1816-8949 1816-8949 S1816-89492021000300161 10.18004/anales/2021.054.03.161 Paraguay Paraguay 00 12 2021 00 12 2021 54 3 161 166

1 1993 165 9-14 2 2001 234 549-59 3 2012 16 815-20 4 2013 19 38 38 6348-52 5 2008 10 1 1 4-12 6 2010 12 334-41