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Protozoans - Hemo flagellates

  • Key Genera
    • Trypanosoma species
    • Leishmania spp.
Morphologic Forms of Trypanosoma
  • Amastigote (Leishmanial form)
  • Promastigote (Leptomonad)
  • Epimastigote (Crithidia)
  • Trypomastigote (Trypanosomal)

Trypanosoma spp.

Trypanosoma cruzi
  • Common Name: American trypanosomes
  • Disease: Causes Chaga's disease
Trypanosoma brucei complex
  • Common Name: African trypanosomes
  • Disease: Causes Sleeping sickness
    • T. brucei rhodesiense: East African Sleeping sickness
    • T. brucei gambiense: West African Sleeping sickness
Diagnostic Procedure
  • Blood smear used to identify infection
Vectors
  • American Trypanosomes
    • Vectored by the Reduviid bug (Triatomine), also known as Kissing bug
  • African Trypanosomes
    • Vectored by Tsetse fly (Glossina)
Lifecycle
  • Metacyclic trypanosomes passed out with the feces of the bug invade muscle in American Trypanosomes.
  • Metacyclic trypomastigote passed out through salivary glands invading CNS in African Trypanosomes.

Pathology

Trypanosoma cruzi (Chaga's disease)
  • Romana Sign: Unilateral swelling of the eye
  • Cardiomegaly
  • Megadisease: Enlargement of organs
  • Chagoma: Nodule at bite site
Trypanosoma brucei complex
  • Winterbottom Sign: Enlargement of lymph nodes
  • Chancre: At the bite site
  • Nagana disease: Affects animals
  • Kerandell sign

Lab Diagnosis

  • For T. cruzi
    • Amastigote found in tissue scraping
    • Xenodiagnosis: Trypanosome detection via vectors
    • Finding Leishman-Donovan bodies in heart at autopsy
    • Trypomastigote found in blood: C-shaped, thick organism with prominent kinetoplast.
Treatment
  • African Sleeping Sickness: Pentamidine, Suramin, Melarsoprol (for late-stage with CNS involvement)
  • Chagas Disease: Nifurtimox, Bezuidazole, Eflornithine (resurrection drug)

Leishmania spp.

Transmission
  • All species transmitted by the sandfly (Phlebotomus spp.)
Morphological Forms
  • Amastigote form: Observed in humans
  • Promastigote form: Found in the gut of the sandfly
Diseases
  • L. tropica: Oriental sore or Old World cutaneous leishmaniasis
  • L. mexicana: Chiclero's ulcer or New World cutaneous leishmaniasis
  • L. braziliensis: Espundia or mucocutaneous leishmaniasis
  • L. donovani: Kala-azar or visceral leishmaniasis (black fever)
Diagnosis
  • Blood smear, needle aspiration, punch/wedge biopsy
  • Culture: Novy-McNeal-Nicolle (NNN)
  • Intrademal test: Dr. Montenegro Skin Test.

Apicomplexan

  • Characteristics
    • No locomotor organelles
    • Structural features include micronemes, subpellicular tubules, polar ribs, conoids, rhoptries.
  • Complex life cycle stages: Sporogony, gamogony, schizogony.
Coccidians
  • Includes Plasmodium spp., Babesia spp., Toxoplasma gondii.
Plasmodium spp.
  • Infections: Most common cause of malaria.
Lifecycle Details
  • Spends part of its life cycle in mosquitoes, infects and ruptures blood cells.
  • Main stages include schizogony (asexual reproduction), gamogony (gamete formation), and sporogony (sexual reproduction).

Malaria Overview

  • Common Terms: Defined as "bad air."
Host Information
  • Definitive Host: Anopheles mosquitoes
  • Intermediate Host: Humans
Vectors in the Philippines
  • Anopheles minimus var. flavirostris is principal malaria vector.
Plasmodium species and their characteristics
  • P. falciparum: Most frequent; causing malignant tertian malaria, 48h cycle.
  • P. vivax: Benign tertian malaria, 48h cycle.
  • P. malariae: Quartan malaria, 72h cycle.
  • P. ovale: Exclusive rare, benign tertian malaria, 48h cycle.
  • P. knowlesi: Simian malaria parasite; isolated from humans since 1965.

Symptoms of Malaria

  • Cold Stage: Feeling of intense cold, vigorous shivering, lasts 15-60 minutes.
  • Hot Stage: Intense heat, dry skin, lasts 2-6 hours.
  • Sweating Stage: Profuse sweating, exhausted, lasts 2-4 hours.

Plasmodium falciparum

  • Associated with "Black water fever" due to hemoglobin excreted in urine.
Diagnostic Features
  1. Trophozoite stage
  2. Schizont stage
  3. Gametocyte stage
Features of Plasmodium spp.
  • Characteristics such as vacuoles, nuclei/chromatin dots, and cytoplasm are key identification markers.

Plasmodium knowlesi

  • Found primarily in long-tailed monkeys, also infects humans as the fifth malaria parasite.
  • Diagnostically similar to P. malariae but with a rapid 24-hour erythrocytic cycle.
  • Confirmed through PCR analysis; often misreported as P. malariae.

Parasite Counting in Diagnostics

  • Key for determining parasitological severity and monitoring treatment responses.
Methods of Counting
  • Thick Film: Recommended cross-sectional method; count parasites after observing 200 WBCs; results = Number of parasites x 8000/200 WBCs.
  • Example Counting: 115 rings/trophozoites x 8000/200 WBCS = 4,600/µL blood.

Laboratory Diagnosis of Malaria

  • Thick smear: Gold standard for detecting parasites.
  • Thin smear: Used for species identification post thick-film detection.

Babesia spp.

Babesia microti
  • Infects RBC; closely related to Plasmodium falciparum causing non-Tufted fever/Babesiosis.
  • Transmitted mainly by ticks (Isodes scapularis).
Diagnostic Features
  • Recognized by "Tetrad formation" and "Maltese cross".
Other Babesia spp.
  • Babesia canis: Infectious jaundice in dogs.
  • Babesia bigemina: Red water syndrome in carabaos.

Toxoplasma gondii

  • Host Information: Cats are definitive hosts, others like cattle, pigs, etc., act as intermediate hosts.
Infective Stage
  • Mature oocysts containing two sporocysts, each with four sporozoites.
Transmission Routes
  • Includes ingestion, blood transfusion, bone marrow transplantation, and transplacental.
Lifecycle in Humans
  • Humans serve as intermediate hosts; tachyzoites are rapidly formed in tissues and can cause serious health issues during pregnancy.

Other Coccidians

  • Isospora belli and Cryptosporidium parvum: Notable causes of diarrhea.
    • Identification methods include sugar concentration and other specialized techniques.
    • Cyclospora cayetanensis: Characterized by round, fluorescent structures.