MLS Review - Parasitology - Nematodes

MEDICAL LABORATORY SCIENCE REVIEW CLINICAL PARASITOLOGY: NEMATODES SPECIES OF NEMATODES • OUTLINE • Nematodes o General Characteristics o Species of Nematodes o Modes of Infection and Infective Stages o Ascaris lumbricoides o Trichuris trichuria o o o o o o o Enterobius vermicularis Hookworms Strongyloides stercoralis Trichinella spiralis Dracunculus medinensis Capillaria philippinensis Filarial Worms NEMATODES GENERAL CHARACTERISTICS • • • • • • • • • • • Basically named as roundworms Elongated, cylindrical unsegmented worms with tapering ends Cuticula - thick hyaline protective coating Male is generally smaller than female with posterior end which is either curved or coiled. Dioecious - having male & female reproductive systems in separate sex Complete with mouth, nervous system, & digestive system o Digestive system - allow them to absorb nutrients Homoxenous - requiring only one host in life cycle Heteroxenous - requires two kinds of host to complete its life cycle; 1st host - larval stage; 2nd host - maturation All are equipped with amphid o Amphid - cephalic chemoreceptors (paired sensitive sensory organs located anteriorly at level of cephalic papillae) Some are equipped with phasmid o Phasmid - caudal chemoreceptors (paired structures found posteriorly/tail) o TTC - Trichuris, Trichinella, Capillaria ▪ Group of Aphasmidea or Adenophorea roundworms without caudal chemoreceptors o SAHE - Strongyloides, Ascaris, Hookworm, Enterobis ▪ Phasmidea or Sercenentea - roundworms with caudal chemoreceptors Life cycle: o Ova/egg → rhabditiform larva → filariform larva → adult o Nematodes have the simplest life cycle • • Intestinal Nematodes o Capillaria phillipinensis - Pudoc worm ▪ Discovered in Barrio Pudoc, Ilocos Norte o Ascaris lumbricoides - Giant intestinal rounworm/ Eel worm/ Largest Roundworm of man o Strongyloides stercoralis - Threadworm o Necator americanus - New world hookworm o Ancylostoma duodenale - Old world hookworm o Trichuris trichiura - whipworm o Enterobius vermicularis - Pinworm/ Seatworm ▪ Seatworm - can pass through linen Intestinal – Extra Intestinal Nematodes o Trichinella spiralis - Trichina worm or muscle Roundworm o Dracunculus medinensis - Guinea worm, Dragon worm, Serpent worm Blood and Tissue Nematodes o Lymphatic System ▪ Wuchereria bancrofti - Bancroft filarial ▪ Brugia malayi - Malayan filarial o Subcutaneous Tissue ▪ Loa loa - eye worm ▪ Onchocerca volvulus - Convoluted filarial ▪ Mansonella streptocerca - formerly known as Dipetalonema streptocerca • Parasite of chimpanzee o Serous Cavities ▪ Mansonella ozzardi - Ozzard filarial/New world filaria ▪ Mansonella perstans - Persistent filarial PRIMARILY ZOONOTIC NEMATODES • • • • • • Toxocara canis - Ascaris of dogs Toxocara cati - Ascaris of cats Ancylostoma caninum - Hookworm of dogs Ancyclostoma braziliensi - Hookworm of cats Dirofilaria immitis - Dog Heart Worm Angiostrongylus cantonensis - Rat lung worm o Can be very fatal to man TYPES OF FEMALE NEMATODES • • • • Oviparous o Eggs without fully-developed larva o Ascaris lumbricoides, Trichuris trichiura, Hookworms Viviparous/larviparous o Females deliver fully-developed larva o Trichinella spiralis, Dracunculus medinensis, Filarial Worms Ovoviparous o Eggs with fully-developed larva o Enterobius vermicularis, Strongyloides stercoralis NOTE: Capillaria philippinesis: o Typical: with flattened bipolar plugs o Atypical: without flattened bipolar pliugs MODES OF INFECTION AND INFECTIVE STAGE • Ingestion of Embryonated Egg o Ascaris lumbricoides, Trichuris trichiura, Enterobius vermicularis 7 • • • • • • Ingestion of Larvae within Intermediate Host o Dracunculus medinensis, Capillaria philippinesis Ingestion of Encysted Larvae in Muscle of Definitive Host o Trichinella spiralis Skin Penetration of Filariform Larva o Hookworms, Strongyloides stercoralis Skin Inoculation of Third Stage Larva o Filarial Worms Inhalation of Dust containing embryonated ova (rare) o Ascaris lumbricoides, Enterobius vermicularis Undergo Heart to Lung Migration – HAS - Hookworm, Ascaris, Strongyloides (LARVA) o Parasite can migrate to heart lungs, liver, & brain o • Ectopic Ascariasis (Wanderlust) ▪ Ascaris migrates to fallopian tube, o Some cases observed ascaris in umbilicus, empyema, inguinal hernia Laboratory Diagnosis o Stool (Qualitative or Quantitative) / Fecalysis o Sputum (For pneumonic/pulmonary ascariasis) o ELISA (Serologic) • Life Cycle: o Infection begins following the ingestion of embryonated ova o → In the small intestine, larvae will emerge from the egg o → The larva will undergo hepatic/lung/intestinal migration for further development then return to the small intestine where it will become adult ▪ Intestine - most common maturation site o → The female adult will lay egg which will be passed on the stool where it needs soil to be embryonated and taken up by man to repeat the cycle ▪ Man is required form maturation ▪ Soil must be moist for optimal maturation • Ascaris lumbricoides adult o Superficially resemble earthworm/spaghetti strands o With trilobate inconspicuous lips o Male - have curved posterior end and attenuated pencil-lid appearance of posterior end o Female - ventrolateral, having rounded posterior end ▪ Significantly larger than male • Ascaris lumbricoides ova o Unfertilized ▪ Without embryo ▪ Having disorganized germ cell ▪ Coarsely granular ▪ Amorphous mass of cytoplasm ▪ Have no further development LARVA MIGRANS • Larva Migrans – do not develop into adult worms but only elicit swelling, creeping eruption and/or inflammation o Migration of immature larva to various parts of body Visceral Larva Cutaneous Larva Migrans Migrans (within (Creeping Eruption) (skin) internal organs) “Sandworm disease” Eosinophilia Usually seen Rarely seen (can be normal) Transmission Larva migrates Larva migrates through the through various skin surfaceof the host internal organs Serological Well developed Not well developed Test Zoonotic Toxocara canis Ancylostoma caninum Nematodes Ascaris suum Ancyclostoma braziliense (pig ascaris) Toxocara cati Baylisascaris procyonis (Raccoon roundworm) • B. procyonis - very rare but having serious cause of neurological and ocular disease Ascaris lumbricoides • • • • Giant intestinal roundworm o Can grow into spaghetti-like adults Most common parasite among Filipino children (soiltransmitted) Oviparous/ Embryonated egg on soil / Heart and Lung Migration (even liver and brain larval invasion) Pathogenicity o Intestinal Ascariasis - found in intestine o o Pulmonary Ascariasis or Ascaris Pneumonia or Loeffler Syndrome - lung migration Spoliative or Nutrition Deficiency 8 o o Corticated (Fertilized) ▪ With embryo ▪ Has mammillation/cortication with organized germ cell and finely granular ▪ Subspherical in shape ▪ 3 layers: • Coarse outer albuminous (albumin) • Middle transparent (glycogen part), • Inner lipoidal (lipid) ▪ Can develop into larva & adult • T. trichiura Ova o Barrel or Football shape o w/ Embryo o w/ prominent/protruding bipolar plugs o “ Japanese Lantern Ova” Decorticated (Fertilized) ▪ Round; w/ embryo ▪ 2 layers: w/o outer albumino1us coat ▪ Can develop into larva & adult Enterobius vermicularis • Trichuris trichiura • • • • Oviparous/ Embryonated egg on soil Has no hepatic/pulmonary migration Life Cycle of Trichuris trichiura o Ingestion of embryonated ova initiates the infection. o The larvae emerge from the eggs in small intestine. o The larvae proceed to cecum, where they become adult. o Eggs are passed in the stool by the adult worm. Soil molting happens where it become embryonated ova. Pathogenecity o Trichuriasis/ Whipworm infection/Trichocephaliasis o Rectal Prolapse - Heavy Trichuriasis • • • • • • • Laboratory Diagnosis o Stool (Qualitative or Quantitative) (DFS) o Sigmoidoscopy – checks sigmoid colon (lower part of colon where female T. trichuria mature & release egg) T. trichiura Adult o Whiplike structure o Prominent/Thickened Posterior o Male prominent coiled tail Most common parasite in the world; most common helminth infection o Ascaris, Trichuris, Enterobius - common in Filipino children Ovoviparous/ Embryonated egg Life Cycle of Enterobius vermicularis o It is initiated by in the ingestion of embryonated ova. o Eggs hatch in the small intestine to become larvae. o It matures into an adult worm in the large intestine. o After copulation, the nocturnal gravid female worm migrates to the perianal region o Has no hepatic/pulmonary migration Pathogenecity o Enterobiasis/ Oxyuriasis / Pinworm Infection o Pruritis ani - intense itchiness of the sigmoid muscle of anus o Retroinfection- pinworm migrate back to the host body to develop and reproduce o Autoinfection - if infective pinworm eggs are ingested via hand-to-mouth contamination Laboratory Diagnosis o Perianal swab or Scotch Tape Swab o Fingernail Scrapings E. vermicularis Adult o Cervical alae/papillae o Prominent double esophageal bulb 9 • E. vermicularis ova o Lopsided or D-shaped with larva inside the ova (embryonated) o Outer thick-walled colorless shell • • HOOKWORMS • • • • • Two Species significant to man: Necator americanus and Ancylostoma duodenale Oviparous/ Skin penetration of filariform larva (infective stage), soil-transmitted Pathogenicity o Ancyclostomiasis/ Uncinariasis – allergic reaction in skin ground itch or coolie itch or dew itch. o Microcytic Hypochromic Anemia - due to ingestion of blood in the small intestine o Pneumositis or Eosinophilia during larval migration in the lungs Laboratory Diagnosis o Ova – Direct fecal smear and concentration technique o Species identification – culture method is preferred (Harada-Mori method - allows maturation of parasite germ cell into larva) o Reverse Enzyme Immunoassay for specific IgE – alternative method (serological test) ▪ IgE - ab for allergic reaction o Complete Blood Count - RBC, MCV and MCHC with eosinophilia Life Cycle o The third stage filariform larva will penetrate the skin. It will migrate to the lympathics and blood system. It will undergo lung migration and it will mature as adult in the small intestine o Eggs will be passed on the stool and upon contact to the soil will become first stage rhabditiform larvae afterwards and eventually becoming filariform larva repeating the life cycle. o Hookworm ova o Clear thin shell o With blastomeres that resemble morula balls (4-8) o Hookworm Larva o Rhabditiform Larva ▪ Feeding stage ▪ Non-pathogenic/non-infective o o Filariform Larva ▪ Infective stage o Comparison of Species A. duodenale Size Large and thicker Shape “C” Teeth 4 ventral teeth (2 pairs) Copulatory Two separate bursa spicules with dorsal (Umbrella like ray single; Tridigitate Structure) Rate of Faster Development Pathogenicity More • N. americanus Small and slender “S” Semilunar cutting plate Two spicules fused at the tip, dorsal ray split; Bidigitate Slower Less 10 ▪ • • • • • • A - 0 - (N. americanus) - 0/no pair of teeth B - 1 - (A. braziliense) - 1 pair of teeth C - 3 - (A. canicum) - 3 pairs of teeth D - 2 - (A. duodenale) - 2 pairs of teeth OTHERS: o Ancyclostoma braziliense - 1 pair of buccal teeth o Ancyclostoma caninum - 3 pairs of buccal teeth • • Strongyloides stercoralis • • • • • • • Smallest nematode to infect human Also known as threadworm Female is classified as parthenogenic o Parthenogenic - natural form of asexual reproduction o Embryos can develop in the absence of fertilization o Male in not required for fertilization Ovoviparous, Skin penetration of filariform larva Pathogenicity o Strongyloidosis or Vietnam Diarrhea or Cochin China Diarrhea o Racing larva or Larva currens – after skin penetration of filariform larva o Autoinfection o Bronchopneumonia - pulmonary migration of S. stercoralis larva may be seen Laboratory Diagnosis o Qualitative and Quantitative Stool or Duodenal Aspirates o Concentration Method – Zinc Sulfate Flotation Method o Stool Culture – Harada Mori; Baermann Technique ▪ Harada Mori - for hookworm ▪ Baermann - specific for Strongyloides o ELISA o CBC o Beale String Test Life Cycles o Direct ▪ Occurs within the host and soil ▪ Same with hookworm ▪ Filariform larva will survive in soil for weeks ▪ But ova may hatch in the stool because it is only occasionally found in stool sample o Indirect/ Free Living ▪ Filariform larva in the soil can become free and proceed to hatching o Autoinfection Rhabditiform larva may transform to filariform larva and penetrate the perianal region or undergoes heart to lung migration ▪ Cycle occurs exclusively in the host S. stercoralis ova o Smaller than hookworms o Well-developed larva o Rarely seen in stool o “Chinese Lantern Ova” S. stercoralis larva o Comparison with hookworm Filariform larva Hookworm S. stercoralis Esophagus Shorter Longer Tail Pointed tail-end Notched tail-end Sheath With extra lining Without lining • • Trichinella spiralis • • • • • • Also known as pork muscle roundworm o Found in hogs or pigs Adult: small intestine Encysted Larva: encysted or striated muscles Human becomes the terminal host Viviparous, Ingestion of inadequately cooked pork within a definitive host Pathogenicity o Trichinosis ▪ Stage 1: Intestinal Invasion: presence of diarrhea and GIT disturbances ▪ Stage 2: Muscle Invasion: larval migration in mast cells for 4-5 weeks (highest eosinophilia seen) 11 ▪ • • Stage 3: Encystment (encysted larva remains viable for several years), Symptoms subside Laboratory Diagnosis o Muscle biopsy o Bachman Intradermal Test o X-ray – presence of calcified cyst o Serological Test – Bentonite flocculation test and ELISA o Elevation of muscular enzymes T. spiralis encysted larva o Coiled larva encysted in the nurse cell of striated muscle • C. philippinensis Ova (Embryonated in Water) Typical Ova Atypical Ova Peanut shaped Not peanut shape Flattened bipolar plugs No flattened polar plug Striated shell Angiostrongylus cantonensis • • • Dracunculus medinensis • • • • • • • Guinea worm/ Medina worm/ Serpent worm / Dragon worm Viviparous, Ingestion of larvae within intermediate host Definitive Host: Man Intermediate Host: Copepods Secretes a toxin that causes blister formation discharging a milky fluid with numerous larva Released worm after bathing the ulcer with water/NSS (Detection) – winding of larva Life cycle o Infected copepods → ingested by man → larva digested out into the stomach penetrates into intestinal wall → develops into adult in body cavities → adult worm goes to skin and produce blister o Adults search for subcutaneous areas o In water, from open blisters, adults will discharge larva ▪ Larva can be ingested by copepods again • • • • Aka rat lung worm Definitive Host: Rat Intermediate hosts: mollusks, slugs and snails (Human as terminal host) Man acquired it through ingestion of third larval stage (L3) o L3 enters circulation and can migrate to the brain and spinal cord o L3 can migrate to lungs causing pneumonitis o After 2 weeks, adult female start to lay eggs Can cause Eosinophilic Meningoencephalitis Diagnosed through CSF test, CT scan, serological tests Possess “barbed wire” appearance • FILARIAL WORMS • • • • Capillaria philippinensis • • • • • Aka Mystery disease/ Pudoc worm Oviparous and Ovoviparous / Ingestion of larvae within intermediate host Definitive Host: Man o (Piscivorous birds – reservoir for pudoc worm)herons, egrets and bitterns Intermediate Host: fishes from lagoons in northern Luzon (Hypselotris bipartita) / Brackish Water Fishes Causative agent of Mystery disease or Borborygmus (Gurgling stomach) – Chronic diarrhea; Autoinfection may occur in man Viviparous/ Skin inoculation of vector with L3 larva Definitive Host: man/vertebrates Intermediate Host: arthropods/invertebrates Life Cyle Of Microfilaria o L3 Larva will be introduced by the vector through skin inoculation. o Inside the body, larva migrates to o the tissue and becomes adult. o The adult worms may reside in the lymphatic, subcutaneous tissue or internal body cavities. o Adult female worms lay alive microfilariae in which it may be released in the body via blood meal by the arthropod vector. o L1 transforms until L3 in body of the blood sucking insects and repeat life cycle 12 • • • • Specimen requirements: o Microfilaria as adult female ▪ Adult female give birth to larval embryo → microfilaria (infective stage) → L3 → appear in blood for one year ▪ Nocturnal Periodic (9PM – 4AM) - largest number of microfilaria at night ▪ Diurnal Periodic (10:15AM-2:15PM) - largest number of microfilariae at day ▪ Non-periodic - constant levels day and night ▪ Sub-periodic or nocturnal sub-periodic - Can be detected at day but high numbers in late afternoon or night Laboratory Diagnosis o Blood – Giemsa Stained or filtering of heparinized blood using nucleopore filter (Stage: chronic infection) o Scraping from infected nodule and skin snip o Concentration technique – Knott (for small amount of microfilaria) or 1mL blood immersed in 10mL 2% formalin solution to lyse red cells. o Serological Test o Opthalmologic examination using slit lamp – filarial worms residing in eyes o Ultrasonography – presence of filarial dance sign Pathogenicity o Wuchereria bancrofti ▪ Elephantiasis - tissue swelling due to obstruction of lymph glands • Occur in the lower extremetiies • “Malabar Leg” ▪ Hydrocoele - collection of fluid in the membrane surrounding of testes causing swelling of scrotum o Loa loa ▪ Fugitive swelling or Calabar swelling or transcient subcutaneous swellings ▪ Occur in retina of the eyes ▪ Stays in the soft tissues of the eyes o Onchocerva volvulus ▪ River blindess - second causing preventable blindness in the world ▪ Onchocercomata - painless nodules ▪ Sowdah / onchodermatitis ▪ Nodding syndrome - believed to be associated with this parasite Structure o W. bancrofti - nuclei not extend to the tip of the tail o B. malayi - two distinct terminal nuclei o L. loa - nuclei extends to the tip of the tail • Filarial Species Periodicity Wuchereria Nocturnal bancrofti Brugia malayi Nocturnal Subperiodic Loa loa Diurnal Onchocerca volvulus Mansonella streptocerca Mansonella ozzardi (New world Filaria) Mansonella perstans Vector Culex, Aedes, Anopheles Aedes, Anopheles, Mansonia Chrysops, Deer fly, Mango fly Non periodic Simulium, Black fly Non periodic Culicoides Location Lower lymphatics, lower extremities Upper lymphatics Subcutaneous tissue, Conjunctiva Subcutaneous nodule, Conjunctiva Subcutaneous Non periodic Culicoides, Simulium Serous cavity Non periodic Culicoides Serous cavity Dirofilaria immitis • • • • • Definitive Host: Dog Intermediate Host: Aedes, Culex, Anopheles and Mansonia (arthropod-transmitted) Partial nocturnal, Unsheathed and Arthropod borne infection In human heart, dead worm becomes embolus producing pulmonary infarct Dead worm in hearts – coin lesion on x-ray • • Specimens required for each species o Blood - W. bancrofti, B. malayi, L. loa, M. perstans, M. ozzardi o Aspiration of serous fluid - M. pertans, M. ozzardi o Skin snips - O. volvulus 13