lecture #34

Course Information and Learning Objectives

  • Course Title: Infections of hemolymphatic system - II (Lecture #34)
  • Instructor: Dr. Mrigendra Rajput, B.Vet. Sc., M.Vet. Sc., Ph.D.
  • Affiliation: Associate Professor of Microbiology, Richard A. Gillespie College of Veterinary Medicine, Lincoln Memorial University, Harrogate, TN
  • Credits: PPT adapted from Dr. Ashutosh Verma’s lectures
  • References and Sources:     * Veterinary Microbiology and Microbial Diseases, Quinn et al., 2nd ed.     * Veterinary Microbiology, Songer and Post     * Clinical Veterinary Microbiology, Markey et al., 2nd ed.     * Infectious Diseases of the Dog and Cat, Greene, 4th ed.     * Veterinary Microbiology, Hirsh et al., 2nd ed.
  • Learning Objectives:     * List etiological agent(s) and their characteristic features for caseous lymphadenitis, ulcerative lymphangitis, and erysipelas     * Discuss affected host species, epidemiology, and clinical findings of caseous lymphadenitis, ulcerative lymphangitis, and erysipelas     * Discuss diagnosis of caseous lymphadenitis, ulcerative lymphangitis, and erysipelas     * Discuss treatment and control of caseous lymphadenitis, ulcerative lymphangitis, and erysipelas

Overview of Key Pathogens and Core Pathologies

  • Caseous Lymphadenitis (CL): Primarily affecting sheep and goats, caused by Corynebacterium pseudotuberculosis.
  • Ulcerative Lymphangitis: Affecting horses and cattle, caused by Corynebacterium pseudotuberculosis.
  • Erysipelas: Primarily affecting swine and turkeys, caused by Erysipelothrix rhusiopathiae.

General Characteristics of Corynebacterium Species

  • Morphology and Staining:     * Small, Gram-positive bacteria.     * Non-spore forming.     * Facultative anaerobes.     * Pleomorphic shapes, including coccoid, club, and rod forms.     * In stained smears, they occur singly, in palisades of parallel cells, or in angular clusters resembling "Chinese characters."
  • Biochemical Characteristics:     * Catalase-positive.     * Most pathogenic members are urease-positive.     * Pathogenic corynebacteria are non-motile.
  • Growth Requirements:     * Require enriched media for growth.
  • Ecology and Habitat:     * Many species are commensals on mucous membranes.     * Corynebacterium pseudotuberculosis is specifically noted for its ability to survive for months in the environment.
  • Infection and Lesions:     * Tissue trauma typically precedes infection establishment. Examples of trauma include cuts, abrasions, shearing wounds, fighting injuries, or thorn/prick injuries.     * Resulting lesions are characterized by suppuration (pus formation).

Summary of Pathogenic Corynebacteria and Host Diseases

  • C. bovis:     * Host: Cattle.     * Condition: Subclinical mastitis.     * Habitat: Teat cistern.
  • C. diphtheriae:     * Host: Humans (Primary) and Horses (Rare).     * Condition: Diphtheria; wound infection (rarely in horses).     * Habitat: Human pharyngeal mucosa.
  • C. kutscheri:     * Host: Laboratory rodents.     * Condition: Superficial abscesses and caseopurulent foci in liver, lungs, and lymph nodes.     * Habitat: Mucous membranes and environment.
  • C. pseudotuberculosis (Non-nitrate-reducing biotype):     * Host: Sheep and goats.     * Condition: Caseous lymphadenitis.     * Habitat: Skin, mucous membranes, and environment.
  • C. pseudotuberculosis (Nitrate-reducing biotype):     * Host: Horses and cattle.     * Condition: Ulcerative lymphangitis and abscesses.     * Habitat: Environment.
  • C. renale group (Type I: C. renale; Type II: C. pilosum; Type III: C. cystitidis):     * Host: Cattle, sheep, and goats.     * Condition: Cystitis, pyelonephritis (Type I, III); Ulcerative (enzootic) balanoposthitis in sheep/goats (Type I); Severe cystitis (Type III).     * Habitat: Lower Urinary Genital Tract (LUGT) of cows and bulls, prepuce.
  • C. ulcerans:     * Host: Cattle, cats, humans.     * Condition: Mastitis (cattle); rare Upper Respiratory Tract (URT) infection (cats); Diphtheria-like illness (humans).     * Habitat: Human pharyngeal mucosa.

Caseous Lymphadenitis (CL)

  • Definition: A chronic, contagious bacterial disease manifesting as abscesses of peripheral and/or internal lymph nodes and organs.
  • Etiological Agent: Corynebacterium pseudotuberculosis (specifically the non-nitrate-reducing biotype).
  • Microscopic/Cultural Characteristics:     * Small white colonies.     * Late $\beta$-hemolysis (weak).     * CAMP Test: Demonstrates synergistic hemolysis when C. pseudotuberculosis (drawn horizontally) is crossed against Rhodococcus equi.
  • Economic Impact:     * Significant endemic infection in sheep/goat regions worldwide, including North America.     * Losses due to condemnation of infected carcasses and devaluation of hides.
  • Epidemiology:     * Entry: Penetration of skin or mucous membranes. Most common through injuries from shearing, tagging, tail docking, castration, or environmental trauma.     * Transmission: Contact with purulent material draining from active lesions. Bacteria can also be inhaled or ingested.     * Survival: Can survive on fomites (bedding/wood) for 22 months and in soil for 88 months. Survival is enhanced by organic material, shade, and moisture.     * Incubation: Varied period of 11 to 33 months, leading to encapsulated abscesses.
  • Pathogenesis:     * Facultative intracellular pathogen (survives/replicates in phagocytes).     * Virulence Factors: Cell wall lipids and an exotoxin called Phospholipase D (PLD).     * PLD Function: Leukotoxic; damages endothelial cells to promote spread from initial site to regional lymph nodes and viscera.     * Cell Wall Lipid: High lipid content allows the organism to resist killing by phagocytes and maintain chronic infection.     * Immune Response: Antibodies against PLD help prevent the spread of infection.
  • Clinical Signs and Presentations:     * Superficial Form: Involves palpable nodes near skin (intermandibular, parotid, retropharyngeal, cervical, prescapular, prefemoral, and supramammary). More common in goats.     * Visceral Form: Abscesses in internal organs and lymph nodes (lungs, kidney, liver, mesenteric lymph nodes). Associated with chronic weight loss and ill thrift ("Internal CL"). More common in sheep.     * Lesion Character: Purulent material is thick and non-odorous. Chronic lesions show an "onion ring" appearance in cross-section with encapsulated layers. Initial pus is greenish, later becoming putty-colored and caseous.
  • Diagnosis:     * Based on clinical signs and animal species.     * Direct Gram-stain examination of pus/exudate (shows pleomorphism).     * Definitive diagnosis via culture of active lesions.     * ELISAs to detect antibodies against cell wall antigens or PLD.
  • Treatment and Control:     * Treatment: Intralesional or systemic antimicrobial therapy; supportive care. Lesions must be isolated until dry/resolved.     * Strict Biosecurity: Elimination of diseased animals, prepurchase serologic screening, and quarantine (1−31-3 months based on incubation).     * Management: Disinfection of equipment (shearing, tagging), removal of environmental hazards, and vaccination.

Ulcerative Lymphangitis

  • Etiological Agent: Nitrate-reducing biotype of Corynebacterium pseudotuberculosis.
  • Host Species: Horses and cattle.
  • Clinical Presentation:     * Lymphangitis of Lower Limbs: Onset is slow, and condition is chronic. Lymphatic vessels become swollen and firm with nodules forming along the length.     * Edema: Develops in affected limbs; ulcerated nodules exude thick, odorless, greenish, blood-tinged pus.     * "Pigeon Breast" or "Pigeon Fever": Abscessation in the pectoral region (pectoral muscles); abscesses can reach the size of a grapefruit.
  • Diagnosis: Isolation and identification of C. pseudotuberculosis from lesions.
  • Treatment: Systemic antibiotic therapy combined with topical treatment, such as iodophor shampoo.

Erysipelas in Swine

  • Etiological Agent: Erysipelothrix rhusiopathiae.
  • Agent Characteristics:     * Gram-positive, non-motile, non-spore forming small rods (smooth form) or filaments (rough form).     * Catalase-negative, coagulase-positive.     * Facultative anaerobe.     * Exhibits alpha-hemolysis (greenish) on blood agar.     * Produces H2SH_2S along the stab line in Triple Sugar Iron (TSI) agar.
  • Epidemiology:     * Carried by up to 50%50\% of healthy pigs, primarily in tonsillar tissue.     * Shed in feces and oronasal secretions.     * Infection occurs via ingestion of contaminated feed/water or through skin abrasions.     * The organism survives the stomach environment and remains viable in feces for several months.     * Immunity: Maternal antibodies provide passive immunity for young pigs. Older pigs develop active immunity via exposure.
  • Clinical Manifestations:     * Acute Form: Septicemia (leads to sudden death, fever) and cutaneous erythema.     * Chronic Form: Arthritis (proliferative, non-suppurative polysynovitis) and vegetative endocarditis.     * Diamond Skin Disease (Urticarial Form): Red to purple rhomboidal (diamond-shaped) patches on skin.         * Pathogenesis of patches: Bacteria in circulation damage vessel endothelium $\rightarrow$ Deposition of antigen-antibody complexes $\rightarrow$ Microthrombi formation $\rightarrow$ Ischemia $\rightarrow$ Necrosis.
  • Diagnosis:     * Diamond-shaped skin lesions are pathognomonic.     * Bacterial culture from fresh tissues (spleen, kidney, long bones, heart blood), fluid, or blood.     * Identification criteria: Colony morphology (48 h), no growth on MacConkey, negative catalase, positive coagulase, H2SH_2S production in TSI.
  • Treatment and Control:     * Susceptibility: Highly susceptible to beta-lactam antibiotics (Penicillin is the primary recommendation).     * Herd Treatment: Tetracyclines in feed or water.     * Ancillary Care: NSAIDs for fever; Erysipelas antiserum (adjunct, though less available).     * Control: Vaccination is very effective (though stress can cause failure); sanitation, hygiene, and culling clinically ill pigs.

Erysipelas in Other Species

  • Poultry (Birds):     * Manifests as acute septicemia worldwide.     * Outbreaks are sudden with mortality ranging from less than 1%1\% to 50%50\%.     * Species Affected: Turkeys (most important), chickens, ducks, and geese.     * Key Sign: Dark-colored, swollen snoods in turkeys.
  • Humans (Erysipeloid):     * Occurs via occupational exposure (veterinarians, butchers, fish handlers, abattoir workers).     * Skin infection leads to erythematous swelling at entry site and ulceration.     * Can progress to systemic septicemia, endocarditis, or arthritis.     * Predisposing Factors: Alcoholism, malignancy, or steroid use.