Parasitology

Plasmodium Species you need to know

• P. vivax

• P. malaria

• P. falciparum

• P. knowlesi

• Babesia microti

Malaria

• cause = sporazoa from plasmodium genus (P. malaria and P. falciparum

• found in tropical and subtropical areas.

• causes paroxysms that cause RBCs to rupture via release of merozoites (toxins)

• symptoms of paroxysm phase = headache, deep bone pain, nausea or flu like symptoms, and a violent shaking chill that last 10 to 15 minutes initiates the paroxysm, which is followed by a fever with the temperature

• long-term effects of malaria = damage to the liver and spleen caused by deposits of malarial pigments, otherwise known as hemozoin

Clinical signs of Malaria

• Ring form refers to a ring like appearance of a malarial parasites following the invasion of a previously healthy red blood cell. The typical ring consists of a blue cytoplasmic circle connected with or to a red chromatin dot. The space inside is a vacuole.

• The appearance of the developing trophozoite varies among the plasmodium species.

• Mature schizonts are characterized by the emergence of merozoites. The number and arrangement of the merozoites vary within each malarial species.

• The gametocyte can be divided into microgametocytes and macrogametocytes.

• The microgametocytes is roundish in shape, with the exception of Plasmodium falciparum, which is banana or crescent shape.

• Macrogametocytes range in shape from round to oval, with the exception of Plasmodium falciparum again, which is crescent shaped.

• the gametocytes stain pink/purple.

Plasmodium vivax: ring form

• Red blood cells infected with plasmodium vivix tend to become enlarged and distorted in response to the presence of the growing parasites.

Plasmodium vivax: Trophozoite form

• a single large chromatin dot is present among the cytoplasmic material.

• The vacuole remains visible and basically intact.

• The presence of brown pigments, which is a remnant of the parasite feeding on the red blood cells hemoglobin, becomes apparent in the site of cytoplasm.

• Schuffner’s dots may also be present.

• take on amoeboid shape

Plasmodium vivax: schizont

• Mature schizonts generally contain about 12 to 24 merozoites.

• Merozoites are created by the division of the chromatin

• Brown pigment and Schuffner’s dots may also be present.

Plasmodium Vivax: Gametocyte

• Plasmodium vivax gametocyte consists of a large pink to purple chromatin mass, which is surrounded by a colorless pale halo.

• Evenly distributed cytoplasmic brown pigments is usually visible.

Plasmodium vivax Clinical Significance

• found in tropical and subtropical areas

• transmitted by the anopheles mosquito

• infectious form = sporozoite

• causes benign tertian malaria

• gametocyte fills and enlarges RBCs

Plasmodium malaria: Ring form

• only infect mature RBCs (smaller cells) and have lower parasitic load.

• Delicate cytoplasmic ring ⅙ RBC diameter connected by a heavy chromatin dot

• Vacuole appears “filled in”

• Pigment forms early

• RBCs are not distorted

Plasmodium malaria: trophozoite

• The formation of a non-amoeboid solid cytoplasm that may assume an oval, band or bar shape is characteristic for the plasmodium malaria.

• The cytoplasm consists of a coarse dark-brown pigment that often mask the chromatin material.

• Vacuoles are absent in the mature forms of this stage.

• The band and oval shapes are diagnostic

Plasmodium malaria: Schizont

• Plasmodium malaria schizont typically contains about 6 to 12 merozoites that are generally arranged in rosettes or irregular clusters.

• A central arrangement of brown-green pigment may also be visible at this stage

Plasmodium malaria: gametocyte

• The plasmodium malaria gametocyte resembles that of plasmodium vivax, but it’s smaller. 

• The brown pigment is darker and coarser than that of Plasmodium vivax.

• Other forms of this stage also tend to assume an oval shape.

• There are no Schuffner’s dots present in this form in plasmodium malaria.

Clinical Significance of Plasmodium malaria

• causes quartan malaria or malarial malaria

• found in tropic, subtropic, and temperate regions of the world

• attacks only mature RBCs

• paroxysms every 72 hours, repeated attacks over 20 years

• spontaneous recovery may occur.

• may lead to nephrotic syndrome, which arises from the deposition of circular circulating immune complexes of the malarial antigen and antibody on the basement membrane of the glomerulus, which is causing an auto immune reaction in the patient.

Plasmodium falciparum: Ring form

• Plasmodium falciparum, or falciparum, can infect red blood cells of all ages, so the parasitic load of this parasite tends to be the highest.

• The typical small, delicate ring form of Plasmodium falciparum consists of scanty cytoplasm connected to one or two small chromatin dots.

• A small vacuole is also always visible.

• Multiple rings in the red blood cells are frequently seen, and you can see applique forms where the ring form lines up against the edge of the red blood cells.

• multiple rings = key characteristic

Plasmodium falciparum: Trophozoite

• The Plasmodium falciparum developing trophozoite is characterized by the presence of heavy ring forms.

• Fine pigment and granules may also be visible.

• Mature stages of this form are not routinely seen in the peripheral blood.

Plasmodium falciparum: Schizont

• The schizont of Plasmodium falciparum is the only visible form in patients with severe infection.

• The typical schizont contains 24 merozoites, but it can contain anywhere from 8-36, and the cluster arrangement may also be present, but it is rarely seen.

Plasmodium falciparum: gametocyte

• The gametocyte of Plasmodium falciparum is typically sausage- or crescent-shaped. 

• The chromatin is usually compact, and black pigment surrounds the chromatin, which may be visible.

• This form is diagnostic for Plasmodium falciparum, meaning that is not seen with other Plasmodium species.

Plasmodium falciparum: Clinical Significance

• ruptures RBCs at irregular intervals

• gametocyte form is diagnostic

• invades RBCs at any stage

• causes malignant tertian malaria, most deadly of all plasmodium species.

• infective form = sporozoite from anopheles mosquito

• The primary complication is central nervous system involvements, and the organism reduces oxygen delivery to the tissues resulting in tissue anoxia, the patient ends up having severe headaches may be confused and ultimately lapses into a coma if untreated.

• A second but less common complication of infection is called blackwater fever. Black urine due to mass intravascular hemolysis and hemoglobinuria. Renal complications/failure can occur.

Plasmodium ovale

morphologically similar to P. vivax, difficult to differentiate.

Plasmodium knowlesi

• resembles P. malaria, and may resemble P. falciparum

• causes life-threatening malaria

• primarily zoonotic, affecting primates

• if detected early, infections in humans can be treated

Babesia microti Clinical Significance

• Found worldwide, but most commonly in Northeastern US (New England), Wisconsin, Connecticut

• Symptoms = typically develop a hemolytic anemia and experience jaundice, weakness, fever, chills, sweating, headache, and hepatosplenomegaly. Renal failure is possible. Most cases are self-limiting.

• Vector = Ixodes scapularis tick (deer tick)

• official term is babesiosis, but look for hemolytic anemia.

• prevention = avoid tick-infested areas, insect repellent, long sleeves and pants.

• treat with Quinine and Clindamycin

Lab diagnosis

• ring form is similar to P. falciparum

• travel history and clinical signs

Babesia microti: Ring form

• The rings of Babesia consists of a small chromatin dots and a scant amount of cytoplasm.

• More mature versions may exhibit two or more chromatin dots.

• Infected red blood cells usually contain 2 to 4 rings.

• The stippling and malarial pigments are absent in Babesia

• multiple rings with center cross-form is diagnostic

Isospora belli/Cytoisospora belli: Oocyst

• oocyst = oval and transparent, 25-35 um

• The polyvinyl alcohol-preserved sediment makes it difficult to see the oocyst because the cyst wall is very thin and retractile.

• They're variably stained in the modified acid-fast stain; some will stain light pink to purple, while others may remain unstained.

• Their internal structure will not be seen, and some oocysts may appear collapsed or distorted on one side.

Isospora belli/Cytoisospora belli: Clinical Significance

• infective form = oocyst

• it is spread via fecal-oral route human-to-human, and contaminated food/water

• humans are the only host

• infection is confined to intestinal tract, and many people are asymptomatic

• Symptoms: anorexia, nausea, abdominal pain, diarrhea, and possible malabsorption syndrome.

• Treatment = trimethoprim-sulfamethoxazole

Cryptosporidium parvum

• 4-5 um, round, thick cell wall

• 4 sporozoites

• easily mistaken as yeast

• modified acid-fast stain is used for diagnosis, otherwise an enzyme immunoassay for Ag detection or molecular diagnostic tests.

Cryptosporidium parvum: Oocyst

• often have distinct walls and stain from a light pink to bright red color

• Mature oocyst have discernible sporozoites (up to four), with a blue background and the pink or magenta color staining oocyst, on your modified acid fast stain.

• the infective form = oocyst

Cryptosporidium parvum: Clinical Significance

• spread through fecal-oral route, contaminated food/water

• common in midwest

• domestic animals harbor oocysts

• An infection can be fatal for patients that are severely immunocompromised

• treatment often not recommended, but use paromomycin.

Cyclospora cayetanensis: Oocyst

• resembles cryptosporidium

• 7-10 um diameter, round-oval, transparent, when mature contains 2 sporocysts with 2 sporozoites each. May contain granules and have a wrinkled appearance.

• The oocysts are variably stained on a modified acid fast stain, some will stain the light pink to deep purple, while others may remain unstained.

• modified acid-fast stain and molecular diagnostics used for diagnosis

Cyclospora cayetanensis: Clinical Significance

• The infectious form for Cyclospora cayetanensis is the oocyst through fecal-oral contamination.

• Transmitted by contaminated food or water.

• Infection causes self-limiting diarrhea that can take 3 to 4 days to resolve itself, but relapses can occur over a period of 2 to 3 weeks.

• Antidiarrheal medications can provide relief of the symptoms, and Trimethoprim-sulfamethoxazole can reduce the possibility of relapse.

Size Comparison of Cryptosporidium parvum, Cyclospora, and Isospora belli

Toxoplasma gondii

• sporozoan parasite that infects nucleated cells of almost all animals and birds

• non-specific invasion, difficult to diagnose

• Diagnosis involves detection of IgG and IgM ab by enzyme immunoassay.

Toxoplasma gondii: Clinical Significance

• Humans become infected by ingesting the infective oocyst in contaminated food or drink or by accidental hand-to-mouth transmission of contaminated soil or cat litter.

• If an immunocompromised person is infected, their symptoms can present like mono with swollen lymph nodes, fever, fatigue, hepatosplenomegaly, or an enlarged spleen, and absolute lymphocytosis. If severe enough, it causes encephalitis, myocarditis, hepatitis, pneumonia, and/or eye inflammation depending on location of organism.

• If a fetus were to be infected, it's called congenital toxoplasmosis, so a fetus can be infected by toxoplasma by crossing the placenta from the mother.

• Symptoms in the infant can include hydrocephaly, microcephaly, intracerebral calcification, chorioretinitis, convulsions, and psychomotor disturbances.

• The diagnosis in infants is made by detection of IgM antibodies in an enzyme immunoassay method from the infant themselves.

• generally, causes congenital toxoplasmosis.

Microsporidia

• They are tissue parasites and are recognized to cause infections in immunocompromised patients that include enteritis, encephalitis, nephritis, and keratoconjunctivitis.

• Diagnosis of the different species of Microsporidium varies.

• Serologic tests look for antibody production, and tests are available for the detection of some species.

Entamoeba histolytica: Trophozoite

• Motility is progressive and rapid. 

• Finger-like pseudopods

• 12-60 um

• 1 nucleus

• PC = fine

• K = central

• Cytoplasm appears green. Vacuoles can be present.

• Can have inclusions (RBCs)→ good differentiator btw histolytica and dispar.

Entamoeba histolytica: Cyst

• 10-20 um

• Spherical in shape

• Mature = nucleus

• Immature = 4 nuclei

• PC = fine, een

• K = small, compact, central

• Cytoplasm = sometimes chromatid bodies are present

• Elongated with blunt or rounded smooth edges.

• Glycogen granules may be present

• infective form!

Entamoeba histolytica: Clinical Significance

• Found in subtropical and tropical areas of the world + Alaska, Russia, and Canada

• Poor sanitation practices in areas that use human waste as fertilizer contribute to the infection

• Infection occurs through ingestion of contaminated food or drink.

• difficult to differentiate btw histolytica and dispar, so often notated as histolytica/dispar

Amoebic dysentery

• Infective form: cyst

• Intestinal ulceration

• Diarrhea, bloody stool, dehydration, dehydration, abdominal cramping

• Diagnosis: observe cysts and trophs

• Differentiate from Shigella dysentery

• resistant to chlorine

• The organism can easily or can spread to the liver; it can spread the other body sites, primarily the liver, brain and lungs.

Entamoeba histolytica vs Shigella

• white blood cells, or PMN. Entamoeba histolytica generally does not have very many whites present in the stool, where Shigella does, and they're often degraded.

• Entamoeba histolytica generally doesn't have a lot of mucus in the stool, where Shigella does.

Entamoeba hartmanni: trophozoite

• 5-12 um

• Non-progressive motility

• One nucleus

• PC = fine granules, even distribution

• K = small, central

• Clean cytoplasm

• No inclusions!!

Entamoeba hartmanni: Cyst

• 5-10 um

• Spherical/round 

• 2-4 nuclei

• PC = fine, present

• K = small, central

• Cytoplasm = chromatid bodies

• Glycogen vacuoles sometimes present

Entamoeba hartmanni: Clinical Significance

• commensal, non-pathogenic

• patients are asymptomatic and not treated

Entamoeba coli: Trophozoite

• 15-50 um

• Largest of the amoeba

• Motile, sluggish, non-directional due to blunt pseudopods

• 1 nucleus

• PC = clumped, uneven

• K = large, non-central

• Cytoplasm = dirty appearance. Granular, vacuolated.

• Inclusions = bacteria, yeast, debris

Entamoeba coli: Cyst

• 35 um

• Spherical or oval

• Up to 8 nuclei

• PC = coarse, granular

• K = large, non-central

• Cytoplasm = chromatoidal bodies present, generally splinter-shaped with rough pointed ends.

• This is the only amoeba you can definitively identify with the cyst only

Entamoeba coli: Clinical Significance

• commensal, non-pathogenic, not treated

• reported on stool report as Ent. coli

Endolimax nana: Trophozoites

• 6-12 um

• Sluggish motility, non-progressive

• 1 nucleus

• PC = none

• K = very large, like a blot

• Cytoplasm = granular, vacuolated, possible ingested bacteria

Endolimax nana: Cyst

• 5-10 um

• Oval, round

• Nucleus: 2-4

• PC = absent

• K = smaller than in troph, but larger than Entamoeba

• Cytoplasm = chromatid bodies

• Glycogen is usually diffuse if present

Endolimax nana: Clinical Significance

• commensal, non-pathogenic, not treated

• it’s reported when found in stool

• Typically lives in warm, moist regions with poor hygiene

Iodamoeba butschlii: Trophozoite

• Motility = sluggish, non-progressive

• 8-20 um

• 1 nucleus

• PC = none

• K = large, can be surrounded by refractile granules

• Cytoplasm = granular, heavily vacuolated. 

Iodamoeba butschlii: Cyst

• 13 um

• Nucleus = 1

• PC = absent

• K = large, eccentric

• Achromatic granules

• Glycogen vacuole

Iodamoeba butschlii: Clinical significance

• commensal, non-pathogenic

• asymptomatic, not treated

• report if seen on O&P

Blastocystis hominis:

• Trophozoite

• Clinical significance

Trophozoite

• Nucleus = 2-6

• Cyst-like structure

• 5-30 um

• Large central body

Clinical Significance

• Can cause gastrointestinal disease in travelers and AIDS patients

• typically commensal and non-pathogenic

• spread fecal-oral