It’s hard to point at a single game that has made the transition from browser-based flash game to iOS platform well. “Infection: Human Race Extinction” draws its lineage from a popular flash game known as “Pandemic.” It has not only expanded on the premise and fixed a number of bugs in that game, but it has added levels of gameplay that were previously unavailable.

One of the core problems of free games, from both the consumer and the designer standpoint, is what they call “monetization” or, how to make money off the game. “Infection” does a wonderful job of this, with the in-app premium purchases subtle and easy to access, rather than obnoxious and necessary to complete the game.

Fun Games for Free, the publishing company for “Infection,” did a delightful job of using the touch screen mechanics to make their game feel interactive and intuitive. Not only do you progress through individual games by infecting new countries (and collecting “DNA” to upgrade your disease), but the meta-progress mechanics are smooth, useful and engaging. The basic game is simple and easy to learn, but the real earmark of “Infection” being a good game is the potential endurance and addictiveness of the upgrade system.

All in all, I’m mildly surprised that this game has not done better in the iOS marketplace. I suppose it lacks the mindless, hair-pulling frustration that has made “Flappy Bird” and its knockoffs such a hit. But if you enjoy strategy, biology and world domination, “Infection” is a game for you.