- - AGRICULTURE CORE CURRICULUM - - (CLF3000) Advanced Core Clusters: ANIMAL SCIENCE (CLF3300) Unit Title: ANIMAL HEALTH ____________________________________________________________________________ (CLF3302) Topic: CAUSES OF DISEASE Time Year(s) 2 hours 3 / 4 ____________________________________________________________________________ Topic Objectives: Upon completion of this lesson, the student will be able to: Learning Outcome #: (E-2) - Identify five categories of pathogens and list the major classes of each. Special Materials and Equipment: Supplemental Handout #1, microscopes, prepared slides of pathogens such as bacteria and parasites or preserved samples of pathogens. References: California Vocational Agriculture Curriculum Guidelines, ANIMAL PRODUCTION, "Animal Health", Vol.1. Ensminger, M.E. (1983). THE STOCKMAN'S HANDBOOK. Ensminger, M.E. (1983). ANIMAL SCIENCE. Meyer, Norvan L. 1984 YEARBOOK OF AGRICULTURE. Evaluation: Quiz by instructor. TOPIC PRESENTATION: CAUSES OF DISEASE A. Disease: Any condition that jeopardizes the survival of an animal in a particular environment. B. Characteristics: Change of normal appearance, behavior, or movements; including dull, inflamed eyes, rough-soiled hair, fur, or feathers, difficulty with walking or running, abnormal lumps, and discoloration of skin. C. Disease Causing Entity: 1. Any agent that may bring about an abnormal condition to any or all of the tissues of the body by transmission via eggs, contact, food, or a vector. a. The 2 major types of disease entities can be grouped as: 1) Infectious agents including a) bacteria, b) viruses, and c) parasites. 2) Noninfectious agent including a) injuries, b) poisons and chemicals, c) poor nutrition, d) birth defects, and e) tumors. D. Infectious Disease Causing Agents: 1. Terms: a. Pathogen - a disease causing agent (such as bacteria). b. Virulence - the ability of a particular pathogen to overcome the body's defenses and produce a disease. c. Host - any animal serving as a residence for a pathogen. 2. Bacteria: a. The smallest and simplest form of plant life that does not contain chlorophyll. b. Bacteria are single-celled and vary in size and shape. c. They are very numerous in nature, and the majority are beneficial. For example, 1) fermentation in vinegar and cheese is caused by bacteria. d. Can be classified by these distinguishing characteristics: 1) Shape - a) rod shaped (bacilli), b) spherical (cocci), and c) spiral (spirilli). 2) Oxygen need - a) no oxygen (anaerobic), or b) oxygen required (aerobic). 3) Ability to absorb a "gram's stain" - a) gram positive, or b) gram negative. 4) Their ability to release toxins. 5) Their ability to form "spores" which are shell-like coverings which may allow bacteria to survive several years despite environmental conditions. 3. Viruses: a. Can only be seen using electron microscopes. b. Can cause serious, contagious diseases. c. They are classified according by the type of tissue they invade, by their appearance, and by the host they normally affect. d. They are not a plant nor an animal, but must have living cells to parasitize if they are to grow and reproduce, since they cannot live independently of living cells. 4. Parasites: REVIEW: Basic Core Curriculum CLF275. a. Can be grouped into 4 major areas: 1) protozoa, 2) helminths, 3) arthropods, and 4) fungi. b. Definition of a parasite: Organisms living on, in, or at the expense of another living organism. c. They cause damage by: 1) absorbing food from the digestive tract (worm parasites), 2) sucking blood or lymph (worm parasites, arthropods), 3) feeding on tissues of the host (all), 4) obstructing passages (worm parasites) (which is rare), 5) causing irritations (all), and 6) transmitting diseases (arthropods). d. Protozoa: 1) The simplest form of animal life consisting of only a single cell. 2) Most are common in the environment and only a few concern the animal health industry, causing diseases such as coccidiosis and trichomoniasis. e. Helminths (worm parasites): 1) Helminths are many-celled animals varying greatly in size, shape, structure, and physiology. 2) Most undergo some development outside the host. 3) There are 4 general types of helminths: a) Flukes (trematodes) - soft, flat, leaf-shaped worms. They usually have 2 or more hosts, one of which is a mollusk. b) Tapeworms (cestodes) - can grow up to 10 feet long. They live in the intestinal tract and rob the host of nutrients. c) Roundworms (nematodes) - long, cylindrical, unsegmented worms. Some are microscopic. d) Thorny-headed worms (acanthocephala) - they have a retractable snout armed with hooks. f. Arthropods: 1) May act as vectors (intermediate hosts) that carry disease organisms or transmit parasites. 2) There are 6 common types of arthropods affecting livestock: a) Flies - most suck blood, deposit eggs in necrotic dead or dying) tissue, cause annoyance, and congregate where there is filth and waste matter. b) Mosquitoes - they suck blood and transmit disease, and are especially prevalent in areas where water is allowed to accumulate. c) Ticks - they suck blood, carry disease, lay eggs in the hair of the animal, and transmit parasites. d) Fleas - they suck blood, transmit disease and parasites, and live in hair and bedding. e) Lice - they are a small, flat, wingless insect, which causes and scratching eventually resulting in a general decline in overall health and appearance. Infestation usually occurs during the winter months. f) Mites - they are very small insects that produce mange so eventually the skin becomes rough and wrinkled. Some burrow into the skin (sarcoptic) and others suck blood (psoroptic). g. Fungi: 1) Are simple plant forms that do not contain chlorophyll. 2) They do not cause many common livestock diseases. 3) The most common fungal disease is ringworm. __________________________________________________________ ACTIVITY: 1. Use microscopes to observe bacteria, protozoa and various parasites. Students can diagram the organisms they see. 2. Use Supplemental Handout #1 for discussion questions. __________________________________________________________ Supplemental Worksheet #1 Discussion Questions CAUSES OF DISEASE NAME___________________________________ DATE___________________________________ PER.___________________________________ 1. CAN YOU THINK OF ANY BACTERIA THAT CAUSE DISEASE? 2. CAN YOU THINK OF CONDITIONS OR CIRCUMSTANCES THAT MAY LEAD TO DISEASE? 3. CAN YOU THINK OF ANY EXAMPLES OF BENEFICIAL BACTERIA? 4. CAN YOU THINK OF DISEASES CAUSED BY VIRUSES THAT AFFECT HUMANS OR LIVESTOCK? 5. CAN YOU THINK OF ANY PARASITES THAT AFFECT HUMANS OR LIVESTOCK? 4/15/90 sg/gv #%&C