MTAP 1: WEEK 5 - NEMATODES AND PROTOZOANS

Endoparasite

parasite living inside the body of the host

Ectoparasite

parasite living outside the body of the host

Obligated parasite

requires host to complete its developmental cycle

Facultative parasite

can be free-living or become parasitic

Accidental/incidental parasite

establishes itself in a host where it does not ordinarily live

Permanent parasite

remains in or on the host for the entire life

Temporary parasite

lives in the host only for a short period of time

Spurious parasite

free-living organism that passes through the digestive tract without infecting the host

Definitive/Final host

the parasite attains sexual maturity

Intermediate host

harbors the larval stages of the parasite

Paratenic host

parasite remains alive and is able to infect other susceptible host

Biologic vector

transmits the parasite after the completion of its development in the host; necessary for the completion of its life cycle

Mechanical/Phoretic vector

no development of the parasitic life cycle; only transports the parasite

Specific parasite

found only in one specie and cannot survive in other species

Nonspecific parasite

can reside to other host

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Adult nematode

elongated, cylindrical worm, primarily bilaterally symmetrical

Anterior end

equipped with hooks, teeth, plates and papillae for abrasion, attachment and sensory response

Supporting body wall

Outer hyaline noncellular cuticle, subcuticular epithelium, layer of muscle cells

Alimentary tract

simple tube extending from mouth to anus

Amphid

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Phasmid

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Class Enoplea (Adenophorea; Aphasmidea)

without caudal chemoreceptor organ (phasmids); examples: Trichuris trichiura, Trichinella spiralis, Capillaria philippinensis

Class Rhabditea (Secernentia; Phasmidea)

with caudal chemoreceptor organ (phasmids); examples: Ascaris lumbricoides, Strongyloides stercoralis, Enterobius vermicularis, Angiostrongylus cantonensis, Filarial worms, Hookworms, Dracunculus medinensis

Intestinal nematodes

Enterobius vermicularis, Trichuris trichiura, Ascaris lumbricoides, Necator americanus, Ancylostoma duodenale, Strongyloides stercoralis, Capillaria philippinensis

Extraintestinal nematodes

Trichinella spiralis, Dracunculus medinensis, Angiostrongylus, Filarial worms

Life Cycle

> > __

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Ascaris lumbricoides common name

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Mode of transmission of Ascaris lumbricoides

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Infective stage of Ascaris lumbricoides

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Diagnostic stage of Ascaris lumbricoides

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Pathology of Ascaris lumbricoides (larval migration)

pneumonia, cough, fever, eosinophilia

Pathology of Ascaris lumbricoides (adult worms)

vomiting, abdominal pain, intestinal perforation, malnutrition, worm bolus, asymptomatic if few eggs

Laboratory diagnosis of Ascaris lumbricoides

Stool exam, ELISA, adult worms in small intestine, gall bladder, liver, appendix

Treatment of Ascaris lumbricoides

Albendazole, Mebendazole

Epidemiology of Ascaris lumbricoides

most common helminth worldwide, transmits Dientamoeba fragilis

Prevention of Ascaris lumbricoides

avoid using feces as fertilizer, proper sanitation, personal hygiene

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Enterobius vermicularis common name

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Mode of transmission of Enterobius vermicularis

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Infective stage of Enterobius vermicularis

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Diagnostic stage of Enterobius vermicularis

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Pathology of Enterobius vermicularis

pruritus ani, lack of sleep

Autoinfection

Infected individuals reinfect themselves by ingesting infective pinworm eggs via hand-to-mouth contamination

Retroinfection

Infective pinworm eggs migrate back into host body, develop and reproduce rather than being dislodged

Treatment of Enterobius vermicularis

Albendazole, Mebendazole, Pyrantel pamoate

Epidemiology of Enterobius vermicularis

worldwide, most common helminth in US, transmits Dientamoeba fragilis

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Trichuris trichiura common name

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Mode of transmission of Trichuris trichiura

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Infective stage of Trichuris trichiura

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Diagnostic stage of Trichuris trichiura

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Pathology of Trichuris trichiura

bloody/mucoid diarrhea, abdominal pain, rectal prolapse, weight loss

Morphology of Trichuris trichiura eggs

barrel-shaped/football-shaped/lemon-shaped, prominent hyaline polar plugs, yellowish brown, 50–55μm by 25μm

Morphology of Trichuris trichiura adults

anterior end slender and colorless, posterior end pinkish-gray whip handle

Laboratory diagnosis of Trichuris trichiura

stool exam, macroscopic adult worms

Treatment of Trichuris trichiura

Albendazole, Mebendazole

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Capillaria philippinensis common name

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Mode of transmission

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Infective stage

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Diagnostic stage

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Pathology

abdominal pain, diarrhea, borborygmi, malabsorption

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Hookworms (Necator americanus)

New world hookworm; buccal capsule with semilunar cutting plates; copulatory bursa + spicule

Hookworms (Ancylostoma duodenale)

Old world hookworm; adult has 2 pairs of ventral teeth, C-shape

Ancylostoma braziliense

Cat hookworm; cutaneous larva migrans; copulatory bursa broad & long

Ancylostoma caninum

Dog hookworm; cutaneous larva migrans + eosinophilic enteritis; adult has 3 ventral teeth

Pathology of hookworms (larva)

dermatitis “ground itch”, Wakana disease

Pathology of hookworms (adult)

malnutrition, hookworm anemia, IDA

Diagnosis of hookworms

DFS, Harada-Mori technique

Treatment of hookworms

Mebendazole, Pyrantel pamoate

L1 Rhabditiform larva

1st stage, short & stout, open mouth, feeding

L3 Filariform larva

3rd stage, long & slender, closed mouth, non-feeding

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Strongyloides stercoralis common name

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Mode of transmission

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Infective stage

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Diagnostic stage

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Pathology

Skin: allergic reaction at penetration; Migration: pneumonia; Intestines: abdominal pain, diarrhea, vomiting, eosinophilia

Diagnosis

Zinc sulfate concentration, duodenal aspirates, Harada-Mori culture

Treatment

Ivermectin, Albendazole

Hookworm vs Threadworm (larva morphology)

Hookworm: long buccal cavity, small primordium, sheathed pointed tail; Strongyloides: short buccal cavity, prominent primordium, unsheathed notched tail

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Trichinella spiralis common name

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Mode of transmission

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Infective stage

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Diagnostic stage

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Pathology

Intestine: edema, nausea, diarrhea; Larvae: fever, eosinophilia, facial edema; Muscle: pain, edema, encystation

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Filarial worm Wuchereria bancrofti

Habitat: lymphatics; Vector: Aedes, Anopheles; Specimen: blood; Microfilaria: sheathed, no nuclei in tail; Periodicity: nocturnal

Filarial worm Brugia malayi

Habitat: lymphatics; Vector: Mansonia; Specimen: blood; Microfilaria: sheathed, 2 terminal nuclei; Periodicity: subperiodic, nocturnal

Filarial worm Loa loa

Habitat: subcutaneous tissue; Vector: Chrysops (mango fly); Specimen: blood; Microfilaria: sheathed, nuclei continuous to tail tip; Periodicity: diurnal

Filarial worm Onchocerca volvulus

Habitat: subcutaneous tissue; Vector: Simulium (black fly); Specimen: skin snips; Microfilaria: unsheathed, no nuclei in tail; Periodicity: nonperiodic

Filarial worm Mansonella ozzardi

Habitat: body cavities; Vector: Culicoides; Specimen: blood; Microfilaria: unsheathed, no nuclei in tail; Periodicity: nonperiodic

Filarial worm Dipetalonema perstans

Habitat: body cavities; Vector: Culicoides; Specimen: blood; Microfilaria: unsheathed, nuclei up to tail tip; Periodicity: nonperiodic

Dirofilaria immitis

common filarial parasite of dogs; human infection: coin lesions in lungs or subcutaneous nodules

Dracunculus medinensis common name

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Intermediate host

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Angiostrongylus cantonensis common name

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Disease

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Anisakis

common name: ; 1st IH: ; 2nd IH: ; 3rd IH: ; FH/DH:

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Protozoans general characteristics

unicellular, animal-like protists, no cell wall, endoplasm + ectoplasm, nuclei, locomotor organelles, vacuoles

Sarcodina

locomotion by pseudopodia

Mastigophora

locomotion by flagella

Ciliophora

locomotion by cilia

Sporozoa

no locomotion, obligate intracellular

Trophozoite

motile, feeding, vegetative stage, found in diarrheal/liquid stools