1. Definitive host – a host that harbors a parasite in the adult stage or where the parasite undergoes a sexual method of reproduction.
2.Intermediate host - harbors the larval stages of the parasite or an asexual cycle of development takes place. In some cases, larval development is completed in two different intermediate hosts, referred to as first and second intermediate hosts.
3. Paratenic host – a host that serves as a temporary refuge and vehicle for reaching an obligatory host, usually the definitive host, i.e. it is not necessary for the completion of the parasites life cycle.
4. Reservoir host – a host that makes the parasite available for the transmission to another host and is usually not affected by the infection.
5.Natural host – a host that is naturally infected with certain species of parasite.
6.Accidental host – a host that is under normal circumstances not infected with the parasite.
There is a dynamic equilibrium which exists in the interaction of organisms. Any organism that spends a portion or all of its life cycle intimately associated with another organism of a different species is considered as Symbiont (symbiote) and this relationship is called symbiosis (symbiotic relationships). The following are the three common symbiotic relationships between two organisms:
Mutualism - an association in which both partners are metabolically dependent upon each other and one cannot live without the help of the other; however, none of the partners suffers any harm from the association. One classic example is the relationship between certain species of flagellated protozoa living in the gut of termites. The protozoa, which depend entirely on a carbohydrate diet, acquire their nutrients from termites. In return they are capable of synthesizing and secreting cellulases; the cellulose digesting enzymes, which are utilized by termites in their digestion.
Commensalism - an association in which the commensal takes the benefit without causing injury to the host. E.g. Most of the normal floras of the humans’ body can be considered as commensals.
Parasitism - an association where one of the partners is harmed and the other lives at the expense of the other. E.g. Worms like Ascaris lumbricoides reside in the gastrointestinal tract of man, and feed on important items of intestinal food causing various illnesses.
Once we are clear about the different types of associations between hosts and parasites, we can see the effect the parasite brings to the host and the reactions which develop in the host’s body due to parasitic invasion.
There is a dynamic equilibrium which exists in the interaction of organisms. Any organism that spends a portion or all of its life cycle intimately associated with another organism of a different species is considered as Symbiont (symbiote) and this relationship is called symbiosis (symbiotic relationships). The following are the three common symbiotic relationships between two organisms:
Mutualism - an association in which both partners are metabolically dependent upon each other and one cannot live without the help of the other; however, none of the partners suffers any harm from the association. One classic example is the relationship between certain species of flagellated protozoa living in the gut of termites. The protozoa, which depend entirely on a carbohydrate diet, acquire their nutrients from termites. In return they are capable of synthesizing and secreting cellulases; the cellulose digesting enzymes, which are utilized by termites in their digestion.
Commensalism - an association in which the commensal takes the benefit without causing injury to the host. E.g. Most of the normal floras of the humans’ body can be considered as commensals.
Parasitism - an association where one of the partners is harmed and the other lives at the expense of the other. E.g. Worms like Ascaris lumbricoides reside in the gastrointestinal tract of man, and feed on important items of intestinal food causing various illnesses.
Once we are clear about the different types of associations between hosts and parasites, we can see the effect the parasite brings to the host and the reactions which develop in the host’s body due to parasitic invasion.
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