http://www.bing.com/images/search?q=nematodes+and+fungus&FORM=HDRSC2 look at some of these images and it will give you a clear picture of whats going on ... http://www.alwayshelpfulveterinaryservices.com/wp-content/uploads/SafeGuardEquine_instructions.pdf I haven't had any fungul problems since I started the fenbendazole back in January . the fungus seems to live on the dead cuticles(skin) of the nematode or helps in its cycle , not sure this is all theory but read up on nematodes and fungus . I read a lot of vet articles on this back in the beginning of treatment with consultation from the farm vets on why treatment needs to be with mectins and bendazoles .