Lymphangitis

Lymphangitis of Horses and Cattle

• Also known as Pigeon Fever or Dry Land Distemper

• Caused by:

  • Corynebacterium pseudotuberculosis

    • A gram-positive, soil-dwelling bacterium

    • Infection is common and economically important worldwide

    • Increasing in frequency in North America

• Affected Species:

  • Horses

  • Cattle

  • Occasionally camels, alpacas, llamas, and buffalo

• Pathogenesis:

  • Bacteria enter via skin wounds

  • Transmission via arthropod vectors such as stable flies, horn flies, and house flies

  • Transmission by contact with contaminated environment

  • Onset in horses is variable

  • Peak incidence in horses is during summer and fall, when flying insects are present

• Clinical Findings:

  • General signs (in horses and cattle):

    • Diffuse or localized swellings

    • Ventral pitting edema

    • Ventral midline dermatitis

      • Painful and mildly pruritic

      • Associated with alopecia, exudation, crusting, and ulceration

    • Lameness

    • Draining abscesses or tracts

    • Fever

    • Weight loss

    • Depression

    • Abscesses can be large, up to 20 cm in diameter before rupturing

    • Abscesses take weeks to months to resolve

    • Nonhealing abscesses or wounds may be concurrently affected with cutaneous habronemiasis (“summer sores”)

  • Clinical findings in Horses:

    • Chronic abscesses along lymphatic chains (lymphangitis) on the limbs

    • Ulcerative lymphangitis (infection of the lower limbs)

      • Usually manifests as painful inflammation, nodules, and ulcers, especially in the lower limb region

      • Lameness and edematous swelling can extend up the entire limb

      • The exudate is odorless, thick, tan, and blood tinged

      • Usually only one leg is involved

      • If not treated aggressively, lesions and swelling usually progress and become chronic with relapses

    • Chronic abscesses in the pectoral region (most common location)

    • Chronic abscesses in the ventral abdominal region

    • Chronic abscesses in the preputial or mammary regions

    • Secondary dissemination to internal organs

    • Internal infection

      • Can affect the liver, spleen, kidneys, or lungs

      • Suggested by a marked or prolonged fever, anorexia, or weight loss

      • Clinical signs may include weight loss, colic, splinted abdomen, or lethargy

  • Clinical findings in Cattle:

    • Most commonly causes cutaneous excoriated granulomas

    • Large, ulcerative skin lesions resembling infected granulation tissue

    • Lymphangitis may occur in 2%-5% of cows

    • Location varies, but is often associated with skin trauma

    • Healing often occurs without treatment or with limited topical treatment in 2–4 weeks

    • Abortion and mastitis may also occur

    • Visceral involvement has been reported but occurs much less commonly than in horses

  • Clinicopathologic Findings (usually present):

    • Anemia

    • Leukocytosis

    • Neutrophilia

    • Hyperfibrinogenemia

    • Increased concentrations of serum amyloid A (SAA)

    • Hyperglobulinemia (indicative of inflammation)

• Diagnosis:

  • Confirmation by isolation of the bacteria from lesions

  • Bacterial culture of pus from external abscesses

  • Samples for culture in horses: Aspirates of abscesses, swabs of purulent exudate beneath crusts, punch biopsies

  • Abdominal ultrasonographic examination to detect internal infection or abscesses

  • Clinicopathologic evidence of inflammation

  • Serologic testing for internal infection

    • In horses, the synergistic hemolysis inhibition (SHI) test detects IgG to the phospholipase D exotoxin

    • Useful adjunct for diagnosis of internal infection in the absence of external infection

    • By itself, serologic testing is not sufficient to diagnose infection

  • PCR testing of abdominal fluid for C. pseudotuberculosis

  • Ultrasonography of the abdomen and thorax is useful for detecting internal infection (liver, spleen, kidneys, lungs)

  • Ultrasonography is also useful for detecting and draining deep abscesses (e.g., in the triceps musculature of horses)

  • Transtracheal aspirates are required to confirm pneumonia

  • Differential diagnoses include:

    • Pyoderma, abscesses, or lymphangitis due to other bacteria (e.g., Staphylococcus aureus, Rhodococcus equi, Streptococcus spp, or Dermatophilus spp)

    • Dermatophytosis (in cattle or horses)

    • Sporotrichosis

    • Equine cryptococcosis

    • North American blastomycosis

    • Onchocerciasis

• Treatment:

  • Lancing and drainage of external abscesses

    • Abscesses are lanced and flushed with dilute antiseptic solutions

    • Deep abscesses require ultrasonography to guide placement of an indwelling drain

    • External swellings treated with hot packs, poultices, or hydrotherapy until they rupture or are drained surgically

  • Longterm antimicrobials

    • Required for ulcerative lymphangitis, limb infection, and internal infection

    • Minimum of 1 month duration or as directed by follow-up ultrasonography

    • The organism is susceptible to many commonly administered antimicrobials

    • Antimicrobial treatment of uncomplicated external abscesses may prolong the disease by delaying abscess maturation

  • Fly control

  • Systemic administration of phenylbutazone or flunixin meglumine relieves pain and swelling

  • General supportive and nursing care is indicated

  • If treatment is successful, swelling gradually recedes over days or weeks

• Prevention:

  • Isolation of infected animals

  • Comprehensive fly control including insect growth regulators

  • Good sanitation

  • A conditionally licensed bacterin or toxoid is currently available for horses

• Prognosis/Outcome:

  • In cattle, healing often occurs without treatment or with limited topical treatment in 2–4 weeks

  • If not treated aggressively, the disease in horses is often chronic

  • Severe or untreated lymphangitis cases often become chronic, leading to fibrosis and induration of the leg

  • Internal infection in horses has a 30%–40% mortality rate, even with appropriate treatment

Caseous Lymphadenitis (CL) of Sheep and Goats

• Also Known As: (Not explicitly mentioned as having other common names like the Horse/Cattle Lymphangitis sources did, but the context refers to it solely as Caseous Lymphadenitis)

• Caused By: Corynebacterium pseudotuberculosis

  • Gram-positive, facultative, intracellular coccobacillus

  • Soil-dwelling bacterium (Implied by hardy environmental survival and contamination from environment)

  • Two biotypes identified:

    • Nitrate-negative (infects sheep and goats)

    • Nitrate-positive (infects horses)

  • Produces phospholipase D exotoxin

    • Enhances dissemination by damaging endothelial cells

  • Has external lipid coat virulence factor

    • Provides protection from phagocyte enzymes

• Affected Species:

  • Sheep

  • Goats

  • (C. pseudotuberculosis isolates from cattle are heterogeneous)

• Pathogenesis:

  • Bacteria penetrate skin or mucous membranes

  • Most common entry: Skin injury (shearing, tagging, tail docking, castration, environmental hazards)

  • Transmission:

    • Contact with purulent material from draining lesions (most common source)

    • Inhalation or ingestion (less common)

    • Contamination of environment (draining lesions, nasal discharge/coughing from internal form)

  • Bacteria are hardy in environment

    • Survive on fomites (bedding, wood) for 2 months

    • Survive in soil for 8 months

  • Movement to lymph nodes via regional lymphatics

  • Establishment in lymph nodes and viscera

  • Bacteria replicate in phagocytes, which rupture

  • Ongoing replication and cell death forms abscesses

  • Incubation period: 1–3 months

  • Culminates in encapsulated abscesses

• Clinical Findings:

  • Chronic, infectious disease

  • Characterized by abscess formation

  • Purulent material is thick and nonodorous

  • Lesions increase with age

  • Forms of the Disease:

    • External (Peripheral) Form:

      • Abscesses in region of peripheral lymph nodes (single or multiple)

      • More common in goats

      • Common sites: submandibular, parotid, prescapular, prefemoral

      • Less common: supramammary, inguinal, ectopic locations

      • If untreated, lesions mature into open, draining abscesses

      • Purulent material consistency: soft/pasty (goats), thick/caseous (sheep)

      • Skin heals with scarring after draining

      • Recurrence is common (often months later)

    • Internal Form:

      • Abscesses within internal organs and lymph nodes

      • More common in sheep ("thin ewe syndrome")

      • Typically manifests as chronic weight loss and ill thrift

      • Presence of other signs depends on organs involved

      • Lung abscessation is common

        • Signs: chronic ill thrift, cough, purulent nasal discharge, fever, tachypnea, increased lung sounds

• Diagnosis:

  • Physical examination (especially for external abscesses)

  • Bacterial Culture:

    • Definitive diagnosis

    • Culture of purulent material from an intact abscess

    • Culture of transtracheal aspirate (for internal form/pneumonia)

    • Isolate animals pending culture results (differentiates from other pyogenic organisms)

  • Serologic Testing:

    • Synergistic Hemolysin Inhibition (SHI) test

      • Detects antibodies against phospholipase D exotoxin

      • Available at many labs

      • Results interpreted with caution (consider history, active infection, vaccination)

      • Positive titers indicate: past resolved infection, recent exposure, recent vaccination, or active/developing lesions

      • Correlation between high titer and active/developing abscesses varies

      • Repeat titer in 2–4 weeks if status uncertain

      • Rising titer + clinical signs = CL assumed

      • False negatives possible: within first 2 weeks post-exposure, chronic walled-off abscesses

      • Colostrum-derived titers in young (< 6 months) require caution

    • Not sufficient alone for diagnosis of active cases if abscesses not accessible

  • Other Tools (especially for internal form):

    • Radiography and ultrasonography (detect lesions)

    • Exclusion of other causes of chronic weight loss (Johne's disease, parasitism, poor dentition)

• Economic Losses:

  • Death

  • Condemnation and trimming of infected carcasses

  • Hide and wool loss

  • Loss of sales for breeding animals

  • Premature culling

  • Major concern for small ruminant producers in North America

• Zoonotic Potential:

  • Care should be taken when handling infected animals or purulent exudate

• Treatment:

  • CL is not considered a curable disease

  • Treatment mainly for aesthetic reasons and limiting infectivity (animals with genetic/emotional value)

  • Options:

    • Lancing and draining of external abscesses

      • Cavity lavage with dilute iodine solution

      • Isolate animal until lesion stops draining and heals

      • Carefully collect and dispose of drainage material

      • High recurrence rates

    • Surgical excision of intact accessible abscesses

      • More expensive

      • Undetected abscesses often present

      • High recurrence rates

    • Formalin injection of lesions (strongly discouraged - FDA bans extra-label use of potent carcinogens in food animals)

    • Antimicrobials (extra-label use, strict adherence to guidelines/VCPR mandatory)

      • Intralesional and/or Systemic

      • Longterm procaine penicillin G and rifampin successful in some cases

      • Penicillin alone unlikely to penetrate capsule

      • Highly lipid-soluble tulathromycin may help internal cases

        • Studies show efficacy of SC and/or intralesional tulathromycin in resolving lesions without lancing

        • Effective concentrations achieved within walled-off abscesses after single SC dose of tulathromycin

      • Intralesional oxytetracycline eliminated bacterial growth in tissue cages in one study

      • IM oxytetracycline did not eliminate growth in tissue cages in one study

      • Recurrence remains a problem despite efficacy

      • Cannot be considered curative

      • Acceptable alternative when culling is not an option

  • Supportive care

  • Owner education stressing persistent, recurrent nature

• Control and Prevention:

  • Focus on strict biosecurity measures

  • Goals: Eliminate CL from herd/flock, decrease new cases

  • Measures:

    • Elimination of diseased animals (Culling)

      • Best way to eliminate CL from herd/flock

      • Cull immediately if possible

      • Animals with draining abscesses should not be sent through sale barns

      • Dividing herds/flocks into clean and infected groups

      • Eliminating older/less genetically valuable animals over time

    • Isolation of infected animals

      • Until lesions are dry and/or resolved

      • If immediate removal is not possible

    • Vaccination

      • Commercial CL vaccines licensed for sheep and goats

      • Use only in species labeled (adverse reactions reported in goats given sheep vaccine)

      • Rigid adherence to schedules can decrease prevalence/incidence

      • Efficacy not 100%

      • Will not clear infected animals

      • Consider for young replacement animals

      • Stop vaccination in clean herds/flocks (no history)

      • Gradually cull older infected animals as economics allow

      • Cull seropositive unvaccinated animals once prevalence is low

    • Disinfection

      • Shearing equipment and other instruments between animals

      • Dilute bleach and chlorhexidine effective on hard surfaces/fomites (after cleaning organic material)

      • Shearers understanding hazards and vector potential

      • Dipping-tank solutions kept fresh

    • Environment Modification:

      • Removal of hazards (barbed wire, exposed nails, rough feeders) to decrease injury and transmission from fomites

    • Prevention of Introduction of New Animals

      • Common way CL is introduced/reintroduced

      • Clinically normal animals can be incubating

      • Hazardous to buy from unknown histories

      • Prepurchase examination for lesions/scars

      • Serologic screening for CL

      • Quarantine before introduction

      • Only seronegative animals with no evidence of present/past lesions allowed

      • Raising young from infected dams on pasteurized milk away from infected animals (limited success)

• Prognosis:

  • Chronic disease

  • Challenging to eliminate within an individual animal or herd

  • Not considered a curable disease

  • Recurrence is common

  • Internal form is difficult to definitively diagnose antemortem

  • Internal form serves as a reservoir of infective animals

  • Economic losses include death.