Final answer:
Pathogens are sometimes harmful and are capable of producing disease, therefore the correct answer is d. 2 and 3 only. Factors such as the host's immunity and presence of opportunistic conditions influence the severity of an infection caused by pathogens.
Step-by-step explanation:
The correct answer is d. 2 and 3 only. Pathogens are sometimes harmful and are capable of producing disease. The term virulence refers to the degree to which a pathogen can cause disease. Some pathogens are highly virulent and almost always lead to a disease state when introduced into the body, which may include multi-organ and body system failure. On the other end of the spectrum, we find pathogens with low virulence, which may cause mild symptoms or in some instances, no symptoms at all (asymptomatic).
Primary pathogens are capable of causing disease in a healthy individual, whereas opportunistic pathogens can only cause disease when the individual's defenses are compromised. Factors such as the immune system's strength, preexisting conditions, and environmental factors can influence the severity of infection caused by pathogens.
Some pathogens are implicated in significant human diseases, such as bacteria causing infections that can be treated with antibiotics. However, not all bacteria are harmful; many are harmless and even beneficial to the human body.