Antiviral, antifungal, antiparasitic, and antiprotozoal drugs are used to treat infections caused by viruses, fungi, parasites, and protozoa respectively. Antiviral drugs work by targeting the enzymes needed for viral replication, and must generally be administered within 48 hours of infection onset. Antifungal drugs target the cell wall of fungi. Antiparasitic drugs expel or kill parasitic worms from the body. Antiprotozoal drugs treat diseases caused by protozoan parasites like malaria and African sleeping sickness.