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Medical Parasitology

Medical Parasitology •Parasitology is the science that deals with parasites, which infect man temporarily or permanently. •Parasitism indicates that one species (parasite) depends upon another species (host) to derive benefits such as food, shelter and maintenance of species. •This association may show harmful effects to the host

The Association between 2 Organisms • Mutualism: The two organisms get benefit from each other.( ) • Symbiosis: Mutual benefit but organisms can’t live independently.(

the )


• Commensalism: One organism gets benefit while the other (host) is not affected. (some of Normal flora) • Parasitism: One organism (parasite) gets benefit and lives on the expense of another organism (host) that usually loses or suffers.

Description of Parasites • Obligate

Parasite: Can’t live independent from the host i.e.

permanent residence.

• Facultative

Parasite: Can live free far from the host or as


• Ectoparasite: Live on the outside of the host (infestation


• Endoparasite: Live within the body of the host (infection). • Permanent Parasite: Remain most or entire of its life cycle in its host.

• Temporary Parasite: It visits its host from time to time. • Accidental Parasite: Found in an abnormal situation in the host. • Coprozoic Parasite: Non human or free living parasite passing through the alimentary tract without infecting man. It also applies to parasites, which lodge on feces after they have been passed.

• Pseudo parasite: An artifact mistaken for a parasite.

Pseudo parasite • Yeast cells are often mistaken for Giardia cysts or other parasites while examining fecal saline smears.

Types Of Hosts • Final or Definitive Host: Harbors the sexually mature parasite (adult worm or sexual stage of protozoa). • Intermediate Host: Harbors the immature or asexual stage. • Reservoir Host: Animal that harbors the same species of parasites as man and so is a potential source (store) of infection to man with this parasite. • Vector: Usually an arthropod that carries the parasite to its host.

Mode Of Transmission Of Parasitic Diseases 1- Contact: Direct contact with infested persons e.g. scabies, lice . Indirect contact with infected person’s towels, bed sheets contact e.g. scabies . Sexual contact e.g. Trichomonas vaginalis.

2- Food and drink: Is the most common. Eating or drinking contaminated water or food e.g. helminthes ova, protozoan cysts. Eating raw or under cooked or under salted fishes e.g. Heterophyes heterophyes. Eating raw or undercooked meat e.g. Taenia saginata (in cattle meat), T. solium and Trichenella spiralis (in pig or pork meat).

3-By arthropods – Mechanically by non-blood sucking insects e.g. housefly transmit protozoal cysts or helminthes ova. – Biologically by bite of blood sucking insects e.g. malaria, Filariasis, Trypanosomiasis. – Ingestion of insect containing the infective stage: e.g. infected flea (in Hymenolepis nana) and other insects (in H. diminuta) or infected Cyclops in water (in Dracunculus medinensis).

• 4- By contact with motile larval stages in the external environment: – Cercaria of Schistosoma in water (swimming, washing or irrigation). – Larvae of Ancylostoma in soil (penetrate the skin of persons walking bare-footed in muddy soil).

• 5- Blood transfusion and contaminated syringes e.g. malaria. • 6- Transplacental e.g. Toxoplasma, Trypanosomiasis.

Effects Of Parasitic Infection On The Host • 1- Anemia due to • • • •


Sucking of blood & blood loss e.g. Ancylostoma. Destruction and feeding on Red cells hemoglobin e.g. malaria. Depression of bone marrow e.g. Leishmania donovani. Vit B12 deficiency e.g. Diphyllobothrium latum.

• 2- Loss of weight due to: • Sucking digested food e.g. Taenia and Ascaris. • Preventing fat absorption e.g. Giardia lamblia.

• 3- Mechanical effects as in: • Intestinal obstruction in heavy Ascariasis and in Taeniasis. • Intestinal perforation (Ascariasis, Taeniasis). • Pressure atrophy in Hydatid (liver and lung).

4- Poisoning or allergic reaction due to toxic substances produced by the parasite in blood. e.g. Malaria, Hydatid. 5Localized irritation e.g. gastrointestinal disturbances with colic, dyspepsia ‫ عسر سوء هضم‬, diarrhea, dysentery. 6- Facilitating secondary bacterial infection.

Methods of control of parasites 1- Control of hosts Man. Vector. mosquito Intermediate hosts Reservoir host


. (snail of bilharzias) .(Carrier)

2- Personal hygienic measures . 3- General hygienic measures .

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باراسيتولوجي محاضرة ثانية

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باراسيتولوجي محاضرة ثانية