． (1) Symbiosis（共同生活） Two different organisms live together and interact on each other, in this association one partner lives in or on the other, including 3 types: Mutualism, Commensalism, Parasitism.
． (2) Mutualism（互利共生或共生） is a permanent association in which two different organisms so dependent on each other that life apart is impossible, from which two partners all benefit, such as termite and flagellate.
． (3) Commensalism（片利共生或共栖）is the association of two different organisms, in which one partner is benefited while the other neither benefited nor injured, such as E. coli and man.
． (4) Parasitism（寄生关系）is the association of two different organisms, in which one partner is benefited while the other is injured, such as Ascaris lumbricoides and man.
． (5) Parasite（寄生虫） In parasitism, it is the benefited partner. It is an animal organism which lives in or on the host in order to obtain nourishment and shelter and does harms to the host.
． (6) Host（宿主） In parasitism, it is the injured partner which supplies the parasite with nourishment and shelter.
． (7) Carrier（带虫者） A person who harbors parasites has no any clinical symptom. He is a hid and important source of infection in epidemiology
． (8)*Definitive (final) host（终宿主）is the host which harbors the adult or sexually reproductive stage of a parasite. Man is the final host of ascarid.
． (9)*Intermediate host（中间宿主）is the host which harbors the larval or asexually reproductive stage of a parasite, according to priority they are classified into first intermediate host, second intermediate host and so on. Mosquitoes are the intermediate host of filariae.
． (10)*Reservoir host（保虫宿主）is the vertebrate animal host which harbors the same species of parasite at the same stage as a human definitive host does. It is the animal source of infection in epidemiology. Cat is the reservoir host of liver fluke.
． (11)*Parasitic zoonosis（人兽共患或动物源性寄生虫病）refers to animal’s parasitic diseases which can be transmitted to man. (These animals infected with parasites are called reservoir host.) Liver fluke disease is a zoonosis.
． (12) Paratenic host or transport host（转续宿主）is an abnormal host in which some parasitic larvae can survive but can not develop into the adult stage. If the larvae have a chance to enter their appropriate hosts, they can continue to develop into adults there.
． (13)*Larva migrans（幼虫移行症）means that the parasitic larva lives in an abnormal human host in which they can not grow into the adult stage but can wander everywhere and cause the local and systemic pathological lesions.
． (14) Life cycle（生活史） is the process of a parasite’s growth, development and reproduction, which proceeds in one or more different hosts various from species to species.
(15) * Infective Stage（感染期）A parasite develops into a certain stage when it can invade human body and continue to live there. The infective stage of ascarid is the embryonate egg.
(16)*Infective Route感染途径）is the specific entrance through which the parasite invades the human body. Hookworms invade human body by skin. Man gets infection with ascarid by mouth.
(17) Infective Mode（感染方式）means how the parasite invades human body, such as the cercariae of the blood fluke actively penetrate the skin of a swimming man and the infective ascaris eggs are swallowed by man.
． (18)*Geohelminth refers to the helminths which complete their life cycles not requiring the processes of development in intermediate host. They have only one host and a simple life cycle, such as ascarid, hookworm, pinworm and etc.
． (19) * Biohelminth refers to the helminths which have to undergo the development in intermediate hosts to complete their life cycles, such as filaria, liver fluke, pork tapeworm and so on.
． (20) Alternation of Generation: In life cycles of some parasites, there is the regular alternation of sexual and asexual reproductions, this phenomenon is called alternation of generation, such as it is in the life cycle of Plasmodium vivax.
． (21)*Trophozoite is a living stage of protozoa when they can move, take food and reproduce. (It is usually the pathogenic stage.)
． (22)* Cyst is the resting stage of a protozoa with a protective wall. It is usually the infective stage. Its functions are protection, transmission and multiplication.
． (22)*Mechanical Transmission: Arthropods play a role of the transportation of pathogens, which is not indispensable for the disease transmission, such as flies carry typhoid bacilli, ascarid eggs and amoebic cysts.
． (23)*Biological Transmission: Pathogens have to spend a part of their life cycle in the specific arthropods in which they multiply or develop into the infective stage and then invade the human body under the help of the arthropods, such as Anopheles mosquitoes transmit malaria.
