actually do we have any right now? Could we get some for some mutation points?
You have quite a few symptoms of infection right now. Your larval transmission vector is recognized and fought by the targets immune system. While this is rarely effective in fighting off your parasites, the target will often experience fevers, chills, nausea, and other general symptoms of illness. Since this attack against the immune system is necessary to obtain control, it can be fairly expensive to suppress it or work around it.
After you've obtained control, the symptoms are also fairly obvious - while you can suppress the bodies immune response to you, your general weakness, slowness, jerky movements (especially those points in spastic), aggressive nature, etc. etc. are all fairly easy to notice and identify.
Note that some mutations may have unintended side effects, such as more obvious symptoms (say, a mutation that creates "spore burst growths" on the body that allow the parasite to spread through the air in large numbers). Other symptom like mutations (like vomiting and bleeding) may allow for easier transmission vectors while making you more noticeable. Since you are parasitic and not viral, these are generally less effective however.
Note that with mutations it is impossible to not only subdue those symptoms, but obtain a more subtle form of control until you have a secure hold over the target - like the heightened self-preservation symptoms listed above.
You might also want to consider "carrier" parasites who only deal in this subtle form of control so as to better infiltrate enclaves or escape quarantines later on. It's a lot cheaper to let an unaware host control that sort of situation than to build up the necessary intellectual and physical capabilities of your parasite.