside of "pure-bred" aliens (which have softer brains), but once human genetics are introduced (alien-human hybrids), the parasite becomes active and begins burrowing into the brain of the host (which is more rigid, harder and more painful to get around). The body and immune system is completely unaware, as the parasite was developed in the brain during the fetal stages. Anyway, the parasite essentially creates its own alien brain tissue (as that's its regular "habitat") and creates a mess of alien and human brain tissue inside of the host's skull. The host begins having short spasms, memory loss, and feelings of being light headed depending on where the parasite does its work. The bigger problem is that the host also begins experiencing episodes of extreme violence. Characters in the story have noticed that hosts of the parasite are almost animal-like in how they act. This is because the parasite is in need of certain nutrients that only "pure-bred" humans can produce, so the parasite only targets humans. This nutrient allows the parasite to grow stronger and create offspring.
Leave a comment if you need more clarification or an example from my story. I am not interested in talking about the origins of the parasite. I only want to make it more plausible. I have done my research so I know the symptoms are alright, but I'm worried that if I write this into the story, there will be a lot of unexplained things/a lot of questions.
Additional information: If you could not already tell, this take places in a different solar system and it is in the future. I just want to explore these cool ideas, as we really don't know what's out there in space. But I don't want my ideas to sound stupid. I understand if I need to make major changes to the function of the parasite.
Edit: The aliens I am speaking of evolved in a similar way that humans evolved, and through science, they are able to reproduce with each other.