Parasites or protozoa share cell homology with human cells because both are eukaryotic cells. The similarity in their cellular structures has limited the number of available antiprotozoal agents used for treating some parasitic infections in humans. Some parasites like viruses are intracellular organisms (e.g. Plasmodium species and Trypanosoma species) that reside within the cells of their human hosts. Antimicrobial agents directed towards the protozoan leave untoward effects in the hosts taking the drug. Of great importance is the fact that most of these agents used for treating parasitic infections are toxic in humans, and this has limited their use for treatment. Humans depend largely on their immune system to fight certain parasitic infections aside the use of some antiprotozoal agents to manage the situation. Several human parasites have complicated life cycles which are shared among their human/animal hosts and insect vectors that aid in their transmission. These factors inclusive of protozoa resistance to some drug influence and reduce the pace of developing newer antiprotozoal agents.
Antiprotozoal agents are antimicrobial agents or drugs used to treat infections caused by parasites in humans. Parasites are organisms that live in or on the body of humans and other animals. They include helminthes and worms. Some notable parasitic or protozoal infections in humans include malaria (caused by Plasmodium species), leishmaniasis (caused by Leishmania species), trichomoniasis (caused by Trichomonas species), giardiasis (caused by Giardia species), amebiasis (caused by Entamoeba species), and toxoplasmosis (caused by Toxoplasma species). A wide variety of protozoal infections are prevalent in subtropical and tropical regions of the world especially in places where public hygiene, water supply and environmental sanitation are still at a pitiable state. Metronidazole (flagyl), pentamidine, Ivermectin, pyrantel, albendazole, primaquine, and artemisinin, quinine and mefloquine are some antiprotozoal agents used to treat different parasitic infections in humans. Some antibacterial agents such as tetracycline, sulpha drugs and doxycycline are also co-administered with some antiprotozoal agents to treat parasitic diseases in humans. For some parasite diseases such as malaria (caused by Plasmodium species) prophylactic measures and other preventive practices such as sleeping under insecticide treated net (ITN) are most appropriate to the containment of the disease rather than treatment. Vector control for human parasitic infections is also critical to the prevention of a wide variety of parasitic diseases since most of their causative agents are transmitted to humans via insects and other animal carriers through a bite especially when taking blood meal. Most antiprotozoal drugs act by interrupting key stages in the lifecycle of the parasite in vivo; and the mechanism of action of these drugs varies from each other, and they should always be used with caution. The search for potent antiprotozoal agents with minimal or lesser toxicity on human hosts is still ongoing.
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