1816-8949 1816-8949 S1816-89492018000200089 10.18004/anales/2018.051(02)89-091 Paraguay 00 08 2018 00 08 2018 51 2 89 91 1 20/0 2/ 20 2 2010 3 4 2014 5 15/1 2/ 20 6 31/0 8/ 20