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• Symbiosis - Form of relationship by 2 unlike organism
• Parasitism - 1 species (symbiont/ parasite) benefits to the detriment of the other
• Parasite – lives on and in other living organism for survival
• Host – harbor the parasite and provide its nourishment
• Commensalism - a relationship between individuals of two species in which one species obtains food or other benefits from the other without either harming or benefiting the latter.
• Mutualism - relationship where two organisms mutually benefit each other. Inside our own bodies, there are hundreds of different types of bacteria that live just in our large intestine.
• Protozoa - Single celled
• Sporozoan (sporozoans) – No movement

  Sarcodina (amoebas) – No feet Mastigophora (flagellates) - Flagella d) Ciliata (ciliates) - Cilia; hairlike structures
• Metazoan (Helminths) - Multicellular
• Platyhelminthes – flatworms
• Nemathelminths – roundworms
• Ectoparasites - Those that live outside of host body (fleas, lice)

  Infestation – invasion of the body by ectoparasites
• Endoparasites - Lives inside the body of host (helminths or worms)

  Infection – invasion of the body by endoparasites.
• Facultative parasites - Can live independently of the host (free-living)
• Obligate parasites - Must exist as parasite inside a host. Majority of parasites that infect humans are obligate parasites. (ex: Plasmodium hookworms)
• Permanent parasites - Remain in a host from early life to maturity
• Intermittent parasites - Simply visit the host during feeding time

  Ex: Non-pathogenic parasites, mosquito
• Incidental parasites - Occur on an unusual host

  Ex: dog tapeworm in humans
• Transitory parasites - Larva develops in a host while the free-living during adult stages

  Ex: Echinococcus granuloses/ dog tapeworm
• Erratic Parasites - Becomes fixed in an unusual organ, different form that which it ordinarily parasitized.

  Ex: Ascaris lumbricoides
• Aberrant Parasites - Wandering parasites infects host where it cannot develop any further

  Ex: dog roundworm in human
• Definitive Host - Harbors the adult stage or sexual stage
• Intermediate Host - Harbor the larval or asexual stage of the parasite
• Reservoir Host - Vertebrate hosts which harbor parasite and act as source of infection in man
• Paratenic Host - Serve as means of transport for parasites
• Accidental Host - Living organism that can serve as a host in a particular parasites life cycle but is not a usual host in the life cycle