Which statement best defines an infectious disease?

Which statement best defines an infectious disease?

• A. A non-contagious disease caused by toxins
• B. A contagious disease caused by pathogens and can be spread by a vector
• C. A disease caused by mere exposure to pathogens with no transmission
• D. A genetic condition passed from parents

Answer: (B)

Infectious diseases come from disease-causing organisms—pathogens like bacteria, viruses, fungi, or parasites—and have the potential to move from one person to another. That transmission can happen in several ways, including direct contact, inhalation, or via vectors such as mosquitoes or ticks. The statement that describes a contagious disease caused by pathogens and that can be spread by a vector best matches this idea, because it links the illness to a pathogen and to the ability to transmit between hosts. The other options describe conditions that are not caused by pathogens or not transmissible: toxins produce non-infectious illness, exposure without transmission isn’t infectious, and genetic conditions are inherited rather than caused by pathogens.

Infectious diseases come from disease-causing organisms—pathogens like bacteria, viruses, fungi, or parasites—and have the potential to move from one person to another. That transmission can happen in several ways, including direct contact, inhalation, or via vectors such as mosquitoes or ticks. The statement that describes a contagious disease caused by pathogens and that can be spread by a vector best matches this idea, because it links the illness to a pathogen and to the ability to transmit between hosts. The other options describe conditions that are not caused by pathogens or not transmissible: toxins produce non-infectious illness, exposure without transmission isn’t infectious, and genetic conditions are inherited rather than caused by pathogens.