General structures of parasites

• A parasite is a living organism that acquires some of its basic nutritional requirements through its intimate contact with another living organism temporarily or permanently.
• Undulating membrane is a fin-like extension usually associated with the flagellum and enhances motility of the parasite in a viscous fluid, such as blood.
• Cilia are short eyelashlike filaments that are numerous on tissue cells of most animals and provide the means for locomotion of protozoans of the phylum Ciliophora.
• Infections can be asymptomatic or life threatening depending on the species and strain of the parasite and the resistance of the host.
• Protozoa are further divided into sub-phylum Sarcomastigophora which move by pseudopodia, sub-phylum Ciliata (Sililar) which includes Balantidium coli, and sub-phylum Apicomplexa which are obligate intracellular parasites with specialized organelles at the tip of cells that penetrate host tissues and are non-motile.
• The host is the organism in, or on, which the parasite lives and causes harm.
• Pseudopod is a temporary protrusion of the protoplasm, as of certain protozoans, usually serving as an organ of locomotion.
• Motility in protozoa is achieved through flagella, pseudopod, and cilia.
• Protozoa have two main life forms: Trophozoite (vegetative stage) which is active, motile, and disease-causing, and Cyst form which is resistant to environmental conditions.
• Protozoa are unicellular, microscopic eukaryotes that contain specific organelles.
• A definitive host is the organism in which the adult or sexually mature stage of the parasite lives.
• An intermediate host is the organism in which the parasite lives during a period of its development only.
• A reservoir host is where the parasite is maintained in nature and which acts as a source for individual new cases.
• A paratenic host is where larval stages of parasite may live but cannot become adult.
• Eggs of trematodes may have an operculum (Fasciola hepatica) or a spine (Schistosoma spp.).
• All parasitic organisms are eukaryotes.
• Trematodes are a type of parasitic flatworm with a leaf-shaped, flat segment, no body holes, a simple digestion system with no anus, and their body is covered with tegument.
• Dipyllobothrium latum and Hymenolepis diminuta are examples of cestodes that have larvae living in the human intestine.
• Mosquitoes (Anopheles spp., Culex spp., Aedes spp.) and sand flies (Phlebotomus sp., Lutzomyia spp.) are medically important arthropods.
• All trematodes are hermaphrodites except for Schistosoma spp., and they have a complex life cycle with at least one intermediate host (snail, fish, etc.).
• Some cestodes can have adult, larvae or both living in the human body.
• Arthropods are invertebrate animals having an exoskeleton (external skeleton), a segmented body, and jointed appendages.
• Cestode larvae living in human tissues can cause diseases
• Helminths have a complex reproductive system and individuals produce many eggs that can infect another host.
• Most human infections of Round worms occur through ingestion of egg or larva.
• Flat worms can grow from 1 mm to 5 meters long.
• Helminths are eukaryotic, multicellular animals that usually have digestive, circulatory, nervous, excretory, and reproductive systems.
• Round worms, or Nematodes, are elongated, round, unsegmented and have a complete digestive system with separate sexes (male/female).
• Protozoa are unicellular organisms, such as Plasmodium (malaria).
• Adult flat worms have a body consisting of an anterior attachment organ (scolex) and a body (strobila) consisting of a chain of segments called proglottids.
• The scolex (head) of flat worms is characterized by the presence of sucking disks or lateral grooves.
• Round worms have a body covered with three layers: Cuticle, subcuticle and muscular layer.
• Flat worms, or Cestodes, are flat worms with no body cavity and have hermaphrodites (male and female organs (+)).
• Helminths may lack a digestive system and absorb nutrients from the host's food, body fluids, or tissues.
• Ciliates are represented by the genus Balantidium coli.
• Helminths have a reduced nervous system and means of locomotion is reduced or absent.
• Metazoa are multicellular organisms, such as helminths (worms) and arthropods (ticks, lice).
• An ectoparasite is a parasite that lives on the external surface of another living organism.
• Obligatory Parasite: A parasite that lives in all life forms, such as Pediculus capitis (head lice).
• Parasitism: An association which is beneficial to one partner (the parasite) and harmful to the other partner (the host), such as Taenia in the intestines.