Complex sentence: If this mutation were to occur, chikungunya would be more of a public health concern to the US because the "A. albopictus" or Asian tiger mosquito is more widespread in the US and is more aggressive than the "A. aegypti".
Split into simpler sentences: If this mutation were to occur, chikungunya would be more of a public health concern to the US. The "A. albopictus" or Asian tiger mosquito is more widespread in the US and is more aggressive than the "A. aegypti".