introduction to parasitology

introduction
Parasite –an organism that lives in or on other organisms (host) and obtains its food from host.
Parasitology - the science or study of host-parasite relationships.
Medical parasitology - study of parasites which infect humans.
Host - the partner providing food and/or protection. Some parasites require more than one host to complete their life cycle; Or may not require a host during some stage(s).
Definitive host - the host in which sexual maturity and reproduction takes place.
Intermediate host - the host in which the parasite undergoes essential development.
Reservoir (carrier) host - the host harboring a parasite in nature, serving as a source of infection for other susceptible hosts. Reservoir hosts show no sign or symptom of disease.
Paratenic host - an accidental host serving as a holding place for a parasite.

Vector - “carrier” of a parasite from one host to another. Often an insect.
Host-parasite relationship:
Symbiosis - “living together,” a close association between two organisms.
Mutualism - both organisms are benefited (bacteria in bowel).
Commensalism - “eating at the same table;” One organism is benefited, the other is unaffected.
Parasitism - one organism is benefited at the expense of another (the host).
A parasite is successful - when it is in delicate balance with the host. If the balance is upset, the host may destroy or expel the parasite; If the host is overly damaged, it may die - as will the parasite.

Parasitology is important - because this balance is not always maintained.
Protozoans are microscopic one-celled organisms that are classified according to their method of movements
Ciliates – the only parasitic ciliate that causes disease in humans in Balantidium coli
Flagellates – three of the most common and medically significant include Giardia lamblia, Trypanosome sp. and Trichomonas vaginalis
Parasitic Damage to Host:
Trauma - damage to tissues, intestine, liver, eye.
Lytic action - activity of enzymes elaborated by organism.
Tissue response - localized inflammation, eosinophilia.
Blood loss - heavy infection with hookworm may cause anemia.
Secondary infections - weakened host susceptible to bacterial infection, etc.