Blood and Tissue Protozoa

Malaria - Mosquito's Deadly Gift

• Causative Agents: Plasmodium spp. (P. vivax, P. falciparum, P. malariae, P. ovale, P. knowlesi).
• Vector: Female Anopheles mosquito.
• Key Life Cycle Stages:
  • Sporozoites (infective to humans) → Liver schizogony.
  • Merozoites → Infect RBCs (erythrocytic schizogony).
  • Gametocytes (infective to mosquitoes).
  • P. vivax/ovale: Hypnozoites in liver cause relapses.
• Clinical Features: Periodic fever paroxysms (chills, rigor, fever, sweats), anemia, splenomegaly.
  • P. falciparum: Severe malaria (cerebral malaria, blackwater fever, ARDS, hypoglycemia). Irregular fever.
• Diagnosis:
  • Peripheral Smear (Giemsa): Ring forms, gametocytes.
    • P. falciparum: Multiple rings/RBC, appliqué forms, crescentic gametocytes, Maurer's dots.
    • P. vivax/ovale: Schüffner's dots.
  • Rapid Diagnostic Tests (RDTs): Detect HRP-2 (P. falciparum specific), pLDH (pan-Plasmodium).
• 
• ⭐ > Blackwater fever, a severe complication of P. falciparum malaria, is characterized by intravascular hemolysis, hemoglobinuria, and renal failure.

Trypanosomes - Sleep & Heart Wreckers

• Flagellated protozoa: Cause African Trypanosomiasis (Sleeping Sickness) & American Trypanosomiasis (Chagas Disease).

African Trypanosomiasis (Trypanosoma brucei)

• Vector: Tsetse fly.
• Forms:
  • T.b. gambiense (West African): Chronic; Winterbottom's sign (posterior cervical lymphadenopathy).
  • T.b. rhodesiense (East African): Acute.
• Stages: Hemolymphatic (fever, chancre) → CNS invasion (somnolence, coma).
• Rx: Suramin/Pentamidine (early); Melarsoprol/Eflornithine (late). 📌 Mnemonic: "SuPe MEla" (Suramin, Pentamidine, Melarsoprol, Eflornithine).

American Trypanosomiasis (Trypanosoma cruzi - Chagas Disease)

• Vector: Reduviid (kissing) bug.
• Acute: Chagoma (local inflammation), Romaña's sign (unilateral palpebral edema).
• Chronic: Cardiomyopathy (apical aneurysm, arrhythmias), megaesophagus, megacolon.
• Rx: Benznidazole, Nifurtimox.

⭐ T. cruzi amastigotes in cardiac muscle are a hallmark of chronic Chagas cardiomyopathy.

Leishmania - Sandfly's Skin & Spleen Saga

• Vector: Sandfly (Phlebotomus/Lutzomyia).
• Forms: Promastigote (infective, in sandfly); Amastigote (diagnostic, Leishman-Donovan/LD bodies, in human macrophages).
• Clinical Syndromes & Key Species:
  • Visceral Leishmaniasis (VL) / Kala-azar: L. donovani, L. infantum. Features: fever, massive splenomegaly, pancytopenia, weight loss. 📌 Kala Don!
  • Cutaneous Leishmaniasis (CL): L. tropica, L. major. Features: chronic, non-healing skin ulcers (e.g., Oriental Sore).
  • Mucocutaneous Leishmaniasis (MCL): L. braziliensis. Features: destructive lesions of nose, mouth, throat mucosa (Espundia).
• Diagnosis:
  • VL: LD bodies in bone marrow/spleen aspirate; rK39 antigen test.
  • CL/MCL: LD bodies in skin biopsy; Montenegro skin test (positive in CL/MCL, negative in active VL).
• Treatment: Amphotericin B (liposomal), Miltefosine, Pentavalent antimonials (e.g., Sodium Stibogluconate).

⭐ Hypergammaglobulinemia (polyclonal) is a characteristic feature of Visceral Leishmaniasis, often leading to a reversed albumin-globulin ratio.

Toxoplasma & Others - Stealthy Tissue Threats

• Toxoplasma gondii
  • Transmission: Cysts (undercooked meat), oocysts (cat feces).
  • Clinical:
    • Immunocompetent: Asymptomatic/mono-like illness.
    • Immunocompromised (AIDS): Encephalitis, chorioretinitis, multiple ring-enhancing brain lesions.
    • Congenital (TORCH): Classic triad of chorioretinitis, hydrocephalus, intracranial calcifications.
  • Dx: Serology (IgM, IgG), PCR. Brain biopsy: tachyzoites.
  • Rx: Pyrimethamine + Sulfadiazine + Leucovorin (folinic acid).
• Babesia microti
  • Vector: Ixodes tick (NE USA). Zoonotic (rodents, deer).
  • Clinical: Malaria-like symptoms (fever, chills, sweats, hemolytic anemia). Severe in asplenia, elderly.
  • Dx: Blood smear: intraerythrocytic ring forms, Maltese cross (tetrads). PCR.
  • Rx: Atovaquone + Azithromycin.
• Free-living Amoebae
  • Naegleria fowleri
    • Entry: Nasal inhalation (warm freshwater swimming).
    • Disease: Primary Amoebic Meningoencephalitis (PAM) - acute, fulminant, rapidly fatal.
    • Dx: Motile amoebae in CSF.
  • Acanthamoeba spp.
    • Entry: Corneal trauma (e.g., contact lenses), skin, inhalation.
    • Disease: Keratitis (severe eye pain, ring infiltrate), Granulomatous Amebic Encephalitis (GAE) in immunocompromised.
    • Dx: Cysts/trophozoites in corneal scraping/biopsy.

⭐ Toxoplasma gondii: In AIDS patients with CD4 < 100/µL, prophylaxis with TMP-SMX is given to prevent toxoplasmic encephalitis.

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High‑Yield Points - ⚡ Biggest Takeaways

• Malaria: P. falciparum causes severe malaria; crescentic gametocytes. P. vivax shows Schüffner's dots.
• Kala-azar (L. donovani): LD bodies in macrophages, PKDL, sandfly vector.
• Chagas disease (T. cruzi): Romana's sign, cardiomyopathy, megaesophagus, reduviid bug vector.
• Toxoplasmosis (T. gondii): Congenital triad; ring-enhancing brain lesions in AIDS; cat definitive host.
• Babesiosis: Maltese cross in RBCs; tick-borne; severe in asplenia.
• Naegleria fowleri: Rapidly fatal Primary Amoebic Meningoencephalitis (PAM) from freshwater exposure.