If you are trekking in and around Brasilia there is a good chance that you will have issues sooner or later with ticks, especially around Lake Paranoa.
One of the main spreaders of ticks are the capybaras around the lake, so special care has to be taken were they are roaming around.
The most common tick in and around Brasilia is the Amblyomma cajennense or Cayenne tick.
To protect yourself against ticks you can use any mosquito repellent that includes a 20-30% DEET concentration like OFF from Johnson & Johnson. You can buy this product in any supermarket or pharmacy. While DEET typically lasts for about 12 hours against mosquitos, it will only remain effective against ticks for around 8 hours maximum.