Detailed Notes on Protozoan Parasites and Related Diseases

Phylum of Sporozoa

  • Plasmodium spp.
  • Babesia
  • Toxoplasma gondii

Phylum of Sarcomastigophora

  • Class Flagellates:
    • Leishmania spp.
    • Trypanosoma spp.
  • Class Amoeba:
    • Naegleria fowleri
    • Acanthamoeba spp.

Plasmodium Species

  • Sporozoan parasites of blood cells, causing malaria.
  • Human-infecting species:
    • Plasmodium vivax
    • Plasmodium ovale
    • Plasmodium malariae
    • Plasmodium falciparum (most severe)
    • Plasmodium knowlesi (rare)

Transmission and Lifecycle

  • Vector:
    • Female Anopheles gambiae mosquito
  • Lifecycle Overview:
    • Sporozoites injected → invade liver cells → form merozoites → invade red blood cells (RBC) → develop into ring trophozoite → divide into schizonts and merozoites
    • Duration:
    • Cycle leading to clinical symptoms takes 43-48 hours.

Clinical Symptoms

Mild Malaria Symptoms:

  • Non-specific, flu-like symptoms, including:
    • Chills
    • Headache
    • Back and joint pain
    • Gastrointestinal symptoms (nausea, vomiting)
    • Fatigue

Acute Malaria Symptoms:

  • Intensification leading to:
    • Irregular high fever
    • Anxiety and delirium
    • Severe exhaustion
    • Enlarged spleen (splenomegaly) and liver
    • Anemia

Severe Symptoms (mainly P. falciparum):

  • Cerebral malaria: diminished consciousness, seizures
  • Renal failure and hepatic dysfunction
  • Blackwater malaria: hemoglobinuria, increased risk of death (especially in pregnant women and children < 5 years)

Laboratory Diagnosis

  • Diagnostic Features:
    • Thick or thin blood film
    • Infected RBCs enlarged with pink granules (Schuffner’s dots)
    • Trophozoite appears ring-shaped
    • Schizonts can contain up to 24 merozoites

Specific Species Diagnosis:

  • Plasmodium vivax:
    • Incubation: 10-17 days; symptoms every 48 hours (benign tertian malaria)
  • Plasmodium malariae:
    • Longest incubation (18-40 days); fever every 72 hours (quartan malaria)
    • Complication: nephrotic syndrome

Treatment of Malaria

  • Combination of supportive measures and chemotherapy
  • Chemotherapeutic regimens:
    • Suppressive: Aims to avoid infection
    • Therapeutic: Eradicating erythrocytic cycle
    • Radical cure: Aiming to eradicate exoerythrocytic cycle in the liver
  • Common drugs used:
    • Chloroquine (resistance concerns)
    • Quinine sulfate
    • Mefloquine
    • Artimisinin derivatives
    • Primoquine for dormant liver forms

Babesia Species

  • Intracellular sporozoan, primarily zoonotic (reservoirs: animals)
  • Transmission: Via ixodid ticks (e.g., ixodes dammini)
  • Symptoms include:
    • Often mild with fever
    • Severe infections in splenectomied or immunocompromised patients
  • Lab Diagnosis: Blood smear showing parasites

Toxoplasma gondii

  • Intracellular parasite commonly seen in warm-blooded animals
  • Transmission: Exposure to sporulated oocysts, undercooked meat
  • Clinical Features:
    • Asymptomatic or mild symptoms
    • Severe in immunocompromised patients (e.g., AIDS)
  • Prevention: Proper food handling, avoiding cat feces

Leishmania

  • Vector-borne disease transmitted by sandflies.
  • Clinical Diseases:
    • Visceral Leishmaniasis (L. donovani)
    • Cutaneous Leishmaniasis (L. tropica)
    • Mucocutaneous Leishmaniasis (L. braziliensis)
  • Diagnosis: Amastigote stage observed in biopsies or cultures; serology
  • Treatment: Stibogluconate and protective measures against sandflies

Trypanosomes (Sleeping Sickness)

  • Diseases:
    • African trypanosomiasis (Trypanosoma brucei) transmitted by tsetse flies
    • Chagas disease (Trypanosoma cruzi) transmitted by kissing bugs
  • Clinical Symptoms: Variable; including CNS involvement, fever, potentially fatal without treatment
  • Lab Diagnosis: Blood films, serology, PCR, treatment with suramin and pentamidine

Free-Living Amebae

  • Naegleria fowleri: Causes PAM, infects via nasal passages
    • Symptoms: Rapid onset headache, fever, stiff neck
    • Lab Diagnosis: Trophozoites in CSF
  • Acanthamoeba spp.: Keratitis and potentially fatal CNS infections
    • Lab Diagnosis: Cysts and trophozoites in tissues