Parasitology MTAP421 & SEMR421

• Specimen Collection and Processing

  Routine Collection

  Stool: three specimens, every other day within 10 days

  • Clean, water-tight container with tight lid

  • 5 g, not contaminated with water, urine, barium, or other substances

  • Liquid or near-liquid specimens examined within 30 minutes of collection to preserve motile trophozoites

  • Soft specimens examined within 60 minutes of collection

  • Formed specimens processed within 24 hours, may be

  refrigerated
• • Fixatives: Two-vial system, usually formalin and polyvinyl

  alcohol or one-vial system of sodium acetate formalin

  • 3 parts fixative to 1 part stool

  • 5% to 10% formalin, concentration methods, and iodine-stained mounts

  • PVA, concentration methods, trichrome, and other permanent stains

  • SAF: Concentration methods and permanent stains

  • PVA contains mercury, SAF is a mercury-free alternative
• Concentration methods

  • Fresh or preserved stools

  • Sedimentation: Formalin-ethyl acetate

  • Floatation, zinc sulfate with a specific gravity of 1.18 to 1.20

  Macroscopic

  • Consistency

  • Appearance, color

  • Contaminants

  • Larva, proglottids

  Microscopic

  • Calibrated ocular micrometer

  • Direct saline wet mount for motile trophozoites

  • Iodine-stained wet mount from processed specimen

  • Permanent stains from processed specimen
• • Trichrome stain: Cytoplasm is blue-green, purple; nuclear structures, red to pink

  • Iron hematoxylin: Primarily for intestinal protozoa, the cytoplasm is blue to purple, nuclear structures are blue to black

  • Modified acid-fast: For coccidian protozoa, oocysts are red
• Other specimen types

  • Specimen of choice depending on the organism in question and clinical situation

  • Duodenal contents

  • Sigmoidoscopy specimens

  • Enterotest

  • Blood

  • Urine

  • CSF and other fluids

  • Sputum

  • Tissue specimens
• Ectoparasites and Vectors of Disease

  •Lice, ticks, fleas, mites, bedbugs, mosquitos

  •Structures used in arthropod identification

  •Body parts, legs, wings, antenna, mouth parts
• Ectoparasites and Vectors of Disease

  Lice

  • Lice occur worldwide and in all socioeconomic classes

  •Vector for typhus (Rickettsia prowazekii), trench fever (Bartonella quintana), and relapsing fever (Borrelia recurrentis)

  • Spread from human to human

  • Body lice usually on the body and head

  • Crab lice usually in pubic region, spread to the armpits, facial hair, eyebrows, and eyelashes
• Ectoparasites and Vectors of Disease

  Pediculus humanus humanus - Body louse

  Pediculus humanus capitis - Head louse

  Phthirus pubis

  • Crab lice usually in pubic region, spread to the armpits, facial hair, eyebrows, and eyelashes
• HARD TICKS

  Ixodes scapularis

  • Deer tick

  • Main vector of Lyme disease

  • Ixodes pacificus in the U.S. West Coast states also able to transmit Lyme disease

  
  

  Dermacentor andersoni

  • Rocky Mountain wood tick, western United States

  • Vector of many diseases, including Rocky Mountain spotted fever, tularemia, Colorado tick fever, and Q fever

  
  

  Dermacentor variabilis

  • American dog tick, eastern United States
• SOFT TICKS

  • Ornithodoros spp.

  • Parasitize mammals

  • Transmit relapsing fever
• Fleas

  • Cat flea: Ctenocephalides felis

  • Dog flea: C. canis can be found on cats and dogs

  • Serve as intermediate host for tapeworms

  • Feed on humans as well as pets

  • Cause a localized skin reaction
• Mites

  • Sarcoptes scabei is the cause of scabies worldwide

  • Transmitted by contact

  • Organisms burrow into the skin on the webbing side of fingers, later spreading to the wrists, elbows and beyond
• Bedbugs

  • True insect

  • Cimex lectularius

  • Preferential feeding host is human

  • Nocturnal blood meals

  • Symptoms occur days after bite
• Mosquitos

  • True insect

  • Blood meals

  • Transmit malariae, filariasis, dengue fever, yellow fever, West Nile virus

  • Species include Culex, Anopheles, Aedes, Mansonia
• Major Medically Important Parasites

  Nematodes: Intestinal

  Ascaris lumbricoides

  Enterobius vermicularis

  Necator americanus

  Ancylostoma duodonale

  Strongyloides stercoralis

  Trichiuris trichiura
• Major Medically Important Parasites

  Nematodes: Nonintestinal

  Dracunculus medinensis

  Trichinella spiralis
• Major Medically Important Parasites

  Ptotozoa: Amoeba

  Entamoeba histolytica

  Entamoeba coli

  Entamoeba hartmanni

  Endolimax nana

  Iodamoeba butschlii

  Acanthamoeba spp.

  Naeglatria fowleri
• Major Medically Important Parasites

  Protozoa: Flagellates

  Giardia lamblia

  Thrichomonas vaginalis

  Chilomastix mesnili

  Trichomonas hominis

  Dientamoeba fragilis
• Protozoa: Ciliate

  Balantidium coli
• Protozoa, Intestinal

  Amebae - Single-celled organisms; pseudopodia (motility), trophozoite, and cyst stages in the life cycle.

  Exceptions: Some have no identified cyst.

  Fecal-oral transmission of the infective cyst.

  Entamoeba histolytica causes amebiasis and is the most significant organism in this group.
• Protozoa, Intestinal

  Flagellates - Protozoa with characteristic flagella.

  Fecal-oral transmission.

  Exceptions: Trichomonas has a trophozoite and no cyst stage. Reproduction by longitudinal binary fission.

  Examples: Giardia duodenalis and Dientamoeba fragilis.
• Protozoa, Intestinal

  Ciliates - Single-celled protozoa; cilia (motility), which beat in a coordinated, rhythmic pattern, moving the trophozoite in a spiral path.

  Trophozoite and cyst stages in the life cycle; both stages show a large macronucleus and a micronucleus.

  Fecal-oral transmission.

  Neobalantidium coli is the single human pathogen in the group.
• Protozoa, Intestinal

  Coccidia - Protozoa; asexual and sexual life cycles.

  Fecal-oral transmission via contaminated food and/or water. Infective stage (oocyst) containing sporocysts and/or sporozoites.
• Protozoa, Intestinal

  Microsporidia - Small (1–2.5 μm) intestinal protozoa.

  Transmission by ingestion, inhalation, or direct inoculation of spores.

  Nine genera cause disease in humans; the two most important are Encephalitozoon and Enterocytozoon.
• Protozoa, Other Sites

  Amebae - Pathogenic free-living organisms associated with warm freshwater environments.

  Except for Entamoeba gingivalis (found in the mouth), they have been isolated from the central nervous system, eye, and other body sites.

  Examples: Naegleria fowleri;acute CNS infection and death. Chronic CNS disease (Acanthamoeba spp., Balamuthia mandrillaris), and Acanthamoeba spp. can also cause keratitis.
• Site


  • Red cells
  • White cells
  • Whole blood/plasma
  • Bone marrow
• Parasites in red cells

  • Plasmodium spp.
  • Babesia spp.
• Parasites in white cells

  • Leishmania spp.
  • Toxoplasma gondii
• Parasites in whole blood/plasma

  • Trypanosoma spp.
  • Microfilariae
• Parasites in bone marrow

  • Leishmania spp.
  • Trypanosoma cruzi
  • Plasmodium spp.
• Ascaris lumbricoides


  • Worldwide; most common intestinal helminth infection
  • Ova - stool
  • Ova - infective stage
  • Ova - diagnostic
  • Ova 85 to 95x38 to 45 um. Corticated or decorticated. Unfertilized ovoid, 40 to 74 x 30 to 50 um
  • Embryonate in soil, resist environmental conditions
  • Adult larva largest intestinal nematode, 22 to 35 cm in length
  • Larva emerge in small intestine, migration to blood-stream, liver, lung, to pharynx; swallowed, return to intestine
  • GI symptoms, fever, pulmonary or asymptomatic, eosinophilia
  • 250,000 ova per day, so worm burden can be high
• Nematodes: Intestinal

  Scientific Name Other Name

  Ascaris lumbricoides Roundworm

  Enterobius vermicularis Pinworm

  Necator americanus New World hookworm

  Ancyclostoma duodenale Old World hookworm

  Strongyloides stercoralis Threadworm

  Trichuris trichiura Whipworm
• NEMATODES: Non-intestinal

  Scientific name Other name

  Trichinella spiralis Trichina worm

  Dracunculus medinensis Guinea worm
• Enterobius vermicularis

  • Pinworm

  • Worldwide; most common intestinal helminth infection in the United States

  • Scotch tape preparation is the specimen of choice, ova or adult larva

  • Ova are infective stage

  • Ova and larva are the diagnostic stages

  • Ova 48 to 60 20 to 35 mm; oval, thick shell; flat on one side; developing larva folded inside

  • Adult larva female 7 to 14 mm, male 2 to 4 mm, white to light yellow
• Enterobius vermicularis

  • Hatch in small intestine, adults in colon; migrate to anus to deposit ova

  • Severe anal itching, inflammation

  • Ova infective in 4 to 6 hours, deposit in clothes, bed linens, toys

  • Highly communicable

  • Retroinfection: Ova hatch in anus but migrate back into the colon to reproduce

  • Autoinfection: Infective ova are ingested, hand to mouth

  • Human is the only known host

  • Ova may carry Dientamoeba fragilis, dual infections are seen
• Necator americanus

  • New World hookworm

  • North and South America typically

  • Ova are the diagnostic stage, larva can also be found in stool

  • Infection caused by third-stage filariform larval penetration of the skin, typically the foot

  • Ova 60 to 75 40 mm, cell cleavage can be seen, thin shell

  • Rhabditiorm larvae 15 270 mm, long buccal cavity, and small genital primordium, cutting plates

  • Filariform larvae is the third stage, short esophagus, pointed tail
• Ancyclostoma duodenale

  • Old World hookworm

  • Europe, Far East, Asia, Africa typically

  • Ova is considered to be indistinguishable from those of N. americanus, although A. duodenale ova are 55 to 60 x 40 um

  • Buccal cavity has teeth

  • Other details are same as for N. americanus
• Strongyloides stercoralis

  • Threadworm

  • Worldwide

  • Larva in stool at rhabditiform stage are the diagnostic stage,

  ova rarely seen

  • Infection caused by third-stage filariform larval penetration

  of skin, typically the foot

  • Ova 48 x 35 um, advanced cleavage state, indistinguishable from hookworm

  • Rhabditiform larvae 15 x 220 um, short buccal cavity and

  prominent genital primordium
• Strongyloides stercoralis

  • Filariform larvae is the third stage, long esophagus, notched tail

  • Adult female 2 mm, short buccal cavity, long esophagus

  • Unique life cycle, three mechanisms

  • Direct: Same as that of hookworm

  • Indirect: Larva freely living in environment, produce infective

  rhabditiform larva

  • Autoinfection: Filariform larva develop in host’s intestine,

  invade bloodstream

  • Asymptomatic if light infection; GI symptoms, malabsorption, weight loss, breathing difficulty, bloody sputum, cough, eosinophilia

  • Repeated infection can cause dermal irritation, ground itch
• Trichuris trichiura

  • Whipworm

  • Ova in stool, Ova are infective stage, and Ova are diagnostic

  • Ova 50 to 55x25 um, barrel-shaped with bipolar hyaline plugs

  • Adult larva 2 to 5 cm, male smaller with curled tail; the posterior end is large, resembles a whip handle; the anterior end is smaller, resembles whip; can be found in stool

  • Larva emerge in small intestine, migrate to cecum then to the colon. Asymptomatic with light infection; heavier worm burden includes GI symptoms, weight loss, weakness, eosinophilia; children’s symptoms can include GI, anemia, and, if untreated, prolapsed rectum