Insurance giant UnitedHealth Group Inc. said it has agreed to acquire Brazil's largest healthcare company for $4.9 billion in cash, continuing a recent buying spree by U.S. insurers. UnitedHealth, the largest U.S. health insurer with about 36 million customers, said it will acquire Amil Participacoes SA to capture more growth from Latin America. Amil has annual revenue of about $5 billion and in addition to providing health benefits it also runs 22 hospitals and nearly 50 clinics. In Brazil, UnitedHealth sees a fast-growing economy where the private health market is still largely untapped. The company said only about 25% of the population has private insurance compared with nearly 80% in the U.S.