There are four types of can affect the human body. these viruses are that infect a host's cells to reproduce rapidly. are the best way to combat viral infections, preventing them in the first place. bacteria are usually organisms that get their nutrients from the environment around them. some bacteria are harmful, such as those that cause while others are beneficial, such as those that with the digestion of food. fungi obtain nutrients from both living and nonliving sources of their bodies. fungal infections are typically treated with drugs and creams. parasites live on or in a and get their nutrients from that organism. typically, parasites do not kill the host, but they often make the host