Parasitology Short Notes
The topic ‘ Parasitology Short Notes for MCQs’ will serve as a capsule for candidates who are participating post for medical lab technician, medical lab technologist, and such related fields.
Some Common Terms Used in Parasitology
Parasite: Organism which receives food and shelter from another organism.
Host: Which harbor the parasite
Symbiosis: an association in which both are dependent upon each other and non of them harm each other
Commensalism: an association in which parasite only is driving benefit without causing any harm to its host.
Parasitism: an association in which a parasite is the deriving benefit and causing harm to its host.
Facultative parasite: Actually not parasite but lives a parasitic life when the opportunity arises.
Obligate parasite:
The strict parasite can not exist without parasite life.
Wandering or aberrant parasite:
Happens to reach a place where it can not live.
Occasionally are the accidental parasite
Attack an unusual host.
Vector: Organism responsible for parasite transfer from one host to another host( e.g. insects, tickets, etc)
Classes of host
- Definitive host (Primary host)
The host where parasite utilize the sexual method of reproduction ( adult stage of the parasite)
- Intermediate host ( Secondary host)
The host where parasite utilizes an asexual method of reproduction ( larva stage of the parasite)
1. Majority of parasite infections in man is the definitive host except for malaria and Hydatid.
- Paratonic host ( carrier/ transport host)
A host where parasites remain viable without further development.
Classification of parasite
Human parasite
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Cestoda
- Taenia solium ( Pork Tapeworm)
- T. saginata ( Beef Tapeworm)
- Diphyllobothrium latum ( fish tapeworm)
- Echinococcus granlosus ( Dog tapeworm )
- Hymenolepsis nana ( dwarf tapeworm)
- H. diminuta (rat tapeworm)
Nematoda
- Reside on the Small intestine
- Hookworm ( Ancylostoma)
- Ascaris (roundworm)
- Strongyloides
2. Large intestine
- Enterobius ( Pinworm/threadworm/sheatworm)
(Plano concave larva is found in Enterobius)
- Trichuris ( whipworm)
3. Lymphatics
- Wuchereria
- Burgia
4. Conjunctiva → Loa loa
5. Subcutaneous
- Dracunculus (Guinea worm/ serpent worm)
- Onchocerca
Based on whether they lay egg or larvae
1. Oviparous: laying the egg
- Unsegmented: Ascaris, Trichuris
- Segmented: Ancylostoma, Nector
- egg containing larva: Enterobius
2. Viviparous: producing larvae
e.g.
- Wuchereria
- Trichinella
- Dracunculus
- Burgia
3. Ovoviparous ( laying eggs containing fully formed larvae which hatch out immediately)
e.g. Strongyloides
Man is the intermediate host( Secondary host) in:
- Plasmodium
- Echinococcus granulosus
- Toxoplasma gondii
Auto infection occurs in
- H. nana
- E. vermicularis
- T. Sodium
- Strongyloides stercoralis
@HELTS
Eggs float in a concentrated saturated solution
- H. nana
- All nematodes ( except unfertilized egg of Ascaris
Worms that crawl out
- Enterobius vermicularis
- T. saginata
Parasite associated with malignancy
- Schistosoma haematobium: bladder carcinoma
- Clonorchis: Bile duct carcinoma
- Optisthorchis: Bile duct carcinoma
The cystic stage is absent in
- Trichomonas vaginalis
- Trichomonas intestinalis
- Entamoeba gingivalis
Undulating membrane is seen in-
- Hemoflagellates
- Trichomonas species
Worm passes through the lung during its life cycle
- Schistosoma hematobium ( lung acts as 2nd filter)
- Echinococcus
- A. duodenale
- Paragoniums
- Strongyloids
- Ascaris
Intracellular Parasite
- Leishmania ( amastigote form)
- Plasmodium
- Sarcocystis
- Toxoplasma gondii
- Trypanosoma (amastigote form)
- Babesia
Neuro Parasites
- E. histolytica
- Trypanosoma
- M.falciaparum
- T. gondii
- Asaris lumbricoides
- Strongloids
- T. solium
- Echinococcus granulosus
- Schistosoma hematobium
- F. hepatica
Parasite, their infective stages, habit, and disease cause
Giardia Iamlia
- Most common intestinal (duodenum) protozoan parasite
- Two form
- Trophozoites
- Pyriform/ heart/ tennis or badminton racket shaped
- 4 P flagella with 2 nuclei
- Divide by longitudinal binary fission
- Pass in stool but non-infective
- Motility resemble ” falling leaf”
- Size (15 ×10)μm
2. Cysts
- Size (7 × 10)μm
- Infective stage (4 nuclei/quadrinucleate cyst
- Pass in stool and infectious
- Infective dose = 10 cyst
- Also called “Grand old man of intestine”
- ”Entero test is done for diagnosis
Entamoeba Histolytica
- commonest causes of amoebic dysentery and liver abscess
- Two form
- Trophozoites( feeding stage)
- size – 20 to 30 μm
- motility → progressive and directional
- Contractile vacuole absent
- Cytoplasm (i) ectoplasm (ii) endoplasm
Cyst
- Size – 12 to 15 μm ( as the size of WBC)
- Contain Glycogen mass→ brown with an iodine stain
- 1 to 4 chromatid body → refractive
- Quadrinuclate cyst → infective stage
- are not developed inside of metastatic invasion ( lung, liver)
- developed in the lower colon
- The cystic stage is absent in the liver and lung
- ”Diamond” medium is used to cultivate both E. histolytica and Giardia
- Culture for E. histolytica→ NIH medium
Plasmodium
- Intracellular, absence of locomotory organ
- life cycle (Digenetic)
- Man:- intermediate host ( Asexual cycle)
- Infective stage → sporozoites
Life cycle
- Pre erythrocytic schizogony → liver cell → cryptozoites/ merozoites
- exoerythrocytic schizogony → liver cell → metacryptozoites
- erythrocytic cycle → in RBC
In RBC
Trophozoites → signet ring → Amoeboid form → schizont = gametocyte, merozoite
In Mosquito
Gametogony → Male gamete+ Female gamete → zygote → ookinete → oocysts → sporozoites
Lab diagnosis
- Preparation of blood smear ( Gold standard)
- Thick smear → quicker detection of malaria
- Thin smear → for differentiating different species of malaria
2. Serology:- Detection of Ab ( optional test)
3. Culture:- not required
Biological control:
Use of larvivorous fish eg. Gambusia affinis and Lebirtus reticulatus.
Differentiating properties
Important points
- relapse is not seen in P. falciparum
- Blackwater disease is due to P. falciparum
- Sporozoites are the infective stage of malaria
- Exo erythrocytic cycle is absent in P. falciparum
- Plasmodium does not infect RBC of G6PD deficient, Hbs, HbF, HbC, and HbE.
Leishmania donovani
- Cause visceral leishmaniasis or kala-azar
- Amastigote form is found in the R E system of vertebrate ( man ) and promastigote form (Flaggelate stage ) in culture and in sandfly.
- infective stage → promastigote form
- Laboratory diagnosis
- Blood smear: thick, thin
- Culture: bone marrow
- NNN medium (Navy Nichel and Mac Neal media)
- Hockymeyer’s medium.
3. Serology:
- Aldehyde test is positive for leishmania
- k- 39 test is more specific and more sensitive for leishmaniasis.
Coccodian Parasites.
- Isospera belli
- Cryptosporidium parvum
- Toxoplasma gondii
- Plasmodium species
- Emeria species
- Sarcocystis species
Important points
- Cryptosporidium parvum causes chronic diarrhea
- Neuro cysticercosis is caused by T. solium
- Infection caused by ectoparasite is called as an infestation
- Balantidium coli is the largest protozoan parasite
- Only protozoan ” parasite found in the lumen of human intestine → Giardia lamblia
- Parasitic larva found in urine → S. haematobium
- eggs of Trichuris trichuria → barrel-shaped
- eggs of Enterobius is caused by → Ascaris lumbricoides
- Size of roundworm ( male-15 to 30 cm and female 20 to 35 cm)
- Oriental sore is caused by L. tropica
- Casoni’s test is done -to detect hydatid cyst.
Toxoplasma gondii
- obligate intracellular sporozoan
- only protozoan which all stages are infectious for men. (Trachyzoits/tissue cyst/oocysts)
Life cycle
- Definitive host: Domestic cat, Bengal tiger
- Intermediate host: Human, mice, and other non-feline hosts like goat, sheep, pig, cattle. swine
Two-cycle
- Enteric cycle ( Intestinal cycle ) → in the homologous host (e.g. cat)
- Exoteric cycle ( extraintestinal cycle) → in the heterogeneous host ( e.g. man)
Made of infection
- Congenital ( transplacental route)
- Acquired ( undercooked meat)
- By inhalation (droplet infection)
- By inoculation:- ( through the skin)
Diagnosis
- Serological → TORCH
- Sabin and Feldman dye test
- Toxoplasma skin test of Frankel
Different between Amoebic dysentery and Bacillary dysentery.
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