How do pathogens generally affect their host?

Pathogens are organisms that cause disease in their hosts. When they invade a host, they can disrupt normal physiological functions, leading to infections and various disease symptoms. This can include inflammation, damage to tissues, and alterations in metabolic processes. The primary interaction of pathogens with their hosts is detrimental, manifesting in a range of illness that varies from mild to severe, depending on the pathogen's virulence and the host's immune response.

While some organisms may enhance immune response under certain conditions or have other beneficial effects in specific contexts, this is not the general or primary role of pathogens. Their main characteristic lies in their ability to cause harm, which is seen across a variety of pathogens, including bacteria, viruses, fungi, and parasites. The other choices reflect roles that are typically not associated with the harmful effects of pathogens, which is why they are less representative of the impact pathogens generally have on their hosts.