Ehhh...
A perfectly fine idea, but soo basic. There's nothing special in it - it's just plain.
I mean, why did you call it 'Parasite X' at all? It could be called 'Meteor Defense' or 'Monkeys Eating Fruit' and still be the exact same gameplay mechanics. You need to work on, as the guy beneath me says, the 'WAW' factor. For a game like this, you could look Pandemic and Pandemic 2 for ideas as to upgrades or enemies. Maybe you parasite could be on a journey through the host's body.
As it is, it really seems like you had the idea clearly, but either couldn't find a niche to fill or just didn't put enough time into it.
Good luck tho. I'll look for you in the top 50.