While this is pretty cool, and quite fun too, there are some issues that I think should be sorted.
First of all, The Survival Arena. It's a pretty cool concept that, as far as I've seen, appears once. I feel like it should be it's own game mode, with upgrade tiers as you go, as opposed to a single stage.
Speaking of upgrade tiers, this game could benefit in abundance from them! Now, I'm not saying you should be able to use the laser or multi-gun all of the time. That would be silly. Instead, you should be able to upgrade your overall health, speed and fire rate, and maybe even your bullet range. This would also benefit the point system, and would give an overall incentive to actually earn them.
Also, while this is quite a trivial matter, I think that different difficulties would be great! I found that some levels were super easy, and some were hard-ish. So, if there was an Easy, Hard and Insane difficulty, that could be solved. Even if the levels weren't switched around, there could be less energy pods on hard and all green viruses would be replaced with red viruses and etc. On Insane, there would be NO energy pods and a unique virus that poisons you, so on and so forth.
Overall, a pretty fun and addicting game! The spreading of the viruses as opposed to the traditional moving was a neat touch, and a breath of fresh air, and the controls are pretty tight - too! :)