parasitology

What is a host?

Organism on which parasite lives and grows.

Parasite

Organism that grows on or in host, causing injury.

Obligate parasite

Cannot survive without the host

Facultative parasite

May exist in free living state as well as a parasite.

Accidental/incidental host

Not the usual host, life cycle may not be completed.

Definitive host

Adult and sexual stages of a parasite occur.

Intermediate host

Larval and asexual stages of a parasite occur.

Carriers (carrier host)

Parasite present as commensal but no signs of infection, can transmit the parasite to other plant and animal host.

Vectors

Arthropods or other carriers that transmit the parasite to the host.

Ectoparasites

Live on or outside the body of the host (ex: ticks)

Stool specimens for parasite exams

Many parasites cause GI infections, require a stool specimen.

What to avoid during specimen collection of stools?

Barium sulfate procedures, medications the interfere with the detection.

What medications interfere with the detection of parasites in a stool specimen?

Barium, mineral oil, bismuth, anti diarrheal prep, anti malarial, antibiotics.

Stool specimen macroscopic examination

Proglottids and adult worms.

Stool specimen microscopic examination

Calibrated micrometer, 5-100x objectives, scan under low power and identify under higher power.

Direct saline smear of stool specimen

Detect motile trophozoite and flagellates, detect helminth eggs, larvae, and protozoan cysts.

Direct iodine smear of stool specimen

Protozoan cysts, yellow cyptoplasm and pale nuclei, brown glycogen inclusions when present.

Stool concentration

Used to detect protozoan cysts, Helmont larvae, and eggs, two methods flotation and sedimentation.

Floatation stool concentration

Zinc sulfate, parasitic eggs and cysts float to the top and are skimmed off (clean concentrate, operculated eggs and Protozoa do not float)

Sedimentation stool concentration

Formalin-ether, all Protozoa, eggs, and larvae can be sedimented (following centrifuge, parasitic eggs, cysts, larvae sediment to lowest layer).

Permanently stained mounts

Fix with PVA or schaudinns fixative, merthiolate-iodine, trichome, iron hematoxylin, modified acid fast.

Merthiolate-iodine formation

Combination preservative, fixative, and stain.

Trichome stain

Wealthy modification, fresh PVA preserved material (blue green-purple cyptoplasm with red to red purple nuclei)

Iron hematoxylin

Fresh and PVA preserved material, background debris and parasites stain grey blue to black; nuclei stain black.

Modified acid fast stain

Cyclospora, cystoisospora, and other coccidia like organisms.

Blue green color on trichome stain

Cytoplasm of cysts and trophozoites

Purple color on trichome stain

Cytoplasm of entamoeba coli

Dark red purple of trichome stain

Nuclear chromatin, karyosomes, chromatoidal bars, RBCs.

Red on trichome stain

Eggs and larvae

Green on trichome stain

Background debris and yeast

Modified acid fast stain I

Enhanced detection of oocysts of cryptosporidium, isopora belli, cyclospora cauetanemsis, oocysts appear magenta with a blue background.

Blood specimens and parasite exams

For detection of plasmodium sp., babesia, tryphah, somes, microfilaria

Blood specimens

Collect blood on 3 consecutive days at 6-18 hour intervals, giemsa or wrights stain, thick smear and thin smear.

Thick blood smear

Large volume of blood examined, not fixed so red cells lyse, higher sensitivity than thin, used as a screen, screen for parasites 100x-1000x.

Thin blood smear

Fix and stain, identify parasite when screen (thick smear) is positive.

Identification using immuno diagnostics

Direct antigen detection using EIA, immunochromatogenic assays, DFA.

Identification using molecular testing

Conventional and real time PCR, plasmodium, multiplex PCR and film arrays for parasitic and viral gastrointestinal pathogens.

Protoza 4 groups

Amoeba-motile by pseudopods, flagellates- motile by flagella, ciliates-covered with short hair like structures, coccidia.

Intestinal amoebae

Average size range smaller than that of most other parasitic organisms, must be distinguished from artifacts and cells that appear in the clinical specimen, most are non pathogenic, permanently stained slides best method for id.

Intestinal amoebae identification

Size, number of nuclei, nuclear structure, presence of specific internal structure.

Protoza cyst form

Found in formed stool, rigid, non-motile, infectious form, resistant to environment changes, usually asymptomatic or carrier host.

Protoza trophozoite form

Found in liquids stool, pleomorphic, active feeding form, active disease, sensitive to environmental changes.

Intestinal amoebae: entamoeba histolytica

Amoebic dysentery, ingested red cells in the cytoplasm, causes 40-50 million cases of colitis and hepatic ulcers a year, account for 40k look deaths a year, prevalence according to socioeconomic status (more common in poorly developed countries).

Acute symptoms of entamoeba histolytica

Abdominal cramping, fever, tenderness, 20 diarrheal stools in a day with trophozoite and blood, characteristic lesion in intestinal mucosa, flask shaped ulcer, may penetrate the lungs.

Where is entamoeba histolytica mainly found?

Found mainly in tropics/sub tropics

Trophozoites entamoeba histolytica

Seen in wet Mount or trichome stain, 10-50 um, refractile bulls eye nucleus with small central karyosome, ingested RBC is diagnostic but not usually seen.

Cysts of entamoeba histolytica

10-40um, have 1-4 nuclei, each have small central karyosome, cyptoplasm may have chromatoidal bars.

Intestinal amoebae entamoeba Hartmanni

Non pathogenic, trophozoite average size 4-12um, cysts average size 5-10um, has eccentric karyosome or uneven peripheral chromatin.

Intestinal amoebae entamoeba coli

Common fecal contaminant in food or water, non pathogenic, trophozoite average size 5-50um (large eccentric karyosome, course uneven peripheral chromatin), immature cyst (1-2 large nuclei, large glycogen vacuole), mature cyst (8 nuclei).

Intestinal amoebae endolimax nana

Non pathogenic, trophozoite (large laryosome with no peripheral chromatin, 5-12um, cytoplasm granular and vacuolated), cyst (oval or spherical, 5-12 um, up to 4 large nuclei resembling button holes)

Intestinal amoebae lodamoeba bütschlii

Troph (6-20um, vacuolated cytoplasm), cyst (6-15um, single large karyosome, large well defined glycogen vacuole).

Miscellaneous Protoza: blastocystis hominis

Reclassified several times as yeast and protozoan, lacks cell wall and multiplies by binary fissions, gastrointestinal disease, transmitted through contaminated food and water, most common, over 50% developing countries, travel abroad, colitis and ib.

Blastocystis hominis diagnosis

Difficult to see in concentrated wet mounts, observe in concentrated stool mounts (round with a large central body and small nuclei).

Blastocystis hominis Classification unresolved

Originally yeast currently an ameba, related to brown algae and water molds.

toxoplasma gondii

Human are accidental host and cats are definitive host, oocyst shed in cat feces, attacks nervous system, both asexual and sexual life cycles, ingested meat, toxoplasmosis.

Toxoplasmosis

Mild in immunocompetent host, serious effects are rare (encephalitis, myocarditis, pneumonitis, dissemination)

Congenital of toxoplasmosis

Serious in babies born to infected, sometimes sero negative mothers, affects central nervous system, severity depends on when in fetal development exposure occurred, this is why recommend pregnant women eat well done meat and don’t change litter.

Diagnosis of toxoplasmosis

Extremely difficult because no single organ is invaded, pear shaped or crescent shaped tachyzoites or in tissue stained with hematoxylin, an IgM specific test may be used indirect fluorescent antibody. Rise in titer count indicate acute infection.

Free living amoebae

Found in many water sources, vegetation, sewage, direct contact with contaminated water-swimming in lakes, breaks in skin, inhalation of aerosols.

Naegleria flowleri

Soil and warm fresh water lakes, ponds, around the world, primary amoebic menimgoencephalitis.

Early stage of primary amoebic meninimhoencephalitis or flowleri

Vague, upper respiratory distress, headache, lethargy.

Acute stage of primary amoebic meninimhoencephalitis or flowleri

Sore throat, nasal congestion, severe headache, fever, vomiting, neck stiffness, coma and death.

Where is flowleri most frequent?

Texas, Florida, Virginia, California, people who have been swimming in warm water lakes.

Diagnosis of flowleri

Enters nasal cavity and invades nasal mucosa, brain eating, cannot be differentiated from bacterial meningitis.

3 stage life cycle of flowleri or primary amoebic meningoencephalitis

Amebold trophozoite, cyst, flagellated form.

Acanthamoeba spp

Amoebic keratitis and acanthamoeba balamuthia

Acanthamoeba balamuthia

Granulomatous amoebic encephalitis, brain lesions, acute fever, headache, neck pain.

Two stages of Acanthamoeba balamuthia

1. Resistant cyst 15-20um (spherical, double walled with wrinkled appearance), 2. Motile troph 20-40um (single nucleus with prominent endospore, blunt pseudopods and characteristic spine like projections of cytoplasm seen on wet mounts)

Amoebic keratitis

Associated with acanthamoeba, soft and extended wear contact lens wearers develop, home made saline, history of corneal trauma, wearing contact during swimming.

Flagellates

Motile by flagella, more rigid than amoeba can maintain shape, cause infections in the GI tract, blood and urogenital tract.

Medically significant flagellates

Giardia duodenalis (previously lamblia), trich vaginalis, trich hominid, chilomastix mesnii, dientamoeba fragilis.

Giardia duadenalis

Common gastrointestinal parasite-most common intestinal Protoza in us, world wide distribution, low infections dose.

2 names cause by giardiasis

Travelers among bacteria and Protoza causing montezumas revenge, backpackers diarrhea from hikers untreated water.

How is giardiasis’ passes?

Contact or ingestion of cysts in contaminated water.

Trophozoites of giardiasis

Pear/teardrop shaped, resembles an old man’s face or monkey face, bilateral symmetry, 2 nuclei and four pairs of flagella, falling leaf motility, large ventral sucking disk.

Cyst of giardiasis

Oval, 8-12×7-10um, up to 4 nuclei, cytoplasm often pulled away from cyst wall, retracted flagella and internal structures give cluttered appearance, adheres to intestinal mucosa, interferes with adsorption of nutrients/vitamins.

Symptoms of giardiasis

Acute-self limiting diarrhea with malaise, cramps, nausea, 12-14 days after exposure is explosive foul smelling non bloody diarrhea that last 1-4 weeks.

Diagnosis of Giardiasis

Multiple stool samples as cyst shedding is irregular.

Treatment of giardiasis

Metronidazole (flagyl) or albendazole.

Lab detection of giardiasis

EIA using monoclonal antibodies available, detects soluble antigens in stool, antigens are free and dispersed in the fecal matter, direct fluorescent antibody used to identify cysts.

Chilomastix mesnii (intestinal flagellates)

Pear shaped trophozoite, curved cytosomal fibril resembles Shepard crook, non pathogenic, cyst lemon shaped with nipple.

Dientamoeba fragilis (intestinal flagellates)

Only binucleate flagellate that infects humans, sluggish motility, diarrheal syndrome, lacks a cyst stage, troph 5-12um, some studies show transmitted to humans via ingestion of helminth egg of enterobius vermiculars, co infection.

Trichomonas vaginalis

Causes trichomononiasis, most common non viral STD, 3-5 million cases a year women 15-24 of age, humans are only host, increased HIV risk due to compromised barrier, lacks a cyst stage.

Increased adverse pregnancy outcomes from trichomoniasis

Transmission in new born, cervicql neoplasia, pelvic inflammatory disease.

Trophozoite of trichomoniasis

Pear shaped with undulating membrane (1/2 length of organism), have an anterior flagella, jerky motility.

Infections of trichomonas

Vaginitis, urethritis, sexual contact.

Lab test of trich

Wet prep, antigen detection methods, PCR method, most places rely on wet mount, jerky motility, motion of flagella and undulating membrane may be seen:

Giemsa stain for trichomnas

Axostyle extends the length of organism with chromatic granules extending length of axostyle, single nucleus near anterior end.

Symptoms and treatment of trichamonas

Males are usually asymptomatic carriers and may develop non specific urethritis with a milky discharge that last up to 4 weeks, females infection is localized to vagina, itchy and produces frothy, creamy, discharge and dysuria, treated with metronidazole (flagyl).

Trichomonas Hominis

Usually non pathogenic, 6-14um, prominent axostyle extending through posterior, 4 anterior flagella, oval nucleus with small laryosome, undulating membrane extends the length of organism.

Balantidium Coli

The only known pathogenic ciliate, largest protozan (oval shaped with uniform cilia, propelling motility with rotary motion, kidney shaped macro nucleus), lives in large intestine and does not migrate else where,

Symptoms of balantidium coli

Most people asymptomatic, may experience self limiting diarrhea, ingest cysts and fecally contaminated water or food, humans are accidental host, pigs are important reservoir.

Cyst the infective stage in balantidium coli

45-75, cilia may be seen retracted within cyst wall.

Trophozoite of balantidium coli

Oval shape, slightly pointed anterior end, cytoplasm contains food vacuoles.

Balantidium Coli is characterized by?

Presence of nucei in trophozoite and cyst, a kidney bean shaped macro nucleus? A small round micro nucleus situated in the curve of macro nucleus (rarely visable).

Cystoisospora belli

Intracellular parasites with both asexual and sexual life cycle.

Where does cystiosospora bell life cycle occur?

The cytoplasm of the epithelial cells cells of the small intestine.

How is cystiosospora transmitted?

Isosporoasis, ingest infective oocysts in contaminated food or water, no secondary host needed.

Diagnosis of cystoisospora belli

Oocysts in stool in modified acid fast stains or iodine preparations, immature oocysts shows a single sporoblast, mature oocysts shows as 2 sporocysts with 4 elongated sporozoites within each, most serious in immunocompromised.

How is the life cycle of cystoisospora belli

oocysts are not sporulated when passed in stool, direct fecal oral transmission does not occur, immature oocysts are excreted into stool, usually contains on sporoblast that divides into two and secretes a cysts wall, the sporocysts divide and become sporozoites, 2 oocysts are ingested and excyst, sporozoites are released and invite epithelial cells and then inside multiply asexually after 1 week male and female gametocytes develop, after fertilization the oocysts shed in stool: