Introduction to Veterinary Medicine (VMED110) - Principles of Animal Diseases Recognition and Treatment

Fundamental Concepts of Veterinary Pathology and Physiology

  • Definition of Disease:

    • Any deviation from the normal or healthy physiological status of an animal.

    • An alteration of the body or body organs which interrupts or disturbs the body's function.

  • Pathology: The scientific study of diseases.

    • Gross Pathology: The study of disease-related changes visible to the naked eye.

    • Microscopic Pathology: The study of tissues and cells using a microscope to identify disease.

  • Physiology: The study of normal organ and body function.

Etiology: The Causes of Disease

  • Etiology is defined as the study of the causes of disease. A disease often results from a combination of two or more causes categorized as indirect or direct.

  • Indirect (Predisposing) Causes: These factors lower the animal's resistance and make them more susceptible to illness.

    • Environmental Stressors:

      • Temperature Change:

        • Heat Stress: Dogs are the most sensitive species to heat due to a lack of sweat glands.

        • Extreme Cold: Young animals and neonates are the most sensitive to cold temperatures.

      • Poor Ventilation or Overcrowding: Can lead to ammonia-induced irritation of the eyes and respiratory system. This is common in chickens, beef cattle, sheep, and goats.

      • Inadequate Feeding or Watering: Lack of proper nutrition or hydration reduces immune function.

      • Housing Conditions: Factors include floor type, hygiene, and exposure to other animals.

    • Individual Variations:

      • Age: Young and geriatric animals are more vulnerable.

      • Gender: Genetic predispositions or hormonal differences.

      • Underlying Health Conditions: Chronic issues like diabetes, heart disease, or genetic disorders.

      • Allergies: Hypersensitivity to environmental or dietary factors.

      • Behavioral Issues: Aggression or food guarding.

    • Other Factors:

      • Exercise Level: Specific to dogs and sport animals.

      • Owner-Animal Relationship: Dominance hierarchies and general welfare.

      • Vaccination Status: Lack of preventative care.

  • Direct (Determining) Factors: Factors that produce the actual disease.

    • Germs (Pathogens/Micro-organisms): Bacteria, viruses, parasites, fungi, mycoplasma, and protozoa.

    • Trauma: Physical injury.

    • Inherited Genetic Conditions: Congenital disorders.

    • Toxins and Chemicals: Insecticides, poisonous plants, venomous animals/insects, and toxic food.

    • Nutritional Deficiency: Diseases caused specifically by poor nutrition.

Specific Toxins and Dietary Hazards

  • Foods Toxic to Dogs: Chocolate, coffee, alcohol, avocados, grapes, onions, garlic, and macadamia nuts.

  • Medication Hazards: Paracetamol (Panadol®) is highly toxic to cats.

  • Livestock Toxins: Aflatoxins found in moldy grains, such as moldy corn, are toxic to livestock.

Clinical Signs of Disease in Animals

  • Changes in Appetite & Drinking:

    • Reduced appetite or complete refusal to eat (anorexia).

    • Polydipsia (drinking much more) or reduced water intake.

    • Sudden weight loss or weight gain.

  • Changes in Behavior:

    • Lethargy, depression, or appearing "not themselves."

    • Restlessness, irritability, or aggression.

    • Hiding (specifically common in cats).

    • Reduced interaction, weakness, or collapse.

  • Fever and Temperature:

    • Fever (Hyperthermia): Characterized by dullness and reduced appetite.

    • Hypothermia: Low body temperature, occurring in shock, severe illness, or neonates.

  • Signs of Pain:

    • Vocalizing or grinding teeth (bruxism).

    • Reluctance to move or be touched.

    • Guarding a specific body area.

    • Abnormal posture: Hunched back or tucked abdomen.

    • Lameness and licking the site of pain.

  • Breathing Problems:

    • Coughing, sneezing, and nasal discharge.

    • Rapid breathing (tachypnea) or labored breathing (dyspnea).

    • Open-mouth breathing or wheezing.

  • Digestive Signs:

    • Diarrhea and constipation.

    • Vomiting or regurgitation.

    • Bloating or abdominal distension.

    • Excess salivation (ptyalism) and straining to defecate (tenesmus).

    • Blood or mucus in feces.

  • Urinary Signs:

    • Straining to urinate (stranguria) or frequent urination of small amounts (pollakisuria).

    • Blood in urine (hematuria) or urinating in unusual places.

    • Incontinence/dribbling.

    • Anuria (no urination), which is a medical emergency in small animals.

  • Reproductive Signs:

    • Abnormal vaginal discharge and failure to conceive.

    • Prolonged labor (dystocia) and retained placenta.

    • Mastitis: Swollen, painful udders.

  • Skin and Coat Changes:

    • Alopecia (hair loss) and a dull coat.

    • Pruritus (itching), rubbing, or licking.

    • Erythema (redness), scabs, sores, and swellings/abscesses.

  • Eye and Ear Signs:

    • Ocular discharge, redness, squinting, or cloudiness.

    • Head shaking, ear scratching, discharge, or bad odor from the ear canal.

  • Neurological and Musculoskeletal Signs:

    • Neurological: Seizures, tremors, head tilt, incoordination (ataxia), circling, or sudden blindness.

    • Musculoskeletal: Lameness, stiffness, joint swelling/heat, muscle atrophy, and crepitus (grating sound in joints).

Disease Classification

  • Infectious Disease: Caused by living organisms (bacteria, virus, fungus, parasite) that invade the animal's body.

  • Contagious Disease: An infectious disease that is transmitted directly or indirectly from an infected animal to a healthy one.

  • Zoonotic Disease: Diseases that transmit between animals and humans.

Principles of Treatment and Medication

  • Treatment Methods:

    • Medicinal: Using drugs to restore, correct, or change body functions.

    • Conservative: Non-surgical approaches such as physiotherapy, braces, or applying heat/cold.

    • Surgical: Invasive procedures to treat conditions.

    • Others: Radiation therapy or dialysis.

  • Drug Classification (Level of Control):

    1. Over-the-Counter (OTC): Vitamins, supplements, mild anti-inflammatories (e.g., Ibuprofen).

    2. Pharmacy Only: Dispensed by pharmacists without a prescription (e.g., antihistamines, anti-diarrheals).

    3. Prescription Drugs: Dispensed only via a licensed veterinarian (e.g., antibiotics, insulin).

    4. Controlled/Scheduled Drugs: Strictly regulated due to misuse potential (e.g., anesthetics, opioids like Morphine).

  • Classification by Therapeutic Use:

    • Antipyretic: Reduces fever.

    • Analgesic: Reduces pain.

    • Anticonvulsant: Reduces involuntary convulsions (epilepsy).

    • Antiemetic: Stops vomiting.

    • Laxative: Treats constipation.

    • Antispasmodic: Relaxes muscles inside abdominal organs (used for colic).

Dosage and Administration

  • Drug Half-life: The time required for the concentration of a drug in the body to drop to 50%50\% of its original level.

    • Example Calculations: If a half-life is 44 hours:

      • Initial: 100%100\%

      • After 44 hours: 50%50\%

      • After 88 hours: 25%25\%

      • After 1212 hours: 12.5%12.5\%

  • Absorption Speeds by Route (Fastest to Slowest):

    1. Intravenous (IV): Immediate; no absorption step.

    2. Intraperitoneal (IP): Fast.

    3. Intramuscular (IM): Moderate.

    4. Subcutaneous (SC): Slower.

    5. Intradermal (ID): Slowest.

  • Administering Oral Medications: Options include tablets, capsules, granules, or liquid (syrups/suspensions). In livestock, a stomach tube is used.

    • Species Note: A stomach tube can be inserted via the mouth or nose in most animals, but in horses, it is inserted through the nose only because they have a long soft palate.

  • Injection Angles:

    • IM: 90∘90^{\circ}

    • SC: 45∘45^{\circ}

    • IV: 25∘25^{\circ}

    • ID: 10–15∘10\text{--}15^{\circ}

Species-Specific Injection Sites

  • Horse (IM):

    • Neck: Triangular area bounded by the scapula, cervical spine, and nuchal ligament.

    • Gluteal: Triangle formed by the tuber coxae, tuber ischium, and tuber sacrale.

  • Dog and Cat (IM):

    • Epaxial Muscle: Easily palpable along the spine.

    • Hamstring (Biceps Femoris/Semitendinosus): Large muscle; caution used to avoid hitting the sciatic nerve.

    • Quadriceps: Muscle belly more defined in some breeds.

    • Triceps: Easy to palpate in the forelimb.

  • Intravenous Sites:

    • Horse/Cattle: Jugular vein.

    • Dog/Cat: Cephalic vein (front limb) and lateral saphenous vein (hind limb).

Animal Behavior and Ethology

  • Ethology: Branch of biology studying animal behavior under natural conditions.

  • Social Groupings:

    • Herd: Cattle, Elephants, Horses, Buffaloes, Sheep.

    • Flock: Birds (Ducks, Pigeons, Flamingos, Parrots).

    • Pack: Canines/Carnivores (Wolves, African wild dogs).

    • Solitary: Tigers, Leopards, Bears, Koalas, Sloths.

  • Predator vs. Prey Dynamics:

    • Predators: Forward-facing eyes (binocular vision), sharp canines/beaks, simple stomach, short digestive tract.

    • Prey: Side-positioned eyes (peripheral vision), flat molars, complex digestive systems with fermentation, long slim limbs with hooves.

  • Stress Responses:

    • Fight: Defend and defeat.

    • Flight: Escape danger.

    • Freeze: Become still to avoid detection.

    • Fawn: Use non-threatening posturing to defuse conflict.

Symbiosis

  • Mutualism: Both species benefit (e.g., bees and flowers).

  • Commensalism: One benefits, the other is unaffected (e.g., barnacles on whales).

  • Parasitism: One benefits, the other is harmed (e.g., ticks on mammals).

  • Amensalism: One organism is destroyed, the other is unaffected (e.g., penicillin mold killing bacteria).

Disease Prevention and Control Strategies

  • Pasture Rotation: Subdividing fields and rotating livestock within 55 days to stay ahead of the internal parasite cycle (eggs reach infective stage in approximately 66 days).

    • Larval Development: Infective larvae (L3L3) can develop in as little as 22 weeks in warm, damp weather or take months in extreme cold.

    • Multi-species Grazing: Cattle and horses do not share the same parasites as sheep and goats, helping to break life cycles.

  • Quarantine and Isolation:

    • Quarantine period should be no less than 2121 days for new or returning animals.

    • Isolation refers to immediate separation of sick animals from the healthy population.

  • Biosecurity Principles:

    1. Prevent disease introduction onto the farm (limit human access, test new stock).

    2. Prevent disease spread within the farm (separate young from adults, sanitize equipment).

    3. Increase animal resistance (good nutrition, colostrum for newborns, vaccination).

Carcass Disposal Methods

Carcasses must be disposed of promptly (36–4836\text{--}48 hours) and sanitarily.

  • Burial: Must account for soil depth, proximity to water wells, and potential for secondary toxicosis. Carcasses should be punctured or vented before burial.

  • Incineration: Effective for destroying infectious agents; however, open-air burning may have air quality and legal restrictions.

  • Composting: Environmentally friendly; involves mixing 11 part carcass, 22 parts litter, and 11 part straw in layers.

  • Rendering: Industrial process cooking carcasses down to protein (for pet food) and fat (for biodiesel). Animals euthanized with barbiturates are not accepted because the drug remains in the rendered product.

  • Associated Disease Risks: Improper disposal can spread Brucellosis (foetus/blood), Anthrax (spores), Q-fever (placenta/ticks), and Leptospirosis (urinary contamination).