Primary Cause of Fungal infections. The primary cause of Fungal infections is the result: 1  of transmission of an infectious agent by another person by one or more of the following: saliva, air, cough, fecal-oral route, surfaces, blood, needles, blood transfusions, sexual contact, mother to fetus, etc.auses of Types of Fungal infections: Review the cause informationfor the various types of Fungal infections: 1  Candida. 2  Vaginal Candidiasis. 3  Oral thrush. 4  Athlete's foot. 5  Tinea. 6  Yeast infections. 7  Ringworm-not a worm but a fungus.