Parasitic infections occur when parasites invade the body and live off the host's nutrients. These parasites can be microscopic, like protozoa, or larger organisms, such as worms and insects. Common examples include malaria, caused by a protozoan transmitted by mosquitoes, and giardiasis, caused by a microscopic parasite found in contaminated water. Symptoms of parasitic infections vary widely and may include fever, fatigue, digestive issues, and skin rashes. Diagnosis typically involves laboratory tests to identify the specific parasite. Treatment often includes medications that target the parasite, helping to restore the host's health and eliminate the infection.