CH 28: Non-intestinal protozoa

Naegleria fowleri

• ubiquitous in environment

• causes primary amoebic meningoencephalitis (PAM)

  • fresh, untreated water entering nasal cavity

  • usually fatal

• identification

  • trophozoites found in CSF and brain tissue

  • single nucleus w/ large, dense karyosome

Acanthamoeba spp.

• causes amoebic keratitis and encephalitis

• identification

  • trophozoites or cysts visible in corneal scrapings or brain tissue

  • cysts have 2 walls, a large nucleus, and large dense karyosome

Trichomonas vaginalis

• sexually transmitted flagellate - mostly causes vaginitis

• identifcation

  • trophozoites found in urine and vaginal wet prep

  • ‘jerky,’ non-directional motility

  • pear-shaped, 1 nucleus, 4 flagella

Hemoflagellates

• flagellates that inhabit the blood and tissue of humans

• principle pathogens:

  • Leishmania spp.

  • Trypanosoma cruzi

  • Trypanosoma brucei

Leishmania spp.

• causes leishmaniasis - cutaneous or disseminated infx contracted from bite of SANDFLY

• identification

  • flagellated form or nonmotile stage found in blood or tissue

  • flagellate: long, straight, single flagella

  • non-motile: many organisms infecting human WBC

Trypanosoma cruzi

• Chagas dx - contracted from feces and bite of REDUVIID (kissing) bug

• identification

  • flagellate found in peripheral blood smears

  • C-shape, large, dark posterior kinetoplast

Trypanosoma brucei

• causes African sleeping sickness - contracted from TSETSE FLIES

• identification

  • flagellate found in peripheral blood smears

  • delicate curve w/ smaller kinetoplast

Plasmodium spp.

• sporozoa that cause malaria

  • life-threatening illness that is one of most clinically impactful dx in world

  • 250 million new cases and over 600,000 deaths each year

  • vaccine developed in 2021

• principle pathogens:

  • P. falciparum

  • P. vivax

  • P. ovale

  • P. malariae

Plasmodium spp. identification

• diagnosis made primarily through thick and thin blood smears to view developmental stages of life cycle

• ALL Plasmodium have ring from and diagnose malaria

• P. falciparum: double ring form and large banana-shaped gametocyte

• P. malariae: band form trophozoite

• P. ovale and P. vivzx: Schuffner’s dots difficult to distinguish from each other

Plasmodium falciparum

• large, banana-shaped gametocyte

• multiple rings per RBC

• ‘double dot’ or ‘headphones’ ring form

Plasmodium malariae

• single ring form, NO Schuffner’s dots

• band form trophozoite

Plasmodium ovale and vivax

• ring and trophozoite forms w/ Schuffner’s dots

Babesia microti

• sporozoa that causes babesiosis

  • bloodborne, usually self-limiting infx spread thru tick bites

• identification

  • ring forms similar to Plasmodium and trophozoites in blood smears

  • usually multiple ring forms per cell

  • ‘plus sign’ or ‘maltese cross’ morphology

Toxoplasma gondii

• causes toxoplasmosis

  • associated w/ cat feces and ingestion of undercooked meat, especially in pregnant women

• identification

  • mostly serological testing

  • organisms can be found, but not easily

  • large, curved structures that can be found in CSF, blood, or tissue samples

Trematodes

• flukes

  • flat, hemaphroditic w/ at least 2 suckers

• life cycles

  • eggs usually pass thru feces into water where hatch into free-living organisms

• can infect many organs

  • intestines, liver, lungs

Schistosoma spp.

• blood flukes

• eggs found in feces or urine are diagnostic

• principle pathogens:

  • Schistoma mansoni

  • Schistoma japoriicum

  • Schistoma haemtobium

Schistoma mansoni

• eggs have large lateral spine

Schistoma japoriicum

• eggs have small lateral spine

Schistoma haemtobium

eggs have terminal spine

Paragonimus westemani

• long fluke

• identification

  • eggs is feces or sputum

  • eggs have shouldered operculum (top)

Clonorchis sinensis

• intestinal fluke

• identification

  • eggs in feces

  • eggs have dome shaped, shouldered operculum opposite small knob

Fasiola hepatica

• liver fluke

• identification

  • eggs in feces

  • eggs are rounded w/ non-shouldered operculum

Cestodes

• tapeworms

• adult worms live in humans who shed eggs, which infect an intermediate host

  • host produces larvae which infects humans by consumption of meat

• diagnosis usually made by eggs or proglottid segments in feces

Taenia saginata

• beef tapeworm

• diagnosis

  • eggs indistinguishable from T. solium

  • proglottid segments are wide w/ more lateral segments

  • scolex has 4 suckers and smooth surface

Tenia solium

• pork tapeworm

• diagnosis

  • eggs indistinguishable from T. saginata

  • proglottid segments are more narrow w/ fewer later segments

  • scolex has 4 suckers and hook like projections on surface

Diphyllobothrium latum

• fish tapeworm

• identification

  • eggs are oblong and smooth

  • smooth operculum w/ small knob opposite

  • proglottids are wide w/ central uterine segments

Hymnenolepis nana

• dwarf tapeworm - accidental ingestion of infected arthropods

• identification

  • eggs have 2 layers

  • 3 hooklets inside egg, w/ polar thickening at one end

Nematodes

• roundworms

• wide variety of infxs, and life cycles can be very complex

Enterobius vermicularis

• pinworms - common infx in school age children

  • pruritus and itchiness around anus

• diagnosis

  • gravid females deposit eggs in perianal folds

  • best egg visualization by tape prep from around anus at night

  • eggs have thin shell that is oval-shaped w/ one flattened side

Trichuris trichiura

• whipworm

  • intestinal infections, mostly in children

• diagnosis

  • eggs in stool

  • barrel shaped eggs w/ transparent plugs at each end

Ascaris lumbricoides

• giant intestinal tapeworm

• diagnosis

  • larger worms are so big they can cause intestinal blockages

  • visualized coming out of anus or stool

  • eggs in stool have a thick shell w/ bumpy outer layer

Strongyloides stercoralis

• threadworm

  • burrow into intestinal tissue

  • infx occurs when worms in water sources penetrate through skin

• diagnosis

  • eggs rarely in stool

  • feces contain rhabditiform larvae

  • larvae very similar to hookworms, but have short buccal (mouth) cavity and prominent genital primordium

Necator americanus

• hookworms

  • adults infect the small bowel

  • infx occurs when worms in water sources penetrate through skin

• diagnosis

  • eggs found in stool w/ translucent wall and clusters of spherical embryos

  • rhabditiform larvae also found in stool have long buccal cavity

Trichinella spiralis

• infx of skeletal muscle that causes edema and swelling in muscle tissue

  • contracted from ingestion of undercooked pork

• diagnosis

  • encysted larvae and worms seen in skeletal muscle

Dracunculus medinensis

• guinea worm infxs

  • migrate to skin and cause ulcers

• diagnosis

  • adult worms found in ulcerations

  • treated by removing worms around a stick, 1 inch per day

Filariae

• subset of nematodes that are small, thread-like worms

• mainly inhabit circulatory and lymphatic systems, but can also invade sinus cavities and skeletal muscles

  • elephantiasis

• diagnosis made by identifiying organisms in blood samples

Wuchereria bancrofti

• causes elephantiasis

  • contracted thru bite of mosquitoes

• diagnosis

  • adults worms have no tail nucleu

Brugia malayi

• causes elephantiasis

  • contracted through bite of mosquitoes

• diagnosis

  • adult worms have 2 distinct tail nuclei

Loa loa

• migrate to eyes

• diagnosis

  • adult worms have nuclei that go all way to tip of tail