Veterinary Protozoology Study Notes

Introduction to Protozoa

• Definition: Protozoa is derived from the Greek words proto (meaning first) and zoa (meaning animals).
• Biological Status: They are single-celled eukaryotic organisms.
• Basic Functionality: Unicellular organisms capable of performing all the essential functions of life independently.
• Composition: A protozoon consists of a mass of protoplasm, including the endoplasm.

Nuclear Morphology in Protozoa

Protozoa exhibit various types and numbers of nuclei to perform genetic and regulatory functions:

• Vesicular: Characterized by a visible membrane and scattered chromatin (e.g., Entameba).
• Compact: Dense chromatin with a lack of visible interior structure (e.g., Balantidium).
• Single Nucleus: Possession of only one nucleus (e.g., Trichomonas).
• Double Nuclei: Possession of two nuclei (e.g., Giardia, Balantidium).
• Several Nuclei: Found in specific life stages, such as the cyst stage of Entameba.

Locomotion Mechanisms of Protozoa

There are four primary types of locomotive organs/methods categorized in protozoology:

• Pseudopodia: Temporary cytoplasmic projections used for movement and feeding, characteristic of the Entamoeba trophozoite.
• Flagella: Whip-like structures found in Flagellates, including Trypanosoma, Trichomonas, and Giardia.
• Cilia: Hair-like projections covering the body surface, characteristic of Balantidium.
• Gliding and Twisting: Movement without specialized external appendages, seen in Toxoplasma and Sarcocystis.
• Absence of Locomotion: No active movement organs in certain stages or species, such as Plasmodium.

Nutrition and Excretion in Parasitic Protozoa

Nutritional Modes

1. Holozoic: Utilize preformed food derived from living animals or plants. Food is ingested through either a permanent opening called a cytostome or a temporary opening in the body wall. Ciliates often use pseudopodia or cilia surrounding the cytostome to engulf food and utilize food vacuoles for digestion. Some, like amoebas, ingest host tissue cells.
2. Saprozoic: Absorb nutrients through the body wall via diffusion, utilizing the nutrients directly.
3. Holophytic: Synthesize carbohydrates using chlorophyll. None of these types are parasitic.
4. Autotrophic: Live on organic compounds where proteins, carbohydrates, and lipids are synthesized from other organic compounds.

Excretion Processes

Protozoa excrete waste products through two primary methods:

• Diffusion through the body wall.
• Via the contractile vacuole.

Reproductive Strategies of Protozoa

Asexual Reproduction

All protozoa reproduce asexually. Methods include:

• Binary Fission: A rapid reproductive process where a single organism divides by mitotic division into two identical individuals (clones).
• Multiple Fission (Schizogony): Division into many individuals at once.
• Endodiogeny: A process of internal budding.

Sexual Reproduction

Some protozoa utilize sexual reproduction to exchange genetic material or create resistant stages:

• Gametogony: Two sex cells meet for fertilization. One is male (microgamete) and the other is female (macrogamete). They fuse to form a Zygote, which may be motile or non-motile (Example: Plasmodium, Eimeria).
• Conjugation: Opposite mating strains pair up and exchange genetic DNA. This is seen in Balantidium and Paramecia. The process involves micronuclei dividing by mitosis, transferring between the pair, and fusing before the individuals separate.
• Sporogony: A stage of asexual/sexual development involving spore formation.

Advanced Taxonomy and Subkingdom Protozoa

• Subkingdom: Protozoa (Unicellular, eukaryotic animals).
• Phylum: Sarcomartigophora (Locomotion by pseudopodia and/or flagella).
• Subphylum: Mastigophora.
• Class: Zoomastigophorasida.
• Orders:
  • Kinetoplastorida: Includes Trypanosomes.
  • Diplomonadoridia: Includes Hexamita and Giardia.
  • Trichomonadoridia: Includes Trichomonas.
  • Reteromonadoridia.

Characteristics of Family Trypanosomatidae (Hemoflagellates)

• General Appearance: Typically leaf-like or flat-blade like.
• Structure: Single nucleus (elongate or rounded), nucleus membrane, nucleolus, blepharoplast (basal granule), kinetoplast, and a protruding or non-protruding flagellum.
• Kinetoplast: A specialized DNA-containing organelle located near the flagellar base.

Developmental Stages of Trypanosomatids

1. Promastigote (Leptomonas form): Elongated form; kinetoplast is anterior to the nucleus (antenuclear); flagellum emerges from the anterior end. Found in arthropod hosts.
2. Epimastigote (Crithidial form): Elongated form; kinetoplast is juxtanuclear (near the nucleus); flagellum emerges from the side of the body to run along a short undulating membrane. Found in both arthropod and vertebrate hosts.
3. Trypomastigote: The "true" trypanosome stage. Kinetoplast is postnuclear; flagellum runs along a long undulating membrane. This is the infective stage (metacyclic form) in vertebrates and arthropods.
4. Amastigote (Leishmanial form): Rounded or oval; lacks an external flagellum, possessing only a short internal axoneme.

Genus Trypanosoma: Biology and Groups

• Life Cycle: Usually heteroxenous (requires both an invertebrate and vertebrate host).
• Habitat: Found in blood and tissue fluids of vertebrate hosts; T. cruzi is intracellular. Found in the digestive tracts of invertebrates (arthropods).
• Transmission: All are transmitted by blood-sucking arthropods except Trypanosoma equiperdum.

Classifications of Trypanosomes

• Salivaria (Anterior Station): Develop in the anterior part of the insect vector's digestive tract. New hosts are infected via insect bites.
• Stercoraria (Posterior Station): Develop in the hindgut of the insect vector. Parasites leave with feces and infect new hosts via mucosal membranes or skin lesions made by bites.

Salivaria Groups

• Group 1 (evansi group): T. evansi, T. equinum, T. equiperdium.
• Group 2 (vivax group): T. vivax, T. caprae, T. uniforme.
• Group 3 (congolense group): T. congolense, T. simiae.
• Group 4 (brucei group): T. brucei, T. gambiense, T. rhodesiense.

Stercoraria Groups

• Group 5 (cruzi group): T. cruzi, T. lewisi, T. theileri, T. melophagum.

Pathogenic Trypanosomes of Veterinary and Medical Importance

Trypanosoma evansi

• Diseases: Surra (all hosts); El-Dabab (camels).
• Hosts: Equines, camels, buffaloes, dogs.
• Transmission: Mechanical by biting flies (Tabanus, Stomoxys). No cyclic development in the vector.
• Morphology: Monomorphic (sometimes polymorphic), slender, $15-34\,\mu m$ long, rounded posterior, subterminal kinetoplast, well-developed undulating membrane, long free flagellum.
• Pathogenesis: Progressive anemia, emaciation, high temperature, abortion in camels, testicular degeneration in males.
• Diagnosis: Microscopy (buffy coat), Card Agglutination Trypanosomiasis Test (CATT), Mercuric chloride test, Formol gel test, NNN medium culture.
• Treatment: Suramine, Quinapyramine, Diminazene, Isometamidium.

Trypanosoma equinum

• Disease: Mal de Caderas.
• Distribution: Central and South America.
• Hosts: Horses (highly susceptible), mules, donkeys, cattle, sheep.
• Morphology: Monomorphic, $25\,\mu m$ long, lacks a kinetoplast, long free flagellum.
• Pathogenesis: Incubation period of 1 week; causes posterior paresis (hind quarter paralysis), splenomegaly, and high mortality (death in 2-6 months).

Trypanosoma equiperdium

• Disease: Dourine (meaning "unclean").
• Transmission: Mechanical through coitus (sexual intercourse).
• Morphology: Similar to T. evansi; slender form, $25\,\mu m$ long.
• Pathogenesis Phases:
  • Phase I (Oedema phase): Oedematous genitalia and mucoid discharge.
  • Phase II (Plaque phase): Circular silver-colored urticarial plaques ("dollar spots") measuring $2-3\,cm$ on the flank.
  • Phase III (Paralysis phase): Gradual facial and body paralysis leading to death.

Trypanosoma vivax

• Disease: Souma.
• Host: Cattle, sheep, goat, horse.
• Transmission: Biological by Glossina (Tsetse fly). Development occurs in the proboscis (labial cavity) only.
• Morphology: Monomorphic, $20-27\,\mu m$ long, large terminal kinetoplast, short free flagellum.

Trypanosoma congolense

• Disease: Nagana.
• Host: Cattle (most important), equines, sheep, goat.
• Transmission: Biological by Glossina. Development in the midgut and proboscis (not salivary glands).
• Morphology: Monomorphic, $8-20\,\mu m$ long, lacks or has a very short free flagellum.
• Pathogenesis: Acute fatal disease in cattle (death in 10 weeks); signs include emaciation, congested liver, and splenomegaly.

Trypanosoma brucei Complex

• Species: T. brucei (animals); T. rhodesiense and T. gambiense (man).
• Vector: Tsetse fly (Glossina).
• T. brucei Morphology (Polymorphic):
  • Long slender form: $25-35\,\mu m$.
  • Intermediate form: $23\,\mu m$.
  • Short stumpy form: $15\,\mu m$ without flagellum.
• Diseases:
  • Animal Trypanosomiasis (T. brucei): Acute in horses/dogs (death in 2 weeks); anemia and edema.
  • African Sleeping Sickness (T. rhodesiense & T. gambiense): T. gambiense is chronic (West Africa); T. rhodesiense is acute (East Africa). Pathogenesis includes chancre sores at bite sites, Winterbottom's sign (swollen lymph nodes), and eventually coma.

Trypanosoma cruzi

• Disease: Chagas’ Disease (American Trypanosomiasis).
• Vector: Triatomine bug (Kissing bug).
• Transmission: Parasites in bug feces are rubbed into the bite wound or mucous membranes.
• Morphology: Monomorphic, $16-20\,\mu m$ long, crescent (C-shaped), large subterminal kinetoplast.
• Pathogenesis:
  • Chagoma: Swelling at the site of invasion.
  • Romana’s sign: Unilateral eyelid edema and conjunctivitis.
  • Chronic Stage: Heart damage (myocardial) and gastrointestinal problems (megacolon).
• Diagnosis: Xenodiagnosis, Agglutination tests.

Genus Leishmania

• Diseases: Leishmaniasis (Cutaneous or Visceral).
• Vector: Sand fly (Phlebotomus spp.).
• Life Cycle: Promastigotes are injected into skin by sand fly. They are engulfed by macrophages and transform into amastigotes, which multiply and rupture the host cells.

Leishmania Species and Pathogenesis

1. L. tropica and L. major: Cause Cutaneous Leishmaniasis (Oriental sores/ulcers). Endemic to the Middle East, West-central Africa, and India.
2. L. donovani: Cause Visceral Leishmaniasis (Kala-azar or Dum-dum fever). Infects the reticulo-endothelial system (spleen, liver, bone marrow). Symptoms include fever, chills, anemia, leukopenia, and enlargement of the spleen and liver (hyperplasia).