Split and merge into it. Answer by Ktzkwong. Confidence votes 230. A pathogen by definition is a biological agent that causes disease in its host. Some types of fungi fall under this category but not all. A common fungal pathogen is the Candida species that causes yeast infection.plit and merge into it. Answer by Ktzkwong. Confidence votes 230. A pathogen by definition is a biological agent that causes disease in its host. Some types of fungi fall under this category but not all. A common fungal pathogen is the Candida species that causes yeast infection.