Lesson Notes By Weeks and Term v3 - Senior Secondary 3
Pathogens and Parasites
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Pathogens and Parasites
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Subject: Health Education
Class: Senior Secondary 3
Term: 1st Term
Week: 6
Theme: Communicable And Non-Communicable Diseases
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list pathogens and parasites which cause communicable diseases describe the characteristics of each in relation to diseases causation
life cycles often involve stages that allow for transmission and immune evasion.
Examples (and common diseases in Nigeria): Plasmodium species (Malaria – transmitted by Anopheles mosquito) Entamoeba histolytica (Amoebiasis/amoebic dysentery – waterborne) Trypanosoma brucei (Sleeping sickness/African trypanosomiasis – transmitted by tsetse fly) Giardia lamblia (Giardiasis – waterborne)
B. Parasites: Types and Characteristics (Focusing on non-microbial parasites) Parasites can be broadly categorised into endoparasites (internal) and ectoparasites (external). Protozoa (discussed above) are also endoparasites.
1. Endoparasites (Internal Parasites): Live inside the host's body.
Helminths (Worms): Multicellular eukaryotic organisms. They are macroscopic (visible to the naked eye) and have complex life cycles often involving intermediate hosts or environmental stages.
Roundworms (Nematodes): Unsegmented, cylindrical worms.
Characteristics: Elongated, tapered at both ends. They absorb nutrients from the host's gut or tissues.
Disease Causation: Blockage of intestines, malnutrition (compete for host nutrients), tissue damage, internal bleeding.
Examples (and common diseases in Nigeria): Ascaris lumbricoides (Ascariasis – giant roundworm) Hookworms (Ancylostoma duodenale, Necator americanus) (Hookworm infection – causes anaemia) Wuchereria bancrofti (Filariasis/Elephantiasis – lymphatic filarial worm, transmitted by mosquitoes)
Tapeworms (Cestodes): Flat, segmented worms.
Characteristics: Ribbon-like body with a head (scolex) for attachment. Segments (proglottids) contain reproductive organs.
Disease Causation: Nutrient depletion, abdominal discomfort, blockages. Larval stages can migrate to other organs (e.g., brain, muscles) causing severe disease.
Examples (and common diseases in Nigeria): Taenia solium (Pork tapeworm) Taenia saginata (Beef tapeworm)
Flukes (Trematodes): Flat, leaf-shaped worms.
Characteristics: Flat, unsegmented bodies with suckers for attachment.
Disease Causation: Tissue damage, inflammation, organ dysfunction (e.g., liver, blood vessels).
Examples (and common diseases in Nigeria): Schistosoma species (Bilharzia/Schistosomiasis – blood flukes, causes damage to bladder or intestinal wall)
2. Ectoparasites (External Parasites): Live on the exterior of the host's body. These are typically arthropods.
Characteristics: Possess exoskeletons and jointed appendages. They feed on host blood, skin, or hair.
Disease Causation: Cause itching, skin irritation, allergic reactions. More importantly, many act as vectors, transmitting pathogens (bacteria, viruses, protozoa, helminths) from one host to another.
Examples (and role in Nigeria): Lice (Pediculus humanus): Cause pediculosis (head lice, body lice).
Ticks: Feed on blood, can transmit diseases like Lassa fever virus (e.g., through certain rodents that carry ticks) or Lyme disease (less common in Nigeria but possible).
Fleas: Cause skin irritation, can transmit diseases (e.g., plague, though rare now).
Mites (Sarcoptes scabiei): Cause scabies (intensely itchy skin rash). Mosquitoes (e.g., Anopheles, Aedes, Culex): While not typically "parasites" of humans in the feeding sense, they are critical vectors for many parasites and pathogens. Anopheles transmits Plasmodium (malaria parasite), Aedes transmits dengue and yellow fever viruses, Culex transmits Wuchereria bancrofti (filariasis).
C. Characteristics of Non-Communicable Diseases (as per Evaluation Guide): To address point 2 of the evaluation guide, it is important to briefly clarify NCDs.
Non-Communicable Diseases (NCDs): Also known as chronic diseases, these are conditions that are not passed from person to person. They are of long duration and generally progress slowly.
Characteristics:
1. Non-infectious: They are not caused by pathogens or parasites and are not spread from person to person.
2. Chronic and long-lasting: They typically develop slowly over time and require long-term management.
3. Multifactorial causes: Often result from a combination of genetic, physiological, environmental, and lifestyle factors (e.g., unhealthy diet, physical inactivity, tobacco use, harmful use of alcohol). *
Examples: Heart disease, stroke, cancer, diabetes, chronic respiratory diseases, hypertension. This section provides the foundational knowledge required for the lesson, covering definitions, classifications, and specific examples relevant to disease causation.
Definition of Key Terms: Communicable Diseases: Diseases that can be transmitted from one person or animal to another, directly or indirectly. They are caused by infectious agents.
Pathogens: Biological agents (microorganisms) that cause disease in a host organism. They are typically microscopic.
Parasites: Organisms that live on or in a host organism and obtain nutrients at the host's expense, often causing harm. While many pathogens are parasites (e.g., viruses, bacteria, protozoa), the term "parasite" often specifically refers to larger organisms like helminths (worms) and arthropods (insects, mites, ticks) in health education. Distinction between Pathogens and Parasites (as per Evaluation Guide): While there is an overlap (many pathogens are parasitic in nature, e.g., viruses, bacteria, protozoa), the primary distinction in common usage, especially in health education, is often based on size, complexity, and primary mode of study: Pathogens generally refer to microorganisms (viruses, bacteria, fungi, protozoa) capable of causing disease. Their primary characteristic is their ability to induce illness. Parasites is a broader term for any organism (microscopic or macroscopic) that lives in or on another organism (host) and benefits by deriving nutrients at the host's expense. While many pathogens are parasites, "parasites" often specifically highlights organisms with complex life cycles or larger size like worms (helminths) and external arthropods (ectoparasites). The key is the dependency on the host for sustenance and the detrimental effect.
A. Pathogens: Types and Characteristics Pathogens are broadly classified into several groups based on their biological structure and mode of action.
1. Bacteria: Characteristics: Unicellular (single-celled) prokaryotic organisms (lacking a true nucleus and membrane-bound organelles). They reproduce rapidly by binary fission. Some produce toxins or possess capsules that aid in disease causation.
Disease Causation: They invade host tissues, multiply, and produce toxins that damage cells or interfere with normal bodily functions.
Examples (and common diseases in Nigeria): Salmonella typhi (Typhoid fever) Vibrio cholerae (Cholera) Mycobacterium tuberculosis (Tuberculosis, TB) Staphylococcus aureus (Skin infections, food poisoning) Neisseria gonorrhoeae (Gonorrhea)
2. Viruses: Characteristics: Non-cellular, obligate intracellular parasites. They consist of genetic material (DNA or RNA) enclosed in a protein coat. They cannot reproduce independently and must hijack host cells' machinery to replicate.
Disease Causation: They invade host cells, replicate, and often destroy the host cell in the process, leading to tissue damage and disease symptoms. They evade the immune system by rapid mutation.
Examples (and common diseases in Nigeria): Human Immunodeficiency Virus (HIV) (AIDS) Measles virus (Measles) Poliovirus (Polio) Hepatitis B virus (Hepatitis B) Lassa virus (Lassa fever) SARS-CoV-2 (COVID-19)
3. Fungi: Characteristics: Eukaryotic organisms (possessing a true nucleus). They can be unicellular (yeasts) or multicellular (moulds). They reproduce by spores or budding. Fungi obtain nutrients by absorbing organic material from their environment.
Disease Causation: They can cause superficial infections of the skin, hair, and nails (dermatophytes) or systemic infections, especially in immunocompromised individuals. They often grow on dead tissue but can invade living tissue.
Examples (and common diseases in Nigeria): Candida albicans (Thrush, candidiasis) Dermatophytes (e.g., Tinea capitis - ringworm of the scalp, Tinea pedis - athlete's foot)
4. Protozoa: Characteristics: Unicellular eukaryotic organisms. They are motile (move using flagella, cilia, or pseudopods) and typically found in water or moist environments. Many are parasites with complex life cycles involving different hosts.
Disease Causation: They can directly damage host cells, interfere with nutrient absorption, or block vital organs. Their complex life cycles often involve stages that allow for transmission and immune evasion.
Examples (and common diseases in Nigeria): Plasmodium species (Malaria – transmitted by Anopheles mosquito) Entamoeba histolytica (Amoebiasis/amoebic dysentery – waterborne) Trypanosoma brucei (Sleeping sickness/African trypanosomiasis – transmitted by tsetse fly) Giardia lamblia (Giardiasis – waterborne)
B. Parasites: Types and Characteristics (Focusing on non-microbial parasites) Parasites can be broadly categorised into endoparasites (internal) and ectoparasites (external). Protozoa (discussed above) are also endoparasites.
1. Endoparasites (Internal Parasites): Live inside the host's body.
Helminths (Worms): Multicellular This section outlines the step-by-step approach for delivering the lesson, incorporating teacher-led instruction and student-centred engagement.
A. Teacher Activities: Introduction (10 minutes): Engage: Begin by asking students to name common diseases in their communities. Facilitate a brief discussion on how these diseases are spread.
Define: Introduce the terms "communicable diseases," "pathogens," and "parasites," establishing the scope of the lesson.
State Objectives: Clearly articulate the learning objectives for the lesson (as rephrased for students in the Overview section). Concept Exploration and Explanation (30 minutes): Pathogens: Present each type of pathogen (bacteria, viruses, fungi, protozoa) sequentially. For each type, explain its characteristics (e.g., unicellular/non-cellular, prokaryotic/eukaryotic, mode of reproduction). Provide specific examples of diseases caused by each, focusing on those prevalent in Nigeria (e.g., Typhoid for bacteria, HIV for viruses, Ringworm for fungi, Malaria for protozoa). Use visual aids like charts, diagrams of microorganisms, or pictures of disease symptoms to enhance understanding.
Parasites (Helminths and Ectoparasites): Explain the general concept of parasitism and differentiate between endoparasites and ectoparasites. Focus on helminths (roundworms, tapeworms, flukes), describing their characteristics (multicellular, macroscopic) and their mode of disease causation. Provide Nigerian examples (e.g., Ascaris, Schistosoma). Discuss ectoparasites (lice, ticks, mites, mosquitoes) and their characteristics, highlighting their role as vectors for other pathogens/parasites.
Disease Causation Link: Throughout the explanation, emphasize how the specific characteristics of each pathogen/parasite contribute to its ability to cause disease (e.g., viruses' obligate intracellular nature, bacteria's toxin production, helminths' nutrient competition). Interactive Discussion and Q&A (10 minutes): Facilitate a short question-and-answer session to check for understanding and address misconceptions. Encourage students to ask questions and share local examples or experiences related to the discussed agents.
Activity Guidance (15 minutes): Divide students into small groups (4-5 students). Assign each group one category of pathogen or parasite (e.g., Group 1: Bacteria, Group 2: Viruses, Group 3: Protozoa, Group 4: Helminths, Group 5: Ectoparasites).
Instruct each group to: List three common diseases caused by their assigned agent in Nigeria. Describe two key characteristics of their agent that contribute to disease causation. Suggest one practical preventive measure for a disease caused by their agent, relevant to their community. Circulate among groups, providing clarification and support. Activity Review and Consolidation (10 minutes): Have each group briefly present their findings (2-3 minutes per group). Consolidate key information from each presentation, highlighting the diversity and specific impacts of different pathogens and parasites. Emphasize the overarching message of understanding these agents for effective disease prevention.
B. Student Activities: Active Listening and Note-Taking: Students actively listen to explanations and take comprehensive notes on definitions, characteristics, and examples.
Q&A Participation: Students participate in class discussions, ask clarifying questions, and share relevant observations.
Group Collaboration: Students work collaboratively in assigned groups to discuss their assigned pathogen/parasite, research (if resources are available, otherwise discuss based on class content), and prepare a short presentation.
Presentation: Students present their group's findings to the class. These questions are designed to reinforce understanding of the performance objectives with immediate feedback.
Question 1: List three different types of pathogens and one disease commonly caused by each in Nigeria.
Solution: Bacteria: Salmonella typhi (causes Typhoid fever).
Viruses: Human Immunodeficiency Virus (HIV) (causes AIDS).
Protozoa: Plasmodium species (causes Malaria). (
Commentary: This addresses Objective 1, requiring students to list pathogens and diseases. Focus on Nigerian common diseases.)
Question 2: Describe two distinct characteristics of viruses that explain why they are difficult to treat with antibiotics.
Solution: Obligate Intracellular Parasites: Viruses must replicate inside host cells, hijacking the host's cellular machinery. Antibiotics primarily target bacterial cellular structures or metabolic processes (e.g., cell walls, ribosomes, specific enzymes) that viruses lack.
Non-cellular Structure: Viruses are not true cells; they lack the complex cellular structures (e.g., cell wall, organelles) that antibiotics are designed to disrupt in bacteria. Antibiotics therefore have no target in a virus. (
Commentary: This addresses Objective 2, focusing on the characteristics of a specific pathogen and its implication for disease causation/treatment. It emphasizes critical thinking about microbial biology.)
Question 3: Differentiate between an endoparasite and an ectoparasite, providing one example of each that affects humans in Nigeria.
Solution: An endoparasite lives inside the host's body, typically in organs like the intestines, blood, or liver.
Example: Ascaris lumbricoides (a roundworm) lives in the human intestine, causing ascariasis. An ectoparasite lives on the surface of the host's body.
Example: Head lice (Pediculus humanus capitis) live on the human scalp, causing pediculosis. (
Commentary: This addresses a key distinction within parasites and also links to the evaluation guide's first point, "Differentiate between pathogens and parasites," by clarifying types of parasites. Nigerian examples make it relatable.)
Question 4: Explain how the characteristics of Schistosoma species (flukes) contribute to the development of Bilharzia (Schistosomiasis) in humans.
Solution: Schistosoma species are blood flukes that exhibit characteristics specifically adapted for causing Bilharzia: Complex Life Cycle with Intermediate Host: They have a larval stage (cercariae) that develops in freshwater snails (the intermediate host). These cercariae are released into water and are capable of penetrating human skin, initiating infection. This characteristic allows for environmental transmission in areas with contaminated water bodies, common in many Nigerian rural settings.
Migration and Residence in Blood Vessels: Once inside the human host, the worms migrate to specific blood vessels (e.g., around the bladder or intestines) where they mature and lay eggs. The eggs, many of which get trapped in tissues (liver, bladder, intestines), provoke chronic inflammatory responses, leading to organ damage, fibrosis, and the classic symptoms of schistosomiasis (e.g., blood in urine or stool, abdominal pain). (
Commentary: This targets Objective 2, requiring a detailed explanation of how parasite characteristics lead to disease, using a highly relevant Nigerian example.)
Understanding pathogens and parasites has profound implications for individual and community health in Nigeria. Community Health Initiatives and Disease Prevention: Knowledge of pathogens and parasites directly informs public health campaigns. For instance, understanding that Plasmodium (a protozoan parasite) is transmitted by mosquitoes (ectoparasite vector) reinforces the importance of using insecticide-treated nets, clearing stagnant water, and engaging in malaria eradication programs. Similarly, knowing that Vibrio cholerae (bacteria) and Entamoeba histolytica (protozoan parasite) are waterborne emphasizes the need for safe drinking water sources, proper sanitation (latrine use), and handwashing campaigns to prevent cholera and amoebiasis outbreaks common in many Nigerian communities.
Personal Hygiene and Sanitation Practices: Students can apply this knowledge to improve their personal health habits. Recognizing that fungi cause ringworm or that bacteria cause skin infections encourages regular bathing and keeping skin clean and dry. Understanding that intestinal worms (helminths) are often acquired through contaminated soil or food promotes hand washing before meals, proper cooking of food, and wearing shoes, which are practical preventive measures particularly relevant in rural and peri-urban areas of Nigeria.
Impact on Economy and Development: Communicable diseases caused by pathogens and parasites impose a significant economic burden on Nigeria through healthcare costs, lost productivity due to illness, and reduced quality of life. For example, high rates of malaria or typhoid can severely impact agricultural output or educational attainment. By understanding the causative agents, individuals and communities are better equipped to implement preventive strategies, which in turn contributes to a healthier workforce, improved economic stability, and overall national development.