Protozoa in Veterinary Medicine

Protozoa Overview

• Protozoa are classified as a subkingdom within the kingdom Protista.
• Approximately 32,000 extant (living) species exist, with estimates exceeding 50,000.
• Around 34,000 extinct species have been identified, particularly Foraminifera.
• Distribution: 21,000 species are free-living (aquatic and terrestrial), and 11,000 are parasitic.
• Diverse groups include flagellates (6,900 species), amoebae (11,550 species), ciliates (7,200 species), and sporozoans (5,600 species).

Structure

• Most protozoa are microscopic, with some visible to the naked eye.
• They are unicellular eukaryotes, with a membrane-bound nucleus.
• Exhibit essential life activities: movement, feeding, and reproduction.
• Organelles function analogously to organs in higher animals.
• Plasma membrane encapsulates cytoplasm and locomotory structures (e.g., pseudopodia, cilia, flagella).

Testacea

• Some protozoa have a protective test or shell made of siliceous/chitinoid material.
• Pseudopodia project from the shell to facilitate movement and capture prey.

Foraminifera

• Ancient shelled organisms found primarily in oceans; some inhabit fresh or brackish waters.
• Exhibit a multicameral test composed mainly of calcium carbonate.
• Slender pseudopodia create a protoplasmic net for capturing and digesting prey.

Phylum Mastigophora

• Includes zooflagellates, which can be free-living or parasitic, possessing one or two flagella.
• Common reproduction method is binary fission; cyst formation is noted, while sexual reproduction is rare.

Subphylum Phytomastigina

• Class Euglenoidina: Euglena, found in freshwater, features a pellicle and flagella. Capable of photosynthesis but also absorbs nutrients in darkness.
• Class Volvocaceae: Volvox, a colonial flagellate, reproduces asexually or sexually.

Subphylum Zoomastigina

• Class Protomonadina / Order Bodonida: Ichthyobodo necator is a notable parasite infecting freshwater fish, causing ichthyobodosis.
• Order Trypanosomatids: A group of exclusively parasitic kinetoplastids, primarily affecting insects and occasionally vertebrates. Includes:
  • Trypanosoma: Causes African sleeping sickness through intermediary tsetse flies and leads to severe neurological impacts.
  • Trypanosoma cruzi: Causes Chagas disease in humans and animals in the Americas.

Class Opalinea

• Parasitic protozoans found in the digestive systems of amphibians, characterized by a large body and numerous nuclei.

Phylum Sporozoa

• Composed of endoparasites; lack locomotor structures and possess a tough covering.
• Life cycles often require multiple hosts; reproduction involves asexual (multiple fission) and sexual processes.
• Includes two main classes: Gregarinia (common invertebrate parasites) and Coccidiomorpha (important for medical and veterinary contexts).

Class Coccidiomorpha

• Order Haemosporida and Coccidiida: Eimeria causes coccidiosis, primarily affecting intestines of various animals. Symptoms include severe diarrhea and potentially high mortality.
• Infection mechanics include a life cycle with asexual and sexual reproduction stages, with oocysts excreted in feces leading to new infections through ingestion.
• In 2016, there were 216 million malaria cases and approximately 445,000 deaths globally attributed to malaria due to Plasmodium species, highlighting its public health significance.

Malaria Impact

• Continuous cycling and delayed multiplication in the liver can lead to relapses of the disease.
• Geographic distribution has varied, thus influencing targeted efforts for prevention and control strategies.

Explore the fascinating world of protozoa through this quiz designed for Veterinary Medicine students. Delve into their structure, classification, species, and the role of parasitism. Test your knowledge on major divisions of life as outlined in Whittaker’s five-kingdom system.