Veterinary Parasitology Study Notes

VETERINARY PARASITOLOGY

Introduction

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• Reproduction or transmission in any form requires written permission of the review center associated with College of Veterinary Science and Medicine, Central Luzon State University, Science City of Muñoz, Nueva Ecija 3120.

Protozoology

• A diverse collection of eukaryotic organisms characterized by:
  • Lack of tissue differentiation
  • Being single-celled
  • Independent movement
  • Free-living or parasitic existence
• Parasitic protozoa often have complex life cycles taking place in the cells, bloodstream, and tissues of hosts (can be invertebrates such as ticks and mosquitoes or vertebrates such as mammals and birds).
• A significant number of protozoa are zoonotic, indicating a low host specificity.

Differences between Prophyta and Protozoa

Eukaryotic Cells

• Eukaryotic cells feature a true nucleus housing DNA and RNA.

Components of the Cell

• Protoplasm = cytoplasm + nucleus
• Cytoplasm = ectoplasm + endoplasm
  • Cytoplasm contains:
  • Mitochondria: Acts as the powerhouse of the cell.
  • Ribosomes: Responsible for protein synthesis.
  • Golgi bodies: Collect dehydrated proteins.
  • Lysosomes: Contains enzymes for digestion.
  • Contractile vacuole: Regulates osmotic pressure and eliminates waste material.
  • Parts of the Cytoplasm:
  • Ectoplasm
    • Outer part, homogenous and hyaline appearance.
    • Functions include movement, food ingestion, excretion, respiration, and protection.
  • Endoplasm
    • Granular and pigmented.
    • Contains food vacuoles which play a role in nutrition.
• Nucleus Types:
  • Vesicular Nucleus: Chromatin concentrated in a single mass (karyosome or nucleolus).
  • Compact Nucleus: Chromatin evenly distributed diffusely.
  • Micronucleus: Involved in reproductive functions.
  • Macronucleus: Involved in vegetative functions.

Importance of Protozoa

• Essential for:
  • Obtaining food.
  • Reacting to physical and chemical stimuli.
  • Notably marked movement in flagellates and ciliates, while negligible in sporozoa except during certain life cycle stages.

Modes of Movement

• Gliding: Movement without locomotory organelle (e.g., certain kinds of protozoa).
• Pseudopodia: Utilizing false feet (example: Entamoeba).
• Flagella: Whip-like filamentous structure originating from a basal granule in the ectoplasm (examples include Trypanosomes and Trichomonas).
• Cilia: Short, fine structures used for movement (examples: Paramecium and Balantidium).
  • Undulipodia: A term encompassing flagella and cilia.

Nutrition Types of Protozoa

1. Holophytic: Not of veterinary importance; achieved through photosynthesis similar to plants.
2. Holozoic: Involves the use of pseudopodia or cytostome to ingest food, transferring it to a food vacuole.
   • Examples include:
     • Entamoeba: Uses temporary body openings to ingest tissue through pinocytosis.
     • Eimeria: Utilizes micropyle to ingest fluids/solids.
3. Saprozoic: Absorbs nutrients through diffusion directly used by the organism.
4. Autotrophic: This category primarily consists of photosynthetic organisms (like plants) which can synthesize proteins, carbohydrates, and lipids from inorganic sources.

• Parasitic protozoa: Primarily holozoic or saprozoic; none are autotrophic or holophytic.

Excretion in Protozoa

• Waste is expelled through:
  • Osmotic pressure and Diffusion.
  • Cytopyge opening, which serves as the organ for waste elimination.

Respiration in Protozoa

• Protozoa undergo aerobic respiration; some become facultative or obligate anaerobes, adapting to low oxygen environments (commonly found in the intestines of hosts).

Reproductive Modes of Protozoa

1. Sexual Reproduction
   • Involves male and female individuals.
   • Includes:
     • Conjugation: Seen in ciliates, where nuclear materials are exchanged, leading to regeneration of macronuclei.
     • Syngamy: Fusion of two gametes (microgamete and macrogamete), often leading to formation of a zygote followed by multiple fission.
     • Isogamy: Gametes are of similar size.
     • Anisogamy: Gametes differ in size.
2. Asexual Reproduction
   • Includes various forms such as:
     a) Binary Fission: Formation of two daughter cells from a single parent cell.
     b) Multiple Fission (Merogony, Schizogony): Nucleus divides several times before cytoplasmic division; important in amebas and Apicomplexa.
     c) External Budding: Creation of daughter forms from the parent cell with varying sizes.
     d) Internal Budding (Endopolygeny): Forming daughter cells within the parent that subsequently break off.
     e) Sporogony: A specialized type of multiple fission leading to formation of sporozoites within oocysts.

General Effects of Protozoa Infection

• Absorb host nutrients (example: Trypanosomes).
• Alter normal metabolism (example: Giardia causing nutrient malabsorption).
• Produce toxins (example: Sarcocystis with sarcocystin).
• Destroy blood cells and hematopoietic organs (example: Babesia).

Control Measures for Oral-Fecal Borne Protozoa

• Good sanitation practices.
• Improvement of personal hygiene.
• Effective sewage disposal practices.
• Preventing fecal contamination of food and water sources.

Classification of Subkingdom Protozoa

I. Phylum Sarcomastigophora

• 1. Subphylum Mastigophora: Characterized by the presence of one or more flagella.
• 2. Subphylum Sarcodina: Identified by the presence of pseudopodia.
  II. Phylum Apicomplexa: Recognized for producing spores and lacking locomotory organs.
  III. Phylum Microspora: Known for producing spores with polar filaments.
  IV. Phylum Myxozoa: Has amoeboid germinal elements within multicellular spores; exhibits multicellular trophozoites.
  V. Phylum Ciliophora: Distinguished by the presence of cilia.

Notable Orders and Families

• Order Trypanosomatida: Parasitic members living in blood or tissues of vertebrates at certain life cycle stages; absorb nutrients through their membranes (lacking phagocytosis).
  • Family Trypanosomatidae: Includes genera such as Leishmania and Trypanosoma.

Morphological Characteristics of Trypanosomatidae

• Amastigote: Characteristic of Leishmania - a spheroid form with a short flagellum.
• Promastigote: Elongated with a functional flagellum.
• Epimastigote: Located between the nucleus and the anterior end, with an undulating membrane.
• Trypanomastigote: Characterized by its flagellum running along the surface, found in a variety of Trypanosoma species.

Transmission of Trypanosomiasis

1. Cyclical: Biological vectors (arthropods) facilitate the transfer of parasites.
   • SALIVARIA: Parasites develop in and are transmitted by the saliva of the vector (anterior station).
   • STERCORARIA: Parasites develop in the hindgut and are transmitted through fecal contamination.
2. Noncyclical: Mechanical transmission facilitated by blood-sucking flies.
3. Coitus: Transmission via sexual reproduction.
4. Transplacental: Parasites can be passed from mother to offspring during gestation.
5. Ingestion: Infection can occur through consumption of animal tissues.

Specific Trypanosome Species and Associated Diseases

A. Salivaria Group

• Trypanosoma brucei
  • Disease: Nagana; affects livestock in Africa.
  • Transmitted by Glossina flies (tsetse flies). Pathology includes severe health effects in affected cattle.
• Trypanosoma brucei gambiense
  • Causes chronic sleeping sickness in humans.
  • Symptoms evolve through four progressive stages, leading to invasion of the central nervous system.
• Trypanosoma brucei rhodesiense: Similar to gambiense but generally manifests more acutely.
• Trypanosoma vivax: Causes “Souma”; primarily affects ruminants and produces significant morbidity.

B. Stercoraria Group

• Trypanosoma cruzi: Causes Chagas Disease; transmitted by Reduviid bugs.
  • Pathogen lifecycle includes stages of trypomastigotes, epimastigotes, and amastigotes affecting various tissue types.

General Pathogenic Effects of Trypanosomes

1. Tissue invasion leads to anemia.
2. Blood changes include destruction of RBC and hypoglycemia.
3. Death can occur due to hypoglycemia and related complications.

Immunity and Treatment of Trypanosomes

• Antigenic Variance: Allows tryansomes to evade host immunity, complicating treatment through persistent infections.

• Treatment options include:

  • Suramin: Utilized for various trypanosomiasis cases.
  • Diminazene Aceturate: Regularly used for treatment of African trypanosomiasis.

• Treatment of Leishmania infections requires different approaches depending on whether it is cutaneous or visceral.

• Leishmaniasis can manifest as cutaneous or mucocutaneous types, causing distinct symptoms.

Eimeria and Other Coccidia

• Eimeria: Commonly associated with coccidial infections in various livestock, characterized by enteritis, and can be severe in immunosuppressive conditions.
• Control efforts include the use of coccidiostats and management practices to limit exposure to protozoan oocysts in environments with animals.

Toxoplasma and Associated Zoonotic Risks

• Toxoplasma gondii: Primarily a concern for pregnant women due to potential congenital infections.
• Public health measures are vital to limit infection from undercooked meat and handling of cat litter, emphasizing the role of preventive education.

Coccidia in Animals

• Classification Examples:
  • Isospora: Associated with canids and felids.
  • Sarcocystis: Involves a complex lifecycle with definitive and intermediate hosts, influencing treatment outcomes and management strategies.

Final Thoughts

• Understanding the complexities and implications of protozoan infections is paramount for controlling diseases effectively in both veterinary and public health contexts. Continuous awareness and management strategies are crucial to minimize the impact of these pathogens in affected populations.