Simplify the following text for a Grade 9 native English-speaking person.
Original: One species , A. suum , typically infects pigs , while another , A. lumbricoides , affects human populations , typically in sub-tropical and tropical areas with poor sanitation .
Simplified: One species , A. suum , typically infects pigs , while another , A. lumbricoides , affects humans , typically in sub-tropical and tropical areas with poor sanitation .