Parasite

I itch and itch my arm. I swear it feels like something under my skin. I have felt like this since I had my blood drawn a month ago and it hasn't gotten better. I decide to put on some cortisone and go to sleep. I wake up in the morning feeling refreshed I look at my arm and scream. The spot has gotten bigger.

I decide to cover it with a bandage and go about my day. It seems to not itch so much as it hurts more than itches now. It gets bigger and bigger throughout the week. Until one night I wake up and feel incredible pain from my arm. I hold it screaming. I watch as the skin on my arm peels back and a huge slug like creature hisses at me before latching onto my vein. Blood goes everywhere and I scream as it lunges for my jugular. I choke on my own blood and as my eyes close it looks like the thing is laughing. 

I then have a name for this creature. Parasite.