Parasitic infections are caused by one of three kinds of organisms, protozoa, helminths, or ectoparasites, which all feed off their hosts to survive. Scabies, worms, and bed bugs are among the most common parasitic infections. 

Some parasites will cause few or no symptoms, but others can attack organ systems and other parts of the body, causing illness and parasitic infection. They are particularly common in tropical and subtropical regions, notably malaria, which is one of the most common parasitic infections. 

While malaria is rare in the United States, other parasitic infections are more common, such as trichomoniasis, a sexually transmitted infection, giardiasis, which can cause diarrhea and an upset stomach, and toxoplasmosis, which causes flu-like symptoms. Symptoms of a parasitic infection vary depending on the organism but often include itching, rash, or an allergic reaction.

Treatment of parasitic infection often involves topical treatment with ointments and creams. Drug classes commonly used to the treat parasitic infections are anaerobicides, antinematodal agents, and antitrematodal agents.