@Zande My vet also recommended us to use Nexgard monthly. Since there aren't many basenjis around, I've asked the breeder and he said to avoid pills that provide external protection due to possible liver issues. Ever had issues with Nexgard in that regard?
Unfortunately, I'm limited in options here. For external use, I can only get Frontline Spot On (doesn't seem to be as effective as Plus) or Vectra 3D (which seem to be somewhat similar to Frontline Plus). As for heartworms, I couldn't find anything really, even online is hard to order Nuheart or similar products in EU. But I believe that heartworms are not as prevalent here, either.