Comprehensive Study Guide: General Pathological Conditions in Veterinary Public Health
Fever (Pyrexia) in Veterinary Public Health
Definition: Fever is characterized by an abnormal elevated body temperature.
Classification of Fever: * Septic Fever: Caused by the presence of an infection. Pathogens include viruses, bacteria, bacterial toxins, protozoa, and fungi. * Aseptic Fever: Occurs in the absence of infection. Causes include: * Tissue necrosis: Muscle degradation from intramuscular injections of necrotizing substances, rapidly growing tumors undergoing necrosis, or lysis of burned tissue. * Chemicals or surgery: Administration of specific drugs or the breakdown of tissue and blood following surgical procedures. * Anaphylactic reactions: Response of antibodies to foreign antigens.
Antemortem Findings: * Presence of chills and sweating. * Elevation of body temperature. * Increased pulse and respiration rates. * General depression, dullness, and anorexia. * Obstipation (severe constipation). * Additional signs in septic fever: Diarrhoea, vomiting, urinous or phenolic odour of the breath, shock, convulsions, and coma.
Postmortem Findings: * Rigor mortis. * Putrefaction. * Congestion of the carcass and subcutaneous blood vessels. * Enlarged lymph nodes. * Evidence of cloudy swelling in the heart, liver, and kidneys.
Judgment Criteria: * Condemnation: The carcass is condemned if the fever syndrome is associated with bacteria/bacterial toxins in the blood or findings of antimicrobial substances/drugs. * Hold and Re-examine: If typical signs of a fevered carcass are absent, the carcass should be held for after slaughter for re-examination. * Conditional Approval: If a mild fever syndrome is first detected postmortem, the carcass may be conditionally approved with heat treatment, provided bacteriological and chemical tests are negative.
Differential Diagnosis: * Hyperthermia: Elevation of body temperature caused by physical factors such as high environmental temperature or prolonged muscular exertion, particularly in humid weather. * Septicemia.
Inflammation and Viral Diseases
Nature of Inflammation: Usually secondary to primary cellular changes.
Complications: Secondary bacterial infections frequently complicate viral diseases, especially those involving the skin and respiratory systems.
Clinical Attribution: Malaise, fever, anorexia, or incoordination are attributed to the absorption of injured cell products, viral toxicity, and viral abnormalities causing circulatory disturbances.
Cause of Death: Death in viral diseases is thought to be associated with vascular shock, viral toxicity, and the failure of one or more vital organs.
Septicemia
Definition: A morbid condition caused by the presence of pathogenic bacteria and their associated toxins in the blood.
Diagnosis: While a positive diagnosis requires isolation of the organism from the bloodstream, this is not routine in abattoirs. Evidence is instead gathered from antemortem and postmortem findings.
Antemortem Findings: * Depression. * Body temperature changes: Usually elevated, but may be normal or subnormal in terminal phases. * Difficult and rapid breathing. * Shivering and muscle tremors. * Congestion or petechial haemorrhages on the mouth, conjunctivae, and vulvar mucosae.
Postmortem Findings: * Enlarged, edematous, or haemorrhagic lymph nodes. * Degenerative changes in the liver, heart, and kidneys (parenchymatous organs). * Congestion and petechial or ecchymotic haemorrhages in the heart surface, kidney, mucous/serous membranes, connective tissue, and panniculus adiposis. * Splenomegaly. * Inadequately bled-out carcass (due to high fever). * Blood-stained serous exudate in the thoracic and abdominal cavities. * Anaemia (from bone marrow depression) and icterus (jaundice).
Judgment Rules: * A carcass must be condemned even if only one significant lesion (such as generalized acute lymphadenitis) is present. * Septicemia requires condemnation of the animal, carcass, offal, and all detached portions. * Borderline cases require bacteriological examination. * Associated diseases: Salmonellosis, leptospirosis, swine erysipelas, hog cholera, and anthrax in cattle.
Toxaemia
Definition: The presence and rapid proliferation of exotoxins and endotoxins in the bloodstream, derived from microorganisms or produced by body cells.
Antemortem Findings: * Temperature: Often normal or subnormal; fever occurs only if toxins are from microorganisms. * Neurological: Confusion and convulsions. * Locomotion: Abnormal changes; animal may be unable to rise or rise with great difficulty. * Pain indicators: Grinding of teeth. * Dehydration and moribund state.
Postmortem Findings: * Haemorrhage in organs. * Lymph nodes: Normal or enlarged and edematous (not hyperplastic like in septicemia). * Tissue necrosis and emphysema (in cattle). * Rarely, degenerative changes in parenchymatous organs.
Common Associations: Gangrenous mastitis, metritis, aspiration pneumonia, old injuries/wounds, and diffuse peritonitis (from uterine or reticulum perforation).
Judgment: Carcass and viscera are condemned. Implements, hands, and arms must be disinfected. Comatose or moribund animals are condemned antemortem.
Pigmentation and Anthracosis
Classification: * Exogenous: Synthesized outside the body (e.g., carbon, carotene). * Endogenous: Synthesized within the body (e.g., melanin, lipofuscin, bile pigments).
Anthracosis: Black carbon pigment found in lung tissue and corresponding lymph nodes of urban-raised animals. The lungs are condemned, but the carcass is approved.
Carotenoid Pigments: Exogenous pigments (carotene A, carotene B, xanthophyll) causing greenish-yellow discoloration in fat and muscle, notably in Jersey and Guernsey cattle. * Differentiating from Icterus: Carotenosis shows an enlarged, bright yellow liver; in carotenosis, the liver is condemned as damaged cells cannot metabolize carotene.
Melanosis and Myocardial Lipofuscinosis
Melanosis: Accumulation of endogenous brown-black melanin. * Locations: Heart, lungs, liver, kidneys, brain membranes, spinal cord, connective tissue, and periosteum. * Gray/White Horses: Deposits under the axillary area, shoulder, and ligamentum nuchae. * Pigs: "Seedy belly" or "seedy cut" in mammary tissue of female pigs. Shows a tendency toward neoplasia. * Calves: "Melanosis maculosa" refers to multifocal deposits in the liver, often disappearing after the first year. * Judgment: Extensive melanosis causes condemnation; localized cases require only part/organ condemnation.
Myocardial Lipofuscinosis (Xanthosis): * Known as "Wear-and-Tear" pigment. * Prevalent in Ayrshire cows (found in of normal individuals). * Seen in skeletal and heart muscles of old cows ("cull dairy cows") and chronic wasting diseases.
Icterus (Jaundice)
Definition: Abnormal accumulation of bilirubin or haemoglobin in the blood, staining skin, sclerae, tendons, arteries, and internal organs yellow.
Categories: * Prehepatic (Haemolytic): Excessive red blood cell destruction (e.g., Babesia ovis, Anaplasmosis). Blood pigment overproduction leads to haemoglobinemia and haemoglobinuria (bright red to dark red urine). * Hepatic (Toxic): Direct damage to liver cells (e.g., cirrhosis, systemic infection, chemical/plant poisoning, chronic copper poisoning in sheep). Functional impairment prevents bile secretion. * Posthepatic (Obstructive): Blocked bile drainage into the intestine. Causes include hepatic duct tumors, parasites (flukes), gall stones, bile duct inflammation, or mature ascarides in hogs.
Laboratory Diagnosis (Fouchet's Test): * Mix two drops of serum with two drops of Fouchet's agent on a white tile. * Positive result: Blue/green precipitate. * Fouchet's Reagent Composition: Trichloroacetic acid (), 10\% solution (), Distilled water ().
Judgment: * Suspects antemortem. * Postmortem: Condemn haemolytic, toxic, and obstructive cases. * Less severe cases: Hold in chiller for . If obstructive icterus disappears, the carcass passes.
Differentiating Yellow Fat: Examine the sclera, blood vessel intima, bone cartilage, and renal pelvis. If these are not yellow, icterus is absent. Yellow fat disease (steatitis) in hogs can be caused by fish by-products and has a rancid odour.
Haemorrhage and Haematoma
Types of Haemorrhage: * Petechial: Tiny foci ( diameter). * Ecchymotic: Larger spots (up to ). * Paint Brush: Extensive streaking. * Agonal: Caused by laboured breathing/violent death; involves capillary rupture. * Hematoma: A lump formed from a blood clot, associated with trauma; can exceed one meter in diameter.
Specific Causes: * Stunning issues: Delay between stunning and sticking causes cardiac stimulation and vasoconstriction, leading to "blood splashing." * Mechanical stunning in sheep: Arterial blood pressure can rise from a normal to over . * Deficiencies: Vitamin C deficiency.
Judgment: Approved if minor and physical in origin. Condemned if extensive, associated with septicemia, or caused by blackleg or sweet clover poisoning.
Bruises
Common Locations: * Cattle: Hip, chest, shoulder. * Pigs: Ham. * Sheep: Hind leg. * Poultry: Often associated with fractures or ruptured tendons.
Judgment: * Suspects antemortem. * Carcasses are approved if bruising is local and trimmed. * Condemnation occurs if injuries show systemic changes or lose wholesomeness. * Poultry Rules: Fractures with bruises result in removal/condemnation of tissue. Simple fractures without skin damage may be approved for boning.
Abscesses
Causative Agents: * Liver Abscesses (): Complication of rumenitis in grain-fed feedlot cattle (high acidity causes ulcerative rumenitis, providing passage for bacteria). * General: , , and .
Classification: * Primary: Contact with digestive/respiratory tracts or skin. * Secondary (Hematogenous): Found in brain, bone marrow, renal cortex, ovary, or spleen.
Pigs: Common in the jaw and spine (spinal abscesses often follow tail biting).
Calves: "Sawdust liver" results from umbilical infection (requires carcass condemnation).
Judgment: Condemn if Pyemia (bloodstream spread) is evident with elevated temperature/cachexia or if multiple liver abscesses exist. Single abscesses can be trimmed if no toxaemia is present.
Edema
Types: * Inflammatory (Exudate): Yellow, white, or greenish fluid. * Non-inflammatory (Transudate): Accumulation in subcutaneous tissue, lungs, or brain.
Localized Edema: Caused by venous obstruction (prolonged decubitus/lying down), tumor pressure, or inflammation.
Generalized Edema: Secondary to congestive heart failure, low protein (malnutrition, amyloidosis, parasitism, liver disease), or toxin-induced vascular damage.
Specific Accumulations: * Anasarca: Subcutaneous edema. * Ascites: Peritoneal cavity fluid. * Hydrothorax: Pleural cavity fluid.
Judgment: Generalized cases are condemned. Localized cases are trimmed. Mesentery edema (related to vena cava interference) can be held for re-examination; if serous membranes dry out, it may pass.
Emphysema
Alveolar Emphysema: Tiny air bubbles (bullae if large). Occurs in all species.
Interstitial Emphysema: Primarily in cattle; air migrates into the interstitium due to lack of collateral ventilation.
Clinical Conditions: Chronic obstructive pulmonary disease (COPD/Heaves) in horses; interstitial pneumonia (Fog Fever) in cattle.
Postmortem appearance: Pale, shiny, pearl-like lesions; puffy and crepitant upon palpation.
Judgment: Affected lungs are condemned.
Tumours (Neoplasms)
Classification: * Benign: Slow-growing, non-invasive, circumscribed. * Malignant: Fast-growing, infiltrative, metastatic. Includes Carcinoma (epithelial, lymphatic spread) and Sarcoma (connective tissue, blood spread).
Common Beef Inspection Tumors: Squamous cell carcinoma, lymphosarcoma, pheochromocytoma, mesothelioma.
Judgment: Condemned if metastatic or if multiple benign tumors are present in different organs. Circumscribed benign tumors are approved after removal.
Emaciation
Definition: Loss of flesh and fat due to starvation, cachexia, or chronic disease. Differentiated from "Leanness" (which is physiological thinness).
Characteristics: Serous atrophy of fat (watery/jelly-like fat), edematous musculature, sunken eyes, and rough hair coat.
Judgment and Bone Marrow Test: * Carcass held in a cooler for . If fat "sets" and cavities are dry, it passes. * Objective Test: A pea-sized piece of bone marrow from the distal radius is placed in a ethanol/methanol solution. If it sinks (indicating high water content), the carcass is condemned.
Abnormal Odours
Sources: Fish meal (fishy odour in pigs), Ketosis (sweet acetone odour), Drugs (turpentine, ether, chloroform), and sexual odour (boar taint).
Testing: Enhancing the smell by boiling a piece of muscle in water.
Judgment: * Medicinal/chemical/pronounced drug treatment: Condemned. * Sexual odour: Hold for . If it persists, condemn. If it disappears, approve. * If the odour is removable by chilling or trimming, the carcass may pass for food.