ZOO 312 — The Biology of Tropical: Lecture Note

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LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS

LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS ZOO 312: The Biology of Tropical Parasites (2 Units C: LH 15; PH 45) Course Code: ZOO 312 Course Title: The Biology of Tropical Parasites Course Unit: 2 Units C Series 1: Parasitic Protozoans – Classification, Morphology, and Life Cycles Series 2: Platyhelminths – Adaptations and Parasitic Strategies Series 3: Nematodes – Structure, Life Cycles, and Parasitic Modes Series 4: Parasitic Arthropods – Vectors and Adaptations to Parasitism Series 5: Adaptations to Parasitic Life – External and Internal Modification Series 1 Parasitic Protozoans – Classification, Morphology, and Life Cycles Part 1.1 Classification of parasitic protozoans 1.1.1 Major groups of protozoan parasites 1.1.2 Criteria for classification Part 1.2 Morphology and anatomy of protozoans 1.2.1 External features and adaptations 1.2.2 Internal structures and functions Part 1.3 Life cycles of protozoan parasites 1.3.1 General patterns of protozoan life cycles 1.3.2 Case studies of selected protozoan parasites Introduction Protozoan parasites are among the most significant causes of tropical diseases, affecting millions of people worldwide. Their ability to adapt to different hosts and environments makes them both

LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS fascinating and challenging to study. By examining their classification, morphology, and life cycles, we gain insights into how these organisms survive, reproduce, and spread, which is essential for understanding their impact on human and animal health. The aim of this Series is to introduce you to the biology of parasitic protozoans, focusing on their classification, structural adaptations, and life cycles. This will provide a foundation for appreciating their role in tropical parasitology and for developing practical skills in studying them. We shall commence this Series by exploring the classification of parasitic protozoans, identifying their major groups and the criteria used to distinguish them. Next, we will examine their morphology and anatomy, paying attention to external and internal adaptations that support a parasitic lifestyle. Finally, we will analyse their life cycles, considering both general patterns and selected case studies to illustrate how protozoans complete their development and transmission. Series Learning Outcomes Upon completing this Series, you should be able to: SLO 1.1 define the major groups of parasitic protozoans, SLO 1.2 explain the criteria used in classifying protozoan parasites, SLO 1.3 describe the external features and adaptations of protozoan parasites, SLO 1.4 analyse the internal structures and functions of protozoan parasites, SLO 1.5 demonstrate knowledge of general patterns in protozoan life cycles, and SLO 1.6 evaluate selected case studies of protozoan parasites in relation to their transmission and survival. 1.1 Classification Of Parasitic Protozoans 1.1.1 Major groups of protozoan parasites Protozoans are single-celled organisms that belong to diverse groups, many of which have adapted to a parasitic lifestyle. The major parasitic protozoans include Amoebae, which move using pseudopodia and often inhabit the intestines; Flagellates, which use whip-like structures called flagella for movement and include parasites such as Trypanosoma; Ciliates, which move using cilia and can parasitise fish and other animals; and Sporozoans, which lack locomotory structures in their adult stage and include Plasmodium, the causative agent of malaria. Each group has unique structural and functional features that support survival within hosts. Short description: Diagram showing the major groups of parasitic protozoans (amoebae, flagellates, ciliates, sporozoans).

LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS Caption: Figure 1.1 Major groups of parasitic protozoans Fill in the blank: Protozoans that move using whip-like structures called ______ are known as flagellates. 1.1.2 Criteria for classification The classification of parasitic protozoans is based on several criteria. One key factor is mode of locomotion, which distinguishes amoebae, flagellates, ciliates, and sporozoans. Another criterion is site of infection, as some protozoans inhabit the blood, while others colonise the intestines or tissues. Life cycle patterns also play a role, with some protozoans exhibiting complex alternations between hosts. Finally, morphological features such as the presence of cysts, spores, or specialised organelles are used to differentiate groups. These criteria help parasitologists to organise protozoans systematically and to predict their behaviour in hosts. Box 1.2 Criteria for classification of parasitic protozoans Classification Criterion Description Examples and Categories Locomotion The primary method used by the protozoan for Sarcodina (Amoeboid): Use pseudopodia (e.g., Entamoeba). Mastigophora (Flagellates): Move with one or more flagella (e.g., Giardia,

LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS Classification Criterion Description Examples and Categories movement, which is often a defining feature. Leishmania). Ciliophora (Ciliates): Covered in cilia for movement (e.g., Balantidium). Apicomplexa (Sporozoans): Lack specialized locomotive organelles in adult stages; move by gliding or twisting (e.g., Plasmodium, Cryptosporidium). Site of Infection The specific location within the definitive (final) or intermediate host where the parasite resides and reproduces. Enteric (Intestinal): Inhabit the digestive tract (e.g., Giardia lamblia). Urogenital: Infect the reproductive or urinary systems (e.g., Trichomonas vaginalis). Hemo-lymphatic: Found in the blood and lymph (e.g., Trypanosoma). Systemic: Can invade various tissues and organs (e.g., Toxoplasma gondii). Life Cycle The stages of development a parasite undergoes, which can be direct (requiring one host) or indirect (requiring multiple hosts). Direct (Monoxenous): Involve only one host species (e.g., Entamoeba histolytica). Indirect (Heteroxenous): Require two or more host species to complete their development (e.g., Plasmodium spp. require a human intermediate host and an Anopheles mosquito definitive host). Morphology The distinctive physical characteristics, organelles, and structural features of the parasite's different life stages (trophozoite vs. cyst). Features include: Cell Size and Shape: Which can be highly variable. Specialized Organelles: Such as flagella, cilia, or the apical complex in Sporozoans. Nucleus: Number and structure are key in identification. Stage-Specific Forms: The identification of the feeding (trophozoite) or the infective, resting (cyst) stages is critical for diagnosis. Fill in the blank: The presence of cysts or spores is an example of a ______ feature used in classification. Pilot questions 1.1 Name the four major groups of parasitic protozoans.

LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS Which group includes Plasmodium, the causative agent of malaria? What structure do amoebae use for movement? List one criterion used in classifying parasitic protozoans. Which group of protozoans uses cilia for locomotion? 1.2 Morphology And Anatomy Of Protozoans 1.2.1 External features and adaptations Protozoan parasites exhibit a variety of external features, which are structural characteristics visible at the cell surface. These include protective coverings such as cysts, which are resistant forms that enable survival outside the host, and locomotory structures such as pseudopodia, flagella, or cilia, which allow movement and host invasion. Some protozoans also possess specialised organelles like the pellicle, a flexible outer layer that provides shape and protection. These external adaptations are essential for survival in hostile environments and for transmission between hosts. Short description: Diagram showing external features of protozoans including cysts, pseudopodia, flagella, cilia, and pellicle. Caption: Figure 1.2 External features of protozoan parasites Fill in the blank: The resistant form that enables protozoans to survive outside the host is called a ______. 1.2.2 Internal structures and functions

LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS Protozoans also possess important internal structures that support their parasitic lifestyle. The nucleus controls cellular activities and reproduction, while mitochondria provide energy for survival and movement. Some protozoans contain specialised organelles such as the apicoplast in sporozoans, which is involved in metabolism and host invasion. The contractile vacuole helps regulate water balance, and the food vacuole stores ingested material. These internal adaptations allow protozoans to thrive within host tissues and fluids, ensuring successful infection and reproduction. Box 1.3 Internal structures of protozoan parasites Structure Primary Function(s) Key Details Nucleus Genetic Control Contains the DNA. Parasites may have one (mononuclear) or two (binuclear, like Giardia). It regulates reproduction and protein synthesis. Plasma Membrane (Plasmalemma) Protection & Transport A semi-permeable lipid bilayer that regulates the entry of nutrients and the exit of waste. In some, it is reinforced into a tough pellicle. Cytoplasm Metabolic Support Divided into the clear, outer ectoplasm (for movement/protection) and the granular, inner endoplasm (containing organelles). Mitochondria Energy Production The "powerhouse" that generates ATP. Note: Some anaerobic parasites (like Entamoeba) lack traditional mitochondria and use mitosomes instead. Endoplasmic Reticulum & Golgi Protein Synthesis Responsible for manufacturing, modifying, and transporting proteins and lipids, especially those needed for the cell membrane or secretion. Food Vacuoles Digestion Membrane-bound sacs where ingested food particles are broken down by enzymes (phagocytosis).

LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS Structure Primary Function(s) Key Details Contractile Vacuoles Osmoregulation Primarily found in freshwater protozoa; they pump out excess water to prevent the cell from bursting. Apical Complex Host Invasion A specialized cluster of organelles (rhoptries, micronemes) found in Apicomplexans (e.g., Plasmodium) used to penetrate host cells. Fill in the blank: The organelle that regulates water balance in protozoans is the ______ vacuole. Pilot questions 1.2 What resistant external structure enables protozoans to survive outside the host? Which locomotory structure is used by amoebae? Name one protective outer layer found

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