Protozoa

Classification o protozoa

Class	Examples	Disease
Amoebae (Sarcodina)	Entamoeba histolytica Naegleria fowleri Acanthamoeba spp. Balamuthia mandrillasis	Amoebiasis (dysentery, liver abscess) Primary Amoebic Meningoencephalitis (PAM) Granulomatous Amoebic Encephalitis (GAE), Keratitis
Flagellates (Mastigophora)	Giardia lamblia Trichomonas vaginalis Leishmania donovani Trypanosoma cruzi Trypanosoma brucei	Giardiasis (malabsorption, steatorrhea) Trichomoniasis (vaginitis) Kala-azar (Visceral Leishmaniasis) Chagas disease (American Trypanosomiasis) Sleeping sickness (African Trypanosomiasis)
Ciliates (Ciliophora)	Balantidium coli	Balantidiasis (balantidial dysentery)
Sporozoa (Apicomplexa)	Plasmodium spp. Toxoplasma gondii Cryptosporidium parvum Cystoisospora belli Cyclospora cayetanensis Babesia spp.	Malaria Toxoplasmosis Cryptosporidiosis (diarrhea) Cystoisosporiasis (diarrhea) Cyclosporiasis (diarrhea) Babesiosis

Entamoeba histolytica

Entamoeba Histolytica

• Host: Humans

• Infective Form: Quadrinucleated cyst

• Infective Dose: Small

• Mode of Transmission: Fecal-oral route

• Pathology:

  • Gastrointestinal: Flask-shaped ulcers in the colon

  • Liver: Anchovy sauce pus in amoebic liver abscess

• Diagnosis:

  • Sample: Stool collected across 3 consecutive days

  • Microscopic examination: Trophozoites (T) and Cysts (C)

• Culture Media:

  • Polyxenic Media: Supplemented with bacteria

  • Axenic Media: Pure media without bacteria (Diamond's media)

• Treatment: Metronidazole for 10 days \rightarrow followed by Paromomycin (Luminal amebicide)

Entamoeba histolytica vs entamoeba coli

Entamoeba Histolytica vs. Entamoeba Coli

Feature	Entamoeba histolytica	Entamoeba coli (Non-pathogenic)
Trophozoite (T)	Erythrophagocytosis (Engulfed RBCs present) 1 nucleus with a central karyosome ("Cartwheel" nuclear pattern)	No RBC ingestion 1 nucleus with an eccentric karyosome
Cyst (C)	1 to 4 nuclei Thick chromatoid bodies	1 to 8 nuclei Thin, splinter-like chromatoid bodies

• Chromatoid Body Composition: Consists of Ribonucleoprotein (RNP); visualized best with Iron Hematoxylin stain

Free living amoebas

Free-Living / "Brain-Eating" Amoebae

Feature	Naegleria fowleri	Acanthamoeba spp.	Balamuthia mandrillaris
Disease Caused	Primary Amoebic Meningoencephalitis (PAME)	Granulomatous Amoebic Encephalitis (GAE) Contact lens keratitis	Granulomatous Amoebic Encephalitis (GAE)
Predisposing History	Swimming / dirty water exposure / village water tanks	Immunodeficiency (HIV+) or contact lens use	Immunodeficient or immunocompetent individuals
Infective Forms In Tissue	Trophozoite only (enters via nasal route \rightarrow cribriform plate \rightarrow brain)	Both Trophozoites and Cysts (enters via nasal/oral/eyes \rightarrow blood)	Trophozoite (Fish-shaped appearance)
Culture / Diagnostics	NNA (Non-Nutrient Agar) with E. coli lawn culture • Gold Standard: NAAT	Shows spike-like acanthopodia and double wrinkled-wall cyst	Shows characteristic fish-shaped trophozoites

Balantidium coli

Balantidium Coli

• General Features: Only ciliated parasite of humans

• Infective Form: Cyst

• Key Characteristics ("B" Rule):

  • B - Biggest Protozoa

  • B - Big Intestine: Inhabits the large intestine \rightarrow causes dysentery/diarrhea

  • B - Binucleated:

    • Macronucleus: Big and kidney / bean-shaped

    • Micronucleus: Small and dot-like

• Treatment: Doxycycline

Flagellates and hemoflagellates

Giardia and trichomonas are flagellates .others are hemoflagellates.

Flagellates

Flagellates: Giardia Lamblia

• Epidemiology: Most common parasitic infection globally (detected in stool)

• Transmission & Dose: Fecal-oral route via Cyst; low infective dose

• Habitat: Duodenum

• Clinical Features: Malabsorption syndrome and steatorrhea (foul-smelling, fatty diarrhea)

• Morphology:

  • Trophozoite (T): Pear / tennis racket-shaped; contains 2 nuclei and 4 pairs (8) of flagella

  • Cyst (C): Oval; contains 1 to 4 nuclei

• Motility: Characteristic falling-leaf motility

• Diagnostics:

  • Stool examination across 3 days

  • String Test / Entero-Test: Samples duodenal contents

  • Duodenal biopsy shows luminal trophozoites

• Treatment: Metronidazole or Tinidazole (2 g single dose)

Flagellates: Trichomonas Vaginalis

• Epidemiology: Most common non-viral STI and cause of non-gonococcal urethritis (NGU)

• Transmission & Reservoir: Sexually transmitted; reservoir is females

• Clinical Presentation:

  • Strawberry cervix ("angry looking" punctate hemorrhagic cervix)

  • Frothy, greenish vaginal discharge

• Morphology & Diagnostics:

  • No cyst stage; exists only as Trophozoite (both infective and diagnostic stage)

  • 1 nucleus and 5 flagella (4 anterior + 1 posterior along the undulating membrane)

  • Motility: Twitching motility

• Culture Media:

  • Lash cysteine hydrolysate serum

  • Diamond's medium

• Treatment: Metronidazole (Must treat partner simultaneously)

Hemoflagellates

Hemoflagellates: Morphological Stages

• Amastigote (A): Round/oval; Absent flagella; intracellular stage.

• Promastigote (P): Flagella at anterior end; kinetoplast anterior to nucleus.

• Epimastigote (E): Kinetoplast close to and anterior to nucleus.

• Trypomastigote (T): Post-nuclear (posterior) kinetoplast; undulating membrane runs full length.

Overview of Hemoflagellate Species & Vectors

• Trypanosoma brucei: Caused by Tse-tse fly vector \rightarrow Sleeping Sickness.

• Trypanosoma cruzi: Caused by Reduviid / Triatomine bug (Kissing bug; nocturnal) \rightarrow Chagas Disease.

• Leishmania: Caused by Sandfly vector.

Trypanosoma cruzei

Trypanosoma Cruzi (Chagas Disease / South American Sleeping Sickness)

• Vector: Triatomine / Reduviid Bug ("Kissing Bug")

• Acute Chagas Disease:

  • Romana Sign: Unilateral orbital edema (painless eyelid swelling)

• Chronic Chagas Disease:

  • Mega-esophagus (leads to Achalasia cardia)

  • Mega-colon

  • Dilated Cardiomyopathy

• Diagnosis:

  • Blood Sample: Shows C-shaped Trypomastigotes

  • Culture: NNN Media

• Treatment: Benznidazole

Trypanosoma brusei

Trypanosoma Brucei Subspecies Comparison

Feature	Trypanosoma brucei gambiense	Trypanosoma brucei rhodesiense
Disease Name	West African Sleeping Sickness	East African Sleeping Sickness
Vector	Tse-tse fly	Tse-tse fly
Primary Reservoir	Humans	Animals
Clinical Features	Winterbottom Sign positive (Posterior cervical lymphadenopathy)	Rapidly progressive illness
Severity / Parasitemia	Lower parasitemia & virulence	Higher parasitemia, virulence, and resistance
Treatment	Pentamidine	Early stage: Suramine Late stage (CNS involvement): Melarsoprol

Leshmania donovani

Leishmania Donovani (Kala-Azar / Visceral Leishmaniasis)

• Endemic Regions: Common history of travel/residence in Bihar, Jharkhand

• Vector: Sandfly

• Parasite Stages:

  • Infective Form: Promastigote

  • Diagnostic Form: Amastigote (L.D. Bodies seen inside macrophages; contains nucleus + kinetoplast)

• Clinical Features:

  • Hyperpigmentation of skin (hence "Black Fever")

  • Hepatosplenomegaly (HSM): Massive splenomegaly (Differential Diagnosis: CML, HCL)

• Diagnostic Samples:

  • Spleen Aspirate: Most sensitive

  • Bone Marrow (BM) Aspirate: Most preferred

  • Blood & BAL: In HIV-positive patients

• Diagnostic Tests:

  • Hypergammaglobulinemia (\uparrow Ig): Elicited via Napier's Aldehyde test and Chopra's Antimony test

  • Culture: NNN Media (detects Promastigote stage) — Note: NNN media is used for T. cruzi and Kala-azar

  • Rapid Card Test: rK39 Antigen test

  • PCR: Target DNA for nucleus and kinetoplast

• Treatment: Liposomal Amphotericin B (LAMB)

Post-Kala-Azar Dermal Leishmaniasis (PKDL)

• Presentation: Hypopigmented skin lesions following visceral leishmaniasis treatment

• Treatment: Oral Miltefosine

Other leshmania species

Other Leishmania Species & Clinical Conditions

• Leishmania tropica:

  • Disease: Cutaneous Leishmaniasis

  • Synonyms: Oriental sore, Delhi boil, Aleppo button

• Leishmania braziliensis:

  • Disease: Espundia (Mucocutaneous Leishmaniasis)

• Leishmaniasis Recidivans:

  • Etiology: Occurs due to inadequate or incomplete treatment

  • Presentation: Nodular lesions or active rash forming around a central healed scar

Sporozoa /. Coccidean parasites include

• Plasmodium spp.

• Toxoplasma gondii

• Cryptosporidium parvum

• Cystoisospora belli

• Cyclospora cayetanensis

• Babesia spp.

Toxoplasma gonidii

Toxoplasma Gondii (Coccidean Parasite)

• Definitive Host: Cat / Feline family

• Intermediate Host: Animals (Humans act as accidental hosts)

• Modes of Transmission:

  • Sporulated Oocyst: Ingestion of food, water, or soil contaminated with old cat feces

  • Bradyzoites: Consumption of undercooked meat containing tissue cysts / organ transplantation

  • Tachyzoites: Transfusion of contaminated blood or Mother-To-Child (MTC) transplacental transmission

Clinical Presentations

• Adult Toxoplasmosis: Typically asymptomatic; may present with Lymphadenopathy (LAP)

• HIV / Immunocompromised: Toxoplasma Encephalitis (presents with ring-enhancing lesions on neuroimaging)

• Congenital Toxoplasmosis: Transplacental transmission (MTC)

  • 1st Trimester Transmission: More severe clinical manifestations

  • 3rd Trimester Transmission: More common occurrence

  • Classical Features:

    • C - Chorioretinitis

    • C - Cerebral calcification (intracranial)

    • C - Convulsions

    • M - Microcephaly / Hydrocephalus

    • M - Mental retardation

Differential Diagnosis: Intracranial Calcification Patterns

• Diffuse Cerebral Calcification: Toxoplasma gondii

• Periventricular Calcification: Cytomegalovirus (CMV) (Associated with Microcephaly, MR, SNHL, Chorioretinitis)

• Grey Matter-White Matter (GM-WM) Junction Calcification: Zika Virus

Diagnosis & Management

• Gold Standard Diagnostic Test: Sabin-Feldman Dye Test (detects IgM and IgG antibodies)

• Treatment: Pyrimethamine + Sulfadiazine

Cryptosporidium vs cyclospora vs cystoisospora

Coccidian Parasites Causing Diarrhea in HIV+ / Immunocompromised Hosts

Oocyst Morphology & Structure

• Cryptosporidium: Oocyst contains 4 naked sporozoites (no sporocysts).

• Cyclospora: Oocyst contains 2 sporocysts, with each sporocyst holding 2 sporozoites (Total = 4 sporozoites).

  • Clinical Association: History of consuming contaminated raspberries or imported produce.

• Cystoisospora (Isospora): Oocyst contains 2 sporocysts, with each sporocyst holding 4 sporozoites (Total = 8 sporozoites).

• Biopsy Finding (Cryptosporidium): Organisms lie along the brush border inside a parasitophorous vacuole (intracellular but extracytoplasmic).

Comparison of Intestinal Coccidian Parasites

Feature	Cryptosporidium	Cyclospora	Cystoisospora
Oocyst Size	4 - 6 micron	8 - 12 micron	24 - 36 micron
Shape	Spherical / Round	Spherical / Round	Elliptical / Oval
Acid-Fast Stain (Cold ZN / Kinyoun)	Positive (+) (Uniformly staining)	Variable (\pm) (Cyclical / "Ghost" oocysts)	Positive (+) (Uniformly staining)
Autofluorescence (UV Fluorescence Microscopy)	Negative (-)	Positive (+)	Positive (+)
Treatment	Nitazoxanide	Co-trimoxazole (TMP-SMX)	Co-trimoxazole (TMP-SMX)

Plasmodium species

Hematozoa: Malaria (Plasmodium Species)

Life Cycle & Host Characteristics

• Definitive Host: Female Anopheles Mosquito (FAM) -site of sexual cycle / sporogony.

• Intermediate Host: Humans - site of asexual cycle / schizogony.

• Infective Form to Humans: Sporozoites transmitted via mosquito saliva.

  • Note: Trophozoites are the infective form in blood transfusions or Mother-to-Child (MTC) transmission. Blood transfusion malaria lacks a liver phase, so no relapse occurs.

• Infective Form to Mosquito: Gametocytes (>12 gametocytes/microlitre)

• Hypnozoite Phase: Dormant liver stage seen in P. vivax and P. ovale that leads to Relapse.

Clinical Presentations & Immunity

• Benign Malaria Paroxysm: Cold phase (chills) →Hot phase (fever) → Sweating phase (fever drops).

• Malignant Malaria (P. falciparum):

  • Cerebral Malaria: Marked by Duruk granulomas in the brain.

  • Blackwater Fever: Massive intravascular hemolysis → hemoglobinuria.

  • Algid Malaria: Severe shock / circulatory collapse.

• Genetic Protection:

  • Sickle cell trait,

  • Thalassemia trait,

  • G6PD deficiency, and

  • Duffy-negative RBCs (Duffy antigen serves as receptor for P. vivax).

Plasmodium Species Comparison

Feature	Plasmodium vivax	Plasmodium falciparum	Plasmodium malariae	Plasmodium ovale
Recurrence Mechanism	Relapse (Reactivation of hypnozoites)	Recrudescence (Inadequate therapy)	Recrudescence (Inadequate therapy)	Relapse (Reactivation of hypnozoites)
RBC Stippling	Schuffner's dots	Maurer's clefts	Ziemann's dots	James' dots
Trophozoite Ring	Single ring with 1 chromatin dot	Multiple rings, Accole / Applique forms (peripheral margin)	Compact / Band forms across RBC	Oval RBCs with fimbriated edges
Schizonts in Peripheral Blood	Present	Absent (Sequestrated in cerebral microvasculature via ICAM-1)	Present	Present
Gametocyte Shape	Oval / Round	Banana / Crescent-shaped	Oval / Round	Oval / Round

Laboratory Diagnosis of Malaria

• Light Microscopy (Gold Standard):

  • JSB Stain used. Pigment produced: Hemazoin pigment.

  • Thick Smear: Used for quantification (Sensitivity: 5\text{ parasites/}\mu\text{L}).

  • Thin Smear: Used for species identification (Sensitivity: 200\text{ parasites/}\mu\text{L}).

  • Examine 200-300 oil immersion fields before ruling negative.

• Fluorescent Microscopy: Kawamoto technique using Acridine Orange dye.

• Quantitative Buffy Coat (QBC): Centrifuged capillary tube coated with acridine orange.

• Rapid Diagnostic Tests (RDT): Immunochromatography on nitrocellulose membranes.

  • Pan-Malaria Antigens: Aldolase, LDH.

  • P. falciparum Specific: HRP-2 Antigen.

Plasmodium Knowlesi

• Plasmodium knowlesi: Zoonotic malaria common in Malaysia, transmitted from monkey reservoirs.

Babesia microti

• Babesia microti:

  • Vector: Hard tick / Ixodid tick (Ixodes).

  • Clinical Features: Fever and chills.

  • Microscopy: Intraerythrocytic tetrad forms arranged as a "Maltese Cross".

  • Treatment: Azithromycin + Atovaquone.