There is the initial rapid blinking during the first day of infection. Once that fades, most symptoms are behavior related as the Neurax Firefly tries to alter the hosts mind towards Po's will. In rare cases, the Neurax Firefly reaches a mature stage and causes some Firefly like mutations in the host. I have not decided what the time span and the ratio for mature stage Neurax fireflies would be.
Romans 8:31 What, then, shall we say in response to this? If God is for us, who can be against us?
1 Corinthians 13:1-3 If I speak in the tongues of men or of angels, but do not have love, I am only a resounding gong or a clanging cymbal. If I have the gift of prophecy and can fathom all mysteries and all knowledge, and if I have a faith that can move mountains, but do not have love, I am nothing. If I give all I possess to the poor and give over my body to hardship that I may boast, but do not have love, I gain nothing.