Parasitology

• Parasite - A parasite is an organism that lives on or in another organism and gets its food from it
• Parasite - an organism that is entirely dependent on another organism (host)
• Parasite - a living organism which receives nourishments and shelter from another organism where it lives
• Host - an organism that harbours a parasitic, a mutualistic, a commensalist guest, the guest typically being provided with nourishment and shelter
• Host - may either get benefitted, harmed, or neither
• Host - always has a higher organization
• Parasite - an organism that obtains nourishment and shelter on another organism
• Parasite - always benefits
• Parasite - always less organized than the host
• Pathogen - an organism that causes disease to the host after infection
• Parasite - an organism that lives on or in another organism of another species; usually derives nutrients at the expense of its host
• Pathogen - usually kill their host through diseases
• Pathogen - typically do not require a host to complete its life cycle
• Pathogenicity - the ability of an organism to infect another organism
• Parasite - mostly do not kill their host but do cause some damage
• Parasite - will have to depend on their host to complete their life cycle
• Parasitism - can be considered as a kind of interaction between two species, where one species is benefitted, and the other one is harmed
• CLASSIFICATIONS OF HOST

  • Definitive
  • Intermediate
  • Reservoir
  • Paratenic / Storage
  • Incidental / Accidental
• Definitive Host (Primary) - the host which harbours the adult parasites or where the parasite replicates sexually; can be a mammalian host or other living hosts
• Intermediate Host (Secondary) - refers to the host which harbors the larval stages of a parasite or in which the parasite undergoes asexual multiplication
• Reservoir Host - it is a host which harbors the parasites, possibly grow, and multiply and serves as an important source of infection to other susceptible hosts
• Paratenic Host - a host that serves as a temporary refuge and vehicle for reaching an obligatory host, usually the definitive host
• Incidental / Accidental Host - a host organism that shelters the parasite, but since it can't progress the life cycle development, it is dead-end for it
• Criteria used in classification of parasite according to their:

  • Pathogenicity
  • Need of Host
  • Location
  • Mode of Living
• Symbiotic relationships are usually of four main types:

  • parasitism
  • mutualism
  • commensalism
  • phoresis
• Host-parasite relationship / symbiotic relationship - those in which the organisms (host and parasite) live in close proximity to each other and are dependent on each other in one or another way for their survival
• Mutualism - a symbiotic relationship that is defined as an association between two living things in such a way that both benefit from each other's existence
• Parasitism - a non-mutual symbiotic relationship in which one of the symbionts (the parasite) benefits at the expense of the host, while the host is harmed
• Commensalism - a type of symbiotic relationship where one partner benefits whereas the second partner (the host) are neither helped nor harmed
• Commensal - the organism that receives the refuge and nourishment
• Most of the normal floras of the human body can be considered as commensals
• Humans harbor several species of commensal prostistans such as Entamoeba gingivalis which lives in the mouth where it feeds on bacteria, food particles, and dead epithelial cells but never harms healthy tissues
• Adaptation - any feature of an organism or its part which enables it to exist under conditions of its habitat
• Adaptation - is mainly to withstand the adverse conditions of the environment and to use the maximum benefit of the environment
• Feeding organs are usually absent in endoparasites.
• The presence of well-developed piercing device in some parasites enables them to invade into the host tissue. Example: the stylet in nematodes
• Since endoparasites show restricted movement, the locomotory organs are generally absent or highly reduced in them. Example: gut parasites such as Fasciola and Taenia
• The presence of attachment organs such as rostellum, hooks, or suckers for the securely connecting to the organs of the host as in Fasciola and Taenia.
• The outer covering of the endoparasite is resistant to the enzymatic digestion of the host.
• Some endoparasites such as Ascaris have highly muscular pharynx for the easy absorption of food materials from the host.