Insurance giant WellPoint Inc. today announced it has signed an agreement to purchase Amerigroup Corp., a nearly $5 billion deal that combines two managed care organizations servicing the nation’s burgeoning Medicaid population.

Amerigroup (Ticker: AGP) operates in 13 states with 2.2 million customers. That number includes an unknown number of Medicaid-eligible clients in Middle Tennessee, where AmeriGroup has run the TennCare program since the spring of 2007. Once Indianapolis-based WellPoint (Ticker: WLP) completes its acquisition, it will run Medicaid programs with more than 4.5 million enrollees in 19 states.

Amerigroup officials could not be reached for comment about the deal's local impact Monday.

The $4.9 billion deal is expected to close sometime in the first quarter of 2013 and is subject to regulatory approvals and standard closing agreements typical of such transactions.

In February, Amerigroup signed an agreement with HCA’s TriStar Health System, allowing Amerigroup enrollees access to the TriStar network of hospitals and facilities here.