Pathogens infect other organisms through

• A pathogen can be defined as any external agent that causes a disease in an organism. 
• The pathogen enters the human body and actively tries to avoid the immune response of the body. 
• The pathogen later uses the resources present in the body to multiply itself and affect a larger area in the host’s body. 
• Pathogens can also infect other organisms through skin, body fluids, air and feces. 
• Pathogens can be of various types namely, bacteria, fungi, virus and parasites. 
• Pathogens can enter body through ears, eyes and nose.

Hence, the correct option is D.