Answer :
A pathogen is an organism or substance, particularly a microorganism like bacteria, viruses, protozoa, or fungi, that can cause disease. The primary characteristic of pathogens is their ability to lead to illnesses, such as malaria or gastroenteritis. Option D.
A pathogen is best described as d) an organism or substance, especially a microorganism, capable of causing disease, such as bacteria, viruses, protozoa, or fungi. Pathogens include a variety of organisms that can lead to illness. While they might live on or in another organism (parasitism), and they can sometimes be transmitted from one person to another (contagiousness), the defining characteristic of a pathogen is its ability to cause disease (pathogenicity). Human pathogens include the causative agents of diseases like malaria, African sleeping sickness, and waterborne gastroenteritis. Infectious diseases are all caused by the invasion of these germs into a host, where they can grow to a population size large enough to cause harm. Option D.