Parasite

A parasite is an organism that lives on or inside another organism (its host), deriving nutrients at the host's expense. Unlike mutualistic relationships where both benefit or commensal ones where the host is unaffected, parasites benefit while causing harm to their host. These organisms can be viruses, bacteria, fungi, or larger animals like ticks and fleas. Parasites can infect various parts of the body, leading to illness or weakened health. Their survival depends on their ability to exploit their hosts, often avoiding immune responses, making parasitism a widespread ecological strategy.