parasitology

Medical Parasitology

Deals with the parasites w/c causes human infection & disease

Symbiosis

A relationship where unlike organisms exist together is called?

Commensalism

Is a form of symbiotic relationship in which two species live together, and one species benefits from the other without harming or benefiting the other

Mutualism

Is a symbiotic relationship in which two organisms mutually benefit from each other

Parasitism

Is the form of symbiotic relationship where one party or symbiont (i.e., the parasite) benefits to the detriment of the other (host)

Ectoparasites

Parasites that live outside the host’s body (e.g., fleas, lice)

Infestation

Invasion of the body by ectoparasites

Endoparasites

Parasites that live inside the body of the host (e.g., helminths or worms)

Infection

Invasion of the body by endoparasites

Facultative parasites

Parasites that can live independently of the host / free living

Obligate Parasite

Parasites that must live inside a host

Permanent Parasites

Remain in a host from early life to maturity

ex: plamodium, head lice

Intermittent Parasites

Simply visit the host during feeding time

ex: mosquito

Incidental Parasites

Occur on an unusual host

Ex: dog tapeworm in humans

Transitory Parasites

Larva develops in a host while the adult is free-living

ex: echinococcus granulosus or dog tapeworm

Erratic Parasites

Parasites that are seen in an unusual organ, different from that which it ordinarily parasitizes (ex: ascaris lumbricoides in the lungs or kidneys)

Aberrant Parasites

Wandering parasites…infects host where it cannot develop any further

Definitive hosts

Hosts that harbor the adult stage or sexual stage

Intermediate hosts

Harbor the larval or asexual stage of the parasite

• required by some parasites to complete their life

Paratenic Hosts

Serves as means of transport for parasite (ex: vectors)

→ infective stage of certain parasite reach its final host

Reservoir Hosts

Vertebrate hosts that harbor the parasite and may act as additional source of infection in man

Accidental hosts

Living organism that can serve as a host in a particular parasite’s life cycle, but is not a usual host in that life cycle

Oral transmission (ingestion of contaminated food & water)

most common mode of transmission if most intestinal parasites

Contaminated water

MOT

intestinal protozoa (cyst)

Contaminated food

MOT

contains mature larval stage: Enterobius vermicularis

Skin transmission

MOT

hookworms & strongyloides

Direct transmission > sexual intercourse

MOT

ex: trichomonas vaginalis

Transmammary (milk)

MOT

ex: strongyloides & ancylostoma

Transplacental or congenital infection/vertical transmission

MOT

ex: toxoplasma gondii, malarial parasite

Inhalation of airbone

MOT

ex: eggs of enterobius vermicularis or pin worm

Vector transmission

MOT

ex: mosquito, malaria, leishmaniasis, trypanosomiasis, filariasis

Anus

Most common portal of exit of parasites

• eggs of medically impt roundworms tog w/ human feces & contaminated soil & water

Urine

Portal of exit of parasites

• for trichomonas vaginalis, strongyloides stercoralis, schistosoma haemotobium

Sputum

Portals of Exit of Parasites

• for lung fluke (paragonimus westermani), round worm (ascaris lumbricoides) larval stage

Pathogenesis

• refers to the dynamics of any disease process

• The development of a disease and the chain of events leading to that disease

Inapparent infection

Infection can remain inapparent continuously for long periods of time (malaria)

Type 1: allergy or anaphylactic

IMMUNOPATHOLOGIC REACTIONS

Parasite antigen + IgE attach to mast cells, causing histamine release

Type 2: antibody-mediated

IMMUNOPATHOLOGIC REACTIONS

Antibody + parasite antigen on cell surface cause activation of complement activation or natural killer cells

Type 3: immune complex

IMMUNOPATHOLOGIC REACTIONS

Antibody + extracellular antigen complex with deposition on endothelium of blood vessels

Type 4: cell-mediated

IMMUNOPATHOLOGIC REACTIONS

Sensitized T cell reaction with antigen, release of lymphokines, triggered cytotoxicity