General Parasitology Flashcards
Define protozoa
unicellular eukaryotic cells that perform all physiological functions
Define helminths
Elongated flat or round-worm like parasites measuring few mm - few metres.
Eukaryotic, unicellular, bilaterally symmetrical
Protozoa examples
- Amoeba - E. histolytica, Naegleria, Acanthamoeba
- Flagellates - Giardia, Trichomonas, Leishmania
- Apicomplexa - Malarial, Babesia, Toxoplasma, Sarcocystis, Cyclospora, Cryptosporidium
Helminths examples
- Cestodes - Taenia. Echinococcus, Hymenolepsis
- Trematodes - Schisostoma, Fasciola, Clonorchis
- Intestinal nematodes - Enterobius, Hookworm, Ascaris
- Somatic - Trichinella, Dracunculus
Autoinfection
Reinfection with larvae produced by parasites already in the body.
Ex: Taenia Solium, Enterobius vermicularis, Cryptosporidium parvum, Hymenolepis nana
When should stool specimen be collected?
Before starting anti-parasitic drugs and closer to onset of symptoms
How many times should stool specimen be collected?
3 specimens on alternate days
For intestinal amoebiasis, 6 specimens
When should stool specimen be examined?
Liquid stool - within 30 mins
Semisolid - within 1 hr
Formed stools - within 24 hrs
How can fecal specimens be preserved?
Room temp.
10 percent formalin can be used to maintain morphology of parasitic cysts and eggs
What specimens other than stool can be collected?
Perianal swabs - Taenia, Enterobius vermicularis, Schisostoma mansoni
Duodenal contents - Giardia intestinalis, Strongloides stercoralis
Mucoid bloody stool found in
Amoebic dysentery, intestinal schistosomiasis, invasive balantadiasis
Colour of stool indicates
Dark red - Upper GIT bleeding
Bright red - Lower GIT bleeding
Frothy pale offensive stool seen in
Giardiasis
Chemicals used in direct wet mount
Drops of saline
Lugol’s iodine
Magnification for direct wet mount
10x for helminthic eggs and larvae
40x for protozoan cysts and trophozoites
Charcot Leyden crystals
diamond shaped
Breakdown products of eosinophils
Seen in stool or sputum in amoebic dysentery, ascariasis, bronchial asthma
Saline mount
To detect trophozoites, cysts of protozoan parasites, eggs and larvae of helminths
Motility and bile staining property can be appreciated
Iodine mount
Nuclear details of protozoan cysts, helminthic eggs and larvae can be seen
Motility and bile staining property cannot be appreciated
Non bile staining eggs
Enterobius, Hookworm, Hymenolepis nana
Permanent staining methods
- Iron-hematoxylin stain
- Trichrome stain
- Modified acid fast stain - for coccidian parasites
Concentration techniques
- Sedimentation
2, Floatation - Zinc sulphate flotation
Sheather’s sugar floatation
Floatation technique cannot be used in
unfertilized eggs of Ascaris
larva of Strongyloides
Taenia eggs
operculated eggs of trematodes
Sheather’s sugar floatation technique for
Cryptosporidium
Cystoisospora
Cyclospora
Egg counting methods
esp. for Trichuris, Ascaris, Hookworm
1. Direct smear counting method of Beaver
2. Kato-Katz thick film method
3. Stoll’s method or dilution egg counting method
Blood examination used for
Plasmodium Trypanosoma Leishmania Babesia Wuchereria bancrofti Mansonella
Blood concentration methods
- Sedimentation
- Cytocentrifugation
- Knott concentration
- Gradient centrifugation
- Membrane filtration
Immunodiagnostic methods used when
- Early stages of disease
- Parasites are in very small numbers
- Reside in internal organs
- Time constraint
Ab detection tests useful in
Amoebic liver abscess: ELISA against 170kDa lectin Ag Visceral leishmaniasis Cysticercosis Toxoplasmosis Hydatid disease
Ag detection tests
Amoebiasis
ICT panel detects Giardia, E. histolytica, Cryptosporidium in stool
Malaria
Lymphatic filariasis
Molecular methods
PCR, rt-PCR
LAMP: for visceral leishmaniasis and malaria
Biofire Film Array: detects E. histolytica, G. lamblia, Cryptosporidium, Cyclospora
