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Parasitology
| Question | Answer |
|---|---|
| Specimen Collection and Handling : general | • 3 specimens w/in 10 day every other day • Liquid within 30mins of passage or place in preservative • Soft specimens w/in 30mins of passage or place in preservative • Fformed stools w/in 3-4hrs; place an aliquot in preservative&frige remainder |
| Types of Specimens | • Feces- 95% parasite specimens • Sputum- early morning specimen is best (most concentrated) • Urine- early morning or 1st void • Genitalia- saline wet swabs • Tissue and skin- sterile container • Blood |
| Types of Specimens: feces part 1 | • Collect in clean, dry container with secure lid |
| Types of Specimens: feces part 2 | • Do not accept specimens contaminated with urine (may destroy motile organisms), water (may contain free living organisms), or oil or barium enemas (intestinal protozoa may be undetectable 5-10 days after barium is given) |
| Types of Specimens: feces part 3 | • Antibiotics (such as tetracycline) modify intestinal flora and may prevent parasite recovery for 2 weeks after drug cessation |
| Types of Specimens: blood | • Fresh blood from finger stick (best NOT to use EDTA) • Prepare thick smear for concentration and thin smear for identification |
| Ova, Cyst, and parasite examination: macroscopic part 1 | • Consistency: liquid-trophozoites soft-protozoan cysts and trophozoties formed-protozoan cysts (heiminth eggs can be found in any type of stool) |
| Ova, Cyst, and parasite examination: macroscopic part 2 | • Presence of: mucus, blood or macroscopic parasites • Color: black-blood, clay colored-barium or absence of bile, green-veggies |
| Ova, Cyst, and parasite examination: microscopic | • Heavy amounts of yeast (yeast may be the cause of diarrhea) • Increased WBCs (may indicate a bacterial cause of diarrhea) • All Ova, Cysts, and Parasites |
| Ova, Cyst, and parasite examination: permanent smears | • Iron hematoxylin stain- takes skill to perform; organisms stain shades of purple-gray • Trichrome stain- easy to perform; organisms stain great and nuclear details stain red-black • Lawless stain- rapid, 5mins stain; stains various shades of blue |
| Types of Preservation | • Refrigeration • 10% formalin • MIF (Merthiolate-Iodine-Formalin) • PVA (Palyvinyl Alcohol) • SAF (Sodium Acetate-Acetic Acid-Formalin) |
| Types of Preservation : Refrigeration | Good for eggs, larvae, and amoebic cysts; DO NOT refrigerate if you |
| Types of Preservation : 10% formalin | Good for eggs, larvae and amoebic cysts |
| Types of Preservation : MIF (Merthiolate-Iodine-Formalin) | Concentration procedures as well as preservative; good for eggs and amoebic cysts |
| Types of Preservation : PVA (Palyvinyl Alcohol) | Best for amoebic trophozoites; can prepare permanent stain slides from specimens preserved this way |
| Types of Preservation : SAF (Sodium Acetate-Acetic Acid-Formalin) | Good for amoebic trophozoites; environmentally safer than PVA |
| Concentration techniques: (used to detect small number of parasites) | • Formalin-Ether Technique- Modified version replaces ether with ethyl-acetate (less volatile) • Zinc Sulfate Flotation Technique • MIF |
| Concentration techniques: Formalin-Ether Technique part 1 | • Forms 4 layers: Ether (ethyl acetate) Debris Formalin Sediment (parasites); • Ether removes fats and oils and formalin preserves organisms |
| Concentration techniques: Formalin-Ether Technique part 2 | • Advantages: can stay in formalin stage indefinitely; easy to perform • Disadvantages: small ova and cysts such as Giardia end E. nana do not sediment well |
| Concentration techniques: Zinc Sulfate Flotation Technique part 1 | • Specific gravity of zinc sulfate is greater than ova, cysts, and larvae, therefore they float on top of zinc sulfate solution • Specific gravity of zinc sulfate solution; if specimen is in saline =1.18. if specimen is in formalin =1.20 |
| Concentration techniques: Zinc Sulfate Flotation Technique part 2 | • Advantages- easy to perform; does not use flammable chemicals • Disadvantages- distorts some helminth eggs; large eggs (ex. Schistosomes) and operculated eggs (ex. D. latum) may sink quickly |
| Concentration techniques: MIF part 1 | • Concentration and preservative • After adding stool to the vial, break iodine ampule (mix vial well). Allow to sit undisturbed for at least 2hrs • Forms 3 layers: Top (formalin) Interface (parasites) Bottom (fecal debris) |
| Concentration techniques: MIF part 2 | • Advantages- easy to use; can inoculate on nursing floor • Disadvantages- merthiolate distorts some parasites; does NOT preserve trophozoites |
| Helminths :Intermediate host | • Host which contains the larval form of the parasite |
| Helminths: Definitive host | • Host which contains the adult sexual form of the parasite |
| Helminths: Hermaphroditic | • Contain both sexes in one helminth; cestodes and trematodes (except Schistosomes) |
| Helminths: Gravid proglottid | • Segments filled with eggs |
| Intestinal Nematodes (Roundworms): general characteristics part 1 | • Females larger &have straight tail • Males curved tail with a spicule used for copulation • Unsegmented |
| Intestinal Nematodes (Roundworms): general characteristics part 2 | • Round, elongated from a few millimeters-meter in length • Complete digestive tract (mount to anus) • Found in intestine, blood, and tissue • Worldwide distribution |
| Ascaris lumbricoides (Large intestinal Roundworm) part 1 | • Largest nematode- adult males 150-200mm. Adult females 200-300mm • If no male present in small intestine; female will lay bizarre shaped unfertilized eggs • No intermediate host needed |
| Ascaris lumbricoides (Large intestinal Roundworm) part 2 | • Second most common nematode infection in U.S. 5-9 year old group most revalent in U.S. • Visceral Larval Migrans- dog and cat ascarid (Toxocara canis and cati) migration through viscera resulting in eonsinophilia |
| Ascaris lumbricoides (Large intestinal Roundworm) Diagnosis | • Demonstrated characteristic egg in feces • Recovery of worms from anus, nasal passage, or sputum |
| Ascaris lumbricoides (Large intestinal Roundworm) Clinical disease | • “worm ball” –blockage in intestines • “ascaris pneumonitis” –due to larvae migration in lungs |
| Enterobius vermicularis (Pinworm) part1 | • Adults Males 2-5mm Females 8-13mm • Eggs become embryonated within hours resulting in high rate of autoinfection; treat entire family of an infected individual |
| Enterobius vermicularis (Pinworm) part 2 | • Most common helminth parasite of humans; frequently in children due to poor sanitation habits |
| Enterobius vermicularis (Pinworm) Diagnosis part 1 | • Scotch tape (cellulose tape) preparation- egg and larvae stick to tape. Since migration of female occurs at night the prep is performed after patient has been sleeping or early in the morning |
| Enterobius vermicularis (Pinworm) Diagnosis part 2 | • Adults may become “stuck” to the outside of the stool as it passes the perianal folds where the female migrates to lay eggs |
| Trichuris trichiura (Whipworm) | • Adults Males 30-45mm long, long curved tail prominent spicule Females 30-50mm long • Prolapsed rectum- may occur in heavy infections • Diagnosis- demonstrate characteristic egg in feces |
| Strongyloides stercoralis (Threadworm) | • Adults Smallest nematode Possess a long cylindrical esophagus and lack a posterior bulb • Eggs hatch in mucosa of intestine and are rarely seen in feces |
| Strongyloides stercoralis (Threadworm): Rhabditiform larva (noninfective) | • 250um long • Muscular esophagus (club-shaped anterior, a restriction, and a posterior bulb) • Short buccal cavity (approximately 1/3-1/2 width of body) • Prominent primordial genitalia |
| Strongyloides stercoralis (Threadworm): Filariform larva (infective) | • 600um long • Lacks a bulb on the esophagus • Notch at the end of tail |
| Strongyloides stercoralis (Threadworm): free living cycle part 1 | • Male and female adults mate and the female lay embryonated eggs • Eggs hatch in the soil to release the rhabditiform larvae |
| Strongyloides stercoralis (Threadworm): free living cycle part 2 | • If favorable environmental conditions exist the larvae will mature into a free-living adult • If unfavorable environmental conditions exist the larvae moult into the infective filiariform larvae |
| Strongyloides stercoralis (Threadworm): parasitic cycle part 1 | • Filariform larvae penetrate the skin of the host • Larvae enter the circulatory system and migrate to the heart and then to lungs |
| Strongyloides stercoralis (Threadworm): parasitic cycle part 2 | • In the lungs the larvae exit through alveoli, travel up the trachea, are swallowed and mature in the small intestines • The adults mate and the female burrows into the intestinal mucosa where she lays her eggs |
| Strongyloides stercoralis (Threadworm): parasitic cycle part 3 | • Rhabditiform larvae hatch from the egg and then enter the lumen of the small intestines where they are passed out with the feces where they enter the free living cycle |
| Strongyloides stercoralis (Threadworm): autoinfection | Some of the rhabditiform larvae develop into filariform larvae in the bowel and re-infect the host |
| Strongyloides stercoralis (Threadworm): Clinical disease part 1 | • 3 stages Cutaneous- initial skin penetration Pulmonary- larval migration through lungs Intestinal- symptoms depend on worm load. Immunocompromised patients may exhibit leukocytosis and eosinophilia |
| Strongyloides stercoralis (Threadworm): Clinical disease part 2 | • Hyper-infection syndrome- may lead to death from tissue damage Occurs in the immunocompromised (ADIS, drugs) Can be transferred through organ transplantation |
| Necator americanus (New World Hookworm) and Ancylostoma duodenale (Old world Hookworm): Adults | • Male 8-11mm long; possess a bursa which aids in speciation of hookworm • Females 10-13mm long • Adults may live 2-14 years • Rarely seen in stools since firmly attached to mucosa |
| Necator americanus (New World Hookworm) and Ancylostoma duodenale (Old world Hookworm): Rhabditiform larvae | • 250um long • Bulbous esophagus • Long buccal cavity (approximately as long as width of body) |
| Necator americanus (New World Hookworm) and Ancylostoma duodenale (Old world Hookworm): Infective stage- filariform larvae | • 700um long • Straight esophagus (1/4 length body) • Pointed tail • Long buccal cavity |
| Necator americanus (New World Hookworm) and Ancylostoma duodenale (Old world Hookworm): Clinical disease | • Pneumonitis • Allergic reactions- “ground itch” • Anemia- each adult worm consumes 0.2ml of blood/day • Cutaneous larvae migrans- migration of dog hookworms (Ancyclostoma braziliensis and caninum) through subcutaneous tissue causing intense itching |
| Necator americanus (New World Hookworm) and Ancylostoma duodenale (Old world Hookworm): Diagnosis | • Demonstrate characteristic egg in feces • Do not see larvae in feces (unless specimen left at room temp) |
| Remember: differentiating hookworm adults | • NeCator- Cutting plates • AncylosToma- Teeth or DUOdenale:2 pairs |
| Blood and Tissue Nematodes: Trichinella spiralis (Trichina Worm) adults | • Males 1.5mm long, no copulatory spicule • Females 3mm long. Females bear larvae NOT eggs |
| Trichinella spiralis (Trichina Worm): Infective stage | Ingestion of encysted larvae in under cooked pork |
| Trichinella spiralis (Trichina Worm): Diagnostic stage | Muscle biopsy showing encysted larvae in striated muscle (larvae form pork migrate to skeletal muscle and penetrate individual fibers and begin to grow, eventually becoming encysted by infiltrating leukocytes) |
| Trichinella spiralis (Trichina Worm): Clinical disease | • Destruction of muscle cell • High eosinophilia (may reach 90%) • May have myocardial involvement |
| The Microfilariae general characteristics part 1 | • Required an arthropod as an intermediate host. When infected arthropod takes a blood meal, the microfilariae are released into human host |
| The Microfilariae general characteristics part 2 | • Diagnosis made by examining Giemsa stained think and thin smears (except Onchocerca volvulus- skin scraping from modules) |
| Wuchereria bancrofti: Microfilaria | • Sheathed • NO nuclei in tip of tail • Nocturnal periodicity- 9pm-2am greatest concentration in blood |
| Wuchereria bancrofti: Elephantiasis | Permanent blockage of lymphatic system can occur in the upper extremities |
| Wuchereria bancrofti: Diagnosis | Demonstrate in blood smears (thick and thin) sheathed microfilaria with no nuclei in tip of tail |
| Brugia malayi: Microfilaria | • Sheathed • Nuclei stop then there is a clear space with 2 distinct nuclei at tip of tail • Nocturnal periodicity |
| Brugia malayi: Elephantiasis | Restricted to the lower extremities |
| Brugia malayi: Diagnosis | Demonstrate in blood smear (thick and thin) sheathed microfilaria with 2 terminal nuclei in tail |
| Brugia malayi | Found in Far East |
| Loa Loa (eye Worm) | Found in Africa |
| Loa Loa (eye Worm): Microfilaria | • Sheathed • Nuclei to the tip of tail • Diurnal periodicity (microfilaria shed in peripheral blood constantly day or night) |
| Loa Loa (eye Worm): Causes | Causes calabar swellings (allergic reaction to warm migration in tissue and death in capillaries) |
| Loa Loa (eye Worm): Diagnosis | • Demonstrate in blood smear (thick and thin) sheathed microfilaria with continuous nuclei in tail • Worm may migrate across conjunctiva |
| Onchocerca volvulus (Blinding worm): Microfilaria | • Only pathogenic microfilaria which is NOT sheathed • NO nuclei in tip of tail • Found in nodules under skin, NOT in peripheral blood |
| Onchocerca volvulus (Blinding worm): Clinical disease | • Sever dermatitis (50-70% eosinophilia) • Microfilariae in ocular structures may result in blindness. Leading cause of blindness in Africa |
| Onchocerca volvulus (Blinding worm): Diagnosis | • Demonstrate from skin “snips”/tissue scrapings unsheathed microfilaria with NO nuclei in tail |
| Remember: ONchochercus Volvulus | Only pathogenic microfilariae with no sheath, no nuclei in tip of tail (ON is NO backwards) |
| Remember: Wucheriria BaNcrofti | NO nuclei in tip of tail |
| Remember: Brugia Malyi | B is second letter in alphabet (2 nuclei in tip of tail) |
| Remember: Loa Loa | Name repeats and so do nuclei, continuously in tip of tail |
| Cestodes (Tapeworms) general part 1 | • Flat, ribbon-like, segmented worms • Shape of proglottids (segments), presence or absence of armed rostellum (knob-like protrusion at the extreme anterior end of a tapeworm) and size aid in identification of adults |
| Cestodes (Tapeworms) general part 2 | • Hermaphroditic- mature proglottids contain both male and female reproductive organs • 4 cup shaped suckers on scolex (except Diphyllobothrium latum which has 2 suctorial grooves) • Worldwide distribution |
| Taenia saginata (Beef Tapeworm) | Human is definitive host |
| Taenia saginata (Beef Tapeworm): adults | • Scolex has an unarmed rostellum • Consists of as many as 2,000 proglottids (10-15ft long) • Adults may live 25 years |
| Taenia saginata (Beef Tapeworm): Infective stage | Ingestion of under cooked beef containing larval stage |
| Taenia saginata (Beef Tapeworm): Diagnostic stage | • Find characteristic egg in feces • Proglottids can be stained; note number of major uterine branches (15-30 in T. saginata) |
| Taenia solium (Pork Tapeworm) | Human may serve as definitive or intermediate host |
| Taenia solium (Pork Tapeworm): adults | • Scolex has armed rostellum • Consists of any many as 1,00 proglottids; 6-10ft long |
| Taenia solium (Pork Tapeworm): Cysticercosis part 1 | • Infection caused by larvae of parasite- human is intermediate host Man ingest the egg of T. solium Egg passes through the stomach and hatches in the intestine |
| Taenia solium (Pork Tapeworm): Cysticercosis part 2 | • The embryo penetrates the mucosa and becomes a cysticercus. Most commonly found in the subcutaneous connective tissue, eye, brain, muscle, heart, and lungs • Cysticercosis- inflammatory response to tissue invasion and parasite death |
| Taenia solium (Pork Tapeworm): Diagnostic stage | • Find characteristic egg in feces • Proglottids can be stained; note number of major uterine brances (7-13 in T. solium) |
| Remember the hermaphroditic tapeworm | T: taenia species A: adult- small intestine P: proglottids contains male & female parts E: eggs-6 hooked embryos (hexacanth) W: worldwide nO: respiratory, vascular, digestive system R: ribbon like body. flat M: middle (intermediate) host require |
| Hymenolepis nana (Dwarf Tapeworm) | • Does not require an intermediate host; may have intermediate host such as flea or beetle • Most common human tapeworm in the U.S • Heavy infections can occur through autoinfection |
| Hymenolepis nana (Dwarf Tapeworm): adults | • Small tapeworm; 40mm long • Contains 200 segments • Armed rostellum (short with hooks) |
| Hymenolepis nana (Dwarf Tapeworm): stages | • Infective stage- ingestion of eggs • Diagnostic stage- demonstrate characteristic egg in feces |
| Hymenolepis diminuta (Rat Tapeworm) | • Adult- unarmed rostellum • Man is accidental host via ingestion of infected intermediate arthropod host (ex. Grain beetles in pre-cooked cereals) • Rat is definitive host |
| Hymenolepis diminuta (Rat Tapeworm): stages | • Infective stage- ingestion of flea • Diagnostic stage- demonstrate characteristic egg in feces |
| Diphyllobothrium latum (Broad Fish Tapeworm) | • Only cestodes to produce operculated eggs • High incidence in Finland, Alaska, and Canada |
| Diphyllobothrium latum (Broad Fish Tapeworm) : adults | • Scolex consists of 2 longitudinal sectorial grooves known as bothria, giving it a spoon shape • Uterus in gravid proglottids appears as a rosette • May have an many as 3,000 proglottids |
| Diphyllobothrium latum (Broad Fish Tapeworm) : stages | • Infective - ingestion of larvae in infected undercooked freshwater fish • Diagnostic- demonstrate characteristic egg or proglottids (often in chains of a few inches- feet) in feces (may NOT be seen in flotation techniques; operculated ova may sink) |
| Diphyllobothrium latum (Broad Fish Tapeworm) : clinical disease | • Can cause megaloblastic anemia, since vitamin B12 is absorbed by worm • Sparganosis- disease caused by drinking H2O containing infected copepod. Larva develops in human who is the intermediate host instead of the fish |
| Echinococcus granulosus (Hydatid Tapeworm): adult | • Very small; 3-6cm long • Consists of only 3 proglottids- immature, mature, and gravid • Scolex has an armed rostellum |
| Echinococcus granulosus (Hydatid Tapeworm): normal life sycle | • Normal life cycle • Sheep (intermediate host) ingest eggs • Dog (definitive host) infected from eating infected viscera of butchered animals |
| Echinococcus granulosus (Hydatid Tapeworm): infective stage | • Infective stage- man (intermediate host) ingests egg |
| Echinococcus granulosus (Hydatid Tapeworm): diagnostic stage part 1 | • Hydatid cysts seen in routine x-rays or exploratory surgery (form in various parts of the body- most commonly the liver, lungs, brain, heart). Hydatid cysts contains hydatid sand |
| Echinococcus granulosus (Hydatid Tapeworm): diagnostic stage part 2 | •• Serological test (ELISA, IHA) • Casoni’s skin test- intradermal test using hydatid cyst fluid as antigen |
| Dipylidium caninum (Dog Tapeworm) | • Found worldwide in children |
| Dipylidium caninum (Dog Tapeworm): adult | • Scolex has an armed rostellum with many rows of thorn-shaped hooks • Proglottids resemble pumpkin/cucumber seeds when moist and rice grain when dry |
| Dipylidium caninum (Dog Tapeworm): normal life cycle | • Dog and cat ingest infected fleas containing larvae |
| Dipylidium caninum (Dog Tapeworm): stages | • Infected stage- human (accidental intermediate host) ingests infected flea • Diagnostic stage- demonstrate characteristic egg packet (5-10 eggs are in a hylaline non-cellular egg sac) in feces |
| Trematodes (Flukes): general info | • Flat leaf-shaped organisms • Hermaphroditic- contain both male and female reproductive parts (except Schistosomes) • Required an intermediate host • Snail is always 1st intermediate host • Eggs are operculated (except Schistosomes) |
| Fasciolopsis buski (Giant Intestinal Fluke) | • Found in Asia |
| Fasciolopsis buski (Giant Intestinal Fluke): adults | • Large fluke, 75mm long by 20mm wide • Poorly developed suckers • Live in intestines of pigs and humans |
| Fasciolopsis buski (Giant Intestinal Fluke): stages | • Infective stage- ingestion of raw aquatic vegetation (Ex. Water chestnuts) with encysted metacercariae • Diagnostic stage- demonstration of characteristic eggs in feces (eggs resemble F. hepatica) |
| Fasciolopsis buski (Giant Intestinal Fluke): clinical disease | • Diarrhea, epigastric pain • Symptoms relate to number of worms present |
| Fasciola hepatica (Liver Fluke) | • Sheep and cattle are reservoir host; therefore, high incidence in sheep raising countries |
| Fasciola hepatica (Liver Fluke): adults | • Large fleshy fluke 30mm long 13mm wide • Live in bile ducts of liver |
| Fasciola hepatica (Liver Fluke): stages | • Infective stage- ingestion of raw aquatic vegetation (Ex. Water chestnuts) with encysted metacercariae • Diagnostic stage- detect characteristic eggs in feces (eggs resemble F. buski) |
| Fasciola hepatica (Liver Fluke): clinical disease | • Larvae elicit inflammatory response in liver • Stone formation may occur • Eosinophilia may occur during larvae migration |
| Clonorchis sinensis (Chinese Liver Fluke) | • Found in Japan, Korea, China, Taiwan, and Vietnam (cats and dogs serve as reservoir hosts) |
| Clonorchis sinensis (Chinese Liver Fluke): adults | • Long and narrow, 20mm long and 3-5mm wide • Live in bile ducts of liver |
| Clonorchis sinensis (Chinese Liver Fluke): stages | • Infective stage- ingestion of raw fish infected with metacercariae • Diagnostic stage- demonstration of characteristic eggs in feces (operculated with shoulders and small knobs at abopercular end) |
| Paragonimus westermani (Oriental Lung Fluke) |
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