Step 1: Identifying disease-causing agents.
Different diseases are caused by different groups of organisms such as protozoa, bacteria, fungi and helminths. Step 2: Analyzing the options.
Malaria is caused by a protozoan, acute coryza is viral, and ascariasis is caused by a roundworm. Step 3: Correct identification.
Ringworm infection is caused by fungi like {Microsporum} and {Trichophyton}.